Vibrio parahaemolyticus harbors two type III secretion systems (T3SSs; T3SS1 and T3SS2), of which T3SS1 is involved in host cell cytotoxicity. T3SS1 expression is positively regulated by ExsA, and it is negatively regulated by ExsD. We compared the secretion profiles of a wild-type strain (NY-4) of V. parahaemolyticus with those of an ExsD deletion mutant (Delta exsD) and with a strain of NY-4 that overexpresses T3SS1 (NY-4:pexsA). From this comparison, we detected a previously uncharacterized protein, Vp1659, which shares some sequence homology with LcrV from Yersinia. We show that vp1659 expression is positively regulated by ExsA and is negatively regulated by ExsD. Vp1659 is specifically secreted by T3SS1 of V. parahaemolyticus, and Vp1659 is not required for the successful extracellular secretion of another T3SS1 protein, Vp1656. Mechanical fractionation showed that Vp1659 is translocated into HeLa cells in a T3SS1-dependent manner and that deletion of Vp1659 does not prevent VopS from being translocated into HeLa cells during infection. Deletion of vp1659 significantly reduces cytotoxicity when HeLa cells are infected by V. parahaemolyticus, while complementation of the Delta vp1659 strain restores cytotoxicity. Differential staining showed that Vp1659 is required to induce membrane permeability in HeLa cells. We also show evidence that Vp1659 is required for actin rearrangement and the induction of autophagy. On the basis of these data, we conclude that Vp1659 is a T3SS1-associated protein that is a component of the secretion apparatus and that it is necessary for the efficient translocation of effector proteins into epithelial cells.
