Identification and characterization of the gonadotropin-releasing hormone response elements in the mouse gonadotropin-releasing hormone receptor gene

The response of the pituitary gonadotrope to gonadotropin-releasing hormone (GnRH) correlates directly with the concentration of GnRH receptors (GnRHR ) on the cell surface, which is mediated in part at the level of GnRHR gene expression, Several hormones have been implicated in this regulation, most notably GnRH itself, Despite these observations and the central role that GnRH is known to play in reproductive development and function, the molecul ar mechanism(s) by which GnRH regulates transcription of the GnRHR gene has not been well elucidated. Previous studies in this laboratory have identif ied and partially characterized the promoter region of the mouse GnRHR gene and demonstrated that the regulatory elements for tissue-specific expressi on as well as for GnRH regulation are present within the 1.2-kilobase 5'-fl anking sequence. By using deletion and mutational analysis as well as funct ional transfection studies in the murine gonadotrope-derived alpha T3-1 cel l line, we have localized GnRH responsiveness of the mouse GnRHR gene to tw o DNA sequences at -276/-269 (designated (S) under bar equence (U) under ba r nderlying (R) under bar esponsiveness to (G) under bar nRH-2 (SURG-2), wh ich contains the consensus sequence for the activating protein-1-binding si te) and -292/-285 (a novel element designated SURG-1), and demonstrated tha t this response is mediated via protein kinase C. By using the electrophore tic mobility shift assay, we further demonstrate that a member(s) of the Fo s/Jun heterodimer superfamily is responsible in part for the DNA-protein co mplexes formed on SURG-2, using alpha T3-1 nuclear extracts. These data def ine a bipartite GnRH response element in the mouse GnRHR 5'-flanking sequen ce and suggest that the activating protein-1 complex plays a central role i n conferring GnRH responsiveness to the murine GnRHR gene.