Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a clinically important bacterial enteropathogen that manipulates a variety of host cell signal transduction cascades to establish infection. However, the effect of EHEC O157:H7 on Jak/Stat signaling is unknown. To define the effect of EHEC infection on epithelial gamma interferon (IFN-␥)-Stat1 signaling, human T84 and HEp-2 epithelial cells were infected with EHEC O157:H7 and then stimulated with recombinant human IFN-␥. Cells were also infected with different EHEC strains, heat-killed EHEC, enteropathogenic E. coli (EPEC) O127:H6, and the commensal strain E. coli HB101. Nuclear and whole-cell protein extracts were prepared and were assayed by an electrophoretic mobility shift assay (EMSA) and by Western blotting, respectively. Cells were also processed for immunofluorescence to detect the subcellular localization of Stat1. The EMSA revealed inducible, but not constitutive, Stat1 activation upon IFN-␥ treatment of both cell lines. The EMSA also showed that 6 h of EHEC O157:H7 infection, but not 30 min of EHEC O157:H7 infection, prevented subsequent Stat1 DNA binding induced by IFN-␥, whereas infection with EPEC did not.
Immunoblotting showed that infection with EHEC, but not infection with EPEC, eliminated IFN-␥-induced Stat1 tyrosine phosphorylation in both dose-and time-dependent fashions and disrupted inducible protein expression of the Stat1-dependent gene interferon regulatory factor 1. Immunofluorescence revealed that EHEC infection did not prevent nuclear accumulation of Stat1 after IFN-␥ treatment. Also, Stat1 tyrosine phosphorylation was suppressed by different EHEC isolates, including intimin-, type III secretion-and plasmid-deficient strains, but not by HB101 and heat-killed EHEC. These findings indicate the novel disruption of host cell signaling caused by EHEC infection but not by EPEC infection.Infection of humans with the bacterial enteropathogen enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 causes outbreaks of hemorrhagic colitis and hemolytic uremic syndrome; the latter is related to production of Shiga-like toxins (5) and is an important cause of acute kidney failure (5, 54). The related pathogen enteropathogenic E. coli (EPEC) is an important cause of prolonged watery diarrhea in infants in underdeveloped countries (5,11,51). Once ingested, these bacteria establish infection by manipulating host epithelial cell signal transduction cascades (5, 11, 51). For example, activation of phospholipase C␥, phosphoinositide 3-kinase, and 5-lipoxygenase (20) and mobilization of the second messengers inositol trisphosphate and calcium (6) are important for forming characteristic attaching and effacing lesions and rearrangements of the host cell cytoskeleton. However, these bacteria disrupt intestinal epithelial barrier function by manipulation of differential signal transduction cascades; EHEC does this via protein kinase C and the myosin light-chain kinase (38), and EPEC does it via a myosin light-chain kinase-dependent, protein kinase C-in...
