FBXL8

UniProt ID: Q96CD0
Organism: Homo sapiens
Review Status: COMPLETE
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Gene 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 Review

GO Term Evidence Action Reason
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;
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;
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;
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;
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
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.
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.
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.
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.
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.

Core Functions

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.

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
    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

References

Array MAPPIT: high-throughput interactome analysis in mammalian cells.
A proteome-scale map of the human interactome network.
A human interactome in three quantitative dimensions organized by stoichiometries and abundances.
A High-Density Map for Navigating the Human Polycomb Complexome.
A reference map of the human binary protein interactome.
The FBXL family of F-box proteins: variations on a theme.
  • 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.
Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
Multimodal cell maps as a foundation for structural and functional genomics.
file:human/FBXL8/FBXL8-deep-research-falcon.md
Falcon deep research report for human FBXL8
  • 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.
    "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"
  • 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.
    "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"
  • SCF-FBXL8 recognizes Thr283-phosphorylated cyclin D3 and drives its proteasomal degradation, suppressing lymphoma growth.
    "FBXL8 (as SCF-FBXL8) recognizes **Thr-283 phosphorylated cyclin D3**, polyubiquitylates it, and drives proteasomal degradation."
  • In post-myocardial-infarction cardiac fibroblasts FBXL8 promotes ubiquitin-proteasome degradation of Snail1, reducing RhoA activation and myofibroblast differentiation.
    "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"
  • FBXL8 recognizes and ubiquitylates unphosphorylated c-MYC, a distinct pool from that controlled by FBXW7, and is reported to be largely cytoplasmic.
    "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."
Reactome:R-HSA-8952618
AcM-UBE2M transfers NEDD8 to CRL1 E3 ubiquitin ligase complex
Reactome:R-HSA-8952620
NEDD8:AcM-UBE2M binds CRL1 E3 ubiquitin ligase complex
Reactome:R-HSA-8955241
CAND1 binds cytosolic CRL E3 ubiquitin ligases
Reactome:R-HSA-8955289
COMMDs displace CAND1 from cytosolic CRL E3 ubiquitin ligase complexes
Reactome:R-HSA-8956040
COP9 signalosome deneddylates cytosolic CRL E3 ubiquitin ligase complexes
Reactome:R-HSA-8956200
MyrG-DCUN1D3 binds CRL1 E3 ubiquitin ligase complex
Reactome:R-HSA-983140
Transfer of Ub from E2 to substrate and release of E2
Reactome:R-HSA-983147
Release of E3 from polyubiquitinated substrate
Reactome:R-HSA-983156
Polyubiquitination of substrate
Reactome:R-HSA-983157
Interaction of E3 with substrate and E2-Ub complex

Suggested Questions for Experts

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?

Suggested Experiments

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.

Deep Research

Falcon

(FBXL8-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 30 citations 2 artifacts 2026-06-13T05:59:09.648581

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.

Research Report: Human FBXL8 (UniProt Q96CD0) – Functional Annotation, Mechanisms, and Translational Relevance

0) Target verification (critical disambiguation)

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).

1) Key concepts and definitions (current understanding)

1.1 The SCF ubiquitin-ligase concept

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).

1.2 FBXL-family structural logic (F-box + LRR)

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).

2) Molecular function of FBXL8: what it does biochemically

2.1 Core molecular role

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).

2.2 Experimentally supported substrate/target set (with evidence strength)

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).

3) Subcellular and tissue localization

3.1 Cell-level localization

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.)

3.2 Tissue and cell-type enrichment (cardiac system)

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).

4) Pathways and biological processes linked to FBXL8

FBXL8 appears to sit at the intersection of ubiquitin-mediated proteostasis and several high-impact pathways:

