Fig. 4. Role of the IQGAP1-APC complex in cell polarization and migration. Directional cell migration is usually initiated in response to extracellular cues. Extracellular signals, including growth factors and chemokines, activate Rac1 and Cdc42 through their receptors and certain GEFs at leading edges. Activated Rac1 and Cdc42 induce the polymerization of actin filaments through their effectors. Activated Rac1 and Cdc42 also mark spots where IQGAP1 crosslinks actin filaments. There, APC is recruited through IQGAP1 to actin filaments. IQGAP1 captures the plus-ends of microtubules through CLIP-170. APC then directly and/or indirectly stabilizes microtubules, which are necessary for stable actin meshwork at leading edges.