A novel inducible transactivation domain in the androgen receptor: implications for PRK in prostate cancer

Abstract

In addition to the classical activation by ligands, nuclear receptor activity is also regulated by ligandindependent signalling. Here, we unravel a novel signal transduction pathway that links the RhoA effector protein kinase C-related kinase PRK1 to the transcriptional activation of the androgen receptor (AR). Stimulation of the PRK signalling cascade results in a ligand-dependent superactivation of AR. We show that AR and PRK1 interact both in vivo and in vitro. The transactivation unit 5 (TAU-5) located in the N-terminus of AR suf®ces for activation by PRK1. Thus, TAU-5 de®nes a novel, signal-inducible transactivation domain. Furthermore, PRK1 promotes a functional complex of AR with the co-activator TIF-2. Importantly, PRK signalling also stimulates AR activity in the presence of adrenal androgens, which are still present in prostate tumour patients subjected to testicular androgen ablation therapy. Moreover, PRK1 activates AR even in the presence of the AR antagonist cyproterone acetate that is used in the clinical management of prostate cancer. Since prostate tumours strongly overexpress PRK1, our data support a model in which AR activity is controlled by PRK signalling. Keywords: androgen receptor/nuclear hormone receptor/ prostate cancer/protein kinase C-related kinase/ transcriptional co-activator IntroductionThe androgen receptor (AR) is a member of the steroid hormone receptor family of ligand-activated transcription factors that regulate diverse biological functions including cell growth and differentiation, development, homeostasis and various organ functions in the adult (Mangelsdorf et al., 1995;Cato and Peterzierl, 1998). The AR shares a common modular structure with other nuclear receptors and is composed of several domains that mediate DNA binding, dimerization, ligand binding and transcriptional activity (Mangelsdorf et al., 1995). The ligand binding domain (LBD) performs a number of functions including transcriptional repression or activation by generating the proper interaction surface for multiple partners, including co-repressors and co-activators (Renaud and Moras, 2000). Like other steroid receptors the AR contains a C-terminal ligand-dependent activation function 2 (AF-2) and an additional N-terminal ligand-independent activation function 1 (AF-1). The AR also harbours a less wellde®ned transcription activation unit termed TAU-5 (Jenster et al., 1995;Jenster, 1999). The TAU-5 is located between amino acids 360 and 528 and is required for full activation of the AR (Jenster et al., 1995;Bevan et al., 1999). However, signals that control TAU-5, and thereby AR activity, are unknown. Recent data show agonistinduced interaction between the N-terminal domain (NTD) and the LBD of the AR, supporting the view that both the AF-1 and the AF-2 are required for transcriptional activation (Ikonen et al., 1997;He et al., 2000). It has been suggested that the ligand-induced conformational changes of the LBD in concert with physical interactions with the NTD render the AR fully active (Ikonen et al., 19...

Phosphorylation of histone H3 at threonine 11 establishes a novel chromatin mark for transcriptional regulation

“…PRK1 also regulates the transcriptional activity of other nuclear receptors such as mineralocorticoid and progesterone receptor 6 , possibly via a mechanism similar to that controlling AR target gene expression. This raises questions whether other transcription factors are regulated by PRK1, and whether there exist other H3T11 kinases that control the activity of specific transcription factors.…”

“…Myc-PRK1 and the flag-tagged kinase dead mutant PRK1 K644E 6 were immunoprecipitated from 293 cell lysates with α-myc or α-flag antibody, respectively ( Supplementary Information, Fig. S1g, h) and incubated with bacterially expressed and purified GST-H3 1-44 or GST control protein.…”

“…CV1 and LNCaP cells were cultured and transfected as described 6 . The following amounts were transfected per well: 500 ng of MMTV-LUC, Probasin-LUC, or PSA-LUC; 25 ng of AR expression plasmid; 200 ng (Fig.…”

“…3c) Ro318220 (Roche) as indicated. Luciferase activity was assayed as described 6 . All experiments were repeated at least four times in duplicate.…”

Lysine-specific demethylase 1 restricts hematopoietic progenitor proliferation and is essential for terminal differentiation

“…This is particularly relevant, because previous studies established LSD1 as a potential drug target for cancer treatment. [13][14][15][16][17][18]42 Continuous dox treatment of shLSD1 mice resulted in dramatic changes within different hematopoietic compartments. Mechanistically, enhanced expression of hematopoietic regulatory genes in these mice is presumably caused by the lack of LSD1 repressive activity at H3K4 residues in the gene promoters.…”