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)P 3 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)P 3 -mediated signaling in live cells under basal and stimulated conditions using fluorescence lifetime imaging microscopy. We demonstrate that IQGAP1 interacts strongly with PIPKIγ at intracellular entities and on the plasma membrane, and scaffolds PI3K and PIPKIγ in response to physiological changes. Additionally, we show that IQGAP1 scaffolds phosphoinositides with PI3K, PIPKIγ and EGFR, and forms clusters upon cell stimulation with epidermal growth factor. Importantly, we show that IQGAP1 connects PI(3,4,5)P 3 -mediated signaling and cytoskeletal signaling pathways by binding PIPKIγ 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. IQGAP1 connects PI signaling to cytoskeletal reorganization

IQGAP1 enhances EGFR signaling by Promoting Oligomerization and Preventing Degradation

“…IQGAP1 lacks catalytic activity (1), but serves as a scaffold for components of several signaling pathways (2) such as the PI3K/Akt pathway, where IQGAP1 binds PI(4, 5)P 2 and PI(3, 4, 5)P 3 , the phosphorylation kinases involved in their generation(i.e. PIPKI and PI3K), and signaling molecules downstream of PI3K such as Akt and PDK1 (3)(4)(5). IQGAP1 is also thought to modulate the epidermal growth factor (EGR) signaling pathway that mediates growth (6).…”