One strategy to improve therapies in advanced prostate cancer (PC) involves targeting genes that are activated by androgen withdrawal to delay the emergence of the androgen-independent (AI) phenotype. Heat shock protein 27 (Hsp27) expression becomes highly upregulated in PC cells after androgen withdrawal or chemotherapy, in which it functions as a cytoprotective chaperone to confer broad-spectrum treatment resistance. The purpose of this study is to elucidate anti-apoptotic pathways regulated by Hsp27 that are activated during PC progression. Using two-hybrid experiment, we found that Hsp27 was having a major role in the protein translational initiation process. Furthermore, using complementary DNA (cDNA) microarray analysis, 4E binding protein 1 was identified as being proportionately and highly regulated by Hsp27. These data led us to analyze the protein synthesis initiation pathway, which is a prerequisite for cell growth and proliferation. Using northern and western blot analysis, we found that Hsp27 downregulation decreased eukaryotic translation initiation factor 4E (eIF4E) expression at the protein, but not mRNA, level. The cytoprotection afforded by Hsp27 overexpression was attenuated by eIF4E knockdown using specific eIF4E short interfering RNA (siRNA). Co-immunoprecipitation and co-immunofluorescence confirmed that Hsp27 colocalizes and interacts directly with eIF4E. Hsp27-eIF4E interaction decreases eIF4E ubiquitination and proteasomal degradation. By chaperoning eIF4E, Hsp27 seems to protect the protein synthesis initiation process to enhance cell survival during cell stress induced by castration or chemotherapy. Forced overexpression of eIF4E induces resistance to androgen-withdrawal and paclitaxel treatment in the prostate LNCaP cells in vitro . These findings identify Hsp27 as a modulator of eIF4E and establish a potential mechanism for the eIF4E-regulated apoptosis after androgen ablation and chemotherapy. Targeting Hsp27–eIF4E interaction may serve as a therapeutic target in advanced PC.

Supplementary Data from Clusterin Facilitates COMMD1 and I-κB Degradation to Enhance NF-κB Activity in Prostate Cancer Cells

Figure S1. Expression and localization of ILK protein and EMT-related molecular markers in normal renal epithelial cells and RCC cells. Figure S2. Anti-angiogenic effects of in vivo knockdown of ILK in orthotopic RCC xenografts.

Supplementary Table S3 from GLI2 Knockdown Using an Antisense Oligonucleotide Induces Apoptosis and Chemosensitizes Cells to Paclitaxel in Androgen-Independent Prostate Cancer

