Enteropathogenic Escherichia coli-mediated fast and coordinated Ca^²+ responses regulate NF-κB activation

Enteropathogenic Escherichia coli (EPEC) is a major bacterial enteropathogen causing infectious diarrhea among children in developing countries. Here, we found that EPEC induced isolated Ca²⁺ responses in epithelial cells, triggered by extracellular ATP (eATP). These responses were dependent on type III secretion (T3S) and down-regulated by the bacterial secreted protease EspC, consistent with eATP released by the T3S translocon pore-forming activity in host membranes. By performing high-speed Ca²⁺ imaging, we uncovered that at the onset of infection, low eATP levels triggered Ca²⁺-responses involving the whole cell but showing small amplitude and fast kinetics usually associated with local Ca²⁺ responses. The findings, supported by theoretical modeling, evoke a conceptual shift whereby low amounts of inositol 1, 4, 5-trisphosphate (IP₃) induced by low eATP levels and subsequent moderate Ca²⁺ release enable the fast coordination of IP₃ receptor cluster activation throughout the cell. Importantly, these yet undescribed coordinated fast responses occurred over prolonged time periods and defined a cell state with dampened activation of the pro-inflammatory transcriptional activator NF-kB associated with a decrease in its Ca²⁺-dependent O-linked β-N-acetylglucosamine modification.