Cirtical Role for Salmonella Effector SopB in Regulating Inflammasome Activation.

Objective: Salmonella is known to evolve many mechanisms to avoid or delay inflammasome activation which remain largely unknown. In this study, we investigated whether the SopB protein critical to bacteria virulence capacity was an effector that involved in the regulation of inflammasome activation. Methods: BMDMs from NLRC4-, NLRP3-, caspase-1/-11-, IF116- and AIM2-deficient mice were pretreated with LPS, and subsequently stimulated with a series of SopB-related strains of Salmonella, inflammasome induced cell death, IL-1 beta secretion, cleaved caspase-1 production and ASC speckle formation were detected. Results: We found that SopB could inhibit host IL-1 beta secretion, caspase-1 activation and inflammasome induced cell death using a series of SopB-related strains of Salmonella; however the reduction of IL-1 beta secretion was not dependent on sensor that contain PYD domain, such as NLRP3, AIM2 or IF116, but dependent on NLRC4. Notably, SopB specifically prevented ASC oligomerization and the enzymatic activity of SopB was responsible for the inflammasome inhibition. Furthermore, inhibition of Akt signaling induced enhanced inflammasome activation. Conclusions: These results revealed a novel role in inhibition of NLRC4 inflammasome for Salmonella effector SopB.