You have accessJournal of UrologyBladder Cancer: Basic Research & Pathophysiology I (MP51)1 Apr 2019MP51-15 PREDICTIVE VALUE AND POTENTIALS FOR CO-TARGETED THERAPY OF STAT1 SIGNALING IN GEMCITABINE/CISPLATIN RESISTANT BLADDER CANCER Tetsutaro Hayashi, Kenichiro Ikeda*, Roland Seiler, Robert H Bell, Susan Ettinger, Kendric Wang, Htoo Zarni Oo, Hamidreza Abdi, Wolfgang Jaeger, Tilman Todenhoefer, Colin Collins, Akio Matsubara, and Peter C Black Tetsutaro HayashiTetsutaro Hayashi More articles by this author , Kenichiro Ikeda*Kenichiro Ikeda* More articles by this author , Roland SeilerRoland Seiler More articles by this author , Robert H BellRobert H Bell More articles by this author , Susan EttingerSusan Ettinger More articles by this author , Kendric WangKendric Wang More articles by this author , Htoo Zarni OoHtoo Zarni Oo More articles by this author , Hamidreza AbdiHamidreza Abdi More articles by this author , Wolfgang JaegerWolfgang Jaeger More articles by this author , Tilman TodenhoeferTilman Todenhoefer More articles by this author , Colin CollinsColin Collins More articles by this author , Akio MatsubaraAkio Matsubara More articles by this author , and Peter C BlackPeter C Black More articles by this author View All Author Informationhttps://doi.org/10.1097/01.JU.0000556457.60096.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVES: Gemcitabine (GEM) and cisplatin (CDDP) combination chemotherapy (GC) is the standard treatment for patients with advanced bladder cancer (BC), but responses have been reported in only 60% of patients, and these are rarely durable. We aimed to use a genomic analysis to determine mechanisms of resistance to GC. METHODS: Three chemo-sensitive BC cell lines were treated serially with increasing concentrations of CDDP or GEM in order to establish acquired resistance. Gene expression of the resistant cells was compared to the sensitive parental cells. Results were validated in The Cancer Genome Atlas (n=405) and in a patient cohort treated with neoadjuvant GC (n=223). Immunohistochemistry (IHC) was performed in 14 patient tumors before and after neoadjuvant GC and in 37 patients with metastatic BC treated with GC. Correlative in vitro experiments were conducted to explore the mechanism of acquired chemo-resistance. RESULTS: Gene expression analysis revealed that STAT1 and six interferon-regulated genes were among the most highly up-regulated genes in resistant cells. In the TCGA dataset, STAT1 expression correlated with the expression of the other 6 genes (P<0.001). Highest STAT1 expression was observed in basal/squamous and luminal infiltrated subtypes. Five-year survival in these patients treated without neoadjuvant GC was 49.7% and 47.7% in tumors with high and low STAT1 expression (compared the median), respectively. In a cohort of patients treated with neoadjuvant GC, the corresponding survival was 62.7% and 78.9%. Nuclear STAT1 expression by IHC was absent in tumors prior to GC but detected in 29% after GC, suggesting that GC activates STAT1 in a subset of patients. In patients with metastatic BC, STAT1 expression was higher in patients with progressive disease (P=0.078) and high STAT1 expression correlated with worse prognosis (P=0.012). Knockdown of STAT1 in resistant cells without CDDP/GEM treatment increased cell growth by cell cycle progression, which was accompanied by increased SKP2 and decreased p27. However, STAT1 knockdown with CDDP/GEM treatment decreased cell growth and increased apoptosis, suggesting that STAT1 silencing restored sensitivity to GC. Conclusions: STAT1 signaling is activated in a subset of BC patients and is associated with acquired chemotherapy resistance. Pending further validation, STAT1 may be considered as potential target in combination with GC, as well as a predictive marker of response to GC. Source of Funding: None Hiroshima, Japan; Vancouver, Canada; Bern, Switzerland; Vancouver, Canada; Hiroshima, Japan; Vancouver, Canada© 2019 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 201Issue Supplement 4April 2019Page: e729-e729 Advertisement Copyright & Permissions© 2019 by American Urological Association Education and Research, Inc.MetricsAuthor Information Tetsutaro Hayashi More articles by this author Kenichiro Ikeda* More articles by this author Roland Seiler More articles by this author Robert H Bell More articles by this author Susan Ettinger More articles by this author Kendric Wang More articles by this author Htoo Zarni Oo More articles by this author Hamidreza Abdi More articles by this author Wolfgang Jaeger More articles by this author Tilman Todenhoefer More articles by this author Colin Collins More articles by this author Akio Matsubara More articles by this author Peter C Black More articles by this author Expand All Advertisement PDF downloadLoading ...

Development of neuroendocrine prostate cancer ( NEPC ) is emerging as a major problem in clinical management of advanced prostate cancer ( PC a). As increasingly potent androgen receptor ( AR )‐targeting antiandrogens are more widely used, PC a transdifferentiation into AR ‐independent NEPC as a mechanism of treatment resistance becomes more common and precarious, since NEPC is a lethal PC a subtype urgently requiring effective therapy. Reprogrammed glucose metabolism of cancers, that is elevated aerobic glycolysis involving increased lactic acid production/secretion, plays a key role in multiple cancer‐promoting processes and has been implicated in therapeutics development. Here, we examined NEPC glucose metabolism using our unique panel of patient‐derived xenograft PC a models and patient tumors. By calculating metabolic pathway scores using gene expression data, we found that elevated glycolysis coupled to increased lactic acid production/secretion is an important metabolic feature of NEPC . Specific inhibition of expression of MCT 4 (a plasma membrane lactic acid transporter) by antisense oligonucleotides led to reduced lactic acid secretion as well as reduced glucose metabolism and NEPC cell proliferation. Taken together, our results indicate that elevated glycolysis coupled to excessive MCT 4‐mediated lactic acid secretion is clinically relevant and functionally important to NEPC . Inhibition of MCT 4 expression appears to be a promising therapeutic strategy for NEPC .

