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Updated: Jun 4, 2026
Dissecting Innate Immune Signaling in Viral Evasion of Cytokine Production
Published on: March 2, 2014
PLP2 of mouse hepatitis virus A59 (MHV-A59) targets TBK1 to negatively regulate cellular type I interferon signaling
Gang Wang1, Gang Chen, Dahai Zheng
1Key Laboratory of Infection and Immunity, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
Background:
Coronaviruses such as severe acute respiratory syndrome (SARS) coronavirus (SCoV) and mouse hepatitis virus A59 (MHV-A59) have evolved strategies to disable the innate immune system for productive replication and spread of infection. We have previously shown that papain-like protease domain 2 (PLP2), a catalytic domain of the nonstructural protein 3 (nsp3) of MHV-A59, encodes a deubiquitinase (DUB) and inactivates IFN regulatory factor 3 (IRF3) thereby the type I interferon (IFN) response.
Principal Findings:
Here we provide further evidence that PLP2 may also target TANK-binding kinase-1 (TBK1), the upstream kinase of IRF3 in the IFN signaling pathway. Overexpression experiments showed that PLP2 deubiquitinated TBK1 and reduced its kinase activity, hence inhibited IFN-β reporter activity. Albeit promiscuous in deubiquitinating cellular proteins, PLP2 inactivated TBK1 and IFN-β response in TNF receptor associated factor 3 (TRAF3) deficient cells, suggesting that targeting TBK1 would be sufficient for PLP2 to inhibit IRF3 activation. This notion was further supported by in vitro kinase assays, in which prior treatment of TBK1 with PLP2 inhibited its kinase activity to phosphorylate IRF3. Intriguing enough, results of PLP2 overexpression system and MHV-A59 infection system proved that PLP2 formed an inactive complex with TBK1 and IRF3 in the cytoplasm and the presence of PLP2 stabilized the hypo-phosphorylated IRF3-TBK1 complex in a dose-dependent manner.
Conclusions:
These results suggest that PLP2 not only inactivates TBK1, but also prevents IRF3 nuclear translocation hence inhibits IFN transcription activation. Identification of the conserved DUB activity of PLP2 in suppression of IFN signaling would provide a useful clue to the development of therapeutics against coronaviruses infection.
Insights
Mouse hepatitis virus A59 papain-like protease domain 2 (PLP2) targets TANK-binding kinase-1 (TBK1), inhibiting the interferon (IFN) response. This coronavirus strategy disables innate immunity, offering therapeutic insights.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Coronaviruses like SARS-CoV and MHV-A59 employ strategies to evade innate immune responses for replication.
- The papain-like protease domain 2 (PLP2) of MHV-A59's nonstructural protein 3 (nsp3) acts as a deubiquitinase (DUB), inhibiting the type I interferon (IFN) response by targeting IRF3.
Purpose of the Study:
- To investigate whether PLP2 targets TBK1, a key kinase in the IFN signaling pathway upstream of IRF3.
- To elucidate the mechanism by which PLP2 interferes with IRF3 activation and IFN production.
Main Methods:
- Overexpression experiments in cell lines.
- In vitro kinase assays.
- Analysis of protein complex formation and phosphorylation status.
- Experiments in TNF receptor-associated factor 3 (TRAF3) deficient cells.
Main Results:
- PLP2 deubiquitinates TBK1, reducing its kinase activity and inhibiting IFN-β reporter activity.
- PLP2 effectively inhibits TBK1 and IFN-β response even in TRAF3-deficient cells, indicating TBK1 is a sufficient target.
- In vitro assays confirm PLP2 inactivates TBK1's ability to phosphorylate IRF3.
- PLP2 forms an inactive complex with TBK1 and IRF3 in the cytoplasm, stabilizing hypo-phosphorylated IRF3-TBK1.
Conclusions:
- PLP2 inactivates TBK1 and prevents IRF3 nuclear translocation, thereby inhibiting IFN transcription.
- The conserved DUB activity of PLP2 in suppressing IFN signaling provides a potential target for developing therapeutics against coronavirus infections.
