Journal Article

Cytosolic PLA2 in Zymogen Granule Fusion and Amylase Release: Inhibition of GTP-induced Fusion by Arachidonyl Trifluoromethyl Ketone Points to cPLA2 in G-Protein-mediated Secretory Vesicle Fusion

Akm A. Sattar and Reazul Haque

in The Journal of Biochemistry

Published on behalf of The Japanese Biochemical Society

Volume 141, issue 1, pages 77-84
Published in print January 2007 | ISSN: 0021-924X
Published online December 2006 | e-ISSN: 1756-2651 | DOI: https://dx.doi.org/10.1093/jb/mvm007
Cytosolic PLA2 in Zymogen Granule Fusion and Amylase Release: Inhibition of GTP-induced Fusion by Arachidonyl Trifluoromethyl Ketone Points to cPLA2 in G-Protein-mediated Secretory Vesicle Fusion

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Previously we reported that the G-protein Gαi3 localized in pancreatic zymogen granule (ZG) membrane participates in vesicular fusion at the cell plasma membrane (PM). In the present study, the presence of cytosolic phosholipase A2 (cPLA2) in rat ZGs was demonstrated and its potential role in G-protein-mediated ZG–PM fusion was investigated. In vitro fusion assays utilizing both enzymatic and fluorimetric techniques demonstrate that ZGs fuse with PM with a greater potency in the presence of GTP. Arachidonyl trifluoromethyl ketone (AACOCF3) at 40 µM reduces GTP-induced ZG–PM fusion by 25–50%. Anti-cPLA2 antibody reduces ZG–PM fusion in a dose-dependent manner and a 50% reduction of the fusion takes place in the range of 0.48–0.64 ratios of cPLA2 antibody to ZG proteins. PLAP, a cPLA2 activator synthetic peptide increases ZG–PM fusion in a limited dose-dependent manner and tends to inhibit at higher concentrations. Exogenous arachidonic acid inhibits GTP-induced ZG–PM fusion in a dose-dependent manner. Furthermore, a non-hydrolysable GTP analogue, Gpp(NH)p, reduces PLAP effect in ZG–PM fusion; and the net effect of Gpp(NH)p and PLAP differs significantly from the net effect of GTP and PLAP on ZG–PM fusion suggesting that cPLA2 is involved in G-protein-mediated secretory vesicle fusion.

Keywords: phospholipase A2; phospholipase A2 inhibitor; G-protein; membrane fusion; pancreas; zymogen granule

Journal Article.  5036 words.  Illustrated.

Subjects: Biochemistry

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