Androgen receptor acetylation sites differentially regulate gene control

Abstract

Androgen receptor (AR) function is modulated by post-translational modifications such as acetylation, ubiquitylation, sumoylation, and phosphorylation. Concerning acetylation, three lysines residues located in a consensus KxKK motif of the AR hinge domain have been identified. For a better evaluation of the role of this modification, the activity of AR modified at different acetylation sites was determined by comparing the effects on natural and synthetic promoters. We found that mutation of AR acetylation sites affected both potency and efficacy of androgen-dependent response. Remarkably, elimination of all three acetylation sites was still compatible with strong AR activity on the PSA and MMTV promoters, but not on the Pem promoter. This differential effect was seen at various wild-type (wt) to mutant AR receptor ratios and at changing hormone concentrations. Subcellular localization studies showed that both mutated and wt AR efficiently translocated into the cell nucleus. Plasmid immunoprecipitation revealed comparable binding of both receptor forms to the Pem promoter. The differential effects observed for the Pem promoter were partially due to an androgen response element (ARE) named ARE-1 which was only poorly stimulated by the AR acetylation site mutant. Finally, AR mutants impaired in their N/C interaction elicited intact stimulation of the Pem promoter, suggesting that AR acetylation was not influenced by this inter-domain communication. The promoter-selective effects seen for the AR acetylation site mutants strongly suggest this post-translational modification to be important in the fine-tuning of the effects of androgens on different target genes.

Regulation of the androgen receptor by post-translational modifications

“…P-Ser81 is inhibited by the topoisomerase inhibitor camptothecin, which results in decreased AR activity as a result of reduced androgen binding and nuclear translocation (Liu et al 2010a). Androgen-independent PC cell line models have reported increased levels of p-Ser81 (Hsu et al 2011), with AR stabilisation (Golsteyn et al 1989, Faus & Haendler 2008) and regulation of promoter specificity (Lee et al 2007) being described as functional outcomes. Ser81 phosphorylation occurs in the nucleus, similar to Ser256 and Ser308 (Kesler et al 2007), w4 h post-androgen stimulation, suggesting that this residue is not responsible for enhancing nuclear translocation or DNA binding; hence, rapidly induced genes do not require this phosphorylation event .…”

“…For example, upon mutation of all acetyl acceptors, the mouse Muc1 (Pem) promoter is not activated while prostate-specific antigen (PSA; KLK3) remains active and the MMTV promoter is activated to a higher level than with WT AR. This differential transcriptional ability of acetylation site mutants of AR suggests the receptor can recruit different coregulator proteins depending on which sites can be acetylated (Faus & Haendler 2008). One study specifically addressed the role of the hinge region, which contains the KLKK motif, in the regulation of AR activity by generating an AR mutant that lacked residues 629-636.…”

The Rhox genes

“…This conclusion comes from several lines of evidence, including: i) Rhox5 mRNA levels (measured with either Rhox5 or Pp-specific probes) are dramatically reduced in animals deficient in the ability to produce LH (the peptide hormone responsible for inducing testosterone production in Leydig cells) as a result of hypophysectomy, chemical treatment, or genetic mutations , 1996c, Maiti et al 1996a, Sutton et al 1998; ii) testosterone reverses the defect in Rhox5 expression caused by loss of LH , Sutton et al 1998; and ix) the Pp possesses four androgen-response elements (AREs), each of which is required for its AR-and androgen-dependent expression in transfected cell lines (Barbulescu et al 2001, Geserick et al 2003, Bhardwaj et al 2008, Faus & Haendler 2008. Together, these studies strongly suggest that the Rhox5 Pp is a direct target of AR in Sertoli cells.…”

EGCG suppresses prostate cancer cell growth modulating acetylation of androgen receptor by anti-histone acetyltransferase activity

“…Here, we demonstrate that EGCG can effectively suppress androgen-dependent prostate cancer cell growth and proliferation. Transcription factors, such as AR and ERα, are regulated through acetylation by HATs (7,8) and there is strong evidence that AR acetylation is involved in the regulation of prostate cell growth, apoptosis and proliferation (13). Therefore, we examined whether the growth inhibitory effects of EC, EGC and EGCG on androgen-dependent prostate cancer cells are dependent on their anti-HAT activities.…”

“…It has recently become clear that human prostate cancer development involves post-transcriptional modifications, such as acetylation and phosphorylation of the androgen receptor (7). Histone acetyltransferase (HAT) is one of the histone modifier proteins that acetylates AR during prostate cancer cell growth (8). AR is acetylated by p300, P/CAF, and TIP60, leading to the recruitment of co-regulators to the basal transcription machinery of AR target genes and growth properties of the receptors, in cultured cells and in vivo (7).…”