Interleukin-1 beta- and forskolin-induced synthesis and secretion of group II phospholipase A2 and prostaglandin E2 in rat mesangial cells is prevented by transforming growth factor-beta 2.
Interleukin-1 beta and forskolin induce prostaglandin E2 release as well as 14-kDa group II phospholipase A2 gene expression and secretion of the enzyme from rat glomerular mesangial cells. We now report that pretreatment of mesangial cells with transforming growth factor-beta 2 prior to stimulation with interleukin-1 beta or forskolin inhibits the induced release of prostaglandin E2. At the same time the secretion of group II phospholipase A2, measured both as enzyme activity with sn-2-labeled phosphatidylethanolamine as substrate and as enzyme protein in immunoblot experiments, is dose-dependently inhibited by pretreatment of the cells with transforming growth factor-beta 2. Analyses of enzyme activity and enzyme protein levels in the cells indicated that this is not due to inhibition of enzyme secretion with a concomitant increase in cellular levels of the enzyme. Rather, pretreatment of the cells with transforming growth factor-beta 2 largely prevented both the interleukin-1 beta- and the forskolin-induced synthesis of phospholipase A2. This is the first report indicating an inhibition of group II phospholipase A2 gene expression by transforming growth factor-beta 2. In line with those results, transforming growth factor-beta 2 did not induce the synthesis and secretion of group II phospholipase A2. However, under conditions where the interleukin-1 beta-induced expression of group II phospholipase A2 is fully suppressed by transforming growth factor-beta 2, the growth factor itself stimulated prostaglandin E2 synthesis by a mechanism apparently not involving group II phospholipase A2. The immunochemical identification of the inducible and secretable phospholipase A2 from rat mesangial cells as a group II enzyme was confirmed by purification and N-terminal amino acid sequence determination.
Schalkwijk
C
C
Centre for Biomembranes and Lipid Enzymology, Utrecht, The Netherlands.
Pfeilschifter
J
J
Märki
F
F
van den Bosch
H
H
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002846:Chromatography, Affinity; D005576:Colforsin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004790:Enzyme Induction / Q000187:drug effects; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism*; D007375:Interleukin-1 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008969:Molecular Sequence Data; D010741:Phospholipases A / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D054467:Phospholipases A2; D051381:Rats; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D007375:Interleukin-1; D016212:Transforming Growth Factor beta; D005576:Colforsin; D010741:Phospholipases A; D054467:Phospholipases A2; D015232:Dinoprostone