Granins markers of the regulated secretory pathway.

The granins are a family of acidic secretory proteins made up of chromogranin A, chromogranin B, and secretogranin II, which exhibit widespread distribution in endocrine and neuronal cells. The numerous potential sites for proteolytic processing have suggested a role for these peptides as prohormones: several potential degradation products of chromogranin A, pancreastatin, and chromostatin have autocrine activity. On the other hand, an intracellular role for the granins is supported by their propensity to aggregate in a low-pH, high-calcium environment such as found in the trans-Golgi network followed by their efficient sorting to the regulated pathway. As a result, the granins are considered markers for the regulated pathway and may play a role in secretory granule formation.