Affinage

CACTIN

Splicing factor Cactin · UniProt Q8WUQ7

Length
758 aa
Mass
88.7 kDa
Annotated
2026-06-09
14 papers in source corpus 12 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/6 claims corpus-supported (83%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

Cactin is a conserved nuclear protein that functions as a spliceosome-associated factor required for efficient pre-mRNA splicing, and through this activity governs diverse cellular processes including chromosome cohesion, cell proliferation, and collective cell migration (PMID:28062851, PMID:35612426). In human cells it physically associates with the spliceosomal helicase DHX8 and the splicing co-activator SRRM2, and its depletion causes inefficient splicing of thousands of pre-mRNAs, premature sister chromatid separation, genome instability, and proliferation arrest; the cohesion defect is largely attributable to incomplete splicing of the sororin (CDCA5) pre-mRNA (PMID:28062851). Cactin orthologs show a specialized role in splicing introns with a branchpoint-distant 3' splice site, an evolutionarily conserved function demonstrated in fission yeast and conserved into intron-rich eukaryotes (PMID:25398909, PMID:36095128). In Drosophila border cells the same splicing function controls cluster polarity and migration by sustaining correct isoform expression of the COPII components Sec23/Sec24CD that traffic the apical determinant Crumbs (PMID:35612426). Independently, Cactin acts as a nuclear negative regulator of innate immune signaling: human Cactin suppresses TLR-induced NF-κB and interferon-regulatory factor activation, interacts with the IκB-like protein IκBL, and requires nuclear localization for this activity (PMID:20829348), a regulatory role first foreshadowed by its identification as a partner of the Drosophila IκB protein Cactus in the Rel/NF-κB pathway (PMID:10842059). Cactin abundance and activity are tuned post-translationally: TRIM39 stabilizes Cactin to restrain NF-κB signaling (PMID:26363554), Usp14 removes K48- and K63-linked polyubiquitin chains to block proteasomal degradation (PMID:38563731), and PGK-mediated phosphorylation at IDR serines 99/104 converts Cactin from stable aggregates into dynamic liquid droplets and enhances antiviral activity against Drosophila C virus (PMID:38446061).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2000 Medium

    Established the first functional link between Cactin and Rel/NF-κB signaling by placing it physically and genetically with the IκB protein Cactus.

    Evidence Yeast two-hybrid screen and genetic epistasis in Drosophila embryos

    PMID:10842059

    Open questions at the time
    • Molecular mechanism of how Cactin acts within the pathway undefined
    • No biochemical activity assigned
  2. 2010 Medium

    Showed human Cactin is a nuclear negative regulator of innate immune signaling, generalizing the NF-κB connection to mammalian TLR responses.

    Evidence Reciprocal overexpression/siRNA reporter assays, co-IP with IκBL, and nuclear localization mutant analysis in human cells

    PMID:20829348

    Open questions at the time
    • Direct molecular target of inhibition not defined
    • How nuclear localization mechanistically blocks signaling unknown
  3. 2010 Medium

    Demonstrated a cell-autonomous developmental role in cell migration through genetic interaction with the Rac GTPase pathway.

    Evidence RNAi screen, cell-specific RNAi, and genetic epistasis in C. elegans distal tip cells

    PMID:20188721

    Open questions at the time
    • Whether migration role reflects splicing function not addressed
    • Direct biochemical activity unknown
  4. 2012 Medium

    Linked Cactin to cell cycle progression and developmental gene expression, showing it is nuclear, oligomerizes, and is essential for G1 progression.

    Evidence Temperature-sensitive mutant, subcellular fractionation/imaging, co-IP, and expression profiling in Toxoplasma gondii

    PMID:22486860

    Open questions at the time
    • Mechanism connecting Cactin to gene expression not resolved
    • Composition of the complex not defined
  5. 2014 High

    Provided the first direct evidence that Cactin functions in pre-mRNA splicing, connecting splicing of a target gene to telomere homeostasis and genome stability.

    Evidence cay1Δ deletion, splicing assays, ChIP, telomere length analysis, and Rap1 rescue in fission yeast

    PMID:25398909

    Open questions at the time
    • Did not define which spliceosome step Cactin acts at
    • Generality of splicing requirement across introns untested at this stage
  6. 2014 Medium

    Extended the developmental role of Cactin to Wnt signaling and cell proliferation via the LIT-1/NLK kinase.

