FBXL8 (F-box/LRR-repeat protein 8, FBL8) is a member of the FBXL subfamily of F-box proteins. It has an N-terminal F-box domain through which it docks onto the SKP1 adaptor and, via SKP1, onto CUL1 and the catalytic RING subunit RBX1, assembling a Cullin-RING (SCF) E3 ubiquitin ligase in which the F-box protein serves as the substrate-recognition subunit. Despite the "LRR" in its name, UniProt notes that FBXL8 does not actually contain canonical leucine-rich repeats; nonetheless its C-terminal substrate-binding region is functionally required for substrate engagement (deletion of either the F-box or the C-terminal region abolishes substrate turnover). FBXL8 acts as the substrate-recognition subunit of SCF-FBXL8 and targets several substrates in a strongly context-dependent manner: it promotes ubiquitination and proteasomal degradation of the tumor suppressor p53 (in colorectal cancer), of Thr283- phosphorylated cyclin D3 (CCND3) (in lymphoma), of Snail1 (in post-myocardial- infarction cardiac fibroblasts, dampening RhoA signaling and myofibroblast differentiation), and of unphosphorylated c-MYC (a distinct c-MYC pool from that controlled by FBXW7, with reported heterotypic K48/K63 chains); CCND2 and IRF5 are additional candidate substrates accumulating upon FBXL8 knockdown. Reported localization is predominantly cytoplasmic (loss of FBXL8 causes nuclear c-MYC accumulation), and in heart FBXL8 is enriched in cardiac fibroblasts. Its net effect is context-dependent rather than uniformly oncogenic or tumor-suppressive: oncogenic in colorectal and breast cancer, but tumor-suppressive in lymphoma and anti-fibrotic after myocardial infarction.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
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GO:0005515
protein binding
|
IPI
PMID:19159283 Array MAPPIT: high-throughput interactome analysis in mammal... |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the Array MAPPIT high-throughput screen. The SKP1 interaction is the defining F-box-domain partnership, but the bare protein binding term is uninformative.
Reason: Records the functionally meaningful FBXL8-SKP1 interaction (the basis of SCF assembly), but bare protein binding is uninformative per curation guidelines; the SCF/SCF-degradation annotations capture this relationship.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
|
|
GO:0005515
protein binding
|
IPI
PMID:25416956 A proteome-scale map of the human interactome network. |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a proteome-scale interactome map. Bare protein binding is uninformative.
Reason: Records the FBXL8-SKP1 interaction underlying SCF assembly, but bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
|
|
GO:0005515
protein binding
|
IPI
PMID:26496610 A human interactome in three quantitative dimensions organiz... |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a quantitative-interactome study. Bare protein binding is uninformative.
Reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
|
|
GO:0005515
protein binding
|
IPI
PMID:27705803 A High-Density Map for Navigating the Human Polycomb Complex... |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the Polycomb complexome AP-MS study. Bare protein binding is uninformative.
Reason: Records the FBXL8-SKP1 interaction, consistent with SCF assembly rather than a Polycomb-specific function; bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
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|
GO:0005515
protein binding
|
IPI
PMID:32296183 A reference map of the human binary protein interactome. |
KEEP AS NON CORE |
Summary: IntAct binary-interactome interactions captured here include ALAS1 (P13196), PICK1 (Q9NRD5) and SKP1 (P63208). SKP1 is the canonical F-box partner; ALAS1/PICK1 are candidate substrates/partners but not experimentally validated as FBXL8 substrates. Bare protein binding is uninformative.
Reason: Records real binary interactions (including the SCF-defining SKP1 partner and candidate substrates ALAS1/PICK1), but bare protein binding is uninformative and no substrate relationship is experimentally established.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P13196: ALAS1; NbExp=3; IntAct=EBI-2321097, EBI-3905054;
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GO:0005515
protein binding
|
IPI
PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the BioPlex dual proteome-scale interactome. Bare protein binding is uninformative.
Reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
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GO:0005515
protein binding
|
IPI
PMID:40205054 Multimodal cell maps as a foundation for structural and func... |
KEEP AS NON CORE |
Summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a multimodal cell-map interactome study. Bare protein binding is uninformative.
Reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;
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GO:0031146
SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
|
NAS
PMID:33234069 The FBXL family of F-box proteins: variations on a theme. |
ACCEPT |
Summary: ComplexPortal/NAS assignment that FBXL8, as an SCF substrate receptor, participates in SCF-dependent proteasomal degradation. This is the core biological process for an F-box protein, and FBXL8-specific degradative substrates are now reported in the primary literature (p53 in colorectal cancer, Thr283-phospho-cyclin D3 in lymphoma, Snail1 in cardiac fibroblasts, and unphosphorylated c-MYC).
Reason: Consistent with FBXL8 being a substrate-recognition subunit of an SCF E3 ligase (documented SKP1/CUL1 interaction); SCF-dependent degradation is the canonical core process for F-box proteins, and multiple FBXL8 substrates whose turnover requires the F-box are now experimentally documented.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
file:human/FBXL8/FBXL8-deep-research-falcon.md
Across multiple primary studies, FBXL8 functions as an **SCF E3 ligase adaptor** that promotes **substrate ubiquitination**, frequently leading to **proteasome-dependent degradation** of specific targets
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GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8952618 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation, propagated across the generic CRL1/neddylation reaction set. The cytosol is a plausible compartment for an SCF substrate receptor.
Reason: Plausible localization for a cytosolic SCF component, but derived from generic CRL pathway membership (one of many identical Reactome reactions) rather than FBXL8-specific evidence.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
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GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8952620 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic CRL1 neddylation reaction set.
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
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GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8955241 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic CRL (CAND1) reaction set.
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
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GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8955289 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic CRL (COMMD/CAND1) reaction set.
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
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GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8956040 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic CRL deneddylation (COP9) reaction set.
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8956200 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic CRL1 (DCUN1D3) reaction set.
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983140 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (transfer of Ub from E2 to substrate).
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983147 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (release of E3 from substrate).
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983156 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (polyubiquitination of substrate).
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983157 |
KEEP AS NON CORE |
Summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (interaction of E3 with substrate and E2-Ub).
Reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
Supporting Evidence:
file:human/FBXL8/FBXL8-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
|
Q: What determines the strikingly context-dependent outcomes of FBXL8 activity (oncogenic in colorectal/breast cancer versus tumor-suppressive in lymphoma and anti-fibrotic in heart)? Is it substrate availability, post-translational state of substrates, or tissue-specific cofactors?
