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Autocrine inhibition of parathyroid cell secretion requires proteolytic processing of chromogranin A.

Authors
Type
Published Article
Journal
Bone and Mineral
0169-6009
Publisher
Elsevier
Publication Date
Volume
17
Issue
3
Pages
323–333
Identifiers
PMID: 1623327
Source
Medline
License
Unknown

Abstract

Chromogranin A (CgA, Secretory Protein-I) is a protein of about 450 amino acids representing a major soluble component of the secretory granules of parathyroid and other endocrine and neuroendocrine cells. In the parathyroid, CgA is costored and cosecreted with parathormone (PTH). We earlier found that CgA and the derived peptide, pancreastatin, inhibited secretion of PTH and CgA by parathyroid cells in culture and that CgA antiserum stimulated secretion above the maximum achieved at low (0.5 mM) Ca2+. In the present study, porcine parathyroid cells were incubated at different cell concentrations at low Ca2+. The amount of secreted CgA increased over the 6-h incubation period at 1 x 10(6) to 4 x 10(6) cells/ml, but plateaued after 3 h at 6 x 10(6) cells/ml. Secretion did not plateau when antisera were added at 3 h. Conditioned medium contained a factor or factors that blocked secretion by fresh parathyroid cells at 0.5 mM Ca2+. Pulse-chase studies revealed that 40% of the secreted CgA was processed after 6 h of chase. alpha-2-macroglobulin, an inhibitor of proteolytic processing, increased the amount of CgA in the medium by 30% at 1 h of chase and decreased the amount processed to 20% by 6 h. Other protease inhibitors similarly enhanced the amount of CgA in the medium. These data indicate that proteolytic processing of intact CgA is requisite for its autocrine inhibitory activity.

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