Group VIA phospholipase A2 (iPLA2β) participates in angiotensin II-induced transcriptional up-regulation of regulator of G-protein signaling-2 in vascular smooth muscle cells

Abstract

Rgs2 (regulator of G-protein signaling-2)-deficient mice exhibit severe hypertension, and genetic variations of RGS2 occur in hypertensive patients. RGS2 mRNA up-regulation by angiotensin II (Ang II) in vascular smooth muscle cells (VSMC) is a potentially important negative feedback mechanism in blood pressure homeostasis, but how it occurs is unknown. Here we demonstrate that group VIA phospholipase A2 (iPLA2β) plays a pivotal role in Ang II-induced RGS2 mRNA up-regulation in VSMC by three independent approaches, including pharmacologic inhibition with a bromoenol lactone suicide substrate, suppression of iPLA2β expression with antisense oligonucleotides, and genetic deletion in iPLA2β-null mice. Selective inhibition of iPLA2β by each of these approaches abolishes Ang II-induced RGS2 mRNA up-regulation. Furthermore, using adenovirus-mediated gene transfer, we demonstrate that restoration of iPLA 2β-expression in iPLA2β-null VSMC reconstitutes the ability of Ang II to up-regulate RGS2 mRNA expression. In contrast, Ang II-induced vasodilator-stimulated phosphoprotein phosphorylation and Ang II receptor expression are unaffected. Moreover, in wild-type but not iPLA 2β-null VSMC, Ang II stimulates iPLA2 enzymatic activity significantly. Both arachidonic acid and lysophosphatidylcholine, products of iPLA2β action, induce RGS2 mRNA up-regulation. Inhibition of lipoxygenases, particularly 15-lipoxygenase, and cyclooxygenases, but not cytochrome P450-dependent epoxygenases inhibits Ang II- or AA-induced RGS2 mRNA expression. Moreover, RGS2 protein expression is also up-regulated by Ang II, and this is attenuated by bromoenol lactone. Disruption of the Ang II/iPLA2β/RGS2 feedback pathway in iPLA2β-null cells potentiates Ang II-induced vasodilator-stimulated phosphoprotein and Akt phosphorylation in a time-dependent manner. Collectively, our results demonstrate that iPLA2β participates in Ang II-induced transcriptional up-regulation of RGS2 in VSMC. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.