FBXL14

FBXL14 is the substrate-recognition subunit of an SCF-type E3 ubiquitin ligase that targets multiple short-lived regulatory proteins for polyubiquitination and proteasomal degradation, positioning it as a post-translational gatekeeper of epithelial-mesenchymal transition (EMT), stem-cell maintenance, and differentiation (PMID:19955572, PMID:27923907, PMID:29070679). It directly binds and ubiquitinates the EMT transcription factor SNAIL1 in the cytoplasm, doing so independently of GSK-3β phosphorylation, and its downregulation under hypoxia stabilizes SNAIL1 (PMID:19955572, PMID:24157836). Beyond SNAIL1, FBXL14 degrades a broad substrate set including Twist1 (PMID:26257063), c-Myc (PMID:27923907), HES1 via the substrate's C-terminal WRPW motif, thereby driving neuronal differentiation (PMID:29070679), the RNA Polymerase I catalytic subunit RPA194 during Pol I inhibition stress (PMID:36372232), CDCP1 to suppress breast cancer metastasis (PMID:29973690), vimentin (PMID:33801272), and DUSP6 to activate NRF2 signaling in macrophages (PMID:40051291). FBXL14 activity is constrained at several levels: the deubiquitinase USP13 reverses FBXL14-imposed K48-linked chains on c-Myc and Twist1 (PMID:27923907, PMID:36732432), NIPSNAP1 sequesters FBXL14 away from c-Myc (PMID:37340421), LKB1 promotes the SNAIL1–FBXL14 interaction (PMID:29601127), and substrate post-translational modifications—BRD4-read acetylation and CBP-mediated β-hydroxybutyrylation of SNAIL—block FBXL14 recognition (PMID:31311807, PMID:40675949).

1. 2009 High

   Established FBXL14 as a bona fide E3 ligase by showing it directly degrades SNAIL1 through a phosphorylation-independent route, defining a parallel arm of EMT control distinct from GSK-3β-dependent turnover.

   Evidence Co-IP, ubiquitination assay, and shRNA knockdown rescue across cell lines, with hypoxia-dependent downregulation

   PMID:19955572

   Open questions at the time

   • Did not define the F-box/SCF complex composition
   • Mechanism of FBXL14 downregulation under hypoxia not resolved
2. 2013 Medium

   Resolved where FBXL14 acts and broadened its substrate range, localizing FBXL14-mediated SNAIL1 degradation to the cytoplasm (distinct from nuclear FBXL5) and implicating Twist1 as an additional EMT-factor substrate.

   Evidence shRNA screening, subcellular fractionation, Co-IP and ubiquitination assays; Twist1 stability assays distinguishing phosphorylation-independent from β-TRCP-dependent degradation

   PMID:23375009 PMID:24157836

   Open questions at the time

   • FBXL14-Twist1 interaction interface not mapped in these studies
   • Single-lab evidence for compartmentalization
3. 2016 High

   Connected FBXL14 to oncogenic c-Myc turnover and stem-cell fate, showing it degrades c-Myc to promote glioblastoma stem-cell differentiation, with USP13 acting as the opposing deubiquitinase.

   Evidence Overexpression/knockdown, ubiquitination assay, rescue with ubiquitin-insensitive T58A-c-Myc, and tumor growth assays

   PMID:27923907

   Open questions at the time

   • Whether c-Myc recognition requires a specific degron not defined
   • Direct competition kinetics between FBXL14 and USP13 not quantified
4. 2017 High

   Defined the substrate degron for one FBXL14 target, demonstrating that the conserved C-terminal WRPW motif of HES1 is required for binding and degradation, linking SCF-FBXL14 proteolysis to neuronal differentiation.

   Evidence siRNA knockdown, Co-IP, ubiquitination assay, HES1 half-life measurement, WRPW motif mutagenesis, and neuronal differentiation assays in mES and F9 cells

   PMID:29070679

   Open questions at the time

   • Whether other substrates use analogous motifs unknown
   • Structural basis of WRPW-FBXL14 recognition not solved
5. 2018 Medium

   Extended FBXL14 substrate scope to CDCP1 and identified upstream regulatory inputs, with miR-17/20a controlling FBXL14 levels and LKB1 enhancing SNAIL1-FBXL14 association.

