Affinage

CASC3

Protein CASC3 · UniProt O15234

Length
703 aa
Mass
76.3 kDa
Annotated
2026-06-09
24 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/7 claims corpus-supported (86%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CASC3 (MLN51/BTZ) is an RNA-binding protein that functions as a peripheral component of the exon junction complex (EJC), coupling spliced-mRNA marking to downstream cytoplasmic gene-expression control (PMID:15166247). Through its conserved SELOR domain it associates with the EJC core components Magoh, Y14, and NFX1/TAP and co-precipitates with spliced mRNAs in both nucleus and cytoplasm (PMID:15166247). CASC3 acts as a potent allosteric activator of the EJC helicase eIF4AIII, lowering its KM for ATP and increasing kcat to enhance ATPase and RNA-helicase activity and clamp the complex onto RNA (PMID:17375189). Beyond core assembly, CASC3 directly contacts eIF3 and ribosomal subunits to enhance translation of intron-containing mRNAs via the EJC (PMID:23530232), and it is required transcriptome-wide for nonsense-mediated mRNA decay, equipping the EJC with persistent NMD-signaling capability such that tethered CASC3 stimulates mRNA decay and endonucleolytic cleavage at the termination codon (PMID:32621609). Genetic studies establish that CASC3 is a substoichiometric, non-constitutive EJC subunit whose loss causes developmental delay rather than the severe microcephaly and apoptosis seen with core EJC haploinsufficiency (PMID:27780844). CASC3 protein levels are controlled by Smurf2-mediated ubiquitination at K254 and proteasomal degradation, a route that constrains leukemia cell viability (PMID:40978141). CASC3 has additional cytoplasmic roles in processing-body dynamics (PMID:25205763) and in GM-CSF-driven synoviocyte proliferation (PMID:17101062, PMID:18513326).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2004 High

    Established CASC3 as an EJC-associated RNA-binding protein, answering whether it physically links to the spliced-mRNA-marking machinery and through what module.

    Evidence Co-immunoprecipitation of endogenous proteins, mRNA co-precipitation, and SELOR-domain mapping in human cells

    PMID:15166247

    Open questions at the time
    • Did not resolve whether CASC3 is constitutive or peripheral to the EJC
    • Functional consequence of EJC association not yet defined
  2. 2007 High

    Defined a biochemical mechanism for CASC3 within the EJC by showing it allosterically activates the eIF4AIII helicase, explaining how it could stabilize the complex on RNA.

    Evidence In vitro reconstituted ATPase and RNA-helicase assays with kinetic analysis of the eIF4AIII–MLN51 complex

    PMID:17375189

    Open questions at the time
    • In vitro kinetics not linked to a cellular phenotype
    • Interplay with Y14–Magoh inhibition in vivo unresolved
  3. 2013 High

    Extended CASC3 function to translation, answering whether the EJC-bound protein influences protein synthesis and through which factor.

    Evidence Co-IP, in vitro binding to eIF3 and ribosomal subunits, cell-free translation extracts, and reporter assays with siRNA knockdown

    PMID:23530232

    Open questions at the time
    • Structural basis of the eIF3 contact not defined
    • Selectivity for intron-containing mRNAs mechanistically unexplained
  4. 2014 Medium

    Connected CASC3 to cytoplasmic RNA granule dynamics, showing its abundance influences P-body composition.

    Evidence Fluorescence microscopy, live-cell imaging, and P-body/stress-granule marker analysis, including HER2+ breast cancer cells

    PMID:25205763

    Open questions at the time
    • Mechanism of P-body disassembly unknown
    • Identity and function of the novel CASC3 foci undefined
  5. 2016 High

    Resolved the in vivo status of CASC3 within the EJC, showing it is substoichiometric and non-essential relative to core subunits.

    Evidence Two Casc3 mouse alleles with brain histology, cell counting, and protein stoichiometry by western blot

    PMID:27780844

    Open questions at the time
    • Molecular basis of milder phenotype versus core EJC loss not defined
    • Tissue-specific requirements beyond brain unaddressed
  6. 2020 High

    Established CASC3 as a peripheral EJC factor that confers NMD-signaling competence, clarifying its distinct role from core assembly and splicing.

    Evidence CASC3 knockout cells, transcriptome-wide RNA-seq, tethering and endonucleolytic cleavage assays, and EJC composition mass spectrometry

    PMID:32621609

    Open questions at the time
    • How CASC3 communicates with NMD effectors not detailed
    • Determinants of CASC3 loading onto specific EJCs unknown
  7. 2008 Medium

    Placed CASC3 in a signaling-driven proliferation pathway, showing GM-CSF/p38 MAPK regulation and action upstream of FLIP in rheumatoid arthritis synoviocytes.

    Evidence siRNA knockdown, pharmacological MAPK inhibition, transcriptional analysis, and western blot in FLSs (extending 2006 proliferation findings)

    PMID:17101062 PMID:18513326

    Open questions at the time
    • Molecular link between EJC/RNA functions and FLIP regulation unclear
    • Confined to a single disease cell type
  8. 2025 Medium

    Identified the post-translational control of CASC3 abundance, showing Smurf2-mediated ubiquitination and degradation with functional consequences in leukemia.

