FIG. 3.

Model for regulation of the FSHR promoter. Exon 1 of the FSHR gene is indicated as a black rectangle; important regulatory elements are shown by shaded white rectangles. Straight arrows indicate the transcriptional start sites. Regulatory elements, indicated below the depicted promoter, are the Inr, GATA, and E2F sites, located within exon 1, and the E box, AP-1 site, and two SF-1-like binding sites, SLBS-3 and SLBS-2, located within the promoter region. GATA-1 binds the GATA site, the upstream factor (USF) proteins (USF1 and USF2) bind and activate transcription through the E box, while SF1 induces FSHR transcription through the SLBS-2 and SLBS-3 elements. Following binding to SLBS-2 and SLBS-3, SF-1 is postulated to interact either directly or indirectly with the USF proteins, resulting in transcriptional stimulation. Activation of protein kinase A (PKA) by cAMP interferes with the ability of SF1 to transactivate the FSHR promoter. In the absence of the upstream SF-1 binding sites, cAMP stimulation results in the induction of cfos-containing complexes that bind the AP-1 site and stimulate FSHR promoter activity.