Plays a crucial role in regulating the dynamics and assembly of the actin cytoskeleton. Binds to activated CDC42 but does not stimulate its GTPase activity (PubMed:16968698). It associates with calmodulin. Could serve as an assembly scaffold for the organization of a multimolecular complex that would interface incoming signals to the reorganization of the actin cytoskeleton at the plasma membrane. May promote neurite outgrowth. May play a possible role in cell cycle regulation by contributing to cell cycle progression after DNA replication arrest. Interacts with CDC42; the interaction is demonstrated with IQGAP1 in GTP-bound and in nucleotide-free state (PubMed:16968698). Interacts with RAC1 (By similarity). Does not interact with RHOA (By similarity). Interacts with TSG101 (By similarity). Interacts with PAK6 (By similarity). Interacts with SASH1 (By similarity). Interacts with PJVK (PubMed:28089576). (Microbial infection) In case of infection, interacts with S.typhimurium protein sseI (PubMed:19956712). Subcellular distribution is regulated by the cell cycle, nuclear levels increase at G1/S phase (PubMed:20883816). Expressed widely in developing cortex. Regions C1 and C2 can either interact with nucleotide-free CDC42, or interact together.