The action of androgens in regulating development and growth is mediated by androgen receptor (AR). AR is a member of the steroid hormone receptor superfamily, a class of receptors that function through their ability to regulate the transcription of specific genes. The AR is located in various target tissues, with its levels and activity altered with the onset of various cellular events (e.g., sexual development, malignant transformation). The modulation of AR levels occurs through a number of mechanisms, including transcription, and is regulated by various factors (e.g., androgens). The ability of AR to modulate gene transcription is through its interaction with specific DNA sequences located near or within the target gene promoter. The importance of the AR in reproductive physiology has been emphasized by the finding of AR mutations, leading to a variety of disorders, including testicular feminization syndrome. In this article, we review the structure and function of AR and the role AR plays in the function of the mammalian system.

Amino acid sequence analysis indicates that the human TR4 orphan receptor (TR4) is a member of the estrogen/thyroid receptor subfamily of the steroid/thyroid receptor superfamily and recognizes the AGGTCA direct repeat (DR) of the hormone response element. Here we demonstrate using the electrophoretic mobility shift assay that TR4 binds specifically to DR with a spacing of 1 and 5 base pairs (DR1 and DR5), which are the response elements for retinoic acid receptor (RAR) and retinoid X receptor (RXR), respectively. A reporter gene assay using chloramphenicol acetyltransferase demonstrated that TR4 repressed RA-induced transactivation in a TR4 dose-dependent manner. Inhibition of the retinoid signal pathway also occurs through natural response elements found in CRBPII and RAR␤ genes. Our data suggest that the mechanism of repression may not involve the formation of functionally inactive heterodimers between TR4 and RAR or RXR. Instead, we show that TR4 may compete for hormone response elements with RAR and RXR due to its higher binding affinity. Furthermore, treatment of F9 murine teratocarcinoma (F9) cells with 10 ؊6 M all-trans-retinoic acid increased TR4 mRNA levels, and this change was accompanied by an increased amount of endogenous TR4 protein that can bind to RXRE in electrophoretic mobility shift assay. Our data therefore strongly suggest that the retinoid signal pathway can be regulated by TR4 in a negative feedback control mechanism, which may restrict retinoic acid signaling to certain elements in a cell-specific fashion.The steroid/thyroid hormone receptor superfamily is a large group of related transcriptional factors that control cellular differentiation, development, and homeostasis by direct interaction with distinct cis-elements in target genes (1). This superfamily includes receptors for steroids, thyroid, vitamin D 3 , retinoids, and a large number of orphan receptors whose cognate ligands are still unknown (2). Regardless of whether transcriptional activity is controlled by ligand binding, each of these proteins is able to bind to specific DNA sequences called hormone response elements (HREs) 1 in their target genes. The sequence-specific DNA binding properties of nuclear receptors are determined by their highly conserved DNA binding domains (DBD). The P box of the DBD formed by three amino acids at the C-terminal base of the first zinc finger is responsible for the recognition of response elements. Based on the sequence within the P box and the generic recognition sequence of the P box for the HRE, the steroid/thyroid hormone receptor superfamily can be divided into the GR and ER/TR subfamilies (3). The GR group, which includes GR, MR, PR, and AR, prefers to bind to the glucocorticoid response element (5Ј-AGAACAnnnTGTTCT-3Ј) palindromic consensus sequence. Other receptors that have glutamic acid and glycine at the first two positions of the P box are assigned to the ER/TR subfamily. This subfamily, which includes ER, T 3 R, VD 3 R, RARs, RXRs, and most of the orphan receptors, recognize the ...

A conserved hormone response element, CNTFR-DR1 (5-AGGTCAGAGGTCAGG-3), has been identified in the 5th intron of the ␣ component of the ciliary neurotrophic factor receptor (CNTFR␣) gene for the human TR4 orphan receptor (TR4). Electrophoretic mobility shift assay showed a specific binding with high affinity (K d ‫؍‬ 0.066 nM) between TR4 and the CNTFR-DR1. A reporter gene assay using chloramphenicol acetyltransferase demonstrated that the 5th intron of CNTFR␣ has an enhancer activity which could be induced by TR4 in a dose-dependent manner. Furthermore, our in situ hybridization data showed that abundant TR4 transcripts were detected in adult brain, in regions of cortical and hippocampal neurons, as well as in many developing neural structures, including brain, spinal cord, ganglia (sympathetic and sensory), and neuronal epithelia (retinal, otic, olfactory, and gustatory). The striking similarities in the expression patterns of TR4 and CNTFR␣ in the developing and postnatal nervous systems further support the potential role of TR4 in neurogenesis. Collectively, these data suggest that the human CNTFR␣ gene could represent the first identified neural-specific gene induced by TR4.Members of the steroid/thyroid hormone receptor superfamily are transcription factors that can bind to specific DNA sequences called hormone response elements (HRE) 1 and thereby regulate the expression of their target genes (1). This superfamily includes receptors for steroid, thyroid, vitamin D 3 , and retinoids, and a large number of orphan receptors whose cognate ligands are still unknown (1). These members have been grouped into three categories according to their binding preference to HREs, the palindromic half-site AGAACA is preferred for the binding by the androgen, glucocorticoid, mineralocorticoid, and progesterone receptors; the direct repeat with various spacing is preferentially recognized by the estrogen, thyroid, retinoic acid, retinoid X, vitamin D, and many orphan receptors; and the single half-site of AGGTCA preceded by two specific flanking nucleotides is favored by some members which bind as a monomer, such as the steroidogenic factor 1 (2), TR3 orphan receptor (TR3)/NGFI-B/nur77 (3), and the thyroid receptor (4). Some receptors, i.e. thyroid hormone receptor and chicken ovalbumin upstream promoter-transcription factors (COUP-TFs), are shown to be promiscuous for binding to different arrangements of the AGGTCA half-site (4, 5).The human and rat TR4 cDNAs were isolated from testis and hypothalamus by degenerative PCR cloning (6). The TR4 cDNA shows high homology in nucleotide sequence with the TR2 orphan receptor (TR2; another orphan receptor isolated from our laboratory (7)), suggesting that these two orphan receptors constitute an unique subfamily within the steroid receptor superfamily. TR4 mRNA are widely expressed in the adult rat brain (6). Within the supraoptic nucleus, TR4 is one of the most abundant steroid receptors expressed there with the order thyroid hormone receptor Ͼ COUP-TFII Ͼ TR4 ϭ COUP-TFI (8). Des...

