DDX50

DDX50 is a DExD/H-box RNA helicase that operates across innate antiviral signaling, genome maintenance, and cell differentiation (PMID:35215908, PMID:39764852, PMID:40043837). In the immune context, DDX50 promotes IRF3-dependent antiviral responses: its loss impairs IRF3 phosphorylation and downstream cytokine/chemokine production after cytoplasmic dsRNA stimulation or viral infection, and it acts through the adaptor TRIF independently of the related sensor DDX1 to restrict both RNA and DNA viruses (PMID:35215908). Independently, DDX50 safeguards genome stability by resolving transcription-coupled R-loops; its depletion increases RNA-DNA hybrids, provokes DNA damage and replication stress, and these phenotypes are reversed by RNase H1 overexpression or transcription inhibition, establishing the helicase as a hybrid-resolution factor at the transcription-replication interface (PMID:40043837). In differentiation, glucose binding to conserved ATP-binding sequences in DDX50 triggers a conformational change that monomerizes the protein, allowing it to bind STAU1 and divert it from a UPF1 RNA-decay complex into a DDX50-STAU1 ribonuclear complex that stabilizes and remodels pro-differentiation transcripts including JUN, OVOL1, CEBPB, PRDM1, and TINCR (PMID:39764852).

1. 2017 Medium

   Established the first functional link between DDX50 and antiviral immunity by showing it restricts flavivirus replication via interferon induction, rather than being a passive RNA-binding protein.

   Evidence DDX50 knockdown/overexpression with DENV-2 RNA quantitation and IFN-β promoter reporter assays in cell lines

   PMID:28181036

   Open questions at the time

   • Direct adaptor or sensor partner not identified
   • Cooperation with RIG-I/MDA5 shown only as additive promoter activity, not as physical mechanism
2. 2017 Low

   Tested whether DDX50 behaves like antiviral paralogs and instead found it may favor viral replication in a different infection context, hinting at virus-specific roles.

   Evidence In-cell Western assay of viral protein after DDX50 modulation in Hantaan virus-infected cells

   PMID:28676847

   Open questions at the time

   • Single method (ICW) and described as 'probably' — effect not confirmed
   • No mechanistic basis for the contrast with antiviral activity in other contexts
   • No reciprocal validation or genetic perturbation
3. 2022 High

   Resolved how DDX50 feeds into innate signaling by placing it on the TRIF-IRF3 axis, distinguishing it from the related sensor DDX1 and demonstrating broad viral restriction.

   Evidence CRISPR/shRNA deletion in mouse and human cells, IRF3 phosphorylation and cytokine assays, TRIF Co-IP, and viral restriction across vaccinia, HSV, and Zika

   PMID:35215908

   Open questions at the time

   • Whether DDX50 directly senses viral nucleic acid or acts downstream of a sensor is unresolved
   • Structural basis of the DDX50-TRIF interaction not defined
   • Catalytic (helicase) requirement for IRF3 activation not tested
4. 2024 Medium

   Identified a post-translational regulatory input by showing DDX50 carries a Pro/N-degron recognized by the CTLH ubiquitin ligase substrate receptor GID4, linking its abundance to targeted degradation.

   Evidence BioID proximity proteomics and quantitative proteomics using the PFI-7 chemical antagonist of GID4 Pro/N-degron binding

   PMID:38773330

   Open questions at the time

   • Ubiquitination and degradation of DDX50 not directly demonstrated
   • Functional consequence of GID4-mediated turnover for any DDX50 activity unknown
   • Single study
5. 2025 High

   Defined a genome-protective function by showing DDX50 resolves transcription-generated R-loops to prevent replication stress and DNA damage.

   Evidence DDX50 knockdown with H2AX phosphorylation, comet, DNA fiber, RPA focus, and RNA-DNA hybrid assays, rescued by RNase H1 overexpression and transcription inhibition

   PMID:40043837

   Open questions at the time

   • Direct in vitro hybrid-unwinding activity on R-loops not shown
   • Genomic sites of action and recruitment mechanism unknown
   • Relationship between this role and its immune/differentiation functions undefined
6. 2025 High

   Uncovered a glucose-sensing, conformation-switched mechanism by which DDX50 controls mRNA fate to drive differentiation, redirecting STAU1 from decay to stabilization of pro-differentiation transcripts.

   Evidence Glucose-binding and conformation assays, DDX50-STAU1 and STAU1-UPF1 Co-IP, RNA-binding and structure probing, RNA stability assays, and depletion with differentiation phenotype readouts

   PMID:39764852

   Open questions at the time

   • How glucose binding at ATP-binding sequences mechanistically links to monomerization at atomic resolution is not defined
   • Whether the same conformational switch governs its immune or R-loop functions is untested
   • Generality of target RNA set beyond the listed transcripts

• It remains unknown whether DDX50's three documented roles — IRF3/TRIF antiviral signaling, R-loop resolution, and STAU1-mediated mRNA stabilization — represent a single biochemical activity deployed in different contexts or distinct functions, and how its GID4-mediated turnover integrates with them.
• No unifying biochemical assay connects the helicase activity to all three roles
• Direct catalytic substrate(s) of the helicase not defined in any context