Coronavirus Nucleocapsid Protein Enhances the binding of p-PKCα to RACK1: Implications for Inhibition of Nucleocytoplasmic Trafficking and Suppression of the Innate Immune Response
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The hallmark of coronavirus infection lies in its ability to evade host immune defenses, a process intricately linked to the nuclear entry of transcription factors crucial for initiating the expression of antiviral genes. Central to this evasion strategy is the manipulation of the nucleocytoplasmic trafficking system, which serves as an effective target for the virus to modulate the expression of immune response-related genes. In this investigation, we discovered that infection with the infectious bronchitis virus (IBV) dynamically impedes the nuclear translocation of several transcription factors such as IRF3, STAT1, STAT2, NF-κB p65, and the p38 mitogen-activated protein kinase (MAPK), leading to compromised transcriptional induction of key antiviral genes such as IFNβ, IFITM3, and IL-8. Further examination revealed that during the infection process, components of the nuclear pore complex (NPC), particularly FG-Nups (such as NUP62, NUP153, NUP42, and TPR), undergo cytosolic dispersion from the nuclear envelope; NUP62 undergoes phosphorylation, and NUP42 exhibits a mobility shift in size. These observations suggest a disruption in nucleocytoplasmic trafficking. Screening efforts identified the IBV nucleocapsid protein (N) as the agent responsible for the cytoplasmic distribution of FG-Nups, subsequently hindering the nuclear entry of transcription factors and suppressing the expression of antiviral genes. Interactome analysis further revealed that the IBV N protein interacts with the scaffold protein RACK1, facilitating the recruitment of activated protein kinase C alpha (p-PKCα) to RACK1 and relocating the RACK1-PKCα complex to the cytoplasm. These observations are conserved across pan-coronaviruses N proteins. Concurrently, the presence of both RACK1 and PKCα/β proved essential for the phosphorylation and cytoplasmic dispersion of NUP62, the suppression of antiviral cytokine expression, and efficient virus replication. These findings unveil a novel, highly effective, and evolutionarily conserved mechanism.
Author summary
Coronaviruses employ diverse strategies to suppress the host innate immune defense. In this study, we uncovered a novel and highly effective strategy utilized by pan-coronaviruses to inhibit the innate immune response. Specifically, we found that the coronavirus N protein facilitates the binding of p-PKCα to RACK1, leading to the phosphorylation of NUP62 and the cytoplasmic redistribution of multiple FG-Nups. This phenomenon is accompanied by the disruption of nuclear translocation of several innate immune response-related transcription factors and suppression of antiviral/pro-inflammatory genes expression. Our research represents the first elucidation of how the N protein targets and impairs NPC function through the promotion of RACK1-PKCα interaction and NUP62 phosphorylation/disassembly. This discovery unveils a novel mechanism employed by pan-coronaviruses to counteract the host immune response.
