Bio

Academic Appointments


Research & Scholarship

Current Research and Scholarly Interests


Transcriptional control is a key step in the regulation of eukaryotic gene expression. Our lab focuses on understanding the molecular mechanism of transcription factors that govern the transformation of normal mammalian cells to a neoplastic state. We are especially interested in the biological role of androgen receptor (AR), a nuclear hormone receptor, in development and related human diseases. Most prostate cancer cells express the AR and are androgen-dependent. Therefore, androgen ablation therapy has been routinely used for treatment of advanced prostate cancer. While the treatment initially achieves dramatic therapeutic response, it eventually fails in nearly all patients. Consequently, the patients develop castration resistant prostate cancer (CRPC) after two to three years following the therapy, for which there is no curable treatment. Our current efforts mainly focus on understanding the mechanisms underlying androgen signaling in prostate cancer progression and CRPC development. Ongoing projects in the lab are addressing several unknown and important questions in the field.

1) Multiple lines of evidence have shown a critical role of AR in ligand-independent prostate cancer cell growth, which implies that androgen-independent cells may still be ôAR dependentö and that the AR can be used as a therapeutic target for future treatment. However, there is no appropriate animal model that can be used to directly evaluate ligand-independent AR action during the course of prostate cancer progression. We currently develop and generate a new generation of mouse models that can be used to recapitulate the critical role of AR during the course of disease progression. These mouse models are also important for future drug development.

2) Although nuclear hormone receptors in general are ligand-dependent transcriptional activators, their roles in transcriptional repression have also been suggested. We have identified a ligand induced AR repression on a pro-oncoprotein, c-Met, expression in prostate cancer cells. Because activation of c-Met induces prostate cancer invasion, metastasis, and hormonal refractoriness, our finding of the AR as a dual transcriptional activator and repressor in prostate cancer cells implies a novel molecular mechanism for prostate cancer progression and CRPC development. Our results further suggest that the current androgen ablation therapy may attenuate the repressive role of the AR on c-Met expression and actually induce CRPC development. Currently, we are using both in vitro and in vivo approaches to test our hypothesis in order to develop a more effective therapeutic strategy for patients.

3) AR-mediated transcription is facilitated through direct or indirect interactions with different signaling pathways and co-regulators. Emerging evidence suggests a promotional role of the Wnt/beta-catenin signaling pathway in prostate tumorigenesis. Because mutations in beta-catenin and other components of the beta-catenin destruction complex are rare in prostate cancer cells, the molecular mechanisms underlying beat-catenin oncogenic activation in prostate cancer may be different from those observed in human colorectal cancer or other malignancies. Currently, we are using several unique and novel models that were developed by us to investigate androgen and Wnt action and their interactions in prostate development and oncogenesis.

Clinical Trials


  • Identification and Characterization of Novel Proteins and Genes in Head and Neck Cancer Recruiting

    Through this study, we hope to learn more about the mechanisms, which may contribute to development and progression of head and neck cancer. The long-term goal of this study will be to develop new strategies and drugs for the diagnosis and treatment of head and neck cancer.

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Teaching

2013-14 Courses


Graduate and Fellowship Programs


Publications

Journal Articles


  • Identification of a Novel Role of ZMIZ2 Protein in Regulating the Activity of the Wnt/▀-Catenin Signaling Pathway. journal of biological chemistry Lee, S. H., Zhu, C., Peng, Y., Johnson, D. T., Lehmann, L., Sun, Z. 2013; 288 (50): 35913-35924

    Abstract

    ZMIZ2, also named ZIMP7, is a protein inhibitor of activated STAT (PIAS)-like protein and a transcriptional coactivator. In this study, we investigated the interaction between ZMIZ2 and ?-catenin, a key regulator of the Wnt signaling pathway. We demonstrated that the expression of exogenous ZMIZ2 augments TCF (T cell factor) and ?-catenin-mediated transcription. In contrast, shRNA knockdown of ZMIZ2 expression specifically represses the enhancement of TCF/?-catenin-mediated transcription by ZMIZ2. Using Wnt3a-conditioned medium, we demonstrated that ZMIZ2 can enhance Wnt ligand-induced TCF/?-catenin-mediated transcription. We also showed a promotional role of ZMIZ2 in enhancing ?-catenin downstream target gene expression in human cells and in Zmiz2 null (Zmiz2(-/-)) mouse embryonic fibroblasts (MEFs). The regulatory role of Zmiz2 in Wnt-induced TCF/?-catenin-mediated transcription can be restored in Zmiz2(-/-) MEFs that were infected with adenoviral expression vectors for Zmiz2. Moreover, enhancement of Zmiz2 on TCF/?-catenin-mediated transcription was further demonstrated in Zmiz2 knockout and Axin2 reporter compound mice. Furthermore, the protein-protein interaction between ZMIZ2 and ?-catenin was identified by co-immunoprecipitation and in vitro protein pulldown assays. We also observed recruitment of endogenous ZMIZ2 onto the promoter region of the Axin 2 gene, a ?-catenin downstream target promoter, in a Wnt ligand-inducible manner. Finally, a promotional role of ZMIZ2 on cell growth was demonstrated in human cell lines and Zmiz2 knockout MEFs. Our findings demonstrate a novel interaction between ZMIZ2 and ?-catenin and elucidate a novel mechanism for PIAS-like proteins in regulating Wnt signaling pathways.

    View details for DOI 10.1074/jbc.M113.529727

    View details for PubMedID 24174533

  • Deletion of Leucine Zipper Tumor Suppressor 2 (Lzts2) Increases Susceptibility to Tumor Development JOURNAL OF BIOLOGICAL CHEMISTRY Johnson, D. T., Luong, R., Lee, S. H., Peng, Y., Shaltouki, A., Lee, J. T., Lin, D., Wang, Y., Sun, Z. 2013; 288 (6): 3727-3738

    Abstract

    Using an Lzts2 knock-out mouse model, we characterized the biological role of Lzts2 in tumorigenesis. Both heterozygous and homozygous deletion of the Lzts2-targeted allele in mice shows an increased incidence in spontaneous tumor development, although Lzts2 homozygous knock-out mice show significantly higher incidences than heterozygous mice. Treatment of Lzts2-deficient mice with a carcinogen, N-butyl-N-(4-hydroxybutyl) nitrosamine, increases the susceptibility to N-butyl-N-(4-hydroxybutyl) nitrosamine-induced bladder carcinoma development. Examination of human prostate cancer tissue specimens shows a reduction of LZTS2 protein expression in prostate cancer cells. Further analyses of mouse embryonic fibroblasts isolated from Lzts2 knock-out embryos show that loss of Lzts2 enhances cell growth. These data provide the first line of evidence demonstrating that deletion of Lzts2 increases susceptibility to spontaneous and carcinogen-induced tumor development.

    View details for DOI 10.1074/jbc.M112.417568

    View details for Web of Science ID 000314845000005

    View details for PubMedID 23275340

  • Conditional Deletion of the Pten Gene in the Mouse Prostate Induces Prostatic Intraepithelial Neoplasms at Early Ages but a Slow Progression to Prostate Tumors PLOS ONE Kwak, M. K., Johnson, D. T., Zhu, C., Lee, S. H., Ye, D., Luong, R., Sun, Z. 2013; 8 (1)

    Abstract

    The PTEN tumor suppressor gene is frequently inactivated in human prostate cancer. Using Osr1 (odd skipped related 1)-Cre mice, we generated a novel conditional Pten knockout mouse strain, Pten(LoxP):Osr1-Cre. Conditional biallelic and monoallelic Pten knockout mice were viable. Deletion of Pten expression was detected in the prostate of Pten(LoxP/LoxP):Osr1-Cre mice as early as 2 weeks of age. Intriguingly, Pten(LoxP/LoxP):Osr1-Cre mice develop high-grade prostatic intraepithelial neoplasms (PINs) with high penetrance as early as one-month of age, and locally invasive prostatic tumors after 12-months of age. Pten(LoxP/+):Osr1-Cre mice show only mild oncogenic changes after 8-weeks of age. Castration of Pten(LoxP/LoxP):Osr1-Cre mice shows no significant regression of prostate tumors, although a shift of androgen receptor (AR) staining from the nuclei to cytoplasm is observed in Pten null tumor cells of castrated mice. Enhanced Akt activity is observed in Pten null tumor cells of castrated Pten(LoxP/LoxP):Osr1-Cre. This study provides a novel mouse model that can be used to investigate a primary role of Pten in initiating oncogenic transformation in the prostate and to examine other genetic and epigenetic changes that are required for tumor progression in the mouse prostate.

    View details for DOI 10.1371/journal.pone.0053476

    View details for Web of Science ID 000313429800053

    View details for PubMedID 23308230

  • The Leucine Zipper Putative Tumor Suppressor 2 Protein LZTS2 Regulates Kidney Development JOURNAL OF BIOLOGICAL CHEMISTRY Peng, Y., Clark, C., Luong, R., Tu, W. H., Lee, J., Johnson, D. T., Das, A., Carroll, T. J., Sun, Z. 2011; 286 (46): 40331-40342

    Abstract

    Members of the leucine zipper putative tumor suppressor (LZTS) family play crucial roles in transcription modulation and cell cycle control. We previously demonstrated that LZTS2 functions as a novel ?-catenin-interacting protein and represses ?-catenin-mediated transcription on T-cell factor/lymphoid enhancing factor. Here, we investigate the biological role of LZTS2 using newly established Lzts2 KO mice. Homozygosity for loss-of-function of the Lzts2-targeted allele resulted in severe kidney and urinary tract developmental defects, including renal/ureteral duplication, hydroureter, and hydronephrosis, which were visible prenatally. Altered ureteric bud outgrowth was identified in Lzts2 null embryos. Further analysis indicated that ?-catenin subcellular localization was altered in fibroblasts isolated from Lzts2 null embryos. In addition, Wnt growth factor-induced ?-catenin-mediated transcriptional activity was increased in Lzts2 null fibroblasts, suggesting a direct role for Lzts2 in the Wnt signaling pathway. These data demonstrate a critical role of LZTS2 in renal development and implicate LZTS2 as a critical regulator of ?-catenin-mediated nephrogenesis.

    View details for DOI 10.1074/jbc.M111.302059

    View details for Web of Science ID 000296925700064

    View details for PubMedID 21949185

  • The beta-Catenin Binding Protein ICAT Modulates Androgen Receptor Activity MOLECULAR ENDOCRINOLOGY Zhuo, M., Zhu, C., Sun, J., Weis, W. I., Sun, Z. 2011; 25 (10): 1677-1688

    Abstract

    Androgens have important roles in the development of the prostate gland and in prostate cancer. Since the finding that ?-catenin is a cofactor of the androgen receptor (AR) and can augment AR signaling, several proteins have been found to affect AR signaling through their interaction with ?-catenin. Here, we investigated inhibitor of ?-catenin and T-cell factor (ICAT), a ?-catenin binding protein that inhibits the canonical Wnt/?-catenin signaling pathway, in AR signaling. We demonstrated that expression of ICAT in two AR positive prostate cancer cell lines, LNCaP and LAPC4, augments ligand-dependent AR-mediated transcription. In contrast, short hairpin RNA knockdown of ICAT and ?-catenin specifically blocks enhanced AR-mediated transcription by ICAT. Using both stable expression of ICAT and short hairpin RNA knockdown of ICAT expression approaches, we further showed that ICAT enhances expression of endogenous PSA and KLK2, two androgen response genes, and ligand-induced cell growth. In addition, we identified that ICAT and AR can form a ternary complex with ?-catenin using in vitro glutathione S-transferase protein pulldown assays. Moreover, we detected the endogenous protein complex containing ICAT, AR, and ?-catenin in prostate cancer cells using immunoprecipitation assays. Recruitment of endogenous ICAT onto the promoter region of the human PSA gene, an AR downstream target promoter, was also identified in LNCaP cells. Finally, using in vitro protein binding assays, we examined the effect of full-length and truncated ICAT on the AR-?-catenin interaction and observed that addition of full-length ICAT retained the interaction between ?-catenin and AR proteins. Intriguingly, the truncated ICAT comprising the N-terminal helical domain showed a more pronounced effect on ?-catenin binding to AR proteins. Our findings suggest a novel molecular mechanism underlying the cross talk between androgen and Wnt signaling pathways.

