Endocrine Abstracts

Expression of the ACTH receptor, MC2-R, is highly restricted, being detectable in the mouse only in the adrenal cortex and adipose tissue. The promoter of the murine MC2-R contains binding sites for SF-1, a transcription factor that has been shown to be essential for the transcriptional activity of a number of steroidogenic genes. However, SF-1 is not expressed in adipocytes and therefore is not essential for MC2-R expression in these cells. We have investigated the requirement for SF-1 binding sites in the mMC2-R promoter for basal activity of this promoter in murine adrenal (Y1) cells. A minimal mMC2-R promoter construct containing two SF-1 sites, at minus 31 and plus 31, that both bind SF-1 in EMSAs, is active in Y1 cells. Mutation of the upstream site reduces the basal activity of the promoter by approximately 40%, whereas mutation of both sites has no effect. However, a deletion that impinges upon the downstream SF-1 site reduces the basal activity of the promoter by approximately 50% and a deletion that removes the site altogether is largely inactivated. Taken together these data suggest that a factor that binds at or near the downstream SF-1 site, distinct from SF-1, is important for the basal activity of the promoter in Y1 cells. EMSA analysis of this region showed the presence of complexes that were unaffected by the mutations introduced into the SF-1 binding site. The sequence downstream of the minus 31 SF-1 site contains a consensus site for an AP-1-like factor, TCF11. Comparing the factors binding to this sequence and consensus sites for AP-1 and TCF11 in EMSAs showed complexes of similar mobility which were verified by competition and antibody analysis. It therefore appears that AP-1 and TCF11 may be important for the basal transcription of the murine MC2-R gene in Y1 cells.