E-Syt1 ubiquitination by Nedd4 limits the caspase-11-mediated non-canonical inflammasome and endotoxemia

Abstract

Abstract Sepsis caused by gram-negative bacteria is thought to be largely due to the host’s response to LPS or endotoxin. Upon sensing LPS by its cytosolic receptor, caspase-11 (Casp-11) assembles a higher order structure that enables the activation of Casp-11 protease function, leading to gasdermin D cleavage and pyroptosis. However, the mechanisms for negatively regulating the activation of the Casp-11-dependent non-canonical inflammasome during sepsis are largely unknown. Nedd4 is a HECT-type E3 ubiquitin ligase that positively regulate T cell activation. However, its role in innate immunity is largely unknown. In this study, we found that although macrophages lacking Nedd4 produce comparable amounts of TNF-α and IL-6 in response to different TLR ligands, they produce more IL-1β upon LPS priming and stimulation with cholera toxin B (CTB) and EHEC but not ATP, nigericin, or other inflammasome stimuli. These data suggest that Nedd4 specifically regulates non-canonical inflammasomes. In support of this notion, mice lacking Nedd4, or lacking Nedd4 in myeloid cells, succumb to endotoxemia, which is rescued by deficiency for Casp-11 but not NLRP3. Mechanistically, Nedd4 appears to specifically bind to extended synaptotagmin 1 (E-Syt1), and targets E-Syt1 for ubiquitination, and loss of Nedd4 stabilize E-Syt1 protein which potentiates Casp-11 oligomerization and activation. Therefore, our data unveil a novel mechanism by which Nedd4 puts a brake on the Casp-11-dependent non-canonical inflammasome, thus preventing over-activation of innate immune responses during sepsis. The molecular insights gained in this study provide novel targets for modulating Casp-11-dependent inflammasome-mediated sepsis in patients.