Q: Are the binary-interactome partners ALAS1 and PICK1 genuine FBXL8 substrates, distinct from the validated p53/CCND3/Snail1/c-MYC set, and under what conditions are they degraded?
Q: What is the basis of FBXL8 substrate recognition given that it lacks canonical leucine-rich repeats yet its C-terminal region is required for substrate engagement?
Experiment: Perform affinity purification-mass spectrometry of tagged FBXL8 (stabilized with proteasome and neddylation inhibitors) across multiple cell types (colorectal, lymphoma, cardiac fibroblast) to map the tissue-dependent substrate repertoire relative to an F-box-deletion mutant unable to assemble into SCF.
Experiment: Reconstitute SCF-FBXL8 in vitro and test direct ubiquitination of validated and candidate substrates (p53, phospho-Thr283 cyclin D3, Snail1, unphosphorylated c-MYC, ALAS1, PICK1), mapping ubiquitin-chain linkage type and the C-terminal residues required for substrate binding.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The literature synthesized here is consistent with the UniProt target Q96CD0, annotated as F-box/LRR-repeat protein 8 (FBXL8) in Homo sapiens. Experimental studies explicitly manipulate FBXL8 F-box and LRR regions (ΔFbox and ΔLRR constructs) to test SCF-complex binding and substrate turnover, aligning with the UniProt-described domain architecture and SCF-adaptor role (yao2023scf‐fbxl8contributesto pages 7-10, yao2023scf‐fbxl8contributesto pages 10-14).
FBXL8 is best understood as a substrate receptor/adaptor within an SCF-type E3 ubiquitin ligase. In the SCF architecture, F-box proteins recruit substrates while SCF core proteins (e.g., SKP1, CUL1, RBX1) provide the catalytic scaffold to support ubiquitin transfer and (often) proteasome-directed degradation (mason2020thefbxlfamily pages 1-2).
A key organizing principle is that FBXL proteins contain (i) an F-box domain that engages SCF core components and (ii) leucine-rich repeats (LRRs) that mediate protein–protein interactions underlying substrate selectivity. Review synthesis emphasizes that despite similar LRR architectures across FBXL proteins, substrate specificity can diverge substantially, producing distinct interactomes (mason2020thefbxlfamily pages 1-2). Structural modeling in an FBXL-family review includes FBXL8 among family members, emphasizing diversity in predicted conformations and confidence values within this subfamily (mason2020thefbxlfamily pages 5-6).
Across multiple primary studies, FBXL8 functions as an SCF E3 ligase adaptor that promotes substrate ubiquitination, frequently leading to proteasome-dependent degradation of specific targets (yao2023scf‐fbxl8contributesto pages 1-3, bajpai2022ubiquitylationofunphosphorylated pages 88-95, li2024fbxl8inhibitspostmyocardial pages 1-2, yoshida2021fbxl8suppresseslymphoma pages 9-11).
FBXL8 has been linked to several substrates across contexts:
(A) TP53 (p53) – colorectal cancer context (strong biochemical + functional evidence)
FBXL8 physically associates with p53 (co-immunoprecipitation), increases p53 ubiquitination, and accelerates p53 turnover in cycloheximide chase experiments; both the F-box and LRR regions are required for this effect, because ΔFbox and ΔLRR constructs fail to influence p53 stability like full-length FBXL8 (yao2023scf‐fbxl8contributesto pages 7-10, yao2023scf‐fbxl8contributesto pages 10-14). Functionally, FBXL8 knockout reduces CRC cell growth/migration and stemness markers, while p53 knockdown rescues key anti-tumor effects, supporting an SCF–FBXL8–p53 axis (yao2023scf‐fbxl8contributesto pages 10-14).
(B) Snail1 – cardiac fibrosis after MI (strong biochemical + in vivo evidence; 2024 development)
In post-myocardial infarction (MI) remodeling, FBXL8 interacts with Snail1 and promotes its ubiquitin–proteasome degradation, with a defined interaction requirement (FBXL8 ΔC3 domain requirement). This down-modulates downstream RhoA activation and dampens myofibroblast differentiation (li2024fbxl8inhibitspostmyocardial pages 1-2). Figure evidence in the same paper shows FBXL8 downregulation after MI/TGFβ, and experimental support for Snail1 ubiquitination/stability changes with FBXL8 modulation (li2024fbxl8inhibitspostmyocardial media 22acda4a).
(C) Cyclin D3 (CCND3), specifically phospho-Thr283 cyclin D3 – lymphoma context (strong biochemical + functional evidence)
FBXL8 (as SCF-FBXL8) recognizes Thr-283 phosphorylated cyclin D3, polyubiquitylates it, and drives proteasomal degradation. Proliferation attenuation depends on Thr-283 because a non-phosphorylatable cyclin D3T283A mutant rescues the phenotype. Xenograft results show tumor suppression when FBXL8 is overexpressed, whereas an FBXL8ΔF mutant loses that effect (yoshida2021fbxl8suppresseslymphoma pages 9-11).
(D) c-MYC – cancer cell-cycle proteostasis (strong biochemical evidence; pool-specific model)
FBXL8 recognizes and ubiquitylates unphosphorylated c-MYC, distinct from the canonical phospho-degron recognition by FBXW7. Concurrent loss of FBXL8 and FBXW7 additively elevates c-MYC, consistent with regulation of distinct c-MYC pools. The study also reports heterotypic K48/K63 ubiquitin linkages on c-MYC by FBXL8 and suggests FBXL8 is largely cytoplasmic, with knockout causing nuclear c-MYC accumulation (bajpai2022ubiquitylationofunphosphorylated pages 95-99).
(E) CCND2 and IRF5 – breast-cancer context (moderate evidence: association + inverse protein correlation)
In breast-cancer studies, CCND2 and IRF5 are reported as FBXL8-associated tumor suppressors that accumulate upon FBXL8 knockdown and are detected in FBXL8-containing complexes, suggesting regulation through FBXL8-mediated turnover; however, compared with p53/CCND3/Snail1/c-MYC, the mechanistic chain (direct ubiquitination reconstitution) is less extensively shown in the excerpted evidence (chang2020humanfbxl8is pages 12-15, chang2020globalrnaseqidentified pages 20-23).
In the c-MYC study, FBXL8 is described as exclusively cytoplasmic, with FBXL8 loss associated with increased nuclear c-MYC, consistent with FBXL8 regulating a cytoplasmic c-MYC pool (bajpai2022ubiquitylationofunphosphorylated pages 95-99). (Note: this is study-specific and may vary by cell type.)
