HCP-FAMILY PROTEINS SECRETED VIA TYPE VI SECRETION SYSTEM COORDINATELY REGULATE ESCHERICHIA COLI Kl INTERACTION WITH HUMAN BRAIN MICROVASCULAR ENDOTHELIAL CELLS

摘要

The type VI secretion systems (T6SSs) are involved in the pathogenicity of several Gram-negative bacteria. Based on the sequence analysis, we found that a cluster of E. coli virulence factors (EVF) encoding a putative T6SS exists in the genome of a meningitiscausing E. coli Kl strain RS218. The T6SS-associated deletion mutants exhibited significant defects in binding to and invasion of human brain microvascular endothelial cells (HBMEC) compared with the parent strain. Hep-family proteins (the hallmark of T6SS) including Hcpl and Hcp2 were localized in the bacterial outer membrane, but the involvements of Hcpl and Hcp2 are shown to differ in E. co/i-HBMEC interaction. The deletion mutant of hcp2 showed defects in bacterial binding to and invasion of HBMEC, while Hcpl was secreted in T6SS dependent manner and induced actin cytoskeleton rearrangement, apoptosis and release of IL-6 and IL-8 while interacting with HBMEC. These findings demonstrate that the T6SS is functional in E. coli Kl and two Hep-family proteins participate in different steps of E. coli interaction with HBMEC in a coordinate manner, e.g., association with and invasion of HBMEC, the cytokine and chemokine release followed by cytoskeleton rearrangement and apoptosis in HBMEC. Taken together, this is the first demonstration of the role of T6SS in meningitis-causing E. coli Kl and T6SS associated Hep-family proteins are likely to contribute to the pathogenesis of E. coli meningitis.