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Arachidonic acid release from NIH 3T3 cells by group‐I phospholipase A 2 : Involvement of a receptor‐mediated mechanism
Author(s) -
Xing Mingzhao,
Miele Lucio,
Mukherjee Anil B.
Publication year - 1995
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041650315
Subject(s) - phospholipase a2 , arachidonic acid , enzyme , receptor , biochemistry , protein kinase c , mechanism of action , phospholipase a , prostacyclin , chemistry , phospholipase c , biology , in vitro
Group I pancreatic phospholipase A 2 (PLA 2 I) is primarily a digestive enzyme. Recently, however, in addition to its catalytic activity a receptor‐mediated function has been described for this enzyme. PLA 2 I binding to its receptor induces cellular chemokinesis, proliferation, and smooth muscle contraction. This enzyme also induces the production of prostaglandin E 2 in certain cells and may have a proinflammatory role. However, despite its ability to hydrolyze phospholipids in in vitro assays, PLA 2 ‐I does not efficiently catalyze release of AA from intact cells. Here, we demonstrate that while short‐term exposure of NIH 3T3 cells to PLA 2 ‐I is ineffective, exposure of 6 h or longer significantly increases the basal release of AA. Dose‐response curve of PLA 2 ‐I‐induced AA release was saturable with an EC 50 of 14.01 ± 1.36 nM (n = 3). [ 3 H]‐AA was preferentially released over [ 3 H]‐oleic acid by PLA 2 ‐I, inactivated with 4‐bromophenacyl bromide, was fully capable of mediating AA release. These data suggest that a non‐catalytic, receptor‐mediated mechanism is involved in PLA 2 ‐I‐induced AA release in NIH‐3T3 cells. This relase of AA is not dependent on protein kinase C or Ca 2+ concentration. Comparison of the effect of PLA 2 ‐I with those of ATP and platelet‐derived growth factor indicates that each of these agonists regulates AA release via independent pathways. Neither the basal enzymatic activity of the 85‐kDa cytosolic PLA 2 nor the protein level of this enzyme was affected by treatment of cells with PLA 2 ‐I. However, the increase in basal enzymatic activity of 85 kDa PLA 2 due to protein kinase C activation was further enhanced by pretreatment of cells with PLA 2 ‐I. We conclude that: (1) short‐term exposure of cells to PLA 2 I does not cause measurable AA release; (2) release of AA from intact cells by this enzyme requires long‐term exposure; (3) AA release is not mediated by a direct catalytic effect of PLA 2 I; and (4) AA release by PLA 2 I is accomplished via a receptor‐mediated process. Taken together, these results raise the possibility that PLA 2 I, in addition to its digestive function, may also contribute to aggravate preexisting inflammatory processes and/or to initiate new ones when chronic exposure of cells to this enzyme occurs. © 1995 Wiley‐Liss Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.

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