Phospholipase D Of Epithelial Cells Regulates Internalization Of Listeria Monocytogenes Into Host Cells

The pathogen Listeria monocytogenes is able to induce its own internalization into non-phagocytes. This entry process (phagocytosis) is regulated tightly by dynamics of actin cytoskeleton. Here we report on a novel regulator for this phagocytosis, phospholipase D (PLD), which is closely related to actin cytoskeleton rearrangement. We demonstrated that L. monocytogenes is able to stimulate the host PLD activation significantly during its internalization into vero cells. The pretreatment of vero cells with two PLD inhibitors, 1-butanol and 2,3-diposphoglycerate (2,3-DPG) depressed the entry of L. monocytogenes in association with reduction of L. monocytogenes-induced PLD activation. Down regulation of PLD activity by expression of PLD lipase-inactive mutants or silence of endogenous PLD brought clear decrease on Listeria-internalization. Only theΔInlB mutant with the deletion of Listeria surface protein Internalin B (InlB) lost its ability largely to induce the host PLD activation. The purified InlB protein was capable to stimulate strongly the host PLD activity and rescue the inhibitory effect ofΔInlB mutant; moreover, this capacity was controlled by Met receptor. Finally, L. monocytogenes and InlB were able to induce cofilin-phosphorylation in the vero cells. The hyperactivation of cofilin by expressing nonphosphorylatable S3A cofilin or slingshot 1L inhibited not only the Listeria internalization but also the InlB-induced PLD activation. In contrast, the impairment of cofilin activity by expressing phosphorylation-mimic S3D cofilin inhibited the Listeria internalization, but enhanced the InlB-induced PLD activation and rescued the InlB-induced PLD activation in cofilin-slienced vero cells. In conclusion, our data indicated that InlB of L. monocytogenes might be a new agonist to PLD in vero cells and through cofilin-PLD cascade PLD may play as a novel regulator on internalization.