    View details for DOI 10.1210/me.2011-1023

    View details for Web of Science ID 000295322700001

    View details for PubMedID 21885566

  • Conditional Expression of the Androgen Receptor Induces Oncogenic Transformation of the Mouse Prostate JOURNAL OF BIOLOGICAL CHEMISTRY Zhu, C., Luong, R., Zhuo, M., Johnson, D. T., McKenney, J. K., Cunha, G. R., Sun, Z. 2011; 286 (38): 33478-33488

    Abstract

    The androgen signaling pathway, mediated through the androgen receptor (AR), is critical in prostate tumorigenesis. However, the precise role of AR in prostate cancer development and progression still remains largely unknown. Specifically, it is unclear whether overexpression of AR is sufficient to induce prostate tumor formation in vivo. Here, we inserted the human AR transgene with a LoxP-stop-loxP (LSL) cassette into the mouse ROSA26 locus, permitting "conditionally" activated AR transgene expression through Cre recombinase-mediated removal of the LSL cassette. By crossing this AR floxed strain with Osr1-Cre (odd skipped related) mice, in which the Osr1 promoter activates at embryonic day 11.5 in urogenital sinus epithelium, we generated a conditional transgenic line, R26hAR(loxP):Osr1-Cre+. Expression of transgenic AR was detected in both prostatic luminal and basal epithelial cells and is resistant to castration. Approximately one-half of the transgenic mice displayed mouse prostatic intraepithelial neoplasia (mPIN) lesions. Intriguingly, four mice (10%) developed prostatic adenocarcinomas, with two demonstrating invasive diseases. Positive immunostaining of transgenic AR protein was observed in the majority of atypical and tumor cells in the mPIN and prostatic adenocarcinomas, providing a link between transgenic AR expression and oncogenic transformation. An increase in Ki67-positive cells appeared in all mPIN and prostatic adenocarcinoma lesions of the mice. Thus, we demonstrated for the first time that conditional activation of transgenic AR expression by Osr1 promoter induces prostate tumor formation in mice. This new AR transgenic mouse line mimics the human disease and can be used for study of prostate tumorigenesis and drug development.

    View details for DOI 10.1074/jbc.M111.269894

    View details for Web of Science ID 000294968800065

    View details for PubMedID 21795710

  • ZMIZ1 Preferably Enhances the Transcriptional Activity of Androgen Receptor with Short Polyglutamine Tract PLOS ONE Li, X., Zhu, C., Tu, W. H., Yang, N., Qin, H., Sun, Z. 2011; 6 (9)

    Abstract

    The androgen receptor (AR) is a ligand-induced transcription factor and contains the polyglutamine (polyQ) tracts within its N-terminal transactivation domain. The length of polyQ tracts has been suggested to alter AR transcriptional activity in prostate cancer along with other endocrine and neurologic disorders. Here, we assessed the role of ZMIZ1, an AR co-activator, in regulating the activity of the AR with different lengths of polyQ tracts as ARQ9, ARQ24, and ARQ35 in prostate cancer cells. ZMIZ1, but not ZMIZ2 or ARA70, preferably augments ARQ9 induced androgen-dependent transcription on three different androgen-inducible promoter/reporter vectors. A strong protein-protein interaction between ZMIZ1 and ARQ9 proteins was shown by immunoprecipitation assays. In the presence of ZMIZ1, the N and C-terminal interaction of the ARQ9 was more pronounced than ARQ24 and ARQ35. Both Brg1 and BAF57, the components of SWI/SNF complexes, were shown to be involved in the enhancement of ZMIZ1 on AR activity. Using the chromatin immunoprecipitation assays (ChIP), we further demonstrated a strong recruitment of ZMIZ1 by ARQ9 on the promoter of the prostate specific antigen (PSA) gene. These results demonstrate a novel regulatory role of ZMIZ1 in modulating the polyQ tract length of AR in prostate cancer cells.

    View details for DOI 10.1371/journal.pone.0025040

    View details for Web of Science ID 000295260400040

    View details for PubMedID 21949845

  • Efficacy of c-Met inhibitor for advanced prostate cancer BMC CANCER Tu, W. H., Zhu, C., Clark, C., Christensen, J. G., Sun, Z. 2010; 10

    Abstract

    Aberrant expression of HGF/SF and its receptor, c-Met, often correlates with advanced prostate cancer. Our previous study showed that expression of c-Met in prostate cancer cells was increased after attenuation of androgen receptor (AR) signalling. This suggested that current androgen ablation therapy for prostate cancer activates c-Met expression and may contribute to development of more aggressive, castration resistant prostate cancer (CRPC). Therefore, we directly assessed the efficacy of c-Met inhibition during androgen ablation on the growth and progression of prostate cancer.We tested two c-Met small molecule inhibitors, PHA-665752 and PF-2341066, for anti-proliferative activity by MTS assay and cell proliferation assay on human prostate cancer cell lines with different levels of androgen sensitivity. We also used renal subcapsular and castrated orthotopic xenograft mouse models to assess the effect of the inhibitors on prostate tumor formation and progression.We demonstrated a dose-dependent inhibitory effect of PHA-665752 and PF-2341066 on the proliferation of human prostate cancer cells and the phosphorylation of c-Met. The effect on cell proliferation was stronger in androgen insensitive cells. The c-Met inhibitor, PF-2341066, significantly reduced growth of prostate tumor cells in the renal subcapsular mouse model and the castrated orthotopic mouse model. The effect on cell proliferation was greater following castration.The c-Met inhibitors demonstrated anti-proliferative efficacy when combined with androgen ablation therapy for advanced prostate cancer.

    View details for DOI 10.1186/1471-2407-10-556

    View details for Web of Science ID 000283493100001

    View details for PubMedID 20946682

  • Xeno-oestrogens and phyto-oestrogens are alternative ligands for the androgen receptor ASIAN JOURNAL OF ANDROLOGY Wang, H., Li, J., Gao, Y., Xu, Y., Pan, Y., Tsuji, I., Sun, Z., Li, X. 2010; 12 (4): 535-547

    Abstract

    The androgen receptor (AR) plays a critical role in prostate cancer development and progression. This study aimed to use a computerized docking approach to examine the interactions between the human AR and phyto-oestrogens (genistein, daidzein, and flavone) and xeno-oestrogens (bisphenol A, 4-nonylphenol, dichlorodiphenyl trichloroethane [DDT], diethylstilbestrol [DES]). The predicted three-dimensional structure of AR and androgens was established using X-ray diffraction. The binding of four xeno-oestrogens and three phyto-oestrogens to AR was analysed. The steroids estradiol and dihydrotestosterone (DHT) were used as positive controls and thyroxine as negative control. All the ligands shared the same binding site except for thyroxine. The endogenous hormones DHT and 17beta-oestradiol showed the strongest binding with the lowest affinity energy (< -10 kcal mol(-1)). All three phyto-oestrogens and two xeno-oestrogens (bisphenol A and DES) showed strong binding to AR. The affinities of flavone, genistein, and daidzein were between -8.8 and -8.5 kcal mol(-1), while that of bisphenol A was -8.1 kcal mol(-1) and DES -8.3 kcal mol(-1). Another two xeno-oestrogens, 4-nonylphenol and DDT, although they fit within the binding domain of AR, showed weak affinity (-6.4 and -6.7 kcal mol(-1), respectively). The phyto-oestrogens genistein, daidzein and flavone, and the xeno-oestrogens bisphenol A and DES can be regarded as androgenic effectors. The xeno-oestrogens DDT and 4-nonylphenol bind only weakly to AR.

    View details for DOI 10.1038/aja.2010.14

    View details for Web of Science ID 000279471200009

    View details for PubMedID 20436506

  • A Novel Role for Protein Inhibitor of Activated STAT (PIAS) Proteins in Modulating the Activity of Zimp7, a Novel PIAS-like Protein, in Androgen Receptor-mediated Transcription JOURNAL OF BIOLOGICAL CHEMISTRY Peng, Y., Lee, J., Zhu, C., Sun, Z. 2010; 285 (15): 11465-11475

    Abstract

    The PIAS proteins (protein inhibitor of activated STAT) were originally identified as inhibitors of the JAK-STAT pathway. Subsequently, their roles on transcriptional regulation have been identified in modulation of the androgen receptor (AR) and other nuclear hormone receptor-mediated actions. Zimp7, also named Zmiz2, is a novel PIAS-like protein and functions as a transcriptional co-activator. In this study, we demonstrate an interaction between Zimp7 and PIAS proteins with higher preference for PIAS3. A modified mammalian one-hybrid assay showed that the NH(2)-terminal proline-rich domain of Zimp7 and the region spanning amino acids 321-486 of PIAS3 were the primary interaction segments. The interaction between Zimp7 and PIAS3 proteins was further confirmed by in vitro protein pull-down and co-immunoprecipitation assays with both exogenous and endogenous proteins. Expression of exogenous PIAS3 further enhances Zimp7-mediated augmentation of AR transcription. Knockdown of the endogenous PIAS3 protein using a specific PIAS3 small hairpin RNA reduced the augmentation of Zimp7 on AR-mediated transcription. Co-localization of Zimp7 and PIAS3 proteins was observed in the nuclei of cells by immunostaining. Exogenous PIAS3 expression enhances the stability of the Zimp7 protein. Using chromatin immunoprecipitation assays, we showed that PIAS3 is involved in the AR- and Zimp7-formed protein complex(es) in the AR downstream target promoter to facilitate androgen-induced transcription. Finally, we further demonstrated that loss of Zimp7 significantly impaired PIAS3-mediated enhancement on AR activity in mouse Zimp7 null (zimp7(-/-)) embryonic fibroblasts. Taken together, these results demonstrate a novel interaction between PIAS and PIAS-like proteins and elucidate a novel regulatory mechanism for PIAS proteins in AR-mediated transcription.

    View details for DOI 10.1074/jbc.M109.079327

    View details for Web of Science ID 000276286200053

    View details for PubMedID 20159969

  • The PIAS-like protein Zimp10 is essential for embryonic viability and proper vascular development MOLECULAR AND CELLULAR BIOLOGY Beliakoff, J., Lee, J., Ueno, H., Aiyer, A., Weissman, I. L., Barsh, G. S., Cardiff, R. D., Sun, Z. 2008; 28 (1): 282-292

    Abstract

    Members of the PIAS (for protein inhibitor of activated STAT) family play critical roles in modulating the activity of a variety of transcriptional regulators. Zimp10, a novel PIAS-like protein, is a transcriptional coregulator and may be involved in the modification of chromatin through interactions with the SWI/SNF chromatin-remodeling complexes. Here, we investigate the biological role of Zimp10 in zimp10-deficient mice. Homozygosity for the Zimp10-targeted allele resulted in developmental arrest at approximately embryonic day 10.5. Analysis of knockout embryos revealed severe defects in the reorganization of the yolk sac vascular plexus. No significant abnormality in hematopoietic potential was observed in zimp10 null mice. Microarray and quantified reverse transcription-PCR analyses showed that the expression of the Fos family member Fra-1, which is involved in extraembryonic vascular development, was reduced in yolk sac tissues of zimp10 null embryos. Using fra-1 promoter/reporter constructs, we further demonstrate the regulatory role of Zimp10 on the transcription of Fra-1. This study provides evidence to demonstrate a crucial role for Zimp10 in vasculogenesis.

