Abstract 2966: The role of histone demethylase GASC1 in promoting prostate cancer progression

Prostate cancer affects 1 in 6 American men, and is the second leading cause of cancer-related deaths in males. The defiance of castration-resistant prostate cancer (CRPC) to currently available treatments represents the most challenging aspect of this disease. Although resistant to androgen deprivation treatment, most CRPCs continue to express the androgen receptor (AR) and remain dependent on AR signaling for growth and proliferation. Previously, we cloned a novel gene, GASC1 (gene amplified in squamous cell carcinoma 1), from 9p24 amplified cancer cells. Recently, the GASC1 protein has been identified as a key histone demethylase that controls chromatin-mediated regulation of gene expression. Importantly, the GASC1 protein interacts with the AR and serves as a co-activator of AR-induced transcription in prostate cells. In this study, we demonstrated that various aggressive tumors, including CRPCs, have upregulated GASC1. We used an shRNA approach to determine whether GASC1 knockdown would affect the proliferation and transformation of CRPC cell lines. We found that knocking down GASC1 inhibits growth and colony formation of CRPC cells (C4-2B and CWR22Rv1) in vitro. Previously, it was reported that the GASC1 protein interacts with the AR and functions as a co-activator of AR-induced transcription in LNCaP cells. The GASC1 protein contains N-terminal Jumonji catalytic domains and C-terminal Tudor and PHD domains; however, which domains are responsible for the association of GASC1 with the AR have not yet been identified. To address this question, we generated stable LNCaP cell lines expressing V5-tagged N-terminal Jumonji catalytic domains and C-Terminal PHD/Tudor domains, and performed Co-IP analyses. We found that the C-terminal region is essential for GASC1 association with the AR in prostate cancer cells. To explore the contribution of GASC1 to endogenous AR-regulated gene expression in AR-positive CRPC cells, we performed quantitative RT-PCR assays to measure the expression of both classical AR target genes (including PSA/KLK3, KLK2, FKBP5, and NDRG1) and CRPC-specific genes (including UBE2C, CDK1, CDC20, and CCNA2) in C4-2B cells with or without GASC1 knockdown. We found that knocking down GASC1 significantly reduced transcript levels of a set of classical and CRPC-specific AR target genes in either the presence or absence of the AR ligand. Our data demonstrates that GASC1 is a target of substantial relevance to aggressive prostate cancers, includin