Synthesis of proteins that mimic natural host cell ligands and induce uptake of bacteria expressing them is an effective invasion strategy used by several pathogenic bacteria. Listeria monocytogenes, which causes serious infections in immunocompromised individuals and pregnant women,produces two such proteins: InlA and InlB. In a Commentary on, Hélène Bierne and Pascale Cossart discuss work that is shedding light on how InlB functions. The protein binds to hepatocyte growth factor receptors (HGF-Rs) on the surface of hepatocytes, epithelial cells and endothelial cells. This stimulates internalization of the bacterium by a mechanism similar to phagocytosis: the cell extends membrane around the particle and forms a continuous F-actin cup, which is disassembled following engulfment. Interestingly, in addition to stimulating pathways required for phagocytosis,InlB has other effects on target cells. It acts as a tyrosine kinase receptor agonist, regulating signalling cascades involving phospholipase Cγ1, Akt and NF-κB. This could be important after internalization and might promote cell survival once the bacterium is released into the cytosol.
