Endocytic protein intersectin-I regulates actin assembly via Cdc42 and N-WASP

Intersectin-s is a modular scaffolding protein regulating the formation of clathrin-coated vesicles(1,2). In addition to the Eps15 homology (EH) and Src homology 3 (SH3) domains of intersectin-s, the neuronal variant (intersectin-I) also has Dbl homology (DH), pleckstrin homology (PH) and C2 domains(1,3-7). We now show that intersectin-I functions through its DH domain as a guanine nucleotide exchange factor (GEF) for Cdc42. In cultured cells, expression of DH-domain-containing constructs cause actin rearrangements specific for Cdc42 activation. Moreover, in vivo studies reveal that stimulation of Cdc42 by intersectin-I accelerates actin assembly via N-WASP and the Arp2/3 complex. N-WASP binds directly to intersectin-I and upregulates its GEF activity, thereby generating GTP-bound Cdc42, a critical activator of N-WASP. These studies reveal a role for intersectin-I in a novel mechanism of N-WASP activation and in regulation of the actin cytoskeleton.