E3 ubiquitin ligase SYVN1 mediates K63-linked ubiquitination of DDX3X to activate Macrophage NLRP3 Inflammasome.

DDX3X (DEAD-box helicase 3, X-linked) is a common and essential component for both stress granules and NLRP3 inflammasome assembly and their activation; however, the upstream cellular stress signals driving DDX3X to activate the contrasting cellular pathway remain unclear. We identified the pivotal role of the E3 ubiquitin ligase SYVN1(Synoviolin) as the upstream regulator of DDX3X and thereby controlling NLRP3 activation and stress granule assembly. We observed SYVN1 silencing in macrophages prevented both NLRP3-driven inflammation and stress granule formation. SYVN1 deficiency prevented LPS-induced inflammatory lung injury and increased the survival rate of the mice. SYVN1 sustains DDX3X gene expression and promotes stimulus-dependent ubiquitination of DDX3X. Under inflammatory conditions, SYVN1 mediated 63-linked ubiquitination of DDX3X, a requirement for NLRP3 inflammasome activation. Conversely, stress conditions reduced K63-linked DDX3X ubiquitination in coordination with activity of the deubiquitinase OTUB1 (OTU domain-containing ubiquitin aldehyde-binding protein 1). Thus, the balance between SYVN1 and OTUB1 functioned to optimize DDX3X activity and activation of NLRP3 or stress granule. These findings show the upstream role of SYVN1-OTUB1 axis in integrating cellular stress signals to decide the cell fate and suggest that ubiquitination of DDX3X is a potential target for inflammasome driven inflammation.