| Summary: | Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen that
causes acute and chronic diarrhea in a number of clinical settings. EAEC diarrhea
involves bacterial aggregation, adherence to intestinal epithelial cells and elaboration of
several toxigenic bacterial mediators. The molecular pathogenesis of EAEC diarrhea is
not understood completely. Flagellin (FliC-EAEC), a major bacterial surface protein of
EAEC, has been shown to induce IL-8 release from several epithelial cell lines. The aim
of this study is to elucidate the mechanisms of IL-8 secretion by FliC-EAEC in epithelial
cells lines.
Toll-like receptors (TLRs) have been described as important component of the
innate immune response in humans. It is known that host response to Gram-negative
flagellin is mediated by TLR5, which signals through NF-KB to induce transcription of
pro-inflammatory cytokines. Our results show that FliC-EAEC activates Akt (PKB) and
1-KB degradation (downstream targets of PI-3K) as observed in Western blots.
Experiments with pharmacological inhibitors and dominant negative PI-3K indicated that
PI-3K/Akt signaling is not necessary for FliC-EAEC induced IL-8 secretion.
p38 MAP kinase is one of a family of stress-related kinases that influence a
diverse range of cellular functions including inflammatory responses to microbial
products. To determine whether this enzyme mediates IL-8 release, a pharmacological
inhibitor of p38 MAP kinase, SB 203580, was used to inhibit FliC-EAEC induced IL-8
release. We found that IL-8 secretion is regulated by p38 MAP kinase, which undergoes
activation in Caco-2 and THP-1 cells, as determined by Western analysis.
Exposure of HEp-2 cells transiently expressing TLR5 resulted in p38 MAP kinase
dependent IL-8 secretion. Activation of IRAK was also observed in TLR5-transfected
HEp-2 cells after treatment with FliC-EAEC. These results suggest that FliC-EAECinduced
IL-8 secretion is regulated by p38 MAP kinase and involves TLR5 in epithelial
cells. === Medicine, Faculty of === Medicine, Department of === Experimental Medicine, Division of === Graduate
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