Androgen receptor
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content
Androgen receptor
Structure of the ligand binding domain of the androgen receptor (rainbow cartoon) complexed with testosterone (white sticks) based on PDB 2AM9.
Available structures: 1e3g, 1gs4, 1i37, 1i38, 1r4i, 1t5z, 1t63, 1t65, 1t73, 1t74, 1t76, 1t79, 1t7f, 1t7m, 1t7r, 1t7t, 1xj7, 1xnn, 1xow, 1xq3, 1z95, 2am9, 2ama, 2amb, 2ao6, 2ax6, 2ax7, 2ax8, 2ax9, 2axa, 2ihq, 2nw4, 2oz7
Identifiers
Symbols AR; AIS; DHTR; HUMARA; KD; NR3C4; SBMA; SMAX1; TFM
External IDs OMIM: 313700 MGI: 88064 HomoloGene: 28
RNA expression pattern

More reference expression data
Orthologs
Human Mouse
Entrez 367 11835
Ensembl ENSG00000169083 ENSMUSG00000046532
Uniprot P10275 P19091
Refseq NM_000044 (mRNA)
NP_000035 (protein)		 NM_013476 (mRNA)
NP_038504 (protein)
Location Chr X: 66.68 - 66.87 Mb Chr X: 94.35 - 94.52 Mb
Pubmed search [1] [2]

The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor[1] which is activated by binding of either of the androgenic hormones testosterone or dihydrotestosterone.[2] The androgen receptor is most closely related to the progesterone receptor, and progestins in higher dosages can block the androgen receptor.[3][4]

The main function of the androgen receptor is as a DNA binding transcription factor which regulates gene expression;[5] however, the androgen receptor has other functions as well.[6] Androgen regulated genes are critical for the development and maintenance of the male sexual phenotype.

Contents

Function

Androgenic hormones and their effect on development

In some cell types testosterone interacts directly with androgen receptors while in others testosterone is converted by 5-alpha-reductase to dihydrotestosterone, an even more potent agonist for androgen receptor activation.[7] Testosterone appears to be the primary androgen receptor activating hormone in the Wolffian duct while dihydrotestosterone is the main androgenic hormone in the urogenital sinus, urogenital tubercle, and hair follicles.[8] Hence testosterone is primarily responsible for the development of male primary sexual characteristics while dihydrotestosterone is responsible for secondary male characteristics.

Androgens cause slow epiphysis, or maturation of the bones, but more of the potent epiphysis effect comes from the estrogen produced by aromatization of androgens. Steroid users of teen age may find that their growth had been stunted by androgen and/or estrogen excess. People with too little sex hormones can be short during puberty but end up taller as adults as in androgen insensitivity syndrome or estrogen insensitivity syndrome.[9]

Mechanism of androgen receptor action

Genomic

The primary mechanism of action for androgen receptors is direct regulation of gene transcription. The binding of an androgen to the androgen receptor results in a conformational change in the receptor which in turn causes dissociation of heat shock proteins, transport from the cytosol into the cell nucleus, and dimerization. The androgen receptor dimer binds to a specific sequence of DNA known as a hormone response element. Androgen receptors interact with other proteins in the nucleus resulting in up or down regulation of specific gene transcription.[10] Up-regulation or activation of transcription results in increased synthesis of messenger RNA which in turn is transcribed by ribosomes to produce specific proteins. One of the known target genes of androgen receptor activation is insulin-like growth factor I (IGF-1).[11] Thus, changes in levels of specific proteins in cells is one way that androgen receptors control cell behavior.

Non-genomic

More recently, androgen receptors have been shown to have a second mode of action. As has been also found for other steroid hormone receptors such as estrogen receptors, androgen receptors can have actions that are independent of their interactions with DNA.[6][12] Androgen receptors interact with certain signal transduction proteins in the cytoplasm. Androgen binding to cytoplasmic androgen receptors can cause rapid changes in cell function independent of changes in gene transcription, such as changes in ion transport. Regulation of signal transduction pathways by cytoplasmic androgen receptors can indirectly lead to changes in gene transcription, for example, by leading to phosphorylation of other transcription factors.

One function of androgen receptor that is independent of direct binding to its target DNA sequence, is facilitated by recruitment via other DNA binding proteins. One example is serum response factor, a protein which activates several genes that cause muscle growth.[13]

Genetics

Gene

The AR gene for the androgen receptor is located on the X chromosome at Xq11-12.[14][15]

AR deficiencies

The androgen insensitivity syndrome, formerly known as testicular feminization, is caused by a mutation of the Androgen Receptor gene located on the X chromosome (locus:Xq11-Xq12).[16] The androgen receptor seems to affect neuron physiology and is defective in Kennedy disease.[17][18] In addition, point mutations and trinucleotide repeat polymorphisms has been linked to a number of additional disorders.[19]

Structure

Structural domains of the two isoforms (AR-A and AR-B) of the human androgen receptor. Numbers above the bars refer to the amino acid residues which separate the domains starting from the N-terminus (left) to C-terminus (right). NTD = N-terminal domain, DBD = DNA binding domain. LBD = ligand binding domain. AF = activation function.
Structural domains of the two isoforms (AR-A and AR-B) of the human androgen receptor. Numbers above the bars refer to the amino acid residues which separate the domains starting from the N-terminus (left) to C-terminus (right). NTD = N-terminal domain, DBD = DNA binding domain. LBD = ligand binding domain. AF = activation function.

Isoforms

Two isoforms of the androgen receptor (A and B) have been identified:[20]

  • AR-A - 87 kDa - N-terminus truncated (lacks the first 187 amino acids)
  • AR-B - 110 kDa - full length

Domains

Like other nuclear receptors, the androgen receptor is modular in structure and is comprised of the following functional domains labeled A through F:[21]

  • A/B) - N-terminal regulatory domain contains:[22]
    • activation function 1 (AF-1) between residues 101 and 370 required for full ligand activated transcriptional activity
    • activation function 5 (AF-5) between residues 360-485 is responsible for the constitutive activity (activity without bound ligand)
    • dimerization surface involving residues 1-36 (containing the FXXLF motif where F = phenylalanine, L = leucine, and X = any amino acid residue) and 370-494 which both interact with the LBD in an intramolecular[23][24][25] head-to-tail interaction[26][27][28]
  • C) - DNA binding domain (DBD)
  • D) - Hinge region - flexible region that connects the DBD with the LBD; along with the DBD, contains a ligand dependent nuclear localization signal[29]
  • E) - Ligand binding domain (LBD) containing
    • activation function 2 (AF-2), responsible for agonist induced activity (activity in the presence of bound agonist)
    • AF-2 binds either the N-terminal FXXFL motif intramolecularly or coactivator proteins (containing the LXXLL or preferably FXXFL motifs)[28]
    • A ligand dependent nuclear export signal[30]
  • F) - C-terminal domain

References

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See also

External links