Despite many advances in the understanding of cancer biology, patient survival has only modestly improved over the past few decades. This is partly due to the dismissal of an important phase of cancer progression called therapy-induced dormancy which arises during the course of (neo) adjuvant therapy. This review describes recent efforts in understanding the mechanisms that 'dormant' cancer cells adopt to survive and develop resistance prior to their relapse into secondary tumors. The focus is particularly on metabolic reprogramming that ensues as a consequence of tumor adaptation to therapy.

Abstract Neuroendocrine prostate cancer (NEPC) is a highly aggressive subtype of prostate cancer (PCa) that is becoming increasingly common in the clinic. While the vast majority of PCa presents as androgen-dependent adenocarcinoma, recent uses of increasingly potent therapeutics targeting the androgen receptor signaling axis has resulted in the promotion of NEPC transdifferentiation as a mechanism of treatment resistance. Unfortunately, there is currently no effective treatment option for NEPC. Altered cancer metabolism is now recognized as a hallmark of cancer and a crucial factor for promoting tumour growth and spread. In particular, altered glucose metabolism and the resultant acidification of the tumor microenvironment via increased lactic acid production has been shown to play an important role in multiple cancer-promoting processes, including tissue invasion/metastasis, angiogenesis, and suppression of local anticancer immunity. While increased glycolysis is not generally considered a phenomenon relevant to primary treatment-naive PCa, we have recently demonstrated its relavance to castration-resistant prostate cancer (CRPC) and thus suspect that it is also relevant to the more aggressive NEPC. Our laboratory has also developed a number of unique serially transplantable patient-derived xenograft (PDX) models of NEPC that are histologically highly similar to the donor tissues and retain important genetic and epigenetic features. In particular, we have developed the first spontaneous NEPC transdifferentiation model in the field (LTL331/331R). The gene expression profiles of these NEPC PDX models were compared to that of PCa adenocarcinoma PDX models. To determine whether certain metabolic pathway alterations were specific to NEPC, genes from a number of key metabolic pathways were compiled and overall pathway scores were generated using average expression z-scores. Furthermore, publically available gene expression data from NEPC patient tumors were used to validate our findings. From our analysis, we found that genes in the glycolysis pathway were signficiantlly upregulatied in both our PDX models and also in patient NEPC samples. Of particular interest is the upregulation of genes involved in the production and secretion of lactic acid, such as LDHA and MCT4. As such, our results suggest that elevated glycolysis and production of lactic acid could be a clinically important NEPC phenotype. Furthermore, the inhibition of glycolysis and particularly the inhibition of lactic acid secretion via MCT4 could be a potentially viable therapeutic strategy for NEPC. Citation Format: Stephen Y. Choi, Susan L. Ettinger, Dong Lin, Hui Xue, Robert H. Bell, Fan Mo, Michael Pollak, Colin C. Collins, Yuzhuo Wang. Elevated glycolytic gene signature in patient-derived neuroendocrine prostate cancer xenograft models and its clinical relevance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4420. doi:10.1158/1538-7445.AM2017-4420

To avoid over- or under-treatment of primary prostate tumours, there is a critical need for molecular signatures to discriminate indolent from aggressive, lethal disease. Reprogrammed energy metabolism is an important hallmark of cancer, and abnormal metabolic characteristics of cancers have been implicated as potential diagnostic/prognostic signatures. While genomic and transcriptomic heterogeneity of prostate cancer is well documented and associated with tumour progression, less is known about metabolic heterogeneity of the disease. Using a panel of high fidelity patient-derived xenograft (PDX) models derived from hormone-naïve prostate cancer, we demonstrated heterogeneity of expression of genes involved in cellular energetics and macromolecular biosynthesis. Such heterogeneity was also observed in clinical, treatment-naïve prostate cancers by analyzing the transcriptome sequencing data. Importantly, a metabolic gene signature of increased one-carbon metabolism or decreased proline degradation was identified to be associated with significantly decreased biochemical disease-free patient survival. These results suggest that metabolic heterogeneity of hormone-naïve prostate cancer is of biological and clinical importance and motivate further studies to determine the heterogeneity in metabolic flux in the disease that may lead to identification of new signatures for tumour/patient stratification and the development of new strategies and targets for therapy of prostate cancer.

