Lim J, Ghadessy F J, Abdullah A A, Pinsky L, Trifiro M, Yong E L
Department of Obstetrics and Gynecology, National University of Singapore, Republic of Singapore.
Mol Endocrinol. 2000 Aug;14(8):1187-97. doi: 10.1210/mend.14.8.0499.
The androgen receptor (AR) is a ligand-dependent X-linked nuclear transcription factor regulating male sexual development and spermatogenesis. The receptor is activated when androgen binds to the C-terminal ligand-binding domain (LBD), triggering a cascade of molecular events, including interactions between the LBD and the N-terminal transactivation domain (TAD), and the recruitment of transcriptional coactivators. A nonconservative asparagine to lysine substitution in AR residue 727 was encountered in a phenotypically normal man with subfertility and depressed spermatogenesis. This N727K mutation, although located in the LBD, did not alter any ligand-binding characteristic of the AR in the patient's fibroblasts or when expressed in heterologous cells. Nonetheless, the mutant AR displayed only half of wild-type transactivation capacity when exposed to physiological or synthetic androgens. This transactivation defect was consistently present when examined with two different reporter systems in three cell lines, using three androgen-driven promoters (including the complex human prostate-specific antigen promoter), confirming the pathogenicity of the mutation. In mammalian two-hybrid assays, N727K disrupted LBD interactions with the AR TAD and with the coactivator, transcription intermediary factor 2 (TIF2). Strikingly, the transactivation defect of the mutant AR can be rectified in vitro with mesterolone, consistent with the ability of this androgen analog to restore sperm production in vivo. Mesterolone, but not the physiological androgen dihydrotestosterone, restored mutant LBD interactions with the TAD and with TIF2, when expressed as fusion proteins in the two-hybrid assay. Our data support an emerging paradigm with respect to AR mutations in the LBD and male infertility: pathogenicity is transmitted through reduced interdomain and coactivator interactions, and androgen analogs that are corrective in vitro may indicate hormonal therapy.
雄激素受体（AR）是一种依赖配体的X连锁核转录因子，调节男性性发育和精子发生。当雄激素与C端配体结合域（LBD）结合时，该受体被激活，引发一系列分子事件，包括LBD与N端反式激活域（TAD）之间的相互作用以及转录共激活因子的募集。在一名表型正常但生育力低下且精子发生受抑制的男性中，发现AR第727位残基发生了非保守的天冬酰胺到赖氨酸的替换。这种N727K突变虽然位于LBD中，但在患者成纤维细胞中或在异源细胞中表达时，并未改变AR的任何配体结合特性。尽管如此，当暴露于生理或合成雄激素时，突变型AR仅表现出野生型反式激活能力的一半。当在三种细胞系中使用三种雄激素驱动的启动子（包括复杂的人前列腺特异性抗原启动子）通过两种不同的报告系统进行检测时，这种反式激活缺陷始终存在，证实了该突变的致病性。在哺乳动物双杂交试验中，N727K破坏了LBD与AR TAD以及与共激活因子转录中介因子2（TIF2）的相互作用。引人注目的是，突变型AR的反式激活缺陷在体外可被甲睾酮纠正，这与这种雄激素类似物在体内恢复精子生成的能力一致。在双杂交试验中以融合蛋白形式表达时，甲睾酮而非生理雄激素双氢睾酮恢复了突变型LBD与TAD以及与TIF2的相互作用。我们的数据支持了关于LBD中AR突变与男性不育的一个新范式：致病性是通过结构域间和共激活因子相互作用的减少来传递的，并且在体外具有纠正作用的雄激素类似物可能提示激素治疗。
