FBXL15 (F-box/LRR-repeat protein 15; F-box only protein 37, FBXO37) is a substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex. Its F-box motif binds SKP1 to dock it onto the CUL1-RBX1 catalytic scaffold, while its leucine-rich repeat domain provides substrate selectivity. SCF(FBXL15) targets the HECT-type E3 ubiquitin ligase SMURF1 for ubiquitination and proteasomal degradation; by lowering SMURF1 levels it acts as a positive regulator of bone morphogenetic protein (BMP) signaling. FBXL15 recognizes the large subdomain within the N-lobe of the SMURF1 HECT domain and promotes SMURF1 ubiquitination on lysines in the WW-HECT linker (Lys357 primary, Lys355 secondary), and it can also ubiquitinate the related HECT ligases SMURF2 and WWP2. Because SMURF1 is an inhibitor of BMP signaling, SCF(FBXL15)-driven SMURF1 turnover relieves this inhibition and enhances BMP/SMAD transcriptional output, including induction of canonical BMP target genes such as ID1 and SMAD6. Through this control of SMURF1 stability, FBXL15 contributes to dorsal/ventral pattern formation during embryonic development and to bone mass maintenance. It acts in the cytoplasm.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: Electronic transfer of cytoplasmic localization from the UniProt subcellular location; supported by IDA evidence.
Reason: Correct localization, directly supported (IDA) in the SMURF1/BMP study.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005515
protein binding
|
IPI
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
KEEP AS NON CORE |
Summary: IntAct interactions with the HECT ligases SMURF1/SMURF2/WWP2 (the FBXL15 substrates) from the BMP-signaling study. Bare protein binding is uninformative.
Reason: Records the functionally important FBXL15-SMURF1/SMURF2/WWP2 substrate interactions, but bare protein binding is uninformative; the relationship is captured by the catabolic-process annotations.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
INTERACTION WITH SMURF1; SMURF2 AND WWP2
|
|
GO:0030282
bone mineralization
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: Ortholog-based electronic assignment of a bone-mineralization role, consistent with the rat study showing FBXL15 knockdown reduces bone mass and mineral density.
Reason: Supported downstream physiological role (via SMURF1/BMP control) but a generic developmental/physiological process distinct from the core substrate-receptor activity.
Supporting Evidence:
PMID:21572392
Injection of FBXL15 siRNAs into rat bone tissues leads to a significant loss of bone mass and decrease in bone mineral density
|
|
GO:0016567
protein ubiquitination
|
IEA
GO_REF:0000041 |
ACCEPT |
Summary: UniPathway-derived general protein ubiquitination process, consistent with FBXL15's role in SMURF1 ubiquitination.
Reason: Correct but generic; the SCF-dependent catabolic process term better captures the role. Supported by direct SMURF1 ubiquitination.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
mediates the ubiquitination and subsequent proteasomal degradation of SMURF1
|
|
GO:0019005
SCF ubiquitin ligase complex
|
IPI
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Evidence (ComplexPortal) that FBXL15 is part of the SCF(FBXL15) E3 ubiquitin ligase complex. Core cellular component.
Reason: Core complex membership; FBXL15 is the substrate-recognition subunit of SCF(FBXL15) (CUL1, SKP1, RBX1, FBXL15).
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Part of the SCF (SKP1-CUL1-F-box) E3 ubiquitin-protein ligase complex SCF(FBXL15) composed of CUL1, SKP1, RBX1 and FBXL15
|
|
GO:0030510
regulation of BMP signaling pathway
|
NAS
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
KEEP AS NON CORE |
Summary: Author statement (ComplexPortal NAS) that FBXL15 regulates BMP signaling, consistent with its positive regulation via SMURF1 degradation.
Reason: Supported regulatory role downstream of SMURF1 turnover; a context-specific pathway outcome rather than the core ligase substrate-receptor function. The more specific positive-regulation term is also annotated.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
thereby acting as a positive regulator of the BMP signaling pathway
|
|
GO:0031146
SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
|
NAS
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Author statement (ComplexPortal NAS) that FBXL15 functions in SCF-dependent proteasomal protein catabolism. Captures the core biological process.
Reason: Core biological process for an SCF F-box substrate receptor; directly supported by SMURF1 degradation.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
mediates the ubiquitination and subsequent proteasomal degradation of SMURF1
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8952618 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within generic CRL1/NEDD8-cycle reactions.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery rather than FBXL15-specific function. Consistent with cytoplasmic localization.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8952620 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic CRL1 NEDD8-binding reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8955241 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic CAND1/CRL reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8955289 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic COMMD/CAND1/CRL reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8956040 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic COP9-signalosome deneddylation reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-8956200 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic DCUN1D3/CRL1 reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983140 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic E2-to-substrate ubiquitin-transfer reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983147 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic E3-release reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983156 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic substrate-polyubiquitination reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0005829
cytosol
|
TAS
Reactome:R-HSA-983157 |
KEEP AS NON CORE |
Summary: Reactome cytosolic localization within a generic E3-substrate-E2 interaction reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0000086
G2/M transition of mitotic cell cycle
|
IMP
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
UNDECIDED |
Summary: Mutant-phenotype annotation of a G2/M transition role from the SMURF1/BMP study. The cached abstract emphasizes BMP signaling, dorsoventral patterning and bone, not cell-cycle phenotypes; the supporting full-text evidence cannot be verified here.
