Abstract 1171: IQGAP1 Promotes ROS-dependent PDGF Receptor Signaling From Caveolae/lipid rafts to Focal Adhesions: Role in Vascular Migration
Platelet-derived growth factor (PDGF) promotes vascular migration and neointima formation in response to injury primary through the PDGF receptor beta (PDGFR). This effect is dependent upon both the caveolae/lipid rafts (C/LR) and the reactive oxygen species (ROS) derived from Rac1-dependent NADPH oxidase in vascular smooth muscle cells (VSMCs). Underlying molecular mechanisms are poorly understood. We previously identified IQGAP1 as a novel VEGFR2 binding protein expressed in endothelial cells. IQGAP1 regulates cellular motility by interacting with actin and active Rac1; however, its role in VSMC is unknown. Here we show that IQGAP1 is robustly expressed in VSMCs and that it is upregulated (4.1 fold) at 12hr after PDGF stimulation. IQGAP1 binds to PDGFR basally and PDGF stimulation promotes their association within 15 min. Overexpression of IQGAP1 using adenovirus (Ad.IQGAP1) significantly enhances PDGF-induced PDGFR autophosphorylation (2.0-fold) and downstream activation of phospholipase Cγ (3.0-fold), Rac1 activation (1.5-fold) and ROS production (1.5-fold) without affecting ERK1/2 phosphorylation. Detergent-free cell fractionation demonstrates that both PDGFR and IQGAP1 are present in C/LR and associate with caveolin-1 in the basal state. Dissociation of PDGFR from caveolae/caveolin-1 is essential step for PDGFR tyrosine phosphorylation-mediated signaling. Ad.IQGAP1 promotes the egress of PDGFR out of C/LR after PDGF stimulation (46% reduction), which is cotemporaneous with formation of pY14-Cav1 and p-PDGFR and their colocalization at focal adhesions. Overexpression of IQGAP1 increases PDGF-stimulated VSMC migration, which is blocked by catalase, suggesting a role of H2O2 in this response. Of note, knockdown of endogenous IQGAP1 by siRNA inhibits PDGF-stimulated ROS production (80.1%) and VSMC migration (83.5%). Moreover, IQGAP1 expression is dramatically upregulated in the neointima lesion in wire-injured mice femoral artery. In summary, IQGAP1 promotes ROS-dependent PDGFR signaling from C/LR to focal adhesions, thereby stimulating VSMC migration, which may contribute to neointima formation and vascular remodeling in response to injury.