In the post-MI fibrosis model, FBXL8 is reported as primarily expressed in cardiac fibroblasts with minimal signal in cardiomyocytes. Co-localization with α-SMA-positive cells in LV sections supports enrichment in activated fibroblast/myofibroblast populations (li2024fbxl8inhibitspostmyocardial pages 2-4). Figure panels supporting these localization/expression conclusions were retrieved from the original paper (li2024fbxl8inhibitspostmyocardial media 22acda4a).
FBXL8 appears to sit at the intersection of ubiquitin-mediated proteostasis and several high-impact pathways:
A 2023 study proposes that FBXL8 is upregulated in CRC and associates with poor prognosis, promoting invasion/migration and stem-like features. Mechanistically, FBXL8 binds p53 and promotes its ubiquitination and degradation; ΔFbox and ΔLRR mutants fail to phenocopy full-length FBXL8, indicating both SCF engagement and substrate-binding modules are required (yao2023scf‐fbxl8contributesto pages 1-3, yao2023scf‐fbxl8contributesto pages 7-10, yao2023scf‐fbxl8contributesto pages 10-14).
In vivo, xenograft and spleen-injection metastasis models show that FBXL8 knockout reduces tumor growth and liver metastasis (12 mice total; 6 per group; p<0.001 reported for comparisons) (yao2023scf‐fbxl8contributesto pages 10-14).
Publication: 2023-02 (Clinical and Translational Medicine). URL: https://doi.org/10.1002/ctm2.1208 (yao2023scf‐fbxl8contributesto pages 1-3).
A 2024 Cell Death & Disease paper positions FBXL8 as an anti-fibrotic regulator in the injured heart. FBXL8 is reduced after MI and after TGFβ stimulation in cardiac fibroblasts, and AAV9-mediated FBXL8 overexpression improves function and reduces fibrosis. Mechanistically, FBXL8 targets Snail1 for ubiquitin–proteasome degradation and reduces RhoA activation; domain mapping indicates a specific binding interface requirement (li2024fbxl8inhibitspostmyocardial pages 1-2, li2024fbxl8inhibitspostmyocardial pages 2-4, li2024fbxl8inhibitspostmyocardial media 22acda4a).
Quantitatively, FBXL8 knockdown increased TGFβ-induced fibroblast migration and proliferation by ~1.4-fold and ~1.3-fold, and increased active RhoA-GTP ~2.9-fold; time-course heart expression studies used n=5 and in vitro quantifications used n=3 (li2024fbxl8inhibitspostmyocardial pages 2-4). These primary conclusions are supported by figure panels retrieved from the article (li2024fbxl8inhibitspostmyocardial media 22acda4a).
Publication: 2024-04 (Cell Death & Disease). URL: https://doi.org/10.1038/s41419-024-06646-1 (li2024fbxl8inhibitspostmyocardial pages 1-2).
An authoritative 2023 editorial argues that ubiquitin ligases and adaptors represent a large and incompletely exploited space of therapeutic targets; it explicitly mentions FBXL8 (with FZR1) as potential targets in breast cancer, framing ligase adaptors as actionable nodes once cancer-specific dependencies are established (vriend2023roleofubiquitin pages 1-2).
Publication: 2023-07-01 (Cancers, editorial). URL: https://doi.org/10.3390/cancers15133460 (vriend2023roleofubiquitin pages 1-2).
The post-MI study provides a concrete translational prototype: AAV9-mediated FBXL8 overexpression in vivo improved cardiac outcomes and reduced fibrosis burden (li2024fbxl8inhibitspostmyocardial pages 1-2, li2024fbxl8inhibitspostmyocardial media 22acda4a). While not yet a clinical therapy, this is a real-world implementable modality (cardiac AAV gene transfer) with mechanistic anchoring in Snail1 degradation.
FBXL8 is presented as (i) a candidate prognostic marker in CRC (high FBXL8 associated with worse overall survival) and (ii) a potential therapeutic axis via restoring p53 signaling (yao2023scf‐fbxl8contributesto pages 1-3, yao2023scf‐fbxl8contributesto pages 10-14). In lymphoma, the opposite direction is suggested—FBXL8 appears tumor-suppressive by degrading cyclin D3 (yoshida2021fbxl8suppresseslymphoma pages 9-11). Together, this implies context-dependent stratification would be essential for any FBXL8-based therapy.
A dedicated FBXL-family review emphasizes that F-box proteins are substrate-recruiting subunits of SCF ligases and that the FBXL subfamily’s LRRs mediate selective substrate engagement, but family-wide structural similarity does not guarantee functional similarity—an expert framing consistent with FBXL8’s diverse substrate set across tissues (mason2020thefbxlfamily pages 1-2). This viewpoint supports an interpretive model where FBXL8’s biological effects are dominated by which substrates are expressed/accessible and which post-translational states are present in a given tissue.
Key quantitative findings extracted from the available full text include:
The most defensible functional annotation for human FBXL8 is:
FBXL8 is an SCF-type E3 ubiquitin ligase substrate receptor (F-box + LRR protein) that determines substrate specificity and promotes ubiquitination of distinct targets in a context-dependent manner, influencing proteasomal degradation or other ubiquitin-mediated outcomes (mason2020thefbxlfamily pages 1-2, yao2023scf‐fbxl8contributesto pages 7-10).
FBXL8 has been reported to promote tumor aggressiveness in breast cancer and CRC (via cytokine milieu changes and p53 destabilization, respectively) yet suppress lymphoma growth by degrading cyclin D3, and protect the heart after MI by degrading Snail1 and suppressing fibrotic signaling (chang2020humanfbxl8is pages 12-15, yao2023scf‐fbxl8contributesto pages 1-3, yoshida2021fbxl8suppresseslymphoma pages 9-11, li2024fbxl8inhibitspostmyocardial pages 1-2). This argues against a single “oncogene vs tumor suppressor” label and supports a substrate-availability and signaling-state model.
