Tanya Stoyanova

All Publications

• The Exosome Total Isolation Chip. ACS nano Liu, F., Vermesh, O., Mani, V., Ge, T. J., Madsen, S. J., Sabour, A., Hsu, E. C., Gowrishankar, G., Kanada, M., Jokerst, J. V., Sierra, R. G., Chang, E., Lau, K., Sridhar, K., Bermudez, A., Pitteri, S. J., Stoyanova, T., Sinclair, R., Nair, V. S., Gambhir, S. S., Demirci, U. 2017

  Abstract

  Circulating tumor-derived extracellular vesicles (EVs) have emerged as a promising source for identifying cancer biomarkers for early cancer detection. However, the clinical utility of EVs has thus far been limited by the fact that most EV isolation methods are tedious, nonstandardized, and require bulky instrumentation such as ultracentrifugation (UC). Here, we report a size-based EV isolation tool called ExoTIC (exosome total isolation chip), which is simple, easy-to-use, modular, and facilitates high-yield and high-purity EV isolation from biofluids. ExoTIC achieves an EV yield ∼4-1000-fold higher than that with UC, and EV-derived protein and microRNA levels are well-correlated between the two methods. Moreover, we demonstrate that ExoTIC is a modular platform that can sort a heterogeneous population of cancer cell line EVs based on size. Further, we utilize ExoTIC to isolate EVs from cancer patient clinical samples, including plasma, urine, and lavage, demonstrating the device's broad applicability to cancers and other diseases. Finally, the ability of ExoTIC to efficiently isolate EVs from small sample volumes opens up avenues for preclinical studies in small animal tumor models and for point-of-care EV-based clinical testing from fingerprick quantities (10-100 μL) of blood.

  View details for DOI 10.1021/acsnano.7b04878

  View details for PubMedID 29090896

• Low CD38 Identifies Progenitor-like Inflammation-Associated Luminal Cells that Can Initiate Human Prostate Cancer and Predict Poor Outcome CELL REPORTS Liu, X., Grogan, T. R., Hieronymus, H., Hashimoto, T., Mottahedeh, J., Cheng, D., Zhang, L., Huang, K., Stoyanova, T., Park, J. W., Shkhyan, R. O., Nowroozizadeh, B., Rettig, M. B., Sawyers, C. L., Elashoff, D., Horvath, S., Huang, J., Witte, O. N., Goldstein, A. S. 2016; 17 (10): 2596-2606

  Abstract

  Inflammation is a risk factor for prostate cancer, but the mechanisms by which inflammation increases that risk are poorly understood. Here, we demonstrate that low expression of CD38 identifies a progenitor-like subset of luminal cells in the human prostate. CD38(lo) luminal cells are enriched in glands adjacent to inflammatory cells and exhibit epithelial nuclear factor κB (NF-κB) signaling. In response to oncogenic transformation, CD38(lo) luminal cells can initiate human prostate cancer in an in vivo tissue-regeneration assay. Finally, the CD38(lo) luminal phenotype and gene signature are associated with disease progression and poor outcome in prostate cancer. Our results suggest that prostate inflammation expands the pool of progenitor-like target cells susceptible to tumorigenesis.

  View details for DOI 10.1016/j.celrep.2016.11.010

  View details for Web of Science ID 000390894200010

  View details for PubMedID 27926864

• v-Src Oncogene Induces Trop2 Proteolytic Activation via Cyclin D1 CANCER RESEARCH Ju, X., Jiao, X., Ertel, A., Casimiro, M. C., Di Sante, G., Deng, S., Li, Z., Di Rocco, A., Zhan, T., Hawkins, A., Stoyanova, T., Ando, S., Fatatis, A., Lisanti, M. P., Gomella, L. G., Languino, L. R., Pestell, R. G. 2016; 76 (22): 6723-6734