Reason: Experimental (IMP) annotation whose supporting data are not visible in the abstract-level cache; per curation guidance, an experimental annotation should not be removed merely because the abstract foregrounds a different phenotype. Cannot verify the G2/M evidence, so left undecided.
|
|
GO:0005737
cytoplasm
|
IDA
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Direct evidence for cytoplasmic localization from the SMURF1/BMP study. Core localization.
Reason: IDA-supported cytoplasmic localization, consistent with the UniProt subcellular location.
Supporting Evidence:
file:human/FBXL15/FBXL15-uniprot.txt
Cytoplasm {ECO:0000269|PubMed:21572392}
|
|
GO:0009953
dorsal/ventral pattern formation
|
ISS
GO_REF:0000024 |
KEEP AS NON CORE |
Summary: Sequence-similarity transfer of a dorsoventral patterning role, consistent with the zebrafish phenotype where fbxl15 knockdown causes dorsalization phenocopying BMP-deficient mutants.
Reason: Supported developmental role via BMP control, but downstream of and distinct from the core substrate-receptor activity.
Supporting Evidence:
PMID:21572392
Knockdown of fbxl15 expression in zebrafish embryos by specific antisense morpholinos causes embryonic dorsalization phenocoping BMP-deficient mutants
|
|
GO:0016567
protein ubiquitination
|
IDA
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Direct evidence that SCF(FBXL15) ubiquitinates SMURF1. A general parent of the SCF-dependent catabolic process.
Reason: Directly demonstrated substrate ubiquitination; accurate, though the SCF-dependent catabolic process term is more specific.
Supporting Evidence:
PMID:21572392
targets Smurf1 for ubiquitination and proteasomal degradation
|
|
GO:0019005
SCF ubiquitin ligase complex
|
IDA
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Direct evidence that FBXL15 forms an SCF(FBXL15) ubiquitin ligase complex. Core cellular component.
Reason: Core complex membership directly demonstrated.
Supporting Evidence:
PMID:21572392
forms an Skp1-Cullin1-F-box protein-Roc1 (SCF)(FBXL15) ubiquitin ligase complex
|
|
GO:0030282
bone mineralization
|
ISS
GO_REF:0000024 |
KEEP AS NON CORE |
Summary: Sequence-similarity transfer of a bone-mineralization role, consistent with the rat study showing FBXL15 knockdown reduces bone mass and mineral density.
Reason: Supported downstream physiological role via SMURF1/BMP control; a generic physiological process distinct from the core substrate-receptor activity.
Supporting Evidence:
PMID:21572392
Injection of FBXL15 siRNAs into rat bone tissues leads to a significant loss of bone mass and decrease in bone mineral density
|
|
GO:0030513
positive regulation of BMP signaling pathway
|
IMP
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
KEEP AS NON CORE |
Summary: Mutant-phenotype evidence that FBXL15, by degrading SMURF1, positively regulates BMP signaling. A well-supported downstream regulatory role.
Reason: Directly supported positive regulation of BMP signaling via SMURF1 turnover, but a context-specific pathway outcome rather than the core ligase substrate-receptor function. Falcon confirms the downstream transcriptional readout (reduced ID1/SMAD6 induction on FBXL15 knockdown).
Supporting Evidence:
PMID:21572392
FBXL15 positively regulates BMP signalling in mammalian cells
file:human/FBXL15/FBXL15-deep-research-falcon.md
FBXL15 knockdown reduces BMP-2-stimulated signaling outputs, including reduced BRE reporter activity and decreased induction of BMP/Smad target genes ID1 and SMAD6 by qRT-PCR
|
|
GO:0031146
SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
|
IDA
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
ACCEPT |
Summary: Direct evidence that SCF(FBXL15) drives proteasomal degradation of SMURF1. Core biological process.
Reason: Core biological process directly supported by SMURF1 turnover.
Supporting Evidence:
PMID:21572392
Smurf1 stability is suppressed by SCF(FBXL15)-mediated ubiquitination
|
|
GO:1990756
ubiquitin-like ligase-substrate adaptor activity
|
IDA
PMID:21572392 SCFFBXL¹⁵ regulates BMP signalling by directing the degradat... |
NEW |
Summary: Proposed core molecular function. As the LRR substrate-recognition subunit of SCF(FBXL15), FBXL15 selects the HECT ligase SMURF1 (and SMURF2/WWP2) for SCF-dependent ubiquitination. This more informative MF term is not in the GOA.
Reason: Captures the precise molecular function of FBXL15 as an SCF substrate-recognition adaptor, more informative than the bare protein binding annotation.
Supporting Evidence:
PMID:21572392
FBXL15, through its leucine-rich repeat domain, specifically recognizes the large subdomain within the N-lobe of the Smurf1 HECT domain
|
Q: Beyond SMURF1/SMURF2/WWP2, does SCF(FBXL15) have additional substrates, and what degron does its LRR recognize on the HECT N-lobe?
Q: Is the reported G2/M transition role (GO:0000086) a genuine SCF(FBXL15) function, and if so which substrate mediates it?
Experiment: Reconstitute SCF(FBXL15)-mediated ubiquitination of SMURF1 in vitro with purified SKP1-CUL1-RBX1-FBXL15 and an E2 to confirm direct ubiquitination and map the WW-HECT linker lysines (e.g. K355/K357).