| Aspect | Key findings | Evidence type | Key citations with year and DOI URL |
|---|---|---|---|
| Identity/domains | FBXL8 matches the UniProt target Q96CD0: a human FBXL-family F-box protein with leucine-rich repeats (LRRs), consistent with an SCF substrate receptor architecture. Review-level structural analysis places FBXL proteins as substrate-recruiting subunits of SKP1-CUL1-RBX1 E3 ligases; Yao 2023 experimentally showed both the F-box and LRR regions are required for FBXL8-mediated p53 ubiquitination and degradation. (mason2020thefbxlfamily pages 1-2, yao2023scf‐fbxl8contributesto pages 7-10) | Review, biochemical, cell | Mason and Laman 2020, Open Biology, https://doi.org/10.1098/rsob.200319; Yao et al. 2023, Clinical and Translational Medicine, https://doi.org/10.1002/ctm2.1208 |
| SCF complex role | FBXL8 functions as the substrate-recognition adaptor of an SCF E3 ubiquitin ligase. Breast-cancer and CRC studies support interaction with SCF components, while Yao 2023 showed full-length FBXL8, but not ΔFbox or ΔLRR mutants, supports p53 destabilization and oncogenic phenotypes. (chang2020globalrnaseqidentified pages 7-11, yao2023scf‐fbxl8contributesto pages 7-10, yao2023scf‐fbxl8contributesto pages 10-14) | Biochemical, cell | Chang et al. 2020, medRxiv, https://doi.org/10.1101/2020.06.09.20127068; Yao et al. 2023, Clinical and Translational Medicine, https://doi.org/10.1002/ctm2.1208 |
| Validated substrates | Experimentally supported FBXL8-associated substrates or interactors include TP53 in CRC, unphosphorylated c-MYC, phospho-Thr283 cyclin D3, and Snail1 in cardiac fibroblasts. CCND2 and IRF5 were found in FBXL8-containing complexes in breast-cancer cells and increase upon FBXL8 knockdown, but evidence there is strongest for association or candidate degradation rather than full biochemical reconstitution. (yao2023scf‐fbxl8contributesto pages 1-3, bajpai2022ubiquitylationofunphosphorylated pages 95-99, bajpai2022ubiquitylationofunphosphorylated pages 88-95, li2024fbxl8inhibitspostmyocardial pages 1-2, chang2020humanfbxl8is pages 12-15) | Biochemical, cell, in vivo | Yao et al. 2023, https://doi.org/10.1002/ctm2.1208; Bajpai et al. 2022, https://doi.org/10.1080/15384047.2022.2061279; Yoshida et al. 2021, https://doi.org/10.1038/s41388-020-01532-4; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1; Chang et al. 2020, Cancers, https://doi.org/10.3390/cancers12082210 |
| Localization | Available evidence suggests FBXL8 is largely cytoplasmic in the c-MYC study, where loss of FBXL8 caused nuclear c-MYC accumulation, implying regulation of a cytoplasmic c-MYC pool. In heart, FBXL8 is enriched in cardiac fibroblasts and co-localizes with α-SMA-positive cells, with little signal in cardiomyocytes. (bajpai2022ubiquitylationofunphosphorylated pages 95-99, li2024fbxl8inhibitspostmyocardial pages 2-4) | Cell, imaging | Bajpai et al. 2022, https://doi.org/10.1080/15384047.2022.2061279; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1 |
| Pathways | Current evidence links FBXL8 to p53 tumor-suppressor control in CRC, c-MYC proteostasis and G1-S progression, cyclin D3-Rb-Ki67 cell-cycle regulation in lymphoma, and Snail1-RhoA-α-SMA fibrotic signaling after MI. In breast cancer, FBXL8 also shapes a pro-tumor cytokine and chemokine milieu, connecting ubiquitin signaling to tumor microenvironment regulation. (yao2023scf‐fbxl8contributesto pages 1-3, bajpai2022ubiquitylationofunphosphorylated pages 95-99, yoshida2021fbxl8suppresseslymphoma pages 9-11, li2024fbxl8inhibitspostmyocardial pages 1-2, chang2020humanfbxl8is pages 12-15) | Biochemical, cell, in vivo | Yao et al. 2023, https://doi.org/10.1002/ctm2.1208; Bajpai et al. 2022, https://doi.org/10.1080/15384047.2022.2061279; Yoshida et al. 2021, https://doi.org/10.1038/s41388-020-01532-4; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1; Chang et al. 2020, Cancers, https://doi.org/10.3390/cancers12082210 |
| Disease contexts | FBXL8 shows context-dependent disease associations: oncogenic in breast cancer and colorectal cancer, but tumor-suppressive in lymphoma models and anti-fibrotic after myocardial infarction. This makes FBXL8 notable as a context-dependent SCF adaptor rather than a uniformly oncogenic or suppressive factor. (chang2020humanfbxl8is pages 12-15, yao2023scf‐fbxl8contributesto pages 1-3, yoshida2021fbxl8suppresseslymphoma pages 9-11, li2024fbxl8inhibitspostmyocardial pages 1-2) | Cell, in vivo, clinical correlation | Chang et al. 2020, Cancers, https://doi.org/10.3390/cancers12082210; Yao et al. 2023, https://doi.org/10.1002/ctm2.1208; Yoshida et al. 2021, https://doi.org/10.1038/s41388-020-01532-4; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1 |
| Quantitative findings/statistics | Breast cancer: FBXL8 mRNA was reported 23-fold higher in MCF7 and 15-fold in MDA-MB231 versus MCF10A; siRNA knockdown reached up to 95 percent, reduced viability by about 52.5 percent at 48 h, reduced proliferation 2 to 3-fold, increased early apoptosis to 20 percent and 24 percent, slowed migration by 14 percent and 40 percent, and reduced invasion 4 to 8-fold; patient-scale analyses included n = 1349 matched tissues and stage-associated increases with p < 0.01 to p < 0.001. CRC: 100 patients were analyzed, including 36 non-metastatic and 64 liver-metastatic cases; xenograft and metastasis studies used 12 nude mice total, 6 per group, with FBXL8 knockout reducing tumor burden and liver metastasis at p < 0.001. Cardiac fibrosis: rat heart time-course n = 5 and cardiac-fibroblast western quantitation n = 3; FBXL8 knockdown increased TGFβ-induced cardiac-fibroblast migration and proliferation by 1.4-fold and 1.3-fold, and RhoA-GTP rose 2.9-fold. Lymphoma: low-density assays used 1 × 10^4 cells, n = 4, with p = 0.02 and p < 0.01; xenografts used 2 × 10^6 CA46 cells in SCID mice, n = 10, with tumor-volume and tumor-weight reductions reported at p = 0.02, p = 0.02, p = 0.03, and p < 0.01. (chang2020globalrnaseqidentified pages 7-11, chang2020humanfbxl8is pages 12-15, yao2023scf‐fbxl8contributesto pages 1-3, yao2023scf‐fbxl8contributesto pages 10-14, li2024fbxl8inhibitspostmyocardial pages 2-4, yoshida2021fbxl8suppresseslymphoma pages 9-11) | Cell, in vivo, clinical correlation | Chang et al. 2020, medRxiv, https://doi.org/10.1101/2020.06.09.20127068; Chang et al. 2020, Cancers, https://doi.org/10.3390/cancers12082210; Yao et al. 2023, https://doi.org/10.1002/ctm2.1208; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1; Yoshida et al. 2021, https://doi.org/10.1038/s41388-020-01532-4 |
| Applications/therapeutic angle | No FBXL8-targeted therapy is established clinically, but the literature repeatedly frames FBXL8 as a potential therapeutic node: inhibition may be attractive in breast and colorectal cancer where FBXL8 promotes tumor traits, whereas augmentation or gene delivery may be beneficial after MI where AAV9-FBXL8 reduced fibrosis. Editorial commentary highlights ubiquitin-ligase adaptors such as FBXL8 as promising but underdeveloped therapeutic targets, including in targeted protein degradation strategies. (yao2023scf‐fbxl8contributesto pages 1-3, li2024fbxl8inhibitspostmyocardial pages 1-2, vriend2023roleofubiquitin pages 1-2) | Editorial, translational interpretation, in vivo | Vriend 2023, Cancers, https://doi.org/10.3390/cancers15133460; Yao et al. 2023, https://doi.org/10.1002/ctm2.1208; Li et al. 2024, https://doi.org/10.1038/s41419-024-06646-1 |
Table: This table summarizes the main functional-annotation evidence for human FBXL8 or Q96CD0 across molecular function, substrates, localization, pathways, disease roles, and translational implications. It is useful as a compact evidence map that distinguishes validated findings from broader review and editorial interpretation.
