Affinage

FBXO38

F-box only protein 38 · UniProt Q6PIJ6

Length
1188 aa
Mass
133.9 kDa
Annotated
2026-06-09
25 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FBXO38 is an F-box protein that serves as the substrate receptor of SCF(FBXO38) E3 ubiquitin ligase complexes, directing Lys48-linked poly-ubiquitination and proteasomal degradation of multiple substrates and thereby governing centromere integrity, immune cell function, and vascular homeostasis (PMID:35813202, PMID:37938970). As a degradation receptor it directly ubiquitylates the zinc-finger proteins ZXDA and ZXDB, restraining CENP-A/CENP-B-positive centromeric chromatin, a function that is required for Sertoli cell maturation and spermatogonial differentiation in vivo (PMID:35813202, PMID:35769260). The same degradative activity targets the LAG-3 ligand FGL1 and the NADPH oxidase Nox1, linking FBXO38 to CD8+ T cell-mediated immune surveillance and to endothelial redox balance under shear stress (PMID:37938970, PMID:40313652). Beyond canonical SCF activity, FBXO38 is itself stabilized by the deubiquitylase USP7 and acts non-degradatively to stabilize the cytokinesis kinesin KIF20B at the midbody, such that loss of either USP7 or FBXO38 causes cytokinetic defects (PMID:30804394). Independently of ubiquitin ligase function, FBXO38 (MoKA) is a nucleocytoplasmic shuttling transcriptional coactivator of KLF7 that stimulates target genes including p21(WAF1/Cip1), an activity disrupted by the p.Cys206Arg mutation associated with impaired motor neuron neurite outgrowth (PMID:14729953, PMID:24207122). At the organismal level FBXO38 exerts cell-type-specific control over immune responses, promoting M2-like macrophage polarization via MAPK/IRF4 signaling and supporting IL-15 responsiveness of NK cells by restraining TGF-β/Smad signaling (PMID:37821621, PMID:38990095). Its reported role in degrading PD-1 in T cells (PMID:30487606) has been contradicted by genetic re-examination finding FBXO38 dispensable for PD-1 regulation (PMID:39266770).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2004 High

    Established the first molecular function of FBXO38 (MoKA) as a transcriptional coactivator, defining a partner and a downstream target before its ubiquitin ligase role was known.

    Evidence Y2H, GST pull-down, Co-IP, ChIP and reporter assays linking FBXO38 to KLF7 and p21 transcription

    PMID:14729953

    Open questions at the time
    • Did not address how coactivation relates to any ubiquitin ligase activity
    • Domain basis of KLF7 interaction not resolved structurally
  2. 2006 High

    Resolved how FBXO38 traffics between compartments, mapping discrete NLS, CRM1-dependent and CRM1-independent export signals and the acidic activation domain controlling its transcriptional function.

    Evidence Fusion protein localization, leptomycin B treatment, deletion/mutation analysis and GAL4 chimeric reporter assays in mammalian cells

    PMID:16990251

    Open questions at the time
    • Did not connect shuttling regulation to substrate degradation
    • Physiological signals regulating shuttling not identified
  3. 2013 Medium

    Connected a disease-associated missense variant to loss of KLF7 coactivation, providing the first genotype-phenotype link for the transcriptional function.

    Evidence Reporter assays and patient-derived fibroblasts plus primary motor neuron neurite outgrowth assay for the p.Cys206Arg mutation

    PMID:24207122

    Open questions at the time
    • Mechanism by which the mutation impairs coactivation not defined
    • Single lab; effect on ligase function not tested
  4. 2018 High

    Reframed FBXO38 as an E3 ubiquitin ligase by reporting Lys48-linked ubiquitination and degradation of PD-1, with a tumor immunity phenotype in conditional knockout mice.

    Evidence In vitro ubiquitination with linkage specificity, T cell-specific conditional knockout, tumor growth and anti-PD-1 rescue

    PMID:30487606

    Open questions at the time
    • Substrate relationship later contradicted by genetic re-examination
    • SCF complex requirement for PD-1 not dissected here
  5. 2019 High

    Defined the upstream stabilizer of FBXO38 and a non-degradative output, showing USP7 protects FBXO38 which in turn stabilizes KIF20B for cytokinesis independently of SCF.

    Evidence AP-MS, BioID, Co-IP, siRNA knockdown, proteasome inhibition and cytokinesis rescue experiments

    PMID:30804394

    Open questions at the time
    • Molecular basis of SCF-independent KIF20B stabilization unknown
    • How USP7 selectively targets FBXO38 not defined
  6. 2022 High

    Identified bona fide SCF(FBXO38) substrates ZXDA/B and linked their degradation to centromeric chromatin control, both in cells and in a Sertoli cell/fertility context.

