Helicobacter pylori-induced modification of the histone H3 phosphorylation status in gastric epithelial cells reflects its impact on cell cycle regulation

Post-translational modifications of core histones are important components of the epigenetic landscape. Recent investigations of bacterial or toxin-induced effects on histone phosphorylation and acetylation in host cells have linked the changes to transcriptional alterations of key cellular response pathways. However, these changes may have other reasons and functional consequences. Here, we show that infection of gastric epithelial cell lines with the carcinogenic bacterium Helicobacter pylori leads to changes in histone H3 phosphorylation: type IV secretion system (T4SS)-dependent decreases of H3 phosphorylation levels at serine 10 (pH3Ser10) and threonine 3 (pH3Thr3) were observed. Immunofluorescence experiments with pH3Ser10 and cyclin B1 revealed that a H. pylori-induced transient pre-mitotic arrest was responsible for the observed reduction. This causal link was substantiated further by showing that H. pylori causes a strong decrease of the cell division cycle 25 (CDC25C) phosphatase. As a consequence, mitotic histone H3 kinases such as vaccinia-related kinase 1 (VRK1) and Aurora B were not fully activated in infected cells. We show that VRK1 activity, measured using a kinase activity assay, was reduced after H. pylori infection by approximately 40%. Moreover, overexpression of VRK1, but not Aurora B, compensated for the H. pylori-induced decrease of pH3Ser10. Rephosphorylation of H3Ser10 was I kappa B kinase alpha (IKK alpha)-dependent and occurred at later time points of infection. Taken together, our work highlights the impact of bacterial pathogens on host cell chromatin; this modulation reflects the subversion of key cellular processes such as cell cycle progression.