References
(yao2023scf‐fbxl8contributesto pages 7-10): Jing Yao, Xin‐Ping Wang, Jun Yang, Zhe Yang, and Zheng‐Yun Zhang. 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, Feb 2023. URL: https://doi.org/10.1002/ctm2.1208, doi:10.1002/ctm2.1208. This article has 12 citations and is from a peer-reviewed journal.
(yao2023scf‐fbxl8contributesto pages 10-14): Jing Yao, Xin‐Ping Wang, Jun Yang, Zhe Yang, and Zheng‐Yun Zhang. 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, Feb 2023. URL: https://doi.org/10.1002/ctm2.1208, doi:10.1002/ctm2.1208. This article has 12 citations and is from a peer-reviewed journal.
(mason2020thefbxlfamily pages 1-2): Bethany Mason and Heike Laman. The fbxl family of f-box proteins: variations on a theme. Open Biology, Nov 2020. URL: https://doi.org/10.1098/rsob.200319, doi:10.1098/rsob.200319. This article has 51 citations and is from a peer-reviewed journal.
(mason2020thefbxlfamily pages 5-6): Bethany Mason and Heike Laman. The fbxl family of f-box proteins: variations on a theme. Open Biology, Nov 2020. URL: https://doi.org/10.1098/rsob.200319, doi:10.1098/rsob.200319. This article has 51 citations and is from a peer-reviewed journal.
(yao2023scf‐fbxl8contributesto pages 1-3): Jing Yao, Xin‐Ping Wang, Jun Yang, Zhe Yang, and Zheng‐Yun Zhang. 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, Feb 2023. URL: https://doi.org/10.1002/ctm2.1208, doi:10.1002/ctm2.1208. This article has 12 citations and is from a peer-reviewed journal.
(bajpai2022ubiquitylationofunphosphorylated pages 88-95): Sagar Bajpai, Hong Ri Jin, Bartosz Mucha, and J. Alan Diehl. Ubiquitylation of unphosphorylated c-myc by novel e3 ligase scffbxl8. Cancer Biology & Therapy, 23:348-357, Apr 2022. URL: https://doi.org/10.1080/15384047.2022.2061279, doi:10.1080/15384047.2022.2061279. This article has 6 citations and is from a peer-reviewed journal.
(li2024fbxl8inhibitspostmyocardial pages 1-2): Ya Li, Caojian Zuo, Xiaoyu Wu, Yu Ding, Yong Wei, Songwen Chen, Xiaofeng Lu, Juan Xu, Shaowen Liu, Genqing Zhou, and Lidong Cai. Fbxl8 inhibits post-myocardial infarction cardiac fibrosis by targeting snail1 for ubiquitin-proteasome degradation. Cell Death & Disease, Apr 2024. URL: https://doi.org/10.1038/s41419-024-06646-1, doi:10.1038/s41419-024-06646-1. This article has 9 citations and is from a peer-reviewed journal.
(yoshida2021fbxl8suppresseslymphoma pages 9-11): A. Yoshida, A. Yoshida, Jaewoo Choi, H. Jin, Yan Li, Sagar Bajpai, Sagar Bajpai, Shuo Qie, and J. Diehl. Fbxl8 suppresses lymphoma growth and hematopoietic transformation through degradation of cyclin d3. Oncogene, 40:292-306, Oct 2021. URL: https://doi.org/10.1038/s41388-020-01532-4, doi:10.1038/s41388-020-01532-4. This article has 33 citations and is from a domain leading peer-reviewed journal.
(li2024fbxl8inhibitspostmyocardial media 22acda4a): Ya Li, Caojian Zuo, Xiaoyu Wu, Yu Ding, Yong Wei, Songwen Chen, Xiaofeng Lu, Juan Xu, Shaowen Liu, Genqing Zhou, and Lidong Cai. Fbxl8 inhibits post-myocardial infarction cardiac fibrosis by targeting snail1 for ubiquitin-proteasome degradation. Cell Death & Disease, Apr 2024. URL: https://doi.org/10.1038/s41419-024-06646-1, doi:10.1038/s41419-024-06646-1. This article has 9 citations and is from a peer-reviewed journal.
(bajpai2022ubiquitylationofunphosphorylated pages 95-99): Sagar Bajpai, Hong Ri Jin, Bartosz Mucha, and J. Alan Diehl. Ubiquitylation of unphosphorylated c-myc by novel e3 ligase scffbxl8. Cancer Biology & Therapy, 23:348-357, Apr 2022. URL: https://doi.org/10.1080/15384047.2022.2061279, doi:10.1080/15384047.2022.2061279. This article has 6 citations and is from a peer-reviewed journal.
(chang2020humanfbxl8is pages 12-15): Shu-Chun Chang, Wayne Hsu, Emily Chia-Yu Su, Chin-Sheng Hung, and Jeak Ling Ding. Human fbxl8 is a novel e3 ligase which promotes brca metastasis by stimulating pro-tumorigenic cytokines and inhibiting tumor suppressors. Cancers, 12:2210, Aug 2020. URL: https://doi.org/10.3390/cancers12082210, doi:10.3390/cancers12082210. This article has 19 citations.