    View details for DOI 10.1128/MCB.00771-07

    View details for Web of Science ID 000251925300024

    View details for PubMedID 17967885

  • A promoting role of androgen receptor in androgen-sensitive and -insensitive prostate cancer cells NUCLEIC ACIDS RESEARCH Li, T., Zhao, H., Peng, Y., Beliakoff, J., Brooks, J. D., Sun, Z. 2007; 35 (8): 2767-2776

    Abstract

    Although the vital role of the androgen receptor (AR) has been well demonstrated in primary prostate cancers, its role in the androgen-insensitive prostate cancers still remains unclear. Here, we used a small hairpin RNA approach to directly assess AR activity in prostate cancer cells. Reduction of AR expression in the two androgen-sensitive prostate cancer cell lines, LNCaP and LAPC4, significantly decreased AR-mediated transcription and cell growth. Intriguingly, in two androgen-insensitive prostate cell lines, LNCaP-C42B4 and CWR22Rv1, knockdown of AR expression showed a more pronounced effect on AR-induced transcription and cell growth than androgen depletion. Using cDNA microarrays, we also compared the transcriptional profiles induced by either androgen depletion or AR knockdown. Although a significant number of transcripts appear to be regulated by both androgen depletion and AR knockdown, we observed a subset of transcripts affected only by androgen depletion but not by AR knockdown, and vice versa. Finally, we demonstrated a direct role for AR in promoting tumor formation and growth in a xenograft model. Taken together, our results elucidate an important role for the AR in androgen-insensitive prostate cancer cells, and suggest that AR can be used as a therapeutic target for androgen-insensitive prostate cancers.

    View details for DOI 10.1093/nar/gkm198

    View details for Web of Science ID 000247239600029

    View details for PubMedID 17426117

  • The androgen receptor negatively regulates the expression of c-Met: Implications for a novel mechanism of prostate cancer progression CANCER RESEARCH Verras, M., Lee, J., Xue, H., Li, T., Wang, Y., Sun, Z. 2007; 67 (3): 967-975

    Abstract

    The precise molecular mechanisms by which prostate cancer cells progress from androgen-sensitive to androgen-insensitive status still remain largely unclear. The hepatocyte growth factor/scatter factor (HGF/SF) plays a critical role in the regulation of cell growth, cell motility, morphogenesis, and angiogenesis. The aberrant expression of HGF/SF and its receptor, c-Met, often correlates with poor prognosis in a variety of human malignancies, including prostate cancer. Here, we investigate a potential link between androgen signaling and c-Met expression in prostate cancer cells. First, we showed that the androgen receptor (AR) represses the expression of c-Met in a ligand-dependent manner. Using different c-Met promoter/reporter constructs, we identified that Sp1 induces the transcription of c-Met and that AR can repress the Sp1-induced transcription in prostate cancer cells. Moreover, the data from electrophoretic mobility shift assay showed that AR interferes with the interaction between Sp1 and the functional Sp1 binding site within the c-Met promoter. Furthermore, we tested the effect of AR on c-Met expression in an androgen-insensitive prostate cancer cell line, CWR22Rv1. Finally, the repressive role of androgen signaling on c-Met expression was confirmed in prostate cancer xenografts. The above data indicate a dual role of AR in transcriptional regulation. Although the current androgen ablation therapy can repress the expression of growth-promoting genes that are activated by the AR, it may also attenuate the repressive role of AR on c-Met expression. Therefore, the therapeutic strategies to inhibit the activation of the HGF/c-Met pathway may be of benefit when combined with current androgen ablation treatment.

    View details for DOI 10.1158/0008-5472.CAN-06-3552

    View details for Web of Science ID 000244137300019

    View details for PubMedID 17283128

  • The novel PIAS-like protein hZimp10 is a transcriptional co-activator of the p53 tumor suppressor NUCLEIC ACIDS RESEARCH Lee, J., Beliakoff, J., Sun, Z. 2007; 35 (13): 4523-4534

    Abstract

    The tumor suppressor, p53, plays critical roles in the cell cycle progression, DNA repair and apoptosis. The PIAS proteins (protein inhibitor of activated STAT) were originally identified as inhibitors of the JAK-STAT pathway. Subsequently, crosstalk between the PIAS proteins and other signaling pathways has been shown to be involved in various cellular processes. Particularly, previous studies have demonstrated that PIAS proteins regulate p53-mediated transcription through sumoylation. hZimp10, also named zmiz1, is a novel PIAS-like protein and functions as a transcriptional co-activator. We recently identified p53 to be an hZimp10 interacting protein in the yeast two-hybrid screen. The interaction between p53 and hZimp10 was confirmed by GST pull-down and co-immunoprecipitation assays. Co-localization of p53 and hZimp10 proteins was also observed within cell nuclei by immunostaining. Moreover, we show that expression of exogenous hZimp10 enhances the transcriptional activity of p53 and knockdown of endogenous hZimp10 reduces the transcriptional activity of p53. Furthermore, using chromatin immunoprecipitation assays, we demonstrate that hZimp10 binds to p53 on the p21 promoter. Finally, p53-mediated transcription is significantly impaired in Zimp10 null embryonic fibroblasts. Taken together, these results provide the first line of evidence to demonstrate a role for Zimp10 in regulating p53 function.

    View details for DOI 10.1093/nar/gkm476

    View details for Web of Science ID 000249390600027

    View details for PubMedID 17584785

  • LZTS2 is a novel beta-catenin-interacting protein and regulates the nuclear export of beta-catenin MOLECULAR AND CELLULAR BIOLOGY Thyssen, G., Li, T., Lehmann, L., Zhuo, M., Sharma, M., Sun, Z. 2006; 26 (23): 8857-8867

    Abstract

    Beta-catenin plays multiple roles in cell-cell adhesion and Wnt signal transduction. Through the Wnt signal, the cellular level of beta-catenin is constitutively regulated by the multicomponent destruction complex containing glycogen synthase kinase 3beta, axin, and adenomatous polyposis coli. Here, we present multiple lines of evidence to demonstrate that LZTS2 (lucine zipper tumor suppressor 2) interacts with beta-catenin, represses the transactivation of beta-catenin, and affects the subcellular localization of beta-catenin. The LZTS2 gene is located at 10q24.3, which is frequently lost in a variety of human tumors. A functional nuclear export signal (NES) was identified in the C terminus of the protein (amino acids 631 to 641). Appending this motif to green fluorescent protein (GFP) induced nuclear exclusion of the GFP fusion protein. However, introducing point mutations in either one or two leucine residues of this NES sequence abolished the nuclear exclusion of the LZTS2 protein. The nuclear export of LZTS2 can be blocked by leptomycin B (LMB), an inhibitor of the CRM1/exportin-alpha pathway. Intriguingly, beta-catenin colocalizes with LZTS2 in the cytoplasm of cells in the absence of LMB but in the nuclei of cells in the presence of LMB. Increasing the LZTS2 protein in cells reduces the level of nuclear beta-catenin in SW480 cells. Taken together, these data demonstrate that LZTS2 is a beta-catenin-interacting protein that can modulate beta-catenin signaling and localization.

    View details for DOI 10.1128/MCB.01031-06

    View details for Web of Science ID 000242203700016

    View details for PubMedID 17000760

  • The novel PIAS-like protein hZimp10 enhances Smad transcriptional activity JOURNAL OF BIOLOGICAL CHEMISTRY Li, X., Thyssen, G., Beliakoff, J., Sun, Z. 2006; 281 (33): 23748-23756

    Abstract

    Transforming growth factor beta (TGF-beta) plays critical roles in the control of cell proliferation, differentiation, and apoptosis. Smad proteins are substrates of the TGF-beta type I receptor and are responsible for transducing receptor signals to target genes in the nucleus. The PIAS (protein inhibitor of activated STAT) proteins were originally identified as transcriptional co-regulators of the JAK-STAT pathway. Subsequently, cross-talk between the PIAS proteins and other signaling pathways has been shown to be involved in various cellular processes. Importantly, PIAS proteins modulate TGF-beta signaling by regulating the transcriptional activity of Smad3. In this study we tested whether hZimp10, a novel PIAS-like protein, acts as other PIAS proteins to regulate Smad3-mediated transcription. We show that expression of exogenous hZimp10 enhances the transcriptional activity of Smad3, which appears to be Smad4-dependent and responsive to TGF-beta induction. Furthermore, knockdown of endogenous hZimp10 reduced the transcriptional activity of Smad3. A protein-protein interaction between Smad3 and Smad4 with hZimp10 was identified in glutathione S-transferase-pulldown and co-immunoprecipitation assays. The Miz domain of hZimp10 and the MH2 domains of Smad3 and Smad4 were mapped as the regions responsible for binding. Results from immunostaining assays further demonstrated that Smad3, Smad4, and hZimp10 co-localize within cell nuclei. Finally, we demonstrated that Smad3/4-mediated transcription is significantly impaired in response to TGF-beta induction in Zimp10 null (zimp10-/-) embryonic fibroblasts. Taken together, these results provide the first line of evidence to demonstrate a role for Zimp10 in regulating the TGF-beta/Smad signaling pathway.

    View details for DOI 10.1074/jbc.M508365200

    View details for Web of Science ID 000239702900050

    View details for PubMedID 16777850

  • Roles and regulation of Wnt signaling and beta-catenin in prostate cancer CANCER LETTERS Verras, M., Sun, Z. 2006; 237 (1): 22-32

    Abstract

    The Wnt signaling pathway and its key component beta-catenin play critical roles in embryonic development as well as in human diseases, including various malignancies. Accumulated evidence has demonstrated a significant role for the Wnt pathway in the development and progression of human prostate cancer. The recent discovery of an interaction between beta-catenin and the androgen receptor (AR) suggests a possible mechanism of cross talk between Wnt and androgen signaling pathways. In this review, we summarize the recent progresses in this interesting and growing field. Particularly, we focus on the observation that the activation of the Wnt-mediated signal occurs in a different manner in prostate cancer than in colorectal cancer or other human malignancies. Since mutations in Adenomatous polyposis coli (APC), beta-catenin, and other components of the beta-catenin destruction complex are rare in prostate cancer cells, other regulatory mechanisms appear to play dominant roles in the activation of beta-catenin, such as loss or reduction of E-cadherin, a component of cell adhesion complex, and abnormal expression of Wnt ligands, receptors, inhibitors, and other co-regulators. Understanding the role and regulation of the Wnt signaling pathway in prostate cancer cells may help identify new targets for the prostate cancer therapy.

    View details for DOI 10.1016/j.canlet.2005.06.004

    View details for Web of Science ID 000238247300003

    View details for PubMedID 16023783

  • Cyclin D1 and p16 expression in recurrent nasopharyngeal carcinoma. World journal of surgical oncology Lin, H., Berry, G. J., Sun, Z., Fee, W. E. 2006; 4: 62-?

    Abstract

    Cyclin D1 and p16 are involved in the regulation of G1 checkpoint and may play an important role in the tumorigenesis of nasopharyngeal carcinoma (NPC). Previous studies have examined the level of expression of cyclin D1 and p16 in primary untreated NPC but no such information is available for recurrent NPC. We set out in this study to examine the expression level of cyclin D1 and p16 in recurrent NPC that have failed previous treatment with radiation +/- chemotherapy.A total of 42 patients underwent salvage nasopharyngectomy from 1984 to 2001 for recurrent NPC after treatment failure with radiation +/- chemotherapy. Twenty-seven pathologic specimens were available for immunohistochemical study using antibodies against cyclin D1 and p16.Positive expression of cyclin D1 was observed in 7 of 27 recurrent NPC specimens (26%) while positive p16 expression was seen in only 1 of 27 recurrent NPC (4%).While the level of expression of cyclin D1 in recurrent NPC was similar to that of previously untreated head and neck cancer, the level of p16 expression in recurrent NPC samples was much lower than that reported for previously untreated cancer. The finding that almost all (96%) of the recurrent NPC lack expression of p16 suggested that loss of p16 may confer a survival advantage by making cancer cells more resistant to conventional treatment with radiation +/- chemotherapy. Further research is warranted to investigate the clinical use of p16 both as a prognostic marker and as a potential therapeutic target.

