Dependence of Selective Gene Activation on the Androgen Receptor NH2- and COOH-terminal Interaction

Abstract

The agonist-induced androgen receptor NH2- and COOH-terminal (N/C) interaction is mediated by the FXXLF and WXXLF NH2-terminal motifs. Here we demonstrate that agonist-dependent transactivation of prostate-specific antigen (PSA) and probasin enhancer/promoter regions requires the N/C interaction, whereas the sex-limited protein gene and mouse mammary tumor virus long terminal repeat do not. Transactivation of PSA and probasin response regions also depends on activation function 1 (AF1) in the NH2-terminal region but can be increased by binding an overexpressed p160 coactivator to activation function 2 (AF2) in the ligand binding domain. The dependence of the PSA and probasin enhancer/promoters on the N/C interaction for transactivation allowed us to demonstrate that in the presence of androgen, the WXXLF motif with the sequence433WHTLF437 contributes as an inhibitor to AR transactivation. We further show that like the FXXLF and LXXLL motifs, the WXXLF motif interacts in the presence of androgen with AF2 in the ligand binding domain. Sequence comparisons among species indicate greater conservation of the FXXLF motif compared with the WXXLF motif, paralleling the functional significance of these binding motifs. The data provide evidence for promoter-specific differences in the requirement for the androgen receptor N/C interaction and in the contributions of AF1 and AF2 in androgen-induced gene regulation. The agonist-induced androgen receptor NH2- and COOH-terminal (N/C) interaction is mediated by the FXXLF and WXXLF NH2-terminal motifs. Here we demonstrate that agonist-dependent transactivation of prostate-specific antigen (PSA) and probasin enhancer/promoter regions requires the N/C interaction, whereas the sex-limited protein gene and mouse mammary tumor virus long terminal repeat do not. Transactivation of PSA and probasin response regions also depends on activation function 1 (AF1) in the NH2-terminal region but can be increased by binding an overexpressed p160 coactivator to activation function 2 (AF2) in the ligand binding domain. The dependence of the PSA and probasin enhancer/promoters on the N/C interaction for transactivation allowed us to demonstrate that in the presence of androgen, the WXXLF motif with the sequence433WHTLF437 contributes as an inhibitor to AR transactivation. We further show that like the FXXLF and LXXLL motifs, the WXXLF motif interacts in the presence of androgen with AF2 in the ligand binding domain. Sequence comparisons among species indicate greater conservation of the FXXLF motif compared with the WXXLF motif, paralleling the functional significance of these binding motifs. The data provide evidence for promoter-specific differences in the requirement for the androgen receptor N/C interaction and in the contributions of AF1 and AF2 in androgen-induced gene regulation. activation function 1 androgen receptor NH2-terminal and COOH-terminal activation function 2 transcriptional intermediary factor 2 glutathione S-transferase glucocorticoid receptor luciferase prostate-specific antigen mouse mammary tumor virus dihydrotestosterone Steroid receptors are ligand-activated transcription factors that regulate gene activation through a series of events triggered by high affinity hormone binding and mediated by receptor binding to response element DNA and coactivators. At least two domains have been identified that mediate nuclear receptor interactions with coregulators. These are activation function 1 (AF1)1in the NH2-terminal region and activation function 2 (AF2) in the ligand binding domain. The AF2 binding surface in the ligand binding domain is comprised of helices 3, 4, and 12 and forms after hormone binding. For many nuclear receptors, transactivation depends on AF2 recruitment of p160 coactivator complexes that have histone acetyl transferase activity to modify chromatin structure (1Spencer T.E. Jenster G. Burcin M.M. Allis C.D. Zhou J. Mizzen C.A. McKenna N.J. Onate S.A. Tsai S.Y. Tsai M.J. O'Malley B.W. Nature. 1997; 389: 194-198Crossref PubMed Scopus (1070) Google Scholar). The p160 coactivators are a group of proteins that include steroid receptor coactivator 1 (SRC1), transcriptional intermediary protein 2 (TIF2, GRIP1 or SRC2), and the steroid receptor coactivator 3 subfamily (SRC3). Interaction with AF2 is mediated by the p160 coactivator LXXLL motif that forms an amphipathic α-helix and binds the AF2 hydrophobic binding surface in the nuclear receptor ligand binding domain (2Heery D.M. Kalkhoven E. Hoare S. Parker M.G. Nature. 1997; 387: 733-736Crossref PubMed Scopus (1778) Google Scholar, 3Darimont B.D. Wagner R.L. Apriletti J.W. Stallcup M.R. Kushner P.J. Baxter J.D. Fletterick R.J. Yamamoto K.R. Genes Dev. 1998; 12: 3343-3356Crossref PubMed Scopus (832) Google Scholar, 4Nolte R.T. Wisely G.B. Westin S. Cobb J.E. Lambert M.H. Kurokawa R. Rosenfeld M.G. Willson T.M. Glass C.K. Milburn M.V. Nature. 1998; 395: 137-143Crossref PubMed Scopus (1700) Google Scholar, 5Shia