Clusterin (CLU) is a stress-activated molecular chaperone that confers treatment resistance to taxanes when highly expressed. While CLU inhibition potentiates activity of taxanes and other anti-cancer therapies in preclinical models, progression to treatment-resistant disease still occurs implicating additional compensatory survival mechanisms. Taxanes are believed to selectively target cells in mitosis, a complex mechanism controlled in part by balancing antagonistic roles of Cdc25C and Wee1 in mitosis progression. Our data indicate that CLU silencing induces a constitutive activation of Cdc25C, which delays mitotic exit and hence sensitizes cancer cells to mitotic-targeting agents such as taxanes. Unchecked Cdc25C activation leads to mitotic catastrophe and cell death unless cells up-regulate protective mechanisms mediated through the cell cycle regulators Wee1 and Cdk1. In this study, we show that CLU silencing induces a constitutive activation of Cdc25C via the phosphatase PP2A leading to relief of negative feedback inhibition and activation of Wee1-Cdk1 to promote survival and limit therapeutic efficacy. Simultaneous inhibition of CLU-regulated cell cycle effector Wee1 may improve synergistic responses of biologically rational combinatorial regimens using taxanes and CLU inhibitors.

Abstract Renal cell carcinoma (RCC) is the most common malignancy in the kidney. Antiangiogenic targeted therapies inhibit the progression of RCC, but have limited impacts on invasion or metastasis of tumor cells. Integrin-linked kinase (ILK) is a serine/threonine kinase implicated in the regulation of cell growth/survival, cell-cycle progression, epithelial–mesenchymal transition (EMT), invasion/migration, and angiogenesis. However, the role of ILK in RCC has not been evaluated. We investigated the role of ILK on cancer progression and metastasis and the therapeutic potential of ILK inhibition in RCC. Our investigation reveals that ILK is expressed at a low level in normal cells and low-stage RCC cells and is highly expressed in advanced and metastatic cells. Caki-1, a metastatic RCC cell line, showed higher expression of molecular EMT markers, including Snail and Zeb1, but decreased activity of GSK3β. Knockdown of ILK using small interference (si)-ILK minimally inhibited tumor proliferation and cell-cycle progression was not significantly affected. However, ILK knockdown suppressed the formation of stress fibers and focal adhesions and impeded phenotypic EMT markers, including cell migration and invasion, in Caki-1 and UMRC-3 cells. Finally, in vivo knockdown of ILK suppressed the progression, invasion, and metastasis of primary RCC in nude mice by downregulation of EMT markers (Snail, Zeb1, vimentin, and E-cadherin). Our results show that ILK may be essential for invasion and metastasis in RCC and regulates vimentin and E-cadherin expression by regulating the EMT-related transcription factors Snail and Zeb1. These results suggest that ILK may be a potential target in RCC. Mol Cancer Ther; 14(4); 1024–34. ©2015 AACR.

Vascular endothelial growth factor (VEGF)-targeted antiangiogenic therapy significantly inhibits the growth of clear cell renal cell carcinoma (RCC). Eventually, therapy resistance develops in even the most responsive cases, but the mechanisms of resistance remain unclear. Herein, we developed two tumor models derived from an RCC cell line by conditioning the parental cells to two different stresses caused by VEGF-targeted therapy (sunitinib exposure and hypoxia) to investigate the mechanism of resistance to such therapy in RCC. Sunitinib-conditioned Caki-1 cells in vitro did not show resistance to sunitinib compared with parental cells, but when tested in vivo, these cells appeared to be highly resistant to sunitinib treatment. Hypoxia-conditioned Caki-1 cells are more resistant to hypoxia and have increased vascularity due to the upregulation of VEGF production; however, they did not develop sunitinib resistance either in vitro or in vivo. Human endothelial cells were more proliferative and showed increased tube formation in conditioned media from sunitinib-conditioned Caki-1 cells compared with parental cells. Gene expression profiling using RNA microarrays revealed that several genes related to tissue development and remodeling, including the development and migration of endothelial cells, were upregulated in sunitinib-conditioned Caki-1 cells compared with parental and hypoxia-conditioned cells. These findings suggest that evasive resistance to VEGF-targeted therapy is acquired by activation of VEGF-independent angiogenesis pathways induced through interactions with VEGF-targeted drugs, but not by hypoxia. These results emphasize that increased inhibition of tumor angiogenesis is required to delay the development of resistance to antiangiogenic therapy and maintain the therapeutic response in RCC.

