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 P4 50scc, which catalyzes the synthesis of steroids from cholesterol. Thi s gene is expressed only in steroidogenic organs such as the adrenal, gonad, placenta, and brain. We have characterized an upstream regulato ry element of the human CYP11A1 gene, termed AdE, which contributed to its cell type-specific expression. The AdE sequence contains two prot ein 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 mutagenesi s of the binding sites. When cloned in front of the CYP11A1 promoter o r the heterologous thymidine kinase promoter, AdE sequences enhanced e xpression of the reporter gene in steroidogenic cell lines of the adre nal, gonad, and placental origin but not in nonsteroidogenic cell line s such as COS-1 and Rat-1. The function of AdE1 and AdE2 was lower whe n present individually than together. The combined action of multiple transcription factors binding to the AdE sequence brings about the fin al activation of the CYP11A1 gene in a tissue-specific manner.