Affinage

FBXL8

F-box/LRR-repeat protein 8 · UniProt Q96CD0

Length
374 aa
Mass
40.5 kDa
Annotated
2026-06-09
10 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FBXL8 is an F-box protein that operates as the substrate-recognition subunit of SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase complexes, coupling target recognition to ubiquitination across cell-cycle, oncogenic, and inflammatory programs (PMID:33122824, PMID:36855778). Its canonical mode is K48-linked polyubiquitination driving proteasomal degradation: it targets phospho-Thr-283 cyclin D3 to antagonize cell-cycle progression and oncogene-induced transformation (PMID:33122824), and it degrades c-myc through a phosphorylation-independent route distinct from the Fbxw7 phospho-degron, such that combined loss of FBXL8 and Fbxw7 synergistically elevates c-myc (PMID:35438057). In cancer settings FBXL8 likewise promotes turnover of TP53, with FBXL8 knockout stabilizing p53 and suppressing colorectal tumor proliferation, invasion, and liver metastasis in vivo (PMID:36855778), and it engages Snail1 via its C3-binding domain to limit RhoA activation and TGFβ-induced cardiac fibroblast activation, with AAV9-delivered FBXL8 ameliorating post-myocardial-infarction fibrosis (PMID:38615011). Beyond degradative activity, FBXL8 binds dephosphorylated IκBα and assembles K63-linked, non-degradative polyubiquitin at K38, stabilizing IκBα to block NF-κB p65 nuclear translocation within a YY1-mediated feedforward loop (PMID:41608629). This dual degradative/stabilizing repertoire positions FBXL8 as a context-dependent regulator of proliferation, apoptosis, EMT, and inflammation.

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2020 High

    Established the first defined SCF-FBXL8 substrate, answering whether FBXL8 acts as a functional E3 recognition subunit and linking it to cell-cycle control via phospho-degron recognition.

    Evidence Co-IP, ubiquitylation assays, and cyclin D3 T283A non-phosphorylatable mutant rescue with proliferation/transformation readouts

    PMID:33122824

    Open questions at the time
    • Did not define the kinase generating the phospho-Thr-283 degron in this context
    • Structural basis of FBXL8 substrate binding not resolved
  2. 2020 Medium

    Extended the FBXL8 substrate set to CCND2 and IRF5 in breast cancer, addressing whether FBXL8 loss has tumor-relevant functional consequences.

    Evidence Co-IP with protein accumulation on FBXL8 knockdown plus migration, invasion, and apoptosis assays in breast cancer cells

    PMID:32784654

    Open questions at the time
    • No direct ubiquitylation assay reported for CCND2 or IRF5
    • Linkage type and degradation route not directly demonstrated
  3. 2021 Medium

    Tested whether FBXL8 contributes to CCNF turnover, clarifying redundancy with another E3 pathway.

    Evidence Co-IP pulldown and double knockdown of FBXL8 and FZR1 with CCNF accumulation readout in breast cancer cells

    PMID:34201347

    Open questions at the time
    • No direct ubiquitylation assay for CCNF
    • Relative contribution of FBXL8 versus FZR1 not quantified
  4. 2022 High

    Resolved whether FBXL8 targets c-myc independently of the canonical Fbxw7 phospho-degron, defining a parallel route of c-myc control.

    Evidence Co-IP, ubiquitylation assay, gain/loss-of-function, protein stability assay, and Fbxl8+Fbxw7 double-loss epistasis

    PMID:35438057

    Open questions at the time
    • Degron or interaction surface on c-myc recognized by FBXL8 not mapped
    • Physiological setting where this pool dominates not defined
  5. 2023 Medium

    Demonstrated FBXL8-mediated degradation of TP53 in vivo, connecting FBXL8 to tumor suppressor turnover and metastatic phenotypes.

    Evidence Co-IP, ubiquitination assay, FBXL8 knockout, and xenograft mouse model in colorectal cancer

    PMID:36855778

    Open questions at the time
    • Ubiquitin linkage type on p53 not specified
    • Relationship to MDM2-dependent p53 control not addressed
  6. 2024 High

    Identified a domain-specific Snail1 interaction and degradation by FBXL8, establishing an anti-fibrotic role via RhoA signaling.

    Evidence Co-IP, FBXL8ΔC3 deletion mutant, proteasome inhibition, Snail1 rescue, and AAV9 overexpression in a myocardial infarction mouse model

    PMID:38615011

    Open questions at the time
    • Direct ubiquitin linkage on Snail1 not characterized
    • Mechanism linking Snail1 loss to reduced RhoA activation not fully resolved
  7. 2026 High

    Revealed a non-degradative FBXL8 function, answering how FBXL8 can suppress rather than promote substrate function through K63-linked ubiquitination.

    Evidence Co-IP, K63-linkage-specific ubiquitination assay with K38 site mutagenesis, dephosphorylation experiments, p65 nuclear translocation readout, and YY1 transcriptional feedback analysis

    PMID:41608629

    Open questions at the time
    • Whether the same SCF complex configuration mediates both degradative and stabilizing activities is unresolved
    • Determinants selecting K63 versus K48 output by FBXL8 not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How FBXL8 selects between degradative (K48) and stabilizing (K63) ubiquitin outputs across its diverse substrates, and the structural basis of its phosphorylation-dependent and -independent substrate recognition, remain unresolved.
  • No structural model of FBXL8-substrate complexes
  • Mechanism determining linkage-type choice unknown
  • No unified accounting of which substrates dominate in which tissue contexts

