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  • Title: Evidence for the involvement of Rab3A in Ca(2+)-dependent exocytosis from adrenal chromaffin cells.
    Author: Holz RW, Brondyk WH, Senter RA, Kuizon L, Macara IG.
    Journal: J Biol Chem; 1994 Apr 08; 269(14):10229-34. PubMed ID: 8144603.
    Abstract:
    Bovine chromaffin cells are nondividing primary secretory cells that store and secrete catecholamine and a variety of proteins including chromogranins, opiate peptides, and opiate precursors. A transient transfection technique based upon the expression of human growth hormone as a reporter for the regulated secretory pathway was used to study the role of a Ras-like, GTP-binding protein, Rab3a, in Ca(2+)-dependent exocytosis. Immunocytochemistry and flow cytometry revealed that growth hormone and Rab proteins were coexpressed in the same cells. Overexpression of the wild type protein and expression of a mutant protein Rab3aQ81L both inhibited nicotinic agonist-stimulated exocytosis in intact cells. Expression of Rab3aQ81L also inhibited Ca(2+)-dependent secretion from permeabilized cells. Two other mutants, Rab3aN135I and Rab3aT36N, which correspond to dominant acting mutants of Ras, caused limited and no inhibition, respectively, of agonist-stimulated exocytosis. These data provide direct evidence that Rab3a plays an important role in Ca(2+)-triggered exocytosis. We suggest that Rab3a is an inhibitor of secretion, perhaps as part of a pre-fusion complex with secretory vesicles. Elevated Ca2+ may trigger exocytosis by overcoming the inhibition by Rab3a.
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