Enteropathogenic E. coli (EPEC) Transfers Its Receptor for Intimate Adherence into Mammalian Cells

Abstract

Enteropathogenic E. coli (EPEC) belongs to a group of bacterial pathogens that induce epithelial cell actin rearrangements resulting in pedestal formation beneath adherent bacteria. This requires the secretion of specific virulence proteins needed for signal transduction and intimate adherence. EPEC interaction induces tyrosine phosphorylation of a protein in the host membrane, Hp90, which is the receptor for the EPEC outer membrane protein, intimin. Hp90-intimin interaction is essential for intimate attachment and pedestal formation. Here, we demonstrate that Hp90 is actually a bacterial protein (Tir). Thus, this bacterial pathogen inserts its own receptor into mammalian cell surfaces, to which it then adheres to trigger additional host signaling events and actin nucleation. It is also tyrosine-phosphorylated upon transfer into the host cell.

Identification of the intimin-binding domain of Tir of enteropathogenic Escherichia coli

“…We have shown previously that puri®ed intimin binds denatured Tir in a gel-overlay assay (Kenny et al, 1997a). We have used this approach and the Tir truncated forms isolated from yeast to map the Tir domains that bind to intimin.…”

“…In the second step, there is effacement of the microvilli, and several signal transduction pathways are activated in the host cell, including release of IP3 and phosphorylation of proteins (Rosenshine et al, 1992;Foubister et al, 1994). During this stage, the bacteria translocate a protein called Tir (for translocated intimin receptor) to the mammalian cell membrane, where it acts as the receptor for EPEC's adhesion molecule intimin (Kenny et al, 1997a). Finally, the Tir±intimin interaction brings about the intimate attachment of the bacteria to the host cell and promotes other signal transduction events, such as tyrosine phosphorylation of phospholipase C gamma (Kenny and Finlay, 1997), signi®cant actin recruitment and pedestal formation.…”

“…Rosenshine et al (1996a) demonstrated by several methods that a fusion protein MBP/Int280 binds to a tyrosine-phosphorylated protein (Hp90) in epithelial cell surfaces in cells preinfected with an eae mutant. Later, Kenny et al (1997a) showed that Hp90 is the phosphorylated form of Tir, and that a His±T7Int280 fusion also binds to the unphosphorylated form of Tir secreted by EPEC (Rosenshine et al, 1996;Kenny et al, 1997a).…”

“…By focusing actin, Tir is proposed to act as a bridge connecting intimin to the host cytoskeleton. The mechanism of how EPEC inserts Tir into the eukaryotic membrane is unknown, but requires the Esp proteins and the type III secretion apparatus (Kenny et al, 1997a). The type III EPEC secreted proteins, EspA, EspB and EspD, are involved in signal transduction, A /E lesion formation and Tir delivery (Donnenberg et al, 1993b;Kenny et al, 1996;Lai et al, 1997).…”

Functional studies of intimin in vivo and ex vivo: implications for host specificity and tissue tropism

“…Indeed, when expressed as an N-terminal fusion with carrier proteins, Int280 binds directly to epithelial cells (Frankel et al , 1994) and interacts with nucleolin (Sinclair & O'Brien, 2004) and integrin (Frankel et al , 1996a). Int280 also binds the LEE-encoded effector protein Tir, which connects the extracellular bacterium to the host cell cytoskeleton (Kenny et al , 1997). …”