The role of Listeria adhesion protein (LAP) during the intestinal phase of Listeria monocytogenes pathogenesis.

摘要

Listeria monocytogenes is an intracellular, foodborne pathogen which causes systemic listeriosis in physiologically stressed or immunocompromised individuals. Early interaction with the intestinal epithelium is essential for Listeria infection, and involves the concerted action of multiple virulence factors. We identified Listeria adhesion protein (LAP) and demonstrated that LAP facilitated adhesion to intestinal epithelial cells and promoted full virulence during oral infection of mice. Our early work indicated that LAP expression was influenced by stressors common to the host gastrointestinal (GI) tract, including anaerobiosis. However, the mechanism by which LAP was exported to the bacterial cell surface was unclear, as was the influence of GI-related stressors on LAP-mediated infectivity. The epithelial receptor for LAP was identified as the human stress response chaperone, heat shock protein 60 (Hsp60). Hsp60 was shown to be necessary for LAP-mediated binding to intestinal epithelial cells, but the precise role for the LAP-Hsp60 interaction during Listeria infection was unknown. Others have shown that stressors, including infection, can alter host Hsp60 expression, but it was unclear how such a stress response might impact LAP-mediated infection. Therefore, the goals of the following studies were to characterize the role of both LAP and Hsp60 during Listeria infection. Here we examined a potential mechanism for LAP secretion and surface localization, as well as the influence of anaerobiosis on LAP cellular localization and LAP-mediated infectivity. We also evaluated the role of the LAP-Hsp60 interaction in bacterial adhesion to, invasion of and transepithelial translocation through Caco-2 intestinal epithelial monolayers, and determined the influence of Listeria infection on host Hsp60 expression and LAP-mediated infection. Data indicate that LAP is secreted by the SecA2 system, and that anaerobiosis increases LAP secretion in L. monocytogenes. Exposure of L. monocytogenes to an anaerobic environment also increased LAP-mediated adhesion to Caco-2 cells and enhanced bacterial translocation to the liver and spleen of mice in a LAP-specific manner. By altering Hsp60 expression in Caco-2 cells, we confirmed that the LAP-Hsp60 interaction promotes Listeria adhesion, and also demonstrated its role in mediating bacterial transepithelial translocation. Further, L. monocytogenes infection increased Caco-2 expression of Hsp60, which rendered host cells more susceptible to LAP-mediated adhesion and translocation by L. monocytogenes. Data offer new insight into the role of LAP as a virulence factor during the intestinal phase of Listeria pathogenesis, and pose new questions regarding the dynamics between the host stress response and pathogen infection.