Androgen Receptor Acetylation Governs trans Activation and MEKK1-Induced Apoptosis without Affecting In Vitro Sumoylation and trans-Repression Function

Abstract

The androgen receptor (AR) is a nuclear hormone receptor superfamily member that conveys both trans repression and ligand-dependent trans-activation function. Activation of the AR by dihydrotestosterone (DHT) regulates diverse physiological functions including secondary sexual differentiation in the male and the induction of apoptosis by the JNK kinase, MEKK1. The AR is posttranslationally modified on lysine residues by acetylation and sumoylation. The histone acetylases p300 and P/CAF directly acetylate the AR in vitro at a conserved KLKK motif. To determine the functional properties governed by AR acetylation, point mutations of the KLKK motif that abrogated acetylation were engineered and examined in vitro and in vivo. Steroid receptors, including the androgen receptor (AR), are members of the nuclear receptor (NR) superfamily which generally function as ligand-dependent transcriptional regulators (9, 31, 84). The AR is expressed in a variety of cell types and plays an important role in development, male sexual differentiation, and prostate cellular proliferation. The functional domains of the AR (termed A to F) are conserved with other members of the classical receptor subclass. The C-terminal region of the AR, including the hinge region and ligand-binding domain (LBD), is responsible for ligand binding and dimerization. The well-conserved DNA binding domain consists of 68 amino acids with two zinc finger structures. The N-terminal region contributes to transcriptional activation through its activation function 1 (AF-1) (5). In contrast to several other hormone-regulated NRs, the AR lacks an intrinsic AF-2 function in the LBD. The LBD, which consists of 12 ␣ helices projecting away from the hormone-binding pocket in the absence of ligand, undergoes substantial conformational changes in the presence of ligand. The folding of the most carboxyl-terminal helix 12 over the ligand-binding pocket in turn creates new structural surfaces that bind coactivators required for efficient transactivation.Several AR coactivators have been identified, including the p160 proteins, the p300/CREB-binding protein (CBP) family, Ubc9, ARA70, ARA55, and TIP60 (1,5,15,68,92). The efficient recruitment of coactivators to the AR involves an association between both the AR amino terminus and the LBD (5, 34). The coactivator proteins regulate gene expression through several distinct mechanisms. CBP and the related functional homologue p300 (CBP/p300) convey a bridging function between the DNA-bound transcription factor and the basal apparatus and provide a scaffold to assemble high-molecular-weight enhanceosomes (reviewed in reference 26). In addition, the cointegrator proteins p300/CBP share the capacity to acetylate histones, which correlates, under certain circumstances, with their transcriptional coactivator function (54,87). Acetylation facilitates binding of transcription factors to * Corresponding author. Mailing address: The Albert Einstein Can-

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