Characterization of VOPQ, A Type III Secreted Effector Protein from Vibrio Parahaemolyticus
Burdette, Dara Lesley
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Vibrio parahaemolyticus is a Gram-negative bacterium responsible for gastroenteritis associated with the consumption of raw or undercooked shellfish. Its most well-characterized virulence factors are hemolysins that cause b-hemolysis on a special blood agar. Mutants lacking these hemolysins are still virulent in animal and tissue culture models of infection. These phenomena can be attributed in part to one of two type III secretion systems; one on chromosome 1 and the other on chromosome 2. We demonstrate that Vibrio parahaemolyticus utilizes the type III secretion system on chromosome 1 to induce a temporally regulated series of events that initiates with the induction of autophagy, followed by cellular rounding and finally cellular lysis and death. To the best of our knowledge, no other Gram-negative extracellular bacterium has been shown to induce autophagy during infection. To understand the mechanism of Vibrio parahaemolyticus induced cell death, we focused our analysis on VopQ, a type III secreted effector encoded by the type III locus on chromosome 1. We demonstrate that VopQ contributes to cytotoxicity as DvopQ strains induce cell lysis less efficiently. In addition, VopQ is necessary and sufficient for the induction of autophagy during infection. VopQ-mediated autophagy occurs independently of phosphatidylinositol 3-kinases and prevents phagocytosis. Additional experiments using Saccharomyces cerevisiae demonstrate VopQ induces autophagy and cell death through an evolutionarily conserved mechanism. Results presented herein delineate a novel virulence mechanism used by Vibrio parahaemolyticus to cause disease. This study also highlights the effector VopQ as a novel inducer of autophagy and a key mediator of cytotoxicity during infection.