All Publications

  • Effects of Low-Dose Bisphenol A on DNA Damage and Proliferation of Breast Cells: The Role of c-Myc ENVIRONMENTAL HEALTH PERSPECTIVES Pfeifer, D., Chung, Y. M., Hu, M. C. 2015; 123 (12): 1271-1279


    Humans are exposed to low dose Bisphenol A (BPA) through plastic consumer products and dental sealants with BPA. While a number of studies have investigated the mammary gland effects after high-dose BPA exposure, the study findings differ. Furthermore, there has been a lack of mechanistic studies.The objective of this study is to investigate the effect and the mechanism of low dose BPA in mammary gland cells.We evaluated DNA damage following BPA exposure using the comet assay and immunofluorescence staining, and used cell counting and three-dimensional cultures to evaluate effects on proliferation. We examined the expressions of markers of DNA damage and cell-cycle regulators by immunoblotting and performed siRNA-mediated gene silencing to determine the role of c-Myc in regulating BPA's effects.Low-dose BPA significantly promoted DNA damage, upregulated c-Myc and other cell-cycle regulatory proteins, and induced proliferation in parallel in estrogen receptor-α (ERα)-negative mammary cells. Silencing c-Myc diminished these BPA-induced cellular events, suggesting that c-Myc is essential for regulating effects of BPA on DNA damage and proliferation in mammary cells.Low-dose BPA exerted c-Myc-dependent genotoxic and mitogenic effects on ERα-negative mammary cells. These findings provide significant evidence of adverse effects of low-dose BPA on mammary cells.

    View details for DOI 10.1289/ehp.1409199

    View details for Web of Science ID 000367587000014

    View details for PubMedID 25933419

  • The Novel Ribonucleotide Reductase Inhibitor COH29 Inhibits DNA Repair In Vitro MOLECULAR PHARMACOLOGY Chen, M., Zhou, B., Zhang, K., Yuan, Y., Un, F., Hu, S., Chou, C., Chen, C., Wu, J., Wang, Y., Liu, X., Smith, D. L., Li, H., Liu, Z., Warden, C. D., Su, L., Malkas, L. H., Chung, Y. M., Hu, M. C., Yen, Y. 2015; 87 (6): 996-1005


    COH29, a novel antimetabolite drug developed at City of Hope Cancer Center, has anticancer activity that stems primarily from the inhibition of human ribonucleotide reductase (RNR). This key enzyme in deoxyribonucleotide biosynthesis is the target of established clinical agents such as hydroxyurea (HU) and gemcitabine because of its critical role in DNA replication and repair. Herein we report that BRCA-1-defective human breast cancer cells are more sensitive than wild-type BRCA-1 counterparts to COH29 in vitro and in vivo. Microarray gene expression profiling showed that COH29 reduces expression of DNA repair pathway genes, suggesting that COH29 interferes with these pathways. It is well-established that BRCA1 plays a role in DNA damage repair, especially homologous recombination (HR) repair, to maintain genome integrity. In BRCA1-defective HCC1937 breast cancer cells, COH29 induced more double-strand breaks (DSB) and DNA-damage response (DDR) than in HCC1937+BRCA1 cells. By EJ5- and DR-GFP reporter assay, we found COH29 could inhibit NHEJ efficiency and that no HR activity was detected in HCC1937 cells, suggesting the repression of the NHEJ repair pathway may be involved in COH29-induced DSB in BRCA1-deficient HCC1937 cells. Furthermore, we observed accumulation of nuclear Rad51 foci in COH29-treated HCC1937+BRCA1 cells, suggesting BRCA1 plays a crucial role in repairing/recovering drug-induced DNA damage by recruiting Rad51 to damage sites. In summary, we have described additional biological effects of the RNR inhibitor COH29 that potentially strengthen its utility as an anticancer agent.

