Affinage

FBXL18

F-box/LRR-repeat protein 18 · UniProt Q96ME1

Length
718 aa
Mass
78.9 kDa
Annotated
2026-06-09
12 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FBXL18 is the substrate-recognition subunit of an SCF (Skp1-Cul1-Rbx1) E3 ubiquitin ligase that selects distinct targets and imposes different ubiquitin-chain fates, making its net cellular effect substrate- and context-dependent (PMID:25654763, PMID:41390767). As a degradative ligase, SCF^FBXL18 catalyzes K48-type-style polyubiquitination and proteasomal turnover of FBXL7 via Lys109 and an FQ recognition motif, thereby restraining FBXL7-induced apoptosis (PMID:25654763); it also targets phosphorylated LRRK2 in a phosphorylation-dependent manner, with PKC activation enhancing degradation and protecting against LRRK2-driven cell death (PMID:27890708), and degrades XPB following CDK7-dependent phosphorylation at Ser90 (PMID:30762924). Recognition of several substrates is thus gated by prior phosphorylation (PMID:27890708, PMID:30762924). FBXL18 also assembles non-degradative chains: K63-linked ubiquitination of AKT activates AKT signaling to drive proliferation, migration, and radioresistance through downstream effectors including FOXO3a, CCND1, and CCK-8-measured growth (PMID:27926990, PMID:38883375, PMID:41655990), and K63-linked ubiquitination of RPS15A stabilizes it to elevate SMAD3 and promote hepatocellular carcinoma proliferation (PMID:37378633). In innate immunity, FBXL18 promotes K11-linked ubiquitination of BST2 at Lys109/Lys110, stabilizing BST2 to hyperactivate the IκBα/NF-κB axis and IL-6-driven inflammation during rabies virus infection in astrocytes (PMID:41390767). Through these activities FBXL18 modulates apoptosis, cell proliferation, neurodegeneration, and innate immune responses depending on which substrate is engaged.

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2015 High

    Established FBXL18 as an SCF substrate-recognition subunit and defined its first substrate with a precise acceptor site, answering whether FBXL18 directs targeted protein degradation.

    Evidence Co-IP, in vitro ubiquitination with Lys109/FQ-motif mutagenesis, and siRNA loss-of-function apoptosis assays in HeLa cells

    PMID:25654763

    Open questions at the time
    • Chain linkage type on FBXL7 not explicitly resolved
    • Physiological contexts beyond apoptosis regulation not defined
  2. 2016 Medium

    Showed FBXL18 is not solely degradative but can assemble activating K63 chains on AKT, and that it selectively targets phosphorylated LRRK2, establishing phosphorylation-gated substrate choice and dual ubiquitin outcomes.

    Evidence K63-linked ubiquitination assays with FOXO3a/BCL2L11 epistasis in glioma cells; reciprocal Co-IP, phosphatase and PKC treatments, and caspase/cell-death readouts for LRRK2

    PMID:27890708 PMID:27926990

    Open questions at the time
    • E3 ligase that builds the AKT K63 chain not reconstituted in vitro
    • LRRK2 phospho-site and kinase generating it not mapped
    • Findings from single labs
  3. 2019 High

    Demonstrated that a defined kinase-phosphosite event licenses FBXL18 recognition, by showing CDK7-dependent Ser90 phosphorylation of XPB drives SCF^FBXL18-mediated degradation.

    Evidence siRNA screen, Co-IP, ubiquitination assays, XPB Ser90 mutagenesis, and CDK7 inhibition

    PMID:30762924

    Open questions at the time
    • Whether CDK7 directly phosphorylates XPB Ser90 not biochemically confirmed
    • Physiological (non-drug-induced) trigger of this degradation unknown
  4. 2023 Medium

    Extended the non-degradative K63 mode to a ribosomal protein, showing FBXL18 stabilizes RPS15A to elevate SMAD3 and drive proliferation, broadening its output beyond turnover.

    Evidence K63 ubiquitination assays, Co-IP, RPS15A/SMAD3 knockdown rescue, and an FBXL18 transgenic mouse HCC model

    PMID:37378633

    Open questions at the time
    • RPS15A ubiquitin acceptor sites not mapped
    • Mechanism linking RPS15A stability to SMAD3 induction unresolved
    • Single lab
  5. 2024 Medium

    Reinforced FBXL18-driven AKT activation as a recurrent oncogenic mechanism by replicating K63-AKT ubiquitination in a second cancer context.

    Evidence Co-IP, K63 ubiquitination assays, and MK-2206 AKT-inhibitor rescue in ovarian cancer cells

    PMID:38883375

    Open questions at the time
    • AKT acceptor lysines not identified
    • Direct vs. indirect role of FBXL18 in the K63 reaction not separated
  6. 2025 High

    Defined a chain-type-specific stabilizing function in immunity, showing FBXL18 builds K11 chains on BST2 Lys109/Lys110 to amplify NF-κB/IL-6 inflammation during viral infection.