  Abstract

  Proteomic analysis of castration-resistant prostate cancer demonstrated the enrichment of SRC tyrosine kinase activity in approximately ninety percent of patients. Src is known to induce cyclin D1, and a cyclin D1-regulated gene expression module predict poor outcome in human prostate cancer. The tumor-associated calcium signal transducer 2 [TACSTD2/Trop2/M1S1] is enriched in the prostate, promoting prostate stem cell self-renewal upon proteolytic activation via a γ-secretase cleavage complex (PS1, PS2) and TACE (ADAM17), which releases the Trop2 intracellular domain (Trop2 ICD). Herein, v-Src transformation of primary murine prostate epithelial cells increased the proportion of prostate cancer stem cells as characterized by gene expression, epitope characteristics and prostatosphere formation. Cyclin D1 was induced by v-Src, and Src kinase induction of Trop2 ICD nuclear accumulation, required cyclin D1. Cyclin D1 induced abundance of the Trop2 proteolytic cleavage activation components (PS2, TACE) and restrained expression of the inhibitory component of the Trop2 proteolytic complex (Numb). Prostate cancer patients with increased nuclear Trop2 ICD and cyclin D1, and reduced Numb, had reduced recurrence-free survival probability (hazard ratio 4.35). Cyclin D1 therefore serves as a transducer of v-Src-mediated induction of Trop2 ICD by enhancing abundance of the Trop2 proteolytic activation complex.

  View details for DOI 10.1158/0008-5472.CAN-15-3327

  View details for Web of Science ID 000388742100029

  View details for PubMedID 27634768

• Activation of Notch1 synergizes with multiple pathways in promoting castration-resistant prostate cancer PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Stoyanova, T., Riedinger, M., Lin, S., Faltermeier, C. M., Smith, B. A., Zhang, K. X., Going, C. C., Goldstein, A. S., Lee, J. K., Drake, J. M., Rice, M. A., Hsu, E., Nowroozizadeh, B., Castor, B., Orellana, S. Y., Blum, S. M., Cheng, D., Pienta, K. J., Reiter, R. E., Pitteri, S. J., Huang, J., Witte, O. N. 2016; 113 (42): E6457-E6466

  Abstract

  Metastatic castration-resistant prostate cancer (CRPC) is the primary cause of prostate cancer-specific mortality. Defining new mechanisms that can predict recurrence and drive lethal CRPC is critical. Here, we demonstrate that localized high-risk prostate cancer and metastatic CRPC, but not benign prostate tissues or low/intermediate-risk prostate cancer, express high levels of nuclear Notch homolog 1, translocation-associated (Notch1) receptor intracellular domain. Chronic activation of Notch1 synergizes with multiple oncogenic pathways altered in early disease to promote the development of prostate adenocarcinoma. These tumors display features of epithelial-to-mesenchymal transition, a cellular state associated with increased tumor aggressiveness. Consistent with its activation in clinical CRPC, tumors driven by Notch1 intracellular domain in combination with multiple pathways altered in prostate cancer are metastatic and resistant to androgen deprivation. Our study provides functional evidence that the Notch1 signaling axis synergizes with alternative pathways in promoting metastatic CRPC and may represent a new therapeutic target for advanced prostate cancer.

  View details for DOI 10.1073/pnas.1614529113

  View details for Web of Science ID 000385610400019

  View details for PubMedID 27694579

• Phosphoproteome Integration Reveals Patient-Specific Networks in Prostate Cancer. Cell Drake, J. M., Paull, E. O., Graham, N. A., Lee, J. K., Smith, B. A., Titz, B., Stoyanova, T., Faltermeier, C. M., Uzunangelov, V., Carlin, D. E., Fleming, D. T., Wong, C. K., Newton, Y., Sudha, S., Vashisht, A. A., Huang, J., Wohlschlegel, J. A., Graeber, T. G., Witte, O. N., Stuart, J. M. 2016; 166 (4): 1041-1054