    View details for DOI 10.1124/mol.114.094987

    View details for Web of Science ID 000354617000010

    View details for PubMedID 25814515

  • Reprogramming ovarian and breast cancer cells into non-cancerous cells by low-dose metformin or SN-38 through FOXO3 activation SCIENTIFIC REPORTS Hu, T., Chung, Y. M., Guan, M., Ma, M., Ma, J., Berek, J. S., Hu, M. C. 2014; 4


    Cancer is a leading cause of death worldwide. Because the cytotoxic effects of conventional chemotherapies often harm normal tissue cells along with cancer cells, conventional chemotherapies cause many unwanted or intolerable side effects. Thus, there is an unmet medical need to establish a paradigm of chemotherapy-induced differentiation of cancer cells with tolerable side effects. Here we show that low-dose metformin or SN-38 inhibits cell growth or survival in ovarian and breast cancer cells and suppresses their tumor growth in vivo. Low-dose metformin or SN-38 increases FOXO3 nuclear localization as well as the amount of DNA damage markers and downregulates the expression of a cancer-stemness marker CD44 and other stemness markers, including Nanog, Oct-4, and c-Myc, in these cancer cells. This treatment also inhibits spheroid body-formation in 3-dimensional culture. In contrast, silencing FOXO3 diminishes all these cellular events when ovarian/breast cancer cells are treated with the mentioned drugs. These results suggest that low-dose metformin or SN-38 may reprogram these cancer cells into non-cancerous cells in a FOXO3-dependent manner, and may allow patients to overcome these cancers with minimal side effects.

    View details for DOI 10.1038/srep05810

    View details for Web of Science ID 000339420400001

    View details for PubMedID 25056111

  • FOXO3 signalling links ATM to the p53 apoptotic pathway following DNA damage NATURE COMMUNICATIONS Chung, Y. M., Park, S., Tsai, W., Wang, S., Ikeda, M., Berek, J. S., Chen, D. J., Hu, M. C. 2012; 3


    DNA damage as a result of environmental stress is recognized by sensor proteins that trigger repair mechanisms, or, if repair is unsuccessful, initiate apoptosis. Defects in DNA damage-induced apoptosis promote genomic instability and tumourigenesis. The protein ataxia-telangiectasia mutated (ATM) is activated by DNA double-strand breaks and regulates apoptosis via p53. Here we show that FOXO3 interacts with the ATM-Chk2-p53 complex, augments phosphorylation of the complex and induces the formation of nuclear foci in cells on DNA damage. FOXO3 is essential for DNA damage-induced apoptosis and conversely FOXO3 requires ATM, Chk2 and phosphorylated p53 isoforms to trigger apoptosis as a result of DNA damage. Under these conditions FOXO3 may also have a role in regulating chromatin retention of phosphorylated p53. These results suggest an essential link between FOXO3 and the ATM-Chk2-p53-mediated apoptotic programme following DNA damage.

    View details for DOI 10.1038/ncomms2008

    View details for Web of Science ID 000308801100016

    View details for PubMedID 22893124

  • Involvement of the nuclear proteasome activator PA28 gamma in the cellular response to DNA double-strand breaks CELL CYCLE Levy-Barda, A., Lerenthal, Y., Davis, A. J., Chung, Y. M., Essers, J., Shao, Z., van Vliet, N., Chen, D. J., Hu, M. C., Kanaar, R., Ziv, Y., Shiloh, Y. 2011; 10 (24): 4300-4310


    The DNA damage response (DDR) is a complex signaling network that leads to damage repair while modulating numerous cellular processes. DNA double-strand breaks (DSBs), a highly cytotoxic DNA lesion, activate this system most vigorously. The DSB response network is orchestrated by the ATM protein kinase, which phosphorylates key players in its various branches. Proteasome-mediated protein degradation plays an important role in the proteome dynamics following DNA damage induction. Here, we identify the nuclear proteasome activator PA28? (REG?; PSME3) as a novel DDR player. PA28? depletion leads to cellular radiomimetic sensitivity and a marked delay in DSB repair. Specifically, PA28? deficiency abrogates the balance between the two major DSB repair pathways--nonhomologous end-joining and homologous recombination repair. Furthermore, PA28? is found to be an ATM target, being recruited to the DNA damage sites and required for rapid accumulation of proteasomes at these sites. Our data reveal a novel ATM-PA28?-proteasome axis of the DDR that is required for timely coordination of DSB repair.

