No abstract

The androgen receptor interacts with the p160 coactivators via two surfaces, one in the ligand binding domain and one in the amino-terminal domain. The ligand binding domain interacts with the nuclear receptor signature motifs, whereas the amino-terminal domain has a high affinity for a specific glutamine-rich region in the p160s. We here describe the implication of two conserved motifs in the latter interaction. The amino-terminal domain of the androgen receptor is a very strong activation domain constituent of Tau5, which is mainly active in the absence of the ligand binding domain, and Tau1, which is only active in the presence of the ligand binding domain. Both domains are, however, implicated in the recruitment of the p160s. Mutation analysis of the p160s has shown that the relative contribution of the two recruitment mechanisms via the signature motifs or via the glutamine-rich region depend on the nature of the enhancers tested. We propose, therefore, that the androgen receptor-coactivator complex has several alternative conformations, depending partially on the context of the enhancer. The androgen receptor (AR)1 is a member of the steroid receptor family of transcription factors. Steroid receptors are ligand-inducible sequence-specific transcription factors with highly conserved DNA binding domains (DBDs), moderately conserved ligand binding domains (LBDs), and divergent amino-terminal domains (NTD) (1-4). Two transactivating functions (AFs) have been characterized, AF1 in the NTD and AF2 in the LBD. For the AR, AF1 has strong constitutive activity, since deletion of the LBD results in a molecule that can activate a reporter gene to the same extent as the full-length receptor in the presence of ligand, whereas AF2 appears to be weak (5-8). This is in contrast to what occurs in most other nuclear receptors, for example for the estrogen receptor (ER), in which AF2 is the major activation domain (9). The precise residues and mechanisms that contribute to the AF1 activity of the AR have not been conclusively established. Almost the entire NTD is required for full transcriptional activity of the full-length receptor, whereas a core region located between residues 101 and 360 (Tau1) contributes 50% of activity (10). When a constitutively active AR mutant lacking an LBD is studied, the region necessary for transcriptional activation shifts to the region 370 -494 (Tau5) (10).Binding of the appropriate hormones to the steroid hormone receptors causes a translocation of the receptors to enhancer elements in the promoters of target genes. Transcriptional coactivators are recruited to the promotor through proteinprotein interaction with the receptor (11-14). Most known coactivators are complex proteins that harbor multiple activation domains and receptor-interacting domains (15-16). The best studied group of coactivators is the p160 family of 160-kDa proteins. Three family members have been identified. The first p160 coactivators cloned were the human steroid receptor coactivator 1 (SRC1) and the transcription inte...

The androgen receptor has a subset of target DNA sequences, which are not recognized by any other steroid receptors. The androgen selectivity of these sequences was proposed to be the consequence of the ability of the androgen receptor to dimerize on direct repeats of 5'-TGTTCT-3'-like sequences. This is in contrast with the classical non-selective elements consisting of inverted repeats of the 5'-TGTTCT-3' elements separated by three nucleotides and which are recognized by other steroid receptors in addition to the androgen receptor. We demonstrate that while the DNA-binding domain of the oestrogen receptor is unable to dimerize on direct repeats, dimeric binding can be rescued by replacing the second Zn finger and part of the hinge region by the corresponding fragment of the androgen receptor, but not the glucocorticoid receptor. In this study, we investigate the androgen receptor binding to all natural androgen-selective response elements described so far. We show that a 12-amino acid C-terminal extension of the DNA-binding domain is required for high-affinity binding of the androgen receptor to all these elements. For one androgen-specific low-affinity binding site, the flanking sequences do not contribute to the in vitro affinity of the androgen receptor DNA-binding domain. Surprisingly, however, they control the transcriptional activity of the androgen receptor in transient transfection experiments. In conclusion, we give evidence that the alternative DNA-dependent dimerization of the androgen receptor on direct repeats is a general mechanism for androgen specificity in which the second Zn finger and hinge region are involved. In addition, the sequences flanking an androgen-response element can control the activity of the androgen receptor.

Androgens play an important role in male reproductive development and function. These steroid hormones mediate their actions by binding to the androgen receptor (AR). Diseases such as androgen insensitivity syndrome, prostate cancer, Kennedy's disease, and infertility can be caused by mutations in the AR. To get a better insight into the molecular working mechanisms of the AR, several knockout and knock-in mouse models have been developed. These models are reviewed here and are compared with human diseases.

The androgen receptor (AR) can be small ubiquitin-like modifier (SUMO)-ylated in its amino-terminal domain at lysines 385 and 511. This SUMO-ylation is responsive to several agonists, but is not induced by the pure antagonist hydroxyflutamide. We show that the main site of interaction of Ubc9, the SUMO-1 conjugating enzyme, resides in transcription activation unit 5. Overexpression of SUMO-1 represses the AR-mediated transcription, and this effect is abolished after mutating both SUMO-1 acceptor sites. On the other hand, the mutation of lysine 385 clearly affects the cooperativity of the receptor on multiple hormone response elements. Lysine 511 is not implicated in this function. Surprisingly, these effects on cooperativity clearly depend on the nature of the response elements. When selective androgen response elements, which are organized as direct repeats of 5'-TGTTCT-3'-like sequences, were tested, the lysine 385 mutation did not increase the androgen response. Point mutations changing the direct-repeat elements into inverted-repeat elements restored the effects of the lysine 385 mutation on cooperativity. In conclusion, SUMO-ylation of the AR might have a differential function in the control of cooperativity, depending on the conformation of the AR dimer bound to DNA.