Aging-Associated Vascular Disease Research Center, Department of Biochemistry & Molecular Biology, College of Medicine, Yeungnam University, Daegu, South Korea.
Mol Pharmacol. 2010 Sep;78(3):478-85. doi: 10.1124/mol.110.064394. Epub 2010 Jun 17.
Regulator of G protein signaling 2 (RGS2) is a GTPase-activating protein for Galpha(q), which is involved in regulating various vascular functions. To understand how RGS2 regulates foam cell formation, the present study identified signaling pathways controlled by lipopolysaccharide (LPS) and discovered new mechanisms whereby protein kinase C (PKC)-eta and phospholipase D (PLD) 2 regulate RGS2 expression. The toll-like receptor (TLR) 4 agonist LPS caused foam cell formation of Raw264.7 macrophages and dramatically decreased RGS2 mRNA expression. RGS2 down-regulation by LPS was partially recovered by TLR4 small interfering RNA (siRNA). Peritoneal macrophages were separated from wild-type and TLR4 mutant mice, and treatment with LPS showed RGS2 expression decrease in wild-type macrophages but no change in TLR4 mutant macrophages. RGS2 overexpression was suppressed, whereas RGS2 down-regulation accelerated foam cell formation by LPS. Treatment of PKC-eta pseudosubstrate weakened foam cell formation and recovered RGS2 down-regulation by LPS. In addition, LPS or phorbol 12-myristate 13-acetate stimulated PLD activity, and the pretreatment of PLD inhibitor weakened foam cell formation and recovered RGS2 down-regulation. Inhibition of PLD2 expression by siRNA also weakened foam cell formation and partially recovered LPS-mediated RGS2 down-regulation. On the other hand, PLD2 overexpression intensified RGS2 down-regulation and foam cell formation by LPS. These results suggest that LPS causes foam cell formation by increasing PKC-eta and PLD2 activity by down-regulating RGS2 expression via TLR4 dependently.
G 蛋白信号调节蛋白 2（RGS2）是 Galpha(q) 的 GTP 酶激活蛋白，参与调节各种血管功能。为了了解 RGS2 如何调节泡沫细胞形成，本研究鉴定了脂多糖（LPS）控制的信号通路，并发现了蛋白激酶 C（PKC）-eta 和磷脂酶 D（PLD）2 调节 RGS2 表达的新机制。TLR4 激动剂 LPS 导致 Raw264.7 巨噬细胞泡沫细胞形成，并显著降低 RGS2 mRNA 表达。LPS 引起的 RGS2 下调部分被 TLR4 小干扰 RNA（siRNA）恢复。从野生型和 TLR4 突变小鼠中分离出腹腔巨噬细胞，用 LPS 处理显示野生型巨噬细胞中 RGS2 表达减少，但 TLR4 突变巨噬细胞中没有变化。RGS2 过表达被抑制，而 RGS2 下调加速了 LPS 诱导的泡沫细胞形成。PKC-eta 假底物处理减弱了泡沫细胞形成，并恢复了 LPS 引起的 RGS2 下调。此外，LPS 或佛波醇 12-肉豆蔻酸 13-醋酸盐刺激 PLD 活性，PLD 抑制剂预处理减弱了泡沫细胞形成，并恢复了 LPS 引起的 RGS2 下调。siRNA 抑制 PLD2 表达也减弱了泡沫细胞形成，并部分恢复了 LPS 介导的 RGS2 下调。另一方面，PLD2 过表达增强了 LPS 引起的 RGS2 下调和泡沫细胞形成。这些结果表明，LPS 通过 TLR4 依赖性下调 RGS2 表达增加 PKC-eta 和 PLD2 活性，从而导致泡沫细胞形成。
