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Updated: Apr 15, 2026

A High Resolution Method to Monitor Phosphorylation-dependent Activation of IRF3
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A High Resolution Method to Monitor Phosphorylation-dependent Activation of IRF3

Published on: January 24, 2016

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RIOK3-mediated phosphorylation of MDA5 interferes with its assembly and attenuates the innate immune response

Ken Takashima, Hiroyuki Oshiumi, Hiromi Takaki

    Cell Reports
    |April 14, 2015
    PubMed

    Insights

    RIOK3 phosphorylates the MDA5 sensor, inhibiting its ability to detect viral RNA and trigger immune responses. This discovery reveals a new regulatory mechanism for MDA5 activation in cells.

    Area of Science:

    • Immunology
    • Molecular Biology
    • Virology

    Background:

    • MDA5 (MDA5) is a cytoplasmic sensor for viral double-stranded RNA (dsRNA).
    • MDA5 activation requires filament assembly along dsRNA to signal through the MAVS adaptor.
    • PP1α and PP1γ phosphatases are known to dephosphorylate and activate MDA5.

    Purpose of the Study:

    • To identify protein kinases that regulate MDA5 activity.
    • To elucidate the role of RIOK3 in MDA5-mediated innate immune signaling.

    Main Methods:

    • RIOK3 was identified as an MDA5-interacting protein kinase.
    • RIOK3 knockout and ectopic expression were used to study MDA5 signaling.
    • Phosphorylation site analysis and mutation studies (MDA5-S828D) were performed.

    Main Results:

    • RIOK3 phosphorylates the C-terminal region of MDA5.
    • RIOK3 knockout enhanced type I IFN and IFN-inducible gene expression after measles virus infection.
    • RIOK3 expression or MDA5 phosphorylation attenuated MDA5 signaling by impairing filament formation.

    Conclusions:

    • RIOK3 acts as a negative regulator of MDA5 by phosphorylating its C-terminal region.
    • MDA5 C-terminal phosphorylation by RIOK3 inhibits MDA5 multimerization and downstream signaling.
    • This identifies a novel regulatory pathway controlling cytoplasmic viral RNA sensing by MDA5.

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