    View details for DOI 10.4161/cc.10.24.18642

    View details for Web of Science ID 000298407200031

    View details for PubMedID 22134242

  • ATM-mediated phosphorylation of polynucleotide kinase/phosphatase is required for effective DNA double-strand break repair EMBO REPORTS Segal-Raz, H., Mass, G., Baranes-Bachar, K., Lerenthal, Y., Wang, S., Chung, Y. M., Ziv-Lehrman, S., Strom, C. E., Helleday, T., Hu, M. C., Chen, D. J., Shiloh, Y. 2011; 12 (7): 713-719


    The cellular response to double-strand breaks (DSBs) in DNA is a complex signalling network, mobilized by the nuclear protein kinase ataxia-telangiectasia mutated (ATM), which phosphorylates many factors in the various branches of this network. A main question is how ATM regulates DSB repair. Here, we identify the DNA repair enzyme polynucleotide kinase/phosphatase (PNKP) as an ATM target. PNKP phosphorylates 5'-OH and dephosphorylates 3'-phosphate DNA ends that are formed at DSB termini caused by DNA-damaging agents, thereby regenerating legitimate ends for further processing. We establish that the ATM phosphorylation targets on human PNKP-Ser 114 and Ser 126-are crucial for cellular survival following DSB induction and for effective DSB repair, being essential for damage-induced enhancement of the activity of PNKP and its proper accumulation at the sites of DNA damage. These findings show a direct functional link between ATM and the DSB-repair machinery.

    View details for DOI 10.1038/embor.2011.96

    View details for Web of Science ID 000292325700023

    View details for PubMedID 21637298

  • Requirement of ATM-Dependent Monoubiquitylation of Histone H2B for Timely Repair of DNA Double-Strand Breaks MOLECULAR CELL Moyal, L., Lerenthal, Y., Gana-Weisz, M., Mass, G., So, S., Wang, S., Eppink, B., Chung, Y. M., Shalev, G., Shema, E., Shkedy, D., Smorodinsky, N. I., van Vliet, N., Kuster, B., Mann, M., Ciechanover, A., Dahm-Daphi, J., Kanaar, R., Hu, M. C., Chen, D. J., Oren, M., Shiloh, Y. 2011; 41 (5): 529-542


    The cellular response to DNA double-strand breaks (DSBs) is mobilized by the protein kinase ATM, which phosphorylates key players in the DNA damage response (DDR) network. A major question is how ATM controls DSB repair. Optimal repair requires chromatin relaxation at damaged sites. Chromatin reorganization is coupled to dynamic alterations in histone posttranslational modifications. Here, we show that in human cells, DSBs induce monoubiquitylation of histone H2B, a modification that is associated in undamaged cells with transcription elongation. We find that this process relies on recruitment to DSB sites and ATM-dependent phosphorylation of the responsible E3 ubiquitin ligase: the RNF20-RNF40 heterodimer. H2B monoubiquitylation is required for timely recruitment of players in the two major DSB repair pathways-nonhomologous end-joining and homologous recombination repair-and optimal repair via both pathways. Our data and previous data suggest a two-stage model for chromatin decondensation that facilitates DSB repair.

    View details for DOI 10.1016/j.molcel.2011.02.015

    View details for Web of Science ID 000288150700006

    View details for PubMedID 21362549

  • Inhibition of FOXO3 Tumor Suppressor Function by beta TrCP1 through Ubiquitin-Mediated Degradation in a Tumor Mouse Model PLOS ONE Tsai, W., Chung, Y. M., Zou, Y., Park, S., Xu, Z., Nakayama, K., Lin, S., Hu, M. C. 2010; 5 (7)


    The ubiquitin-proteasome system is the primary proteolysis machine for controlling protein stability of the majority of regulatory proteins including those that are critical for cancer development. The forkhead box transcription factor FOXO3 plays a key role in regulating tumor suppression; however, the control of FOXO3 protein stability remains to be established. It is crucial to elucidate the molecular mechanisms underlying the ubiquitin-mediated degradation of FOXO3 tumor suppressor.Here we show that betaTrCP1 oncogenic ubiquitin E3-ligase interacts with FOXO3 and induces its ubiquitin-dependent degradation in an IkappaB kinase-beta phosphorylation dependent manner. Silencing betaTrCP1 augments FOXO3 protein level, resulting in promoting cellular apoptosis in cancer cells. In animal models, increasing FOXO3 protein level by silencing betaTrCP1 suppresses tumorigenesis, whereas decreasing FOXO3 by over-expressing betaTrCP1 promotes tumorigenesis and tumor growth in vivo.This is a unique demonstration that the betaTrCP1-mediated FOXO3 degradation plays a crucial role in tumorigenesis. These findings significantly contribute to understanding of the control of FOXO3 stability in cancer cells and may provide opportunities for developing innovative anticancer therapeutic modalities.

