Pituitary adenylate cyclase-activating polypeptide and cyclic adenosine 3 ',5 '-monophosphate stimulate the promoter activity of the rat gonadotropin-releasing hormone receptor gene via a bipartite response element in gonadotrope-derived cells

Specific type I receptors for pituitary adenylate cyclase-activating polype ptide (PACAP) are present in gonadotrope cells of the anterior pituitary gl and. By transient transfection of mouse gonadotrope-derived alpha T3-1 cell s, which are direct targets for PACAP and express gonadotropin-releasing ho rmone receptor (GnRH-R), a marker of the gonadotrope lineage, we provide th e first evidence that PACAP stimulates rat GnRH-R gene promoter activity. T he EC50 of this stimulation is compatible with a mediation via activation o f the cyclic AMP-dependent signaling pathway and, consistently, co-transfec tion of an expression vector expressing the protein kinase A inhibitor caus es reduction in PACAP as well as cholera toxin-stimulated promoter activity . Deletion and mutational analyses indicate that PACAP activation necessita tes a bipartite response element that consists of a first region (-272/-237 ) termed PACAP response element (PARE) I that includes a steroidogenic fact or-1 (SF-1)-binding site and a second region (-136/-101) referred to as PAR E II that contains an imperfect cyclic AMP response element. Gel shift expe riments indicate the specific binding of the SF-1 and a potential SF-1-inte racting factor to PARE I while a protein inununologically related to the cy clic AMP response element-binding protein interacts with PARE II. These fin dings suggest that PACAP might regulate the GnRH-R gene at the transcriptio nal level, providing novel insights into the regulation of pituitary-specif ic genes by hypothalamic hypophysiotropic signals.