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Commun Biol ; 5(1): 483, 2022 05 19.
Article in English | MEDLINE | ID: covidwho-1852521


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ORF6 is an antagonist of interferon (IFN)-mediated antiviral signaling, achieved through the prevention of STAT1 nuclear localization. However, the exact mechanism through which ORF6 prevents STAT1 nuclear trafficking remains unclear. Herein, we demonstrate that ORF6 directly binds to STAT1 with or without IFN stimulation, resulting in the nuclear exclusion of STAT1. ORF6 also recognizes importin α subtypes with different modes, in particular, high affinity to importin α1 but a low affinity to importin α5. Although ORF6 potentially disrupts the importin α/importin ß1-mediated nuclear transport, thereby suppressing the nuclear translocation of the other classical nuclear localization signal-containing cargo proteins, the inhibitory effect of ORF6 is modest when compared with that of STAT1. The results indicate that the drastic nuclear exclusion of STAT1 is attributed to the specific binding with ORF6, which is a distinct strategy for the importin α1-mediated pathway. Combined with the results from a newly-produced replicon system and a hamster model, we conclude that SARS-CoV-2 ORF6 acts as a virulence factor via regulation of nucleocytoplasmic trafficking to accelerate viral replication, resulting in disease progression.

COVID-19 , SARS-CoV-2 , Viral Proteins/metabolism , Animals , Antiviral Agents , Biological Transport , Cricetinae , Viral Proteins/genetics , Virus Replication , alpha Karyopherins/genetics , alpha Karyopherins/metabolism
Cell Rep ; 31(3): 107549, 2020 04 21.
Article in English | MEDLINE | ID: covidwho-100496


Importin-α adaptor proteins orchestrate dynamic nuclear transport processes involved in cellular homeostasis. Here, we show that importin-α3, one of the main NF-κB transporters, is the most abundantly expressed classical nuclear transport factor in the mammalian respiratory tract. Importin-α3 promoter activity is regulated by TNF-α-induced NF-κB in a concentration-dependent manner. High-level TNF-α-inducing highly pathogenic avian influenza A viruses (HPAIVs) isolated from fatal human cases harboring human-type polymerase signatures (PB2 627K, 701N) significantly downregulate importin-α3 mRNA expression in primary lung cells. Importin-α3 depletion is restored upon back-mutating the HPAIV polymerase into an avian-type signature (PB2 627E, 701D) that can no longer induce high TNF-α levels. Importin-α3-deficient mice show reduced NF-κB-activated antiviral gene expression and increased influenza lethality. Thus, importin-α3 plays a key role in antiviral immunity against influenza. Lifting the bottleneck in importin-α3 availability in the lung might provide a new strategy to combat respiratory virus infections.

Influenza A virus/immunology , Influenza, Human/immunology , Orthomyxoviridae Infections/immunology , alpha Karyopherins/biosynthesis , A549 Cells , Animals , Cell Line, Tumor , Chlorocebus aethiops , Down-Regulation , Female , HEK293 Cells , Humans , Influenza, Human/genetics , Influenza, Human/virology , Mice , Mice, Inbred C57BL , Mice, Knockout , Middle Aged , Orthomyxoviridae Infections/genetics , Orthomyxoviridae Infections/virology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Vero Cells , alpha Karyopherins/genetics , alpha Karyopherins/immunology