Identification of RNF213 as intracellular ISG15 receptor with antimicrobial activity

During infection, interferon production leads to upregulation of the interferon-stimulated gene 15 (ISG15). ISG15 counteracts intracellular infection by viral and bacterial pathogens and exerts its function either as a free intracellular or extracellular molecule, or as a ubiquitin-like conjugate to substrate proteins in a process called ISGylation. Until today, no intracellular protein machinery has been described to recognize ISGylated proteins. Hence, unlike proteins modified by ubiquitin and SUMO, the fate of ISGylated proteins inside infected cells is unknown. Using a viral-like particle trapping technology coupled with mass spectrometry, we identified RNF213 as an intracellular receptor for ISG15 and/or ISGylated proteins. RNF213 is a poorly characterized protein that forms a macromolecular complex with unknown function. Together with ISG15 and its conjugation machinery, RNF213 is upregulated upon infection. Interestingly, RNF213 was originally discovered as a susceptibility gene for Moyamoya disease, a rare cerebrovascular disorder leading to stroke. In patients carrying RNF213 polymorphisms, microbial infections have been suggested to trigger onset of the disease. We confirmed binding of ISG15 and RNF213 by GST pull down and we showed that knockdown of RNF213 promotes infection by Listeria monocytogenes, Respiratory syncytial virus and Coxsackie virus B3. In contrast, overexpression of RNF213 restricted infection, suggesting a broad antimicrobial activity of RNF213 similar to ISG15. Together, we hypothesize that the RNF213 complex operates as a long sought binding platform for ISG15 and/or ISGylated proteins, and functions as a first step in a yet undiscovered cellular pathway that processes ISGylated proteins