You have accessJournal of UrologyBladder Cancer: Basic Research III1 Apr 2015MP49-09 ACTIVATION OF IFN/STAT1 SIGNALING IN CISPLATIN/GEMCITABINE RESISTANT BLADDER CANCER Tetsutaro Hayashi, Roland Seiler, Robert H. Bell, Susan Ettinger, Kendric Wang, Shannon Awrey, Kilian Gust, Wolfgang Jäger, Tilman Todenhoefer, Manuel Altamirano-Dimas, Akio Matsubara, Colin Collins, and Peter Black Tetsutaro HayashiTetsutaro Hayashi More articles by this author , Roland SeilerRoland Seiler More articles by this author , Robert H. BellRobert H. Bell More articles by this author , Susan EttingerSusan Ettinger More articles by this author , Kendric WangKendric Wang More articles by this author , Shannon AwreyShannon Awrey More articles by this author , Kilian GustKilian Gust More articles by this author , Wolfgang JägerWolfgang Jäger More articles by this author , Tilman TodenhoeferTilman Todenhoefer More articles by this author , Manuel Altamirano-DimasManuel Altamirano-Dimas More articles by this author , Akio MatsubaraAkio Matsubara More articles by this author , Colin CollinsColin Collins More articles by this author , and Peter BlackPeter Black More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.513AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Cisplatin-based combination chemotherapy (CBCC) is the standard treatment for patients with advanced bladder cancer (BC). Although responses are observed in up to 60% of patients, these are rarely durable, and most patients with advanced BC succumb to their disease. In the neoadjuvant setting, approximately 40% of patients have a major response to CBCC, while the other 60% have no benefit and may even be harmed by the delay in definitive local therapy. In both settings predictive molecular markers are desirable for individualization of therapy, and novel targets are essential for designing new treatments. Here we aimed to identify a genomic signature associated with resistance to cisplatin (CDDP) and gemcitabine (GEM) in BC. METHODS Three chemosensitive BC cell lines (RT112, UM-UC3, UM-UC13) were treated serially with increasing concentrations of CDDP up to 10μM, 3.3μM, 3.3μM, or GEM up to 10μM, 10μM, 1μM, respectively in order to establish resistance (CDDP-R and GEM-R). Gene expression microarray analysis of the resistant cell lines compared to the sensitive parental lines was conducted on the Agilent SurePrint G3 Human GE 8x60K v2 Microarray. RESULTS We ranked the top differentially expressed genes between the parental chemosensitive cell lines and the derived chemoresistant cell lines. Genes related to interferon (IFN) signaling made up 21 of the top 100 and 10 of the top 15 up-regulated genes. Pathway analysis revealed that IFN/STAT1 signaling is activated in chemoresistant cell lines. With quantitative RT-PCR we confirmed that STAT1, IFITM1, IFI27, IFI44L, IFIT1 and OSA2 were up-regulated in chemoresistant cell lines. Knockdown of STAT1 in these chemoresistant cell lines decreased expression of IFITM1, IFI27, IFI44L, IFIT1 and OSA2 which are downstream target genes of IFN/STAT1 signaling. In addition, STAT1 depletion in chemoresistant cells partially restored chemotherapy sensitivity. CONCLUSIONS IFN/STAT1 signaling is activated in chemoresistant bladder cancer cell lines and its inhibition can re-sensitize to chemotherapy. These genes warrant further study for their potential as predictive markers and for rational co-targeting in the context of CBCC. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e606 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Tetsutaro Hayashi More articles by this author Roland Seiler More articles by this author Robert H. Bell More articles by this author Susan Ettinger More articles by this author Kendric Wang More articles by this author Shannon Awrey More articles by this author Kilian Gust More articles by this author Wolfgang Jäger More articles by this author Tilman Todenhoefer More articles by this author Manuel Altamirano-Dimas More articles by this author Akio Matsubara More articles by this author Colin Collins More articles by this author Peter Black More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Tumor microenvironments are characterized by decreased oxygen and nutrition due to the rapid and progressive nature of tumors and also stresses induced by several anti-tumor therapies. These intense cell stressors trigger a protective cell survival mechanism heralded by the unfolded protein response (UPR). The UPR is induced by an accumulation of unfolded proteins in the endoplasmic reticulum (ER) following cell starvation. Although the ER stress response is implicated in cytoprotection, its precise role during anti-angiogenic therapy remains unclear. One of the major proteins involved in ER stress is glucose-regulated protein 78 (GRP78), which binds to unfolded proteins and dissociates from membrane-bound ER stress sensors. To determine the role of ER stress responses during anti-angiogenic therapy and the potential role of GRP78 in combined therapy in renal cell carcinoma (RCC), we used GRP78 overexpressing or knockdown RCC cells under hypoxic or hypoglycemic conditions in vitro and in animal models treated with sunitinib. Here, we report that GRP78 plays a crucial role in protecting RCC cells from hypoxic and hypoglycemic stress induced by anti-angiogenic therapy. Knockdown of GRP78 using siRNA inhibited cancer cell survival and induced apoptosis in RCC cells in vitro and also resulted in ER stress-induced apoptosis and hypoxic/hypoglycemic stress-induced apoptosis by inactivating the PERK/eIF-2 alpha pathway. Finally, GRP78 knockdown showed potent suppression of tumor growth and enhanced the antitumor effect of sunitinib in RCC xenografts. Our findings suggest that GRP78 may serve as a novel therapeutic target in combination with anti-angiogenic therapy for the management of RCC.