(chang2020globalrnaseqidentified pages 20-23): Shu-Chun Chang, Wayne Hsu, Emily Chia-Yu Su, Chin-Sheng Hung, and Jeak Ling Ding. Global rna-seq identified fbxl8 as a novel e3 ligase which modulates tumor suppressors to promote brca advancement. medRxiv, Jun 2020. URL: https://doi.org/10.1101/2020.06.09.20127068, doi:10.1101/2020.06.09.20127068. This article has 0 citations.
(li2024fbxl8inhibitspostmyocardial pages 2-4): Ya Li, Caojian Zuo, Xiaoyu Wu, Yu Ding, Yong Wei, Songwen Chen, Xiaofeng Lu, Juan Xu, Shaowen Liu, Genqing Zhou, and Lidong Cai. Fbxl8 inhibits post-myocardial infarction cardiac fibrosis by targeting snail1 for ubiquitin-proteasome degradation. Cell Death & Disease, Apr 2024. URL: https://doi.org/10.1038/s41419-024-06646-1, doi:10.1038/s41419-024-06646-1. This article has 9 citations and is from a peer-reviewed journal.
(chang2020globalrnaseqidentified pages 7-11): Shu-Chun Chang, Wayne Hsu, Emily Chia-Yu Su, Chin-Sheng Hung, and Jeak Ling Ding. Global rna-seq identified fbxl8 as a novel e3 ligase which modulates tumor suppressors to promote brca advancement. medRxiv, Jun 2020. URL: https://doi.org/10.1101/2020.06.09.20127068, doi:10.1101/2020.06.09.20127068. This article has 0 citations.
(vriend2023roleofubiquitin pages 1-2): Jerry Vriend. Role of ubiquitin ligases and conjugases in targeted cancer therapy. Cancers, 15:3460, Jul 2023. URL: https://doi.org/10.3390/cancers15133460, doi:10.3390/cancers15133460. This article has 1 citations.
(chang2020humanfbxl8is pages 1-3): Shu-Chun Chang, Wayne Hsu, Emily Chia-Yu Su, Chin-Sheng Hung, and Jeak Ling Ding. Human fbxl8 is a novel e3 ligase which promotes brca metastasis by stimulating pro-tumorigenic cytokines and inhibiting tumor suppressors. Cancers, 12:2210, Aug 2020. URL: https://doi.org/10.3390/cancers12082210, doi:10.3390/cancers12082210. This article has 19 citations.
...|F-box|LRR subtype. The review captures this caveat in its description; the PN subtype label is therefore mildly inaccurate for this member (subtype is no_mapping, so no propagation harm). Falcon substrates (p53, phospho-Thr283 CCND3, Snail1, unphospho c-MYC) are UNVERIFIED leads, correctly not added as GO terms.protein binding (SKP1) and no SCF-process IDA. The review's core_functions assigns GO:1990756, but — unlike FBXL7/FBXL12 — it is NOT added as an action: NEW entry in existing_annotations. This is the one batch-pattern deviation: the adaptor MF that PN projects as new_to_goa is endorsed in core_functions but never materialized as a reviewable annotation. Conclusion: ADD GO:1990756 as NEW to existing_annotations for parity.GO:1990756 as action: NEW in FBXL8 existing_annotations (mirror FBXL7/FBXL12) so the PN-projected adaptor MF is materialized; [MAP] consider noting the non-canonical (no-LRR) status on the F-box|LRR subtype for FBXL8.UPS|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box|LRR ; PN-node mapping: group-level mapped / ok_for_propagation_to_go / GO:1990756; class context_only / too_broad / GO:0061630....|F-box|LRR subtype. The review captures this caveat in its description; the PN subtype label is therefore mildly inaccurate for this member (subtype is no_mapping, so no propagation harm). Falcon substrates (p53, phospho-Thr283 CCND3, Snail1, unphospho c-MYC) are UNVERIFIED leads, correctly not added as GO terms.protein binding (SKP1) and no SCF-process IDA. The review's core_functions assigns GO:1990756, but — unlike FBXL7/FBXL12 — it is NOT added as an action: NEW entry in existing_annotations. This is the one batch-pattern deviation: the adaptor MF that PN projects as new_to_goa is endorsed in core_functions but never materialized as a reviewable annotation. Conclusion: ADD GO:1990756 as NEW to existing_annotations for parity.|LRR subtype label is a misnomer here; (2) no PMID-validated substrate in existing_annotations — adaptor MF is inferred-only. Scope/status otherwise correct.GO:1990756 as action: NEW in FBXL8 existing_annotations (mirror FBXL7/FBXL12) so the PN-projected adaptor MF is materialized; [MAP] consider noting the non-canonical (no-LRR) status on the F-box|LRR subtype for FBXL8.This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
id: Q96CD0
gene_symbol: FBXL8
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
FBXL8 (F-box/LRR-repeat protein 8, FBL8) is a member of the FBXL subfamily of
F-box proteins. It has an N-terminal F-box domain through which it docks onto
the SKP1 adaptor and, via SKP1, onto CUL1 and the catalytic RING subunit RBX1,
assembling a Cullin-RING (SCF) E3 ubiquitin ligase in which the F-box protein
serves as the substrate-recognition subunit. Despite the "LRR" in its name,
UniProt notes that FBXL8 does not actually contain canonical leucine-rich
repeats; nonetheless its C-terminal substrate-binding region is functionally
required for substrate engagement (deletion of either the F-box or the
C-terminal region abolishes substrate turnover). FBXL8 acts as the
substrate-recognition subunit of SCF-FBXL8 and targets several substrates in a
strongly context-dependent manner: it promotes ubiquitination and proteasomal
degradation of the tumor suppressor p53 (in colorectal cancer), of Thr283-
phosphorylated cyclin D3 (CCND3) (in lymphoma), of Snail1 (in post-myocardial-
infarction cardiac fibroblasts, dampening RhoA signaling and myofibroblast
differentiation), and of unphosphorylated c-MYC (a distinct c-MYC pool from
that controlled by FBXW7, with reported heterotypic K48/K63 chains); CCND2 and
IRF5 are additional candidate substrates accumulating upon FBXL8 knockdown.
