DDX50

DDX50 is a nucleolar DExD/H-box RNA helicase that functions at the intersection of innate immunity, genome maintenance, and mRNA metabolism. It promotes type I interferon responses by facilitating IRF3 phosphorylation and IFN-β production through a TRIF-dependent, DDX1-independent pathway, thereby restricting replication of diverse RNA and DNA viruses (PMID:35215908, PMID:28181036). DDX50 resolves transcription-dependent R-loops to prevent DNA damage and replication stress, as demonstrated by rescue of DDX50-depletion phenotypes with RNase H1 overexpression or transcription inhibition (PMID:40043837). Glucose-induced dissociation of DDX50 dimers into monomers enables formation of a DDX50–STAU1 ribonucleoprotein complex that antagonizes Staufen-mediated mRNA decay and stabilizes pro-differentiation transcripts, making DDX50 essential for cellular differentiation programs (PMID:39764852).

1. 2002 Medium

   Establishing where DDX50 resides was a prerequisite for understanding its function; proteomic mapping placed it in the nucleolus, implicating it in RNA-related nuclear processes.

   Evidence Mass spectrometry of isolated HeLa nucleoli

   PMID:11790298

   Open questions at the time

   • No functional role assigned at this stage
   • Nucleolar localization confirmed by fractionation-MS but not by imaging
2. 2005 Medium

   Quantitative nucleolar proteomics revealed DDX50 is dynamically associated with the nucleolus, with its abundance changing upon metabolic perturbation, suggesting regulated shuttling rather than static residence.

   Evidence SILAC-based quantitative proteomics of nucleolar fractions under actinomycin D treatment

   PMID:15635413

   Open questions at the time

   • Signals driving nucleolar retention or release unknown
   • Functional consequence of redistribution not tested
3. 2012 Medium

   UV-crosslinking interactome capture identified DDX50 as a direct mRNA-binding protein, extending its substrate repertoire beyond ribosomal RNA processing expectations for a nucleolar helicase.

   Evidence UV crosslinking and oligo(dT) capture followed by mass spectrometry in HeLa cells

   PMID:22658674

   Open questions at the time

   • Specific mRNA targets not identified
   • Whether mRNA binding is functionally consequential was unknown
4. 2017 Medium

   The first functional role for DDX50 emerged in antiviral immunity: DDX50 restricted dengue virus replication by promoting IFN-β production, cooperating additively with RIG-I and MDA5, placing it in the innate immune sensing pathway.

   Evidence siRNA knockdown and overexpression with IFN-β reporter assays and ISG qRT-PCR during DENV-2 infection

   PMID:28181036

   Open questions at the time

   • Signalling adaptor through which DDX50 operated was not identified
   • A separate study reported a pro-viral role for DDX50 during hantavirus infection, raising context-dependency questions (PMID:28676847)
5. 2022 High

   The mechanistic basis of DDX50's antiviral function was resolved: DDX50 interacts with TRIF to promote IRF3 phosphorylation independently of DDX1, establishing it as a bona fide restriction factor against both RNA and DNA viruses.

   Evidence CRISPR knockout in mouse and human cells, co-immunoprecipitation with TRIF, IRF3 phosphorylation and cytokine assays, viral replication assays for vaccinia, HSV, and Zika viruses

   PMID:35215908

   Open questions at the time

   • Direct RNA-sensing activity versus adaptor role not biochemically resolved
   • Crystal or cryo-EM structure of DDX50–TRIF complex unavailable
6. 2024 Medium

   Identification of a Pro/N-degron in DDX50 recognized by the CTLH E3 ligase receptor GID4 revealed a potential ubiquitin-dependent regulatory mechanism controlling DDX50 turnover.

   Evidence BioID proximity biotinylation and quantitative proteomics with chemical probe PFI-7

   PMID:38773330

   Open questions at the time

   • Whether GID4 binding leads to DDX50 degradation or non-degradative ubiquitination not resolved
   • Physiological conditions triggering GID4-mediated regulation unknown
7. 2025 High

   A genome maintenance role was uncovered: DDX50 resolves transcription-dependent R-loops, and its depletion causes DNA damage and replication stress that is rescued by RNase H1, establishing DDX50 as a guardian of genome integrity.

   Evidence siRNA depletion with γH2AX, comet assay, DNA fiber analysis, S9.6 antibody detection of R-loops, RNase H1 rescue, transcription inhibition rescue

   PMID:40043837

   Open questions at the time

   • Whether R-loop resolution uses the same helicase activity as mRNA-related functions is unclear
   • Relationship to DDX37, which shares R-loop resolution activity, not mechanistically dissected
8. 2025 High

   A metabolic sensing mechanism was revealed: glucose binds DDX50 at its ATP-binding cassettes, triggering dimer-to-monomer conversion that enables formation of a DDX50–STAU1 complex, which stabilizes pro-differentiation mRNAs by sequestering STAU1 from UPF1-dependent decay.

   Evidence Glucose-binding assays, oligomerization analysis, co-immunoprecipitation, RNA immunoprecipitation, RNA structure probing, differentiation assays in multiple cell types

   PMID:39764852

   Open questions at the time

   • Whether glucose-dependent monomerization also regulates DDX50's antiviral or R-loop resolution activities is unknown
   • Structural basis of glucose binding to the ATP-binding cassette not determined

• Key unresolved questions include whether DDX50's distinct functions — innate immune signalling, R-loop resolution, and mRNA stabilization — are coordinated or independently regulated, and what structural features allow glucose and ATP to differentially modulate its activity.
• No structural model of DDX50 in any functional state
• Crosstalk between antiviral, genome stability, and mRNA decay functions untested
• In vivo phenotyping in DDX50-null organisms not reported