?CYP11A1, also known as cytochrome P450C11A1, cytochrome P450scc and cytochrome P450, subfamily XIA, is an enzyme that catalyzes the first step of steroid biosynthesis under the modulation of cAMP signal. CYP11A1 in steroidogenic cells converts cholesterol to pregnenolone, which is determined by hormonal control of cholesterol availability. Expression of the CYP11A1 gene is controlled by the transcription factor SF-1, and the upstream SF-1 binding site in the CYP11A1 gene is required for hormonal stimulation. c-Jun and SF-1 may act synergistically to activate CYP11A1 gene expression. Both Forskolin and 8-Br-cAMPS elevate CYP11A1 mRNA levels in the interstitial cell monolayer, which has a fully functional adenylate cyclase.