The 56 kDa androgen-binding protein in human genital skin fibroblasts: its relation to the human androgen receptor

Physiological insights into all-trans-retinoic acid biosynthesis

All-trans-retinoic acid (atRA) provides essential support to diverse biological systems and physiological processes. Epithelial differentiation and its relationship to cancer, and embryogenesis have typified intense areas of interest into atRA function. Recently, however, interest in atRA action in the nervous system, the immune system, energy balance and obesity has increased considerably, especially concerning postnatal function. atRA action depends on atRA biosynthesis: defects in retinoid-dependent processes increasingly relate to defects in atRA biogenesis. Considerable evidence indicates that physiological atRA biosynthesis occurs via a regulated process, consisting of a complex interaction of retinoid binding-proteins and retinoid recognizing enzymes. An accrual of biochemical, physiological and genetic data have identified specific functional outcomes for the retinol dehydrogenases, RDH1, RDH10, and DHRS9, as physiological catalysts of the first step in atRA biosynthesis, and for the retinal dehydrogenases RALDH1, RALDH2, and RALDH3, as catalysts of the second and irreversible step. Each of these enzymes associates with explicit biological processes mediated by atRA. Redundancy occurs, but seems limited. Cumulative data support a model of interactions among these enzymes with retinoid binding-proteins, with feedback regulation and/or control by atRA via modulating gene expression of multiple participants. The ratio apo-CRBP1/holo-CRBP1 participates by influencing retinol flux into and out of storage as retinyl esters, thereby modulating substrate to support atRA biosynthesis. atRA biosynthesis requires the presence of both an RDH and an RALDH: conversely, absence of one isozyme of either step does not indicate lack of atRA biosynthesis at the site. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

Effect of coenzymes and thyroid hormones on the dual activities of Xenopus cytosolic thyroid-hormone-binding protein (xCTBP) with aldehyde dehydrogenase activity

A cytosolic thyroid-hormone-binding protein (xCTBP), predominantly responsible for the major binding activity of T3 in the cytosol of Xenopus liver, has been shown to be identical to aldehyde dehydrogenase class 1 (ALDH1) [Yamauchi, K., Nakajima, J., Hayashi, H., Horiuchi, R. & Tata, J.R. (1999) J. Biol. Chem. 274, 8460-8469]. Within this paper we surveyed which signaling, and other, compounds affect the thyroid hormone binding activity and aldehyde dehydrogenase activity of recombinant Xenopus ALDH1 (xCTBP/xALDH1) while examining the relationship between these two activities. NAD+ and NADH (each 200 microm), and two steroids (20 microm), inhibit significantly the T3-binding activity, while NADH and NADPH (each 200 microm), and iodothyronines (1 microm), inhibit the ALDH activity. Scatchard analysis and kinetic studies of xCTBP/xALDH1 indicate that NAD+ and T3 are noncompetitive inhibitors of thyroid-hormone-binding and ALDH activities, respectively. These results indicate the formation of a ternary complex consisting of the protein, NAD+ and thyroid hormone. Although the in vitro studies indicate that NAD+ and NADH markedly decrease T3-binding to xCTBP/xALDH1 at approximately 10-4 m, a concentration equal to the NAD content in various Xenopus tissues, photoaffinity-labeling of [125I]T3 using cultured Xenopus cells demonstrates xCTBP/xALDH1 bound T3 within living cells. These results raise the possibility that an unknown factor(s) besides NAD+ and NADH may modulate the thyroid-hormone-binding activity of xCTBP/xALDH1. In comparison, thyroid hormone, at its physiological concentration, would poorly modulate the enzyme activity of xCTBP/xALDH1.

Characterization of Xenopus cytosolic thyroid-hormone-binding protein (xCTBP) with aldehyde dehydrogenase activity

Multiple cytosolic thyroid-hormone-binding proteins (CTBPs) with varying characteristics, depending on the species and tissue, have been reported. We first purified a 59-kDa CTBP from Xenopus liver (xCTBP), and found that it is responsible for major [125I]T(3)-binding activity in Xenopus liver cytosol. Amino acid sequencing of internal peptide fragments derived from xCTBP demonstrated high identity to the corresponding sequence of mammalian aldehyde dehydrogenases 1 (ALDH1). To confirm whether or not xCTBP is identical to xALDH1, we isolated cDNAs encoding xALDH1 from an adult Xenopus hepatic cDNA library. The amino acid sequences deduced from the two isolated xALDH1 cDNAs were very similar to those of mammalian ALDH1 enzymes. The recombinant xALDH1 protein exhibited both T(3)-binding activity and ALDH activity converting retinal to retinoic acid (RA), which were similar to those of xCTBP purified from liver cytosol. The T(3)-binding activity was inhibited by NAD, while the ALDH activity was inhibited by thyroid hormones. Our results demonstrate that xCTBP is identical to ALDH1 and suggest that this protein might modulate RA synthesis and intracellular concentration of free T(3). Communications between thyroid hormone and retinoid pathways are discussed.

