DDX60

DDX60 is an interferon-inducible cytoplasmic DExH-box helicase that functions as a sentinel in antiviral innate immunity by binding viral RNA and DNA, promoting RIG-I-dependent type I interferon signaling, and protecting cytoplasmic dsRNA from RISC-mediated degradation. DDX60 physically associates with RIG-I (DDX58), MDA5, and LGP2 to facilitate RIG-I ligand recognition and downstream IFN-β production, and DDX60 knockout mice show reduced virus-induced type I IFN responses in vivo (PMID:21791617, PMID:25981042). Independent of RIG-I signaling, DDX60 selectively inhibits translation from type II viral internal ribosome entry sites (IRESs) by reducing ribosome loading, thereby restricting replication of picornaviruses such as EMCV (PMID:36256515). DDX60 transcription is regulated by STAT3 phosphorylation downstream of the KRAS–AKT–GSK3β axis and by NEAT1 lncRNA-mediated sequestration of the transcriptional repressor SFPQ, while virus-induced EGFR-dependent phosphorylation of DDX60 attenuates its antiviral functions (PMID:39365875, PMID:41222990, PMID:25981042).

1. 2011 High

   The foundational question—whether DDX60 participates in cytoplasmic antiviral sensing—was answered by showing that DDX60 binds RIG-I, MDA5, and LGP2, promotes RIG-I–dsRNA association, binds viral nucleic acids directly, and is required for RIG-I/MDA5-dependent but not TLR3-dependent IFN induction.

   Evidence Co-IP of endogenous proteins, in vitro helicase-domain RNA/DNA binding, siRNA knockdown with IFN reporter assays in human cells

   PMID:21791617

   Open questions at the time

   • No in vivo validation of DDX60 requirement at this stage
   • Structural basis for DDX60–RIG-I interaction unknown
   • Whether DDX60 has antiviral functions independent of RLR signaling untested
2. 2015 Medium

   In vivo genetic evidence established DDX60 as an upstream activator of RIG-I signaling in a ligand-specific manner, and epistasis with MAVS revealed a parallel DDX60-dependent viral RNA degradation pathway; however, a concurrent independent study using Ddx60-deficient murine cells found no impairment of IFN production or RLR interaction, creating an unresolved discrepancy.

   Evidence DDX60 KO and DDX60/MAVS double-KO mice with in vivo IFN assays (PMID:25981042); independent Ddx60-deficient murine fibroblasts and myeloid cells with RLR agonists, co-IP, and overexpression (PMID:26457795)

   PMID:25981042 PMID:26457795

   Open questions at the time

   • Conflicting results between two independent KO studies remain unreconciled—cell-type, viral ligand, or genetic background differences not resolved
   • Identity of DDX60 nuclease or degradation mechanism not defined
3. 2015 Medium

   Virus-induced EGFR-mediated phosphorylation of DDX60 was identified as a viral immune evasion mechanism that attenuates both RIG-I signaling promotion and RNA degradation by DDX60.

   Evidence Phosphorylation assays and EGFR inhibitor rescue during viral infection

   PMID:25981042

   Open questions at the time

   • Specific phosphorylation sites on DDX60 not mapped
   • How phosphorylation biochemically disrupts DDX60 function not determined
4. 2022 High

   A second, RLR-independent antiviral mechanism was established: DDX60 selectively inhibits cap-independent translation from type II viral IRESs (EMCV, FMDV) by reducing ribosome loading, without affecting type I IRES or 5′-capped translation.

   Evidence IRES reporter translation assays, IRES-swap poliovirus mutagenesis, ribosome/polysome profiling

   PMID:36256515

   Open questions at the time

   • Direct binding target on the IRES RNA not mapped
   • Whether helicase activity is required for translational inhibition untested
   • In vivo relevance for type II IRES viruses not demonstrated
5. 2024 Medium

   DDX60's dsRNA-protective function was placed in a transcriptional regulatory circuit: DDX60 shields cytoplasmic dsRNAs from RISC-mediated degradation, and oncogenic KRAS suppresses DDX60 transcription through AKT–GSK3β-mediated inhibition of STAT3 phosphorylation, linking immune evasion in KRAS-driven cancers to DDX60 loss.

   Evidence DDX60 OE/KD with dsRNA accumulation assays, RISC co-IP, pharmacological AKT/GSK3β/STAT3 pathway inhibition, STAT3 phosphorylation immunoblots

   PMID:39365875

   Open questions at the time

   • Direct biochemical mechanism of dsRNA protection (sequestration vs. enzymatic) not resolved
   • STAT3 binding site on DDX60 promoter not validated by ChIP
   • Relevance in primary human tumors not confirmed
6. 2025 Medium

   An additional transcriptional regulatory layer was defined: the lncRNA NEAT1 promotes DDX60 expression by sequestering the repressor SFPQ into paraspeckles, and DDX60 then cooperates with MDA5 to drive IFN-β via IRF7.

   Evidence NEAT1 KD/OE with DDX60 mRNA and protein assays, SFPQ–DDX60 promoter interaction analysis, IFN-β reporter assays

   PMID:41222990

   Open questions at the time

   • SFPQ binding site on DDX60 promoter not mapped at nucleotide resolution
   • Whether NEAT1-DDX60 axis is broadly relevant across cell types or virus-specific not established

• Key unresolved questions include the structural basis for DDX60 selectivity toward type II IRESs, the biochemical mechanism by which DDX60 protects dsRNA from RISC, the reconciliation of conflicting KO phenotypes regarding RLR dependence, and the physiological significance of DDX60 in cancer immune evasion versus antiviral defense.
• No crystal or cryo-EM structure of DDX60 or its complexes
• IRES vs. dsRNA protection vs. RLR promotion—whether these are unified or separable biochemical activities is unclear
• Contradictory KO phenotypes from independent labs remain unresolved