Experiment: Generate FBXL15-knockout cells/animals and measure SMURF1 levels, BMP/SMAD signaling output, bone mineralization, and any cell-cycle (G2/M) phenotypes to test the breadth of FBXL15 function.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The evidence reviewed here explicitly concerns human FBXL15, an F-box / leucine-rich repeat (LRR) protein that functions as a substrate receptor in an SCF (Skp1–Cul1–Roc1) E3 ubiquitin ligase complex. Its domain architecture reported in mechanistic work—F-box (aa 22–64) and six LRRs (aa 113–269)—matches the UniProt-provided F-box/LRR-repeat protein identity for Q9H469. (cui2011scffbxl15regulatesbmp pages 1-2, cui2011scffbxl15regulatesbmp media 37c24d2f)
FBXL15 belongs to the FBXL (F-box + LRR) family of F-box proteins. In SCF complexes, the F-box domain binds Skp1 and thereby couples the substrate receptor to the Cul1–Roc1 catalytic core, whereas additional domains (here LRRs) typically mediate substrate recognition and recruitment for ubiquitination and proteasome-dependent degradation. FBXL15 is experimentally shown to assemble into a functional SCF complex (Skp1/Cul1/Roc1-dependent) that catalyzes ubiquitination of specific targets. (cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp pages 1-2)
FBXL15 is not an enzyme that transfers ubiquitin directly (that is the E2/E3 catalytic machinery of the SCF core). Its primary molecular function is as a substrate-recognition adaptor that confers target specificity to an SCF-type RING E3 ligase, thereby promoting K48-like degradative ubiquitination and proteasomal turnover of the recruited substrate(s). This is supported by direct in vivo and in vitro ubiquitination assays with SCF(FBXL15). (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6)
A seminal mechanistic study identified SMURF1 as a direct substrate of SCF(FBXL15). In HEK293T cells, FBXL15 co-expression increases SMURF1 ubiquitination; conversely, depletion of SCF components (Cul1, Roc1) or FBXL15 decreases SMURF1 ubiquitination and stabilizes endogenous SMURF1 in cycloheximide chase experiments. In vitro reconstitution with a semi-purified SCF–GST-FBXL15 complex further supports direct ubiquitination activity toward SMURF1 (with UbcH5c tested as an E2, among others). (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6)
Figure-based evidence from the same study shows FBXL15 domain structure and representative ubiquitination experiments supporting SCF-dependent SMURF1 ubiquitination. (cui2011scffbxl15regulatesbmp media 37c24d2f, cui2011scffbxl15regulatesbmp media 80856dca)
The same work reports that FBXL15 associates with multiple Nedd4 family members and can ubiquitinate SMURF2, suggesting FBXL15 may regulate a subset of SMURF/Nedd4-like HECT ligases. (cui2011scffbxl15regulatesbmp pages 8-9)
SMURF1 ubiquitination and degradation depend on lysines in the SMURF1 WW–HECT linker region, with K357 as a primary and K355 as a secondary site for FBXL15-mediated degradation; a K355/K357 double mutant attenuates ubiquitination and stabilizes SMURF1, and a triple K→R mutation blocks degradation in the reported assays. (cui2011scffbxl15regulatesbmp pages 6-7)
SMURF1 is a negative regulator of BMP signaling; therefore, FBXL15-mediated SMURF1 degradation is expected to relieve this inhibition.
Consistent with this model, a BMP-responsive BRE luciferase reporter assay shows that SMURF1 suppresses BMP-induced reporter activity, whereas co-expression of wild-type FBXL15 antagonizes this suppression; FBXL15 mutants lacking a functional F-box module do not show this rescue, supporting the requirement for SCF complex formation. (cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp media 37c24d2f)
At the transcriptional level, FBXL15 knockdown reduces BMP-2–stimulated signaling outputs, including reduced BRE reporter activity and decreased induction of BMP/Smad target genes ID1 and SMAD6 by qRT–PCR in the reported systems. (cui2011scffbxl15regulatesbmp pages 8-9)
A cancer-pathway review summarizes FBXL15 as an SCF substrate receptor that ubiquitinates SMURF1/SMURF2 and thereby intersects with TGF-β/BMP pathway components that are frequently implicated in oncogenesis and tumor suppression. This should be interpreted as pathway-contextual expert synthesis rather than new primary evidence for FBXL15 in cancer. (randle2016fboxproteininteractions pages 9-11)
Direct localization experiments for FBXL15 were not identified in the retrieved primary mechanistic excerpts. A curated cancer-focused review table lists FBXL15 as cytoplasmic, but annotates its broader function as “unclear” in that compilation despite listing SMURF1 as a substrate and BMP pathway linkage. This should be treated as secondary annotation pending additional experimental localization studies. (tekcham2020fboxproteinsand pages 11-12)
A 2024 research-highlight article (Signal Transduction and Targeted Therapy) summarizes Poirson et al. (Nature, 2024) proteome-scale screens for proximity-dependent protein (de)stabilization. In these experiments, effectors were recruited to a model substrate (eGFP-ABI1) and degradation was quantified by the eGFP/BFP ratio.
