beA in meningitic Escherichia coli 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+ E. coli K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ E. coli 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)-vim... More
beA in meningitic Escherichia coli 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+ E. coli K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ E. coli 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 Ser82 by CaMKII (Ca2+/calmodulin-dependent protein kinase II) and IbeA+ E. coli-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+ E. coli invasion. Fourthly, IbeA+ E. coli and IbeA-coated beads induced the clustering of vimentin that was correlated with increased entry of bacteria and beads. Lastly, IbeA+ E. coli 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 E. coli 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 E. coli K1 invasion.