  1. p53 tumor suppressor pathway (CRC): FBXL8 ubiquitinates and destabilizes p53, promoting proliferation, migration/invasion, and stem-like markers; p53 downregulation reverses major anti-tumor effects of FBXL8 loss, supporting pathway dependence (yao2023scf‐fbxl8contributesto pages 10-14).
  2. EMT/fibrosis axis via Snail1 → RhoA signaling (post-MI heart): FBXL8 promotes Snail1 degradation, reducing RhoA activation and myofibroblast behaviors (li2024fbxl8inhibitspostmyocardial pages 1-2, li2024fbxl8inhibitspostmyocardial pages 2-4, li2024fbxl8inhibitspostmyocardial media 22acda4a).
  3. Cell-cycle control via Cyclin D3 → RB phosphorylation and proliferation (lymphoma): FBXL8-mediated degradation of phospho-cyclin D3 reduces phospho-RB and proliferation markers (Ki67) in tumor models (yoshida2021fbxl8suppresseslymphoma pages 9-11).
  4. MYC proteostasis and G1/S progression: FBXL8 controls an underphosphorylated c-MYC pool with distinct ubiquitin-linkage features (K48/K63 heterotypic chains) and additive interplay with FBXW7 (bajpai2022ubiquitylationofunphosphorylated pages 95-99).
  5. Tumor microenvironment/inflammatory signaling (breast cancer): FBXL8 knockdown reduced multiple cytokines/chemokines and induced apoptosis while suppressing migration/invasion, consistent with a role in shaping a pro-tumor cytokine milieu (chang2020humanfbxl8is pages 12-15, chang2020globalrnaseqidentified pages 7-11).

5) Recent developments (prioritizing 2023–2024)

5.1 2023: FBXL8 drives CRC liver metastasis and stem-like traits via p53 degradation

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).

5.2 2024: FBXL8 attenuates post-MI cardiac fibrosis by degrading Snail1

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).

6) Current applications and real-world implementations

6.1 Therapeutic targeting logic: adaptor proteins as drug targets

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).

6.2 Gene therapy direction in fibrosis/heart disease

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.

6.3 Oncology: biomarker and pathway-stratification possibilities

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.

7) Expert opinions and authoritative synthesis

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.

8) Relevant statistics and quantitative data (recent and foundational)

Key quantitative findings extracted from the available full text include:

  • Breast cancer cell models (preprint): FBXL8 reported 23-fold (MCF7) and 15-fold (MDA-MB231) higher vs MCF10A; knockdown up to 95% reduced viability by ~52.5% at 48 h, reduced proliferation 2–3-fold, increased early apoptosis to ~20% and ~24%, slowed migration (14% in MCF7; 40% in MDA-MB231 over 30 h), and reduced invasion 4–8-fold (chang2020globalrnaseqidentified pages 7-11).
  • Breast cancer patient-scale analysis (journal article): stage-associated increases in FBXL8 reported with p<0.01 to p<0.001 in cohorts including n=134 (Taiwan BioBank) and n=1215 (TCGA), and an ex vivo analysis n=1349 matched tissues is described (chang2020humanfbxl8is pages 12-15, chang2020humanfbxl8is pages 1-3).
  • CRC clinical cohort: 100 CRC patients (36 non-metastatic; 64 with liver metastasis) (yao2023scf‐fbxl8contributesto pages 1-3).
  • CRC in vivo models: xenograft and metastasis experiments used 12 nude mice total, split 6/6 per condition; liver metastasis and tumor metrics reported with p<0.001 (yao2023scf‐fbxl8contributesto pages 10-14).
  • Post-MI cardiac remodeling: heart time-course measures n=5; TGFβ fibroblast quantitation n=3; FBXL8 knockdown increased migration/proliferation by 1.4-fold/1.3-fold and increased RhoA-GTP by 2.9-fold (li2024fbxl8inhibitspostmyocardial pages 2-4). Supporting figure panels were retrieved (li2024fbxl8inhibitspostmyocardial media 22acda4a).
  • Lymphoma functional models: low-density growth assays used 1×10^4 CA46 cells (n=4; p=0.02 and p<0.01). Xenograft experiments injected 2×10^6 CA46 cells into SCID mice (n=10), with significant tumor volume and weight reductions reported (p-values including 0.02, 0.03, and <0.01) (yoshida2021fbxl8suppresseslymphoma pages 9-11).

9) Synthesis: primary functional annotation and context dependence

9.1 Primary functional role (most supported)

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).

9.2 Why context dependence is central for FBXL8

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.

Evidence map (summary table)

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.

Key figures retrieved (visual evidence)

  • Post-MI downregulation of FBXL8 in heart and reduction with TGFβ in cardiac fibroblasts; and anti-fibrotic effects of AAV9-FBXL8 plus Snail1 ubiquitination/stability evidence (li2024fbxl8inhibitspostmyocardial media 22acda4a).