Key quantitative takeaways relevant to FBXL15:
- In a targeted screen of ~300 human ligases tethered to a GFP-binding nanobody, approximately half significantly decreased the reporter ratio relative to control. (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
- When screened across ten model substrates with different subcellular localizations, FBXL15 (along with FBXL12, FBXL14, KBTBD7, PRAME) destabilized most of them, implying relatively broad activity across localizations—an attractive property for induced-proximity degrader development. (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
This line of work does not establish endogenous FBXL15 substrates beyond those known from mechanistic studies; rather, it positions FBXL15 as a potentially useful “recruitable” degradation effector in engineered proximity systems. (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
URLs / publication info:
- Hermanns & Hofmann. Signal Transduction and Targeted Therapy (published online 2024-07). https://doi.org/10.1038/s41392-024-01884-3 (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
- Poirson et al. Nature (2024-03). https://doi.org/10.1038/s41586-024-07224-3 (supporting screen description and gating strategy in supplement excerpt) (poirson2024proteomescalediscoveryof pages 1-2)
The DEGRONOPEDIA resource paper includes FBXL15 as an example protein for degron inspection and reports an experimental HiBiT/LgBiT luminescence assay comparing N- vs C-terminal tagging. A 4-hour cycloheximide chase showed that C-terminal HiBiT tagging caused a notable increase in measured FBXL15 stability compared with N-terminal tagging, and the proteasome inhibitor MG132 increased accumulation of both variants (particularly the C-terminally tagged protein). These results support that FBXL15 turnover is proteasome-dependent and emphasize that terminal degron/sequence context can strongly affect measured stability (relevant for construct design in functional studies and degrader engineering). (szulc2024degronopediaaweb pages 7-8)
URL / publication info:
- Szulc et al. Nucleic Acids Research (2024-04). https://doi.org/10.1093/nar/gkae238 (szulc2024degronopediaaweb pages 7-8)
The clearest mechanistic axis for FBXL15 is FBXL15 → SMURF1 degradation → increased BMP signaling outputs, supported by in-cell reporter and transcriptional readouts. This implies potential utility in experimental systems where BMP pathway tone is tuned by altering SMURF1 abundance or turnover. (cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp media 37c24d2f)
However, the retrieved evidence does not yet support a standardized clinical application (e.g., approved diagnostics or therapeutics) directly targeting FBXL15.
Engineered proximity approaches (e.g., nanobody-based recruitment screens; broader PROTAC-like concepts) are increasingly interested in identifying ligases/adaptors that can degrade diverse targets. FBXL15’s performance as a “broad destabilizer” across substrates with different localizations suggests it may be a candidate for future TPD tool development, though this remains preclinical and platform-focused. (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
Open Targets returned low-score associations between FBXL15 and several disease terms including deafness, autosomal recessive nonsyndromic hearing loss 9, and several MODY-related terms (e.g., MODY, MODY type 3, MODY type 10), each with evidence count = 5 but without linked literature identifiers in the retrieved evidence rows. These should be interpreted as hypothesis-generating rather than established causal roles. (OpenTargets Search: -FBXL15)
Reviews discussing F-box proteins in cancer place FBXL15 in the conceptual framework of SCF ligases regulating hallmark pathways, in part due to its regulation of SMURF1/2 and thus BMP/TGF-β signaling nodes. The retrieved review material does not provide FBXL15-specific clinical statistics; instead, it contextualizes plausible pathway relevance. (randle2016fboxproteininteractions pages 9-11, tekcham2020fboxproteinsand pages 11-12)
| Claim / Functional annotation | Evidence type | Key experimental details (cell type / assay / mutants) | Main quantitative / statistical outputs if stated | Source (paper, year, DOI URL) |
|---|---|---|---|---|
| FBXL15 is the substrate-recognition subunit of a functional SCF E3 ubiquitin ligase complex | Biochemical, cell-based | Human FBXL15/FBXO37 identified as an F-box/LRR protein; co-immunoprecipitation showed association with Skp1, Cullin1, and Roc1; FBXL15 deletion mutants lacking an intact F-box failed to support activity; HEK293T-based ubiquitination/degradation assays | Domain architecture reported as F-box aa 22-64 and six LRRs aa 113-269; knockdown of Cullin1, Roc1, or FBXL15 stabilized endogenous Smurf1 and increased its half-life in CHX chase assays (cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp pages 1-2, cui2011scffbxl15regulatesbmp media 37c24d2f) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp pages 1-2, cui2011scffbxl15regulatesbmp media 37c24d2f) |
| Smurf1 is a direct FBXL15 substrate targeted for ubiquitination and proteasomal degradation | Biochemical, cell-based | Yeast two-hybrid and GST pull-down supported direct interaction; HEK293T co-expression of Myc-FBXL15 increased Smurf1 ubiquitination; denaturing IP ubiquitination assays; MG132-sensitive degradation; in vitro reconstituted SCF-GST-FBXL15 ubiquitination assay | FBXL15 promoted Smurf1 ubiquitination in vivo and in vitro; siRNA against Cullin1, Roc1, or FBXL15 reduced Smurf1 ubiquitination; UbcH5c used as E2 in vitro (UbcH7 also tested) (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp media 37c24d2f) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp media 37c24d2f) |
| FBXL15-mediated ubiquitination of Smurf1 maps primarily to lysines in the WW-HECT linker | Biochemical, mutational mapping | Smurf1 lysine-to-arginine mutants tested in ubiquitination/degradation assays and CHX chase; mapping focused on linker between WW domains and HECT domain | K357 identified as the primary residue and K355 as a secondary residue for FBXL15-mediated degradation; K355+K357R attenuated ubiquitination and stabilized Smurf1; triple K-to-R mutation blocked degradation (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 1-2) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 1-2) |
