IDENTIFICATION AND CHARACTERIZATION OF A 3',5'-CYCLIC ADENOSINE MONOPHOSPHATE-RESPONSIVE ELEMENT IN THE HUMAN CORTICOTROPIN-RELEASING HORMONE GENE PROMOTER

The regulation of human corticotropin-releasing hormone (hCRH) gene promoter activity by inducers of cAMP was investigated by transient transfection with a construct containing the hCRH gene promoter fused to the chloramphenicol acetyltransferase gene. Expression of hCRH-chloramphenicol acetyltransferase was strongly enhanced by forskolin in the neuroblastoma SK-N-MC and choriocarcinoma JAR cell lines. Overexpression of the catalytic subunit of protein kinase A dispensed the need for forskolin, and cotransfection of cAMP-responsive element-binding protein cDNAs enhanced forskolin-dependent expression of the hCRH promoter. Progressive 5'-end deletions of the hCRH promoter delineated a cAMP- responsive region between -226 and -164 base pairs. This fragment contained the sequence TGACGTCA at -221 base pairs, consistent with the consensus motif for a CRE. A homologous oligonucleotide responded to cAMP when cloned in either orientation in front of the thymidine kinase promoter. However, the level of constitutive and inductive cAMP expression was dependent on the cell line and on intrinsic properties of the promoter. Mutation of the wild type CRH-CRE sequence into an AP-1 site (TGAGTCA) completely abolished stimulation by cAMP. In contrast, coexpression of the catalytic subunit of protein kinase A dispensed the need for stimulation with forskolin, which showed that the CRH-CRE oligonucleotide served as a functional equivalent of the native CRE element.