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Androgens influence transcription of their target genes through the activation of the androgen receptor (AR) that subsequently interacts with specific DNA motifs in these genes. These DNA motifs, called androgen response elements (AREs), can be classified in two classes: the classical AREs, which are also recognized by the other steroid hormone receptors; and the AR-selective AREs, which display selectivity for the AR. For in vitro interaction with the selective AREs, the androgen receptor DNA-binding domain is dependent on specific residues in its second zinc-finger. To evaluate the physiological relevance of these selective elements, we generated a germ-line knockin mouse model, termed SPARKI (SPecificity-affecting AR KnockIn), in which the second zinc-finger of the AR was replaced with that of the glucocorticoid receptor, resulting in a chimeric protein that retains its ability to bind classical AREs but is unable to bind selective AREs. The reproductive organs of SPARKI males are smaller compared with wild-type animals, and they are also subfertile. Intriguingly, however, they do not display any anabolic phenotype. The expression of two testis-specific, androgen-responsive genes is differentially affected by the SPARKI mutation, which is correlated with the involvement of different types of response elements in their androgen responsiveness. In this report, we present the first in vivo evidence of the existence of two functionally different types of AREs and demonstrate that AR-regulated gene expression can be targeted based on this distinction.DNA-binding domain ͉ fertility ͉ Rhox5 ͉ transcription

The androgen and glucocorticoid hormones evoke specific in vivo responses by activating different sets of responsive genes. Although the consensus sequences of the glucocorticoid and androgen response elements are very similar, this in vivo specificity can in some cases be explained by differences in DNA recognition between both receptors. This has clearly been demonstrated for the androgen response element PB-ARE-2 described in the promoter of the rat probasin gene. Swapping of different fragments between the androgen- and glucocorticoid-receptor DNA-binding domains demonstrates that (i) the first Zn-finger module is not involved in this sequence selectivity and (ii) that residues in the second Zn-finger as well as a C-terminal extension of the DNA-binding domain from the androgen receptor are required. For specific and high-affinity binding to response elements, the DNA-binding domains of the androgen and glucocorticoid receptors need a different C-terminal extension. The glucocorticoid receptor requires 12 C-terminal amino acids for high affinity DNA binding, while the androgen receptor only involves four residues. However, for specific recognition of the PB-ARE-2, the androgen receptor also requires 12 C-terminal residues. Our data demonstrate that the mechanism by which the androgen receptor binds selectively to the PB-ARE-2 is different from that used by the glucocorticoid receptor to bind a consensus response element. We would like to suggest that the androgen receptor recognizes response elements as a direct repeat rather than the classical inverted repeat.

The basis for specificity of gene regulation by steroid hormone receptors remains an important problem in the study of steroid hormone action. One possible mechanism for steroid specificity is the difference in DNA binding characteristics of the receptors, although they share a high homology in their DNA-binding domains. Indeed, the androgen-specific expression of, for example, the probasin (PB) gene can be explained by the presence of an androgen response element (ARE) in its promoter (PB-ARE-2), specifically recognized by the androgen and not by the glucocorticoid receptor. Three residues in the DNA-binding domain of the AR were identified as main determinants for its high affinity for the PB-ARE-2. In addition, the direct repeat nature of this ARE seems to prohibit high affinity binding by the glucocorticoid receptor. This is confirmed by the fact that several imperfect direct repeats of the 5-TGT-TCT-3 core recognition sequence are recognized by the androgen receptor and not by the glucocorticoid receptor. Up to now, only differences between the androgen and glucocorticoid receptor in the transcription activation functions were invoked to explain the specificity of their genomic actions. In the present study, we describe the influence of the DNA-binding domain on the specificity of androgen action. The novelty of our working hypothesis resides in the demonstration of the capacity of the AR-DNA-binding domain to recognize elements with a direct repeat structure.Steroid hormones are important endocrine messengers that activate their receptors, which translocate to the cell nucleus and regulate gene expression mainly after interaction with DNA sequences, called response elements (1, 2). The steroid receptors are a subfamily of the nuclear receptor superfamily, a large group of structurally homologous transcription factors. A problem with the explanation of the specificity of these hormone responses arose when several studies pointed out that the class I receptors (androgen receptor (AR), 1 glucocorticoid receptor (GR), progesterone receptor, and mineralocorticoid receptor) have identical consensus response elements (3, 4) and that their DNA-binding domains were highly conserved (5). This contrasts with the fact that the in vivo expression of several genes is specifically controlled by only one steroid hormone (6). Several possible mechanisms have been described to explain the steroid specificity of transcriptional control, e.g. steroid metabolism, tissue-specific receptor presence (7), influence of coactivator complexes (8), and chromatin structure (9, 10). In addition, more recent reports indicate that the AR on the one hand and the GR, progesterone receptor, and mineralocorticoid receptor on the other exhibit different DNA binding characteristics (11-15). One AR-specific response element was found in the promoter of the rat probasin gene (PB-ARE-2) (12,16,17). Probasin is an androgen-regulated protein exclusively expressed in the dorsolateral epithelium of the prostate (18). Two cis-acting androgen response e...

The promotion and progression of prostate cancer (PCa) are associated with androgen receptor (AR) signalling. AR functions are modulated by a variety of co-factors amongst which we identified the nucleophosmin (NPM/ B23), a member of the histone chaperone family. Here, we show that NPM is overexpressed in PCa compared to normal adjacent tissues. AR and NPM interact in vitro and in vivo, and NPM is critical for androgen-dependent transcriptional activation in LNCaP cells as an anti-NPM siRNA downregulates transcription of a transfected androgen response element (ARE)-containing reporter promoter as well as expression of the endogenous androgen responsive prostate-specific antigen (PSA) gene. By investigating the effect of NPM on AR, we have also observed that NPM enhances AR binding to an ARE in vitro in electrophoretic gel mobility-shift assay experiments. Chromatin immunoprecipitation studies further demonstrated that both AR and NPM associate with AREs of the PSA gene in vivo. Altogether, our data suggest that the molecular histone chaperone NPM could regulate AR functions by promoting assembly of ARcontaining regulatory complexes and that high levels of NPM might alter AR functions in PCa.

We performed a comparative analysis of the effect of high-mobility group box protein 1 (HMGB1) on DNA binding by the DNA-binding domains (DBDs) of the androgen, glucocorticoid, progesterone and mineralocorticoid receptors. The affinity of the DBDs of the different receptors for the tyrosine aminotransferase glucocorticoid response element, a classical high-affinity binding element, was augmented up to 7-fold by HMGB1. We found no major differences in the effects of HMGB1 on DNA binding between the different steroid hormone receptors. In transient transfection assays, however, HMGB1 significantly enhances the activity of the glucocorticoid and progesterone receptors but not the androgen or mineralocorticoid receptor. We also investigated the effect of HMGB1 on the binding of the androgen receptor DBD to a subclass of directly repeated response elements that is recognized exclusively by the androgen receptor and not by the glucocorticoid, progesterone or mineralocorticoid receptor. Surprisingly, a deletion of 26 amino acid residues from the C-terminal extension of the androgen receptor DBD does not influence DNA binding but destroys its sensitivity to HMGB1. Deletion of the corresponding fragment in the DBDs of the glucocorticoid, progesterone and mineralocorticoid receptor destroyed their DNA binding. This 26-residue fragment is therefore essential for the influence of HMGB1 on DNA recognition by all steroid hormone receptors that were tested. However, it is dispensable for DNA binding by the androgen receptor.

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...