Escherichia coli O157:H7 Infection Down-regulates Host Autophagy in HT-29 Cells

Introduction: Escherichia coli O157:H7 is a major foodborne pathogen that causes life-threatening hemolytic–uremic syndrome (HUS) and even death. Autophagy is a pivotal catabolic process that degrades unnecessary proteins and intracellular organelles by activating autophagosomes. It also functions to trap invasive bacteria or virulence factors produced by pathogens for clearance. However, little is known about its roles of autophagosomes in E. coli O157:H7 epithelial infection.

Purpose: To explore the potential effect of E. coli O157:H7 infection on autophagy and apoptosis in host cells

Methods: HT-29 cells were cultured for 24 hours and sampled 4h post E. coli O157:H7 infection and then conducted with immuno-blotting and immunofluorescent staining assays.

Results: Both Western blotting and immunofluorescent staining showed a significant decrease of LC3B (P ≤ 0.05), an autophagic marker, in infected cells as compared to uninfected cells. Because JNK regulates autophagy via Bcl-2 phosphorylation, JNK phosphorylation was further examined and found to be decreased in infected cells (P ≤ 0.05). These data showed the down-regulation of autophagy in infected cells. Consistently, tumor necrosis factor (TNF)-α, a potent activator of JNK, treatment resulted in increased JNK phosphorylation in HT-29 cells, accompanied by elevated LC3B content. In addition, E. coli O157:H7 infection exerted an inhibitory effect on apoptosis of HT-29 cells by blocking the cleavage of poly ADP ribose polymerase (PARP).

Significance: The attenuation of autophagy in infected cells likely promotes E. coli O157:H7 survival and colonization, which needs to be further studied. Knowing the mechanism will help to understanding pathogen and host interaction and find ways to eliminate E. coli O157:H7 contamination related to meat especially beef processing.