Detergent-resistant microdomains mediate activation of host cell signaling in response to attaching–effacing bacteria

Abstract

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes outbreaks of bloody diarrhea and the hemolytic–uremic syndrome. EHEC intimately adheres to epithelial cells, effaces microvilli and induces attaching–effacing (AE) lesions. Detergent-resistant microdomains (lipid rafts) serve as membrane platforms for the recruitment of signaling complexes to mediate host responses to infection. The aim of this study was to define the role of lipid rafts in activating signal transduction pathways in response to AE bacterial pathogens. Epithelial cell monolayers were infected with EHEC (MOI 100:1, 3 h, 37°C) and lipid rafts isolated by buoyant density ultracentrifugation. Phosphoinositide 3-kinase (PI3K) localization to lipid rafts was confirmed using PI3K and anti-caveolin-1 antibodies. Mice with cholesterol storage disease Niemann–Pick, type C were used as in vivo models to confirm the role of lipid rafts in mediating signaling response to AE organisms. In contrast to uninfected cells, PI3K was recruited to lipid rafts in response to EHEC infection. Metabolically active bacteria and cells with intact cholesterol-rich microdomains were necessary for the recruitment of second messengers to lipid rafts. Recruitment of PI3K to lipid rafts was independent of the intimin (eaeA) gene, type III secretion system, and production of Shiga-like toxins. Colonization of NPC−/− colonic mucosa by Citrobacter rodentium and AE lesion formation were both delayed, compared with wild-type mice infected with the murine-specific AE bacterial pathogen. C. rodentium-infected NPC−/− mice had reduced colonic epithelial hyperplasia (64±8.251 vs 112±2.958 μm; P<0.05) and decreased secretion of IFN-γ (17.6±17.6 vs 71±26.3 pg/ml, P<0.001). Lipid rafts mediate host cell signal transduction responses to AE bacterial infections both in vitro and in vivo. These findings advance the current understanding of microbial–eukaryotic cell interactions in response to enteric pathogens that hijack signaling responses mediated through lipid rafts.