Antibody-dependent Intracellular neutralisation by TRIM21 is potentiated by HOIP and linear ubiquitin chains

Antibody-dependent intracellular neutralisation (ADIN) promotes the rapid proteasomal degradation of viruses and other large substrates in the cytosol. It is dependent on detection of intracellular virus-bound antibodies by the Fc receptor and E3 ligase TRIM21, followed by disassembly of the virus by the unfoldase VCP/p97. It is not known how VCP is recruited to TRIM21. We performed a limited siRNA knock-down screen of known VCP adaptors to determine their involvement in ADIN. Knock-down of HOIP, the only ubiquitin E3 ligase capable of generating linear ubiquitin chains, resulted in impaired virus neutralisation. HOIPIN-8, a HOIP inhibitor, showed concentration-dependent reduction in virus neutralisation. We found that the activity of HOIP in ADIN is dependent on its ubiquitin binding domains and its PUB domain which recruits VCP. Knock-down of OTULIN, the only deubiquitinating enzyme that exclusively cleaves linear ubiquitin chains, potentiated neutralisation of the virus. Our results expand the role of HOIP and linear ubiquitin chains in proteostasis.