Abstract 1581: Androgen receptor action in prostate cancer partitions into distinct transcriptional codes that differ in clinical relevance
Authors: Kumari Sangeeta , Venkadakrishnan Varadha Balaji , Senapati Dhirodatta , Hu Qiang , Liu Song , Heemers Hannelore V. 
Published: July 2017

Abstract
With few exceptions the 30,000 prostate cancer (CaP) deaths annually in the US are due to failure of androgen deprivation therapy (ADT). ADT prevents ligand-activation of androgen receptor (AR). Despite remission, CaP progresses while continuing to rely on AR. AR’s transcriptional output that controls CaP behavior is an alternative therapeutic target, but its molecular regulation is poorly understood. Here, we determined the androgen dependence of hundreds of direct AR target genes on 18 coregulators that are relevant to CaP progression, and uncovered that the AR-dependent transcriptome breaks down in coregulator-dependent gene sets. Pairwise comparison and unsupervised clustering showed limited overlap between the gene subsignatures. Neither ChIP nor qRT-PCR studies revealed differences in the kinetics of coregulator recruitment to Androgen Response Elements (AREs) or of androgen regulation of different gene sets. Rather, Cistrome analyses of AR binding sites demonstrated preferential enrichment in binding motifs for distinct transcription factors (TFs) between coregulator-dependent gene sets. Pathway and GSEA analyses of these signatures indicated associations with select biological processes and differential enrichments between normal prostate and CaP, CaPs of different stages, and CaP and bone marrow microenvironment. These results suggested that coregulators may unite the action of DNA-bound AR and TF(s) to control select aspects of androgen-dependent CaP cell biology. The presence and functionality of such novel predicted AR transcriptional codes, namely AR-WDR77-p53 and AR-STAT3-IRF1 with projected roles in CaP cell proliferation and stemness respectively, was confirmed in Co-IP and gene expression profiling. As AR and p53 are the major drivers of lethal CaP, the AR-WDR77-p53 code was explored further. Mass spectrometry after WDR77 and p53 IP independently identified PGAM5, a recently isolated serine/threonine protein phosphatase that regulates cell death and unknown to be relevant to AR signaling or CaP biology, as part of the AR-WDR77-p53 complex. Co-IP assays verified IP-mass spectrometry results and ChIP studies confirmed recruitment of PGAM5 to WDR77-dependent AREs. Expression profiling demonstrated significant overlap in genes for which androgen regulation was altered after silencing of WDR77, PGAM5 or p53. Co-IP and ChIP studies showed that androgen-dependent recruitment of p53 to ARE-bound AR requires WDR77 and PGAM5. Western blotting and flow cytometry analyses indicated that WDR77 and PGAM5 and their dependent AR target genes control G1/S cell cycle progression, which was maintained in presence of clinically relevant gain-of-function p53 mutants. These novel insights indicate that disrupting select protein-protein and protein-DNA interactions may be a viable strategy to inhibit AR action that drives CaP lethal progression.
Citation Format: Sangeeta Kumari, Varadha Balaji Venkadakrishnan, Dhirodatta Senapati, Qiang Hu, Song Liu, Hannelore V. Heemers. Androgen receptor action in prostate cancer partitions into distinct transcriptional codes that differ in 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 1581. doi:10.1158/1538-7445.AM2017-1581