[Chromogranin A. Prohormonal function and synthesis regulation in neuroendocrine cells]

Chromogranins, which were originally found in adrenal medullary chromaffin cells, are a family of proteins exclusively localized in secretory granules of endocrine cells and neurons. Studies on primary structure have shown the presence of basic amino acid pairs which are putative cleavage sites. Recently, two chromogranin A-derived peptides, pancreastatin and chromostatin, have been characterized which supports the assumption of chromogranin A to be a prohormone. These two peptides have autocrine and paracrine biological functions. Mechanisms which regulate chromogranin synthesis appear to be highly complex depending on the stimulated receptor and involving protein kinase C and cyclic AMP. The promoter region of the chromogranin A gene possesses numerous consensus transcriptional control elements (TATA box, cyclic AMP responsive element, SP1 site, phorbol ester regulatory element, oestrogen regulatory element,...), showing the complexity of the mechanisms regulating the expression of this gene, which is tissue- and neuroendocrine cell-specific.