Involved in plasma membrane dynamics. Potentiated PDGF-mediated formation of membrane ruffles and lamellipodia in fibroblasts, acting via RAC1 activation. May function in actin bundling. Interacts (via IMD domain) with RAC1; this interaction may be important to potentiate PDGF-induced RAC1 activation. Colocalizes with RAC1 within membrane ruffles. Belongs to the MTSS family.