THE INIB PROTEIN OF LISTERIA-MONOCYTOGENES IS SUFFICIENT TO PROMOTE ENTRY INTO MAMMALIAN-CELLS

InlB is one of the two Listeria monocytogenes invasion proteins requir ed for bacterial entry into mammalian cells, Entry into human epitheli al cells such as Caco-2 requires InlA, whereas InlB is needed for entr y into cultured hepatocytes and some epithelial or fibroblast cell lin es such as Vero, HEp-2 and HeLa cells, InlB-mediated entry requires ty rosine phosphorylation, cytoskeletal rearrangements and activation of the host protein phosphoinositide (PI) 3-kinase, probably in response to engagement of a receptor, In this study, we demonstrate for the fir st time that InlB is sufficient to promote internalization. Indeed, co ating of normally non-invasive bacteria or inert latex beads with InlB leads to internalization into mammalian cells, In addition, a soluble form of InlB also appears to promote uptake of non-invasive bacteria, albeit at a very low level. Similar to entry of L. monocytogenes, upt ake of InlB-coated beads required tyrosine phosphorylation in the host cell, PI 3-kinase activity and cytoskeletal reorganization. Taken tog ether, these data indicate that InlB is sufficient for entry of L. mon ocytogenes into host cells and suggest that this protein is an effecto r of host cell signalling pathways.