Functional Analysis of VopF Activity Required for Colonization in <named-content content-type="genus-species">Vibrio cholerae</named-content>

Abstract

ABSTRACT Vibrio cholerae, a Gram-negative facultative pathogen, is the etiologic agent for the diarrheal disease cholera. We previously characterized a clinical isolate, AM-19226, that translocates a type III secretion system (T3SS) effector protein with actin-nucleating activity, VopF, into the host cells. From comparative genomic studies, we identified a divergent T3SS island in additional isolates which possess a VopF homolog, VopN. Unlike the VopF-mediated protrusion formation, VopN localizes to stress fiber in host cells similarly to VopL, which is present in the pandemic strain of Vibrio parahaemolyticus. Chimera and yeast two-hybrid studies indicated that the amino-terminal regions of VopF and VopN proteins interact with distinct host cell factors. We determined that AM-19226-infected cells are arrested at S phase of the cell cycle and that VopF/VopN are antiapoptotic factors. To understand how VopF may contribute to the pathogenesis of AM-19226, we examined the effect of VopF in an in vitro polarized-epithelial model and an in vivo adult rabbit diarrheal model. Within the T3SS pathogenicity island is VopE, a homolog of YopE from Yersinia, which has been shown to loosen tight junctions. In polarized intestinal epithelia, VopF and VopE compromised the integrity of tight junctions by inducing cortical actin depolymerization and aberrant localization of the tight-junction protein ZO-1. An assay for pathogenicity in the adult rabbit diarrhea model suggested that these effectors are involved in eliciting the diarrheal response in infected rabbits. IMPORTANCE Vibrio cholerae is a bacterial pathogen that causes the diarrheal disease cholera, which remains a major public health problem in many developing countries. While the major virulence factors of the pandemic V. cholerae strains have been characterized, new clinical strains of V. cholerae have arisen, causing sporadic cholera-like diseases using unknown pathogenic mechanisms. Previously, we discovered the type III secretion system in a new clinical strain of V. cholerae and also identified an effector protein, VopF, which is injected into the host cells and induces changes in the actin cytoskeleton. In this work, we identified a homolog of VopF that causes a distinct cellular phenotype and interactions between the effectors and host proteins. We also discovered that both effectors prevent bacterium-induced cell death in infected cells. In our tissue culture and animal models, we showed that VopF contributes to the disruption of epithelial integrity and the diarrheal response.