Characterization of the upstream sequence of the human CYP11A1 gene for cell type-specific expression

The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme P450scc, which catalyzes the synthesis of steroids from cholesterol. This gene is expressed only in steroidogenic organs such as the adrenal, gonad, placenta, and brain. We have characterized an upstream regulatory element of the human CYP11A1 gene, termed AdE, which contributed to its cell type-specific expression. The AdE sequence contains two protein binding regions, AdE1 and AdE2, which bind many proteins including NF1- and Sp1-like proteins as shown by electrophoretic mobility shift assay, footprinting, competition, antibody supershift, and mutagenesis of the binding sites. When cloned in front of the CYP11A1 promoter or the heterologous thymidine kinase promoter, AdE sequences enhanced expression of the reporter gene in steroidogenic cell lines of the adrenal, gonad, and placental origin but not in nonsteroidogenic cell lines such as COS-1 and Rat-1. The function of AdE1 and AdE2 was lower when present individually than together. The combined action of multiple transcription factors binding to the AdE sequence brings about the final activation of the CYP11A1 gene in a tissue-specific manner.