The T3SS1 Effector VopR Requires the Rac1-Erk1/2 Axis to Inhibit the Host Immune Response to Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) has been an emerging foodborne pathogen prevalent worldwide for decades, primarily due to the impact of climate change. The food safety concerns associated with V. parahaemolyticus have led to a potential risk for its control. As VopR is a V. parahaemolyticus T3SS1 effector, the function of VopR is still unclear. To address this knowledge gap, we investigated the host response to VopR during the process of V. parahaemolyticus infection. In our research, the deletion of vopR increased virulence and necrosis in host cells during infection. RNA-seq analysis revealed considerable changes in physiological processes upon V. parahaemolyticus infection. The deletion of vopR increased the transcription of proinflammatory cytokines, such as IL-6 and CXCL8, as well as the transcription of FOS and JUN family genes, indicating that VopR has a negative regulatory role in the host's proinflammatory immune response during infection. An inhibitor used to activate Erk1/2 has demonstrated that VopR suppresses host proinflammatory immune responses by stimulating MAPK-Erk1/2 activation. Coimmunoprecipitation (co-IP) and confocal microscopy confirmed that VopR interacted with host Rac1. Furthermore, when the RAC1 gene was knocked out in HeLa cells, VopR did not inhibit host cell death or decrease the transcription of CXCL8, suggesting that Rac1 is necessary for the function of VopR during V. parahaemolyticus infection. In summary, our findings indicate that VopR plays a crucial role in suppressing the proinflammatory immune response during V. parahaemolyticus infection, which can facilitate the survival of host cells during infection by V. parahaemolyticus, which contains the active T3SS1.