GnRH Stimulates Expression of PACAP in the Pituitary Gonadotropes via Both the PKA and PKC Signaling Systems

Recent studies have demonstrated a clear role for pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of gonadotropin biosynthesis and secretion, both alone and in conjunction with GnRH. First defined as a hypothalamic releasing factor, PACAP subsequently has been identified in the gonadotrope subpopulation of the anterior pituitary gland, suggesting that PACAP may act as an autocrine-paracrine factor in this tissue. In initial studies, we determined that GnRH markedly stimulated endogenous PACAP mRNA levels and promoter-reporter activity in the mature gonadotrope cell line, LβT2. GnRH-stimulated rat PACAP promoter activity was blunted with deletion from position −915 to −402 and eliminated with further truncation to position −77 relative to the transcriptional start site. Site-directed mutagenesis demonstrated a functional requirement for a cAMP response element (CRE)-like site at position −205 and an activating protein-1 (AP-1)-like site at position −275, both of which bound CRE...