The hallmarks of enteropathogenicEscherichia coli(EPEC) infection are formation of attaching and effacing (A/E) lesions on mucosal surfaces and actin-rich pedestals on cultured cells, both of which are dependent on the type III secretion system effector Tir. Following translocation into cultured cells and clustering by intimin, Tir Y474 is phosphorylated, leading to recruitment of Nck, activation of N-WASP, and actin polymerization via the Arp2/3 complex. A secondary, weak, actin polymerization pathway is triggered via an NPY motif (Y454). Importantly, Y454 and Y474 play no role in A/E lesion formation on mucosal surfaces following infection with the EPEC-like mouse pathogenCitrobacter rodentium. In this study, we investigated the roles of Tir segments located upstream of Y451 and downstream of Y471 inC. rodentiumcolonization and A/E lesion formation. We also tested the role that Tir residues Y451 and Y471 play in host immune responses toC. rodentiuminfection. We found that deletion of amino acids 382 to 462 or 478 to 547 had no impact on the ability of Tir to mediate A/E lesion formation, although deletion of amino acids 478 to 547 affected Tir translocation. Examination of enterocytes isolated from infected mice revealed that aC. rodentiumstrain expressing Tir_Y451A/Y471A recruited significantly fewer neutrophils to the colon and triggered less colonic hyperplasia on day 14 postinfection than the wild-type strain. Consistently, enterocytes isolated from mice infected withC. rodentiumexpressing Tir_Y451A/Y471A expressed significantly less CXCL1. These result show that Tir-induced actin remodeling plays a direct role in modulation of immune responses toC. rodentiuminfection.
Citrobacter amalonaticus Inhibits the Growth of Citrobacter rodentium in the Gut Lumen
