Fluxes of Ca2+and K+Are Required for the Listeriolysin O-Dependent Internalization Pathway of Listeria monocytogenes

Abstract

ABSTRACTListeria monocytogenesis responsible for the life-threatening food-borne disease listeriosis. This disease mainly affects elderly and immunocompromised individuals, causing bacteremia and meningoencephalitis. In pregnant women,L. monocytogenesinfection leads to abortion and severe infection of the fetus or newborn. TheL. monocytogenesintracellular life cycle is critical for pathogenesis. Previous studies have established that the major virulence factor ofL. monocytogenes, the pore-forming toxin listeriolysin O (LLO), is sufficient to induceL. monocytogenesinternalization into human epithelial cell lines. This internalization pathway strictly requires the formation of LLO pores in the plasma membrane and can be stimulated by the heterologous pore-forming toxin pneumolysin, suggesting that LLO acts nonspecifically by forming transmembrane pores. The present work tested the hypothesis that Ca2+and K+fluxes subsequent to perforation by LLO controlL. monocytogenesinternalization. We report thatL. monocytogenesperforates the host cell plasma membrane in an LLO-dependent fashion at the early stage of invasion. In response to perforation, host cells undergo Ca2+-dependent but K+-independent resealing of their plasma membrane. In contrast to the plasma membrane resealing process, LLO-inducedL. monocytogenesinternalization requires both Ca2+and K+fluxes. Further linking ion fluxes to bacterial internalization, treating cells with a combination of Ca2+and K+ionophores but not with individual ionophores is sufficient to induce efficient internalization of large cargoes, such as 1-μm polystyrene beads and bacteria. We propose that LLO-inducedL. monocytogenesinternalization requires a Ca2+- and K+-dependent internalization pathway that is mechanistically distinct from the process of plasma membrane resealing.