TheShigellaType III Secretion Effector IpaH4.5 Targets NLRP3 to Activate Inflammasome Signaling

Activation of the NLRP3 inflammasome requires the expression of NLRP3, which is strictly regulated by its capacity to directly recognize microbial-derived substances. Even though the involvement of caspase-1 activation in macrophagesviaNLRP3 and NLRC4 has been discovered, the accurate mechanisms by whichShigellainfection triggers NLRP3 activation remain inadequately understood. Here, we demonstrate that IpaH4.5, aShigellaT3SS effector, triggers inflammasome activation by regulating NLRP3 expression through the E3 ubiquitin ligase activity of IpaH4.5. First, we found that IpaH4.5 interacted with NLRP3. As a result, IpaH4.5 modulated NLRP3 protein stability and inflammasome activation. Bacteria lacking IpaH4.5 had dramatically reduced ability to induce pyroptosis. Our results identify a previously unrecognized target of IpaH4.5 in the regulation of inflammasome signaling and clarify the molecular basis for the cytosolic response to the T3SS effector.