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Articles in PresS, published online ahead of print December 12, 2001
Am J Physiol Gastrointest Liver Physiol, 10.1152/ajpgi.00305.2001
Submitted on July 13, 2001
Accepted on December 6, 2001
1 Department of Pathology, University of Pittsburgh, Pittsburgh, PA, USA
2 Critical Care Medicine Department, National Institutes of Health, Bethesda, MD, USA
* To whom correspondence should be addressed. E-mail: wut{at}msx.upmc.edu.
In an effort to understand the role of key eicosanoid-forming enzymes in the activation of peroxisome proliferator activated receptor (PPAR), this study was designed to study the possible contributions of cytosolic phospholipase A2 (cPLA2) and group IIA secretory phospholipase A2 (sPLA2) in the regulation of PPAR-mediated gene transcription in a human hepatoma cell line (HepG2). The HepG2 cells express both PPAR-
and 
, but not PPAR-ß. Overexpression of cPLA2, but not group IIA sPLA2, in the HepG2 cells caused a significantly increased PPAR/ mediated reporter activity. Antisense inhibition of cPLA2 resulted in a significantly decreased PPAR/ activity. The PPAR/-induced gene transcription in the HepG2 cells was inhibited by the cPLA2 inhibitors methyl arachidonyl fluorophosphonate (MAFP) and arachidonyltrifluoromethyl ketone (AACOCF3), but not by the sPLA2 inhibitor LY311727. The expression of PPAR-mediated endogenous gene apolipoprotein AII was increased in cells with overexpression of cPLA2, decreased in cells with antisense inhibition of cPLA2, but unaltered in cells with overexpression of group IIA sPLA2. The above results demonstrated an important role of cPLA2, but not group IIA sPLA2, in the control of PPAR activation. The cPLA2-mediated PPAR activation was likely mediated by arachidonic acid and prostaglandin E2. This study reveals a novel intracellular function of cPLA2 in PPAR activation in HepG2 cells. The cPLA2 thus may represent a potential therapeutic target for the control of PPAR-related liver and metabolic disorders such as obesity, lipid metabolic disorders, diabetes mellitus, and atherosclerosis.
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