    Evidence E3 ligase screen, Co-IP, K11 ubiquitination assays with BST2 Lys109/110 mutagenesis, IκBα/NF-κB reporter assays, and an in vivo mouse RABV model

    PMID:41390767

    Open questions at the time
    • How linkage choice (K11 vs. K33) is determined at the same lysines unknown
    • Direct biochemical reconstitution of FBXL18 K11 specificity not shown
  7. 2025 Medium

    Added new degradative substrates and downstream pathways, linking FBXL18 to JNK/c-JUN signaling via DUSP16 turnover, to AKT/CCND1-mediated radioresistance, and to FBXL7 suppression in esophageal cancer.

    Evidence Co-IP and ubiquitination assays with DUSP16 rescue (endometrial carcinoma); Co-IP/K63 ubiquitination and CCK-8 radiosensitivity assays (ESCC); overexpression/knockdown with xenograft and irradiation survival assays for FBXL7 regulation

    PMID:39971770 PMID:40382593 PMID:41655990

    Open questions at the time
    • DUSP16 ubiquitin acceptor sites and chain type not defined
    • ESCC FBXL7 regulation inferred from protein levels without a direct ubiquitination assay (Low confidence)
    • Substrate-selection rules across these contexts not unified

Open questions

Synthesis pass · forward-looking unresolved questions
  • How FBXL18 selects between degradative (K48) and stabilizing (K63/K11) ubiquitin-chain outcomes on its various substrates remains the central unresolved mechanistic question.
  • No structural model of FBXL18-substrate recognition
  • Determinants of chain linkage selection unknown
  • Whether different E2 partners govern chain type not addressed

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 9 GO:0098772 molecular function regulator activity 5 GO:0016874 ligase activity 3
Pathway
R-HSA-162582 Signal Transduction 4 R-HSA-392499 Metabolism of proteins 3 R-HSA-5357801 Programmed Cell Death 2 R-HSA-168256 Immune System 1
Partners
AKTBST2DUSP16FBXL7LRRK2RPS15ASKP1XPB
Complex memberships
SCF (Skp1-Cul1-Rbx1) E3 ubiquitin ligase

