RGS proteins share a 120-amino acid residue sequence homology domain (RGS domain) that directly binds the activated α-sub-unit of heterotrimetic G-protein, stimulates its GTPase activity, and thereby attenuates G-protein signaling ( 1). Regulators of G protein signaling (RGS) 2 comprise a family of more than 25 diverse, multifunctional signaling proteins.

Collectively, our results demonstrate that iPLA 2 β participates in Ang II-induced transcriptional up-regulation of RGS2 in VSMC. Disruption of the Ang II/iPLA 2 β/RGS2 feedback pathway in iPLA 2 β-null cells potentiates Ang II-induced vasodilator-stimulated phosphoprotein and Akt phosphorylation in a time-dependent manner. Moreover, RGS2 protein expression is also up-regulated by Ang II, and this is attenuated by bromoenol lactone. Inhibition of lipoxygenases, particularly 15-lipoxygenase, and cyclooxygenases, but not cytochrome P450-dependent epoxygenases inhibits Ang II- or AA-induced RGS2 mRNA expression. Both arachidonic acid and lysophosphatidylcholine, products of iPLA 2 β action, induce RGS2 mRNA up-regulation. Moreover, in wild-type but not iPLA 2 β-null VSMC, Ang II stimulates iPLA 2 enzymatic activity significantly. In contrast, Ang II-induced vasodilator-stimulated phosphoprotein phosphorylation and Ang II receptor expression are unaffected. Furthermore, using adenovirus-mediated gene transfer, we demonstrate that restoration of iPLA 2 β-expression in iPLA 2 β-null VSMC reconstitutes the ability of Ang II to up-regulate RGS2 mRNA expression. Selective inhibition of iPLA 2 β by each of these approaches abolishes Ang II-induced RGS2 mRNA up-regulation. Here we demonstrate that group VIA phospholipase A 2 (iPLA 2β) 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 β expression with antisense oligo-nucleotides, and genetic deletion in iPLA 2 β-null mice. 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. Rgs2 (regulator of G-protein signaling-2)-deficient mice exhibit severe hypertension, and genetic variations of RGS2 occur in hypertensive patients.

Anti actin antibody western blot