STING-Mediated IFI16 Degradation Negatively Controls Type I Interferon Production

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• γ-interferon-inducible protein-16 (IFI16) is a crucial DNA sensor that initiates type I interferon (IFN-I) production and antiviral responses.
• The precise mechanisms for negatively regulating IFI16 to prevent excessive IFN-I production and autoimmunity remain largely unknown.

Purpose of the Study:

• To elucidate the regulatory mechanism of IFI16 degradation by STING.
• To understand how STING-mediated IFI16 regulation impacts antiviral immunity and autoimmunity.

Main Methods:

• Co-immunoprecipitation assays to detect protein-protein interactions between STING and IFI16.
• Western blotting and immunofluorescence to assess IFI16 ubiquitination and degradation.
• Site-directed mutagenesis to identify key residues in IFI16 responsible for ubiquitination and degradation.
• Reporter assays to measure IFN-β and IFN-stimulated gene expression.
• Viral infection assays (HSV-1) to evaluate antiviral responses.

Main Results:

• STING directly interacts with IFI16, promoting its degradation through the ubiquitin-proteasome pathway via recruitment of the E3 ligase TRIM21.
• The 1-pyrin domain of IFI16 mediates the interaction with STING.
• Specific lysine residues (K3, K4, K6) in the N-terminus of IFI16 are critical for STING-mediated ubiquitination and degradation.
• A degradation-resistant IFI16 mutant (IFI16-K3/4/6R) leads to elevated IFN-β and antiviral gene expression upon viral DNA stimulation.
• Cells expressing the degradation-resistant IFI16 mutant exhibit reduced HSV-1 infection.

Conclusions:

• STING negatively regulates IFI16 by promoting its degradation, thereby limiting excessive type I interferon production during antiviral responses.
• This STING-dependent negative feedback loop on IFI16 is essential for maintaining immune homeostasis and preventing autoimmune diseases.