In situ hybridization analysis demonstrated that abundant testicular orphan receptor (TR4) transcripts were detected in kidney, intestine, and bone, which are vitamin D 3 target organs. Cell transfection studies also demonstrated that the expression of the vitamin D 3 target gene, 25-hydroxyvitamin D 3 24-hydroxylase, can be repressed by TR4 through high affinity binding (K d ‫؍‬ 1.32 nM) to the direct repeat 3 vitamin D 3 receptor response element (DR3VDRE). This TR4-mediated repression of DR3VDRE is in contrast to our earlier report that TR4 could induce thyroid hormone target genes containing a direct repeat 4 thyroid hormone response element (DR4T 3 RE). Electrophoretic mobility shift assay using several TR4 monoclonal antibodies when combined with either TR4-DR3VDRE or TR4-DR4T 3 RE showed a distinct supershifted pattern, and proteolytic analysis further demonstrated distinct digested peptides with either TR4-DR3VDRE or TR4-DR4T 3 RE. These results may therefore suggest that TR4 can adapt to different conformations once bound to DR3VDRE or DR4T 3 RE. The consequence of these different conformations of TR4-DR3VDRE and TR4-DR4T 3 RE may allow each of them to recruit different coregulators. The differential repression of TR4-mediated DR3VDRE and DR4T 3 RE transactivation by the receptor interacting protein 140, a TR4 coregulator, further strengthens our hypothesis that the specificity of gene regulation by TR4 can be modulated by protein-DNA and protein-protein interactions.Steroid hormones are key physiological mediators of development and homeostasis (1-4). Understanding the crosstalk between steroid hormone-dependent and -independent signaling pathways is critical for gaining further insight into the integration of cellular regulatory cues that modulate development and tissue-specific gene expression. The biological effects of steroids and related hormones, including derivatives of vitamins A and D 3 , are mediated through their cognate receptors (1-4). These receptors are members of a large group of ligandactivated proteins that act as transcriptional activators or repressors. However, there is another group of nuclear receptors that shares the same molecular structure as steroid hormone receptors but has no known ligands. The members of this group have therefore been named orphan receptors (5). A common characteristic of many of these orphan receptors is that they exert at least part of their function as regulators of other receptors. This may occur by several different mechanisms: competition for the same response element, heterodimer formation with the regulated receptor, or heterodimer formation with the retinoid X receptor (RXR), 1 thus titrating out available RXR protein. For instance, chicken ovalbumin upstream promoter transcription factors have been demonstrated to suppress ligand-induced gene activation, including that of vitamin A, vitamin D 3 , and thyroid hormone target genes (6). This interfering effect might involve the formation of a transcriptional silencing complex with RXR or competition...

Androgens and the androgen receptor (AR) both play critical roles for the development of the male phenotype. To investigate the roles of androgens in the developing nervous system, we examined the AR messenger RNA distribution by in situ hybridization. Our results indicate that AR transcripts were detectable in male mouse embryos at embryonic day 11 (E1111). Intensive AR labeling appears in the neuroepithelium of brain vesicles and spinal cord, as well as in the reproductive organs. During E1 5-E16, new and strong AR labeling appeared in the cortex of cerebrum and hippocampus. Specific AR signals were also present in the brain areas known for hormonal control of copulatory behavior and mediating sensory processing. Interestingly, many ganglia were found to express AR mRNA at E15-E16. These novel AR-expressing sites include the dorsal root, sympathetic, and celiac ganglia, as well as the ophthalmic nerve of trigeminal ganglion. Sex dimorphism of AR expression in brain was also observed during E15-E16. Postnatally, brain and spinal cord can respond to circulating androgen levels by modifying their AR gene expression, but the ganglia cannot. Together, these data suggest androgens may have a great influence on the development and maintenance of the nervous system through the AR.