Context dependent regulatory patterns of the androgen receptor and androgen receptor target genes.

Jan Roger Olsen,Lisha Li,Kristo Marvyin,Karl-Henning Kalland,Waqas Azeem,Anne Margrete Øyan,Yi Qu,Biaoyang Lin,Yaping Hua,Xi-Song Ke,Margrete Reime Hellem

doi:10.1186/s12885-016-2453-4

Abstract

BackgroundExpression of the androgen receptor (AR) is associated with androgen-dependent proliferation arrest and terminal differentiation of normal prostate epithelial cells. Additionally, activation of the AR is required for survival of benign luminal epithelial cells and primary cancer cells, thus androgen deprivation therapy (ADT) leads to apoptosis in both benign and cancerous tissue. Escape from ADT is known as castration-resistant prostate cancer (CRPC). In the course of CRPC development the AR typically switches from being a cell-intrinsic inhibitor of normal prostate epithelial cell proliferation to becoming an oncogene that is critical for prostate cancer cell proliferation. A clearer understanding of the context dependent activation of the AR and its target genes is therefore desirable.MethodsImmortalized human prostate basal epithelial EP156T cells and progeny cells that underwent epithelial to mesenchymal transition (EMT), primary prostate epithelial cells (PrECs) and prostate cancer cell lines LNCaP, VCaP and 22Rv1 were used to examine context dependent restriction and activation of the AR and classical target genes, such as KLK3. Genome-wide gene expression analyses and single cell protein analyses were applied to study the effect of different contexts.ResultsA variety of growth conditions were tested and found unable to activate AR expression and transcription of classical androgen-dependent AR target genes, such as KLK3, in prostate epithelial cells with basal cell features or in mesenchymal type prostate cells. The restriction of androgen- and AR-dependent transcription of classical target genes in prostate basal epithelial cells was at the level of AR expression. Exogenous AR expression was sufficient for androgen-dependent transcription of AR target genes in prostate basal epithelial cells, but did not exert a positive feedback on endogenous AR expression. Treatment of basal prostate epithelial cells with inhibitors of epigenetic gene silencing was not efficient in inducing androgen-dependent transcription of AR target genes, suggesting the importance of missing cofactor(s).ConclusionsRegulatory mechanisms of AR and androgen-dependent AR target gene transcription are insufficiently understood and may be critical for prostate cancer initiation, progression and escape from standard therapy. The present model is useful for the study of context dependent activation of the AR and its transcriptome.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2453-4) contains supplementary material, which is available to authorized users.

Highlights

Expression of the androgen receptor (AR) is associated with androgen-dependent proliferation arrest and terminal differentiation of normal prostate epithelial cells
AR mRNA could not be detected in either of these conditions using Agilent oligonucleotide microarray analyses (Fig.1a), and this was supported by RNA sequencing (RNA-seq) (Table 1) and validated by TaqMan reverse transcription quantitative PCR (RT-qPCR) assays (Fig. 1b)
KLK3 and KLK2 mRNAs were nondetectable using highly sensitive assays (Fig. 1a/b/c and Table 1) and none of these target genes could be induced to higher expression following addition of the synthetic androgen R1881 at different concentrations to the growth media (Fig. 1a/b/c)

Summary

Introduction

Expression of the androgen receptor (AR) is associated with androgen-dependent proliferation arrest and terminal differentiation of normal prostate epithelial cells. Activation of the AR is required for survival of benign luminal epithelial cells and primary cancer cells, androgen deprivation therapy (ADT) leads to apoptosis in both benign and cancerous tissue. In physiological prostate homeostasis the prostate epithelium is dependent upon a paracrine mechanism according to which androgen stimulates the stromal AR to induce expression of diffusible growth factors such as FGF7, FGF10, IGF1 and EGF which are essential for prostate basal epithelial cell proliferation [6]. During progression of prostate cancer the AR switches from an epithelial anti-proliferative transcription factor to an oncogene. This may occur in a stepwise fashion by still incompletely understood molecular mechanisms. Several possibly independent steps in CRPC cell generation encompass the loss of ligand-bound AR-dependent inhibition of proliferation, the oncogenic addiction to AR signaling and the replacement of paracrine AR signaling by autocrine growth factor signaling [7,8,9]

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Discussion

Conclusion