Abstract
Group IIa phospholipase A(2) (GIIa PLA(2)) is released by some cells in response to interleukin-1beta. The purpose of this study was to determine whether interleukin-1beta would stimulate the synthesis and release of GIIa PLA(2) from cardiomyocytes, and to define the role of p38 MAPK and cytosolic PLA(2) in the regulation of this process. Whereas GIIa PLA(2) mRNA was not identified in untreated cells, exposure to interleukin-1beta resulted in the sustained expression of GIIa PLA(2) mRNA. Interleukin-1beta also stimulated a progressive increase in cellular and extracellular GIIa PLA(2) protein levels and increased extracellular PLA(2) activity 70-fold. In addition, interleukin-1beta stimulated the p38 MAPK-dependent activation of the downstream MAPK-activated protein kinase, MAPKAP-K2. Treatment with the p38 MAPK inhibitor, SB202190, decreased interleukin-1beta stimulated MAPKAP-K2 activity, GIIa PLA(2) mRNA expression, GIIa PLA(2) protein synthesis, and the release of extracellular PLA(2) activity. Infection with an adenovirus encoding a constitutively active form of MKK6, MKK6(Glu), which selectively phosphorylates p38 MAPK, induced cellular GIIa PLA(2) protein synthesis and the release of GIIa PLA(2) and increased extracellular PLA(2) activity 3-fold. In contrast, infection with an adenovirus encoding a phosphorylation-resistant MKK6, MKK6(A), did not result in GIIa PLA(2) protein synthesis or release by unstimulated cardiomyocytes. In addition, infection with an adenovirus encoding MKK6(A) abrogated GIIa PLA(2) protein synthesis and release by interleukin-1beta-stimulated cells. These results provide direct evidence that p38 MAPK activation was necessary for interleukin-1beta-induced synthesis and release of GIIa PLA(2) by cardiomyocytes.
Highlights
Interleukin-1 (IL-1)1 has been implicated in the pathophysiology of a variety of myocardial disease states, including cardiac hypertrophy, congestive heart failure, and ischemiareperfusion injury [1,2,3]
We show that IL-1 induced GIIa phospholipase A2 (PLA2) gene expression by cardiomyocytes and that p38 MAPK activation was necessary for IL-1-induced synthesis and release of GIIa PLA2 by these cells
To determine whether IL-1 induced GIIa PLA2 protein synthesis and release by cardiomyocytes, cells were treated with IL-1, and cellular lysates and the extracellular fluid were evaluated by western blot analysis
Summary
Interleukin-1 (IL-1) has been implicated in the pathophysiology of a variety of myocardial disease states, including cardiac hypertrophy, congestive heart failure, and ischemiareperfusion injury [1,2,3]. P38 MAPK activity is increased by phosphorylation on a Thr-Gly-Tyr motif by MAPK kinases, including MKK3 and MKK6 [10, 11]. MKK6 forms a functional complex with p38 MAPK that is dependent on both the presence of a docking site in the N terminus of the MAPK kinase and the selective recognition of an activation (T-loop) of the individual p38 MAPK isoforms [7], and leads to the phosphorylation and activation of p38 MAPK. Mutation of Ser-207 and Thr-211 to Glu had the same effect as phosphorylation of these amino acids and resulted in a constitutively active form of the enzyme, MKK6(Glu) [11]. MKK6(Glu) is a potent and selective activator of p38 MAPK that can be used to study the physiologic effects of myocardial p38 MAPK activation in vitro [7, 9, 13]. Studies have shown that the p38 MAPK-activated protein kinases MNK1, MSK1, and PRAK1 and the 42-kDa
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