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 GO:0098772 molecular function regulator activity 1
Pathway
R-HSA-392499 Metabolism of proteins 4 R-HSA-1640170 Cell Cycle 3 R-HSA-162582 Signal Transduction 2
Complex memberships
SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2020 SCF-Fbxl8 is identified as the E3 ubiquitin ligase for phospho-Thr-283 cyclin D3; it poly-ubiquitylates p-Thr-283 cyclin D3 targeting it for proteasomal degradation, thereby antagonizing cell cycle progression, hematopoietic cell proliferation, and oncogene-induced transformation. Co-immunoprecipitation, ubiquitylation assays, cyclin D3T283A phosphorylation-deficient mutant rescue experiments, cell proliferation and transformation assays Oncogene High 33122824
2022 SCF-Fbxl8 binds and ubiquitylates c-myc independent of phosphorylation (i.e., independent of the Fbxw7 phospho-degron), targeting a distinct pool of c-myc for degradation; loss of Fbxl8 increases c-myc protein levels and stability and increases cell division, while concurrent loss of Fbxl8 and Fbxw7 causes a synergistic increase in c-myc protein. Co-immunoprecipitation, ubiquitylation assay, loss-of-function (Fbxl8 knockdown/loss), gain-of-function (Fbxl8 overexpression), protein stability assay, double-loss epistasis (Fbxl8 + Fbxw7) Cancer biology & therapy High 35438057
2020 FBXL8, as an E3 ubiquitin ligase, interacts with (by Co-IP) and promotes degradation of CCND2 (cyclin D2) and IRF5 in breast cancer cells; knockdown of FBXL8 causes accumulation of CCND2 and IRF5, induces apoptosis, and inhibits cell migration and invasion. Co-immunoprecipitation, FBXL8 knockdown with protein accumulation readout, cell migration/invasion assays, apoptosis assays Cancers Medium 32784654
2021 FBXL8 and FZR1 each independently pull down CCNF (cyclin F); double knockdown of both FBXL8 and FZR1 causes CCNF protein accumulation, indicating both E3 ligases contribute to CCNF degradation in breast cancer cells. Co-immunoprecipitation (pulldown), double knockdown with protein accumulation readout Cancers Medium 34201347
2023 SCF-FBXL8 directly interacts with and ubiquitinates TP53 (p53), promoting its degradation via the proteasome in colorectal cancer cells; FBXL8 knockout stabilizes p53 and inhibits tumor proliferation, invasion, migration, stem-cell-like properties, and liver metastasis in vivo. Co-immunoprecipitation, ubiquitination assay, FBXL8 knockout, xenograft mouse model, western blotting Clinical and translational medicine Medium 36855778
2024 FBXL8 interacts with Snail1 via its C3-binding domain and promotes Snail1 degradation through the ubiquitin-proteasome system, leading to decreased RhoA activation; FBXL8 overexpression in cardiac fibroblasts suppresses TGFβ-induced fibroblast activation (proliferation, migration, contraction, collagen secretion), and AAV9-mediated FBXL8 overexpression ameliorated post-myocardial infarction cardiac fibrosis in vivo. Co-immunoprecipitation, proteasome inhibition assay, FBXL8ΔC3 deletion mutant, FBXL8 overexpression/knockdown in cardiac fibroblasts, Snail1 rescue experiments, AAV9-mediated overexpression in MI mouse model, echocardiography and histology Cell death & disease High 38615011
2026 FBXL8 binds dephosphorylated IκBα (at S32/S36) and mediates K63-linked polyubiquitination at the K38 site of IκBα, thereby stabilizing IκBα (non-degradative ubiquitination) and inhibiting NF-κB p65 nuclear translocation; additionally, NF-κB p65 transcriptionally upregulates YY1, which in turn transcriptionally represses FBXL8, forming a feedforward loop. Co-immunoprecipitation, ubiquitination assay (K63-linkage-specific), site-directed mutagenesis (K38), dephosphorylation experiments, NF-κB p65 nuclear translocation assay, transcription factor binding (YY1-ChIP implied), in vitro and in vivo functional assays International journal of biological sciences High 41608629

Source papers

Stage 0 corpus · 10 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Expression analysis of candidate breast tumour suppressor genes on chromosome 16q. Breast cancer research : BCR 32 16280054
2022 Complete Genome Sequencing and Comparative Genomics of Three Potential Probiotic Strains, Lacticaseibacillus casei FBL6, Lacticaseibacillus chiayiensis FBL7, and Lacticaseibacillus zeae FBL8. Frontiers in microbiology 28 35069490
2020 Fbxl8 suppresses lymphoma growth and hematopoietic transformation through degradation of cyclin D3. Oncogene 21 33122824
2022 DNA methylation analysis of normal colon organoids from familial adenomatous polyposis patients reveals novel insight into colon cancer development. Clinical epigenetics 20 35999641
2021 A Novel Signature of CCNF-Associated E3 Ligases Collaborate and Counter Each Other in Breast Cancer. Cancers 17 34201347
2020 Human FBXL8 Is a Novel E3 Ligase Which Promotes BRCA Metastasis by Stimulating Pro-Tumorigenic Cytokines and Inhibiting Tumor Suppressors. Cancers 16 32784654
2023 SCF-FBXL8 contributes to liver metastasis and stem-cell-like features in colorectal cancer cells by mediating ubiquitination and degradation of TP53. Clinical and translational medicine 12 36855778
2024 FBXL8 inhibits post-myocardial infarction cardiac fibrosis by targeting Snail1 for ubiquitin-proteasome degradation. Cell death & disease 8 38615011
2022 Ubiquitylation of unphosphorylated c-myc by novel E3 ligase SCFFbxl8. Cancer biology & therapy 7 35438057
2026 FBXL8 Stabilizes IκBα and Negatively Regulated NF-κB Activation to Suppress Pancreatic Cancer Progression. International journal of biological sciences 0 41608629

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