Enterohaemorrhagic and enteropathogenic Escherichia coli use different mechanisms for actin pedestal formation that converge on N-WASP.

Enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC), two closely related diarrhoeagenic pathogens, induce actin rearrangements at the surface of infected host cells resulting in the formation of pseudopod-like structures termed pedestals beneath intimately attached bacteria. We have shown previously that N-WASP, a key integrator of signalling pathways that regulate actin polymerization via the Arp2/3 complex, is essential for pedestal formation induced by EPEC using N-WASP-defective cell lines. Here we show that actin pedestal formation initiated by EHEC also depends on N-WASP. Amino acid residues 226-274 of N-WASP are both necessary and sufficient to target N-WASP to sites of EHEC attachment. The recruitment mechanism thus differs from that used by EPEC, in which amino-terminal sequences of N-WASP mediate recruitment. For EPEC, recruitment of N-WASP downstream of Nck has been postulated to be mediated by WIP. However, we find a direct interaction of N-WASP with WIP to be dispensable for EPEC-induced pedestal formation and present data supporting an F-actin-dependent localization of WIP to actin pedestals induced by both EPEC and EHEC. In summary, our data show that EPEC and EHEC use different mechanisms to recruit N-WASP, which is essential for actin pedestal formation induced by both pathogens.