Phospholipase A(2)-mediated activation of mitogen-activated protein kinase by angiotensin II

In renal proximal tubule epithelial cells, a membrane-associated phospholipase A(2) (PLA(2)) is a major signaling pathway linked to angiotensin II (Ang II) type 2 receptor (AT(2)). The current studies were designed to test the hypothesis that membrane-associated PLA(2)-induced release of arachidonic acid (AA) and/or its metabolites may serve as an upstream mediator of Ang II-induced mitogen-activated protein kinase (MAPK) activation. Ang II stimulated transient dose-dependent phosphorylation of MAPK with a maximum at 1 μM (10 min). Inhibition of PLA(2) by mepacrine diminished both AA release and MAPK phosphorylation, induced by Ang II. Furthermore, AA itself induced time- and dose-dependent phosphorylation of MAPK, supporting the importance of PLA(2) as a mediator of Ang II signaling. The effects of both Ang II and AA on MAPK phosphorylation were protein kinase C independent and abolished by the inhibitor of cytochrome P450 isoenzyme, ketoconazole. Moreover, 5,6-epoxyeicosatrienoic acid and 14,15-epoxyeicosatrienoic acid, the cytochrome P450-dependent metabolites of AA, significantly stimulated MAPK activity in renal proximal tubule epithelial cells. These observations document a mechanism of Ang II-induced MAPK phosphorylation, mediated by PLA(2)-dependent release of AA and cytochrome P450-dependent production of epoxy derivatives of AA.