    View details for DOI 10.1371/journal.pone.0011171

    View details for Web of Science ID 000279465700001

    View details for PubMedID 20625400

  • Replicative Senescence Induced by Romo1-derived Reactive Oxygen Species JOURNAL OF BIOLOGICAL CHEMISTRY Chung, Y. M., Lee, S. B., Kim, H. J., Park, S. H., Kim, J. J., Chung, J. S., Do Yoo, Y. 2008; 283 (48): 33763-33771


    Persistent accumulation of DNA damage induced by reactive oxygen species (ROS) is proposed to be a major contributor toward the aging process. Furthermore, an increase in age-associated ROS is strongly correlated with aging in various species, including humans. Here we showed that the enforced expression of the ROS modulator 1 (Romo1) triggered premature senescence by ROS production, and this also contributed toward induction of DNA damage. Romo1-derived ROS was found to originate in the mitochondrial electron transport chain. Romo1 expression gradually increased in proportion to population doublings of IMR-90 human fibroblasts. An increase in ROS production in these cells with high population doubling was blocked by the Romo1 knockdown using Romo1 small interfering RNA. Romo1 knockdown also inhibited the progression of replicative senescence. Based on these results, we suggest that age-related ROS levels increase, and this contributes to replicative senescence, which is directly associated with Romo1 expression.

    View details for DOI 10.1074/jbc.M805334200

    View details for Web of Science ID 000261183700082

    View details for PubMedID 18836179

  • Critical role for Romo1-derived ROS in cell proliferation BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Na, A. R., Chung, Y. M., Lee, S. B., Park, S. H., Lee, M., Yoo, Y. D. 2008; 369 (2): 672-678


    Low levels of endogenous reactive oxygen species (ROS) originating from NADPH oxidase have been implicated in various signaling pathways induced by growth factors and mediated by cytokines. However, the main source of ROS is known to be the mitochondria, and increased levels of ROS from the mitochondria have been observed in many cancer cells. Thus far, the mechanism of ROS production in cancer cell proliferation in the mitochondria is not well-understood. We recently identified a novel protein, ROS modulator 1 (Romo1), and reported that increased expression of Romo1-triggered ROS production in the mitochondria. The experiments conducted in the present study showed that Romo1-derived ROS were indispensable for the proliferation of both normal and cancer cells. Furthermore, whilst cell growth was inhibited by blocking the ERK pathway in cells transfected with siRNA directed against Romo1, the cell growth was recovered by addition of exogenous hydrogen peroxide. The results of this study suggest that Romo1-induced ROS may play an important role in redox signaling in cancer cells.

    View details for DOI 10.1016/j.bbrc.2008.02.098

    View details for Web of Science ID 000254676900064

    View details for PubMedID 18313394

  • Functional interaction between FOXO3a and ATM regulates DNA damage response NATURE CELL BIOLOGY Tsai, W., Chung, Y. M., Takahashi, Y., Xu, Z., Hu, M. C. 2008; 10 (4): 460-U215


    The maintenance of genomic stability in cells is relentlessly challenged by environmental stresses that induce DNA breaks, which activate the DNA-damage pathway mediated by ataxia-telangiectasia mutated (ATM) and its downstream mediators to control damage-induced cell-cycle checkpoints and DNA repair. Here, we show that FOXO3a interacts with ATM to promote phosphorylation of ATM at Ser 1981 and prompting its downstream mediators to form nuclear foci in response to DNA damage. Silencing FOXO3a in cells abrogates the formation of ATM-pS1981 and phospho-histone H2AX foci after DNA damage. Increasing FOXO3a in cells promotes ATM-regulated signalling, the intra-S-phase or G2-M cell-cycle checkpoints, and the repair of damaged DNA, whereas cells lacking FOXO3a did not trigger the DNA-repair mechanism after DNA damage. The carboxy-terminal domain of FOXO3a binds to the FAT domain of ATM, thereby contributing to the activation of ATM. These results suggest that ATM may be regulated directly by FOXO3a in the DNA-damage response.

