Fig. 8.

A model for the role of IQGAP1 in coordinating cell growth and division. IQGAP1 acts as conformational switch regulated by phosphorylation and protein-protein interaction and exists in an auto-inhibitory state in quiescent cells (Le Clainche et al., 2007). An intermediate form generated by binding of exocyst, CDC42 and N-WASP promotes migration in response to motility signals. During growth cycles, in response to nutrients, IQGAP1 operates in a closed form generated by folding of the C-terminus (Rittmeyer et al., 2008) and interaction with mTOR (and the exocyst) to promote cell growth. At a specific cell size, mitogenic signals lead to phosphorylation of IQGAP1, activating CDC42 and promoting cell division. Dynamic exchange between phosphorylated and dephosphorylated IQGAP1 coordinates growth and division to regulate cell proliferation.