   Evidence Co-IP, ubiquitination and protein stability assays, knockdown/overexpression, subcellular fractionation, and metformin/LKB1 modulation

   PMID:29601127 PMID:29973690

   Open questions at the time

   • How LKB1 mechanistically promotes the SNAIL1-FBXL14 interaction unclear
   • miR-17/20a regulation of FBXL14 is correlative at the level shown
6. 2019 Medium

   Showed that substrate post-translational modification gates FBXL14 access, as BRD4 binding to acetylated SNAIL lysines blocks recognition by FBXL14 (and β-TrCP1), preventing degradation.

   Evidence Co-IP, ubiquitination assay, acetylation-site mutagenesis, and protein stability assays

   PMID:31311807

   Open questions at the time

   • FBXL14's role inferred from competition rather than directly assayed
   • Single-lab evidence
7. 2020 Medium

   Placed a kinase upstream of the FBXL14-opposing deubiquitinase, showing CLK3 phosphorylates USP13 to enhance its c-Myc binding and shield c-Myc from FBXL14, coupling the axis to purine metabolism.

   Evidence In vitro kinase assay, Co-IP, ubiquitination assay, phospho-site mutagenesis, and metabolic profiling in cholangiocarcinoma

   PMID:32453420

   Open questions at the time

   • FBXL14 activity not directly measured, inferred via USP13 antagonism
   • Single-lab pathway model
8. 2021 Medium

   Identified a scaffolding mechanism for substrate delivery, with IGFBP-3 bridging vimentin to FBXL14 to drive vimentin degradation and suppress metastasis.

   Evidence Co-IP, protein stability assays, domain mapping with truncation mutants, and in vitro/in vivo metastasis assays

   PMID:33801272

   Open questions at the time

   • Whether IGFBP-3 is generally required for vimentin recognition unknown
   • Single-lab evidence
9. 2022 High

   Revealed an unanticipated role in ribosome biogenesis stress, showing SCF-FBXL14 ubiquitinates and degrades the Pol I catalytic subunit RPA194 upon Pol I inhibition, with conserved lysines mapped in yeast.

   Evidence RNAi screen, Co-IP, ubiquitination assay, lysine-to-arginine mutagenesis in yeast, and protein stability assays

   PMID:36372232

   Open questions at the time

   • Trigger linking Pol I inhibition to FBXL14 engagement not defined
   • Physiological context beyond drug-induced stress unclear
10. 2023 High

    Detailed reversal and sequestration controls on FBXL14, with USP13 cleaving FBXL14-imposed K48 chains on Twist1 and NIPSNAP1 sequestering FBXL14 to spare c-Myc, each embedded in feedback loops; also implicated FBXL14 in cardiomyocyte hypertrophy.

    Evidence Co-IP, GST-pulldown, K48 linkage-specific ubiquitination, ChIP, migration/invasion and metastasis assays; separately, siRNA knockdown with cell-size and 3H-isoleucine incorporation in cardiomyocytes

    PMID:36732432 PMID:36969608 PMID:37340421

    Open questions at the time

    • NIPSNAP1 sequestration mechanism shown by Co-IP in a single lab
    • Cardiomyocyte phenotype lacks an identified molecular substrate
11. 2025 Medium

    Expanded the modification-based evasion paradigm and extended FBXL14 into metabolic/inflammatory signaling, showing CBP-mediated β-hydroxybutyrylation of SNAIL K152 blocks FBXL14 recognition, and that FBXL14 degrades DUSP6 to activate NRF2 in macrophages.

    Evidence Site-specific mutagenesis, ubiquitination assays, CBP inhibitor experiments, and in vivo metastasis and ApoE-/- atherosclerosis models

    PMID:40051291 PMID:40675949

    Open questions at the time

    • DUSP6 degradation evidence is bioinformatics-guided and single-lab
    • Whether multiple acyl modifications converge on the same SNAIL degron unclear

• The structural basis by which FBXL14's leucine-rich repeats recognize its diverse substrate degrons, and the composition/regulation of the assembled SCF-FBXL14 holoenzyme, remain undefined across the corpus.
• No structural model of FBXL14-substrate complexes
• Unifying degron logic across SNAIL1, Twist1, c-Myc, HES1, RPA194, CDCP1, vimentin, DUSP6 unknown
• In vivo loss-of-function phenotype of FBXL14 not established genetically