The inflammasome-activated cytokine IL-1 is targeted for ubiquitylation and proteasomal degradation to limit its inflammatory potential

Interleukin-1B (IL-1B) is pathologically activated by inflammasome-associated caspase-1 in rare autoinflammatory conditions and in wide-spread diseases. Therefore, IL-1B activity must be fine-tuned to enable anti-microbial responses whilst limiting collateral damage. Here we report that, relative to other inflammasome components, IL-1B is rapidly turned over by the proteasome and this correlates with its decoration by K11-, K63- and K48-linked ubiquitin chains. This IL-1 degradation signal is not only a feature of inflammasome priming but is also triggered upon inflammasome activation. We demonstrate that IL-1 K133 is modified by ubiquitin and forms a salt bridge with IL-1B D129. Loss of IL-1 K133 ubiquitylation, or disruption of the K133:D129 electrostatic interaction, stabilizes IL-1Bprotein levels. Accordingly, IL-1B K133R/K133R mice display increased precursor IL-1Bupon inflammasome priming and increased bioactive IL-1B following inflammasome activation, both in vitro and following LPS injection in vivo. These findings reveal new mechanisms for limiting IL-1B activity and safeguarding against damaging inflammation.