    View details for PubMedID 16953893

  • Zimp7 and Zimp10, two novel PIAS-like proteins, function as androgen receptor coregulators. Nuclear receptor signaling Beliakoff, J., Sun, Z. 2006; 4

    Abstract

    The androgen receptor (AR) plays a critical role in male sexual development and in normal and malignant prostate cell growth and survival. It has been shown that AR transcriptional activation is regulated through interactions with a variety of transcriptional co-regulators. The Protein Inhibitors of Activated STATs (PIAS) are transcriptional co-regulators, and have been shown to modulate AR-mediated transcription. In this brief, we summarize our recent studies on two novel PIAS-like proteins, Zimp7 and Zimp10. Particularly, we address the functional interactions between the AR and these two proteins, and potential mechanisms by which they regulate AR mediated transcription. In addition, we explore potential roles of Zimp10 in transcriptional regulation in vivo using a recent Zimp10 knockout mouse model. Taken together, our findings thus far suggest that Zimp7 and Zimp10 are functionally non-redundant and share unique characteristics that have not been described for the PIAS family. Further investigation into the functional roles of these two PIAS-like proteins may help to better understand prostate cancer progression, and yield possible new targets for therapeutic intervention.

    View details for PubMedID 16862223

  • hZimp7, a novel PIAS-like protein, enhances androgen receptor-mediated transcription and interacts with SWI/SNF-like BAF complexes MOLECULAR ENDOCRINOLOGY Huang, C. Y., Beliakoff, J., Li, X. Y., Lee, J., Li, X. M., Sharma, M., Lim, B., Sun, Z. J. 2005; 19 (12): 2915-2929

    Abstract

    Members of the PIAS (protein inhibitor of activated signal transducer and activator of transcription) family are negative regulators of the Janus family of tyrosine kinase (JAK)-signal transducer and activator of transcription pathway. Recently, PIAS proteins have been shown to interact with multiple signaling pathways in various cellular processes, and it has been demonstrated that PIAS and PIAS-like proteins interact with nuclear hormone receptors. In this study, we have identified a novel human PIAS-like protein, provisionally termed hZimp7, which shares a high degree of sequence similarity with hZimp10 (human zinc finger-containing, Miz1, PIAS-like protein on chromosome 10). hZimp7 (human zinc finger-containing, Miz1, PIAS-like protein on chromosome 7) possesses a molecular mass of approximately 100 kDa and contains a conserved Miz (msx-interacting zinc finger) domain, a nuclear translocation signal sequence, and a C-terminal transactivation domain. Northern blot analysis revealed that hZimp7 is predominantly expressed in testis, heart, brain, prostate, and ovary. Moreover, immunohistochemical staining of prostate tissues revealed that endogenous hZimp7 protein localizes to the nuclei of prostate epithelial cells and costains with the androgen receptor (AR). Further analysis of hZimp7 subcellular localization revealed that hZimp7 and the AR colocalize within the nucleus and form a protein complex at replication foci. Transient transfection experiments showed that hZimp7 augments the transcriptional activity of the AR and other nuclear hormone receptors. In contrast, reduction of endogenous hZimp7 protein expression by RNA interference decreased AR-mediated transcription. Finally, we determined that hZimp7 physically associates with Brg1 and BAF57, components of the ATP-dependent mammalian SWI/SNF-like BAF chromatin-remodeling complexes. The above data illustrate a potential role for hZimp7 in modulation of AR and/or other nuclear receptor-mediated transcription, possibly through alteration of chromatin structure by SWI/SNF-like BAF complexes.

    View details for DOI 10.1210/me.2005-0097

    View details for Web of Science ID 000233460500003

    View details for PubMedID 16051670

  • beta-catenin is involved in insulin-like growth factor 1-mediated transactivation of the androgen receptor MOLECULAR ENDOCRINOLOGY Verras, M., Sun, Z. J. 2005; 19 (2): 391-398

    Abstract

    The androgen-signaling pathway is important for the growth and progression of prostate cancer cells. IGF-I and other polypeptide growth factors have been shown to be capable of induction of androgen receptor (AR) activation in the absence of, or at low levels of, ligand. It has been shown that IGF-I increases the cellular level of beta-catenin, an AR coactivator. In this study, we performed several experiments to test whether beta-catenin is involved in IGF-I-induced AR-mediated transcription. We demonstrate that IGF-I enhances the expression of endogenous prostate-specific antigen, an AR target gene, and elevates the level of cytoplasmic and nuclear beta-catenin in prostate cancer cells. Transfection of either wild-type or a constitutively active mutant of the IGF-I receptor augments AR-mediated transcription. An antisense construct of beta-catenin that decreases the cellular level of beta-catenin can reduce IGF-1 receptor-mediated enhancement of AR activity. Moreover, using a pulse-chase experiment, we showed that IGF-I enhances the stability of beta-catenin in prostate cancer cells. Our findings delineate a novel pathway for IGF-I in modulating androgen signaling through beta-catenin.

    View details for DOI 10.1210/me.2004-0208

    View details for Web of Science ID 000226543200009

    View details for PubMedID 15514031

  • Wnt3a growth factor induces androgen receptor-mediated transcription and enhances cell growth in human prostate cancer cells CANCER RESEARCH Verras, M., Brown, J., Li, X. M., Nusse, R., Sun, Z. J. 2004; 64 (24): 8860-8866

    Abstract

    The Wnt signaling pathway plays a critical role in embryogenesis and tumorigenesis. However, biological roles of Wnt growth factors have not been fully characterized in prostate development and the pathogenesis of prostate cancer. In this study, we used Wnt3a-conditioned medium (Wnt3a-CM) and purified Wnt3a proteins to investigate whether there is a direct effect of Wnt3a on androgen receptor (AR)-mediated transcription and to determine its role in the growth of prostate cancer cells. We demonstrated that Wnt3a-CM either induces AR activity in the absence of androgens or enhances AR activity in the presence of low concentrations of androgens, whereas purified Wnt3a showed a pronounced effect in the presence of low concentrations of ligands. We also showed that Wnt3a-CM and the purified Wnt3a enhance the level of cytosolic and nuclear beta-catenin, suggesting an involvement of beta-catenin in this regulation. Moreover, treatment of LNCaP cells with Wnt3a-CM and purified Wnt3a significantly enhances cell growth in the absence of androgens. Our findings demonstrate that Wnt3a plays an important role in androgen-mediated transcription and cell growth. These results suggest a novel mechanism for the progression of prostate cancer.

    View details for Web of Science ID 000225809200013

    View details for PubMedID 15604245

  • An Hsp27-related, dominant-negative-acting intracellular estradiol-binding protein JOURNAL OF BIOLOGICAL CHEMISTRY Chen, H., Hewison, M., Hu, B., Sharma, M., Sun, Z. J., Adams, J. S. 2004; 279 (29): 29944-29951

    Abstract

    New World primates (NWPs) exhibit a compensated form of resistance to gonadal steroid hormones. We demonstrated recently that estrogen resistance in NWP cells was associated with the overexpression of two proteins, a nonreceptor-related, dominant-negative-acting estrogen response element (ERE)-binding protein (ERE-BP) and an intracellular estradiol-binding protein (IEBP). Based on the N-terminal sequences of tryptic fragments of IEBP isolated from a 17beta-estradiol (E2) affinity column we cloned a full-length cDNA for IEBP from the estrogen-resistant NWP cell line, B95-8. Subsequent sequence analysis revealed 87% sequence identity between the deduced peptide for IEBP and human Hsp27. When hormone-responsive, wild-type Old World primate (OWP) cells were transiently transfected with IEBP cDNA, E2-directed ERE reporter luciferase activity was reduced by 50% compared with vector only-transfected OWP cells (p < 0.0018). When IEBP and ERE-BP were cotransfected, ERE promoter-reporter activity was reduced by a further 60% (p < 0.0001). Electrophoresis mobility shift analyses showed that IEBP neither bound to ERE nor competed with the estrogen receptor (ER) for binding to ERE. However, there was evidence of protein-protein interaction of IEBP and ERalpha; IEBP was coimmunoprecipitated with anti-ERalpha antibody in wild-type cells stably transfected with IEBP. A specific interaction between ERalpha and IEBP was confirmed in glutathione S-transferase pull-down and yeast two-hybrid assays. Data indicate that the Hsp27-related IEBP interacts with the ligand binding domain of the ERalpha. In summary, by inhibiting the ERalpha-E2 interaction, IEBP acts to squelch ERalpha-directed ERE-regulated transactivation and promote estrogen resistance in NWP cells.

    View details for DOI 10.1074/jbc.M401317200

    View details for Web of Science ID 000222531900011

    View details for PubMedID 15123601

  • Identification of tyrosine kinases overexpressed in head and neck cancer ARCHIVES OF OTOLARYNGOLOGY-HEAD & NECK SURGERY Lin, H. S., Berry, G. J., Fee, W. E., Terris, D. J., Sun, Z. J. 2004; 130 (3): 311-316

    Abstract

    To identify protein-tyrosine kinases (PTKs) that may be involved in the development and progression of head and neck squamous cell carcinoma (HNSCC).Messenger RNA from 7 HNSCC specimens was reverse transcribed to complementary DNA, and selective amplification of PTK complementary DNA was achieved using polymerase chain reaction (PCR) with degenerate PTK primers. The resulting PTK PCR products from these 7 HNSCC specimens were then cloned and randomly selected for sequencing. The PTKs that were represented multiple times in these randomly selected clones were selected as candidate PTKs that may be overexpressed in HNSCC. Antibodies against these candidate PTKs were then used for immunohistochemical studies on 8 other HNSCC specimens not used in the original selection of the candidate PTKs.Three known (EphA1, Brk, and Ron) and 2 novel (KIAA0728 and KIAA0279) PTKs were found to be highly expressed in the 7 HNSCC samples studied, based on the technique of reverse transcriptase-PCR with degenerate primers. Immunohistochemical studies with antibodies against the 3 known PTKs in 8 other HNSCC specimens not used in the previous reverse transcriptase-PCR reaction demonstrated overexpression of EphA1, Brk, and Ron in 12.5%, 37.5%, and 75% of these specimens.In this study, we identified 5 PTKs that were overexpressed in HNSCC using a reverse transcriptase-PCR technique and confirmed the overexpression of 3 known PTKs in some of the 8 archival HNSCC specimens studied. Our finding suggests that the signaling pathways mediated through EphA1, Brk, and Ron may be involved in the development and progression of HNSCC.

    View details for Web of Science ID 000220067500008

    View details for PubMedID 15023838

  • hZimp10 is an androgen receptor co-activator and forms a complex with SUMO-1 at replication foci EMBO JOURNAL Sharma, M. J., Li, X. Y., Wang, Y. Z., Zarnegar, M., Huang, C. Y., PALVIMO, J. J., Lim, B., Sun, Z. J. 2003; 22 (22): 6101-6114

    Abstract

    The androgen receptor (AR) plays a central role in male sexual development and in normal and malignant prostate cell growth and survival. It has been shown that transcriptional activation of AR is regulated through interaction with various co-factors. Here we identify a novel PIAS-like protein, hZimp10, as an AR-interacting protein. The transactivation domain (TAD) of AR and the central region of hZimp10 were found to be responsible for the interaction. A strong intrinsic transactivation domain was identified in the C-terminal, proline-rich region of hZimp10. Endogenous AR and hZimp10 proteins were co-stained in the nuclei of prostate epithelial cells from human tissue samples. In human prostate cancer cells, hZimp10 augmented the transcriptional activity of AR. Moreover, hZimp10 co-localized with AR and SUMO-1 at replication foci throughout S phase, and it was capable of enhancing sumoylation of AR in vivo. Studies using sumoylation deficient AR mutants suggested that the augmentation of AR activity by hZimp10 is dependent on the sumoylation of the receptor. Taken together, these data demonstrate that hZimp10 is a novel AR co-regulator.

