IQGAP1 connects phosphoinositide signaling to cytoskeletal reorganization

Abstract

IQGAP1 is a multi-domain protein that acts as a scaffold for multiple signaling pathways. IQGAP1 generates the lipid messenger PI(3,4,5)P3 by scaffolding the phosphoinositide kinases PIPKIs and PI3K. The dynamics of this scaffolding protein complex in intact, living cells are unknown. Here, we delineate the role of IQGAP1 in PI(3,4,5)P3-mediated signaling in live cells under basal and stimulated conditions using fluorescence lifetime imaging microscopy. We demonstrate that IQGAP1 interacts strongly with PIPKI{gamma} at intracellular entities and on the plasma membrane, and scaffolds PI3K and PIPKI{gamma} in response to physiological changes. Additionally, we show that IQGAP1 scaffolds phosphoinositides with PI3K, PIPKI{gamma} and EGFR, and forms clusters upon cell stimulation with epidermal growth factor. Importantly, we show that IQGAP1 connects PI(3,4,5)P3-mediated signaling and cytoskeletal signaling pathways by binding PIPKI{gamma} in proximity of the cytoskeletal proteins talin and Cdc42. Our results support a model in which IQGAP1 mediates crosstalk between phosphoinositide signaling and the cytoskeleton to promote directed cell movement.