Vimentin-mediated signalling is required for IbeA+ E. coli K1 invasion of human brain microvascular endothelial cells

摘要

piIbeA/i in meningitic iEscherichia coli/i K1 strains has been described previously for its role in invasion of BMECs (brain microvascular endothelial cells). Vimentin was identified as an IbeA-binding protein on the surface of HBMECs (human BMECs). In the present study, we demonstrated that vimentin is a primary receptor required for IbeA+ iE. coli/i K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ iE. coli/i K1 strain) invasion was blocked by vimentin inhibitors (withaferin A and acrylamide), a recombinant protein containing the vimentin head domain and an antibody against the head domain respectively. Secondly, overexpression of GFP (green fluorescent protein)–vimentin and GFP–VDM (vimentin head domain deletion mutant) significantly increased and decreased bacterial invasion respectively. Thirdly, bacterial invasion was positively correlated with phosphorylation of vimentin at Sersup82/sup by CaMKII (Casup2+/sup/calmodulin-dependent protein kinase II) and IbeA+ iE. coli/i-induced phosphorylation of ERK (extracellular-signal-regulated kinase). Blockage of CaMKII by KN93 and inhibition of ERK1/2 phosphorylation by PD098059 resulted in reduced IbeA+ iE. coli/i invasion. Fourthly, IbeA+ iE. coli/i and IbeA-coated beads induced the clustering of vimentin that was correlated with increased entry of bacteria and beads. Lastly, IbeA+ iE. coli/i K1 invasion was inhibited by lipid-raft-disrupting agents (filipin and nystatin) and caveolin-1 siRNA (small interfering RNA), suggesting that caveolae/lipid rafts are signalling platforms for inducing IbeA–vimentin-mediated iE. coli/i invasion of HBMECs. Taken together, the present studies suggest that a dynamic and function-related interaction between IbeA and its primary receptor vimentin at HBMEC membrane rafts leads to vimentin phosphorylation and ERK-mediated signalling, which modulate meningitic iE. coli/i K1 invasion./p