Enteropathogenic E-coli translocated intimin receptor, Tir, interacts directly with alpha-actinin

Enteropathogenic Escherichia coli (EPEC) triggers a dramatic rearrangement of the host epithelial cell actin cytoskeleton to form an attaching and eff acing lesion, or pedestal. The pathogen remains attached extracellularly to the host cell through the pedestal for the duration of the infection. At t he tip of the pedestal is a bacterial protein, Tir, which is secreted from the bacterium into the host cell plasma membrane, where it functions as the receptor for an EPEC outer membrane protein, intimin [1]. Delivery of Tir to the host cell results in its tyrosine phosphorylation, followed by Tir-i ntimin binding. Tir is believed to anchor EPEC firmly to the host cell, alt hough its direct linkage to the cytoskeleton is unknown. Here, we show that Tir directly binds the cytoskeletal protein alpha-actinin. alpha-actinin i s recruited to the pedestal in a Tir-dependent manner and colocalizes with Tir in infected host cells. Binding is mediated through the amino terminus of Tir. Recruitment of alpha-actinin occurs independently of Tir tyrosine p hosphorylation. Recruitment of actin, VASP, and N-WASP, however, is abolish ed in the absence of this tyrosine phosphorylation. These results suggest t hat Tir plays at least three roles in the host cell during infection: bindi ng intimin on EPEC; mediating a stable anchor with alpha-actinin through it s amino terminus in a phosphotyrosine-independent manner; and recruiting ad ditional cytoskeletal proteins at the carboxyl terminus in a phosphotyrosin e-dependent manner. These findings demonstrate the first known direct linka ge between extracellular EPEC, through the transmembrane protein Tir, to th e host cell actin cytoskeleton via alpha-actinin. (C) 2000 Elsevier Science Ltd. All rights reserved.