    View details for Web of Science ID 000186579300014

    View details for PubMedID 14609956

  • Mechanism of p21-activated kinase 6 (PAK6) - mediated inhibition of androgen receptor signaling J. Biol. Chem Schrantz N, Fowler B, Ge Q, Sun Z, Bokoch GM 2003; 279: 1922-31
  • Linking beta-catenin to androgen-signaling pathway JOURNAL OF BIOLOGICAL CHEMISTRY Yang, F. J., Li, X. Y., Sharma, M., Sasaki, C. Y., Longo, D. L., Lim, B., Sun, Z. J. 2002; 277 (13): 11336-11344

    Abstract

    The androgen-signaling pathway is important for the growth and progression of prostate cancer cells. The growth-promoting effects of androgen on prostate cells are mediated mostly through the androgen receptor (AR). There is increasing evidence that transcription activation by AR is mediated through interaction with other cofactors. beta-Catenin plays a critical role in embryonic development and tumorigenesis through its effects on E-cadherin-mediated cell adhesion and Wnt-dependent signal transduction. Here, we demonstrate that a specific protein-protein interaction occurs between beta-catenin and AR. Unlike the steroid hormone receptor coactivator 1 (SRC1), beta-catenin showed a strong interaction with AR but not with other steroid hormone receptors such as estrogen receptor alpha, progesterone receptor beta, and glucocorticoid receptor. The ligand binding domain of AR and the NH(2) terminus combined with the first six armadillo repeats of beta-catenin were shown to be necessary for the interaction. Through this specific interaction, beta-catenin augments the ligand-dependent activity of AR in prostate cancer cells. Moreover, expression of E-cadherin in E-cadherin-negative prostate cancer cells results in redistribution of the cytoplasmic beta-catenin to the cell membrane and reduction of AR-mediated transcription. These data suggest that loss of E-cadherin can elevate the cellular levels of beta-catenin in prostate cancer cells, which may directly contribute to invasiveness and a more malignant tumor phenotype by augmenting AR activity during prostate cancer progression.

    View details for DOI 10.1074/jbc.M111962200

    View details for Web of Science ID 000174613100075

    View details for PubMedID 11792709

  • A novel zinc finger transcription factor with two isoforms that are differentially repressed by estrogen receptor-alpha JOURNAL OF BIOLOGICAL CHEMISTRY Conroy, A. T., Sharma, M., Holtz, A. E., Wu, C. B., Sun, Z. J., Weigel, R. J. 2002; 277 (11): 9326-9334

    Abstract

    Estrogen receptor-alpha (ERalpha) can induce the expression of genes in response to estrogen by binding to estrogen response elements in the promoters of target genes. There is growing evidence that ERalpha can alter patterns of gene expression in response to ligand by regulating the activity of other factors through a direct protein-protein interaction. To identify other factors that are regulated by ERalpha, a yeast two-hybrid screen was performed that identified a novel Cys(2)His(2) zinc finger protein named ZER6. The ZER6 protein contains a Kruppel-associated box domain and six Cys(2)His(2) zinc fingers. Transcripts from the ZER6 gene can have alternate 5' exons and encode either a p71 or p52 isoform. The p52-ZER6 protein interacts strongly with ERalpha in the presence of 17beta-estradiol, whereas the p71-ZER6 isoform has a HUB-1 amino-terminal domain that inhibits the interaction with ERalpha. A consensus ZER6 binding element was defined using PCR-assisted binding site selection. In COS-1 cells, both the p52 and p71 isoforms can activate transcription through the ZER6 binding element; however, in the presence of ERalpha, transactivation by the p52 isoform is specifically repressed. Overexpression of the p52 isoform was able to abrogate activation by p71-ZER6. Expression of ZER6 was largely restricted to the mammary gland with a lower level of expression in the kidney. We conclude that ZER6 is a novel zinc finger transcription factor in which regulation of transcription in hormone-responsive cells can be controlled by the relative level of expression of two distinct isoforms.

    View details for DOI 10.1074/jbc.M107702200

    View details for Web of Science ID 000174400600080

    View details for PubMedID 11779858

  • Human regulatory factor X 4 (RFX4) is a testis-specific dimeric DNA-binding protein that cooperates with other human RFX members JOURNAL OF BIOLOGICAL CHEMISTRY Morotami-Yano, K., Yano, K., Saito, H., Sun, Z., Iwama, A., Miki, Y. 2002; 277 (1): 836-842

    Abstract

    Regulatory factor X (RFX) members are evolutionarily conserved transcription factors that share a highly conserved winged helix DNA-binding domain. Human RFX4 has been isolated from breast cancer as a partial cDNA encoding a short RFX-type DNA-binding domain fused to the estrogen receptor, but the entire structure of RFX4 has been unknown. Here, we report the molecular cloning and characterization of human RFX4. RFX4 contains evolutionarily conserved regions, including a RFX-type DNA-binding domain, a dimerization domain, and other conserved regions, and is closely related to RFX1, RFX2, and RFX3 in structure. The expression of RFX4 is restricted to testis. In vitro synthesized RFX4 protein bound to typical RFX binding sites in a sequence-dependent manner. Immunoprecipitation analyses showed that RFX4 interacts physically with RFX2, RFX3, and RFX4 itself but not with RFX1. In contrast to other mammalian RFX members that form dimers, RFX4 is revealed to have no distinct transcriptional activation domains. By using a chimeric protein of RFX1 and RFX4, the C-terminal domain of RFX4 was shown to be a possible transcriptional repression domain. Taken together, these results indicate that RFX4 is the first mammalian member of RFX family without transcriptional activation capacity and might function through selective interactions with other RFX members in transcriptional regulation.

    View details for DOI 10.1074/jbc.M108638200

    View details for Web of Science ID 000173087900107

    View details for PubMedID 11682486

  • Regulation of androgen signaling by the phosphatidylinosital 3-kinase/Akt is mediated through GSK3beta/beta-catenin pathway J. Biol. Chem Sharma M, Chuang WW, Sun ZJ 2002; 277: 30935-30941
  • 5 ' TG3 ' interacting factor interacts with Sin3A and represses AR-mediated transcription MOLECULAR ENDOCRINOLOGY Sharma, M., Sun, Z. 2001; 15 (11): 1918-1928

    Abstract

    Like other nuclear receptors, the AR exerts its transcriptional function by binding to cis elements upstream of promoters and interacting with other transcriptional factors (e.g. activators, repressors, and modulators). Among them, histone acetyltransferases (HATs) and histone deacetylases (HDACs) play critical roles in altering the acetylation state of core histones, thereby regulating nuclear hormone receptor-mediated transcription. The nuclear receptor corepressor can repress the TR and RAR in the absence of ligand through either a Sin3A-dependent or -independent manner by recruiting HDACs. AR and some other steroid hormone receptors cannot silence transcription through a similar mechanism in that they are located in the cytoplasm as complexes with heat-shock proteins before exposure to ligand. It has been shown that AR can bind to p160/SRC, cAMP response element-binding protein-binding protein (CBP)/P300 and other coactivators to increase the AR-mediated transcription. However, the molecular mechanism for turning AR from transcriptionally active into silent states is unknown. In this study, we demonstrated that the transcription repressor, 5'TG3' interacting factor (TGIF), selectively represses AR-mediated transcription from several AR-responsive promoters. The repression is mediated through binding of TGIF to the DNA binding domain of AR and is trichostatin sensitive. We also identified a direct protein-protein interaction between TGIF and a transcription corepressor, Sin3A, which suggests a novel pathway for TGIF recruiting HDAC1 to the repression complex. These results provide fresh insight into understanding the mechanism for repressing AR-, and perhaps other steroid hormone receptor-, mediated transcriptions.

    View details for Web of Science ID 000171821200007

    View details for PubMedID 11682623

  • Ligand-dependent interaction of estrogen receptor-alpha with members of the forkhead transcription factor family JOURNAL OF BIOLOGICAL CHEMISTRY Schuur, E. R., Loktev, A. V., Sharma, M., Sun, Z. J., Roth, R. A., Weigel, R. J. 2001; 276 (36): 33554-33560

    Abstract

    Estrogen acting through the estrogen receptor (ER) is able to regulate cell growth and differentiation of a variety of normal tissues and hormone-responsive tumors. Ligand-activated ER binds DNA and transactivates the promoters of estrogen target genes. In addition, ligand-activated ER can interact with other factors to alter the physiology and growth of cells. Using a yeast two-hybrid screen, we have identified an interaction between ER alpha and the proapoptotic forkhead transcription factor FKHR. The ER alpha-FKHR interaction depends on beta-estradiol and is reduced significantly in the absence of hormone or the presence of Tamoxifen. A glutathione S-transferase pull-down assay was used to confirm the interaction and localized two interaction sites, one in the forkhead domain and a second in the carboxyl terminus. The FKHR interaction was specific to ER alpha and was not detected with other ligand-activated steroid receptors. The related family members, FKHRL1 and AFX, also bound to ER alpha in the presence of beta-estradiol. FKHR augmented ER alpha transactivation through an estrogen response element. Conversely, ER alpha repressed FKHR-mediated transactivation through an insulin response sequence, and cell cycle arrest induced by FKHRL1 in MCF7 cells was abrogated by estradiol. These results suggest a novel mechanism of estrogen action that involves regulation of the proapoptotic forkhead transcription factors.

    View details for Web of Science ID 000170910200037

    View details for PubMedID 11435445

  • Androgen receptor specifically interacts with a novel p21-activated kinase, PAK6 JOURNAL OF BIOLOGICAL CHEMISTRY Yang, F., Lio, X. Y., Sharma, M. J., Zarnegar, M., Lim, B., Sun, Z. 2001; 276 (18): 15345-15353

    Abstract

    The androgen receptor (AR) is a hormone-dependent transcription factor that plays important roles in male sexual differentiation and development. Transcription activation by steroid hormone receptors, such as the androgen receptor, is mediated through interaction with cofactors. We recently identified a novel AR-interacting protein, provisionally termed PAK6, that shares a high degree of sequence similarity with p21-activated kinases (PAKs). PAK6 is a 75-kDa protein that contains a putative amino-terminal Cdc42/Rac interactive binding motif and a carboxyl-terminal kinase domain. A domain-specific and ligand-dependent interaction between AR and PAK6 was further confirmed in vivo and in vitro. Northern blot analysis revealed that PAK6 is highly expressed in testis and prostate tissues. Most importantly, immunofluorescence studies showed that PAK6 cotranslocates into the nucleus with AR in response to androgen. Transient transfection experiments showed that PAK6 specifically repressed AR-mediated transcription. This report identifies a novel function for a PAK-homologous protein and suggests a potential unique mechanism by which other signal transduction pathways may cross-talk with AR pathways to regulate AR function in normal and malignant prostate cells.

