Abstract 18886: IQGAP1, a Rac1 Binding Scaffold Protein, Interacts with Copper Transporter ATP7A: Role in ATP7A-mediated PDGF-induced VSMC Migration and Neointimal Formation
Platelet-derived growth factor (PDGF) stimulates vascular smooth muscle cell (VSMC) migration to promote neointimal formation and vascular remodeling. Its mechanism is dependent on actin cytoskeleton, Rac1 activation and translocation to the leading edge. We previously found that PDGF stimulates translocation of copper transporter ATP7A to the leading edge, thereby enhancing VSMC migration through recruitment of Rac1 and lamellipodia formation. Underlying mechanism is still unknown. IQGAP1 is a Rac1 and receptor tyrosine kinase binding scaffolding protein that controls cellular motility and morphogenesis. We thus investigated the role of IQGAP1 in ATP7A-mediated PDGF-induced VSMC migration and neointimal formation. Here we show that both IQGAP1 and ATP7A are expressed in cultured VSMCs and localized in caveolae/lipid rafts. PDGF stimulation promotes recruitment of ATP7A, IQGAP1 and Rac1 to caveolae/lipid rafts fraction, which is inhibited by IQGAP1 depletion. ATP7A associates with IQGAP1 and Rac1 basally and PDGF rapidly promotes ATP7A binding to IQGAP1 and Rac1 (1.94- and 1.95-fold increase, respectively) within 5 min. Co-transfection assay in CHO cells reveals that ATP7A directly binds to IQGAP1. Binding of ATP7A to Rac1 is prevented by knockdown of IQGAP1. Furthermore, in response to wound injury or PDGF stimulation, ATP7A translocates from trans-Golgi network to plasma membrane at the leading edge where it colocalizes with IQGAP1 in actively migrating VSMCs, which is prevented by IQGAP1 siRNA or caveolae/lipid rafts disruptor methyl-beta cyclodextrin. Functionally, PDGF-induced VSMC migration is significantly inhibited by knockdown of ATP7A or IQGAP1 with siRNAs (68% and 70%, respectively). In vivo, both ATP7A and IQGAP1 expression are dramatically increased and copper accumulation was observed by synchrotron-based X-ray fluorescence microscopy at neointimal VSMC in a mouse wire injury model, while ATP7A mutant mice and IQGAP1 knockout mice show reduced neointimal formation (I/M ratio: 70 % and 57% decrease). In summary, IQGAP1 functions as ATP7A and Rac1 binding scaffold protein to organize PDGF-dependent ATP7A translocation to the reading edge, thereby promoting VSMC migration and vascular remodeling.
- © 2010 by American Heart Association, Inc.