ATP scavenging by the intracellular pathogen Porphyromonas gingivalis inhibits P2X7-mediated host-cell apoptosis

The purinergic receptor P2X₇ is involved in cell death, inhibition of intracellular infection and secretion of inflammatory cytokines. The role of the P2X₇ receptor in bacterial infection has been primarily established in macrophages. Here we show that primary gingival epithelial cells, an important component of the oral innate immune response, also express functional P2X₇ and are sensitive to ATP-induced apoptosis. Porphyromonas gingivalis, an intracellular bacterium and successful colonizer of oral tissues, can inhibit gingival epithelial cell apoptosis induced by ATP ligation of P2X₇ receptors. A P. gingivalis homologue of nucleoside diphosphate kinase (NDK), an ATP-consuming enzyme, is secreted extracellularly and is required for maximal suppression of apoptosis. An ndk -deficient mutant was unable to prevent ATP-induced host-cell death nor plasma membrane permeabilization in the epithelial cells. Treatment with purified recombinant NDK inhibited ATP-mediated host-cell plasma membrane permeabilization in a dose-dependent manner. Therefore, NDK promotes survival of host cells by hydrolysing extracellular ATP and preventing apoptosis-mediated through P2X₇.