    Evidence Co-IP, ubiquitination assays, proteasome inhibition, ChIP, and Fbxo38 conditional knockout mice with testis phenotyping

    PMID:35769260 PMID:35813202

    Open questions at the time
    • Direct enzymatic reconstitution of SCF(FBXO38) on ZXDA/B not shown
    • Link between centromeric chromatin changes and the spermatogenic phenotype is correlative
  7. 2023 Medium

    Extended FBXO38 substrate range to FGL1 and assigned a macrophage-intrinsic role in M2 polarization, broadening its immunoregulatory functions.

    Evidence Co-IP/ubiquitination with siRNA and tumor models for FGL1; macrophage-specific knockout with tumor and DSS colitis models and MAPK/IRF4 pathway analysis

    PMID:37821621 PMID:37938970

    Open questions at the time
    • Whether macrophage M2 effect is ubiquitination-dependent not established
    • Direct substrate in the MAPK/IRF4 axis not identified
    • Single lab for each finding
  8. 2024 Medium

    Challenged the original PD-1 model and added new degradation-independent and lysosomal mechanisms, indicating FBXO38 outputs are context- and substrate-specific.

    Evidence Genetic re-examination in T cells (PD-1); lysosome vs proteasome inhibitor dissection of STING; NK-cell conditional knockout dissecting the TGF-β/Smad/Eomes/IL15R axis

    PMID:38277817 PMID:38990095 PMID:39266770

    Open questions at the time
    • Source of discrepancy in PD-1 regulation unresolved
    • Mechanism by which FBXO38 affects STING lysosomal turnover unclear
    • Direct substrate in the NK TGF-β axis not defined
  9. 2025 Medium

    Showed FBXO38 degrades Nox1 to limit endothelial ROS, linking shear-stress-regulated FBXO38 abundance to vascular oxidative stress and apoptosis.

    Evidence Co-IP, gain/loss-of-function in HUVECs, in vitro shear stress model and in vivo partial carotid ligation

    PMID:40313652

    Open questions at the time
    • Ubiquitin linkage specificity on Nox1 not characterized
    • Mechanism reducing FBXO38 under oscillatory shear not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved which FBXO38 functions require SCF-dependent ubiquitination versus degradation-independent or transcriptional activities, and how substrate selection is partitioned across cell types.
  • No structural model of substrate recognition by SCF(FBXO38)
  • Unknown determinants of substrate-specific proteasomal vs lysosomal routing
  • Reconciliation of the contested PD-1 phenotype outstanding

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 4 GO:0016874 ligase activity 2 GO:0140110 transcription regulator activity 2 GO:0098772 molecular function regulator activity 1
Localization
GO:0005634 nucleus 2 GO:0005694 chromosome 2 GO:0005829 cytosol 1
Pathway
R-HSA-168256 Immune System 3 R-HSA-392499 Metabolism of proteins 3 R-HSA-1640170 Cell Cycle 1 R-HSA-74160 Gene expression (Transcription) 1
Complex memberships
SCF(FBXO38)

