The AF1 and AF2 Domains of the Androgen Receptor Interact with Distinct Regions of SRC1

Abstract

The androgen receptor is unusual among nuclear receptors in that most, if not all, of its activity is mediated via the constitutive activation function in the N terminus. Here we demonstrate that p160 coactivators such as SRC1 (steroid receptor coactivator 1) interact directly with the N terminus in a ligand-independent manner via a conserved glutamine-rich region between residues 1053 and 1123. Although SRC1 is capable of interacting with the ligand-binding domain by means of LXXLL motifs, this interaction is not essential since an SRC1 mutant with no functional LXXLL motifs retains its ability to potentiate androgen receptor activity. In contrast, mutants lacking the glutamine-rich region are inactive, indicating that this region is both necessary and sufficient for recruitment of SRC1 to the androgen receptor. This recruitment is in direct contrast to the recruitment of SRC1 to the estrogen receptor, which requires interaction with the ligand-binding domain.The androgen receptor (AR), a member of the nuclear receptor superfamily (6,45), is a ligand-activated transcription factor with the major ligands testosterone and dihydrotestosterone. It has the overall domain structure common to nuclear receptors, comprising an N-terminal activation domain (activation function 1 [AF1]), a central DNA-binding domain (DBD), and a C-terminal ligand-binding domain (LBD). A second, ligand-dependent activation function (AF2) in several nuclear receptors, including other steroid hormone receptors, has been well characterized (5,15,19,66), but until recently there was no evidence to support such a function for the AR LBD. Deletion of the LBD results in a molecule with constitutive activity which in many reporter activation assays is equivalent to the maximum activity of the full-length receptor in the presence of ligand, implying that AF1 contributes all the activity of the receptor (35,56,61,82). This finding is in contrast to what occurs with the closely related estrogen receptor (ER), in which AF2 is the major activation domain and AF1 has little independent activity (67). The situation in the AR is still more complex, in that two discrete, overlapping activation domains exist in the N-terminal domain and their usage is context dependent. While almost the entire N terminus (residues 1 to 494) is required for full activity of the full-length receptor, a core that contributes 50% of activity is located between residues 101 and 360, and this region has been termed TAU1. However, in the absence of the LBD a different region, termed TAU5 (residues 370 to 494), mediates activation (34).Upon binding of ligand, steroid hormone receptors adopt an active conformation that facilitates the dissociation of heat shock proteins, dimerization, and binding to response elements in the promoters of responsive genes. These receptors have been shown to interact with some components of the basal transcriptional machinery (3, 9, 10, 32, 46, 59) and also to promote transcription of the gene by interacting with coactivator proteins (23, 68). Coactiva...

The skeletal response to estrogen is impaired in female but not in male steroid receptor coactivator (SRC)-1 knock out mice

“…The novel finding of the present work is the demonstration of preserved responses to E in trabecular bone in male SRC-1 KO mice, which contrasts with the deficits in E action in trabecular bone we previously observed in the female SRC-1 KO mice [13]. Since SRC-1 interacts both with E and androgen receptors [23,24], the basal deficits in trabecular bone in male SRC-1 KO mice, despite preservation of the response to E in this bone compartment, is consistent with impaired androgen action in trabecular bone in SRC-1 KO mice, as previously demonstrated by Yamada et al [14]. Further defining the mechanism(s) underlying the gender specificity of the defect in E action on bone in SRC-1 KO mice, may provide insights into differential ERα vs. ERβ expression, utilization, or interactions with SRC-1 in male vs. female bones.…”

Cofactor competition between the ligand-bound oestrogen receptor and an intron 1 enhancer leads to oestrogen repression of ERBB2 expression in breast cancer

“…All MOR expression constructs were cloned in the vector pMT2 and have been described previously (Lahooti et al, 1994) with the exception of the MOR 182 ± 599/DH12 mutant which was generated by replacing the 3' Xbal/EcoRI fragment of pMT2MOR182 ± 599 with the equivalent fragment from pJ3MORDH12 (Danielian et al, 1992). The SRC-1 expression clones were in pSG5 and all based on the SRC-1e isoform and expressed at comparable levels (Kalkhoven et al, 1998;Bevan et al, 1999). AIB1 and TIF2 expression constructs have been described elsewhere (Anzick et al, 1997;Voegel et al, 1996).…”

Silencing of androgen-regulated genes using a fusion of AR with the PLZF transcriptional repressor

“…The expression vector pSG5 (Green et al, 1988), pSG5-PLZF (Chen et al, 1993a) and pSVAR 0 , encoding the human AR coding sequence (Bevan et al, 1999), have previously been described. PLZF-AR was generated by site-directed mutagenesis of pSG5-PLZF to create an XhoI site following sequences encoding amino acid 456 of PLZF.…”