Department of Pharmacology, Center for Lung and Vascular Biology, University of Illinois at Chicago, Chicago, Illinois;
Am J Physiol Cell Physiol. 2013 Sep 15;305(6):C591-600. doi: 10.1152/ajpcell.00011.2013. Epub 2013 May 8.
Platelet-derived growth factor (PDGF) stimulates vascular smooth muscle cell (VSMC) migration and neointimal formation in response to injury. We previously identified IQ-domain GTPase-activating protein 1 (IQGAP1) as a novel VEGF receptor 2 binding scaffold protein involved in endothelial migration. However, its role in VSMC migration and neointimal formation in vivo is unknown. Here we show that PDGF stimulation rapidly promotes IQGAP1 association with PDGF receptor-β (PDGFR) as well as IQGAP1 tyrosine phosphorylation in cultured VSMC. Overexpression or knockdown of IQGAP1 enhances or inhibits PDGFR autophosphorylation (p-PDGFR), respectively. Immunofluorescence and cell fractionation analysis reveals that PDGF-induced p-PDGFR localized in focal adhesions (FAs), but not caveolae/lipid rafts, is inhibited by IQGAP1 knockdown with siRNA. PDGF stimulation promotes IQGAP1 association with PDGFR/FA signaling protein complex. Functionally, IQGAP1 siRNA inhibits PDGF-induced FA formation as well as VSMC migration induced by PDGF. In vivo, IQGAP1 expression is markedly increased at neointimal VSMC in wire-injured femoral arteries. Mice lacking IQGAP1 exhibit impaired neointimal formation in response to vascular injury. In summary, IQGAP1, through interaction with PDGFR and FA signaling proteins, promotes activation of PDGFR in FAs as well as FA formation, which may contribute to VSMC migration and neointimal formation after injury. Our findings provide insight into IQGAP1 as a potential therapeutic target for vascular migration-related diseases.
血小板衍生生长因子 (PDGF) 可刺激血管平滑肌细胞 (VSMC) 迁移并形成新内膜，从而对损伤做出反应。我们之前发现 IQ 结构域 GTP 酶激活蛋白 1（IQGAP1）是一种新型的 VEGF 受体 2 结合支架蛋白，参与内皮细胞迁移。然而，其在体内 VSMC 迁移和新内膜形成中的作用尚不清楚。在这里，我们显示 PDGF 刺激可迅速促进 IQGAP1 与 PDGF 受体-β（PDGFR）的结合以及 IQGAP1 酪氨酸磷酸化在培养的 VSMC 中。IQGAP1 的过表达或敲低分别增强或抑制 PDGFR 自身磷酸化（p-PDGFR）。免疫荧光和细胞分级分析表明，PDGF 诱导的 p-PDGFR 定位于局灶黏附（FA），而不是 caveolae/脂筏，这一过程被 siRNA 敲低 IQGAP1 所抑制。PDGF 刺激促进 IQGAP1 与 PDGFR/FA 信号蛋白复合物的结合。功能上，IQGAP1 siRNA 抑制 PDGF 诱导的 FA 形成以及 PDGF 诱导的 VSMC 迁移。在体内，IQGAP1 在 wire 损伤的股动脉新生内膜中的 VSMC 中表达明显增加。缺乏 IQGAP1 的小鼠在血管损伤后表现出受损的新内膜形成。总之，IQGAP1 通过与 PDGFR 和 FA 信号蛋白相互作用，促进 PDGFR 在 FA 中的激活以及 FA 的形成，这可能有助于损伤后 VSMC 的迁移和新内膜的形成。我们的研究结果表明 IQGAP1 是一种潜在的血管迁移相关疾病的治疗靶点。