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 FBXO38 (MoKA) physically interacts with KLF7 transcription factor, confirmed by GST pull-down and co-immunoprecipitation, and functions as a KLF7 coactivator to stimulate transcription of target genes including p21(WAF1/Cip1). Distinct structural motifs of FBXO38 mediate KLF7 interaction and nucleocytoplasmic shuttling. Yeast two-hybrid screen, GST pull-down, co-immunoprecipitation, chromatin immunoprecipitation, transient transfection reporter assays Molecular and cellular biology High 14729953
2006 FBXO38 (MoKA) shuttles between nucleus and cytoplasm via a single functional NLS recognized by karyopherin receptors and three distinct cytoplasmic retention/export sequences: one CRM1-dependent leucine-rich NES and two CRM1-independent export signals. The major transcriptional activation domain maps to a highly acidic sequence between the NLS and NES clusters. Forced expression of fusion proteins in mammalian cells, nuclear export inhibitor (leptomycin B) treatment, deletion/mutation analysis, GAL4 chimeric transcriptional assays Nucleic acids research High 16990251
2013 The FBXO38 p.Cys206Arg missense mutation impairs KLF7-mediated transactivation of a KLF7-responsive promoter and endogenous KLF7 target genes without altering subcellular localization of FBXO38, and this transcriptional dysregulation is associated with impaired neurite outgrowth in primary motor neurons. Transient transfection reporter assays in HEK293T cells, fibroblasts from patients with the mutation, primary motor neuron neurite outgrowth assay American journal of human genetics Medium 24207122
2018 FBXO38 is an E3 ubiquitin ligase that mediates Lys48-linked poly-ubiquitination of PD-1 and subsequent proteasome-dependent degradation after PD-1 internalization in activated T cells. Conditional T cell-specific Fbxo38 knockout led to elevated PD-1 on tumor-infiltrating T cells and faster tumor progression in mice, which was normalized by anti-PD-1 therapy. E3 ligase identification, ubiquitination assay (Lys48-linkage specificity), conditional knockout mice, tumor growth assays, anti-PD-1 rescue experiment Nature High 30487606
2019 USP7 deubiquitylase stabilizes FBXO38 by protecting it from proteasomal degradation in a catalytic-activity-dependent manner. FBXO38 in turn stabilizes KIF20B (a Kinesin-6 required for cytokinesis) independently of an SCF complex. Depletion of either USP7 or FBXO38 reduces KIF20B levels and its midbody localization, causing cytokinetic defects; these defects are rescued by restoring FBXO38 or KIF20B. Affinity purification-mass spectrometry, BioID proximity labeling, co-immunoprecipitation, siRNA knockdown, proteasome inhibitor treatment, cytokinesis phenotype assay, rescue experiments Scientific reports High 30804394
2022 FBXO38 functions as the substrate receptor of the SCF(FBXO38) E3 ubiquitin ligase complex and directly promotes ubiquitination and proteasome-dependent degradation of zinc finger proteins ZXDA and ZXDB. ZXDA/B associate with centromeric protein CENP-B, and their stabilization upon FBXO38 loss leads to upregulation of CENP-A and CENP-B positive centromeric chromatin, establishing a role for cullin-dependent degradation in centromere integrity control. Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, chromatin immunoprecipitation, mutant cell analysis Frontiers in cell and developmental biology High 35813202
2022 In Sertoli cells, FBXO38 controls centromeric chromatin integrity through ZXDB degradation. Loss of FBXO38 in mice causes ZXDB stabilization, upregulated centromeric chromatin, defective Sertoli cell maturation (dysregulation of retinoic acid metabolism and intercellular communication genes), and impaired spermatogonial differentiation, leading to reduced sperm production and fertility. Fbxo38 conditional knockout mice, immunofluorescence, gene expression profiling, histological analysis of testes Frontiers in cell and developmental biology High 35769260
2023 FBXO38 promotes macrophage immunosuppressive (M2-like) polarization by upregulating M2-like gene expression via MAPK and IRF4 signaling pathways, without affecting M1-like polarization. Fbxo38 deletion in macrophages blocks tumor development and protects against DSS-induced colitis in mice. Macrophage-specific conditional knockout mice, tumor growth assay, DSS colitis model, gene expression analysis, pathway analysis (MAPK/IRF4) Cellular & molecular immunology Medium 37821621
2023 FBXO38 interacts with and ubiquitylates FGL1, promoting its proteasome-dependent degradation. Depletion of FBXO38 markedly increases FGL1 abundance, suppresses CD8+ T cell infiltration, and enhances immune evasion. Additionally, FBXO38 deficiency increases IL-6 levels in vivo and in cancer specimens. Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, in vitro and in vivo tumor models, correlation analysis in patient specimens Cell reports Medium 37938970
2024 FBXO38 deficiency reduces STING protein levels through lysosome-mediated (not proteasomal) degradation, thereby inhibiting cGAS-STING pathway activation, reducing downstream IFNA1 and CCL5 production, enhancing tumor proliferation, and reducing CD8+ T cell infiltration. siRNA knockdown, in vitro and in vivo tumor models, lysosome inhibitor vs. proteasome inhibitor treatment, pathway activation assays (IFNA1, CCL5 measurement) Neoplasia Medium 38277817
2024 FBXO38 is dispensable for PD-1 regulation in T cells. Experimental re-examination failed to support the notion that SCF(FBXO38) directly or indirectly controls the abundance and stability of PD-1 in T cells, contradicting the earlier report (PMID:30487606). Genetic T cell-specific knockout/re-examination, protein stability assays in T cells EMBO reports Medium 39266770
2024 FBXO38 deficiency in NK cells enhances TGF-β signaling (elevating Smad2 and Smad3), which suppresses expression of transcription factor Eomes and reduces surface IL15Rβ and IL15Rγc expression on NK cells, leading to NK cell hyporesponsiveness to IL-15 and impaired proliferation/survival. FBXO38 overexpression in human NK cells enhances antitumor activity in vivo. NK-cell-specific conditional knockout mice, tumor growth and metastasis assays, flow cytometry, gene expression analysis, adoptive transfer of FBXO38-overexpressing human NK cells Cancer immunology research Medium 38990095
2025 FBXO38 directly interacts with NADPH oxidase Nox1 and promotes its ubiquitin-proteasome-dependent degradation in endothelial cells. Under low oscillatory shear stress, FBXO38 protein levels are reduced (~60%), leading to Nox1 accumulation (~2-fold), increased ROS production, and endothelial apoptosis. FBXO38 overexpression attenuates Nox1 accumulation and reduces ROS under these conditions. Co-immunoprecipitation, overexpression and knockdown in HUVECs, in vitro shear stress model, in vivo partial carotid ligation mouse model, western blotting, immunofluorescence Cardiovascular therapeutics Medium 40313652

