Affinage

FBXO25

F-box only protein 25 · UniProt Q8TCJ0

Length
367 aa
Mass
43.3 kDa
Annotated
2026-04-28
15 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FBXO25 is the substrate-recognition subunit of an SCF-type E3 ubiquitin ligase complex (with SKP1, CUL1, and RBX1) that ubiquitinates diverse nuclear and cytoplasmic substrates to regulate transcription, apoptosis, signaling, and chromatin remodeling. Within the nucleus, FBXO25 localizes to novel proteasome-enriched compartments (FANDs) where it targets cardiac transcription factors (Nkx2-5, Isl1, Hand1, Tbx5) for proteasomal degradation, promotes H2BK120 monoubiquitination to drive H3K4me3 and osteogenic gene expression, prevents polyglutamine-huntingtin aggregation, and negatively regulates MAPK/ERK signaling independently of MEK (PMID:18287534, PMID:25725482, PMID:31827076, PMID:28389297). PRKCD-mediated phosphorylation directs FBXO25 from the nucleus to mitochondrial HAX-1 for ubiquitination-dependent degradation during apoptotic stress, and monoallelic loss of FBXO25 or stabilizing HAX-1 phosphodegron mutations occur in mantle cell lymphoma, establishing FBXO25 as a haploinsufficient tumor suppressor (PMID:25419709). FBXO25 itself is subject to CUL3-dependent proteasomal turnover recruited by the lncRNA ODIR1, linking its abundance to differentiation-coupled chromatin remodeling (PMID:31827076).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2005 High

    Establishing that FBXO25 is a bona fide F-box protein that assembles into an SCF complex resolved whether this orphan F-box protein could function as an E3 ligase subunit.

    Evidence Yeast two-hybrid, Co-IP with Skp1/Cul1, and site-directed mutagenesis of a critical F-box serine in HEK293 cells

    PMID:16278047

    Open questions at the time
    • No substrate identified
    • Functional consequence of nuclear localization unknown
    • Mechanism of nuclear targeting undetermined
  2. 2006 High

    Demonstrating reconstituted ubiquitin ligase activity in vitro confirmed that the SCF(FBXO25) complex is catalytically competent, not merely a structural assembly.

    Evidence In vitro ubiquitin ligase assay with Co-IP-purified complex, tissue expression profiling by RT-PCR

    PMID:16714087

    Open questions at the time
    • Endogenous substrates still unknown
    • Physiological role in brain (highest expression tissue) uncharacterized
  3. 2008 High

    Discovery of FANDs — novel nuclear domains containing FBXO25, ubiquitin conjugates, and 20S proteasome — established a dedicated subnuclear compartment for FBXO25-mediated proteolysis and showed the complex prevents polyglutamine-huntingtin aggregation.

    Evidence Confocal immunofluorescence with affinity-purified antibodies, actinomycin D/heat-shock perturbation, polyglutamine aggregation assay

    PMID:18287534

    Open questions at the time
    • How FANDs are nucleated is unknown
    • Whether huntingtin is a direct ubiquitination substrate or an indirect target is unresolved
  4. 2010 Medium

    Identifying beta-actin as a FAND component and showing that actin-polymerization inhibitors disrupt FANDs linked nuclear actin organization to FBXO25 compartment integrity and suggested a connection to RNA Pol II transcription.

    Evidence TAP-MS interactome, Co-IP for beta-actin, latrunculin treatment, in vitro transcription assay with FBXO25 antibody interference

    PMID:20473970

    Open questions at the time
    • Transcription link is indirect (antibody interference)
    • Whether beta-actin is a substrate or structural partner is unclear
    • FAND biogenesis mechanism still unknown
  5. 2011 Medium

    Identifying cardiac transcription factors Nkx2-5, Isl1, and Hand1 as FBXO25 substrates provided the first physiological substrates and implicated FBXO25 in cardiac development.

    Evidence Ubiquitination assays with ubiquitin co-expression, MG132 proteasome inhibitor rescue in cardiomyocytes

    PMID:21596019

    Open questions at the time
    • Degron motifs on cardiac substrates not mapped
    • In vivo cardiac phenotype of FBXO25 loss not tested
    • Phosphorylation-dependent recognition not explored
  6. 2014 High

    Identification of HAX-1 as a phosphodegron-dependent substrate and PRKCD as the upstream kinase provided the first complete substrate-recognition mechanism for FBXO25, while genetic evidence in mouse lymphoma models and human MCL established FBXO25 as a haploinsufficient tumor suppressor.

