Chromogranin A Human ELISA

Research topic

Oncology

Summary

Chromogranin A (CgA) is an acidic secretory protein consisting of 439 amino acids in human. The protein is found in a wide variety of hormone and neurotransmitter storage vesicles, and it is known be co-stored and co-released with catecholamines from adrenal medulla and sympathetic neuronal vesicles during exocytosis. O’Conner and Bernstein have first reported radioimmunological measurement of CgA in human plasma under conditions of physiologic, pharmacologic and pathologic alteration of sympathoadrenal function. Accumulated data, thereafter, have confirmed high concentrations of plasma or serum CgA measured by radioimmunoassay (CgA-like immunoreactivity: CgA-LI) in patients with neuroendocrine and endocrine tumors, especially in those with pheochromocytoma, anterior pituitary tumors and rectal and prostatic carcinoma. On the other hand,
Nakane et al. recently discovered that CgA-LI exists in saliva, the concentration of which elevates rapidly under psychosomatic stress even prior to the elevation of salivary cortisol level. Subsequently, Kanno et al. presented an evidence for autonomic control of submandibular CgA-LI secretion in the anaesthetized rat. Most of the reported measurement of CgA by radioimmunoassay utilized native CgA antigens (full or partial length) and antibodies against the native proteins. On the other hand, Yanaihara et al. provided a novel radioimmunoassay system for estimation of CgA-LI level in human plasma with use of synthetic human CgA (344-374) and antibody raised against the synthetic peptide. Nakane et al. also used the assay system in their work on human salivary CgA as mentioned above. CgA molecules contain 9-10 sites of basic amino acid pairs (Arg-Arg, Lys-Arg, etc.), which are generally accepted as the proteolytic processing sites. In fact, the sequences corresponding to CgA-derived peptides having some biological activities, such as β-granin, pancreastatin and parastatin, in CgA molecules are all preceded and followed by basic amino acid pairs. However, it is also known that in the adrenal medulla which is the major site of CgA production, CgA is found to exist predominantly in large molecular forms, supporting the least processing of CgA in adrenal chromaffin cells. In addition, it was shown that there is no rapid degradation of the protein within the blood stream.