UBR5 promotes antiviral immunity by disengaging the transcriptional brake on RIG-I like receptors (ChIP-Seq)

RIG-I like receptors (RLRs) are the major viral RNA sensors essential for the initiation of antiviral immune responses to numerous RNA viruses. RLRs are subjected to stringent transcriptional and posttranslational regulations, of which ubiquitination is one of the most important. However, the role of ubiquitination in RLR transcription is unknown. Here, we generated, screened 375 definite ubiquitin ligase knockout cell lines and identified UBR5 as a positive regulator of RLR transcription. UBR5 deficiency (UBR5-/-) reduced antiviral immune responses to RNA viruses, while increased viral replication in primary cells and mice. Ubr5-/- mice were more susceptible to lethal RNA virus infection than Ubr5+/+ littermates. Mechanistically, UBR5 mediated the Lysine 63-linked ubiquitination of TRIM28, an epigenetic repressor of RLRs. This modification prevented intramolecular SUMOylation of TRIM28, thus disengaged the TRIM28-imposed brake on RLR transcription. In sum, UBR5 enables rapid upregulation of RLR expression to boost antiviral immune responses by ubiquitinating and de-SUMOylating TRIM28. To identify new E3 ligases critical for RLR signaling by a systemic approach, we performed an unbiased screening of 375 individual ubiquitin E3 ligase knockout cell lines by a CRISPR-Cas9 knockout screening system and identified Ubiquitin Protein Ligase E3 Component N-Recognin 5 (UBR5) as a positive regulator of RLR transcription. UBR5 regulates RLR transcriptional expression throug posttranslational modification of TRIM28, we then performed ChIP-seq analysis using DNA obtained from TRIM28 IP in WT and UBR5 knockout HEK293T cells with VSV infection. The ChIP-seq analysis were designed to identify if UBR5 specific control of TRIM28 binding to RLR alleles.