The type 4 adenylyl cyclase, Adcy4, is the least abundant of five different adenylyl cyclase isoforms expressed in the Y1 mouse adrenocortical cell line and is deficient in a Y1 mutant with impaired steroidogenic factor 1 (SF1) activity. This study examines the contributions of SF1 and other DNA promoter/regulatory elements to Adcy4 expression in the Y1 cell line and its derivative Adcy4-deficient mutant. Primer extension and in silico analyses indicate that Adcy4 transcription initiates from multiple sites just downstream of a GC-rich sequence. Luciferase reporter gene assays identify a 124-bp sequence, situated 19 bp upstream of the major transcription start site and highly conserved among several mammalian species, as the major determinant of Adcy4 expression in Y1 cells and as a site of compromised activity in the Adcy4-deficient mutant. EMSAs using competitor nucleotides and specific antibodies indicate that this conserved region contains three specificity protein (Sp)-1/Sp3-binding sites and one SF1-binding site. As determined by site-specific mutagenesis, the 5'-most Sp1/Sp3-site enhances promoter activity, whereas the middle Sp1/Sp3 and SF1 sites each repress Adcy4 promoter activity. In the Adcy4-deficient mutant, mutating the SF1 site restores Adcy4 promoter activity and knocking down SF1 with small interfering RNAs increases Adcy4 expression, confirming the contribution of SF1 to the mutant phenotype. These studies demonstrate roles for Sp1/Sp3 and SF1 in Adcy4 expression in Y1 cells and establish a repressor function for SF1 in certain promoter contexts.
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