    View details for DOI 10.1038/ncb1709

    View details for Web of Science ID 000254561700017

    View details for PubMedID 18344987

  • Forkhead box transcription factor FOXO3a suppresses estrogen-dependent breast cancer cell proliferation and tumorigenesis BREAST CANCER RESEARCH Zou, Y., Tsai, W., Cheng, C., Hsu, C., Chung, Y. M., Li, P., Lin, S., Hu, M. C. 2008; 10 (1)


    Estrogen receptors (ERs) play key roles in breast cancer development and influence treatment outcome in breast cancer patients. Identification of molecules that regulate ER function may facilitate development of breast cancer treatment strategies. The forkhead box class O (FOXO) transcription factor FOXO3a has been suggested to function as a tumor suppressor in breast cancer. Using protein-protein interaction screening, we found that FOXO3a interacted with ER-alpha and ER-beta proteins in the human breast carcinoma cell line MCF-7, suggesting that there exists a crosstalk between the FOXO3a and ER signaling pathways in estrogen-dependent breast cancer cells.The interaction between FOXO3a and ER was investigated by using co-immunoprecipitation and immunoblotting assays. Inhibition of ER-alpha and ER-beta transactivation activity by FOXO was determined by luciferase reporter assays. Cell proliferation in culture was evaluated by counting cell numbers. Tumorigenesis was assessed in athymic mice that were injected with MCF-7 cell lines over-expressing FOXO3a. Protein expression levels of cyclin-dependent kinase inhibitors, cyclins, ERs, FOXM1, and the proteins encoded by ER-regulated genes in MCF-7 cell lines and breast tumors were examined by immunoblotting analysis and immunohistochemical staining.We found that FOXO3a interacted with ER-alpha and ER-beta proteins and inhibited 17beta-estradiol (E2)-dependent, ER-regulated transcriptional activities. Consistent with these observations, expression of FOXO3a in the ER-positive MCF-7 cells decreased the expression of several ER-regulated genes, some of which play important roles in cell proliferation. Moreover, we found that FOXO3a upregulated the expression of the cyclin-dependent kinase inhibitors p21Cip1, p27Kip1, and p57Kip2. These findings suggest that FOXO3a induces cell growth arrest to effect tumor suppression. FOXO3a repressed the growth and survival of MCF-7 cells in cell culture. In an orthotopic breast cancer xenograft model in athymic mice, over-expression of FOXO3a in MCF-7 cells suppressed their E2-induced tumorigenesis, whereas knockdown of FOXO3a in MCF-7 resulted in the E2-independent growth.Functional interaction between FOXO3a and ER plays a critical role in suppressing estrogen-dependent breast cancer cell growth and tumorigenesis in vivo. This suggests that agents that activate FOXO3a may be novel therapeutic agents that can inhibit and prevent tumor proliferation and development in breast cancer.

    View details for DOI 10.1186/bcr1872

    View details for Web of Science ID 000254811400028

    View details for PubMedID 18312651

  • The activity of 2 '-benzoyloxycinnamaldehyde against drug-resistant cancer cell lines JOURNAL OF CHEMOTHERAPY Chung, Y. M., Do Yoo, Y., Kim, J. S., Lee, C. Y., Kim, H. J. 2007; 19 (4): 428-437


    This study investigated the inhibitory effects of 2'-benzoyloxycinnamaldehyde (BCA) on cancer cells, including various drug-resistant cancer cell lines. To observe this activity, the anticancer drug-resistant cell lines were established by continuously exposing the parental cells to 5-fluorouracil (5-FU) and cyclophosphamide (CDDP), and examining the cells with the MTT assay and flow cytometric analysis. The BCA treatment produced similar growth inhibitory effects and apoptotic cell death on the drug-resistant cancer cells as their parental cells. The activation of the p38-mitogen activated protein kinase, an increased level of reactive oxygen species (ROS) generation and downregulation of Bcl-2 were observed in both the drug resistant and non-drug resistant cell lines. The GSH treatment effectively inhibited BCA-induced apoptosis by blocking ROS generation, suggesting that ROS is a major regulator in BCA-induced apoptotic cell death. These results suggest that BCA can be a useful drug candidate for treating drug-resistant cells.

    View details for Web of Science ID 000248612100010

    View details for PubMedID 17855188

  • Drug resistance to 5-FU linked to reactive oxygen species modulator 1 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Hwang, I. T., Chung, Y. M., Kim, J. J., Chung, J. S., Kim, B. S., Kim, H. J., Kim, J. S., Do Yoo, Y. 2007; 359 (2): 304-310