| FBXL15 also associates with and can ubiquitinate Smurf2, extending activity to multiple Nedd4-family ligases | Biochemical, cell-based | Interaction studies and ubiquitination assays reported association with multiple Nedd4 family members; Smurf2 specifically tested as an additional substrate candidate | Evidence snippet states FBXL15 associates with multiple Nedd4 family members and can ubiquitinate Smurf2; no effect size stated in snippet (cui2011scffbxl15regulatesbmp pages 8-9, randle2016fboxproteininteractions pages 9-11) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155; summarized in Randle & Laman, 2016, https://doi.org/10.1016/j.semcancer.2015.09.013 (cui2011scffbxl15regulatesbmp pages 8-9, randle2016fboxproteininteractions pages 9-11) |
| FBXL15 positively regulates BMP signaling by counteracting Smurf1-mediated inhibition | Cell-based reporter assay | HEK293T/HepG2 BMP pathway assays; BMP-responsive BRE-luciferase reporter tested with Smurf1 and FBXL15 WT versus FBXL15 mutants (ΔF or F-box-only constructs) | Smurf1 inhibited BRE-luc activity, while WT FBXL15 antagonized this inhibition; ΔF and F-box-only mutants did not rescue reporter output (qualitative effect described in figure summary) (cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp media 37c24d2f) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp media 37c24d2f) |
| FBXL15 is required for full induction of BMP/Smad target genes after BMP-2 stimulation | Cell-based, gene expression | siRNA depletion of FBXL15 (and of Cullin1/Roc1 in related assays) followed by BMP-2 stimulation; qRT-PCR readout of canonical targets | Knockdown of FBXL15 reduced BMP-2-stimulated BRE reporter activity and diminished induction of ID1 and SMAD6 transcripts; no numeric fold changes stated in snippet (cui2011scffbxl15regulatesbmp pages 8-9) | Cui et al., 2011, EMBO Journal, https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 8-9) |
| FBXL15 shows broad induced-proximity destabilizer activity in 2024 degrader screens, suggesting utility for targeted protein degradation platforms | Screen, functional genomics | Proteome-scale and focused induced-proximity screens tethered effectors to model substrates via anti-GFP nanobody or ABI1/PYL1 system; follow-up tested 10 model substrates with different subcellular localizations | Approximately half of ~300 tested human ligases significantly decreased the eGFP/BFP ratio; FBXL15 was among a small set (with FBXL12, FBXL14, KBTBD7, PRAME) that destabilized most tested substrates across localizations (hermanns2024proximitydependentprotein(de)stabilization pages 1-2) | Hermanns & Hofmann, 2024, Signal Transduction and Targeted Therapy, https://doi.org/10.1038/s41392-024-01884-3; discussing Poirson et al., 2024, Nature, https://doi.org/10.1038/s41586-024-07224-3 (hermanns2024proximitydependentprotein(de)stabilization pages 1-2, poirson2024proteomescalediscoveryof pages 1-2) |
| FBXL15 itself appears proteasome-regulated, and its C-terminus can influence apparent stability in tagging assays | Omics/methods, cell-based stability assay | DEGRONOPEDIA report used HiBiT/LgBiT luminescence with N- versus C-terminal HiBiT-tagged FBXL15; CHX chase and MG132 treatment used to monitor turnover | C-terminal HiBiT tagging caused a notable increase in FBXL15 stability after a 4-hour CHX chase versus N-terminal tagging; MG132 increased accumulation of both variants, especially the C-terminally tagged form (szulc2024degronopediaaweb pages 7-8) | Szulc et al., 2024, Nucleic Acids Research, https://doi.org/10.1093/nar/gkae238 (szulc2024degronopediaaweb pages 7-8) |
| Current disease links for FBXL15 are limited and low-confidence in target-disease databases rather than mechanistically established | Database | Open Targets search for FBXL15 target-disease associations | Reported associations included deafness, autosomal recessive nonsyndromic hearing loss 9, MODY, MODY type 3, and MODY type 10; each listed with evidence count = 5 and low association scores (~0.04-0.057); no supporting literature identifiers were provided in the retrieved evidence rows (OpenTargets Search: -FBXL15) | Open Targets Platform search result for FBXL15, accessed via tool output (OpenTargets Search: -FBXL15) |
Table: This table compiles the strongest available evidence for the identity, molecular function, pathway role, and emerging translational relevance of human FBXL15/FBXO37. It separates direct mechanistic findings from newer screening-based and database-based observations so the final report can distinguish established function from inference and low-confidence associations.
Cui et al. (2011) figure crops provide direct visual support for (i) FBXL15 domain architecture (F-box + LRRs), (ii) SCF-dependent SMURF1 ubiquitination assays, and (iii) BRE-luciferase pathway rescue by wild-type FBXL15 but not F-box mutants. (cui2011scffbxl15regulatesbmp media 37c24d2f, cui2011scffbxl15regulatesbmp media 80856dca, cui2011scffbxl15regulatesbmp media ff1c10bb)
References
(cui2011scffbxl15regulatesbmp pages 1-2): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(cui2011scffbxl15regulatesbmp media 37c24d2f): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(cui2011scffbxl15regulatesbmp pages 5-6): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(cui2011scffbxl15regulatesbmp pages 6-7): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(cui2011scffbxl15regulatesbmp media 80856dca): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(cui2011scffbxl15regulatesbmp pages 8-9): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
(randle2016fboxproteininteractions pages 9-11): Suzanne J. Randle and Heike Laman. F-box protein interactions with the hallmark pathways in cancer. Seminars in Cancer Biology, 36:3-17, Feb 2016. URL: https://doi.org/10.1016/j.semcancer.2015.09.013, doi:10.1016/j.semcancer.2015.09.013. This article has 74 citations and is from a peer-reviewed journal.
