LUBAC-mediated linear ubiquitination participates in programmed cell death by pyroptosis

Pyroptosis is a highly inflammatory lytic form of programmed cell death triggered by infectious and sterile insults. Pyroptosis plays a crucial role in inflammation and protective immunity, and its dysregulation causes human diseases. Pyroptosis involves the formation of supramolecular complexes named inflammasomes to recruit and activate caspase-1 (CASP1), which maturates inflammatory cytokines and induces cell lysis. However, the mechanisms involved in the regulation of pyroptosis remain elusive. Here, we report that the assembly of linear ubiquitin chains during pyroptosis is a prerequisite for the execution of pyroptosis. Combining chemical small molecules with genetic models and optogenetic tools, we show that inhibiting or dismantling the Linear Ubiquitin Chain Assembly Complex (LUBAC), which catalyzes atypical linear ubiquitin chains, prevents CASP1 activation and plasma membrane rupture. Conversely, cells deficient for OTULIN, a debiquitinase that antagonizes LUBAC activity, display excessive accumulation of linear ubiquitin chains and enhanced pyroptotic cell death. We also find that LUBAC complex undergoes post-translational modifications, with some of its subunits cleaved during pyroptosis, likely by CASP1, suggesting a tightly regulated feedback mechanism. Our findings reveal a previously unrecognized role for linear ubiquitination in pyroptosis and identify LUBAC as a potential therapeutic target for modulating inflammatory responses in disease.