    While acute oxidative stress triggers cell apoptosis or necrosis, persistent oxidative stress induces genomic instability and has been implicated in tumor progression and drug resistance. In a previous report, we demonstrated that reactive oxygen species modulator 1 (Romo1) expression was up-regulated in most cancer cell lines and suggested that increased Romo1 expression might confer chronic oxidative stress to tumor cells. In this study, we show that enforced Romo1 expression induces reactive oxygen species (ROS) production in the mitochondria leading to massive cell death. However, tumor cells that adapt to oxidative stress by increasing manganese superoxide dismutase (MnSOD), Prx I, and Bcl-2 showed drug resistance to 5-FU. To elucidate the relationship between 5-FU-induced ROS production and Romo1 expression, Romo1 siRNA was used to inhibit 5-FU-triggered Romo1 induction. Romo1 siRNA treatment efficiently blocked 5-FU-induced ROS generation, demonstrating that 5-FU treatment stimulated ROS production through Romo1 induction. Based on these results we suggest that cellular adaptive response to Romo1-induced ROS is another mechanism of drug resistance to 5-FU and Romo1 expression may provide a new clinical implication in drug resistance of cancer chemotherapy.

    View details for DOI 10.1016/j.bbrc.2007.05.088

    View details for Web of Science ID 000247494400019

    View details for PubMedID 17537404

  • A novel protein, Romo1, induces ROS production in the mitochondria BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Chung, Y. M., Kim, J. S., Yoo, Y. D. 2006; 347 (3): 649-655


    The majority of endogenous reactive oxygen species (ROS) are produced in the mitochondrial respiratory chain. An imbalance in ROS production alters the intracellular redox homeostasis, triggers DNA damage, and contributes to cancer development and progression. This study identified a novel protein, reactive oxygen species modulator 1 (Romo1), which is localized in the mitochondria. Romo1 was found to increase the level of ROS in the cells. Increased Romo1 expression was observed in various cancer cell lines. This suggests that the increased Romo1 expression during cancer progression may cause persistent oxidative stress to tumor cells, which can increase their malignancy.

    View details for DOI 10.1016/j.bbrc.2006.06.140

    View details for Web of Science ID 000239587200015

    View details for PubMedID 16842742

  • Increased, expression of ICAM-3 is associated with radiation resistance in cervical cancer INTERNATIONAL JOURNAL OF CANCER Chung, Y. M., Kim, B. G., Park, C. S., Huh, S. J., Kim, J., Park, J. K., Cho, S. M., Kim, B. S., Kim, J. S., Young, D. Y., Bae, D. S. 2005; 117 (2): 194-201


    To search for a marker that predicts the efficacy of radiation therapy in human cervical cancer, gene expression profiles between parental SiHa cervical cancer cells and radiation-resistant SiHa/R cells have been compared by the microarray technique. Microarray and Northern blot analyses demonstrated that the ICAM-3 expression was upregulated in SiHa/R cells. This increased expression of ICAM-3 in SiHa cells enhanced cell survival by about 34.3% after a 2 Gy dosage of radiation. In addition, SiHa/ICAM-3 cells showed a 2.45-fold higher level of FAK phosphorylation than that of the control cells. In tumor specimens, ICAM-3 staining was restricted to tumor stromal endothelial cells and lymphocytes. The overexpression of ICAM-3 was significantly more frequent in radiation-resistant cervical cancer specimens when compared with radiation-sensitive specimens (83.3% vs. 35.3%; p = 0.015). With these observations, we can suggest that an increased expression of ICAM-3 is associated with radiation resistance in cervical cancer cells and the expression of ICAM-3 can be used as a valuable biomarker to predict the radiation resistance in cervical cancer that occurs during radiotherapy.

    View details for DOI 10.1002/ijc.21180

    View details for Web of Science ID 000232190900005

    View details for PubMedID 15880373

  • Mitochondrial ribosomal protein L41 suppresses cell growth in association with p53 and p27(Kip1) MOLECULAR AND CELLULAR BIOLOGY Yoo, Y. A., Kim, M. J., Park, J. K., Chung, Y. M., Lee, J. H., Chi, S. G., Kim, J. S., Yoo, Y. D. 2005; 25 (15): 6603-6616