(tekcham2020fboxproteinsand pages 11-12): Dinesh Singh Tekcham, Di Chen, Yu Liu, Ting Ling, Yi Zhang, Huan Chen, Wen Wang, Wuxiyar Otkur, Huan Qi, Tian Xia, Xiaolong Liu, Hai-long Piao, and Hongxu Liu. F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects. Theranostics, 10:4150-4167, Mar 2020. URL: https://doi.org/10.7150/thno.42735, doi:10.7150/thno.42735. This article has 111 citations and is from a domain leading peer-reviewed journal.
(hermanns2024proximitydependentprotein(de)stabilization pages 1-2): Thomas Hermanns and Kay Hofmann. Proximity-dependent protein (de)stabilization: screening the human orfeome for protein degraders and stabilizers. Signal Transduction and Targeted Therapy, Jul 2024. URL: https://doi.org/10.1038/s41392-024-01884-3, doi:10.1038/s41392-024-01884-3. This article has 0 citations and is from a peer-reviewed journal.
(poirson2024proteomescalediscoveryof pages 1-2): Juline Poirson, Hanna Cho, Akashdeep Dhillon, Shahan Haider, Ahmad Zoheyr Imrit, Mandy Hiu Yi Lam, Nader Alerasool, Jessica Lacoste, Lamisa Mizan, Cassandra Wong, Anne-Claude Gingras, Daniel Schramek, and Mikko Taipale. Proteome-scale discovery of protein degradation and stabilization effectors. Nature, 628:878-886, Mar 2024. URL: https://doi.org/10.1038/s41586-024-07224-3, doi:10.1038/s41586-024-07224-3. This article has 81 citations and is from a highest quality peer-reviewed journal.
(szulc2024degronopediaaweb pages 7-8): Natalia A Szulc, Filip Stefaniak, Małgorzata Piechota, Anna Soszyńska, Gabriela Piórkowska, Andrea Cappannini, Janusz M Bujnicki, Chiara Maniaci, and Wojciech Pokrzywa. Degronopedia: a web server for proteome-wide inspection of degrons. Nucleic Acids Research, 52:W221-W232, Apr 2024. URL: https://doi.org/10.1093/nar/gkae238, doi:10.1093/nar/gkae238. This article has 38 citations and is from a highest quality peer-reviewed journal.
(OpenTargets Search: -FBXL15): Open Targets Query (-FBXL15, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(cui2011scffbxl15regulatesbmp media ff1c10bb): Yu Cui, Shan He, Cencan Xing, Kefeng Lu, Jian Wang, Guichun Xing, Anming Meng, Shunji Jia, Fuchu He, and Lingqiang Zhang. Scffbxl15 regulates bmp signalling by directing the degradation of hect‐type ubiquitin ligase smurf1. The EMBO Journal, 30:2675-2689, Jul 2011. URL: https://doi.org/10.1038/emboj.2011.155, doi:10.1038/emboj.2011.155. This article has 79 citations.
protein binding (IPI) as MF. The review adds GO:1990756 as a NEW IDA annotation; bare protein binding kept non-core. Correct call. Downstream BP roles (BMP regulation, bone mineralization, D/V patterning) are already annotated and kept non-core — no UPS NEW-term gap.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; F-box+LRR subtype/type no_mapping; class context_only / too_broad / GO:0061630; branch no_mapping.protein binding (IPI) as MF. The review adds GO:1990756 as a NEW IDA annotation; bare protein binding kept non-core. Correct call. Downstream BP roles (BMP regulation, bone mineralization, D/V patterning) are already annotated and kept non-core — no UPS NEW-term gap.This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
id: Q9H469
gene_symbol: FBXL15
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
FBXL15 (F-box/LRR-repeat protein 15; F-box only protein 37, FBXO37) is a
substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase
complex. Its F-box motif binds SKP1 to dock it onto the CUL1-RBX1 catalytic
scaffold, while its leucine-rich repeat domain provides substrate selectivity.
SCF(FBXL15) targets the HECT-type E3 ubiquitin ligase SMURF1 for
ubiquitination and proteasomal degradation; by lowering SMURF1 levels it acts
as a positive regulator of bone morphogenetic protein (BMP) signaling.
FBXL15 recognizes the large subdomain within the N-lobe of the SMURF1 HECT
domain and promotes SMURF1 ubiquitination on lysines in the WW-HECT linker
(Lys357 primary, Lys355 secondary), and it can also ubiquitinate the related
HECT ligases SMURF2 and WWP2. Because SMURF1 is an inhibitor of BMP signaling,
SCF(FBXL15)-driven SMURF1 turnover relieves this inhibition and enhances
BMP/SMAD transcriptional output, including induction of canonical BMP target
genes such as ID1 and SMAD6. Through this control of SMURF1 stability, FBXL15
contributes to dorsal/ventral pattern formation during embryonic development
and to bone mass maintenance. It acts in the cytoplasm.
existing_annotations:
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: Electronic transfer of cytoplasmic localization from the UniProt subcellular location; supported by IDA evidence.
action: ACCEPT
reason: Correct localization, directly supported (IDA) in the SMURF1/BMP study.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:21572392
qualifier: enables
review:
summary: IntAct interactions with the HECT ligases SMURF1/SMURF2/WWP2 (the FBXL15 substrates) from the BMP-signaling study. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: Records the functionally important FBXL15-SMURF1/SMURF2/WWP2 substrate interactions, but bare protein binding is uninformative; the relationship is captured by the catabolic-process annotations.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: INTERACTION WITH SMURF1; SMURF2 AND WWP2
- term:
id: GO:0030282
label: bone mineralization
evidence_type: IEA
original_reference_id: GO_REF:0000107
qualifier: involved_in
review:
summary: Ortholog-based electronic assignment of a bone-mineralization role, consistent with the rat study showing FBXL15 knockdown reduces bone mass and mineral density.
