A Novel AP-1 Site Is Critical for Maximal Induction of the Follicle-stimulating Hormone β Gene by Gonadotropin-releasing Hormone

Abstract

Regulation of follicle-stimulating hormone (FSH) synthesis is a central point of convergence for signals controlling reproduction. The FSHβ subunit is primarily regulated by gonadotropin-releasing hormone (GnRH), gonadal steroids, and activin. Here, we identify elements in the mouse FSHβ promoter responsible for GnRH-mediated induction utilizing the LβT2 cell line that endogenously expresses FSH. The proximal 398 bp of the mouse FSHβ promoter is sufficient for response to GnRH. This response localizes primarily to an AP-1 half-site (-72/-69) juxtaposed to a CCAAT box, which binds nuclear factor-Y. Both elements are required for AP-1 binding, creating a novel AP-1 site. Multimers of this site confer GnRH induction, and mutation or internal deletion of this site reduces GnRH induction by 35%. The same reduction was achieved using a dominant negative Fos protein. This is the only functional AP-1 site identified in the proximal 398 bp, since its mutation eliminates FSHβ induction by c-Fos and c-Jun. GnRH regulation of the FSHβ gene occurs through induction of multiple Fos and Jun isoforms, forming at least four different AP-1 molecules, all of which bind to this site. Mitogen-activated protein kinase activity is required for induction of FSHβ and JunB protein. Finally, AP-1 interacts with nuclear factor-Y, which occupies its overlapping site in vivo.