References (URLs and publication dates where available)

  • Mason B, Laman H. Open Biology. 2020-11. “The FBXL family of F-box proteins: variations on a theme.” https://doi.org/10.1098/rsob.200319 (mason2020thefbxlfamily pages 1-2, mason2020thefbxlfamily pages 5-6)
  • Chang S-C et al. Cancers (Basel). 2020-08. “Human FBXL8 Is a Novel E3 Ligase…” https://doi.org/10.3390/cancers12082210 (chang2020humanfbxl8is pages 1-3, chang2020humanfbxl8is pages 12-15)
  • Bajpai S et al. Cancer Biology & Therapy. 2022-04. “Ubiquitylation of unphosphorylated c-myc…” https://doi.org/10.1080/15384047.2022.2061279 (bajpai2022ubiquitylationofunphosphorylated pages 95-99, bajpai2022ubiquitylationofunphosphorylated pages 88-95)
  • Yao J et al. Clinical and Translational Medicine. 2023-02. “SCF-FBXL8 contributes to liver metastasis…” https://doi.org/10.1002/ctm2.1208 (yao2023scf‐fbxl8contributesto pages 1-3, yao2023scf‐fbxl8contributesto pages 7-10, yao2023scf‐fbxl8contributesto pages 10-14)
  • Vriend J. Cancers (Editorial). 2023-07-01. “Role of Ubiquitin Ligases and Conjugases in Targeted Cancer Therapy.” https://doi.org/10.3390/cancers15133460 (vriend2023roleofubiquitin pages 1-2)
  • Li Y et al. Cell Death & Disease. 2024-04. “FBXL8 inhibits post-MI cardiac fibrosis…” https://doi.org/10.1038/s41419-024-06646-1 (li2024fbxl8inhibitspostmyocardial pages 1-2, li2024fbxl8inhibitspostmyocardial pages 2-4, li2024fbxl8inhibitspostmyocardial media 22acda4a)
  • Yoshida A et al. Oncogene. 2021-10. “Fbxl8 suppresses lymphoma growth…” https://doi.org/10.1038/s41388-020-01532-4 (yoshida2021fbxl8suppresseslymphoma pages 9-11)

References

  1. (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.

  2. (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.

  3. (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.

  4. (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.

  5. (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.

  6. (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.

  7. (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.

  8. (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.

  9. (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.

  10. (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.

  11. (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.

  12. (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.

  13. (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.

  14. (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.

  15. (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.

  16. (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.

Artifacts

Citations

  1. mason2020thefbxlfamily pages 1-2
  2. mason2020thefbxlfamily pages 5-6
  3. bajpai2022ubiquitylationofunphosphorylated pages 95-99
  4. vriend2023roleofubiquitin pages 1-2
  5. chang2020globalrnaseqidentified pages 7-11
  6. bajpai2022ubiquitylationofunphosphorylated pages 88-95
  7. chang2020globalrnaseqidentified pages 20-23
  8. https://doi.org/10.1002/ctm2.1208
  9. https://doi.org/10.1038/s41419-024-06646-1
  10. https://doi.org/10.3390/cancers15133460
  11. https://doi.org/10.1098/rsob.200319;
  12. https://doi.org/10.1101/2020.06.09.20127068;
  13. https://doi.org/10.1002/ctm2.1208;
  14. https://doi.org/10.1080/15384047.2022.2061279;
  15. https://doi.org/10.1038/s41388-020-01532-4;
  16. https://doi.org/10.1038/s41419-024-06646-1;
  17. https://doi.org/10.3390/cancers12082210
  18. https://doi.org/10.3390/cancers12082210;
  19. https://doi.org/10.1038/s41388-020-01532-4
  20. https://doi.org/10.3390/cancers15133460;
  21. https://doi.org/10.1098/rsob.200319
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  30. https://doi.org/10.3390/cancers15133460,

📚 Additional Documentation

Pn Notes

(FBXL8-pn-notes.md)

FBXL8 PN Consistency Notes

  • Generated: 2026-06-18
  • Project: PROTEOSTASIS
  • Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
  • UniProt: Q96CD0
  • AIGR review status: COMPLETE
  • Review batch: proteostasis-batch-2026-06-13
  • Batch change status: added

Source Files Checked

Deep Research Files

AIGR Review Snapshot

  • 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/core annotation action counts: ACCEPT: 1; KEEP_AS_NON_CORE: 17