Reported localization is predominantly cytoplasmic (loss of FBXL8 causes nuclear
c-MYC accumulation), and in heart FBXL8 is enriched in cardiac fibroblasts. Its
net effect is context-dependent rather than uniformly oncogenic or
tumor-suppressive: oncogenic in colorectal and breast cancer, but
tumor-suppressive in lymphoma and anti-fibrotic after myocardial infarction.
existing_annotations:
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:19159283
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the Array MAPPIT high-throughput screen. The SKP1 interaction is the defining F-box-domain partnership, but the bare protein binding term is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the functionally meaningful FBXL8-SKP1 interaction (the basis of SCF assembly), but bare protein binding is uninformative per curation guidelines; the SCF/SCF-degradation annotations capture this relationship.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:25416956
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a proteome-scale interactome map. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the FBXL8-SKP1 interaction underlying SCF assembly, but bare protein binding is uninformative.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:26496610
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a quantitative-interactome study. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:27705803
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the Polycomb complexome AP-MS study. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the FBXL8-SKP1 interaction, consistent with SCF assembly rather than a Polycomb-specific function; bare protein binding is uninformative.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:32296183
qualifier: enables
review:
summary: IntAct binary-interactome interactions captured here include ALAS1 (P13196), PICK1 (Q9NRD5) and SKP1 (P63208). SKP1 is the canonical F-box partner; ALAS1/PICK1 are candidate substrates/partners but not experimentally validated as FBXL8 substrates. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records real binary interactions (including the SCF-defining SKP1 partner and candidate substrates ALAS1/PICK1), but bare protein binding is uninformative and no substrate relationship is experimentally established.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P13196: ALAS1; NbExp=3; IntAct=EBI-2321097, EBI-3905054;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:33961781
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by the BioPlex dual proteome-scale interactome. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:40205054
qualifier: enables
review:
summary: IntAct interaction with SKP1 (WITH/FROM UniProtKB:P63208) captured by a multimodal cell-map interactome study. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the FBXL8-SKP1 interaction, but bare protein binding is uninformative.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: 'Q96CD0; P63208: SKP1; NbExp=18; IntAct=EBI-2321097, EBI-307486;'
- term:
id: GO:0031146
label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
evidence_type: NAS
original_reference_id: PMID:33234069
qualifier: involved_in
review:
summary: ComplexPortal/NAS assignment that FBXL8, as an SCF substrate receptor, participates in SCF-dependent proteasomal degradation. This is the core biological process for an F-box protein, and FBXL8-specific degradative substrates are now reported in the primary literature (p53 in colorectal cancer, Thr283-phospho-cyclin D3 in lymphoma, Snail1 in cardiac fibroblasts, and unphosphorylated c-MYC).
action: ACCEPT
reason: Consistent with FBXL8 being a substrate-recognition subunit of an SCF E3 ligase (documented SKP1/CUL1 interaction); SCF-dependent degradation is the canonical core process for F-box proteins, and multiple FBXL8 substrates whose turnover requires the F-box are now experimentally documented.
additional_reference_ids:
- file:human/FBXL8/FBXL8-deep-research-falcon.md
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- reference_id: file:human/FBXL8/FBXL8-deep-research-falcon.md
supporting_text: "Across multiple primary studies, FBXL8 functions as an **SCF E3 ligase adaptor** that promotes **substrate ubiquitination**, frequently leading to **proteasome-dependent degradation** of specific targets"
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8952618
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation, propagated across the generic CRL1/neddylation reaction set. The cytosol is a plausible compartment for an SCF substrate receptor.
action: KEEP_AS_NON_CORE
reason: Plausible localization for a cytosolic SCF component, but derived from generic CRL pathway membership (one of many identical Reactome reactions) rather than FBXL8-specific evidence.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8952620
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic CRL1 neddylation reaction set.
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8955241
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic CRL (CAND1) reaction set.
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8955289
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic CRL (COMMD/CAND1) reaction set.
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8956040
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic CRL deneddylation (COP9) reaction set.
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8956200
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic CRL1 (DCUN1D3) reaction set.
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983140
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (transfer of Ub from E2 to substrate).
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983147
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (release of E3 from substrate).
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983156
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (polyubiquitination of substrate).
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983157
qualifier: located_in
review:
summary: Reactome pathway-level cytosol annotation from the generic ubiquitination reaction set (interaction of E3 with substrate and E2-Ub).
action: KEEP_AS_NON_CORE
reason: Plausible but redundant generic-pathway localization; not FBXL8-specific.
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
references:
- id: PMID:19159283
title: 'Array MAPPIT: high-throughput interactome analysis in mammalian cells.'
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: High-throughput MAPPIT interactome; FBXL8 GOA IPI WITH/FROM is SKP1 (P63208), consistent with SCF assembly.
- id: PMID:25416956
title: A proteome-scale map of the human interactome network.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: High-throughput interactome; FBXL8 IPI WITH/FROM is SKP1 (P63208).
- id: PMID:26496610
title: A human interactome in three quantitative dimensions organized by stoichiometries
and abundances.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: Quantitative interactome; FBXL8 IPI WITH/FROM is SKP1 (P63208).
- id: PMID:27705803
title: A High-Density Map for Navigating the Human Polycomb Complexome.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: AP-MS complexome map; FBXL8 IPI WITH/FROM is SKP1 (P63208), reflecting SCF assembly rather than a Polycomb-specific function.
- id: PMID:32296183
title: A reference map of the human binary protein interactome.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: Binary interactome reference map; FBXL8 IPI partners include SKP1 (P63208), ALAS1 (P13196) and PICK1 (Q9NRD5). The latter two are candidate substrates/partners but not experimentally validated as FBXL8 substrates.
- id: PMID:33234069
title: 'The FBXL family of F-box proteins: variations on a theme.'
findings:
- statement: FBXL-family F-box proteins serve as substrate-recognition subunits of SCF E3 ubiquitin ligases, recruiting SKP1/CUL1 via the F-box for substrate ubiquitination and proteasomal degradation.
reference_section_type: LITERATURE_REVIEW
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: Family-level review (full text available) supporting the general FBXL SCF substrate-receptor model; no FBXL8-specific functional data found.
- id: PMID:33961781
title: Dual proteome-scale networks reveal cell-specific remodeling of the human
interactome.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: BioPlex interactome; FBXL8 IPI WITH/FROM is SKP1 (P63208).
- id: PMID:40205054
title: Multimodal cell maps as a foundation for structural and functional genomics.
findings: []
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: Multimodal cell-map interactome; FBXL8 IPI WITH/FROM is SKP1 (P63208).