    Evidence RNAi depletion, reporter assays, POP-1 localization imaging, and epistasis in C. elegans

    PMID:24999833

    Open questions at the time
    • Whether Wnt effect is direct or a downstream consequence of splicing not resolved
  7. 2017 High

    Defined Cactin as a spliceosome-associated factor in human cells and established that its splicing activity sustains sister chromatid cohesion via the sororin transcript.

    Evidence Reciprocal co-IP with DHX8/SRRM2, RNA-seq splicing analysis, chromosome segregation assays, and sororin rescue in human cells

    PMID:28062851

    Open questions at the time
    • Step in the splicing cycle at which Cactin acts not pinpointed
    • Structural basis of DHX8/SRRM2 interaction unknown
  8. 2022 High

    Connected Cactin's splicing activity to epithelial polarity and collective migration through correct isoform expression of trafficking machinery.

    Evidence RNAi, transcriptome/isoform analysis, Sec23/Sec24CD epistasis, Rab5/Rab11 rescue, and live imaging in Drosophila border cells

    PMID:35612426

    Open questions at the time
    • Whether Cactin selectively targets Sec23/Sec24CD introns or acts broadly not distinguished
  9. 2022 Medium

    Defined a mechanistic splicing specificity for Cactin: promoting splicing of introns with branchpoint-distant 3' splice sites, a conserved role.

    Evidence Splicing-specific ura4 reporters, intron engineering, and comparative genomics in S. pombe

    PMID:36095128

    Open questions at the time
    • Biochemical mechanism by which Cactin enables BP-distal 3'ss recognition unknown
    • Whether human Cactin shares this specificity not directly tested
  10. 2024 Medium

    Revealed post-translational control of Cactin via phase separation, showing PGK phosphorylation of IDR serines toggles aggregate-to-droplet state and boosts antiviral activity.

    Evidence Co-IP/MS, LLPS droplet assays, phosphomimetic/phospho-null mutants, and DCV replication assays in Drosophila

    PMID:38446061

    Open questions at the time
    • How LLPS state relates to splicing function not established
    • Whether phosphoregulation is conserved in mammals unknown
  11. 2024 Medium

    Identified Usp14 as a deubiquitinase that stabilizes Cactin by removing K48/K63 chains, linking Cactin abundance to antiviral defense.

    Evidence Deubiquitinase screen, domain-mapped co-IP, chain-type analysis, proteasome inhibitor assays, and in vivo DCV survival in Usp14-deficient flies

    PMID:38563731

    Open questions at the time
    • E3 ligase that adds these chains not identified
    • Relationship to TRIM39-mediated stabilization not integrated

Open questions

Synthesis pass · forward-looking unresolved questions
  • The biochemical step at which Cactin acts within the spliceosome, and how its splicing role mechanistically integrates with its NF-κB/innate-immune regulatory and phase-separation functions, remains unresolved.
  • No structural model of Cactin within a spliceosomal complex
  • Whether immune regulation is splicing-dependent or independent unknown
  • Direct RNA-binding activity not demonstrated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140098 catalytic activity, acting on RNA 3
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-168256 Immune System 3 R-HSA-8953854 Metabolism of RNA 3 R-HSA-1640170 Cell Cycle 2
Partners
CACTUSDHX8IΚBLPGKSRRM2TRIM39USP14
Complex memberships
spliceosome

