Parastatin (porcine chromogranin A347-419), a novel chromogranin A- derived peptide, inhibits parathyroid cell secretion

Abstract

Chromogranin A (CgA), previously referred to as secretory protein-I, is a 50-kilodalton protein present in secretory granules of many endocrine and neuroendocrine cells. In the parathyroid it is present and cosecreted with PTH in response to hypocalcemia. CgA appears to be a precursor of bioactive peptides including pancreastatin, beta-granin, vasostatin, and chromostatin. The presence of several highly conserved pairs of basic amino acids, putative cleavage sites, in the CgA molecule suggests that other yet unidentified bioactive peptides might exist within the molecule. We tested this speculation by subjecting porcine parathyroid CgA to digestion by endoproteinase Lys-C. Resulting CgA-derived peptides were isolated by reverse-phase C18 HPLC and tested for their ability to affect low-Ca2+ stimulated secretion by porcine parathyroid cells. We characterized one peptide, which we named parastatin, that inhibited secretion of both PTH and CgA in a dose-dependent fashion over the range of 0.2-0.6 microM. Parastatin migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent mol wt of 11,000. Edman degradation yielded the sequence L-S-F-R-A-P-A-Y-G-F-R-G-P-G-L corresponding to residues 347-361 of porcine CgA. Amino acid analysis of endoproteinase Lys-C and endoproteinase Asp-N-generated fragments indicated that parastatin corresponds to residues 347-419 of CgA. A synthetic NH2-terminal fragment of rat parastatin corresponding to residues 1-19 was an inhibitory as intact porcine parastatin on parathyroid gland secretion. These results extend the concept that CgA is a precursor of biologically active peptides.

The endocrine role for chromogranin A: A prohormone for peptides with regulatory properties

“…First out was PST [7], thereafter the rat betagranin [30], VS-I (CgA and VS-II (CgA [31,32], parastatin [33] prochromacin and chromacin [34,35] and finally, catestatin [36]. To date only one granin peptide, the CgA-derived catestatin, has been reported to act via a classical type of receptor, the nicotinic acetylcholine receptor [36].…”

“…Catestatin (CgA 344-364 ) is a 21-residue long, cationic and hydrophobic peptide [36] located at the Nterminal end of parastatin [33] and derives from intragranular and extragranular processing of the prohormone [36,115,116]. Several distinct biological activities have been assigned to the catestatin domain, i.e., inhibiting catecholamine secretion from bovine chromaffin cells [36], PTH secretion from porcine parathyroid cells [33,117] and bacterial and fungal growth [55], while activating histamine release in a mastoparan-like manner from rat mast cells [93].…”

“…Several distinct biological activities have been assigned to the catestatin domain, i.e., inhibiting catecholamine secretion from bovine chromaffin cells [36], PTH secretion from porcine parathyroid cells [33,117] and bacterial and fungal growth [55], while activating histamine release in a mastoparan-like manner from rat mast cells [93]. Unlike the helical structure of mastoparan [118], the primary sequence of human catestatin, ssmklsfrar aygfrgpgpql, forms a loosely coiled structure with an electropositive Arg-rich loop that stabilizes the hydrophobic form assumed to be essential for its catechol- amine release-inhibitory action [115].…”

“…While the release of PTH is stimulated by low plasma Ca 2+ levels or IL-8 via the CXC2 type of G protein coupled receptor at normal, 1 mM Ca 2+ [139], it is inhibited via two different pathways, (1) by high plasma Ca 2+ activating the calcium sensor [140], and (2) by three of the CgAderived peptides at low plasma Ca 2+ , namely VS-I and CgA 1-40 [38,102,103], PST [141,142] and parastatin [33,117]. The inhibitory mechanism for high plasma Ca 2+ in human parathyroid cells involves an increase in intracellular Ca 2+ sufficient for enhanced efflux of K + via a tetraethylammonium (TEA)-sensitive, calcium-regulated K + channel [140].…”

“…In the porcine parathyroid yet another highly conserved CgA domain, parastatin (pCgA 347-419 ), was shown to inhibit the co-secretion of PTH and CgA [33], but at a higher concentration range than with VS-I in the bovine parathyroid cells. Carbohydrate metabolism: PST as a regulator in pancreas, hepatocytes and adipocytes The islet cells of the endocrine pancreas represent together with the liver and adipose tissue the essential components in the homeostatic regulation of plasma glucose.…”