- id: file:human/FBXL8/FBXL8-deep-research-falcon.md
title: Falcon deep research report for human FBXL8
findings:
- statement: FBXL8 is the substrate-recognition adaptor of an SCF E3 ubiquitin ligase whose net biological effect is strongly context-dependent rather than uniformly oncogenic or tumor-suppressive.
supporting_text: "FBXL8 is an SCF-type E3 ubiquitin ligase substrate receptor (F-box + LRR protein) that determines substrate specificity and promotes ubiquitination of distinct targets in a context-dependent manner, influencing proteasomal degradation or other ubiquitin-mediated outcomes"
- statement: SCF-FBXL8 binds p53, increases its ubiquitination and accelerates its turnover in colorectal cancer; both the F-box and the C-terminal region are required.
supporting_text: "FBXL8 physically associates with p53 (co-immunoprecipitation), increases p53 ubiquitination, and accelerates p53 turnover in cycloheximide chase experiments; **both the F-box and LRR regions are required** for this effect, because ΔFbox and ΔLRR constructs fail to influence p53 stability like full-length FBXL8"
- statement: SCF-FBXL8 recognizes Thr283-phosphorylated cyclin D3 and drives its proteasomal degradation, suppressing lymphoma growth.
supporting_text: "FBXL8 (as SCF-FBXL8) recognizes **Thr-283 phosphorylated cyclin D3**, polyubiquitylates it, and drives proteasomal degradation."
- statement: In post-myocardial-infarction cardiac fibroblasts FBXL8 promotes ubiquitin-proteasome degradation of Snail1, reducing RhoA activation and myofibroblast differentiation.
supporting_text: "In post-myocardial infarction (MI) remodeling, FBXL8 interacts with **Snail1** and promotes its **ubiquitin–proteasome degradation**, with a defined interaction requirement (FBXL8 ΔC3 domain requirement). This down-modulates downstream **RhoA activation** and dampens myofibroblast differentiation"
- statement: FBXL8 recognizes and ubiquitylates unphosphorylated c-MYC, a distinct pool from that controlled by FBXW7, and is reported to be largely cytoplasmic.
supporting_text: "FBXL8 recognizes and ubiquitylates **unphosphorylated c-MYC**, distinct from the canonical phospho-degron recognition by FBXW7. Concurrent loss of FBXL8 and FBXW7 additively elevates c-MYC, consistent with regulation of distinct c-MYC pools."
reference_review:
relevance: HIGH
correctness: UNVERIFIED
review_notes: Falcon (Edison Scientific) deep research synthesis. Reports multiple experimentally-supported FBXL8 substrates (p53, cyclin D3/CCND3 phospho-Thr283, Snail1, unphosphorylated c-MYC, candidate CCND2/IRF5) from primary literature (Yao 2023, Yoshida 2021, Li 2024, Bajpai 2022, Chang 2020) citing DOIs rather than PMIDs; these primary papers are not in the local cache so the citations are not independently PubMed-verified here. Treated as leads that substantially upgrade the previously "poorly characterized" framing into a well-characterized context-dependent SCF substrate receptor.
- id: Reactome:R-HSA-8952618
title: AcM-UBE2M transfers NEDD8 to CRL1 E3 ubiquitin ligase complex
findings: []
- id: Reactome:R-HSA-8952620
title: NEDD8:AcM-UBE2M binds CRL1 E3 ubiquitin ligase complex
findings: []
- id: Reactome:R-HSA-8955241
title: CAND1 binds cytosolic CRL E3 ubiquitin ligases
findings: []
- id: Reactome:R-HSA-8955289
title: COMMDs displace CAND1 from cytosolic CRL E3 ubiquitin ligase complexes
findings: []
- id: Reactome:R-HSA-8956040
title: COP9 signalosome deneddylates cytosolic CRL E3 ubiquitin ligase complexes
findings: []
- id: Reactome:R-HSA-8956200
title: MyrG-DCUN1D3 binds CRL1 E3 ubiquitin ligase complex
findings: []
- id: Reactome:R-HSA-983140
title: Transfer of Ub from E2 to substrate and release of E2
findings: []
- id: Reactome:R-HSA-983147
title: Release of E3 from polyubiquitinated substrate
findings: []
- id: Reactome:R-HSA-983156
title: Polyubiquitination of substrate
findings: []
- id: Reactome:R-HSA-983157
title: Interaction of E3 with substrate and E2-Ub complex
findings: []
core_functions:
- description: Substrate-recognition subunit of an SCF (SKP1-CUL1-F-box) E3 ubiquitin ligase complex; uses its F-box domain to assemble with SKP1/CUL1/RBX1 and its C-terminal substrate-binding region to recruit substrates for ubiquitination and proteasomal degradation. Despite the gene name it lacks canonical leucine-rich repeats, but the C-terminal region is functionally required for substrate turnover.
molecular_function:
id: GO:1990756
label: ubiquitin-like ligase-substrate adaptor activity
locations:
- id: GO:0005829
label: cytosol
supported_by:
- reference_id: file:human/FBXL8/FBXL8-uniprot.txt
supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex.
- reference_id: file:human/FBXL8/FBXL8-deep-research-falcon.md
supporting_text: "FBXL8 physically associates with p53 (co-immunoprecipitation), increases p53 ubiquitination, and accelerates p53 turnover in cycloheximide chase experiments; **both the F-box and LRR regions are required** for this effect, because ΔFbox and ΔLRR constructs fail to influence p53 stability like full-length FBXL8"
directly_involved_in:
- id: GO:0031146
label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
proposed_new_terms: []
suggested_questions:
- question: What determines the strikingly context-dependent outcomes of FBXL8 activity (oncogenic in colorectal/breast cancer versus tumor-suppressive in lymphoma and anti-fibrotic in heart)? Is it substrate availability, post-translational state of substrates, or tissue-specific cofactors?
- question: Are the binary-interactome partners ALAS1 and PICK1 genuine FBXL8 substrates, distinct from the validated p53/CCND3/Snail1/c-MYC set, and under what conditions are they degraded?
- question: What is the basis of FBXL8 substrate recognition given that it lacks canonical leucine-rich repeats yet its C-terminal region is required for substrate engagement?
suggested_experiments:
- description: Perform affinity purification-mass spectrometry of tagged FBXL8 (stabilized with proteasome and neddylation inhibitors) across multiple cell types (colorectal, lymphoma, cardiac fibroblast) to map the tissue-dependent substrate repertoire relative to an F-box-deletion mutant unable to assemble into SCF.
- description: Reconstitute SCF-FBXL8 in vitro and test direct ubiquitination of validated and candidate substrates (p53, phospho-Thr283 cyclin D3, Snail1, unphosphorylated c-MYC, ALAS1, PICK1), mapping ubiquitin-chain linkage type and the C-terminal residues required for substrate binding.