    Evidence Unbiased substrate screen, Co-IP, ubiquitination assay, PRKCD phosphorylation assays, phosphodegron mutant analysis, Eμ-Myc mouse model, MCL xenotransplant, patient genomics

    PMID:25419709

    Open questions at the time
    • Whether PRKCD-dependent mechanism applies to other substrates is unknown
    • Full spectrum of FBXO25 tumor-suppressive targets beyond HAX-1 not defined
  7. 2015 High

    Extending cardiac substrate repertoire to Tbx5 and demonstrating that FBXO25 silencing impairs cardiomyocyte differentiation established a functional role for FBXO25-mediated proteolysis in cardiac lineage specification.

    Evidence Co-IP (in vitro and in vivo), ts20 temperature-sensitive ubiquitin system, dominant-negative FBXO25 mutant, siRNA knockdown with mESC differentiation readout

    PMID:25725482

    Open questions at the time
    • No Fbxo25 knockout mouse cardiac phenotype reported
    • Whether FBXO25 degrades cardiac factors during normal development or only in overexpression models is unclear
  8. 2017 Medium

    Showing that FBXO25 knockout increases ERK1/2 phosphorylation independently of MEK revealed a non-canonical role in restraining MAPK signaling, though the direct mechanism remains undefined.

    Evidence CRISPR FBXO25 KO in HAP1 cells, phospho-ERK1/2 immunoblot, MEK inhibitor epistasis, cell proliferation assay

    PMID:28389297

    Open questions at the time
    • Direct MAPK pathway substrate of FBXO25 not identified
    • Whether ERK regulation is ubiquitination-dependent or indirect is unresolved
    • Single cell line used
  9. 2019 Medium

    Discovery that FBXO25 promotes H2BK120 monoubiquitination and consequent H3K4me3 at the OSX locus, and that the lncRNA ODIR1 recruits CUL3 to degrade FBXO25, revealed a chromatin-remodeling function and an upstream mechanism controlling FBXO25 abundance during osteogenic differentiation.

    Evidence RNA pulldown, Co-IP (ODIR1–FBXO25, CUL3–FBXO25), ChIP for H2BK120ub and H3K4me3 at OSX, shRNA/overexpression in hUC-MSCs, in vivo osteogenesis

    PMID:31827076

    Open questions at the time
    • Whether FBXO25 directly ubiquitinates H2B or acts through an intermediary is unknown
    • CUL3 adaptor bridging ODIR1 to FBXO25 not identified
    • Single differentiation system tested
  10. 2020 Medium

    Rigorous re-examination disproved ELK-1 as an FBXO25 substrate while reconfirming Hand1 and HAX-1, refining the validated substrate list and highlighting the need for independent replication of F-box protein substrate assignments.

    Evidence Co-IP, cycloheximide chase, ubiquitination assay, RNAi, gene expression analysis in HEK293T cells

    PMID:33428929

    Open questions at the time
    • Identity of the true ELK-1 E3 ligase remains unknown
    • Whether FBXO25–ELK-1 physical interaction serves a non-degradative function is unexplored
  11. 2020 Medium

    In cutaneous SCC, FBXO25 was found to promote tumor growth through Oct-1 downregulation and consequent cyclin D1 stabilization, revealing a context-dependent oncogenic role contrasting with its tumor-suppressive function in MCL.

    Evidence Stable shRNA knockdown, cyclin D1 overexpression rescue, Co-IP (FBXO25–Oct-1), in vivo SCC13 xenograft

    PMID:32335130

    Open questions at the time
    • Whether Oct-1 is a direct ubiquitination substrate or indirectly regulated is not demonstrated
    • Reconciliation of oncogenic (cSCC) versus tumor-suppressive (MCL) roles not mechanistically resolved
    • Single cancer cell line

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis of FBXO25 substrate recognition, the complete inventory of direct substrates and their degron motifs, the biogenesis and regulation of FANDs, whether FBXO25 directly ubiquitinates H2B, and the in vivo developmental consequences of FBXO25 loss in mammals.
  • No structural or cryo-EM model of SCF(FBXO25) exists
  • No Fbxo25 knockout mouse phenotype reported
  • Degron motifs beyond the HAX-1 phosphodegron are unmapped

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 5 GO:0016874 ligase activity 4
Localization
GO:0005634 nucleus 5
Pathway
R-HSA-392499 Metabolism of proteins 4 R-HSA-1266738 Developmental Biology 2 R-HSA-162582 Signal Transduction 1 R-HSA-4839726 Chromatin organization 1 R-HSA-5357801 Programmed Cell Death 1
Partners
CUL1HAND1HAX1NKX2-5PRKCDRBX1SKP1TBX5
Complex memberships
SCF(FBXO25)