  Abstract

  We used clinical tissue from lethal metastatic castration-resistant prostate cancer (CRPC) patients obtained at rapid autopsy to evaluate diverse genomic, transcriptomic, and phosphoproteomic datasets for pathway analysis. Using Tied Diffusion through Interacting Events (TieDIE), we integrated differentially expressed master transcriptional regulators, functionally mutated genes, and differentially activated kinases in CRPC tissues to synthesize a robust signaling network consisting of druggable kinase pathways. Using MSigDB hallmark gene sets, six major signaling pathways with phosphorylation of several key residues were significantly enriched in CRPC tumors after incorporation of phosphoproteomic data. Individual autopsy profiles developed using these hallmarks revealed clinically relevant pathway information potentially suitable for patient stratification and targeted therapies in late stage prostate cancer. Here, we describe phosphorylation-based cancer hallmarks using integrated personalized signatures (pCHIPS) that shed light on the diversity of activated signaling pathways in metastatic CRPC while providing an integrative, pathway-based reference for drug prioritization in individual patients.

  View details for DOI 10.1016/j.cell.2016.07.007

  View details for PubMedID 27499020

• N-Myc Drives Neuroendocrine Prostate Cancer Initiated from Human Prostate Epithelial Cells. Cancer cell Lee, J. K., Phillips, J. W., Smith, B. A., Park, J. W., Stoyanova, T., McCaffrey, E. F., Baertsch, R., Sokolov, A., Meyerowitz, J. G., Mathis, C., Cheng, D., Stuart, J. M., Shokat, K. M., Gustafson, W. C., Huang, J., Witte, O. N. 2016; 29 (4): 536-547

  Abstract

  MYCN amplification and overexpression are common in neuroendocrine prostate cancer (NEPC). However, the impact of aberrant N-Myc expression in prostate tumorigenesis and the cellular origin of NEPC have not been established. We define N-Myc and activated AKT1 as oncogenic components sufficient to transform human prostate epithelial cells to prostate adenocarcinoma and NEPC with phenotypic and molecular features of aggressive, late-stage human disease. We directly show that prostate adenocarcinoma and NEPC can arise from a common epithelial clone. Further, N-Myc is required for tumor maintenance, and destabilization of N-Myc through Aurora A kinase inhibition reduces tumor burden. Our findings establish N-Myc as a driver of NEPC and a target for therapeutic intervention.

  View details for DOI 10.1016/j.ccell.2016.03.001

  View details for PubMedID 27050099

• Multidisciplinary intervention of early, lethal metastatic prostate cancer: Report from the 2015 Coffey-Holden Prostate Cancer Academy Meeting PROSTATE Miyahira, A., Lang, J., Den, R., Garraway, I., Lotan, T., Ross, A., Stoyanova, T., Cho, S., Simons, J., Pienta, K., Soule, H. 2015
• Distinct phases of human prostate cancer initiation and progression can be driven by different cell-types CANCER CELL MICROENVIRON Stoyanova, T., Goldstein, A. 2014
• Metastatic castration-resistant prostate cancer reveals intrapatient similarity and interpatient heterogeneity of therapeutic kinase targets PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Drake, J. M., Graham, N. A., Lee, J. K., Stoyanova, T., Faltermeier, C. M., Sud, S., Titz, B., Huang, J., Pienta, K. J., Graeber, T. G., Witte, O. N. 2013; 110 (49): E4762-E4769

  Abstract

  In prostate cancer, multiple metastases from the same patient share similar copy number, mutational status, erythroblast transformation specific (ETS) rearrangements, and methylation patterns supporting their clonal origins. Whether actionable targets such as tyrosine kinases are also similarly expressed and activated in anatomically distinct metastatic lesions of the same patient is not known. We evaluated active kinases using phosphotyrosine peptide enrichment and quantitative mass spectrometry to identify druggable targets in metastatic castration-resistant prostate cancer obtained at rapid autopsy. We identified distinct phosphopeptide patterns in metastatic tissues compared with treatment-naive primary prostate tissue and prostate cancer cell line-derived xenografts. Evaluation of metastatic castration-resistant prostate cancer samples for tyrosine phosphorylation and upstream kinase targets revealed SRC, epidermal growth factor receptor (EGFR), rearranged during transfection (RET), anaplastic lymphoma kinase (ALK), and MAPK1/3 and other activities while exhibiting intrapatient similarity and interpatient heterogeneity. Phosphoproteomic analyses and identification of kinase activation states in metastatic castration-resistant prostate cancer patients have allowed for the prioritization of kinases for further clinical evaluation.

