Mechanisms of androgen receptor activation and function☆

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Abstract

Androgens play a crucial role in several stages of male development and in the maintenance of the male phenotype. Androgens act in their target cells via an interaction with the androgen receptor, resulting in direct regulation of gene expression. The androgen receptor is a phosphoprotein and modulation of the phosphorylation status of the receptor influences ligand-binding and consequently transcription activation of androgen responsive genes. Androgen binding induces a conformational change in the ligand-binding domain, accompanied by additional receptor phosphorylation. Subsequently the liganded androgen receptor interacts with specific androgen response elements in the regulatory regions of androgen target genes, resulting in stimulation of gene expression. Anti-androgens induce a different conformational change of the ligand-binding domain, which does not or only partially result in stimulation of transactivation. Interestingly, different anti-androgens can induce different inactive conformations of the androgen receptor ligand-binding domain. Recent evidence strongly supports a ligand dependent functional interaction between the ligand-binding domain and the NH2-terminal transactivating domain of the androgen receptor. Two regions in the NH2-terminal domain are involved in this interaction, whereas in the ligand-binding domain the AF-2 AD core region is involved.

Introduction

Androgens play a crucial role in several stages of male development. They act via an interaction with the androgen receptor, a ligand dependent transcription factor which belongs to the superfamily of nuclear receptors. This superfamily includes the nuclear receptors for the other steroid hormones, for the retinoids, for the thyroid hormones, and a still growing number of orphan receptors [1], [2]. In the last decade, since the cloning of the human androgen receptor cDNA, our insights in the mechanism of androgen action have been increased tremendously. Only one androgen receptor cDNA has been identified and cloned, despite the two different ligands [3], [4], [5], [6]. The tissue specific actions of testosterone and 5α-dihydrotestosterone, mediated by the same androgen receptor, suggest a ligand specific recruitment of transcription intermediary factors (TIFs). However, experimental evidence for ligand specific TIFs for the androgen receptor has not been provided as yet. The androgen receptor protein displays a large homology in the DNA-binding domain and in the ligand-binding domain with the other members of the steroid hormone receptor subfamily (e.g. receptors for glucocorticoids, estradiol, progesterone and mineralocorticoids) [5], [7], [8], [9], [10].

The aim of the present review is to present some aspects in androgen action unravelled recently. In this overview information will be given on the functional domain structure of the human androgen receptor with emphasis on the recent findings of functional interactions between the NH2-terminal domain and the ligand-binding domain. Post-translational modifications (phosphorylation) of the androgen receptor protein in relation to function will be discussed next. Throughout the text the numbering of the different codons is based on a total number of 910 amino acid residues of the androgen receptor protein [11]. This number differs from the amino acid content published by others [3], [4], [6]. These differences are caused by the variation in length of the polyglutamine and polyglycine stretches in the NH2-terminal domain of the receptor.

Section snippets

Conformational changes induced by androgens and anti-androgens

Binding of androgens by the androgen receptor results in two conformational changes of the receptor [12], [13]. Initially, a fragment of 35 kDa, spanning the complete ligand-binding domain and part of the hinge region, is protected by the ligand in a partial protease degradation assay, but after prolonged incubation times a second conformational change occurs resulting in protection of a smaller fragment of 29 kDa. In the presence of several anti-androgens (e.g. cyproterone acetate,

Transactivation function in the ligand-binding domain

Deletion and mutation studies, as well as mutations found in patients with either the androgen insensitivity syndrome or prostate cancer have given some insight into which amino acid residues are important for ligand-binding [14], [15], [16]. The overall picture is that large deletions (>10 amino acid residues) severely affect hormone binding, but deletion of the complete ligand-binding domain results in a constitutive active molecule [14], [17].

In the ligand-binding domain of the human

Transactivation functions in the NH2-terminal domain

The boundaries of the NH2-terminal transactivation domain in the androgen receptor (designated as AF-1) are not exactly defined, but generally speaking it appears that the region between amino residues 51–211 is essential for transactivation activity in the full length receptor [14]. This region is not involved in the transactivation capacity of the COOH-terminal truncated androgen receptor, which displays constitutive activity [17]. The most important activating region in the constitutive

Functional interaction of the NH2-terminal domain and the COOH-terminal domain

In the previous section evidence is presented for a possible interaction between the ligand-binding domain and the AF functions in the NH2-terminal domain. Investigating this NH2-terminal domain–COOH-terminal domain (N/C) interaction in more detail reveals that only certain regions in the NH2-terminal domain are involved in the interaction [20], [22], [23], [24]. Interesting is that the AF-1 core region is not involved in this interaction; amino acid residues 3–36 as well as amino acid residues

Hormone independent phosphorylation and function

The newly synthesized androgen receptor migrates as a 110 kDa protein during SDS–PAGE, and becomes phosphorylated within 10 min upon synthesis, resulting in an additional protein band at 112 kDa [25], [26]. This rapid post-translational modification is important for the acquisition of the hormone binding properties of the androgen receptor [27]. Evidence for this phosphorylation function was obtained from experiments in which dephosphorylation of the 112 kDa isoform was associated with a

Hormone dependent phosphorylation and function

A second important phosphorylation step of the androgen receptor occurs upon hormone binding resulting in a third isoform migrating at 114 kDa during SDS–PAGE [26], [32]. All three isoforms (e.g. 110 kDa, 112 kDa and 114 kDa) exist in several androgen responsive cell lines in the presence of androgens and migrate as as triplet. The presence of the triplet correlates very well with DNA-binding by the androgen receptor: mutations of certain amino acid residues in the DNA-binding domain which

Conclusions

Androgen action is mediated by the androgen receptor, a ligand dependent transcription factor, belonging to the superfamily of nuclear receptors. The two most important androgens are testosterone and 5α-dihydrotestosterone and their tissue specific actions are mediated by the same androgen receptor protein.

Binding of androgens by the androgen receptor results in two consecutive conformational changes, which are different from those induced by anti-androgens.

The androgen receptor can use

Acknowledgements

The authors thank Drs Gronemeyer and Chambon for the generous gift of the expression plasmid for TIF2. This research was supported by the Dutch Cancer Society and the Netherlands Organization for Scientific Research through GB-MW.

References (32)

  • C. Chang et al.

    Molecular cloning of human and rat complementary DNA encoding androgen receptors

    Science

    (1988)
  • D.B. Lubahn et al.

    Cloning of human androgen receptor complementary DNA and localization to the X chromosome

    Science

    (1988)
  • W.D. Tilley et al.

    Characterization and expression of a cDNA encoding the human androgen receptor

    Proceedings of the National Academy of Sciences of the United States of America

    (1989)
  • S.M. Hollenberg et al.

    Primary structure and expression of a functional human glucocorticoid receptor cDNA

    Nature

    (1985)
  • S. Green et al.

    Human oestrogen receptor cDNA: sequence, expression and homology to v-erb-A

    Nature

    (1986)
  • J.L. Arriza et al.

    Cloning of human mineralocorticoid receptor complementary DNA: structural and functional kinship with the glucocorticoid receptor

    Science

    (1987)

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