    View details for Web of Science ID 000168528800109

    View details for PubMedID 11278661

  • Cyclin D1 binds the androgen receptor and regulates hormone-dependent signaling in a p300/CBP-associated factor (P/CAF)-dependent manner MOLECULAR ENDOCRINOLOGY Reutens, A. T., Fu, M. F., Wang, C. G., Albanese, C., McPhaul, M. J., Sun, Z. J., Balk, S. P., JANNE, O. A., PALVIMO, J. J., Pestell, R. G. 2001; 15 (5): 797-811

    Abstract

    The androgen receptor (AR) is a ligand-regulated member of the nuclear receptor superfamily. The cyclin D1 gene product, which encodes the regulatory subunit of holoenzymes that phosphorylate the retinoblastoma protein (pRB), promotes cellular proliferation and inhibits cellular differentiation in several different cell types. Herein the cyclin D1 gene product inhibited ligand-induced AR- enhancer function through a pRB-independent mechanism requiring the cyclin D1 carboxyl terminus. The histone acetyltransferase activity of P/CAF (p300/CBP associated factor) rescued cyclin D1-mediated AR trans-repression. Cyclin D1 and the AR both bound to similar domains of P/CAF, and cyclin D1 displaced binding of the AR to P/CAF in vitro. These studies suggest cyclin D1 binding to the AR may repress ligand-dependent AR activity by directly competing for P/CAF binding.

    View details for Web of Science ID 000168393200009

    View details for PubMedID 11328859

  • SMAD3 represses androgen receptor-mediated transcription CANCER RESEARCH Hayes, S. A., Zarnegar, M., Sharma, M., Yang, F. J., Peehl, D. M., ten Dijke, P., Sun, Z. J. 2001; 61 (5): 2112-2118

    Abstract

    The androgen-signaling pathway is important in the growth and progression of prostate cancer. Androgen ablation therapy, which may result in programmed cell death, is often used to treat advanced prostate cancer. The growth-promoting effects of androgen are mediated mostly through the androgen receptor (AR). Transforming growth factor beta (TGF-beta) plays critical roles in controlling prostate cell proliferation, differentiation, and apoptosis. Normal transcripts and proteins of TGF-beta receptors are frequently lost in prostate cancer cells, especially in advanced stages of the disease. However, the mechanisms by which TGF-beta inhibits proliferation and induces apoptosis in prostate cancer cells is not clear. We investigated the molecular mechanism by which TGF-beta inhibits transcriptional activation mediated by AR. Using transient transfection systems, we demonstrated that Smad3 specifically represses transcriptional activation mediated by AR on two natural androgen-responsive promoters. This repression is transmitted through TGF-beta signaling and can be regulated by other Smad proteins. A protein-protein interaction between AR and Smad3 was identified in vitro and in vivo, and the transcription activation domain of AR and the MH2 of Smad3 were identified as being responsible for binding. Additional functional experiments showed that the repression of AR by Smad3 is mediated solely through the MH2 domain. These results provide fresh insight for understanding the mechanism by which TGF-beta regulates the androgen-signaling pathway in prostate cancer cells.

    View details for Web of Science ID 000167568100056

    View details for PubMedID 11280774

  • Androgen receptor interacts with a novel MYST protein, HBO1 JOURNAL OF BIOLOGICAL CHEMISTRY Sharma, M., Zarnegar, M., Li, X. Y., Lim, B., Sun, Z. J. 2000; 275 (45): 35200-35208

    Abstract

    The androgen receptor (AR), a member of the nuclear receptor superfamily, plays a central role in male sexual differentiation and prostate cell proliferation. Results of treating prostate cancer by androgen ablation indicate that signals mediated through AR are critical for the growth of these tumors. Like other nuclear receptors, AR exerts its transcriptional function by binding to cis-elements upstream of promoters and interacting with other transcriptional factors (e.g. activators, repressors and modulators). To determine the mechanism of AR-regulated transcription, we used the yeast two-hybrid system to identify AR-associated proteins. One of the proteins we identified is identical to the human origin recognition complex-interacting protein termed HBO1. A ligand-enhanced interaction between AR and HBO1 was further confirmed in vivo and in vitro. Immunofluorescence experiments showed that HBO1 is a nuclear protein, and Northern blot analysis revealed that it is ubiquitously expressed, with the highest levels present in human testis. HBO1 belongs to the MYST family, which is characterized by a highly conserved C2HC zinc finger and a putative histone acetyltransferase domain. Surprisingly, two yeast members of the MYST family, SAS2 and SAS3, have been shown to function as transcription silencers, despite the presence of the histone acetyltransferase domain. Using a GAL4 DNA-binding domain assay, we mapped a transcriptional repression domain within the N-terminal region of HBO1. Transient transfection experiments revealed that HBO1 specifically repressed AR-mediated transcription in both CV-1 and PC-3 cells. These results indicate that HBO1 is a new AR-interacting protein capable of modulating AR activity. It could play a significant role in regulating AR-dependent genes in normal and prostate cancer cells.

    View details for Web of Science ID 000165422800051

    View details for PubMedID 10930412

  • PDEF, a novel prostate epithelium-specific Ets transcription factor, interacts with the androgen receptor and activates prostate-specific antigen gene expression JOURNAL OF BIOLOGICAL CHEMISTRY Oettgen, P., Finger, E., Sun, Z. J., Akbarali, Y., Thamrongsak, U., Boltax, J., Grall, F., Dube, A., WEISS, A., Brown, L., Quinn, G., Kas, K., Endress, G., Kunsch, C., Libermann, T. A. 2000; 275 (2): 1216-1225

    Abstract

    Prostate cancer, the most frequent solid cancer in older men, is a leading cause of cancer deaths. Although proliferation and differentiation of normal prostate epithelia and the initial growth of prostate cancer cells are androgen-dependent, prostate cancers ultimately become androgen-independent and refractory to hormone therapy. The prostate-specific antigen (PSA) gene has been widely used as a diagnostic indicator for androgen-dependent and -independent prostate cancer. Androgen-induced and prostate epithelium-specific PSA expression is regulated by a proximal promoter and an upstream enhancer via several androgen receptor binding sites. However, little progress has been made in identifying androgen-independent regulatory elements involved in PSA gene regulation. We report the isolation of a novel, prostate epithelium-specific Ets transcription factor, PDEF (prostate-derived Ets factor), that among the Ets family uniquely prefers binding to a GGAT rather than a GGAA core. PDEF acts as an androgen-independent transcriptional activator of the PSA promoter. PDEF also directly interacts with the DNA binding domain of androgen receptor and enhances androgen-mediated activation of the PSA promoter. Our results, as well as the critical roles of other Ets factors in cellular differentiation and tumorigenesis, strongly suggest that PDEF is an important regulator of prostate gland and/or prostate cancer development.

    View details for Web of Science ID 000084836600070

    View details for PubMedID 10625666

  • Tyrosine kinases expressed in vivo by human prostate cancer bone marrow metastases and loss of the type 1 insulin-like growth factor receptor AMERICAN JOURNAL OF PATHOLOGY Chott, A., Sun, Z., Morganstern, D., Pan, J., Li, T., Susani, M., Mosberger, I., Upton, M. P., Bubley, G. J., Balk, S. P. 1999; 155 (4): 1271-1279

    Abstract

    An important biological feature of prostate cancer (PCa) is its marked preference for bone marrow as a metastatic site. To identify factors that may support the growth of PCa in bone marrow, expression of receptor and nonreceptor tyrosine kinases by androgen-independent PCa bone marrow metastases was assessed. Bone marrow biopsies largely replaced by PCa were analyzed using reverse transcriptase-polymerase chain reaction amplification with degenerate primers that amplified the conserved kinase domain. Sequence analyses of the cloned products demonstrated expression of multiple kinases. Expression of the receptor and nonreceptor tyrosine kinases, alpha platelet-derived growth factor receptor and Jak 1, respectively, was confirmed by immunohistochemistry. In contrast, the type 1 insulin-like growth factor receptor, thought to play a role in PCa development, was lost in metastatic PCa. These results implicate several specific growth factors and signaling pathways in metastatic androgen-independent PCa and indicate that loss of the type 1 insulin-like growth factor receptor contributes to PCa progression.

    View details for Web of Science ID 000083183600030

    View details for PubMedID 10514409

  • Tumor susceptibility gene 101 protein represses androgen receptor transactivation and interacts with p300 CANCER Sun, Z. J., Pan, J., Hope, W. X., Cohen, S. N., Balk, S. P. 1999; 86 (4): 689-696

    Abstract

    Functional inactivation of the tsg101 gene in mouse fibroblasts leads to cell transformation and the ability to form metastatic tumors in nude mice. Abnormal TSG101 transcripts with highly-specific deletions in the protein-coding region have been identified in human tumor samples and cancer cell lines, including prostate and breast carcinomas, and have been attributed to alternative splicing of TSG101 mRNA. The function of the TSG101 protein is not known, although its predicted sequence has suggested that it may function as a transcription factor.Human TSG101 N-terminal (encoding amino acids 10-240) and C-terminal (encoding amino acids 230-391) fragments were cloned and used in both transient transfection and protein binding experiments. The transient transfections were carried in CV-1 cells. Protein-protein interactions were determined by both glutathione-S-transferase fusion protein binding and co-immunoprecipitation.The N-terminal region of TSG101, when fused to the GAL4 DNA binding domain, can activate transcription; whereas the C-terminal region mediates transcriptional repression. Full-length TSG101 or its separated regions repressed ligand-dependent transcriptional activation by nuclear receptors, including androgen receptor and estrogen receptor, which play central roles in prostate carcinoma and breast carcinoma, respectively. In addition, a direct association between TSG101 and the transcriptional co-factor p300 was demonstrated in vitro and in vivo.These results indicate that TSG101 can function as a transcription modulator to affect nuclear receptor-mediated transcriptional activation, which raises the possibility that the tumor suppression by TSG101 observed previously may be mediated at least in part by its effects on nuclear receptor function.

    View details for Web of Science ID 000081868100019

    View details for PubMedID 10440698

  • AP-1 mediates stretch-induced expression of HB-EGF in bladder smooth muscle cells AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY Park, J. M., Adam, R. M., Peters, C. A., Guthrie, P. D., Sun, Z. J., Klagsbrun, M., Freeman, M. R. 1999; 277 (2): C294-C301

    Abstract

    Mechanical induction of growth factor synthesis may mediate adaptive responses of smooth muscle cells (SMC) to increases in physical load. We previously demonstrated that cyclic mechanical stretch induces expression of the SMC, fibroblast, and epithelial cell mitogen heparin-binding epidermal growth factor-like growth factor (HB-EGF) in bladder SMC, an observation that suggests that this growth factor may be involved in compensatory bladder hypertrophy. In the present study we provide evidence that the activator protein-1 (AP-1) transcription factor plays a critical role in this mechanoinduction process. Rat bladder SMC were transiently transfected with a series of 5' deletion mutants of a promoter-reporter construct containing 1. 7 kb of the mouse HB-EGF promoter that was previously shown to be stretch responsive. The stretch-mediated increase in promoter activity was completely ablated with deletion of nucleotide positions -1301 to -881. Binding of AP-1, as evaluated by electrophoretic mobility shift assay, to a synthetic oligonucleotide containing an AP-1 binding site increased in response to stretch, and binding was inhibited by excess unlabeled DNA corresponding to nucleotides -993 to -973 from the HB-EGF promoter, a region that contains a previously recognized composite AP-1/Ets site. Stretch-induced promoter activity was significantly inhibited by site-directed mutagenesis of the AP-1 or Ets components of this site. Consistent with the promoter and gel-shift studies, curcumin, an inhibitor of AP-1 activation, suppressed the HB-EGF mRNA induction after stretch. Stretch also specifically increased mRNA levels for matrix metalloproteinase (MMP)-1, the promoter of which contains a functional AP-1 element, but not for MMP-2, the promoter of which does not contain an AP-1 element. The stretch response of the MMP-1 gene was also completely inhibited by curcumin. Collectively, these findings indicate that AP-1-mediated transcription plays an important role in the regulation of gene expression in bladder muscle in response to mechanical forces.