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 FBXO25 (hFBX25) was established as an F-box protein that interacts with Skp1 and Cul1, forming a functional SCF-type ubiquitin ligase complex. An atypical serine residue in the F-box domain was identified as crucial for Skp1 binding. FBXO25 localizes predominantly to the nucleus and is strongly expressed in brain, with neuronal expression in mouse embryos. Yeast two-hybrid and co-immunoprecipitation to verify Skp1/Cul1 interaction; site-directed mutagenesis of the F-box serine; immunolocalization Biochimica et biophysica acta High 16278047
2006 FBXO25 contains a functional F-box domain that binds Skp1, Roc1, and Cul1 to form a productive SCF-type E3 ubiquitin ligase complex with ubiquitin ligase activity in vitro. FBXO25 is highly expressed in brain, kidney, and intestine but not striated muscle, and is not induced during muscle atrophy. Co-immunoprecipitation, in vitro ubiquitin ligase activity assay, RT-PCR across tissues, atrophy models (fasting, dexamethasone, streptozotocin-diabetes) Biochimica et biophysica acta High 16714087
2008 FBXO25, Skp1, Cul1, and Rbx1 form a functional ubiquitin ligase complex that localizes to novel dot-like nuclear structures (FBXO25-associated nuclear domains, FANDs) distinct from clastosomes, which are enriched in ubiquitin conjugates and 20S proteasome. Transcription inhibition (actinomycin D) or heat shock disrupts FANDs. FBXO25-dependent ubiquitin ligase activity prevents aggregation of polyglutamine-containing huntingtin in the nucleus. Confocal immunofluorescence with affinity-purified antibodies, biochemical fractionation, immunoblot, functional ubiquitination assay with polyglutamine-huntingtin aggregation readout Molecular biology of the cell High 18287534
2010 FBXO25 physically interacts with beta-actin through its N-terminus; beta-actin is enriched in FBXO25-associated nuclear domains (FANDs). Inhibitors of actin polymerization disrupt FANDs, indicating nuclear actin organization influences FBXO25 compartments. FBXO25 antibodies interfered with RNA polymerase II transcription in vitro, linking the FAND compartment to transcriptional regulation. Two-step affinity purification followed by mass spectrometry, yeast two-hybrid screen, Co-IP, confocal imaging, in vitro transcription assay with FBXO25 antibody interference Proteomics Medium 20473970
2011 FBXO25 functions as a nuclear E3 ubiquitin ligase in cardiomyocytes that ubiquitinates and promotes proteasomal degradation of cardiac transcription factors Nkx2-5, Isl1, and Hand1. FBXO25 expression is higher in fetal heart than adult heart. Ubiquitination assay (co-expression with ubiquitin constructs), proteasome inhibitor (MG132) rescue of substrate levels, immunofluorescence showing nuclear localization in cardiomyocytes Biochemical and biophysical research communications Medium 21596019
2013 FBXO25 interacts with the transcription factor ELK-1 and mediates its ubiquitination and proteasomal degradation via the SCF(FBXO25) complex, suppressing ELK-1 target genes c-fos and egr-1 in response to PMA. ELK-1 was identified as an FBXO25 substrate using an in-chip ubiquitination screen on a human protein microarray. Human protein microarray ubiquitination screen, co-immunoprecipitation, ubiquitination assay in HEK293T cells, protein turnover assay, gene expression analysis (c-fos, egr-1) The Journal of biological chemistry Medium 23940030
2014 FBXO25 is the substrate-specifying subunit of SCF(FBXO25) E3 ubiquitin ligase that targets the prosurvival protein HAX-1 for ubiquitination and degradation after apoptotic stress. Protein kinase Cδ (PRKCD) phosphorylates both FBXO25 and HAX-1, directing nuclear FBXO25 to mitochondrial HAX-1 to enable substrate recognition. FBXO25 acts as a haploinsufficient tumor suppressor in mantle cell lymphoma (MCL), where monoallelic deletion of FBXO25 and stabilizing HAX1 phosphodegron mutations were identified in primary human MCL. Unbiased substrate screen, Co-immunoprecipitation, ubiquitination assay, genetic epistasis (Eμ-Myc lymphoma mouse model, MCL xenotransplant), phosphorylation assays with PRKCD, phosphodegron mutant analysis, patient sample genomics Nature medicine High 25419709
2015 FBXO25 directly interacts with cardiac transcription factors Tbx5 and Nkx2-5 in vitro and in vivo, and mediates their ubiquitination and proteasomal degradation via the SCF complex. A dominant-negative Fbxo25 mutant (residues 1-236) prevents Tbx5 degradation and increases Tbx5 transcriptional activity. Silencing endogenous Fbxo25 suppresses cardiomyocyte differentiation from mESCs. Co-immunoprecipitation (in vitro and in vivo), proteasome inhibitor MG132 rescue, temperature-sensitive ubiquitin system (ts20 cells), dominant-negative mutant expression, luciferase reporter assay, siRNA knockdown with differentiation readout Biochimica et biophysica acta High 25725482
2017 FBXO25 negatively regulates MAPK/ERK signaling by decreasing ERK1/2 phosphorylation independently of MEK1/2. In FBXO25 knockout HAP1 cells, ERK1/2 is more active upon PMA treatment and cell proliferation is increased under receptor-mediated ERK pathway activation. FBXO25 overexpression and CRISPR knockout (FBXO25KO HAP1 cells), phospho-ERK1/2 immunoblot, MEK inhibitor epistasis, cell proliferation assay Archives of biochemistry and biophysics Medium 28389297
2019 FBXO25 is targeted for proteasome-dependent degradation by the lncRNA ODIR1, which recruits Cullin 3 (CUL3) to facilitate FBXO25 degradation. FBXO25 increases mono-ubiquitination of H2BK120 (H2BK120ub), which subsequently promotes H3K4 trimethylation (H3K4me3), inducing a loose chromatin structure and transcription of the osteoblast transcription factor OSX. RNA pulldown/co-immunoprecipitation (ODIR1-FBXO25 interaction), ChIP assay (H2BK120ub, H3K4me3 at OSX locus), shRNA knockdown and overexpression of ODIR1 in hUC-MSCs, in vitro and in vivo osteogenesis assays Cell death & disease Medium 31827076
2020 FBXO25 and ELK-1 interact in HEK293T cells by co-immunoprecipitation, and FBXO25 is active toward Hand1 and HAX1 substrates; however, FBXO25 does not promote ubiquitination or proteasomal degradation of ELK-1 nor affect ELK-1 transcriptional activity, contradicting an earlier report. This indicates another E3 ligase regulates ELK-1 ubiquitination. Co-immunoprecipitation, protein turnover assay (cycloheximide chase), ubiquitination assay, RNA interference, gene expression analysis in HEK293T cells The Journal of biological chemistry Medium 33428929
2020 In cutaneous squamous cell carcinoma (cSCC), FBXO25 promotes tumor growth and metastasis through cyclin D1 stabilization. FBXO25 interacts with Oct-1, leading to Oct-1 downregulation and consequent cyclin D1 stabilization. Stable silencing of FBXO25 reduces cSCC tumor growth and cyclin D1 levels, while cyclin D1 overexpression rescues growth in FBXO25-deficient tumors. Stable shRNA knockdown, stable cyclin D1 overexpression rescue experiment, co-immunoprecipitation (FBXO25-Oct-1 interaction), in vivo tumor growth assay (SCC13 cells) The Journal of investigative dermatology Medium 32335130

