USP22 promotes IRF3 nuclear translocation and antiviral responses by deubiquitinating the importin protein KPNA2

Abstract

USP22 is a cytoplasmic and nuclear deubiquitinating enzyme, and the functions of cytoplasmic USP22 are unclear. Here, we discovered that cytoplasmic USP22 promoted nuclear translocation of IRF3 by deubiquitianting and stabilizing KPNA2 after viral infection. Viral infection induced USP22-IRF3 association in the cytoplasm in a KPNA2-depedent manner, and knockdown or knockout of USP22 or KPNA2 impaired IRF3 nuclear translocation and expression of downstream genes after viral infection. Consistently, Cre-ER Usp22fl/fl or Lyz2-Cre Usp22fl/fl mice produced decreased levels of type I IFNs after viral infection and exhibited increased susceptibility to lethal viral infection compared with the respective control littermates. Mechanistically, USP22 deubiquitinated and stabilized KPNA2 after viral infection to facilitate efficient nuclear translocation of IRF3. Reconstitution of KPNA2 into USP22 knockout cells restored virus-triggered nuclear translocation of IRF3 and cellular antiviral responses. These findings define a previously unknown function of cytoplasmic USP22 and establish a mechanistic link between USP22 and IRF3 nuclear translocation that expands potential therapeutic strategies for infectious diseases.

Of Keeping and Tipping the Balance: Host Regulation and Viral Modulation of IRF3-Dependent IFNB1 Expression

“…As the influence of the NES seems to prevail the import, the main share of IRF3 molecules localises to the cytoplasm [ 22 ]. The constitutive export of IRF3 was shown to involve exportin 1 (CRM1) [ 21 , 22 ], and the import through nuclear pore complexes involves the importins karyopherin (KPN) subunit α2 (KPNA2), KPNA3 and KPNA4 (or Qip1) [ 22 , 60 ]. Upon infection, phosphorylation of the AIE and accompanying structural rearrangements enable IRF3 to associate with CBP, and this interaction retains the activated holocomplex in the nucleus [ 22 ].…”

“…While inactive IRF3 already shuttles between the cytosol and nucleus in latent conditions, the translocation becomes crucial after its activation in order to exercise the trans -activation activity. Just recently, Cai and colleagues reported that the ubiquitin specific peptidase 22 (USP22) promotes the antiviral response from the cytoplasm by deubiquitinating importin KPNA2 [ 60 ]. After viral infection, KPNA2 associates with IRF3 for nuclear import, and USP22 promotes this critical step by stabilizing KPNA2.…”

Deciphering the Fine-Tuning of the Retinoic Acid-Inducible Gene-I Pathway in Teleost Fish and Beyond

“…YOD1, which acts at a later step along the pathway to abrogate the formation of prion-like aggregates of MAVS ( 80 ), has a limited effect on IFN promotor induction at an early time point post-stimulation. In contrast, mammalian OTUB1 and USP22 were reported with opposite regulatory effects on the RLR pathway ( 67 – 69 , 103 , 104 ). The inhibitory effect observed after ectopic expression of the fish orthologs may be a result of the inherent bias associated with the overexpression of enzymatically-active protein, mislocalization and inadequate cell type and does not allow to distinguish the opposite functions previously described in mammals.…”

Type I and III IFN-mediated antiviral actions counteracted by SARS-CoV-2 proteins and host inherited factors

“…Among SARS-CoV-2 proteins able to antagonize IFN-I production, nsp6 (membrane protein) binds TANK binding kinase 1 (TBK1) to suppress IRF3 phosphorylation, both nsp13, and nsp15 bind and block TBK1 phosphorylation, and ORF6 by localizing at the nuclear pore complex (NPC), binds importin karyopherin-α2 (KPNA2) thus targeting the nuclear import pathway and inhibiting the IRF3 nuclear translocation [ [82] , [83] , [84] , [85] ]. Other strategies to counteract IFN induction include the nsp15 that can cleave the 5’-polyU of the negative-sense viral RNA [ 25 , 86 ], as well as ORF8 and nucleocapsid proteins that showed strong inhibition on IFN-β and NF-κB-responsive promoter by inhibiting ISRE [ 87 ].…”