action: KEEP_AS_NON_CORE
reason: Supported downstream physiological role (via SMURF1/BMP control) but a generic developmental/physiological process distinct from the core substrate-receptor activity.
supported_by:
- reference_id: PMID:21572392
supporting_text: Injection of FBXL15 siRNAs into rat bone tissues leads to a significant loss of bone mass and decrease in bone mineral density
- term:
id: GO:0016567
label: protein ubiquitination
evidence_type: IEA
original_reference_id: GO_REF:0000041
qualifier: involved_in
review:
summary: UniPathway-derived general protein ubiquitination process, consistent with FBXL15's role in SMURF1 ubiquitination.
action: ACCEPT
reason: Correct but generic; the SCF-dependent catabolic process term better captures the role. Supported by direct SMURF1 ubiquitination.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: mediates the ubiquitination and subsequent proteasomal degradation of SMURF1
- term:
id: GO:0019005
label: SCF ubiquitin ligase complex
evidence_type: IPI
original_reference_id: PMID:21572392
qualifier: part_of
review:
summary: Evidence (ComplexPortal) that FBXL15 is part of the SCF(FBXL15) E3 ubiquitin ligase complex. Core cellular component.
action: ACCEPT
reason: Core complex membership; FBXL15 is the substrate-recognition subunit of SCF(FBXL15) (CUL1, SKP1, RBX1, FBXL15).
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: Part of the SCF (SKP1-CUL1-F-box) E3 ubiquitin-protein ligase complex SCF(FBXL15) composed of CUL1, SKP1, RBX1 and FBXL15
- term:
id: GO:0030510
label: regulation of BMP signaling pathway
evidence_type: NAS
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Author statement (ComplexPortal NAS) that FBXL15 regulates BMP signaling, consistent with its positive regulation via SMURF1 degradation.
action: KEEP_AS_NON_CORE
reason: Supported regulatory role downstream of SMURF1 turnover; a context-specific pathway outcome rather than the core ligase substrate-receptor function. The more specific positive-regulation term is also annotated.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: thereby acting as a positive regulator of the BMP signaling pathway
- term:
id: GO:0031146
label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
evidence_type: NAS
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Author statement (ComplexPortal NAS) that FBXL15 functions in SCF-dependent proteasomal protein catabolism. Captures the core biological process.
action: ACCEPT
reason: Core biological process for an SCF F-box substrate receptor; directly supported by SMURF1 degradation.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: mediates the ubiquitination and subsequent proteasomal degradation of SMURF1
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8952618
qualifier: located_in
review:
summary: Reactome cytosolic localization within generic CRL1/NEDD8-cycle reactions.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery rather than FBXL15-specific function. Consistent with cytoplasmic localization.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8952620
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic CRL1 NEDD8-binding reaction.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8955241
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic CAND1/CRL reaction.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8955289
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic COMMD/CAND1/CRL reaction.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8956040
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic COP9-signalosome deneddylation reaction.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-8956200
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic DCUN1D3/CRL1 reaction.
action: KEEP_AS_NON_CORE
reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983140
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic E2-to-substrate ubiquitin-transfer reaction.
action: KEEP_AS_NON_CORE
reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983147
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic E3-release reaction.
action: KEEP_AS_NON_CORE
reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983156
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic substrate-polyubiquitination reaction.
action: KEEP_AS_NON_CORE
reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-983157
qualifier: located_in
review:
summary: Reactome cytosolic localization within a generic E3-substrate-E2 interaction reaction.
action: KEEP_AS_NON_CORE
reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0000086
label: G2/M transition of mitotic cell cycle
evidence_type: IMP
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Mutant-phenotype annotation of a G2/M transition role from the SMURF1/BMP study. The cached abstract emphasizes BMP signaling, dorsoventral patterning and bone, not cell-cycle phenotypes; the supporting full-text evidence cannot be verified here.
action: UNDECIDED
reason: Experimental (IMP) annotation whose supporting data are not visible in the abstract-level cache; per curation guidance, an experimental annotation should not be removed merely because the abstract foregrounds a different phenotype. Cannot verify the G2/M evidence, so left undecided.
- term:
id: GO:0005737
label: cytoplasm
evidence_type: IDA
original_reference_id: PMID:21572392
qualifier: located_in
review:
summary: Direct evidence for cytoplasmic localization from the SMURF1/BMP study. Core localization.
action: ACCEPT
reason: IDA-supported cytoplasmic localization, consistent with the UniProt subcellular location.
supported_by:
- reference_id: file:human/FBXL15/FBXL15-uniprot.txt
supporting_text: 'Cytoplasm {ECO:0000269|PubMed:21572392}'
- term:
id: GO:0009953
label: dorsal/ventral pattern formation
evidence_type: ISS
original_reference_id: GO_REF:0000024
qualifier: involved_in
review:
summary: Sequence-similarity transfer of a dorsoventral patterning role, consistent with the zebrafish phenotype where fbxl15 knockdown causes dorsalization phenocopying BMP-deficient mutants.
