PCIF1 Attenuates Type I Interferon Induction by Inhibiting IRF3 Activation in a Methyltransferase-Independent Manner

Area of Science:

• Immunology
• Molecular Biology
• Gene Expression

Background:

• PCIF1 is known as an RNA methyltransferase involved in gene expression.
• Type I interferon (IFN) induction is critical for antiviral immunity but its dysregulation causes inflammatory and autoimmune diseases.

Purpose of the Study:

• To investigate a potential novel role of PCIF1 in regulating type I IFN induction.
• To elucidate the mechanism underlying PCIF1's regulation of type I IFN responses.
• To determine if PCIF1's RNA methyltransferase activity is required for its role in IFN regulation.

Main Methods:

• Poly(I:C) stimulation in PCIF1-deficient cells.
• Measurement of type I IFN response, STAT1 activation, and ISG expression.
• Analysis of IFNB1 transcription, IRF3 phosphorylation, and nuclear translocation.
• Assessment of PCIF1's methyltransferase-inactive mutant in IFN induction assays.

Main Results:

• PCIF1 deficiency significantly enhances poly(I:C)-induced type I IFN response, STAT1 activation, and ISG expression.
• PCIF1 suppresses IFNB1 transcription by inhibiting IRF3 phosphorylation and nuclear translocation, independent of mRNA stability.
• This suppressive function is independent of PCIF1's RNA methyltransferase activity.

Conclusions:

• PCIF1 acts as a novel, methyltransferase-independent suppressor of type I IFN responses.
• PCIF1 possesses a previously unrecognized non-catalytic function in innate immunity regulation.
• PCIF1's non-catalytic function presents a potential therapeutic target for antiviral immunity and inflammatory diseases.