Department of Physiology, University of Kentucky School of Medicine, Lexington, Kentucky 40536, USA.
J Biol Chem. 2011 Dec 30;286(52):44646-58. doi: 10.1074/jbc.M111.265462. Epub 2011 Nov 4.
Mice deficient in regulator of G-protein signaling-2 (RGS2) have severe hypertension, and RGS2 genetic variations occur in hypertensive humans. A potentially important negative feedback loop in blood pressure homeostasis is that angiotensin II (Ang II) increases vascular smooth muscle cell (VSMC) RGS2 expression. We reported that Group VIA phospholipase A(2) (iPLA(2)β) is required for this response (Xie, Z., Gong, M. C., Su, W., Turk, J., and Guo, Z. (2007) J. Biol. Chem. 282, 25278-25289), but the specific molecular causes and consequences of iPLA(2)β activation are not known. Here we demonstrate that both protein kinases C (PKC) and A (PKA) participate in Ang II-induced VSMC RGS2 mRNA up-regulation, and that actions of PKC and PKA precede and follow iPLA(2)β activation, respectively. Moreover, we identified a conserved cAMP-response element (CRE) in the murine RGS2 promoter that is critical for cAMP-response element-binding protein (CREB) binding and RGS2 promoter activation. Forskolin-stimulated RGS2 mRNA up-regulation is inhibited by CREB sequestration or specific disruption of the CREB-RGS2 promoter interaction, and Ang II-induced CREB phosphorylation and nuclear localization are blocked by iPLA(2)β pharmacologic inhibition or genetic ablation. Ang II-induced intracellular cyclic AMP accumulation precedes CREB phosphorylation and is diminished by inhibiting iPLA(2), cyclooxygenase, or lipoxygenase. Moreover, three single nucleotide polymorphisms identified in hypertensive patients are located in the human RGS2 promoter CREB binding site. Point mutations corresponding to these single nucleotide polymorphisms interfere with stimulation of human RGS2 promoter activity by forskolin. Our studies thus delineate a negative feedback loop to attenuate Ang II signaling in VSMC with potential importance in blood pressure homeostasis and the pathogenesis of human essential hypertension.
RGS2 缺乏的老鼠有严重的高血压，高血压患者中也存在 RGS2 的遗传变异。血压稳态中一个潜在的重要负反馈回路是血管平滑肌细胞（VSMC）中血管紧张素 II（Ang II）增加 RGS2 的表达。我们曾报道过 Group VIA 磷脂酶 A2（iPLA2β）在这一反应中是必需的（Xie, Z., Gong, M. C., Su, W., Turk, J., and Guo, Z. (2007) J. Biol. Chem. 282, 25278-25289），但 iPLA2β 激活的具体分子原因和后果尚不清楚。在这里，我们证明蛋白激酶 C（PKC）和 A（PKA）都参与了 Ang II 诱导的 VSMC RGS2 mRNA 的上调，PKC 和 PKA 的作用分别发生在 iPLA2β 激活之前和之后。此外，我们在鼠 RGS2 启动子中鉴定了一个保守的 cAMP 反应元件（CRE），该元件对于 cAMP 反应元件结合蛋白（CREB）的结合和 RGS2 启动子的激活至关重要。Forskolin 刺激的 RGS2 mRNA 上调被 CREB 隔离或特异性破坏 CREB-RGS2 启动子相互作用所抑制，Ang II 诱导的 CREB 磷酸化和核定位被 iPLA2β 药理抑制或基因缺失所阻断。Ang II 诱导的细胞内 cAMP 积累先于 CREB 磷酸化，并因抑制 iPLA2、环氧化酶或脂氧合酶而减少。此外，在高血压患者中鉴定的三个单核苷酸多态性位于人类 RGS2 启动子 CREB 结合位点。与这些单核苷酸多态性相对应的点突变干扰了 forskolin对人 RGS2 启动子活性的刺激。我们的研究因此描绘了一个负反馈回路，以减弱 VSMC 中的 Ang II 信号，这在血压稳态和人类原发性高血压的发病机制中具有潜在的重要性。
