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J. Biol. Chem., Vol. 277, Issue 43, 40384-40389, October 25, 2002
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From the Institute of Molecular Biology and Genetics, University of
Valladolid School of Medicine, E-47005 Valladolid, Spain
Previous studies have demonstrated that U937
cells are able to mobilize arachidonic acid (AA) and synthesize
prostaglandins in response to receptor-directed and soluble stimuli by
a mechanism that involves the activation of Group IV cytosolic
phospholipase A2
Involvement of Calcium-independent Phospholipase A2
in Hydrogen Peroxide-induced Accumulation of Free Fatty Acids
in Human U937 Cells*
and
. In this paper we show
that these cells also mobilize AA in response to an oxidative stress
induced by H2O2 through a mechanism that
appears not to be mediated by cytosolic phospholipase A2 but by the calcium-independent Group VI phospholipase A2
(iPLA2). This is supported by the following lines of
evidence: (i) the response is essentially calcium-independent, (ii) it
is inhibited by bromoenol lactone, and (iii) it is inhibited by an
iPLA2 antisense oligonucleotide. Enzyme assays
conducted under a variety of conditions reveal that the specific
activity of the iPLA2 does not change as a result of
H2O2 exposure, which argues against the
activation of a specific signaling cascade ending in the
iPLA2. Rather, the oxidant acts to perturb membrane
homeostasis in a way that the enzyme susceptibility/accessibility to
its substrate increases, and this results in altered fatty acid
release. In support of this view, not only AA, but also other fatty
acids, were found to be liberated in an
iPLA2-dependent manner in the
H2O2-treated cells. Collectively, these studies
underscore the importance of the iPLA2 in modulating
homeostatic fatty acid deacylation reactions and document a potentially
important route under pathophysiological conditions for increasing free
fatty acid levels during oxidative stress.
*
This work was supported by Grant BMC2001-2244 from the
Spanish Ministry of Science and Technology, Grant CSI-4/02 from the Education Department of the Autonomous Government of Castile and León, and Grant 011232 from Fundació La Marató
de TV3.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Investigator of the Ramón y Cajal Program, Spanish Research Council.
§
To whom correspondence should be addressed: Instituto de
Biología y Genética Molecular (IBGM-CSIC), Facultad de
Medicina, Universidad de Valladolid, Avenida Ramón y Cajal 7, E-47005 Valladolid, Spain. Tel.: 34-983-423-062; Fax: 34-983-423-588;
E-mail: jbalsinde@ibgm.uva.es.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.
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