Cyclic adenosine monophosphate regulates vasoactive intestinal polypeptide and enkephalin biosynthesis in cultured...

When bovine chromaffin cells are dissociated from the adult adrenal gland and placed in culture, they begin to synthesize vasoactive intestinal polypeptide (VIP); they also contain high levels of enkephalin peptides. The regulation of expression of VIP and enkephalin in these cells by cyclic nucleotides was examined. Exposure of cultured chromaffin cells to cholera toxin (CT), forskolin (F), isobutylmethylxanthine (IBMX), 8-bromo-cyclic AMP (8-Br-cAMP) or dibutyryl cyclic AMP (dbcAMP) increases VIP and met-enkephalin biosynthesis as measured by an increase in total (cellular + secreted) VIP and met-enkephalin in treated versus untreated cells. Enkephalin levels increase 1.5 to 3.0 -fold while VIP levels increase 10 to 20 -fold after 48 hours of exposure to the compounds above. Increased enkephalin levels are maximum by 48 hours of exposure; VIP levels are elevated by forskolin or cholera toxin already at 17 hours of exposure. Neither forskolin nor cholera toxin alter catecholamine levels in cultured cells even after 72 hours of exposure. Thus, VIP and ME expression in cultured chromaffin cells can be regulated by intracellular cAMP. Measurement of preproenkephalin messenger RNA (mRNAenk) by quantitative Northern blot hybridization with a preproenkephalin complementary DNA probe revealed that exposure of chromaffin cells to forskolin elicits a greater than two-fold increase in mRNAenk, suggesting that the regulation of neuropeptide expression by elevated intracellular cAMP occurs at a transcriptional locus.