Enkephalin gene transcription in bovine chromaffin cells is regulated by calcium and protein kinase A signal transduction pathways: identification of DNase I-hypersensitive sites

The bovine enkephalin gene is responsive to multiple signaling pathways in primary chromaffin cell cultures. We examined the effects of activation of the calcium and protein kinase A pathways on accumulation of enkephalin peptide and mRNA, gene transcription, and chromatin structure in the 5' region of the gene. We show here that the increase of enkephalin mRNA and peptide after depolarization of chromaffin cells with KCl or activation of adenylate cyclase with forskolin is preceded by an increase in enkephalin gene transcription. Both enkephalin peptide and mRNA were reduced by co-treatment of KCl- or forskolin-stimulated cultures with phorbol esters. Three enhancer sequences that were previously shown to be responsive to calcium, protein kinase A, and phorbol esters in the human gene in vitro were identified in the bovine enkephalin promoter, identifying a potential locus of control for these pathways in vivo. DNase I hypersensitivity mapping identified two tissue-specific sites that are associated with enkephalin gene expression in adrenal medulla and chromaffin cells; site 1 is in the promoter, which contains the three enhancer elements, and site 2 is in the first intron. These results suggest that regulation of the enkephalin gene in primary chromaffin cells by the calcium, protein kinase A, and protein kinase C signaling pathways occurs by modulation of transcription factor activity at several discrete loci on the enkephalin gene.