Abstract 13874: Protective Role of Scaffold Protein IQGAP1 in Angiotensin II-induced Endothelial Dysfunction Through Regulating Extracellular SOD Activity by Binding to Copper Transporter ATP7A
Angiotensin II (Ang II) increases reactive oxygen species, which are involved in vascular pathophysiologies and mediated through EGFR transactivation. IQGAP1, a scaffold protein, has been shown to bind and modulate EGFR function. Thus, we examined the role of IQGAP1 in Ang II-induced vascular function in vivo and in vitro. Here we show that chronic infusion of Ang II (14 days) caused impaired endothelium dependent vasorelaxation in IQGAP1 knockout (KO) mice to a greater extent than WT mice (44±1% vs 61±2%). This enhanced Ang II-induced endothelial dysfunction in IQGAP1 KO mice is associated with increased superoxide production (1.5 fold), and it is rescued by SOD mimetic tempol. Mechanistically, Ang II-induced increase in vascular specific activity of ecSOD, but not Cu/Zn SOD, is inhibited in IQGAP1 KO mice (75%). Given that Cu transporter ATP7A is essential for full activation of ecSOD activity, we next examined the role of IQGAP1 in ATP7A function using vascular smooth muscle cells. Co-immunoprecipitaion analysis revealed that Ang II promotes association of ATP7A with IQGAP1 that binds to EGFR. Furthermore, subcellular fractionation analysis show that Ang II promotes ATP7A translocation to the caveolin-enriched lipid raft (C/LR) where IQGAP1, EGFR and a small fraction of ecSOD are localized, which may be required for ecSOD to obtain Cu from ATP7A. Importance of novel IQGAP1 interaction with ATP7A is demonstrated by the result that depletion of IQGAP1 prevents ATP7A translocation to C/LR, which may contribute to decreased ecSOD activity in IQGAP1 KO mice. Of note, IQGAP1 siRNA has no effects on Ang II-induced EGFR tyrosine phosphorylation, while inhibition of EGFR transactivation by EGFR kinase inhibitor blocks Ang II-induced ecSOD activity. Moreover, functional significance of ecSOD localization at C/LR is shown by decreased vascular ecSOD activity in caveolin 1 KO mice. In summary, these results suggest that Ang II-EGFR-pY-IQGAP1-ATP7A-ecSOD axis and IQGAP1-mediated molecular assembly at C/LR may be required for the full activation of ecSOD in response to Ang II. This novel IQGAP1-mediated pathway contributes to preserving vascular function. Thus, IQGAP1 is a potential therapeutic target for oxidative stress-dependent cardiovascular diseases.
- © 2011 by American Heart Association, Inc.