The Ca ²⁺ -dependent phosphatase calcineurin dephosphorylates TBK1 to suppress antiviral innate immunity

ABSTRACT Tumor necrosis factor receptor-associated factor family member-associated NF-κB activator-binding kinase 1 (TBK1) plays a key role in the induction of the type 1 interferon (IFN-I) response, which is an important component of innate antiviral defense. Viruses target calcium (Ca 2+ ) signaling networks, which participate in the regulation of the viral life cycle, as well as mediate the host antiviral response. Although many studies have focused on the role of Ca 2+ signaling in the regulation of IFN-I, the relationship between Ca 2+ and TBK1 in different infection models requires further elucidation. Here, we examined the effects of the Newcastle disease virus (NDV)-induced increase in intracellular Ca 2+ levels on the suppression of host antiviral responses. We demonstrated that intracellular Ca 2+ increased significantly during NDV infection, leading to impaired IFN-I production and antiviral immunity through the activation of calcineurin (CaN). Depletion of Ca² + was found to lead to a significant increase in virus-induced IFN-I production resulting in the inhibition of viral replication. Mechanistically, the accumulation of Ca 2+ in response to viral infection increases the phosphatase activity of CaN, which in turn dephosphorylates and inactivates TBK1 in a Ca 2+ -dependent manner. Furthermore, the inhibition of CaN on viral replication was counteracted in TBK1 knockout cells. Together, our data demonstrate that NDV hijacks Ca 2+ signaling networks to negatively regulate innate immunity via the CaN-TBK1 signaling axis. Thus, our findings not only identify the mechanism by which viruses exploit Ca 2+ signaling to evade the host antiviral response but also, more importantly, highlight the potential role of Ca 2+ homeostasis in the viral innate immune response. IMPORTANCE Viral infections disrupt intracellular Ca 2+ homeostasis, which affects the regulation of various host processes to create conditions that are conducive for their own proliferation, including the host immune response. The mechanism by which viruses trigger TBK1 activation and IFN-I induction through viral pathogen-associated molecular patterns has been well defined. However, the effects of virus-mediated Ca 2+ imbalance on the IFN-I pathway requires further elucidation, especially with respect to TBK1 activation. Herein, we report that NDV infection causes an increase in intracellular free Ca 2+ that leads to activation of the serine/threonine phosphatase CaN, which subsequently dephosphorylates TBK1 and negatively regulates IFN-I production. Furthermore, depletion of Ca 2+ or inhibition of CaN activity exerts antiviral effects by promoting the production of IFN-I and inhibiting viral replication. Thus, our results reveal the potential role of Ca 2+ in the innate immune response to viruses and provide a theoretical reference for the treatment of viral infectious diseases.