Anti-CHGA monoclonal antibody, clone DHB525

Chromogranin A (CHGA), a protein participating in the biogenesis of dense core secretory granules in various neuroendocrine tissues, plays a critical role in the release of hormones/peptides and the pathogenesis of pheochromocytoma. However, little is known about the developmental origin of CHGA-expressing cells during embryogenesis. Here, we report the structural characterization and spatio-temporal expression pattern of zebrafish (Danio rerio) ortholog of mammalian CHGA. The earliest expression of chga transcripts was observed at 16 h post fertilization in the developing cranial ganglia as six distinct Cellular masses arranged bilaterally as strings of beads in the dorsal root ganglia (DRG) precursors along the dorsal trunk. With development advancing, the chga transcripts were expressed abundantly in diencephalon, mesencephalon, and rhombencephalon as well as in the DRG. Interestingly, double in situ hybridization assay of chga with genes expressed in pronephros (Wilms' tumor suppressor 1, wt 1), adrenal cortex (side-chain cleavage enzyme, scc), and sympathoadrenal neuron/chromaffin cell (dopamine-beta-hydroxylase, dbh), respectively, showed that the chga-expressing cells are spatially separated from wt1-, scc-, and dbh-positive cell populations during early embryonic development. The pronephros region does not express chga even up to 7 days post fertilization, while chga positive-staining cells bind in the brain and DRG, indicating that chga may play an important role in nervous system development during the early embryonic stages.

The plasma level of chromogranin A (CgA) is elevated in genetic hypertension. Conversely, the plasma level of the CgA peptide catestatin is diminished in individuals with established hypertension and those with a genetic risk of this disease. Resequencing of the human CHGA gene identified three naturally occurring variants of catestatin (Gly364Ser, Pro370Leu, and Arg374Gln) that exhibit different potencies in inhibiting catecholamine secretion. Here, we have examined whether there is any differential processing of the three CHGA variants to catestatin by the endoproteolytic enzyme plasmin. Plasmin digestion of the purified CgA proteins generated a stable biologically active 14-amino acid peptide (human CgA(360-373)) from the wild-type, Gly364Ser, and Arg374Gln proteins despite the disruption of the dibasic site (Arg(373)Arg(374)) in the Arg374Gln variant. Unexpectedly, the action of plasmin in generating the catestatin peptide from the Pro370Leu protein was less efficient. The efficiency of cleavage at the dibasic Arg(373)down arrow Arg(374) site in synthetic human CgA(360-380) was 3-to 4-fold less in Pro370Leu CgA, compared with the wild type. Circular dichroism of the synthetic CgA(352-372) suggested a difference in the amount of alpha-helix and beta-sheet between the wild-type and Pro370Leu CgA peptides. Because the Pro(370) residue is in the P4 position, the local secondary structure in the vicinity of the cleavage site may enforce the specificity or accessibility to plasmin. The less efficient proteolytic processing of the Pro370Leu protein by plasmin, coupled with the strong association of this variant with ethnicity, suggests that the Pro370Leu CHGA gene variant may contribute to the differential prevalence of cardiovascular disease across ethnic groups.