Expression of the Mouse Gonadotropin-Releasing Hormone Receptor Gene in αT3-1 Gonadotrope Cells Is Stimulated by Cyclic 3′,5′-Adenosine Monophosphate and Protein Kinase A, and Is Modulated by Steroidogenic Factor-1 and Nur77

Abstract

Regulation of GnRH receptor (GnRHR) expression levels in the pituitary is a crucial control point in reproduction. The promoter of the mouse GnRHR gene contains nuclear receptor half-sites (NRS) at –244/−236 and −15/−7 relative to the translation start site. Although binding of steroidogenic factor-1 (SF-1) to the –244/−236NRS is implicated in mediating basal and gonadotrope-specific expression, no function or protein-DNA interactions have previously been described for the –15/−7NRS. We report that levels of the endogenous GnRHR mRNA in αT3-1 cells are stimulated by forskolin and 8-bromo-cAMP. We also show that the orphan nuclear receptor Nur77 is expressed in αT3-1 cells, and that both SF-1 and Nur77 bind to the –15/−7NRS and –244/−236NRS in vitro. We show that the activity of the proximal (−579/+1) mouse GnRHR promoter is up-regulated by protein kinase A, via a mechanism that is modulated by SF-1, both positively and negatively, through binding to the –244/−236NRS or the –15/−7NRS, respectively. Nur77 appears to be capable of acting as a negative regulator of this response, via the –15/−7NRS. Furthermore, we show that forskolin up-regulates SF-1 mRNA levels in αT3-1 cells, indicating that the levels of SF-1 play a role in modulating the protein kinase A response.