Listeria hijacks the clathrin-dependent endocytic machinery to invade mammalian cells

The bacterial pathogen Listeria monocytogenes uses the surface protein InlB to invade a variety of cell types. The interaction of InlB with the hepatocyte growth-factor receptor, Met, is crucial for infection to occur. Remarkably, the ubiquitin ligase Cbl is rapidly recruited to InlB-activated Met. Recent studies have shown that ligand-dependent endocytosis of Met and other receptor tyrosine kinases is triggered by monoubiquitination of the receptor, a process that is mediated by Cbl. Here, we show that purified InlB induces the Cbl-dependent monoubiquitination and endocytosis of Met. We then demonstrate that the bacterium exploits the ubiquitin-dependent endocytosis machinery to invade mammalian cells. First, we show that L. monocytogenes colocalizes with Met, EEA1, Cbl, clathrin and dynamin during entry. Then, we assess the role of different proteins of the endocytic machinery during L. monocytogenes infection. Over-expression or down-regulation of Cbl, respectively, increases or decreases bacterial invasion. Furthermore, RNA interference-mediated knock-down of major components of the endocytic machinery (for example, clathrin, dynamin, eps15, Grb2, CIN85, CD2AP, cortactin and Hrs), inhibit bacterial entry, establishing that the endocytic machinery is key to the bacterial internalization process.