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 A 2 (iPLA 2 ␤) 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 iPLA 2 ␤ expression with antisense oligonucleotides, and genetic deletion in iPLA 2 ␤-null mice. Selective inhibition of iPLA 2 ␤ 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 2 ␤-expression in iPLA 2 ␤-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 2 ␤-null VSMC, Ang II stimulates iPLA 2 enzymatic activity significantly. Both arachidonic acid and lysophosphatidylcholine, products of iPLA 2 ␤ 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/iPLA 2 ␤/RGS2 feedback pathway in iPLA 2 ␤-null cells potentiates Ang II-induced vasodilator-stimulated phosphoprotein and Akt phosphorylation in a time-dependent manner. Collectively, our results demonstrate that iPLA 2 ␤ participates in Ang II-induced transcriptional up-regulation of RGS2 in VSMC.

Identification of a cAMP-response Element in the Regulator of G-protein Signaling-2 (RGS2) Promoter as a Key Cis-regulatory Element for RGS2 Transcriptional Regulation by Angiotensin II in Cultured Vascular Smooth Muscles

“…In addition, we demonstrated that expressing iPLA 2 ␤ by adenovirus-mediated gene transfer in iPLA 2 ␤-null VSMC restored the ability of Ang II to increase RGS2 mRNA expression in a concentration-dependent manner (16).…”

“…The sequences of rat iPLA 2 ␤ antisense and sense oligodeoxynucleotides were previously described (16). The sequences of cAMP regulatory element (CRE)-decoy and mismatch controls were described by Park et al (23).…”

“…Increased expression of VSMC RGS2 mRNA by Ang II results in increased levels of RGS2 protein (16,18) and results in negative regulations of Ang II signaling (16,18). That these in vitro observations have physiologic significance is suggested by in vivo studies that indicate that Rgs2-null mice are more sensitive to Ang II-induced hypertension than their WT littermates (7).…”

“…2-lysophosphatidylcholine, LPC). Both AA and LPC have intrinsic second messenger activities and are also precursors of bioactive metabolites that include eicosanoids and platelet activating factor, inter alia (19), and among the pleiotropic effects of these mediators are gene transcriptional regulatory activities (16,20,21). The iPLA 2 ␤ resides predominantly in the cytosol of resting cells, associates with membranes upon activation, does not require Ca 2ϩ for catalytic activity, and is inhibited by the compound bromoenol lactone (BEL) at concentrations that have little effect on members of the sPLA 2 or cPLA 2 families (22).…”

“…Recently, we demonstrated that iPLA 2 ␤ plays an essential role in Ang II-induced RGS2 mRNA up-regulation in VSMC (16), these studies involved pharmacologic inhibition of iPLA 2 ␤ activity with BEL, suppression of iPLA 2 ␤ expression with antisense oligodeoxynucleotides, and genetic deletion of iPLA 2 ␤ in mice by homologous recombination (16). In addition, we demonstrated that expressing iPLA 2 ␤ by adenovirus-mediated gene transfer in iPLA 2 ␤-null VSMC restored the ability of Ang II to increase RGS2 mRNA expression in a concentration-dependent manner (16).…”