Interaction of the Corepressor Alien with DAX-1 Is Abrogated by Mutations of DAX-1 Involved in Adrenal Hypoplasia Congenita

Abstract

DAX-1 is an unusual member of the nuclear hormone receptor (NHR) superfamily. Lack of DAX-1-mediated silencing leads to adrenal hypoplasia congenita and hypogonadotropic hypogonadism. Gene silencing through NHRs such as the thyroid hormone receptor (TR) is mediated by corepressors. We have previously characterized a novel corepressor, termed Alien, which interacts with TR and the ecdysone receptor but not with the retinoic acid receptors RAR or RXR. Here, we show that DAX-1 interacts with the corepressor Alien but not with the corepressor SMRT. This interaction is mediated by the DAX-1-silencing domain. Naturally occurring mutants of the DAX-1 gene fail to interact with Alien and have lost silencing function. Because the silencing domain of DAX-1 is unusual for NHRs, we mapped the interaction of Alien with DAX-1 and with TR. We show that Alien exhibits different binding characteristics to DAX-1 and TR. Furthermore, Northern experiments demonstrate that Alien is expressed in the adrenal gland and testis in tissues where DAX-1 is specifically expressed. Interestingly, a novel adrenal gland-specific mRNA of Alien was discovered. Thus, the impairment of Alien binding seems to play an important role in the pathogenesis mediated by DAX-1 mutants.The gene superfamily of nuclear hormone receptors (NHRs) 1 represents a large class of transcription factors including receptors for steroids, nonsteroids, and members for which no ligand has yet been identified, the so-called orphan receptors (for reviews, see Refs. 1 and 2). Gene silencing is mediated by a few members such as receptors for thyroid hormone (TR (NR1A)) (3) and retinoic acid (RAR (NR1B)) (4 -10). Thereby, the receptor is associated with corepressors, and the complex of receptor and corepressors mediates target gene repression (2, 9 -12). Among corepressors, N-CoR and SMRT represent one class, and Alien represents another class, which interacts in a hormone-sensitive manner with NHR (10 -13). The silencing domain of NHRs is localized in the C terminus and overlaps with the hormone-binding domain to a great extent. In the case of TR and RAR, the silencing domain encompasses 230 amino acids (5,14). Hormone binding by NHRs leads to a conformational change, dissociation of corepressors, subsequent binding of coactivators, and gene activation (for review, see Ref. 15). The transcriptional properties of nuclear receptors can be transferred to heterologous proteins and therefore represent functional domains (for review, see Refs. 2,16,and 17).DAX-1 (NR0B1) is an unusual member of the NHR superfamily (18,19). The DNA-binding domain is unrelated to other nuclear receptors and is composed of four repeat sequences, which are able to recognize and bind to hairpin structures (20). The C terminus, however, is homologous to members of the NHR superfamily (18). Mutations in the DAX-1 gene cause the X-linked disorder of adrenal hypoplasia congenita and the associated hypogonadotropic hypogonadism (18,19,21,22). DAX-1 is predominantly expressed in adrenal gland and testis (18), w...

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Thirteen novel mutations in theNR0B1(DAX1) gene as cause of adrenal hypoplasia congenita

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DAX-1 Functions as an LXXLL-containing Corepressor for Activated Estrogen Receptors

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