Interactions between Salmonella and the cell cycle of the host
Creators: name: Moutinho Mota Dos Santos, Antonio
Publisher: name: Imperial College London
Year: 2013

description: Recognition of host target cells by invasive bacteria is an essential step to infection, but the impact of the host cell cycle on the invasion of bacterial pathogens is still largely unknown. During these studies it was found that mitotic cells were more efficiently targeted for invasion by Salmonella enterica Typhimurium (S. Typhimurium) than cells in other phases of their cell cycle. This targeting was dependent on the SPI-1 (Salmonella pathogenicity island-1) T3SS (type 3 secretion system) translocase SipB, which binds to cholesterol at the surface of host cells. Using the cholesterol binding dye filipin and a fluorescent ester of polyethylene glycolcholesterol, which cannot flip through the plasma membrane, the levels of plasma membrane and cell surface cholesterol along the cell cycle were measured and both found to be maximal during mitosis. This increase was due to a transient loss in cholesterol asymmetry at the plasma membrane during mitosis. It was found that cholesterol changed from a ~20:80 outer:inner leaflet repartition during interphase to ~50:50 during mitosis. This explains the increase in surface levels that make mitotic cells more susceptible to S. Typhimurium invasion and perhaps to other viruses and bacteria that enter cells in a cholesterol-dependent manner. Additionally, it was found that the change in cholesterol partitioning favours the recruitment of phosphatidylinositol 4,5‑bisphosphate (Pi(4,5)P2) and activated ERM (Ezrin, Radixin, Moesin) proteins to the plasma membrane. This recruitment was shown here to support cell rounding during mitosis, as Pi(4,5)P2 and activated ERM are responsible for cross linking the plasma membrane to the actin cytoskeleton during mitosis. Some bacterial pathogens and viruses are known to interfere with the host cell cycle. Although several reports have shown significant correlation between chronic infections and cancer formation caused by Salmonella enterica Typhi, the impact of Salmonella on dividing cells was unclear before this study. During this investigation it was found that intracellular S. Typhimurium causes cytokinesis defects, which lead to binucleation of host cells. Intracellular replication of S. Typhimurium is modulated by the action of bacterial effectors translocated across the Salmonella-containing vacuole (SCV) by the SPI-2 T3SS. In this study it was determined that the cytokinesis failure induced by S. Typhimurium occurs during abscission and is caused by the presence of a cluster of SCVs (microcolony) inside the dividing cell. Translocation of the effectors SseF and SseG is important to induce cytokinesis failure, in a process that seems to depend on the activity of the kinase Aurora B, known to regulate abscission. Importantly, binucleation was also observed in infected cells in the intestinal epithelium of mice previously inoculated with S. Typhimurium. Similarly to other enteric pathogens known to block the cell cycle of the host, perhaps cytokinesis failure caused by S. Typhimurium delays the epithelial cell turnover of the intestine, facilitating its colonization by the bacteria