Actin pedestal formation by enteropathogenic Escherichia coli and intracellular motility of Shigella flexneri are abolished in N-WASP-defective cells

In mammalian cells, actin dynamics is tightly controlled through small GTPa ses of the Rho family, WASP/Scar proteins and the Arp2/3 complex. We employ ed Cre/loxP-mediated gene targeting to disrupt the ubiquitously expressed N -WASP in the mouse germline, which led to embryonic lethality. To elucidate the role of N-WASP at the cellular level, we immortalized embryonic fibrob lasts and selected various N-WASP-defective cell lines. These fibroblasts s howed no apparent morphological alterations and were highly responsive to t he induction of filopodia, but failed to support the motility of Shigella f lexneri. In addition, entero pathogenic Escherichia coli were incapable of inducing the formation of actin pedestals in N-WASP-defective cells. Our re sults prove the essential role of this protein for actin cytoskeletal chang es induced by these bacterial pathogens in vivo and in addition show for th e first time that N-WASP is dispensible for filopodia formation.