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 Cactin was identified as a novel binding partner of the Drosophila IκB protein Cactus via yeast two-hybrid screen. Cactin is a coiled-coil protein with N-terminal RD-like motifs. Overexpression of cactin in a cactus heterozygous background enhances the cactus loss-of-function phenotype (embryonic lethality and ventralization), placing Cactin as a functional component of the Drosophila Rel/NF-κB pathway controlling dorsal-ventral polarity. Yeast two-hybrid screen; genetic epistasis (overexpression in cactus heterozygous background with embryonic phenotype readout) Mechanisms of development Medium 10842059
2010 Human Cactin (hCactin) acts as a negative regulator of TLR signaling: overexpression suppresses TLR-induced NF-κB and interferon-regulatory factor activation, while knockdown augments these responses. hCactin interacts with the MHC Class III protein IκB-like (IκBL). hCactin localizes to the nucleus, and this nuclear localization is required for its inhibitory function on TLR signaling. Overexpression and siRNA knockdown with reporter assays; co-immunoprecipitation with IκBL; subcellular localization by fluorescence microscopy with nuclear localization mutant functional analysis The Journal of biological chemistry Medium 20829348
2010 C. elegans CACN-1/Cactin is required cell-autonomously in distal tip cells (DTCs) for proper pathfinding and cessation of migration. Genetic interaction data place CACN-1 as an inhibitor of the mig-2/Rac GTPase pathway and show it acts in parallel to ced-10/Rac to control DTC pathfinding. Genome-wide RNAi screen; hypomorphic allele analysis; cell-specific RNAi; genetic epistasis with Rac GTPase pathway components Developmental biology Medium 20188721
2012 Toxoplasma gondii TgCactin localizes to the nucleus and is essential for G1 cell cycle progression; a point mutation causes irreversible arrest before mid-G1. TgCactin is present in a protein complex and can oligomerize. Genome-wide expression profiling of the mutant revealed upregulation of extracellular/bradyzoite-stage genes and associated AP2 transcription factors, implicating TgCactin in gene expression control at developmental transition points. Temperature-sensitive mutant analysis; nuclear localization by subcellular fractionation/imaging; co-immunoprecipitation for complex/oligomerization; genome-wide expression profiling Molecular microbiology Medium 22486860
2014 Fission yeast Cactin (Cay1) is required for efficient splicing of rap1+ pre-mRNA; deletion of cay1 reduces Rap1 protein levels also through decreased Rap1 protein stability. Loss of Cay1 leads to accumulation of H3K9ac at telomeres, telomere transcriptional desilencing, telomerase-mediated over-elongation, and chromosomal aberrations. Overexpression of Rap1 in cay1Δ cells reverts telomeric defects, placing Cay1 upstream of Rap1 in telomere regulation. Cay1 also controls processing of Tf2 retrotransposon RNA through a Rap1-independent mechanism. Genetic deletion (cay1Δ); pre-mRNA splicing assays; chromatin immunoprecipitation (H3K9ac); telomere length analysis; epistasis via Rap1 overexpression rescue The EMBO journal High 25398909
2014 C. elegans CACN-1/Cactin modulates Wnt signaling during larval development: depletion causes loss of POP-1 (TCF/LEF) asymmetry and excess POPTOP reporter activation. Genetic interaction studies suggest CACN-1 acts partially through LIT-1/NLK kinase to alter POP-1 localization. CACN-1 is also required for proper seam cell proliferation. RNAi depletion; POPTOP reporter assays; POP-1 localization imaging; genetic epistasis with lit-1/NLK PloS one Medium 24999833
2015 TRIM39 was identified as a binding partner of Cactin via yeast two-hybrid. TRIM39 stabilizes Cactin protein (acting as an E3 ubiquitin ligase that presumably prevents its degradation), and Cactin protein levels are upregulated after TNFα stimulation. TRIM39 knockdown leads to activation of the NF-κB signaling pathway, consistent with TRIM39 negatively regulating NF-κB through Cactin stabilization. Yeast two-hybrid; co-immunoprecipitation; protein stability assays; siRNA knockdown with NF-κB reporter assays Cellular and molecular life sciences : CMLS Medium 26363554
2017 Human Cactin physically interacts with the spliceosome-associated factors DHX8 (an RNA helicase) and SRRM2 (a splicing co-activator). Depletion of human Cactin leads to inefficient splicing of thousands of pre-mRNAs, premature sister chromatid separation, genome instability, and cell proliferation arrest. Incomplete splicing of the sororin (CDCA5) pre-mRNA in Cactin-depleted cells is largely responsible for aberrant chromatid separation, placing Cactin in a pathway where spliceosomal activity sustains cohesion. Co-immunoprecipitation; siRNA depletion with RNA-seq (splicing analysis); chromosome segregation assays; rescue experiments with sororin Journal of cell science High 28062851
2022 In Drosophila border cells, Cactin's spliceosome function is required for collective cell migration, cluster delamination, and polarity. Cactin depletion causes abnormal apical concentration of aPKC and Crumbs (Crb), with loss of overall cluster polarity. Whole-transcriptome analysis revealed altered isoform expression in Cactin-depleted cells. Mutations in two affected splice targets, Sec23 and Sec24CD (which traffic Crb to the apical surface), partially rescue cluster organization and migration; overexpression of Rab5 or Rab11 (promoting Crb/aPKC recycling) similarly rescues, functionally linking Cactin's splicing activity to polarity protein trafficking. RNAi depletion; transcriptome/isoform analysis; epistasis with Sec23/Sec24CD mutants; Rab5/Rab11 overexpression rescue; live imaging of aPKC/Crb localization The Journal of cell biology High 35612426
2022 Fission yeast Cay1 (Cactin ortholog) promotes splicing of introns with a branchpoint-distant 3' splice site (e.g., rap1 intron 2). Using splicing-specific ura4 reporters in S. pombe mutant collections, Cay1 was identified alongside Tls1 and ubiquitin-fold-activated Sde2 as regulators of this process. The role was confirmed by introducing BP-3'ss spacings into a canonical tho5 intron. Cay1/Cactin orthologs are present in intron-rich eukaryotes including humans, suggesting an evolutionarily conserved role in regulating splicing of BP-distal exons. Splicing-specific reporter assays (ura4) in S. pombe deletion mutants; intron engineering experiments; comparative genomics Nucleic acids research Medium 36095128
2024 Drosophila Cactin undergoes liquid-liquid phase separation (LLPS) mediated by its intrinsically disordered region (IDR). Phosphoglycerate kinase (PGK) was identified as a Cactin-interacting protein by co-immunoprecipitation and mass spectrometry, and PGK phosphorylates Cactin at serine residues 99 and 104 within the IDR1 domain. PGK-mediated phosphorylation converts Cactin from stable aggregates to dynamic liquid droplets. Phosphorylation enhances Cactin's antiviral activity against Drosophila C virus (DCV), and PGK overexpression inhibits DCV replication while PGK knockdown increases it. DCV infection increases Cactin phosphorylation. Co-immunoprecipitation and mass spectrometry (interaction and phosphosite identification); LLPS droplet assays; phosphomimetic/phospho-null mutants; DCV replication assays with overexpression/knockdown mBio Medium 38446061
2024 Drosophila Usp14 deubiquitinase was identified as a major deubiquitinase for Cactin through comprehensive deubiquitinase screening. Usp14 interacts with Cactin via its USP domain binding the C_Cactus domain of Cactin. Usp14 removes K48- and K63-linked polyubiquitin chains from Cactin, preventing its degradation by the ubiquitin-proteasome pathway. Usp14 stabilizes Cactin and inhibits DCV replication; Usp14-deficient flies show increased susceptibility to DCV infection. Deubiquitinase screen; co-immunoprecipitation (domain mapping); in-cell ubiquitin chain type analysis; proteasome inhibitor assays; DCV replication assays; in vivo survival assays in Usp14-deficient flies Journal of virology Medium 38563731

