RESEARCH ARTICLE Hypoxia Decreases Invasin-Mediated Yersinia enterocolitica Internalization into Caco-2

Yersinia enterocolitica is a major cause of human yersiniosis, with enterocolitis being a typi-cal manifestation. These bacteria can cross the intestinal mucosa, and invade eukaryotic cells by binding to host β1 integrins, a process mediated by the bacterial effector protein invasin. This study examines the role of hypoxia on the internalization of Y. enterocolitica into intestinal epithelial cells, since the gastrointestinal tract has been shown to be physio-logically deficient in oxygen levels (hypoxic), especially in cases of infection and inflamma-tion. We show that hypoxic pre-incubation of Caco-2 cells resulted in significantly decreased bacterial internalization compared to cells grown under normoxia. This pheno-type was absent after functionally blocking host β1 integrins as well as upon infection with an invasin-deficient Y. enterocolitica strain. Furthermore, downstream phosphorylation of the focal adhesion kinase was also reduced under hypoxia after infection. In good correla-tion to these data, cells grown under hypoxia showed decreased protein levels of β1 integ-rins at the apical cell surface whereas the total protein level of the hypoxia inducible factor (HIF-1) alpha was elevated. Furthermore, treatment of cells with the HIF-1 α stabilizer dimethyloxalylglycine (DMOG) also reduced invasion and decreased β1 integrin protein lev-els compared to control cells, indicating a potential role for HIF-1α in this process. These results suggest that hypoxia decreases invasin-integrin-mediated internalization of Y. enter-ocolitica into intestinal epithelial cells by reducing cell surface localization of host β1 integrins