Differential regulation of the androgen receptor by protein phosphatase regulatory subunits.

James Grey,Sirintra Nakjang,Emma Clark,Dominic Jones,Luke Gaughan,Laura Wilson,Craig Robson,Richard Temperley,Jake Clayton

doi:10.18632/oncotarget.22883

Abstract

The Androgen Receptor (AR) is a key molecule in the development, maintenance and progression of prostate cancer (PC). However, the relationship between the AR and co-regulatory proteins that facilitate AR activity in castrate resistant settings remain understudied. Here we show that protein phosphatase 1 regulatory subunits, identified from a phosphatase RNAi screen, direct PP1 catalytic subunits to a varied yet significant response in AR function. As such, we have characterised the PP1β holoenzyme, myosin phosphatase (MLCP), as a novel ligand independent regulator of the AR. Sustained MLCP activity through down-regulation of the MLCP inhibitory subunit, PPP1R14C, results in impaired AR nuclear translocation, protein stability and transcriptional activity in distinct models of PC progression, culminating in restoration of a non-malignant prostate genotype. Phenotypically, a marked reduction in cell proliferation and migration, characterised by G1 cell cycle arrest is observed, confirming PP1 holoenzyme disruption as a novel treatment approach in PC.

Highlights

Prostate cancer (PC) is the most common noncutaneous cancer in males in western countries and is fast emerging as a significant health risk in the developing world, accounting for the second highest rate of cancer related deaths in men worldwide
Through the implementation of a human phosphatome RNAi screen we demonstrate for the first time that the PP1b catalytic subunit is repressive towards Androgen Receptor (AR) function, but that the impact of Phosphatase 1 (PP1) activity on AR function is entirely dependent upon the association of the catalytic subunit with its respective regulatory subunits
It became clear that RNAi knockdown of PP1 regulatory subunits resulted in distinct, yet highly significant, modulation of AR activity, revealing a more complex role for PP1 holoenzymes in the regulation of AR activity than previously described (Figure 1D)

Summary

INTRODUCTION

Prostate cancer (PC) is the most common noncutaneous cancer in males in western countries and is fast emerging as a significant health risk in the developing world, accounting for the second highest rate of cancer related deaths in men worldwide (www.cancerresearch. co.uk). We characterise the PP1β holoenzyme MLCP as a novel dynamic regulator of the AR, and demonstrate that through downregulation of the endogenous MLCP regulatory inhibitory subunit, PPP1R14C [28], ligand induced AR nuclear translocation, stability, and AR transcriptional activity is significantly reduced in distinct PC cell line models representing both androgen sensitivity and castration resistance. Depletion of PPP1R12A results in increased AR mRNA expression, protein expression and AR transcriptional activity in both the presence and absence of androgen, confirming MLCP as a novel dynamic ligand independent regulator of the AR With this in mind, we propose that the disruption of specific PP1 holoenzymes provides a distinct route of PP1 inhibition, and as such, a viable approach in the treatment of PC and CRPC

RESULTS

DISCUSSION

Method details