Li Fang, Malik Kafait U
Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Room 115, Crowe Building, 874 Union Avenue, Memphis, TN 38163, USA.
J Pharmacol Exp Ther. 2005 Mar;312(3):1043-54. doi: 10.1124/jpet.104.076588. Epub 2004 Nov 3.
Angiotensin II (Ang II) activates cytosolic Ca(2+)-dependent phospholipase A(2) (cPLA(2)), phospholipase D (PLD), p38 mitogen-activated protein kinase (MAPK), epidermal growth factor receptor (EGFR) and Akt in vascular smooth muscle cells (VSMC). This study was conducted to investigate the relationship between Akt activation by Ang II and other signaling molecules in rat VSMC. Ang II-induced Akt phosphorylation was significantly reduced by the PLD inhibitor 1-butanol, but not by its inactive analog 2-butanol, and by brefeldin A, an inhibitor of the PLD cofactor ADP-ribosylation factor, and in cells infected with retrovirus containing PLD(2) siRNA or transfected with PLD(2) antisense but not control LacZ or sense oligonucleotide. Diacylglycerol kinase inhibitor II diminished Ang II-induced and diC8-phosphatidic acid (PA)-increased Akt phosphorylation, suggesting that PLD-dependent Akt activation is mediated by PA. Ang II-induced EGFR phosphorylation was inhibited by 1-butanol and PLD(2) siRNA and also by cPLA(2) siRNA. In addition, the inhibitor of arachidonic acid (AA) metabolism 5,8,11,14-eicosatetraynoic acid (ETYA) reduced both Ang II- and AA-induced EGFR transactivation. Furthermore, ETYA, cPLA(2) antisense, and cPLA(2) siRNA attenuated Ang II-elicited PLD activation. p38 MAPK inhibitor SB202190 [4-(4-flurophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] reduced PLD activity and EGFR and Akt phosphorylation elicited by Ang II. Pyrrolidine-1, a cPLA(2) inhibitor, and cPLA(2) siRNA decreased p38 MAPK activity. These data indicate that Ang II-stimulated Akt activity is mediated by cPLA(2)-dependent, p38 MAPK regulated PLD(2) activation and EGFR transactivation. We propose the following scheme of the sequence of events leading to activation of Akt in VSMC by Ang II: Ang II-->cPLA(2)-->AA-->p38 MAPK-->PLD(2)-->PA-->EGFR-->Akt.
血管紧张素 II（Ang II）可激活血管平滑肌细胞（VSMC）中的胞质钙依赖性磷脂酶 A2（cPLA2）、磷脂酶 D（PLD）、p38 丝裂原活化蛋白激酶（MAPK）、表皮生长因子受体（EGFR）和 Akt。本研究旨在探讨 Ang II 激活 Akt 与大鼠 VSMC 中其他信号分子之间的关系。PLD 抑制剂 1-丁醇可显著降低 Ang II 诱导的 Akt 磷酸化，但其无活性类似物 2-丁醇则无此作用；布雷菲德菌素 A（一种 PLD 辅因子 ADP-核糖基化因子的抑制剂）以及感染含 PLD2 siRNA 的逆转录病毒或转染 PLD2 反义寡核苷酸而非对照 LacZ 或正义寡核苷酸的细胞中，Ang II 诱导的 Akt 磷酸化也显著降低。二酰甘油激酶抑制剂 II 可减少 Ang II 诱导的以及二 C8-磷脂酸（PA）增加的 Akt 磷酸化，这表明 PLD 依赖性 Akt 激活是由 PA 介导的。1-丁醇和 PLD2 siRNA 以及 cPLA2 siRNA 均可抑制 Ang II 诱导的 EGFR 磷酸化。此外，花生四烯酸（AA）代谢抑制剂 5,8,11,14-二十碳四烯酸（ETYA）可降低 Ang II 和 AA 诱导的 EGFR 反式激活。此外，ETYA、cPLA2 反义寡核苷酸和 cPLA2 siRNA 均可减弱 Ang II 引发的 PLD 激活。p38 MAPK 抑制剂 SB202190 [4-(4-氟苯基)-2-(4-羟基苯基)-5-(4-吡啶基)1H-咪唑] 可降低 Ang II 引发的 PLD 活性以及 EGFR 和 Akt 磷酸化。cPLA2 抑制剂吡咯烷-1 和 cPLA2 siRNA 可降低 p38 MAPK 活性。这些数据表明，Ang II 刺激的 Akt 活性是由 cPLA2 依赖性、p38 MAPK 调节的 PLD2 激活和 EGFR 反式激活介导的。我们提出以下 Ang II 在 VSMC 中激活 Akt 的事件序列方案：Ang II→cPLA2→AA→p38 MAPK→PLD2→PA→EGFR→Akt。