  View details for DOI 10.1073/pnas.1319948110

  View details for Web of Science ID 000327744900008

  View details for PubMedID 24248375

• Identification, characterization and targeting of Docetaxel-resistant prostate cancer cells ASIAN JOURNAL OF ANDROLOGY Stoyanova, T. I., Goldstein, A. S. 2013; 15 (1): 83-84

  View details for DOI 10.1038/aja.2012.133

  View details for Web of Science ID 000313209500016

  View details for PubMedID 23202701

• Prostate cancer originating in basal cells progresses to adenocarcinoma propagated by luminal-like cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Stoyanova, T., Cooper , A., Drake, J., Liu, X., Armstrong, A., Pienta, K., Zhang , H., Kohn, D., Huang, J., Witte, O., Goldstein, A. 2013

  View details for DOI 10.1073/pnas.1320565110

• Regulated proteolysis of Trop2 drives epithelial hyperplasia and stem cell self-renewal via beta-catenin signaling GENES & DEVELOPMENT Stoyanova, T., Goldstein, A. S., Cai, H., Drake, J. M., Huang, J., Witte, O. N. 2012; 26 (20): 2271-2285

  Abstract

  The cell surface protein Trop2 is expressed on immature stem/progenitor-like cells and is overexpressed in many epithelial cancers. However the biological function of Trop2 in tissue maintenance and tumorigenesis remains unclear. In this study, we demonstrate that Trop2 is a regulator of self-renewal, proliferation, and transformation. Trop2 controls these processes through a mechanism of regulated intramembrane proteolysis that leads to cleavage of Trop2, creating two products: the extracellular domain and the intracellular domain. The intracellular domain of Trop2 is released from the membrane and accumulates in the nucleus. Heightened expression of the Trop2 intracellular domain promotes stem/progenitor self-renewal through signaling via β-catenin and is sufficient to initiate precursor lesions to prostate cancer in vivo. Importantly, we demonstrate that loss of β-catenin or Trop2 loss-of-function cleavage mutants abrogates Trop2-driven self-renewal and hyperplasia in the prostate. These findings suggest that heightened expression of Trop2 is selected for in epithelial cancers to enhance the stem-like properties of self-renewal and proliferation. Defining the mechanism of Trop2 function in self-renewal and transformation is essential to identify new therapeutic strategies to block Trop2 activation in cancer.

  View details for DOI 10.1101/gad.196451.112

  View details for Web of Science ID 000309978500004

  View details for PubMedID 23070813

• Collaboration of Kras and Androgen Receptor Signaling Stimulates EZH2 Expression and Tumor-Propagating Cells in Prostate Cancer CANCER RESEARCH Cai, H., Memarzadeh, S., Stoyanova, T., Beharry, Z., Kraft, A. S., Witte, O. N. 2012; 72 (18): 4672-4681

  Abstract

  Elevation of the chromatin repression factor enhancer of zeste homolog (EZH2) is associated with progression and poor prognosis in several human cancers including prostate cancer. However, the mechanisms driving EZH2 expression are not fully understood. In this study, we investigated the functional synergy in prostate cancers in mice resulting from activation of the androgen receptor, Kras, and Akt, which drives three of the most frequently activated oncogenic signaling pathways in prostate cancer. Although, any two of these three events were sufficient to promote the formation and progression of prostate cancer, only the synergy of androgen receptor and Kras signaling could elevate EZH2 expression and expand prostate cancer progenitor cells in vivo. Our findings have revealed a genetic mechanism resulting in enhanced EZH2 expression during the progression of aggressive prostate cancer, with important implications for understanding how to target advanced disease where cancer progenitor cells may be critical.

