Abstract
Cell migration requires precise spatial and temporal control of the actin cytoskeleton, which is regulatedby multiple actin binding proteins. Recent work has revealed adenomatous polyposis coli (APC) is apotent actin nucleator in vitro and works collaboratively with formins to assemble actin filaments by a‘Rocket Launcher’ mechanism (Breitsprecher et al., 2012). Further, it was found that APC‐mediated actinnucleation occurs at focal adhesions, where it is critical for microtubule‐induce focal adhesion turnoverand directed cell migration (Juanes et al, 2017). These and other observations suggest that APC, formins,and other key binding partners such as CLIP‐170 may work in concert to control actin assemblyunderlying cell migration. Here, we have investigated how IQGAP mechanistically influences actinassembly, alone and together with APC, formins, and CLIP‐170. IQGAP is a multi‐domain scaffoldingprotein that bundles F‐actin, caps barbed ends, and binds directly to APC, the formin Dia1, and CLIP‐170.Using TIRF microscopy, we have begun defining the effects of full‐length IQGAP on actin assemblydynamics, alone and in the presence of these other factors. Our preliminary in vitro observationssuggest that IQGAP attenuates actin assembly by APC and Dia1, and consistent with these effects, RNAisilencing of IQGAP in HeLa cells led to excessive actin accumulation at the leading edge. Thus, IQGAPmay restrain unregulated actin assembly at the leading edge until specific signals are received, and inthis manner spatially and temporally control cell migration.