    Evidence Co-IP, ubiquitination assay, domain mapping (137–283), K254 mutagenesis, and mouse tumor models

    PMID:40978141

    Open questions at the time
    • Signals triggering Smurf2-mediated turnover unknown
    • Whether degradation reshapes EJC/NMD output not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CASC3 abundance and Smurf2-mediated turnover dynamically select which EJCs become NMD-competent, and how this is integrated with its translation and granule roles, remains open.
  • No structural model of the CASC3–EJC–NMD effector interface
  • Determinants of CASC3 loading onto specific transcripts undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 2 GO:0003723 RNA binding 1 GO:0045182 translation regulator activity 1
Localization
GO:0005829 cytosol 2 GO:0005634 nucleus 1
Pathway
R-HSA-8953854 Metabolism of RNA 2
Partners
EIF3EIF4A3MAGOHNXF1RBM8ASMURF2
Complex memberships
exon junction complex (EJC)

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 MLN51 (CASC3) is an RNA-binding protein that associates with the exon junction complex (EJC) core components Magoh, Y14, and NFX1/TAP via its conserved SELOR (speckle localizer and RNA binding module) domain. It co-precipitates with spliced mRNAs at the EJC deposition position both in nucleus and cytoplasm, and transiently co-localizes with Magoh in nuclear speckles. Co-immunoprecipitation of endogenous proteins, co-precipitation with spliced mRNAs, subcellular localization studies, domain mapping The Journal of biological chemistry High 15166247
2007 MLN51 (CASC3) stimulates both the ATPase and RNA-helicase activities of eIF4AIII: it decreases the KM for ATP by an order of magnitude and increases kcat ~30-fold, and the ATP-bound eIF4AIII–MLN51 complex shows ~100-fold higher RNA affinity than the unbound form. The Y14–Magoh heterodimer partially inhibits MLN51-stimulated ATPase activity but does not return it to background levels. In vitro ATPase assay, RNA-helicase assay, kinetic analysis of eIF4AIII–MLN51 complex PloS one High 17375189
2013 MLN51 (CASC3) directly interacts with eukaryotic translation initiation factor eIF3 and ribosomal subunits, and functions as a translation enhancer: overexpression preferentially increases translation of intron-containing reporters via the EJC, silencing MLN51 decreases translation, and modulation in cell-free extracts confirms a direct role in protein synthesis. Immunoprecipitation, in vitro binding assays, cell-free translation extracts, reporter translation assays, siRNA knockdown Proceedings of the National Academy of Sciences of the United States of America High 23530232
2014 MLN51 (CASC3) is a component of cytoplasmic processing bodies (P-bodies) and its overexpression triggers P-body disassembly and formation of novel small cytoplasmic RNA-containing foci with directed movements distinct from stress granules and P-bodies. A similar reduction in P-body count is observed in HER2+ breast cancer cells naturally overexpressing MLN51. Fluorescence microscopy, live-cell imaging, co-localization assays, RNA staining, P-body marker analysis Journal of cell science Medium 25205763
2016 In vivo mouse studies show CASC3 is not an essential EJC core component for brain development: homozygous Casc3 null embryos are smaller with proportionately reduced brain size due to developmental delay (fewer neurons and progenitors, no apoptosis), contrasting sharply with severe microcephaly and apoptosis caused by haploinsufficiency of other EJC cores (Magoh, Eif4a3, Rbm8a). CASC3 protein is substoichiometric relative to other EJC cores in the developing brain. Genetic mouse models (null and hypomorphic alleles), brain histology, cell counting, protein expression quantification by western blot RNA (New York, N.Y.) High 27780844
2020 CASC3 is required for transcriptome-wide promotion of nonsense-mediated mRNA decay (NMD): CASC3 knockout cells show upregulation of hundreds of NMD-targeted mRNA isoforms without changes in overall EJC composition or EJC-dependent splicing. Tethering CASC3 to reporter mRNAs stimulates mRNA decay and endonucleolytic cleavage at the termination codon. CASC3 functions as a peripheral (not constitutive) EJC component that equips the EJC with cytoplasmic NMD-communicating ability. CASC3 knockout cell lines, transcriptome-wide RNA-seq, tethering assays, endonucleolytic cleavage assays, mass spectrometry of EJC composition Nucleic acids research High 32621609
2006 MLN51 (CASC3) is required downstream of GM-CSF signaling for proliferation of fibroblast-like synoviocytes: siRNA knockdown of MLN51 completely blocks GM-CSF/synovial fluid-mediated proliferation of rheumatoid arthritis FLSs. siRNA knockdown, cell proliferation assay, cytokine treatment Arthritis research & therapy Medium 17101062
2008 In rheumatoid arthritis FLSs, GM-CSF-mediated MLN51 (CASC3) upregulation is controlled at both transcriptional and post-translational levels via p38 MAPK. MLN51 acts upstream of FLICE-inhibitory protein (FLIP) upregulation, which mediates FLS hyperproliferation. siRNA knockdown, MAPK inhibition, western blot, transcriptional analysis The FEBS journal Medium 18513326
2025 CASC3 is a substrate of the E3 ubiquitin ligase Smurf2: Smurf2 interacts with CASC3 and promotes its ubiquitination and proteasomal degradation. The degradation depends on the CASC3 137–283 domain and lysine residue K254. Smurf2-mediated CASC3 degradation reduces leukemia cell viability and tumor growth. Co-immunoprecipitation, ubiquitination assay, domain mapping, lysine mutagenesis, mouse tumor models iScience Medium 40978141