  View details for DOI 10.1158/0008-5472.CAN-12-0228

  View details for Web of Science ID 000309507900009

  View details for PubMedID 22805308

• Oncogene-specific activation of tyrosine kinase networks during prostate cancer progression PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Drake, J. M., Graham, N. A., Stoyanova, T., Sedghi, A., Goldstein, A. S., Cai, H., Smith, D. A., Zhang, H., Komisopoulou, E., Huang, J., Graeber, T. G., Witte, O. N. 2012; 109 (5): 1643-1648

  Abstract

  Dominant mutations or DNA amplification of tyrosine kinases are rare among the oncogenic alterations implicated in prostate cancer. We demonstrate that castration-resistant prostate cancer (CRPC) in men exhibits increased tyrosine phosphorylation, raising the question of whether enhanced tyrosine kinase activity is observed in prostate cancer in the absence of specific tyrosine kinase mutation or DNA amplification. We generated a mouse model of prostate cancer progression using commonly perturbed non-tyrosine kinase oncogenes and pathways and detected a significant up-regulation of tyrosine phosphorylation at the carcinoma stage. Phosphotyrosine peptide enrichment and quantitative mass spectrometry identified oncogene-specific tyrosine kinase signatures, including activation of EGFR, ephrin type-A receptor 2 (EPHA2), and JAK2. Kinase:substrate relationship analysis of the phosphopeptides also revealed ABL1 and SRC tyrosine kinase activation. The observation of elevated tyrosine kinase signaling in advanced prostate cancer and identification of specific tyrosine kinase pathways from genetically defined tumor models point to unique therapeutic approaches using tyrosine kinase inhibitors for advanced prostate cancer.

  View details for DOI 10.1073/pnas.1120985109

  View details for Web of Science ID 000299731400061

  View details for PubMedID 22307624

• p21 Cooperates with DDB2 Protein in Suppression of Ultraviolet Ray-induced Skin Malignancies JOURNAL OF BIOLOGICAL CHEMISTRY Stoyanova, T., Roy, N., Bhattacharjee, S., Kopanja, D., Valli, T., Bagchi, S., Raychaudhuri, P. 2012; 287 (5): 3019-3028

  Abstract

  Exposure to ultraviolet rays (UV) in sunlight is the main cause of skin cancer. Here, we show that the p53-induced genes DDB2 and p21 are down-regulated in skin cancer, and in the mouse model they functionally cooperate to prevent UV-induced skin cancer. Our previous studies demonstrated an antagonistic role of DDB2 and p21 in nucleotide excision repair and apoptosis. Surprisingly, we find that the loss of p21 restores nucleotide excision repair and apoptosis in Ddb2(-/-) mice, but it does not protect from UV-mediated skin carcinogenesis. In contrast, Ddb2(-/-)p21(-/-) mice are significantly more susceptible to UV-induced skin cancer than the Ddb2(-/-) or the p21(-/-) mice. We provide evidence that p21 deletion in the Ddb2(-/-) background causes a strong increase in cell proliferation. The increased proliferation in the Ddb2(-/-)p21(-/-) background is related to a severe deficiency in UV-induced premature senescence. Also, the oncogenic pro-proliferation transcription factor FOXM1 is overexpressed in the p21(-/-) background. Our results show that the anti-proliferative and the pro-senescence pathways of DDB2 and p21 are critical protection mechanisms against skin malignancies.

  View details for DOI 10.1074/jbc.M111.295816

  View details for Web of Science ID 000300295100009

  View details for PubMedID 22167187

• Cul4A is essential for spermatogenesis and male fertility DEVELOPMENTAL BIOLOGY Kopanja, D., Roy, N., Stoyanova, T., Hess, R. A., Bagchi, S., Raychaudhuri, P. 2011; 352 (2): 278-287

