Formation of the Catecholamine Release-inhibitory Peptide Catestatin from Chromogranin A

The catestatin fragment of chromogranin A is an inhibitor of catecholamine release, but its occurrence in vivo has not yet been verified, nor have its precise cleavage sites been established. Here we found extensive processing of catestatin in chromogranin A, as judged by catestatin radioimmunoassay of size-fractionated chromaffin granules. On mass spectrometry, a major catestatin form was bovine chromogranin A332–364; identity of the peptide was confirmed by diagnostic Met346oxidation. Further analysis revealed two additional forms: bovine chromogranin A333–364 and A343–362. Synthetic longer (chromogranin A332–364) and shorter (chromogranin A344–364) versions of catestatin each inhibited catecholamine release from chromaffin cells, with superior potency for the shorter version (IC50 ∼2.01 versus∼0.35 μm). Radioimmunoassay demonstrated catestatin release from the regulated secretory pathway in chromaffin cells. Human catestatin was cleaved in pheochromocytoma chromaffin granules, with the major form, human chromogranin A340–372, bounded by dibasic sites. We conclude that catestatin is cleaved extensivelyin vivo, and the peptide is released by exocytosis. In chromaffin granules, the major form of catestatin is cleaved at dibasic sites, while smaller carboxyl-terminal forms also occur. Knowledge of cleavage sites of catestatin from chromogranin A may provide a useful starting point in analysis of the relationship between structure and function for this peptide.