Androgen Receptor Represses the Expression of Minichromosome Maintenance Proteins: a Mechanism for Androgen Therapy in Castration Resistant Prostate Cancer

Abstract

Standard treatment for metastatic prostate cancer is androgen deprivation therapy (ADT). Though this is often efficacious, for many patients, this invariably leads to the development of a more aggressive form of prostate cancer that is Castration Resistant Prostate Cancer (CRPC). Previous studies have shown that restoration of Androgen Receptor (AR, a member of nuclear receptor transcription factor family) activity plays a critical role in prostate cancer development and progression to CRPC. We have reported that in prostate cancer AR can function as both transcription activator and repressor. The latter suppressive function of AR is mediated by the recruitment of hypophosphorylated Retinoblastoma Protein (Rb), which results in negative regulation of the expression of Minichromosome Maintenance Proteins (MCMs). This protein family is composed of six distinct subunits (MCM2‐7) that form pre‐replication complex and are essential for replication initiation. Preliminary data of AR ChIP‐seq and Rb ChIP‐seq in CRPC cells showed the co‐binding on the promoters of MCM genes. Therefore downregulation the expression and activity of MCMs may be a potential mechanism for Rb‐dependent AR growth suppressive function in CRPC. We hypothesized that in CRPC cells, the AR activity stimulated by androgen treatment can have a repressive effect on the function of MCMs through recruitment of Rb to promoters, can subsequently suppress DNA replication process, and can thereby repress cancer cell proliferation. We alter Rb expression and phosphorylation as well as the expression of MCMs in prostate cancer cell lines (VCaP, LNCaP, and C4‐2) and then measure DNA replication by labeling newly replicated DNA with halogenated nucleotide precursors (BrdU, CldU, IdU) in conjunction with the expression level of MCMs, to determine the role of MCMs in AR mediated growth repressive function in CRPC. This AR growth repressive function may be mediated by downregulation of the expression and activity of MCMs through recruitment of hypophosphorylated Rb.Support or Funding InformationR00CA166507 (PI: Cai) 06/01/2015‐05/31/2017 (R00) NCI/NIH Molecular Basis of Androgen Receptor Mediated Gene Transcriptional Repression Objective: The aims of this project are to determine the molecular basis and functional importance for AR mediated repression of genes in prostate cancer cells. Aim 1. Determine the mechanisms of AR‐mediated repression on the subset of DNA synthesis and repair genes. Aim 2. Assess treatment with high dose androgen in combination with metabolic inhibitors on castration‐resistant PCa cell lines. Contact: Martinson O. Owusu 240‐276‐6297 martinson.owusu@mail.nih.gov