N4BP1 is a unique, dimerization-dependent linear ubiquitin reader that regulates TNFR1 signalling through linear ubiquitin binding and Caspase-8-dependent processing

Signalling through TNFR1 modulates proinflammatory gene transcription and programmed cell death, and its impairment causes autoimmune diseases and cancer. NEDD4 binding protein 1 (N4BP1) was recently identified as a critical suppressor of proinflammatory cytokine production1, whose mode of action remained unknown. Here, we show that N4BP1 is a novel linear ubiquitin receptor that negatively regulates NFB signalling by its unique dimerization-dependent ubiquitin-binding module. N4BP1 homo-oligomerization strategically positions two non-selective ubiquitin-binding domains, ensuring exclusive recognition of linear ubiquitin. Under proinflammatory conditions, N4BP1 is recruited to the nascent TNFR1 signalling complex where it, through linear ubiquitin binding, regulates stability of the TNFR1 signalling complex and duration of proinflammatory signalling. N4BP1 deficiency accelerates TNF-induced cell death by increasing complex II assembly. Under proapoptotic conditions, Caspase-8 mediates proteolytic processing of N4BP1 and the resulting cleavage fragment of N4BP1, which retains the ability to bind linear ubiquitin, is rapidly degraded by the 26S proteasome, accelerating apoptosis. In summary, our findings demonstrate that N4BP1 dimerization creates a unique linear ubiquitin reader that ensures timely and coordinated regulation of TNFR1-mediated inflammation and cell death.