Casein kinase 1γ1 inhibits the RIG-I/TLR signaling pathway through phosphorylating p65 and promoting its degradation

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• Casein kinase 1 (CK1) is crucial for numerous cellular functions through protein phosphorylation.
• The retinoic acid-inducible gene I (RIG-I) pathway is a key component of the innate immune system against RNA viruses.
• NF-κB signaling is central to the inflammatory and immune response.

Purpose of the Study:

• To investigate the role of Casein kinase 1 gamma 1 (CK1γ1) in regulating RNA virus-induced innate immune signaling.
• To elucidate the mechanism by which CK1γ1 affects the RIG-I pathway and NF-κB activation.

Main Methods:

• Ectopic expression and knockdown of CK1γ1 in cellular models.
• Stimulation with Sendai virus (SeV) to activate RIG-I and NF-κB pathways.
• Western blotting to assess protein levels and phosphorylation.
• In vitro kinase assays to confirm direct phosphorylation.
• Co-immunoprecipitation to study protein interactions.
• Analysis of p65 degradation mediated by ubiquitin E3 ligases.

Main Results:

• CK1γ1 expression inhibited IFN-β activation induced by RIG-I signaling.
• Knockdown of CK1γ1 enhanced IFN-β and NF-κB activation upon viral stimulation.
• CK1γ1 directly phosphorylates NF-κB subunit p65 at Ser(536).
• Kinase activity of CK1γ1 is essential for its inhibitory function.
• CK1γ1 promotes p65 degradation via CUL2 and COMMD1, thereby negatively regulating innate immunity.
• CK1γ1 also impacts Toll-like receptor (TLR) signaling.

Conclusions:

• CK1γ1 acts as a novel negative regulator of RNA virus-induced innate immune signaling.
• The mechanism involves CK1γ1-mediated phosphorylation and subsequent degradation of the NF-κB p65 subunit.
• CK1γ1's kinase activity is critical for its role in dampening antiviral responses.