Interleukin 1 alpha causes rapid activation of cytosolic phospholipase A2 by phosphorylation in rat mesangial cells.
We have shown previously that interleukin 1 (IL-1) stimulates eicosanoid production in glomerular mesangial cells (MC) by de novo synthesis of a 14-kD, group II phospholipase A2 (PLA2). IL-1-stimulated prostaglandin E2 synthesis precedes expression of this enzyme, suggesting that another PLA2 isoform must be more rapidly activated. In the presence but not absence of calcium inophore, [3H]arachidonate release is increased significantly as early as 5 min after addition of IL-1, and IL-1 concurrently stimulates a Ca(2+)-dependent phospholipase activity, which was characterized as the cytosolic form of PLA2 (cPLA2). IL-1 does not alter either cPLA2 mRNA expression or mass in serum-stimulated MC, suggesting that cPLA2 activity is increased by a posttranslational modification. IL-1 treatment for 30 min doubles 32P incorporation into immunoprecipitable cPLA2 protein, concordant with the increase in enzyme activity. Immunoblot analysis of extracts derived from IL-1-treated (30 min) cells demonstrates a decreased mobility of cPLA2, and treatment of MC lysates with acid phosphatase significantly reduces cytokine-activated cPLA2 activity, further indicating that IL-1 stimulates phosphorylation of the enzyme. IL-1 treatment (24 h) of serum-deprived MC doubled cPLA2 mRNA, protein, and activity. In summary, IL-1 increases cPLA2 activity in a biphasic, time-dependent manner both by posttranslational modification and de novo synthesis. We consider cPLA2 activation a key step in IL-1-stimulated synthesis of pro-inflammatory, lipid mediators, and an integral event in the phenotypic responses induced in target cells by this cytokine.
Gronich
J
J
Department of Medicine, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44109.
Konieczkowski
M
M
Gelb
M H
MH
Nemenoff
R A
RA
Sedor
J R
JR
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D005920:Glomerular Mesangium / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology*; D010741:Phospholipases A / Q000235:genetics / Q000378:metabolism*; D054467:Phospholipases A2; D010766:Phosphorylation; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats
D007375:Interleukin-1; D012333:RNA, Messenger; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2