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2015 FBXL18 functions as a subunit of the SCF (Skp1-Cul1-F-box) E3 ubiquitin ligase complex that targets FBXL7 for polyubiquitylation and proteasomal degradation. Lys109 within FBXL7 is the essential ubiquitin acceptor site, and an FQ motif within FBXL7 serves as the molecular recognition site for FBXL18 interaction. Depletion of FBXL18 or mutation of Fbxl7 Lys109/FQ motif accentuates Fbxl7-induced apoptosis, while ectopic FBXL18 expression limits this apoptosis. Co-immunoprecipitation, in vitro ubiquitination assay, site-directed mutagenesis (Lys109 and FQ motif), siRNA depletion, apoptosis assays in HeLa cells Cell death & disease High 25654763
2016 FBXL18 promotes K63-linked ubiquitination of Akt, which is required for Akt activation. Depletion of FBXL18 in glioma cells inhibits Akt activity and phosphorylation of FOXO3a, leading to upregulation of BCL2L11 and increased apoptosis. Co-immunoprecipitation, K63-linked ubiquitination assay, siRNA knockdown, western blotting for p-Akt and p-FOXO3a, cell proliferation and apoptosis assays FEBS letters Medium 27926990
2016 Fbxl18 is a component of an SCF (Skp1-Cullin1-F-box) ubiquitin ligase complex that physically associates with LRRK2 and selectively targets phosphorylated LRRK2 for ubiquitination and proteasomal degradation. Dephosphorylation of LRRK2 blocked Fbxl18 association. Protein kinase C activation enhanced LRRK2 degradation by Fbxl18. Fbxl18 prevented caspase activation and cell death caused by LRRK2 and PD-linked mutant LRRK2. Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, phosphatase treatment (dephosphorylation blocking association), PKC activation, caspase/cell death assays Neurobiology of disease Medium 27890708
2019 SCFFBXL18 E3 ligase complex (Skp1, Cul1, FBXL18, Rbx1) mediates spironolactone-induced polyubiquitination and proteasomal degradation of XPB. CDK7 kinase activity is required for this process, and Ser90 of XPB is essential for chemical-induced destabilization, suggesting CDK7 phosphorylates XPB at Ser90 to promote FBXL18-mediated recognition and degradation. siRNA library screening, siRNA knockdown of FBXL18, co-immunoprecipitation, ubiquitination assay, site-directed mutagenesis of XPB Ser90, CDK7 kinase inhibition Genes to cells : devoted to molecular & cellular mechanisms High 30762924
2023 FBXL18 promotes K63-linked ubiquitination of ribosomal protein RPS15A, enhancing its stability (not degradation). This increased RPS15A stability leads to elevated SMAD3 levels and SMAD3 nuclear translocation, promoting HCC cell proliferation. Knockdown of RPS15A or SMAD3 suppressed FBXL18-mediated proliferation. K63-linked ubiquitination assay, co-immunoprecipitation, western blotting, siRNA knockdown of RPS15A/SMAD3, FBXL18 transgenic mouse model, nuclear fractionation Hepatology communications Medium 37378633
2024 FBXL18 physically interacts with Akt in ovarian cancer cells and promotes K63-linked ubiquitination of Akt to activate AKT signaling, increasing phospho-AKT (S473) and driving cell proliferation and migration. AKT inhibitor MK-2206 reversed FBXL18 overexpression-induced phenotypes. Co-immunoprecipitation, K63-linked ubiquitination assay, siRNA knockdown, overexpression, AKT inhibitor (MK-2206) rescue experiment, CCK-8/colony formation/migration assays American journal of translational research Medium 38883375
2025 FBXL18 promotes K11-type ubiquitination of BST2 on Lys109 and Lys110, which stabilizes BST2 (in contrast to K33-type ubiquitination at the same sites by an unknown E3 ligase that promotes degradation). FBXL18-mediated BST2 stabilization leads to hyperphosphorylation of IκBα and excessive NF-κB activation, resulting in enhanced IL-6 production and inflammation in RABV-infected astrocytes. FBXL18 knockdown inhibits IL-6 production and RABV replication in astrocytes. E3 ligase screen, co-immunoprecipitation, K11-linked ubiquitination assay with site-directed mutagenesis (Lys109/110 of BST2), IκBα phosphorylation assay, NF-κB reporter, siRNA knockdown, in vivo mouse RABV model Nature communications High 41390767
2025 FBXL18 physically interacts with DUSP16 (a dual-specificity phosphatase), promoting its ubiquitination and proteasomal degradation, thereby activating the JNK/c-JUN signaling pathway to drive endometrial carcinoma cell proliferation, migration, and invasion. Upregulation of DUSP16 reversed FBXL18 overexpression-induced JNK activation and enhanced cell capacities. Co-immunoprecipitation, ubiquitination assay, western blotting, siRNA/overexpression, JNK pathway analysis, DUSP16 rescue experiment Cancer cell international Medium 40382593
2025 FBXL18 interacts with AKT and promotes K63-linked polyubiquitination of AKT, activating the AKT/CCND1 signaling pathway and maintaining radioresistance in ESCC cells. Silencing FBXL18 reduced radioresistance and decreased p-AKT and CCND1 expression. Co-immunoprecipitation, K63-linked ubiquitination assay by western blotting, RNAi knockdown, CCK-8 radiosensitivity assay BMB reports Medium 41655990
2025 FBXL18 overexpression in ESCC cells suppresses the expression of FBXL7, and this FBXL7 downregulation mediates FBXL18's pro-tumorigenic and radioresistance-reducing effects in ESCC cells. Lentiviral overexpression/knockdown, western blotting for FBXL7 protein, CCK-8 viability assay, colony formation, in vivo xenograft, X-ray irradiation survival assay Strahlentherapie und Onkologie Low 39971770

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 F-box protein Fbxl18 mediates polyubiquitylation and proteasomal degradation of the pro-apoptotic SCF subunit Fbxl7. Cell death & disease 39 25654763
2020 Circular RNA circRNA_103809 Accelerates Bladder Cancer Progression and Enhances Chemo-Resistance by Activation of miR-516a-5p/FBXL18 Axis. Cancer management and research 31 32922071
2016 The F-box protein FBXL18 promotes glioma progression by promoting K63-linked ubiquitination of Akt. FEBS letters 30 27926990
2019 Spironolactone-induced XPB degradation depends on CDK7 kinase and SCFFBXL18 E3 ligase. Genes to cells : devoted to molecular & cellular mechanisms 21 30762924
2016 Fbxl18 targets LRRK2 for proteasomal degradation and attenuates cell toxicity. Neurobiology of disease 14 27890708
2023 Elevated FBXL18 promotes RPS15A ubiquitination and SMAD3 activation to drive HCC. Hepatology communications 12 37378633
2024 FBXL18 is required for ovarian cancer cell proliferation and migration through activating AKT signaling. American journal of translational research 2 38883375
2025 The E3 ubiquitin ligase FBXL18 stabilizes BST2 to promote inflammation in RABV-infected astrocytes. Nature communications 1 41390767
2026 FBXL18 activating AKT/CCND1 signaling pathway mediates radioresistance in esophageal squamous cell carcinoma. BMB reports 0 41655990
2025 FBXL18 increases cell proliferation and reduces cell radiosensitivity in esophageal squamous cell carcinoma. Strahlentherapie und Onkologie : Organ der Deutschen Rontgengesellschaft ... [et al] 0 39971770
2025 FBXL18 promotes endometrial carcinoma progression via destabilizing DUSP16 and thus activating JNK signaling pathway. Cancer cell international 0 40382593
2025 CircRNA_103809/miR-516a/FBXL18 contributes to stemness and gemcitabine resistance of bladder cancer cells. Archives of medical science : AMS 0 41676423

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