Radioimmunoassay of chromogranin A in plasma as a measure of exocytotic sympathoadrenal activity in normal subjects and patients with pheochromocytoma

Bovine chromogranin A sequence and distribution of its messenger RNA in endocrine tissues

Chromogranin A is contained in storage vesicles of chromaffin cells of the adrenal medulla and released with catecholamines when the splanchnic nerve is stimulated. Chromogranin A is similar to secretory protein I (SP-I), a major secreted protein of the parathyroid. Chromogranin A/SP-I immunoreactivity is abundant in endocrine cells that secrete peptide hormones from storage vesicles. Chromogranins may act in neuroendocrine secretion by binding intravesicular calcium. Serum levels of chromogranin are raised in hypertension and endocrine neoplasia. We report here the isolation and sequencing of a cDNA encoding bovine chromogranin A, providing the first complete primary structure of a chromogranin protein. Chromogranin A is a highly acidic protein with an apparent relative molecular mass (Mr) of 75,000 on SDS-PAGE, but an actual Mr of 48,000. Adrenal medulla, brain, pituitary and parathyroid are all sites of synthesis of chromogranin A. The primary structure of chromogranin A, and the presence of chromogranin mRNA in the parathyroid, indicate that chromogranin A and SP-I are identical.

A cloned chromogranin A (CgA) cDNA detects a 2.3Kb mRNA in diverse neuroendocrine tissues

CgA is a 72Kd protein of unknown function that is present in many neuroendocrine tissues and co-secreted with their resident hormones. We prepared a cDNA library to the mRNA from CgA-producing human medullary thyroid carcinoma (MTC) cells in the expression vector lambda gt11. The library was screened with a panel of one polyclonal and two monoclonal antibodies to CgA. The specificity of the antibodies for CgA was demonstrated by immunoassay, immunohistology, and immunoprecipitation of the in vitro translation products of mRNA from CgA-producing tissues. A chromogenic second antibody identified five immunoreactive clones. Their cDNA inserts were isolated after EcoRI digestion and agarose gel electrophoresis. These cDNAs were 32P-labelled and used as probes in Northern hybridization studies. An mRNA of approximately 2.3Kb was detected with the cDNA probes in human cell lines from MTC and lung cancers that were shown to produce CgA and in human pheochromocytoma and bovine adrenal medulla tissue. To confirm its identity, one of the putative CgA cDNAs was subcloned into a plasmid and was used to hybridization-arrest the in vitro translation of CgA mRNA. These studies demonstrate the cloning of cDNAs which hybridize with CgA mRNA from diverse neuroendocrine tissues.

Secretion of chromogranin A by peptide-producing endocrine neoplasms

Chromogranin A, the protein that is co-stored and co-released with catecholamines from the adrenal medulla, has recently been identified in a variety of human endocrine tissues, both normal and neoplastic. We investigated the secretion of chromogranin A by peptide hormone-producing human tumors in studies of patients with the following neoplastic disorders: pheochromocytoma, parathyroid adenoma, primary parathyroid hyperplasia, medullary thyroid carcinoma, thyroidal C-cell hyperplasia, carcinoid tumor, oat-cell lung carcinoma, pancreatic islet-cell tumor, and aortic-body tumor. All these patient groups had elevated concentrations of plasma chromogranin A. We distinguished different forms of immunoreactive plasma chromogranin A by size with the use of gel filtration. Plasma chromogranin A levels were not elevated in patients with diverse "control" conditions--both benign and malignant and both endocrine and nonendocrine--in which peptide hormones are not produced. The sensitivity and specificity of plasma chromogranin A elevations in the diagnosis of peptide-producing endocrine neoplasms were 81 and 100 percent, respectively. The elevation of plasma chromogranin A in our subjects suggests that their neoplasms co-release chromogranin A along with the usual resident hormone of the tumor, that these neoplasms could be characterized as "chromograninomas," and that measurement of plasma chromogranin A may be a useful diagnostic procedure in subjects with endocrine tumors, especially multiple endocrine neoplasia.

The amino terminal sequences of bovine and human chromogranin A and secretory protein I are identical

The amino terminal sequences of bovine and human adrenal medullary chromogranin A have been determined. Their sequences are identical and also identical to the published sequence of secretory protein I from the parathyroid gland. This data indicates that the previously published sequence of chromogranin A is incorrect at residues 2 and 19. These data confirm earlier observations of a substantial similarity between secretory protein I and chromogranin A and, in fact, strongly suggest that they are identical.