  Abstract

  The mammalian Cul4 genes, Cul4A and Cul4B, encode the scaffold components of the cullin-based E3 ubiquitin ligases. The two Cul4 genes are functionally redundant. Recent study indicated that mice expressing a truncated CUL4A that fails to interact with its functional partner ROC1 exhibit no developmental phenotype. We generated a Cul4A-/- strain lacking exons 4-8 that does not express any detectable truncated protein. In this strain, the male mice are infertile and exhibit severe deficiencies in spermatogenesis. The primary spermatocytes are deficient in progression through late prophase I, a time point when expression of the X-linked Cul4B gene is silenced due to meiotic sex chromosome inactivation. Testes of the Cul4A-/- mice exhibit extensive apoptosis. Interestingly, the pachytene spermatocytes exhibit persistent double stranded breaks, suggesting a deficiency in homologous recombination. Also, we find that CUL4A localizes to the double stranded breaks generated in pre-pachytene spermatocytes. The observations identify a novel function of CUL4A in meiotic recombination and demonstrate an essential role of CUL4A in spermatogenesis.

  View details for DOI 10.1016/j.ydbio.2011.01.028

  View details for Web of Science ID 000289180200009

  View details for PubMedID 21291880

• Primitive origins of prostate cancer: In vivo evidence for prostate-regenerating cells and prostate cancer-initiating cells MOLECULAR ONCOLOGY Goldstein, A. S., Stoyanova, T., Witte, O. N. 2010; 4 (5): 385-396

  Abstract

  Tissue stem cells have been linked to cancers of epithelial origin including the prostate. There are three relevant issues concerning stem cells and cancer that rely solely on functional studies: 1. Are there tissue-regenerating stem cells in the adult organ? 2. Can tissue-regenerating cells serve as targets for transformation? 3. Do primary tumors contain tumor-propagating (cancer stem) cells? We will review the recent literature with respect to these critical issues to provide a direct link between primitive cells and prostate cancer.

  View details for DOI 10.1016/j.molonc.2010.06.009

  View details for Web of Science ID 000282566200003

  View details for PubMedID 20688584

• DDB2 (Damaged-DNA binding protein 2) in nucleotide excision repair and DNA damage response CELL CYCLE Stoyanova, T., Roy, N., Kopanja, D., Raychaudhuri, P., Bagchi, S. 2009; 8 (24): 4067-4071

  Abstract

  DDB2 was identified as a protein involved in the Nucleotide Excision Repair (NER), a major DNA repair mechanism that repairs UV damage to prevent accumulation of mutations and tumorigenesis. However, recent studies indicated additional functions of DDB2 in the DNA damage response pathway. Herein, we discuss the proposed mechanisms by which DDB2 activates NER and programmed cell death upon DNA damage through its E3 ligase activity.

  View details for Web of Science ID 000273232300023

  View details for PubMedID 19923893

• Proliferation defects and genome instability in cells lacking Cul4A ONCOGENE Kopanja, D., Stoyanova, T., Okur, M. N., Huang, E., Bagchi, S., Raychaudhuri, P. 2009; 28 (26): 2456-2465

  Abstract

  The Cul4A gene, which encodes a core component of a cullin-based E3 ubiquitin ligase complex, is overexpressed in breast and hepatocellular cancers. In breast cancers, overexpression of Cul4A strongly correlates with poor prognosis. In addition, Cul4A is required for early embryonic development. The early lethality of mouse embryos prevented a detailed analysis of the functions of Cul4A. Here, we used a strain of mice carrying floxed alleles of Cul4A to study its role in cell division, in vitro and in vivo. Embryonic fibroblasts (MEFs) show a severe deficiency in cell proliferation after deletion of Cul4A. We observed that the Cul4A protein is abundantly expressed in the brain, liver and the mammary tissue of pregnant mice. Deletion of Cul4A in the liver impairs hepatocyte proliferation during regeneration after carbon tetrachloride (CCl(4))-induced injury. The Cul4A-deleted cells are slow in entering the S phase, and are deficient in progressing through the early M phase. Several cell-cycle regulators, including p53 and p27Kip1, are deregulated in the Cul4A-deleted cells. Expression of a dominant negative mutant of p53 causes significant reversal of the proliferation defects in Cul4A-deleted cells. The Cul4A-deleted cells show an aberrant number of centrosome, multipolar spindles and micronuclei formation. Furthermore, those cells are sensitive to UV irradiation and show reduced levels of unscheduled DNA synthesis (UDS). Together, our observations indicate that Cul4A is required for efficient cell proliferation, control of centrosome amplification and genome stability.