    The p53 protein arrests the cell cycle at the G1 phase when stabilized by the interaction between ribosomal proteins and HDM2 under growth-inhibitory conditions. Meanwhile, p53, when translocated to the mitochondria in response to cell death signals, induces apoptosis via transcription-independent mechanisms. In this report, we demonstrate that the mitochondrial ribosomal protein L41 (MRPL41) enhances p53 stability and contributes to p53-induced apoptosis in response to growth-inhibitory conditions such as actinomycin D treatment and serum starvation. An analysis of MRPL41 expression in paired normal and tumor tissues revealed lower expression in tumor tissue. Ectopic MRPL41 expression resulted in inhibition of the growth of cancer cells in tissue culture and tumor growth in nude mice. We discovered that MRPL41 protein is localized in the mitochondria, stabilizes the p53 protein, and enhances its translocation to the mitochondria, thereby inducing apoptosis. Interestingly, in the absence of p53, MRPL41 stabilizes the p27(Kip1) protein and arrests the cell cycle at the G1 phase. These results suggest that MRPL41 plays an important role in p53-induced mitochondrion-dependent apoptosis and MRPL41 exerts a tumor-suppressive effect in association with p53 and p27 (Kip1).

    View details for DOI 10.1128/MCB.25.15.6603-6616.2005

    View details for Web of Science ID 000230684400027

    View details for PubMedID 16024796

  • N'-(phenyl-pyridin-2-yl-methylene)-hydrazine carbodithioic acid methyl ester enhances radiation-induced cell death by targeting Bcl-2 against human lung carcinoma cells MOLECULAR CANCER THERAPEUTICS Park, J. K., Chung, Y. M., Kim, B. G., Yoo, Y. A., Yang, B. S., Kim, J. S., Yoo, Y. D. 2004; 3 (4): 403-407


    To develop a new radiosensitizer, we screened a chemical library and selected one chemical reagent, N'-(phenyl-pyridin-2-yl-methylene)-hydrazine carbodithioic acid methyl ester (PHCM), which was already known to have antifungal and antimicrobial properties. PHCM enhanced radiation-induced cell death and its mean calculated dose enhancement ratio was 1.17. PHCM was found to induce the phosphorylation of p38 mitogen-activated protein kinase, and combined treatment with PHCM and radiation down-regulated Bcl-2. In a xenograft assay, the combined PHCM and radiation group showed 39.3 days of growth delay versus the control in terms of tumor growth. The enhancement factor of this combined treatment was determined to be 4.02.

    View details for Web of Science ID 000220912000003

    View details for PubMedID 15078983

  • c-Myc exerts a protective function through ornithine decarboxylase against cellular insults MOLECULAR PHARMACOLOGY Park, J. K., Chung, Y. M., Kang, S., Kim, J. U., Kim, Y. T., Kim, H. J., Kim, Y. H., Kim, J. S., Yoo, Y. D. 2002; 62 (6): 1400-1408


    c-Myc is known to control cell proliferation and apoptosis, and much effort has been focused on elucidating the mechanisms by which c-Myc works. In this study, we show that c-Myc expression is induced by many cellular insults, including cisplatin, doxorubicin, paclitaxel, 5-flourouracil, H(2)O(2), and radiation, and the enhanced expression of c-Myc protects against cell death caused by these cellular insults through ornithine decarboxylase (ODC) induction. To investigate the cellular protective role of c-Myc, we constructed a stable transfectant of ODC, one of the many transcriptional targets of c-Myc in cells, and found that enhanced expression of ODC inhibited cell death induced by cellular insults such as cisplatin, H(2)O(2,) and radiation. We also found that cisplatin activated nuclear factor-kappaB, and this subsequently induced c-Myc expression, resulting in the blocking of apoptosis through ODC induction. The results herein, therefore, strongly suggest another role for c-Myc in a stress-response function; that is, it promotes cell survival under stressful conditions.

    View details for Web of Science ID 000179268900016

    View details for PubMedID 12435808

  • Synergistic effect of peroxiredoxin II antisense on cisplatin-induced cell death EXPERIMENTAL AND MOLECULAR MEDICINE Yoo, Y. D., Chung, Y. M., Park, J. K., Ahn, C. M., Kim, S. K., Kim, H. J. 2002; 34 (4): 273-277


    Peroxiredoxin II (Prx II) is known not only to protect cells from oxidative damage caused by hydrogen peroxide (H202), but also to endow cancer cells with resistance to both H202 and cisplatin and to grant them radioresistance. In this study, we examined whether Prx II antisense could enhance cisplatin-induced cell death. When gastric cancer cells were transfected with various concentrations of Prx II antisense plasmid, pPrxII/AS, and then treated with the same concentrations of cisplatin, Prx II antisense enhanced cisplatin-induced cell death. The combination index (CI) at all doses of the combination was below 1, indicating that Prx II antisense sensitized cisplatin-induced cell death. This synergism was also observed in the cells transfected with a Prx II antisense oligomer. Our present results, therefore, suggest that Prx II antisense would be a very good sensitizer for cisplatin, and that Prx II as a target for chemosensitizers constitutes a promising avenue for future research.

