IQGAP1 mediates the disruption of adherens junctions to promoteEscherichia coliK1 invasion of brain endothelial cells

Abstract

The transcellular entry of E. coli K1 through human brain microvascular endothelial cells (HBMEC) is responsible for tight junction disruption, leading to brain edema in neonatal meningitis. Previous studies demonstrated that outer membrane protein A (OmpA) of E. coli K1 interacts with its receptor, Ecgp96 to induce PKC-α phosphorylation, adherens junction (AJ) disassembly (by dislodging β-catenin from VE-cadherin), and remodeling of actin in HBMEC. We report here that IQGAP1 mediates β-catenin dissociation from AJs to promote actin polymerization required for E. coli K1 invasion of HBMEC. Overexpression of C-terminal truncated IQGAP1 (IQΔC) that cannot bind β-catenin prevents both AJ disruption and E. coli K1 entry. Of note, phospho-PKC-α interacts with the C-terminal portion of Ecgp96 as well as with VE-cadherin after IQGAP1 mediated AJ disassembly. HBMEC overexpressing either C-terminal truncated Ecgp96 (Ecgp96Δ200) or IQΔC upon infection with E. coli showed no interaction of phospho-PKC-α with Ecgp96. These data indicate that the binding of OmpA to Ecgp96 induces PKC-α phosphorylation and association of phospho-PKC-α with Ecgp96, and then signals IQGAP1 to detach β-catenin from AJs. Subsequently, IQGAP1/β-catenin bound actin translocates to the site of E. coli K1 attachment to promote invasion.

Rac1 is deactivated at integrin activation sites via an IQGAP1/filamin-A/RacGAP1 pathway

“…These reports of cytokinesis-and centralspindlin-independent RacGAP1 functions suggest that RacGAP1 has a broader range of functions than previously anticipated. In this context, IQGAP1 is known to localise at cell-cell junctions (Krishnan et al, 2012;Lehtonen et al, 2005;Noritake et al, 2004) and cell-cell junction proteins were identified as IQGAP1-associated proteins (e.g. b-catenin) (supplementary material Table S3).…”

Pathogens Penetrating the Central Nervous System: Infection Pathways and the Cellular and Molecular Mechanisms of Invasion

“…In addition to triggering the internalization of E. coli K1 into HBMECs, the binding of OmpA to its gp96 homologue receptor stimulates inducible nitric oxide synthase and nitric oxide production, which enhances the generation of cyclic GMP (237). This increase in cyclic GMP activates protein kinase C␣ (237), which leads to a Ras GTPase-activating-like protein (IQGAP1)-mediated dissociation of ␤-catenin from vascular endothelial cadherin at adherens junctions (238). Immunofluorescence experiments demonstrated that vascular endothelial cadherin was redistributed from the intercellular junctions to the sites of bacterial attachment (239).…”

The effects of cytotoxic necrotizing factor 1 expression in the uptake ofEscherichia coliK1 by macrophages and the onset of meningitis in newborn mice

“…These results along with invasion data suggest that the CNF1 secreted by E44 into macrophages exert excessive actin redistribution, which partially results in the formation of microspikes, thereby inducing effective sequestration of actin and resulting in the unavailability of the actin required for the optimal invasion of E44. 13,26,28 In contrast, Dcnf1 could not induce microspikes due to lack of CNF1, and thus, all actin in the cells are available for efficient bacterial invasion compared to E44. This is a novel observation that CNF1, a bacterial virulence factor, plays a role in limiting the internalization of the bacteria into the host cell by modulating actin availability.…”

“…We have previously demonstrated that E. coli K1 recruits actin filaments underneath the bacterial attachment sites. 13,[26][27][28][29] Therefore, we treated RAW 264.7 macrophages with various E. coli K1 strains listed above and then stained for actin filaments with phalloidin. E44, as expected, induced actin filament remodeling in these cells beneath the bacterial attachment sites; however, E44 also triggered more microspikes that protruded from RAW 264.7 macrophages compared to uninfected cells ( Fig.…”