Purpose: KU7 is a popular urothelial carcinoma cell line that was isolated from the bladder of a patient at Keio University in 1980. It has subsequently been widely used in laboratories around the world. We describe how routine cell line authentication revealed that KU7 was cross contaminated almost 30 years ago with HeLa, a cervical carcinoma cell line.Materials and Methods: Presumed KU7 clones dating from 1984 to 1999 were provided by M. D. Anderson Cancer Center, Vancouver Prostate Centre, Kyoto University, Tokyo Medical University and Keio University. HeLa was obtained from ATCC (R). Genomic DNA was isolated and short tandem repeat analysis was performed at the M. D. Anderson Cancer Center Characterized Cell Line Core Facility, Johns Hopkins University Fragment Analysis Facility and RIKEN BioResource Center, Ibaraki, Japan. Comparative genomic hybridization was performed on a platform (Agilent Technologies, Santa Clara, California) at Vancouver Prostate Centre.Results: The short tandem repeat profile of all KU7 clones was an exact match with that of HeLa. Comparative genomic hybridization of all samples revealed an abundance of shared chromosomal aberrations. Slight differences in some genomic areas were explained by genomic drift in different KU7 clones separated by many years.Conclusions: Our analysis identified that cross contamination of KU7 with HeLa occurred before 1984 at the source institution. All KU7 clones in the urological literature should be considered HeLa and experimental results should be viewed in this light. Our results emphasize the need to authenticate cell lines in oncological research.

Abstract The androgen receptor (AR) plays a central role in the development of castration-resistant prostate cancer (CRPC), which is a major challenge for hormone therapy of advanced/metastatic prostate cancer (PCa). Here, we demonstrate that the ubiquitin ligase Siah2 targets a select pool of NCOR1-bound, transcriptionally inactive AR for ubiquitination-dependent degradation, and this promotes the subsequent recruitment of p300-bound, transcriptionally active AR to a select group of AR target gene promoters/enhancers. Consequently, Siah2 promotes the expression of ∼13% of androgen-responsive genes involved in lipid metabolism, cell motility and proliferation. The Siah2 binding sites located within the AR ligand-binding domain are mutated in PCa, resulting in attenuation of Siah2-mediated regulation. Siah2 is required for growth of PCa cells under the androgen-deprivation condition in vitro and in vivo. Significantly, inhibition of Siah2 promotes PCa regression upon castration and Siah2 expression is markedly increased in human CRPCs. Collectively our findings identify a key role for Siah2 in CRPC through the selective regulation of AR transcriptional activity. Citation Format: Jianfei Qi, Manisha Tripathi, Natasha Sahgal, Ladan Fazil, Susan Ettinger, William J. Placzek, Giuseppina Claps, Leland W.K. Chung, David Bowtell, Martin Gleave, Neil Bhowmick, Ze'ev Ronai. The E3 ubiquitin ligase Siah2 regulates the androgen receptor activity and contributes to castration-resistant prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5456. doi:10.1158/1538-7445.AM2013-5456 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.