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 LncRNA ODIR1 inhibits osteogenic differentiation of hUC-MSCs through the FBXO25/H2BK120ub/H3K4me3/OSX axis. Cell death & disease 70 31827076
2014 Disruption of the PRKCD-FBXO25-HAX-1 axis attenuates the apoptotic response and drives lymphomagenesis. Nature medicine 53 25419709
2010 Molecular characterization of atrogin-1/F-box protein-32 (FBXO32) and F-box protein-25 (FBXO25) in rainbow trout (Oncorhynchus mykiss): Expression across tissues in response to feed deprivation. Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology 43 20601059
2011 A novel Fbxo25 acts as an E3 ligase for destructing cardiac specific transcription factors. Biochemical and biophysical research communications 26 21596019
2005 Characterization of FBX25, encoding a novel brain-expressed F-box protein. Biochimica et biophysica acta 20 16278047
2013 The F-box protein FBXO25 promotes the proteasome-dependent degradation of ELK-1 protein. The Journal of biological chemistry 16 23940030
2008 FBXO25-associated nuclear domains: a novel subnuclear structure. Molecular biology of the cell 16 18287534
2015 Fbxo25 controls Tbx5 and Nkx2-5 transcriptional activity to regulate cardiomyocyte development. Biochimica et biophysica acta 15 25725482
2006 FBXO25, an F-box protein homologue of atrogin-1, is not induced in atrophying muscle. Biochimica et biophysica acta 13 16714087
2020 FBXO25 Promotes Cutaneous Squamous Cell Carcinoma Growth and Metastasis through Cyclin D1. The Journal of investigative dermatology 10 32335130
2016 FBXO25 promotes cell proliferation, invasion, and migration of NSCLC. Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine 9 27596142
2017 FBXO25 regulates MAPK signaling pathway through inhibition of ERK1/2 phosphorylation. Archives of biochemistry and biophysics 8 28389297
2010 Identification of FBXO25-interacting proteins using an integrated proteomics approach. Proteomics 8 20473970
2019 From man to fly - convergent evidence links FBXO25 to ADHD and comorbid psychiatric phenotypes. Journal of child psychology and psychiatry, and allied disciplines 7 31849056
2020 ELK-1 ubiquitination status and transcriptional activity are modulated independently of F-Box protein FBXO25. The Journal of biological chemistry 4 33428929