Identification of cell surface-exposed proteins involved in the fimbria-mediated adherence of enteroaggregative Escherichia coli to intestinal cells.

Fimbria-mediated adherence to the intestinal epithelia is a key step in enteroaggregative Escherichia coli (EAEC) pathogenesis. To date, four fimbriae have been described for EAEC; aggregative adherence fimbria II (AAF/II) is the most important adherence factor for EAEC prototype strain 042. Previously, we described results showing that extracellular matrix (ECM) components might be involved in the recognition of AAF/II fimbriae by intestinal cells. In this study, we sought to identify novel potential receptors on intestinal epithelial cells recognized by the AAF/II fimbriae. Purified AafA-dsc protein, the major subunit of AAF/II fimbriae, was incubated with a monolayer of T84 cells, cross-linked to the surface-exposed T84 cell proteins, and immunoprecipitated by using anti-AafA antibodies. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of cellular proteins bound to AafA-dsc protein identified laminin (previously recognized as a potential receptor for AAF/II) and cytokeratin 8 (CK8). Involvement of the major subunit of AAF/II fimbriae (AafA protein) in the binding to recombinant CK8 was confirmed by adherence assays with purified AAF/II fimbriae, AafA-dsc protein, and strain 042. Moreover, HEp-2 cells transfected with CK8 small interfering RNA (siRNA) showed reduced 042 adherence compared with cells transfected with scrambled siRNA as a control. Adherence of 042 to HEp-2 cells preincubated with antibodies against ECM proteins or CK8 was substantially reduced. Altogether, our results supported the idea of a role of CK8 as a potential receptor for EAEC.