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2018 FBXO38 mediates PD-1 ubiquitination and regulates anti-tumour immunity of T cells. Nature 248 30487606
2004 Identification of MoKA, a novel F-box protein that modulates Krüppel-like transcription factor 7 activity. Molecular and cellular biology 43 14729953
2013 A dominant mutation in FBXO38 causes distal spinal muscular atrophy with calf predominance. American journal of human genetics 39 24207122
2019 USP7 Regulates Cytokinesis through FBXO38 and KIF20B. Scientific reports 29 30804394
2019 Analysis of genetically driven alternative splicing identifies FBXO38 as a novel COPD susceptibility gene. PLoS genetics 25 31269066
2017 Linoleic acid enhance the production of moncolin K and red pigments in Monascus ruber by activating mokH and mokA, and by accelerating cAMP-PkA pathway. International journal of biological macromolecules 23 29162465
2023 FBXO38 regulates macrophage polarization to control the development of cancer and colitis. Cellular & molecular immunology 22 37821621
2023 FBXO38 mediates FGL1 ubiquitination and degradation to enhance cancer immunity and suppress inflammation. Cell reports 20 37938970
2019 FBXO38 Drives PD-1 to Destruction. Trends in immunology 20 30609969
2006 Multiple pathways regulate intracellular shuttling of MoKA, a co-activator of transcription factor KLF7. Nucleic acids research 14 16990251
2001 Myxococcus xanthus mokA encodes a histidine kinase-response regulator hybrid sensor required for development and osmotic tolerance. Journal of bacteriology 14 11157925
2024 FBXO38 deficiency promotes lysosome-dependent STING degradation and inhibits cGAS-STING pathway activation. Neoplasia (New York, N.Y.) 12 38277817
2019 A novel homozygous FBXO38 variant causes an early-onset distal hereditary motor neuronopathy type IID. Journal of human genetics 11 31420593
2022 FBXO38 Ubiquitin Ligase Controls Sertoli Cell Maturation. Frontiers in cell and developmental biology 8 35769260
2024 FBXO38 is dispensable for PD-1 regulation. EMBO reports 7 39266770
2024 The E3 Ubiquitin Ligase FBXO38 Maintains the Antitumor Function of Natural Killer Cells by Sustaining IL15R Signaling. Cancer immunology research 5 38990095
2024 Comprehensive analysis of chromosome abnormalities by chromosome conformation based karyotyping (C-MoKa) in patients with conception failure and pregnancy loss. Clinica chimica acta; international journal of clinical chemistry 5 39674306
2022 FBXO38 Ubiquitin Ligase Controls Centromere Integrity via ZXDA/B Stability. Frontiers in cell and developmental biology 5 35813202
2026 MOKA: a pipeline for multiomics bridged SNP-set kernel association test. G3 (Bethesda, Md.) 0 41417631
2026 Chebulagic acid targets FBXO38 to enhance natural killer cell-mediated anti-tumor immunity in lung adenocarcinoma. Human cell 0 41546764
2026 [Precise identification of a cryptic balanced translocation in a couple with recurrent spontaneous abortions using C-MoKa technique]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 0 41621847
2026 Identification a rare chromosomal translocation 45,X, der(Y;15)(q11.2;q11.2) in an azoospermic patient using C-MoKa. Molecular cytogenetics 0 41888947
2025 FBXO38 Regulates Nox1 Stability to Reduce Vascular Endothelial Damage Induced by Low Oscillatory Shear Stress. Cardiovascular therapeutics 0 40313652
2024 Identification of rare variants in the FBXO38 gene of patients with chronic inflammatory demyelinating polyradiculoneuropathy. Journal of neuroimmunology 0 38823119
2022 Erratum: FBXO38 ubiquitin ligase controls centromere integrity via ZXDA/B stability. Frontiers in cell and developmental biology 0 36211459

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