    View details for Web of Science ID 000081840000014

    View details for PubMedID 10444406

  • Negative cross-talk between hematopoietic regulators: GATA proteins repress PU.1 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Zhang, P., Behre, G., Pan, J., Iwama, A., Wara-Aswapati, N., Radomska, H. S., Auron, P. E., Tenen, D. G., Sun, Z. J. 1999; 96 (15): 8705-8710

    Abstract

    The process through which multipotential hematopoietic cells commit to distinct lineages involves the induction of specific transcription factors. PU.1 (also known as Spi-1) and GATA-1 are transcription factors essential for the development of myeloid and erythroid lineages, respectively. Overexpression of PU.1 and GATA-1 can block differentiation in lineages in which they normally are down-regulated, indicating that not only positive but negative regulation of these factors plays a role in normal hematopoietic lineage development. Here we demonstrate that a region of the PU.1 Ets domain (the winged helix-turn-helix wing) interacts with the conserved carboxyl-terminal zinc finger of GATA-1 and GATA-2 and that GATA proteins inhibit PU.1 transactivation of critical myeloid target genes. We demonstrate further that GATA inhibits binding of PU.1 to c-Jun, a critical coactivator of PU.1 transactivation of myeloid promoters. Finally, PU.1 protein can inhibit both GATA-1 and GATA-2 transactivation function. Our results suggest that interactions between PU.1 and GATA proteins play a critical role in the decision of stem cells to commit to erythroid vs. myeloid lineages.

    View details for Web of Science ID 000081589400076

    View details for PubMedID 10411939

  • Dimeric RFX proteins contribute to the activity and lineage specificity of the interleukin-5 receptor alpha promoter through activation and repression domains MOLECULAR AND CELLULAR BIOLOGY Iwama, A., Pan, J., Zhang, P., Reith, W., Mach, B., Tenen, D. G., Sun, Z. J. 1999; 19 (6): 3940-3950

    Abstract

    Interleukin-5 (IL-5) plays a central role in the differentiation, proliferation, and functional activation of eosinophils. The specific action of IL-5 on eosinophils and hematopoietically related basophils is regulated by the restricted expression of IL-5 receptor alpha (IL-5Ralpha), a subunit of high-affinity IL-5R, on these cells. We have previously identified an enhancer-like cis element in the IL-5Ralpha promoter that is important for both full promoter function and lineage-specific activity. Here, we demonstrate by yeast one-hybrid screening that RFX2 protein specifically binds to this cis element. RFX2 belongs to the RFX DNA-binding protein family, the biological role of which remains obscure. Using an electrophoretic mobility shift assay, we further show that RFX1, RFX2, and RFX3 homodimers and heterodimers specifically bind to the cis element of the IL-5Ralpha promoter. The mRNA expression of RFX1, RFX2, and RFX3 was detected ubiquitously, but in transient-transfection assays, multimerized RFX binding sites in front of a basal promoter efficiently functioned in a tissue- and lineage-specific manner. To further investigate RFX functions on transcription, full-length and deletion mutants of RFX1 were targeted to DNA through fusion to the GAL4 DNA binding domain. Tissue- and lineage-specific transcriptional activation with the full-length RFX1 fusion plasmid on a reporter controlled by GAL4 binding sites was observed. Distinct activation and repression domains within the RFX1 protein were further mapped. Our findings suggest that RFX proteins are transcription factors that contribute to the activity and lineage specificity of the IL-5Ralpha promoter by directly binding to a target cis element and cooperating with other tissue- and lineage-specific cofactors.

    View details for Web of Science ID 000080416100002

    View details for PubMedID 10330134

  • Two promoters direct expression of the murine Spi-B gene, an Ets family transcription factor GENE Chen, H. M., Gonzalez, D. A., Radomska, H. S., Voso, M. T., Sun, Z., Zhang, P., Zhang, D. E., Tenen, D. G. 1998; 207 (2): 209-218

    Abstract

    Spi-B and PU.1 (Spi-1) comprise the most divergent subfamily of the Ets transcription factor family. Spi-B and PU.1 bind to similar DNA sequences, and can activate the same B-cell and myeloid promoters in vitro. However, PU.1 knockout mice demonstrate defective hematopoietic development of multiple hematopoietic lineages, indicating that Spi-B was not able to compensate for loss of PU.1. One explanation for these results is that, in contrast to PU.1, which is expressed in myeloid and B-cell lines, Spi-B expression is restricted to B-cells. In order to begin to understand the control of regulation of the Spi-B gene, murine Spi-B cDNA and genomic clones were isolated. The exon/intron organization and transcriptional start sites were determined; two major transcriptional start sites were detected. The two Spi-B promoters were isolated and characterized, and displayed differential activity in B-cell lines matching that of the endogenous gene. Further study of the two Spi-B promoters will provide insight into the molecular events regulating the tissue-specific and developmental stage-specific expression of Spi-B in B-cells.

    View details for Web of Science ID 000072270400014

    View details for PubMedID 9511763

  • Frequent abnormalities of TSG101 transcripts in human prostate cancer ONCOGENE Sun, Z. J., Pan, J., Bubley, G., Balk, S. P. 1997; 15 (25): 3121-3125

    Abstract

    TSG101 has been identified as a candidate tumor suppressor gene and abnormal transcripts have been identified in a substantial fraction of breast cancers. To determine whether TSG101 expression is commonly altered in other tumors, a series of 15 primary and metastatic prostate cancers were analysed by reverse transcriptase-PCR amplification. Abnormal transcripts with extensive deletions in the coding region were found in nine of these tumors, while only the normal transcript was found in control and benign prostatic hypertrophy tissues. More than one abnormal transcript was found in four of these nine cases and distinct abnormal TSG101 transcripts were found in separate biopsies taken from one tumor. Importantly, the normal TSG101 transcript was undetectable in two metastatic prostate cancers, indicating the absence of TSG101 protein. Sequence analysis demonstrated that there were at least six distinct deletions, with four of these deletions found in more than one tumor sample. The most commonly identified deletion, from bp 153 to 1055, was identical to a deletion reported previously in breast cancer. These results demonstrate that TSG101 transcripts are frequently abnormal in prostate cancer and suggest that loss of TSG101 protein contributes to disease development or progression.

    View details for Web of Science ID 000070968000012

    View details for PubMedID 9444960

  • Androgen receptor-associated protein complex binds upstream of the androgen-responsive elements in the promoters of human prostate-specific antigen and kallikrein 2 genes NUCLEIC ACIDS RESEARCH Sun, Z. J., Pan, J., Balk, S. P. 1997; 25 (16): 3318-3325

    Abstract

    An increasing number of proteins which bind to hormone-dependent nuclear receptors and mediate their effects on gene expression are being identified. The human prostate-specific antigen (PSA) and kallikrein 2 (KLK2) genes are regulated by the androgen receptor (AR). Using electrophoresis mobility shift assays (EMSA), a common nuclear protein(s) which binds upstream of the androgen-responsive elements (AREs) in the PSA and KLK2 promoters was identified. Binding occurred between bp -539 and -399 and bp -349 and -224 in the PSA and KLK2 promoters respectively, which were shown previously to be necessary for AR-mediated transactivation. Glutathione S-transferase (GST)-AR fusion proteins were constructed to determine whether the AR interacted directly with this protein or protein complex. Specific interactions were observed with AR fusion proteins containing the DNA binding domain. EMSA supershift experiments and GST-AR pull-down experiments followed by Western blotting identified a Fos-related protein(s) of approximately 40 kDa as part of this complex. Competition experiments with a double-stranded oligonucleotide containing an AP-1 binding site demonstrated that DNA binding was not mediated by AP-1. These results indicate that a Fos-containing protein complex distinct from AP-1 binds upstream of the AREs in the PSA and KLK2 promoters, interacts with the AR and may participate in regulation of these two androgen-responsive genes.

    View details for Web of Science ID A1997XR70100020

    View details for PubMedID 9241247

  • Interleukin-5 receptor a subunit gene regulation in human eosinophil development: Identification of a unique cis-element that acts lie an enhancer in regulating activity of the IL-5R alpha promoter MOLECULAR ASPECTS OF MYELOID STEM CELL DEVELOPMENT Sun, Z., Yergeau, D. A., Wong, I. C., TUYPENS, T., Tavernier, J., Paul, C. C., Baumann, M. A., Auron, P. E., Tenen, D. G., Ackerman, S. J. 1996; 211: 173-187

    Abstract

    Further functional and biochemical characterization of the nuclear factor(s) which interacts with the EOS1 enhancer-like element in the IL-5R alpha promoter is currently in progress. Since different transcription factors recognize and interact with DNA in distinct fashions and with distinct structural motifs, we have modeled potential binding of the EOS1 factor to its cis-element based upon its methylation interference pattern (Fig. 2), using a cylindrical DNA helical projection (Fig. 6). Over a length of two helical turns, all nuclear protein contacts indicated by methylation interference map to one side of the DNA helix, suggesting that EOS1 binds in the major groove, across the minor groove, and on only one side of the helix. Further review of the model also reveals a potential diad symmetry for the binding site, suggestive of binding by a homodimer and consistent with the formation of the two DNA-protein complexes in our electrophoretic mobility shift experiments that could represent interactions with monomer versus dimer. Comparison of the EOS1 binding motif to similar models for the binding of other transcription factor families for which structural crystallographic and/or binding data is available suggests a similarity of the EOS1 complex to that of the bacterial helix-turn-helix phage lambda and 434 repressor-operator complexes, and the Cys4 zinc finger glucocorticoid response element (GRE) DNA-binding motifs, all of which show similar diad symmetry and binding in the major groove on one side of the DNA. The possibility that EOS1 functions as a GRE is being investigated, especially since there is a consensus AP-1 site at bp -440 to -432 of the IL-5R alpha promoter, immediately adjacent to the EOS1 binding site (see Fig. 5 in reference [36]) and AP-1/GRE interactions have been identified for composite response elements in the regulation of a number of different genes. The identification or cloning of EOS1, a potentially novel and eosinophil lineage-active transcription factor, should enhance our understanding of the processes involved in eosinophil development in particular and myeloid lineage commitment and differentiation in general.

    View details for Web of Science ID A1996BG27J00018

    View details for PubMedID 8585949

  • PU.1 (SPI-1) AND C/EBP-ALPHA REGULATE EXPRESSION OF THE GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-RECEPTOR ALPHA-GENE MOLECULAR AND CELLULAR BIOLOGY Hohaus, S., Petrovick, M. S., Voso, M. T., Sun, Z. J., Zhang, D. E., Tenen, D. G. 1995; 15 (10): 5830-5845

    Abstract

    Growth factor receptors play an important role in hematopoiesis. In order to further understand the mechanisms directing the expression of these key regulators of hematopoiesis, we initiated a study investigating the transcription factors activating the expression of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor alpha gene. Here, we demonstrate that the human GM-CSF receptor alpha promoter directs reporter gene activity in a tissue-specific fashion in myelomonocytic cells, which correlates with its expression pattern as analyzed by reverse transcription PCR. The GM-CSF receptor alpha promoter contains an important functional site between positions -53 and -41 as identified by deletion analysis of reporter constructs. We show that the myeloid and B cell transcription factor PU.1 binds specifically to this site. Furthermore, we demonstrate that a CCAAT site located upstream of the PU.1 site between positions -70 and -54 is involved in positive-negative regulation of the GM-CSF receptor alpha promoter activity. C/EBP alpha is the major CCAAT/enhancer-binding protein (C/EBP) form binding to this site in nuclear extracts of U937 cells. Point mutations of either the PU.1 site or the C/EBP site that abolish the binding of the respective factors result in a significant decrease of GM-CSF receptor alpha promoter activity in myelomonocytic cells only. Furthermore, we demonstrate that in myeloid and B cell extracts, PU.1 forms a novel, specific, more slowly migrating complex (PU-SF) when binding the GM-CSF receptor alpha promoter PU.1 site. This is the first demonstration of a specific interaction with PU.1 on a myeloid PU.1 binding site. The novel complex is distinct from that described previously as binding to B cell enhancer sites and can be formed by addition of PU.1 to extracts from certain nonmyeloid cell types which do not express PU.1, including T cells and epithelial cells, but not from erythroid cells. Furthermore, we demonstrate that the PU-SF complex binds to PU.1 sites found on a number of myeloid promoters, and its formation requires an intact PU.1 site adjacent to a single-stranded region. Expression of PU.1 in nonmyeloid cells can activate the GM-CSF receptor alpha promoter. Deletion of the amino-terminal region of PU.1 results in a failure to form the PU-SF complex and in a concomitant loss of transactivation, suggesting that formation of the PU-SF complex is of functional importance for the activity of the GM-CSF receptor alpha promoter. Finally, we demonstrate that C/EBP alpha can also active the GM-CSF receptor alpha promoter in nonmyeloid cells. These results suggest that PU.1 and C/EBP alpha direct the cell-type-specific expression of GM-CSF receptor alpha, further establish the role of PU.1 as a key regulator of hematopoiesis, and point to C/EBP alpha as an additional important factor in this process.

