Inhibition of polarity-regulating kinase PAR1b contributes to Helicobacter pylori inflicted DNA Double Strand Breaks in gastric cells.

The serine/threonine kinase Par1 is a core component of the machinery that sets up polarity in the embryo and regulates cell fate decisions but its role in the homeostasis of adult tissues is poorly understood. Inhibition of Par1 by the bacterium Helicobacter pylori (H. pylori) represents the only established pathology that affects Par1 function in an adult epithelium. Thus, during chronic H. pylori infection of the gastric mucosa Par1 is one of the targets of the non-obligate H.pylori cytotoxic protein and oncogene CagA, which stimulates inflammation and triggers morphological changes, both believed to contribute to the gastric cancer risk imposed by H. pylori infection. Based on Par1's role in cell polarity, it has been speculated that Par1 inhibition affects epithelial polarity. Here we report the unexpected finding that CagA-mediated Par1-inhibition promotes the generation of DNA Double Strand Breaks in primary gastric epithelial cells, which likely contributes to the reported accumulation of mutations in chronically infected mucosal cells. Abbreviations: AGS: human gastric adenocarcinoma cell line; CM: CagA Multimerization (and Par1 binding) domain; H. pylori: Helicobacter pylori; DSB: Double Strand Break; HGECs: human (primary) gastric epithelial cells; IB: immunoblot; IF: immunofluorescence; MOI: Multiplicity of Infection; ROS: reactive oxygen species; Par1: Partitioning Defective 1 kinase; WT: wild type.