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 investigations have demonstrated that CgA is selectively cleaved to generate distinct peptides in different neuroendocrine tissues. This investigation employed a site‐specific antiserum that detects residues 98–106 rat CgA to examine the amino‐terminal processing of CgA to generate β‐granin and related peptides in rat neuroendocrine tissues. Immunohistochemistry revealed moderate to intense β‐granin‐like immunostaining in cells scattered throughout the anterior pituitary, thyroid, in the islets of Langerhans and in the mucosa of the gastrointestinal tract. Variable intensities of immunostaining were observed in distinct clusters of chromaffin cells. Quantitatively, the highest concentration of β‐granin‐like immunoreactivity was detected in pituitary extracts. Significantly lower concentrations were detected in adrenal and thyroid glands, brain, ventral and dorsal pancreatic lobes and gastrointestinal tissue extracts. Chromatography resolved three distinct β‐granin‐like immunoreactants; a large CgA‐like form, an intermediate molecular form presumably corresponding to β‐granin (rat CgA1−128) and small immunoreactants that coeluted with the synthetic peptide. Two β‐granin‐like immunoreactants, 21 and 22 kDa, were detected following immunoblot analysis of pituitary extracts. This study has demonstrated that chromogranin A is subject to distinct amino‐terminal patterns of tissue‐and cell‐specific processing to generate a β‐granin‐like immunoreactant which is additionally cleaved in pancreatic, fundic and colonic tissue to generate previously unidentified peptides.