Staphylococcus aureus-induced alteration of histone H3 phosphorylation status in human epithelial cells reveals its impact on cell cycle regulation.

Staphylococcus aureus is a highly versatile Gram-positive pathogen that can cause life-threatening infections. Staphylococcal infection is also a serious concern in animal health: it is a major cause of mastitis in ruminants for which existing prevention or treatment strategies are often inefficient. Epithelial cells are able to sense microbes, creating an early line of defense against pathogens. Pathogen-induced epigenetic modifications may affect host cell function either to facilitate host defense or to allow pathogen perseverance. Post-translational modifications of core histones are the important epigenetic factors. The goal of this work was to investigate the ability of S. aureus to affect host cell cycle and to analyze its effect on histone phosphorylation status of the host cells. Culture of human cervix cancer HeLa epithelial cells were used to study in vitro the effects of S. aureus. Flow cytometry analysis show that S. aureus induces G2/M phase transition delay in synchronous HeLa cells. Using Western blot analysis we show that the addition of S. aureus considerably decreased the relative level of phosporylated histone H3 (p-Ser10 Histone H3) in a dose-dependent manner, while the total level of histone H3 remained constant in all of the cell samples. The results of immunofluorescence reveled that this decrease was associated with the reduction of the number of the mitotic cells and with the diminution of the number of p-Ser10 Histone H3-positive nuclei. These results suggest that most of the infected cells failed to enter mitosis and accumulated in the G2 phase. Altogether, these results suggest that the delay in G2/M phase transition of the infected epithelial cells may be one of the mechanisms employed by S. aureus to survive and to propagate inside the host. Further investigations are ongoing to fully understand the mechanisms associated to this type of S. aureus-host cell interactions. However, the estimation of the relative fluorescence intensity of individual mitotic cells (metaphase) stained with the anti-p-Ser10 Histone H3 antibody revel that this decrease was associated with the reduction of the number of the mitotic cells after S. aureus infection