Abstract 15718: IQGAP1 Interacts with PDGF Receptor and Focal Adhesion Signaling Proteins to Promote Vascular Migration and Neointimal Formation in Response to Vascular Injury
PDGF stimulates vascular smooth muscle cell (VSMC) migration and neointimal formation in response to injury primary through the PDGF receptor β (PDGFR). However, underlying molecular mechanisms are poorly understood. We previously identified IQGAP1 as a novel VEGFR-2 and Rac1 binding scaffold protein expressed in endothelial cell. However, its function in VSMC is unknown. Here we show that PDGF stimulation rapidly promotes IQGAP1 association with PDGFR within 5 min (2.1-fold) in cultured VSMC. Functional significance of IQGAP1 binding to PDGFR is demonstrated by showing that overexpression of IQGAP1 using adenovirus enhances PDGF-induced PDGFR autophosphorylation (1.6-fold), while IQGAP1 knockdown by siRNA inhibits this response (69%). Immunofluorescence and subcellular fractionation analysis reveals that p-PDGFR is found at both focal adhesions (FAs) and caveolae/lipid rafts (C/LR), but p-PDGFR at FAs, but not at C/LR, is inhibited by IQGAP1 siRNA. PDGF stimulation promotes recruitment of Rac1 (1.9-fold) and FAs signaling proteins such as paxillin, vinculin, and FAK (1.7-, 2.7-, 1.6-fold) to the IQGAP1/PDGFR complex. Functionally, IQGAP1 siRNA inhibits PDGF-induced Rac1 translocation and FAs formation at the leading edge as well as VSMC migration induced by PDGF (70%) or wound scratch (73%). Overexpression of IQGAP1 mutant lacking GRD domain, which blocks PDGF-induced Rac1 translocation, also inhibits FAs formation without affecting PDGFR autophosphorylation, thereby inhibiting VSMC migration, suggesting that IQGAP1/Rac1-dependent FA formation is involved in VSMC migration. In vivo, IQGAP1 expression is markedly increased at neointimal VSMC after wire-induced femoral artery injury in wild type (WT) mice. Neointimal formation at day 21 after vascular injury is significantly inhibited in mice lacking IQGAP1 (I/M ratio: 57%) as compared to WT. In summary, IQGAP1, through interaction with PDGFR, Rac1, and components of FAs, promotes activation of PDGFR in FAs as well as Rac1 translocation and FA formation, which may contribute to neointimal formation after vascular injury. Our results will provide new insight into IQGAP1 as a potential therapeutic target for the crucially important events in VSMC migration-related vascular diseases.
- © 2012 by American Heart Association, Inc.