Androgen-Induced Activation of Gonadotropin-Regulated Testicular RNA Helicase (GRTH/Ddx25) Transcription: Essential Role of a Nonclassical Androgen Response Element Half-Site

摘要

GRTH, a testis-specific member of the DEAD-box family of RNA helicases essential for spermatogenesis, is present in Leydig cells (LC) and germ cells. In LC, it exerts an autocrine negative regulation on androgen production induced by gonadotropin. GRTH is transcriptionally upregulated by gonadotropin via cyclic AMP/androgen through androgen receptors (AR). For studies of GRTH regulation by androgen in LC, we utilized in vitro/in vivo models. Androgen-induced GRTH expression was prevented by an AR antagonist. Two putative atypical ARE half-sites are present at bp ?200 and ?827 (ARE1 and ARE2). Point mutation of ARE2 prevented androgen-induced AR binding/function and upregulation of GRTH transcription. Chromatin immunoprecipitation (ChIP) assays showed recruitment of AR, SRC-1, Med-1, transcription factor IIB (TFIIB), and polymerase II (PolII) to GRTH ARE2 (bp ?980/?702) and to the promoter region (bp ?80/+63). ChIP3C assays revealed short-range chromosomal looping between AR/ARE2 and the core transcriptional machinery at the promoter. Knockdown of Med-1 and/or SRC-1 demonstrated the presence of a nonproductive complex which included AR, TFIIB, and PolII and the essential role of these coactivators in the transcriptional activation of GRTH. Our findings provide new insights into the molecular mechanism of androgen-regulated transcription in LC.