The cytosolic aldehyde dehydrogenase gene (Aldh1) is developmentally expressed in Leydig cells

Cytosolic aldehyde dehydrogenase, ALDH1, participates in the oxidation of different aldehydes including that of all-trans retinal to retinoic acid. The accumulation of mouse Aldh1 transcripts is characterized by having different patterns in different tissues. This paper reports the greatest expression of Aldh1 in testis and liver. It was demonstrated that in testis, Aldh1 is specifically expressed in Leydig cells and is under developmental regulation. In vitro studies of cultured Leydig TM3 cells confirmed these results though such gene expression was found not to be mediated by LH regulation. Previous investigations have associated androgen receptors, and hence the androgen insensitivity syndrome in man, with the presence of ALDH1 in genital skin fibroblasts. However, this relationship was not established in a functional cell type, as is reported here for Leydig cells. These results could suggest a model for a molecular pathway from androgen receptor to retinoic acid biogenesis in Leydig cells via the mediation of ALDH.

Characterization of a hepatic protein in nonhuman primates that binds mibolerone but not dihydrotestosterone or methyltrienolone

During our studies of the hepatic androgen receptor in cynomolgus monkeys, tritiated mibolerone +/- a 200-fold excess of unlabeled mibolerone has been used to determine specific binding in cytosol. During time-course studies, high-capacity, unsaturable binding of [3H]mibolerone was noted after short-term incubations (4 h, 4 degrees C). When hepatic cytosol from male monkeys was incubated for 18 h at 4 degrees C, the high-capacity binding disappeared; saturable, high-affinity binding with characteristics consistent with the androgen receptor then could be identified. The characterization of [3H]mibolerone binding in molybdate-stabilized hepatic cytosol using sucrose density gradients and gel filtration yielded an unstable binding peak in addition to that of the androgen receptor. This lower molecular weight protein identified by gel filtration did not bind other androgens, including methyltrienolone, and did not have characteristics of other binding proteins that have been identified previously. This protein was not precipitated from 30% ammonium sulfate, which allowed it to be separated from the androgen receptor. Binding to this protein in ovariectomized female monkeys did not disappear with extended incubation at 4 degrees C, suggesting greater stability or a higher capacity. The function of this protein is not known, but both triamcinolone acetonide and contraceptive progestins appeared to displace tritiated mibolerone that was bound to it. This high-capacity binding of mibolerone interferes in the assessment of androgen receptor levels in these females unless it is eliminated. The synthetic androgen methyltrienolone does not bind to this protein and is a better choice for defining binding to the androgen receptor in these tissues.

An androgenic affinity ligand covalently binds to cytosolic aldehyde dehydrogenase from human genital skin fibroblasts

A 56 kDa protein expressed in human genital skin fibroblasts was first identified by independent laboratories on the basis of its specific expression in androgen target cells and its ability to covalently bind androgenic affinity ligands. Recently, immunoscreening of a cDNA library with antisera directed against this protein resulted in the isolation of a partial cDNA clone identical to human cytosolic aldehyde dehydrogenase (ALDH1). We report here the preparation of a full-length cDNA encoding ALDH1 from human genital fibroblasts. Translation of the encoded protein in a cell-free system yields a 56 kDa product that can be covalently radiolabeled with [3H]dihydrotestosterone 17 beta-bromoacetate (DHT-BA). Expression of the full-length clone in mammalian cells also results in expression of a 56 kDa DHT-BA binding protein. The covalent binding of DHT-BA by ALDH1 is an intrinsic property of the enzyme and is not dependent on androgen receptor expression.

The 56 kDa androgen binding protein is an aldehyde dehydrogenase

We have described a 56 kDa protein from genital skin fibroblasts that specifically binds androgen and that is generally not expressed in genital skin fibroblasts from patients with androgen insensitivity due to genetic defects of the androgen receptor. We have isolated a partial cDNA clone for the 56 kDa protein from an expression library of genital skin fibroblasts. In vitro translation of message selected with this clone faithfully produces the 56 kDa protein which can be immuneprecipitated with an anti-56 kDa antiserum. Northern blots probed with this clone show a 2.2 kb message, which parallels the expression of the 56 kDa protein. The sequence of this 998bp clone is identical to human liver aldehyde dehydrogenase 1, the cytoplasmic isoenzyme. On activity gels of genital skin fibroblast cytosol covalently labelled with androgen, aldehyde dehydrogenase activity comigrates with the single band labelled specifically with androgen. Thus, the 56 kDa androgen binding protein is an aldehyde dehydrogenase, which is prominently expressed in normal genital skin fibroblasts, but not in non-genital skin fibroblasts.

The 56/58 kDa androgen-binding protein in male genital skin fibroblasts with a deleted androgen receptor gene

Human genital skin fibroblasts (GSF) make a relatively abundant 56/58 kDa protein that binds androgens. The protein shares many properties with the approximately 100 kDa androgen receptor that is encoded by a locus in the q12 region of the X chromosome. It does not appear to be androgen-induced, yet is absent in GSF of most patients with complete androgen insensitivity (CAI). A precursor-product relation with the androgen receptor (AR) protein has been largely excluded; that it may be an unorthodox product of the AR gene has not. The 56/58 kDa protein is made by the GSF of a mentally retarded subject who has CAI because of a complete deletion of the coding portion of the AR gene. Hence, the strong constitutional and statistical correlations that have been demonstrated between the two proteins cannot arise because they share the same gene. The subject's genomic DNA hybridizes normally with 11 single-copy probes from Xq11-Xq13. Therefore, we cannot attribute her mental retardation to a contiguous gene syndrome.