The bacterial pathogens Listeria monocytogenes and enteropathogenic Escherichia coli (EPEC) generate motile actin-rich structures (comet tails and pedestals) as part of their infectious processes. Nexilin, an actin-associated protein and a component of focal adhesions, has been suggested to be involved in actin-based motility. To determine whether nexilin is commandeered during L. monocytogenes and EPEC infections, we infected cultured cells and found that nexilin is crucial for L. monocytogenes invasion as levels of internalized bacteria were significantly decreased in nexilin-targeted siRNA-treated cells. In addition, nexilin is a component of the machinery that drives the formation of L. monocytogenes comet tails and EPEC pedestals. Nexilin colocalizes with stationary bacteria and accumulates at the distal portion of comet tails and pedestals of motile bacteria. We also show that nexilin is crucial for efficient comet tail formation as cells pre-treated with nexilin siRNA generate malformed comet tails, whereas nexilin is dispensable during EPEC pedestal generation. These findings demonstrate that nexilin is required for efficient infection with invasive and adherent bacteria and is key to the actin-rich structures these microbes generate.
[Show abstract][Hide abstract] ABSTRACT: Enteropathogenic Escherichia coli (EPEC) interactions with HeLa epithelial cells induced the tyrosine phosphorylation of a host protein of approximately 150 kDa, Hp150. Phosphorylation of this protein band was dependent on the interaction of the EPEC protein intimin with epithelial cell surfaces and was correlated with pedestal formation. Hp150 phosphorylation was specifically inhibited by the addition of cytochalasin D, an inhibitor of actin polymerization, although this appeared to be an indirect effect preventing interaction of intimin with its receptor, tyrosine-phosphorylated Hp90, and thus triggering Hp150 phosphorylation. This suggests the involvement of an actin-based movement of membrane-bound tyrosine-phosphorylated Hp90 to allow its interaction with intimin. Analysis of the tyrosine-phosphorylated Hp150 protein demonstrated that it is heterogeneous in composition, with phospholipase C-gamma1 (PLC-gamma1) being a minor component. Activation of PLC-gamma1 by tyrosine phosphorylation leads to inositol triphosphate and Ca2+ fluxes, events detected following EPEC infection. EPEC also induced tyrosine dephosphorylation of host proteins, including a 240-kDa host protein (Hp240), following EPEC infection. Protein dephosphorylation appears to be a signaling event which occurs independently of intimin. Inhibition of host tyrosine dephosphorylation events by the addition of the tyrosine phosphatase inhibitor sodium vanadate did not prevent actin accumulation beneath the adherent bacteria. We conclude that EPEC induces two sets of signaling events following infection. One set is dependent on EPEC proteins secreted by the type III secretion pathway (EspA and EspB) which induces Hp90 tyrosine phosphorylation and dephosphorylation of host phosphotyrosine proteins. The second set, which is also dependent on the first signaling events, requires intimin interaction with its receptor, tyrosine-phosphorylated Hp90, to trigger Hp150 and PLC-gamma1 tyrosine phosphorylation as well as pedestal formation. Inhibition of pedestal formation by tyrosine kinase inhibitors indicates an important role for tyrosine phosphorylation events during EPEC subversion of host processes.
Infection and Immunity 08/1997; 65(7):2528-36. · 3.73 Impact Factor
[Show abstract][Hide abstract] 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.
Infection and Immunity 06/2001; 69(5):3315-22. DOI:10.1128/IAI.69.5.3315-3322.2001 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacterial toxins and effector proteins hijack eukaryotic enzymes that are spatially localized and display rapid signaling kinetics. However, the molecular mechanisms by which virulence factors engage highly dynamic substrates in the host cell environment are poorly understood. Here, we demonstrate that the enteropathogenic Escherichia coli (EPEC) type III effector protein EspF nucleates a multiprotein signaling complex composed of eukaryotic sorting nexin 9 (SNX9) and neuronal Wiskott-Aldrich syndrome protein (N-WASP). We demonstrate that a specific and high affinity association between EspF and SNX9 induces membrane remodeling in host cells. These membrane-remodeling events are directly coupled to N-WASP/Arp2/3-mediated actin nucleation. In addition to providing a biochemical mechanism of EspF function, we find that EspF dynamically localizes to membrane-trafficking organelles in a spatiotemporal pattern that correlates with SNX9 and N-WASP activity in living cells. Thus, our findings suggest that the EspF-dependent assembly of SNX9 and N-WASP represents a novel form of signaling mimicry used to promote EPEC pathogenesis and gastrointestinal disease.
The Journal of Cell Biology 10/2007; 178(7):1265-78. DOI:10.1083/jcb.200705021 · 9.83 Impact Factor
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