    View details for Web of Science ID A1995RV77200068

    View details for PubMedID 7565736

  • IDENTIFICATION AND CHARACTERIZATION OF A FUNCTIONAL PROMOTER REGION IN THE HUMAN EOSINOPHIL IL-5 RECEPTOR-ALPHA SUBUNIT GENE JOURNAL OF BIOLOGICAL CHEMISTRY Sun, Z. J., Yergeau, D. A., TUYPENS, T., Tavernier, J., Paul, C. C., Baumann, M. A., Tenen, D. G., Ackerman, S. J. 1995; 270 (3): 1462-1471

    Abstract

    The molecular basis for the commitment of multipotential myeloid progenitors to the eosinophil lineage, and the transcriptional mechanisms by which eosinophil-specific genes are subsequently expressed and regulated during eosinophil development are currently unknown. Interleukin-5 (IL-5) is a T cell and mast cell-derived cytokine with actions restricted to the eosinophil and closely related basophil lineages in humans. The high affinity receptor for IL-5 (IL-5R) is composed of an alpha subunit (IL-5R alpha) expressed by the eosinophil lineage, that associates with a beta c subunit shared with the receptors for IL-3 and granulocyte-macrophage colony stimulating factor (GM-CSF). As a prerequisite to studies of the transcriptional regulation of the IL-5R alpha subunit gene, we used three different methods, including primer extension, RNase protection, and 5'-RACE to precisely map the transcriptional start site to a position 15 base pairs (bp) upstream of the 5' end of the published sequence of IL-5R alpha exon 1. To initially identify the IL-5R alpha promoter, 3.5 kilobases (kb) and 561 bp of the 5' sequence flanking the transcriptional start site were subcloned into the promoterless pXP2-luciferase vector. Transient transfection of these constructs into an eosinophil-committed HL-60 subline, clone HL-60-C15, induced the expression of approximately 240-fold greater luciferase activity than the promoterless vector, identifying a strong functionally active promoter region within the 561 bp of sequence proximal to the transcriptional start site and with activity equivalent to pXP2 constructs containing the entire 3.5 kb of upstream sequence. To more precisely localize the cis-acting regulatory elements in this region important for promoter activity, a series of 5' deletion mutants of the 561-bp region were generated in the pXP2-luciferase vector. Deletion of the region between bp -432 and -398 reduced promoter activity by more than 80% in the HL-60-C15 cell line. Further analyses of the activity of the IL-5R alpha promoter constructs in various other eosinophil, myeloid, and non-myeloid cell lines indicated that the promoter was relatively myeloid and eosinophil lineage-specific in its expression. Consensus sequences for known transcription factor binding sites were not present in the 34-bp region of the promoter required for maximal activity, suggesting unique myeloid- and possibly eosinophil-specific regulatory elements.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1995QB15600073

    View details for PubMedID 7836416

  • FUNCTIONAL-CHARACTERIZATION OF THE PROMOTER FOR THE GENE ENCODING HUMAN EOSINOPHIL PEROXIDASE JOURNAL OF BIOLOGICAL CHEMISTRY Yamaguchi, Y., Zhang, D. E., Sun, Z., ALBEE, E. A., Nagata, S., Tenen, D. G., Ackerman, S. J. 1994; 269 (30): 19410-19419

    Abstract

    The molecular basis for commitment of progenitors to the eosinophil lineage and mechanisms by which eosinophil-specific genes are expressed and regulated during differentiation is unknown. Expression of eosinophil peroxidase (EPO) is restricted to the eosinophil lineage. To understand the mechanisms involved in transcriptional regulation of EPO gene expression, we clone the region of the EPO gene upstream of the transcriptional start site and analyzed the cis-acting elements required for EPO promoter activity in an eosinophil-inducible leukemic cell line, HL-60-C15. The 5'-flanking region of the EPO gene containing 1.5 kilobases of sequence upstream of the transcriptional start site was subcloned into the promoterless pXP2-luciferase vector. The EPO-pXP2 construct and 5' deletion mutants were electroporated into HL-60-C15 cells and luciferase reporter activity assessed. The -1.5-kilobase EPO-pXP2 promoter construct reproducibly expressed > 120-fold more luciferase activity than did promoterless pXP2, and a 12-fold (90%) decrease in promoter activity was obtained when sequences between -122 and -45 base pairs (bp) were deleted. The specificity of the EPO promoter for the eosinophil lineage was analyzed by transfecting the EPO-pXP2 constructs and deletion mutants into HL-60-C15 cells and the parental HL-60 line; EPO promoter activity was 8-10-fold less in the HL-60 parental line, suggesting lineage specific elements in the -122 to -45 bp region. To further characterize regulatory sequences important for promoter activity, we performed linker-scanning analysis on the -122 to -45 bp region and identified a number of positively and negatively acting elements in the promoter. DNase I footprinting was performed with HL-60-C15, HL-60, and HeLa nuclear extracts to identify nuclear proteins that may bind to the functional elements; these experiments identified three protected regions of the EPO promoter which correspond to the functional segments defined by linker-scanning analysis and which contain consensus, potential binding sites for Egr-1, H4TF-1, PuF, CTCF, UBP-1, and GaEII transcription factors. Further study of EPO promoter regulation should elucidate unique transcriptional features of eosinophil gene regulation in granulocyte development.

    View details for Web of Science ID A1994NY33200035

    View details for PubMedID 8034708

  • ANALYSIS OF THE IMPERFECT OCTAMER-CONTAINING HUMAN-IMMUNOGLOBULIN V(H)6 GENE PROMOTER NUCLEIC ACIDS RESEARCH Sun, Z. J., Kitchingman, G. R. 1994; 22 (5): 850-860

    Abstract

    The octamer sequence ATGCAAAT is highly conserved in the promoter of immunoglobulin heavy and light chain genes and is one of the sequence motifs involved in the control of transcription of these genes. The promoter region of an human immunoglobulin heavy chain variable gene, the sole member of the VH6 gene family, was found to differ from other VH gene promoters: it contains neither the conserved octamer motif nor a heptamer sequence, and generally bears little resemblance to other VH gene transcriptional control regions. An imperfect octamer sequence with a single nucleotide substitution (AgGCAAAT) is located 108 bp upstream of the ATG translation start site, and 81 bp upstream of the transcription initiation site. We sought to determine which sequence elements within the VH6 promoter were responsible for transcription initiation by creating progressive deletions of a 1 kb fragment from this region and testing their ability to function as promoter elements in B and non-B cells (HeLa). The minimum fragment required for full promoter function was 110 bp, but a fragment with only 65 bp retained 30-50% activity in B cells. Similar levels of transcription were seen when the -146 bp promoter containing two point mutations in the imperfect octamer was tested. Mutation of a possible pyrimidine box sequence located downstream of the TATA box was shown to have only a minor effect (10-30%) on transcription when three nucleotides were changed. Surprisingly, CAT activity was not B cell-specific, as all constructs had virtually the same activity in several B cell lines and in HeLa cells. Removal of the TATA box led to a 50% reduction in CAT activity, and the region upstream of the TATA box functioned as a promoter in both orientations. The transcriptional activity of the VH6 promoter was virtually enhancer independent: only a minor increase was observed when the immunoglobulin or SV40 enhancer was added to the promoter construct. Electrophoretic mobility shift assays of transcription factor binding to the region around the imperfect octamer indicated that binding was weak when nuclear extracts from either B cells or HeLa cells were used. The amount of complex shifted was increased by mutating the imperfect octamer to a perfect one. Chimeras produced between the VH6 promoter and a B cell-specific promoter from a member of the human VH2 gene family demonstrated that the lack of tissue specificity was due to the absence of a repressor of non-B cell transcription in the VH6 promoter. These results indicate that the VH6 promoter is relatively simple, requiring little more than the TATA element and the imperfect octamer, and transcription from this promoter lacks B cell specificity and is not dependent on the enhancer element.

    View details for Web of Science ID A1994NB37500021

    View details for PubMedID 8139927

  • BIDIRECTIONAL TRANSCRIPTION FROM THE HUMAN-IMMUNOGLOBULIN V(H)6 GENE PROMOTER NUCLEIC ACIDS RESEARCH Sun, Z. J., Kitchingman, G. R. 1994; 22 (5): 861-868

    Abstract

    The human immunoglobulin (Ig) heavy chain VH6 gene promoter contains an imperfect octamer (AgGCAAAT) and is not dependent on the Ig heavy chain enhancer for activity; reporter constructs containing this promoter are very active in non-B cells. In experiments designed to characterize regions upstream of the transcriptional start site that are important for promoter function, we produced a series of deletion constructs, including one containing sequences between -74 and -146. Surprisingly, this fragment had promoter activity in both orientations. Inspection of the VH6 promoter sequence indicated that there was a possible TATA box in the proper orientation upstream of the imperfect octamer. The -74 to -146 fragment functioned as a promoter in the reverse orientation in three B cell lines and in non-B (HeLa) cells, with a much higher level of activity seen in the HeLa cells. To determine if the promoter could work in both directions simultaneously, reporter genes were positioned up- and downstream of a VH6 promoter fragment. Reporter gene activity was found for both genes in B cells and HeLa cells. Using a reverse transcriptase-polymerase chain reaction procedure (RT-PCR), we found a transcript corresponding to sequences upstream of the VH6 promoter in RNA from both the lymphoblastoid cell line ML-1, which actively transcribes the VH6 promoter, and the REH cell line, which does not. No transcripts were found in the KB epithelial cell line. Two or three mRNA 5' ends were found that mapped between -137 to -143 from the authentic VH6 transcription site, 31-37 nucleotides upstream of the putative TATA box. Inspection of the sequence upstream of the VH6 promoter demonstrated the presence of an open reading frame capable of coding for 96 amino acids. The VH6 promoter represents the second Ig promoter with bidirectional activity.

    View details for Web of Science ID A1994NB37500022

    View details for PubMedID 7545916

  • Sequencing of selected regions of the human immunoglobulin heavy-chain gene locus that completes the sequence from JH through the delta constant region. DNA sequence Sun, Z. J., Kitchingman, G. R. 1991; 1 (5): 347-355

    Abstract

    Much of the nucleotide sequence between the start of the joining region and the end of the immunoglobulin heavy chain delta gene has already been determined. However, two gaps existed in potentially functionally important regions in this sequence: the region between the 3' end of the joining region and the heavy chain enhancer region and that between the enhancer and the mu constant region. We have determined the nucleotide sequences of these regions. The 734 bp between the joining and enhancer regions contained no additional joining regions. The 4525 bp region between the heavy chain enhancer and the mu constant region contains the mu switch region, which consists of pentameric repeats. Approximately 60% of these repeats are GGGCT and GAGCT. With the determination of these sequences, the entire region of the heavy chain locus starting upstream of the joining region to downstream of the last exon of the delta constant region (a total of more than 29 kb) has now been sequenced.

    View details for PubMedID 1799683

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