PN Consistency Summary

  • Consistency: Mostly consistent, with one structural gap. Review, PN annotation, and node mapping agree FBXL8 is an SCF substrate receptor. Non-canonical F-box: UniProt notes FBXL8 does NOT contain canonical leucine-rich repeats despite the "LRR" name — yet the PN places it under the ...|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.
  • PN story / NEW pressure: PN asserts the generic adaptor MF. FBXL8 GOA has NO MF beyond 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.
  • Evidence alignment: PN cites only "15340381/rev"; review uses SKP1 interactome PMIDs + PMID:33234069 + falcon leads. No PMID overlap with placeholder.
  • Verdict: MAPPING CONSISTENT but YAML gap. Recommended edits: [YAML] add 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.

Full Consistency Review

  • UniProt: Q96CD0 · batch: proteostasis-batch-2026-06-13 · review status: COMPLETE
  • PN placement: 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.
  • Consistency: Mostly consistent, with one structural gap. Review, PN annotation, and node mapping agree FBXL8 is an SCF substrate receptor. Non-canonical F-box: UniProt notes FBXL8 does NOT contain canonical leucine-rich repeats despite the "LRR" name — yet the PN places it under the ...|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.
  • PN story / NEW pressure: PN asserts the generic adaptor MF. FBXL8 GOA has NO MF beyond 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.
  • Mapping strategy: Gene does not change the group GO:1990756 (defensible on F-box + SKP1 grounds). FLAGS: (1) non-canonical F-box (no true LRRs) — PN |LRR subtype label is a misnomer here; (2) no PMID-validated substrate in existing_annotations — adaptor MF is inferred-only. Scope/status otherwise correct.
  • Evidence alignment: PN cites only "15340381/rev"; review uses SKP1 interactome PMIDs + PMID:33234069 + falcon leads. No PMID overlap with placeholder.
  • Verdict: MAPPING CONSISTENT but YAML gap. Recommended edits: [YAML] add 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.

PN Dossier Context

  • review_batch: proteostasis-batch-2026-06-13
  • review_yaml: genes/human/FBXL8/FBXL8-ai-review.yaml
  • PN workbook rows: 1

PN row 1: Ubiquitin Proteasome System | E3 ubiquitin and UBL ligases | Cul1 substrate receptor | F-box | LRR

  • UniProt: Q96CD0
  • In branches: UPS
  • Signature domains: IPR001810
  • Auxiliary domains: IPR032675
  • PN references (titles):
    • 15340381 / rev
  • PN-node mapping records (path + ancestors):
    • [subtype] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box|LRR
      status=no_mapping scope= GO=[]
      rationale: Reviewed as a narrower substrate-receptor, adaptor, domain, or family subdivision already covered by the curated parent adaptor/receptor mapping. No additional direct GO mapping is needed at this node.
    • [type] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box
      status=no_mapping scope= GO=[]
      rationale: Reviewed as a narrower substrate-receptor, adaptor, domain, or family subdivision already covered by the curated parent adaptor/receptor mapping. No additional direct GO mapping is needed at this node.
    • [group] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor
      status=mapped scope=ok_for_propagation_to_go GO=[GO:1990756 ubiquitin-like ligase-substrate adaptor activity]
      rationale: This PN group captures substrate receptors/adaptors for cullin/UBL ligase systems. The shared GO molecular-function target is ubiquitin-like ligase-substrate adaptor activity.
    • [class] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases
      status=context_only scope=too_broad_to_propagate GO=[GO:0061630 ubiquitin protein ligase activity]
      rationale: This class is a genuine E3-ligase context, but its descendants include catalytic ligases, cullin scaffolds, substrate receptors, adaptors, cofactors, regulators, and UBL modifier systems. A class-level propagation would over-annotate.
    • [branch] Ubiquitin Proteasome System
      status=no_mapping scope= GO=[]
      rationale: Reviewed as the top-level UPS branch. It is a project taxonomy umbrella rather than a direct GO assertion; UPS propagation must come from manually curated child nodes.

Projected GO annotations (1)

  • GO:1990756 ubiquitin-like ligase-substrate adaptor activity | scope=ok_for_propagation_to_go | goa_status=new_to_goa | from=Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor

Note

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.

📄 View Raw YAML

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.