Gonadotropin-releasing hormone (GnRH) positively regulates corticotropin-releasing hormone-binding protein expression via multiple intracellular signaling pathways and a multipartite GnRH response element in αT3-1 cells

Abstract

CRH-binding protein (CRH-BP) binds CRH with high affinity and inhibits CRH-mediated ACTH release from anterior pituitary corticotrope-like cells in vitro. In female mouse pituitary, CRH-BP is localized not only in corticotropes, but is also expressed in gonadotropes and lactotropes. To investigate the functional significance of gonadotrope CRH-BP, we examined the molecular mechanisms underlying GnRH-regulated CRH-BP expression in αT3-1 gonadotrope-like cells. CRH-BP is endogenously expressed in αT3-1 cells, and quantitative real-time RT-PCR and ribonuclease protection assays demonstrate that GnRH induces a 3.7-fold increase in CRH-BP mRNA levels. GnRH also induces intracellular CRH-BP (2.0-fold) and secreted CRH-BP (5.3-fold) levels, as measured by [125I]CRH:CRH-BP chemical cross-linking. Transient transfection assays using CRH-BP promoter-luciferase constructs indicate that GnRH regulation involves protein kinase C-, ERK- and calcium-dependent signaling pathways and is mediated via a multipartite GnRH response element that includes activator protein 1 and cAMP response element (CRE) sites. The CRE site significantly contributes to GnRH responsiveness, independent of protein kinase A, representing a unique form of multipartite GnRH regulation in αT3-1 cells. Furthermore, EMSAs indicate that αT3-1 nuclear proteins specifically bind at activator protein 1 and CRE sites. These data demonstrate novel regulation of pituitary CRH-BP, highlighting the importance of the pituitary gonadotrope as a potential interface between the stress and reproductive axes. Copyright © 2005 by The Endocrine Society.