  View details for DOI 10.1038/onc.2009.86

  View details for Web of Science ID 000267601400004

  View details for PubMedID 19430492

• DDB2 decides cell fate following DNA damage PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Stoyanova, T., Roy, N., Kopanja, D., Bagchi, S., Raychaudhuri, P. 2009; 106 (26): 10690-10695

  Abstract

  The xeroderma pigmentosum complementation group E (XP-E) gene product damaged-DNA binding protein 2 (DDB2) plays important roles in nucleotide excision repair (NER). Previously, we showed that DDB2 participates in NER by regulating the level of p21(Waf1/Cip1). Here we show that the p21(Waf1/Cip1) -regulatory function of DDB2 plays a central role in defining the response (apoptosis or arrest) to DNA damage. The DDB2-deficient cells are resistant to apoptosis in response to a variety of DNA-damaging agents, despite activation of p53 and the pro-apoptotic genes. Instead, these cells undergo cell cycle arrest. Also, the DDB2-deficient cells are resistant to E2F1-induced apoptosis. The resistance to apoptosis of the DDB2-deficient cells is caused by an increased accumulation of p21(Waf1/Cip1) after DNA damage. We provide evidence that DDB2 targets p21(Waf1/Cip1) for proteolysis. The resistance to apoptosis in DDB2-deficient cells also involves Mdm2 in a manner that is distinct from the p53-regulatory activity of Mdm2. Our results provide evidence for a new regulatory loop involving the NER protein DDB2, Mdm2, and p21(Waf1/Cip1) that is critical in deciding cell fate (apoptosis or arrest) upon DNA damage.

  View details for DOI 10.1073/pnas.0812254106

  View details for Web of Science ID 000267564300055

  View details for PubMedID 19541625

• The xeroderma pigmentosum group E gene product DDB2 activates nucleotide excision repair by regulating the level of p21(Waf1/Cip1) MOLECULAR AND CELLULAR BIOLOGY Stoyanova, T., Yoon, T., Kopanja, D., Mokyr, M. B., Raychaudhuri, P. 2008; 28 (1): 177-187

  Abstract

  The xeroderma pigmentosum group E gene product DDB2, a protein involved in nucleotide excision repair (NER), associates with the E3 ubiquitin ligase complex Cul4A-DDB1. But the precise role of these interactions in the NER activity of DDB2 is unclear. Several models, including DDB2-mediated ubiquitination of histones in UV-irradiated cells, have been proposed. But those models lack clear genetic evidence. Here we show that DDB2 participates in NER by regulating the cellular levels of p21(Waf1/Cip1). We show that DDB2 enhances nuclear accumulation of DDB1, which binds to a modified form of p53 containing phosphorylation at Ser18 (p53(S18P)) and targets it for degradation in low-dose-UV-irradiated cells. DDB2(-/-) mouse embryonic fibroblasts (MEFs), unlike wild-type MEFs, are deficient in the proteolysis of p53(S18P). Accumulation of p53(S18P) in DDB2(-/-) MEFs causes higher expression p21(Waf1/Cip1). We show that the increased expression of p21(Waf1/Cip1) is the cause NER deficiency in DDB2(-/-) cells because deletion or knockdown of p21(Waf1/Cip1) reverses their NER-deficient phenotype. p21(Waf1/Cip1) was shown to bind PCNA, which is required for both DNA replication and NER. Moreover, an increased level of p21(Waf1/Cip1) was shown to inhibit NER both in vitro and in vivo. Our results provide genetic evidence linking the regulation of p21(Waf1/Cip1) to the NER activity of DDB2.

  View details for Web of Science ID 000251925300015

  View details for PubMedID 17967871