Recruitment of Cytoskeletal and Signaling Proteins to Enteropathogenic and Enterohemorrhagic Escherichia coli Pedestals

Abstract

Enteropathogenic Escherichia coli (EPEC) is a human pathogen that attaches to intestinal epithelial cells and causes chronic watery diarrhea. A close relative, enterohemorrhagic E. coli (EHEC), causes severe bloody diarrhea and hemolytic-uremic syndrome. Both pathogens insert a protein, Tir, into the host cell plasma membrane where it binds intimin, the outer membrane ligand of EPEC and EHEC. This interaction triggers a cascade of signaling events within the host cell and ultimately leads to the formation of an actin-rich pedestal upon which the pathogen resides. Pedestal formation is critical in mediating EPEC- and EHEC-induced diarrhea, yet very little is known about its composition and organization. In EPEC, pedestal formation requires Tir tyrosine 474 phosphorylation. In EHEC Tir is not tyrosine phosphorylated, yet the pedestals appear similar. The composition of the EPEC and EHEC pedestals was analyzed by examining numerous cytoskeletal, signaling, and adapter proteins. Of the 25 proteins examined, only two, calpactin and CD44, were recruited to the site of bacterial attachment independently of Tir. Several others, including ezrin, talin, gelsolin, and tropomyosin, were recruited to the site of EPEC attachment independently of Tir tyrosine 474 phosphorylation but required Tir in the host membrane. The remaining proteins were recruited to the pedestal in a manner dependent on Tir tyrosine phosphorylation or were not recruited at all. Differences were also found between the EPEC and EHEC pedestals: the adapter proteins Grb2 and CrkII were recruited to the EPEC pedestal but were absent in the EHEC pedestal. These results demonstrate that although EPEC and EHEC recruit similar cytoskeletal proteins, there are also significant differences in pedestal composition.