cAMP-dependent transcription of the human CYP21B (P-450C21) gene requires a cis-regulatory element distinct from the consensus cAMP-regulatory element

Abstract

By utilizing chimeric genes constructed from 5'-flanking sequences of the human CYP21B (P-450C21) gene and reporter genes (chloramphenicol acetyltransferase or rabbit beta-globin), a 34-nucleotide sequence has been found to be required for cAMP-dependent transcription. This sequence (-129/-96 base pairs) shows no homology to that of the consensus (CRE) cAMP-regulatory element. Gel retardation analysis shows that a protein-DNA complex is formed between this DNA sequence and nuclear proteins from mouse adrenal Y1 tumor cells or bovine adrenal cortical cells or human fetal adrenal tissue and that formation of this complex cannot be competed by DNA containing the consensus CRE sequence. Even though cAMP-enhanced accumulation of P-450C21 mRNA in primary cultures of bovine adrenocortical cells is inhibited by the protein synthesis inhibitor, cycloheximide, reporter gene transcription enhanced by the cAMP-responsive -129/-96-base pair fragment of the human CYP21B gene is not. We conclude that cAMP-dependent transcription of the human P-450C21 gene (CYP21B), an event required for maintenance of optimal steroidogenic capacity in the adrenal cortex, involves a stable transcription factor(s) distinct from the CRE-binding protein. Furthermore the cAMP-dependent cis-regulatory element of the human P-450C21 gene is distinct from those found associated with the other steroid hydroxylase genes, 17 alpha-hydroxylase cytochrome P-450, cholesterol side chain cleavage cytochrome P-450, and 11 beta-hydroxylase cytochrome P-450, suggesting that each of these genes may require its own set of specific transcription factors for cAMP-dependent regulation.