Analysis of the post-translational processing of chromogranin a in rat neuroendocrine tissue employing an N-terminal site-specific antiserum

Chromogranin A (CgA) is a complex prohormone expressed as a constituent of the regulated secretory pathway of numerous neuroendocrine cells. Recent in vestigations have demonstrated that CgA is selectively cleaved to generate distinct peptides in different neuroendocrine tissues. This investigation e mployed a site-specific antiserum that detects residues 98-106 rat CgA to e xamine the amino-terminal processing of CgA to generate beta -granin and re lated peptides in rat neuroendocrine tissues. Immunohistochemistry revealed moderate to intense beta -granin-like immunostaining in cells scattered th roughout the anterior pituitary, thyroid, in the islets of Langerhans and i n the mucosa of the gastrointestinal tract. Variable intensities of immunos taining were observed in distinct clusters of chromaffin cells. Quantitativ ely, the highest concentration of beta -granin-like immunoreactivity was de tected in pituitary extracts. Significantly lower concentrations were detec ted in adrenal and thyroid glands, brain, ventral and dorsal pancreatic lob es and gastrointestinal tissue extracts. Chromatography resolved three dist inct beta -granin-like immunoreactants; a large CgA-like form, an intermedi ate molecular form presumably corresponding to -granin (rat CgA(1-128)) and small immunoreactants that coeluted with the synthetic peptide. Two beta - granin-like immunoreactants, 21 and 22 kDa, were detected following immunob lot analysis of pituitary extracts. This study has demonstrated that chromo granin A is subject to distinct amino-terminal patterns of tissue-and cell- specific processing to generate a beta -granin-like immunoreactant which is additionally cleaved in pancreatic, fundic and colonic tissue to generate previously unidentified peptides.