Source papers

Stage 0 corpus · 14 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 TRIM39 negatively regulates the NFκB-mediated signaling pathway through stabilization of Cactin. Cellular and molecular life sciences : CMLS 54 26363554
2000 Cactin, a conserved protein that interacts with the Drosophila IkappaB protein cactus and modulates its function. Mechanisms of development 36 10842059
2010 CACN-1/Cactin interacts genetically with MIG-2 GTPase signaling to control distal tip cell migration in C. elegans. Developmental biology 34 20188721
2010 Cactin targets the MHC class III protein IkappaB-like (IkappaBL) and inhibits NF-kappaB and interferon-regulatory factor signaling pathways. The Journal of biological chemistry 33 20829348
2012 Cactin is essential for G1 progression in Toxoplasma gondii. Molecular microbiology 23 22486860
2017 Human cactin interacts with DHX8 and SRRM2 to assure efficient pre-mRNA splicing and sister chromatid cohesion. Journal of cell science 21 28062851
2014 Fission yeast Cactin restricts telomere transcription and elongation by controlling Rap1 levels. The EMBO journal 21 25398909
2014 CACN-1/Cactin plays a role in Wnt signaling in C. elegans. PloS one 14 24999833
2010 Characterisation of expression patterns and functional role of Cactin in early zebrafish development. Gene expression patterns : GEP 12 20348034
2014 Molecular characterization and functional analysis of Cactin gene from Litopenaeus vannamei. Fish & shellfish immunology 9 25462455
2022 Border cell polarity and collective migration require the spliceosome component Cactin. The Journal of cell biology 8 35612426
2022 Splicing of branchpoint-distant exons is promoted by Cactin, Tls1 and the ubiquitin-fold-activated Sde2. Nucleic acids research 8 36095128
2024 Regulation of phase separation and antiviral activity of Cactin by glycolytic enzyme PGK via phosphorylation in Drosophila. mBio 7 38446061
2024 Regulation of ubiquitination and antiviral activity of Cactin by deubiquitinase Usp14 in Drosophila. Journal of virology 3 38563731

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