Source papers

Stage 0 corpus · 24 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 Association of the breast cancer protein MLN51 with the exon junction complex via its speckle localizer and RNA binding module. The Journal of biological chemistry 95 15166247
2013 EJC core component MLN51 interacts with eIF3 and activates translation. Proceedings of the National Academy of Sciences of the United States of America 62 23530232
2020 CASC3 promotes transcriptome-wide activation of nonsense-mediated decay by the exon junction complex. Nucleic acids research 45 32621609
2007 MLN51 stimulates the RNA-helicase activity of eIF4AIII. PloS one 44 17375189
2020 Depletion of circ_0007841 inhibits multiple myeloma development and BTZ resistance via miR-129-5p/JAG1 axis. Cell cycle (Georgetown, Tex.) 37 33131409
2016 Methylation-regulated miR-124-1 suppresses tumorigenesis in hepatocellular carcinoma by targeting CASC3. Oncotarget 34 27029030
2020 Circular RNA circ_0091579 Promotes Hepatocellular Carcinoma Proliferation, Migration, Invasion, and Glycolysis Through miR-490-5p/CASC3 Axis. Cancer biotherapy & radiopharmaceuticals 24 32673066
2014 Overexpression of MLN51 triggers P-body disassembly and formation of a new type of RNA granules. Journal of cell science 24 25205763
2006 MLN51 and GM-CSF involvement in the proliferation of fibroblast-like synoviocytes in the pathogenesis of rheumatoid arthritis. Arthritis research & therapy 24 17101062
2023 Guanidine-modified nanoparticles as robust BTZ delivery carriers and activators of immune responses. Journal of controlled release : official journal of the Controlled Release Society 19 37019286
2023 Drug distribution and efficacy of the DprE1 inhibitor BTZ-043 in the C3HeB/FeJ mouse tuberculosis model. Antimicrobial agents and chemotherapy 19 37791784
2021 circ-NOL10 regulated by MTDH/CASC3 inhibits breast cancer progression and metastasis via multiple miRNAs and PDCD4. Molecular therapy. Nucleic acids 19 34729247
2014 Development of P22 viral capsid nanocomposites as anti-cancer drug, bortezomib (BTZ), delivery nanoplatforms. Macromolecular bioscience 19 24847525
2016 Mouse models of Casc3 reveal developmental functions distinct from other components of the exon junction complex. RNA (New York, N.Y.) 17 27780844
2023 CASC3 Biomolecular Condensates Restrict Turnip Crinkle Virus by Limiting Host Factor Availability. Journal of molecular biology 11 36642157
2023 Pharmacokinetics and Efficacy of the Benzothiazinone BTZ-043 against Tuberculous Mycobacteria inside Granulomas in the Guinea Pig Model. Antimicrobial agents and chemotherapy 10 36975792
2008 FLIP and MAPK play crucial roles in the MLN51-mediated hyperproliferation of fibroblast-like synoviocytes in the pathogenesis of rheumatoid arthritis. The FEBS journal 9 18513326
2022 CTCF-activated SNHG16 facilitates gastrointestinal stromal tumor by targeting miR-128-3p/CASC3 axis. Experimental cell research 6 35358540
2017 [Icaritin Reverses Multidrug Resistance of Multiple Myeloma Cell Line KM3/BTZ]. Zhongguo shi yan xue ye xue za zhi 3 29262899
2021 Cell-Penetrating Peptides Predicted From CASC3, AKIP1, and AHRR Proteins. Frontiers in pharmacology 1 34504427
2026 MLN51 (Metastatic Lymph Node Gene 51)/CASC3 (Cancer Susceptibility Candidate Gene 3), A Putative Tumour Suppressor in Breast Cancer, the Clinical and Therapeutic Connections. Breast cancer (Dove Medical Press) 0 41858529
2025 Identification of CASC3 as a novel SADS-CoV restriction factor through liquid-liquid phase separation inhibiting viral replication. Veterinary microbiology 0 40381606
2025 Smurf2 enhances ubiquitin-mediated degradation of CASC3 and attenuates leukemia progression. iScience 0 40978141
2019 [Effect of Bushen Yanggu Decoction on Multidrug Resistance of Multiple Myeloma Cell Line KM3/BTZ]. Zhongguo shi yan xue ye xue za zhi 0 30998158

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