Transcription Regulation Coupled to Calcium and Protein Kinase Signaling Systems through TRE-and CRE-Like Sequences in Neuropeptide Genes

Abstract

Depolarization and calcium influx stimulates the secretion of catecholamines, neuropeptides, and secretory proteins such as chromogranin A from chromaffin cells. Calcium entry during enhanced secretory activity also triggers biosynthesis of neuropeptides, or ‘stimulus-secretion-synthesis coupling’. Neuropeptide secretion and biosynthesis in chromaffin cells is modulated by second messengers in addition to calcium. Adenylate cyclase stimulation increases long-term but not acute secretion and also upregulates neuropeptide biosynthesis. Stimulation of protein kinase C, after a latency period, causes an augmentation of potassium-induced secretion, followed by inhibition at longer times of exposure. Phorbol esters cause a profound increase in biosynthesis of the neuropeptides (VIP) and a modest increase in enkephalin biosynthesis in acutely cultured chromaffin cells galanin and vasoactive intestinal polypeptide. The effects of second-messenger stimulation on biosynthesis of different neuropeptide genes can also be distinguished on the basis of requirement for new protein synthesis. Several of the cis-active elements on the enkephalin, galanin, and VIP genes responsible for basal and regulated expression in chromaffin and neuroblastoma cells have been characterized. The fos-like protein-containing complex is present in nuclear extracts from quiescent chromaffin cells. Therefore, it, along with CREB, is a candidate for the preexisting trans-acting protein(s) that mediate stimulus-secretion-synthesis coupling in chromaffin cells. VIP gene regulation by protein kinases A and C depends on two separate cis-active elements in the VIP gene. The VIP proximal CRE mediates only the effects of cAMP and is required for basal gene expression in neuroblastoma cells. An upstream consensus TRE mediates the effects of protein kinase C on VIP gene transcription. The chromogranin A CRE element is required for neuroendocrine-specific regulation of chromogranin A gene. Mechanisms of differential regulation of neuroepeptide genes within catecholamine-storing tissues may serve to tailor the mixture of neuropeptides cosecreted with catecholamines and other classical neurotransmitters from neuroendocrine cells to diverse physiological conditions.