    View details for Web of Science ID 000178809500003

    View details for PubMedID 12515392

  • Increased expression of peroxiredoxin II confers resistance to cisplatin ANTICANCER RESEARCH Chung, Y. M., Yoo, Y. D., Park, J. K., Kim, Y. T., Kim, H. J. 2001; 21 (2A): 1129-1133


    Peroxiredoxin II (Prx II) has been known to be induced by various oxidative stimuli and to play an important protective role from oxidative damage by hydrogen peroxide (H2O2). In this study, we observed that cisplatin as well as H2O2 induced Prx II expression. To examine the correlation between the increased expression of Prx II and chemoresistance, we prepared a Prx II-overexpressing cell line, SNU638 cells, and found it to be more resistant to cell death induced by cisplatin and H2O2 than neo-transfectant cells. We also observed that enhanced expression of Prx II inhibited cisplatin- and H2O2-induced apoptosis, demonstrating that resistance to these cytotoxic agents was due to inhibition of apoptosis. The above results led us to suggest that the overexpressed Prx II protein inhibits cisplatin-induced apoptosis, thereby contributing to chemoresistance of tumor cells, especially to oxidative stress producing anticancer drugs.

    View details for Web of Science ID 000169012300043

    View details for PubMedID 11396151

  • Antisense of human peroxiredoxin II enhances radiation-induced cell death CLINICAL CANCER RESEARCH Park, S. H., Chung, Y. M., Lee, Y. S., Kim, H. J., Kim, J. S., Chae, H. Z., Yoo, Y. D. 2000; 6 (12): 4915-4920


    Human peroxiredoxin II (Prx II) has been known to function as an antioxidant enzyme in cells. Using head-and-neck cancer cell lines, we investigated whether Prx II expression is related to the resistance of cells to radiation therapy in vivo and in vitro, and whether a Prx II antisense serves as a radiosensitizer. Increased expression of Prx II was observed in tissues isolated from the patients who did not respond to radiation therapy, whereas Prx II expression was weak in tissues from the patients with regressed tumors. Enhanced expression of Prx II in UMSCC-11A (11A) cells was also observed after treatment with gamma radiation. This increased expression conferred radiation resistance to cancer cells because overexpression of Prx II protected 11A cells from radiation-induced cell death, suggesting that blocking Prx II expression could enhance radiation sensitivity. Treatment of 11A cells with a Prx II antisense decreased induction of Prx II, enhancing the radiation sensitivity. From these results, we suggest that stress-induced overexpression of Prx II increases radiation resistance via protection of cancer cells from radiation-induced oxidative cytolysis and that a Prx II antisense can be used as a radiosensitizer.

    View details for Web of Science ID 000166160200046

    View details for PubMedID 11156252

  • Establishment and characterization of 5-fluorouracil-resistant gastric cancer cells CANCER LETTERS Chung, Y. M., Park, S. H., Park, J. K., Kim, Y. T., Kang, Y. K., Yoo, Y. D. 2000; 159 (1): 95-101


    Two 5-fluorouracil (5-FU)-resistant cell lines from a Korean gastric cancer cell line were established by incubation of the cells with increasing concentration of 5-FU, and the resultant cell lines showed an over 800-fold increased resistance to 5-FU. To identify the mechanism of 5-FU resistance, the expressions of genes involved in 5-FU metabolism were examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Expressions of orotate phosphoribosyltransferase (OPRT), thymidine phosphorylase (TP), and uridine phosphorylase (UP) were significantly downregulated in these cell lines, resulting in low incorporation of 5-FU into nucleic acids. In contrast, an increased expression of thymidine kinase (TK) was observed in 5-FU-resistant cells. These results strongly indicate that blocking of 5-FU incorporation into nucleic acids and TK overexpression may play a major role in 5-FU resistance in these cells. Interestingly, these cell lines showed cross-resistance to paclitaxel, cisplatin, and doxorubicin, suggesting that other factors such as HSP27 and Mn-SOD could be also involved in the mechanism of multidrug resistance in these cell lines.

    View details for Web of Science ID 000166663300013

    View details for PubMedID 10974411