Steroidogenic Factor-1 and The Gonadotrope-Specific Element Enhance Basal and Pituitary Adenylate Cyclase-Activating Polypeptide-Stimulated Transcription of the Human Glycoprotein Hormone α-Subunit Gene in Gonadotropes

In the anterior pituitary, expression of the common glycoprotein hormone α-subunit (αGSU) is mediated in part by multiple response elements residing in the distal promoter (−435 bp). One such site is the gonadotrope-specific element (GSE), which is bound by the orphan nuclear receptor steroidogenic factor-1 (SF-1) and confers pituitary adenylate cyclase-activating polypeptide (PACAP)-stimulated αGSU expression. Here we investigated the functional importance of the GSE and SF-1 phosphorylation in both basal and stimulated αGSU transcription. Mutation of the GSE reduced basal and PACAP-stimulated αGSU promoter activity in the αT3-1 gonadotrope cell line. Overexpression of wild-type SF-1, but not an S203A mutant form of SF-1, enhanced basal and PACAP-stimulated αGSU promoter activity. The effect of PACAP on αGSU promoter activity was inhibited after overexpression of MAPK phosphatase. Helix assembly of the SF-1 ligand-binding domain was stimulated by PACAP in vitro via a MAPK-dependent pathway, as determined using a mammalian two-hybrid assay. PACAP quickly activated MAPK (within 5 min) and also resulted in elevated levels of phospho-cAMP response element-binding protein and phospho-SF-1, as judged by a specific antiphospho-S203 antibody; this effect was blocked by the MAPK kinase inhibitor, UO126. Collectively, these data demonstrate that SF-1 binds to the GSE and activates both basal and PACAP-stimulated αGSU transcription, which is further increased by phosphorylation at Ser203 via MAPK. These data suggest strongly that the induction of αGSU gene expression by peptide hormone signaling is coupled directly to the posttranslational status of SF-1.