action: KEEP_AS_NON_CORE
reason: Supported developmental role via BMP control, but downstream of and distinct from the core substrate-receptor activity.
supported_by:
- reference_id: PMID:21572392
supporting_text: Knockdown of fbxl15 expression in zebrafish embryos by specific antisense morpholinos causes embryonic dorsalization phenocoping BMP-deficient mutants
- term:
id: GO:0016567
label: protein ubiquitination
evidence_type: IDA
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Direct evidence that SCF(FBXL15) ubiquitinates SMURF1. A general parent of the SCF-dependent catabolic process.
action: ACCEPT
reason: Directly demonstrated substrate ubiquitination; accurate, though the SCF-dependent catabolic process term is more specific.
supported_by:
- reference_id: PMID:21572392
supporting_text: targets Smurf1 for ubiquitination and proteasomal degradation
- term:
id: GO:0019005
label: SCF ubiquitin ligase complex
evidence_type: IDA
original_reference_id: PMID:21572392
qualifier: part_of
review:
summary: Direct evidence that FBXL15 forms an SCF(FBXL15) ubiquitin ligase complex. Core cellular component.
action: ACCEPT
reason: Core complex membership directly demonstrated.
supported_by:
- reference_id: PMID:21572392
supporting_text: forms an Skp1-Cullin1-F-box protein-Roc1 (SCF)(FBXL15) ubiquitin ligase complex
- term:
id: GO:0030282
label: bone mineralization
evidence_type: ISS
original_reference_id: GO_REF:0000024
qualifier: involved_in
review:
summary: Sequence-similarity transfer of a bone-mineralization role, consistent with the rat study showing FBXL15 knockdown reduces bone mass and mineral density.
action: KEEP_AS_NON_CORE
reason: Supported downstream physiological role via SMURF1/BMP control; a generic physiological process distinct from the core substrate-receptor activity.
supported_by:
- reference_id: PMID:21572392
supporting_text: Injection of FBXL15 siRNAs into rat bone tissues leads to a significant loss of bone mass and decrease in bone mineral density
- term:
id: GO:0030513
label: positive regulation of BMP signaling pathway
evidence_type: IMP
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Mutant-phenotype evidence that FBXL15, by degrading SMURF1, positively regulates BMP signaling. A well-supported downstream regulatory role.
action: KEEP_AS_NON_CORE
reason: Directly supported positive regulation of BMP signaling via SMURF1 turnover, but a context-specific pathway outcome rather than the core ligase substrate-receptor function. Falcon confirms the downstream transcriptional readout (reduced ID1/SMAD6 induction on FBXL15 knockdown).
supported_by:
- reference_id: PMID:21572392
supporting_text: FBXL15 positively regulates BMP signalling in mammalian cells
- reference_id: file:human/FBXL15/FBXL15-deep-research-falcon.md
supporting_text: >-
FBXL15 knockdown reduces BMP-2-stimulated signaling outputs, including reduced
BRE reporter activity and decreased induction of BMP/Smad target genes ID1 and
SMAD6 by qRT-PCR
- term:
id: GO:0031146
label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
evidence_type: IDA
original_reference_id: PMID:21572392
qualifier: involved_in
review:
summary: Direct evidence that SCF(FBXL15) drives proteasomal degradation of SMURF1. Core biological process.
action: ACCEPT
reason: Core biological process directly supported by SMURF1 turnover.
supported_by:
- reference_id: PMID:21572392
supporting_text: Smurf1 stability is suppressed by SCF(FBXL15)-mediated ubiquitination
- term:
id: GO:1990756
label: ubiquitin-like ligase-substrate adaptor activity
evidence_type: IDA
original_reference_id: PMID:21572392
qualifier: enables
review:
summary: Proposed core molecular function. As the LRR substrate-recognition subunit of SCF(FBXL15), FBXL15 selects the HECT ligase SMURF1 (and SMURF2/WWP2) for SCF-dependent ubiquitination. This more informative MF term is not in the GOA.
action: NEW
reason: Captures the precise molecular function of FBXL15 as an SCF substrate-recognition adaptor, more informative than the bare protein binding annotation.
supported_by:
- reference_id: PMID:21572392
supporting_text: FBXL15, through its leucine-rich repeat domain, specifically recognizes the large subdomain within the N-lobe of the Smurf1 HECT domain
references:
- id: GO_REF:0000024
title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
by curator judgment of sequence similarity
findings: []
- id: GO_REF:0000041
title: Gene Ontology annotation based on UniPathway vocabulary mapping
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied by
UniProt
findings: []
- id: GO_REF:0000107
title: Automatic transfer of experimentally verified manual GO annotation data to
orthologs using Ensembl Compara
findings: []
- id: PMID:21572392
title: SCFFBXL¹⁵ regulates BMP signalling by directing the degradation of HECT-type
ubiquitin ligase Smurf1.
findings:
- statement: SCF(FBXL15) targets the HECT E3 ligase SMURF1 (also SMURF2/WWP2) for ubiquitination and proteasomal degradation, recognizing the N-lobe of the SMURF1 HECT domain; by lowering SMURF1 it positively regulates BMP signaling, affecting dorsoventral patterning (zebrafish) and bone mass (rat).
reference_section_type: ABSTRACT
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: PubMed-verified (EMBO J 2011), full text available; establishes SMURF1 as the defining SCF(FBXL15) substrate and the BMP/bone/dorsoventral roles.
- 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: []
- id: file:human/FBXL15/FBXL15-deep-research-falcon.md
title: Falcon deep research report for human FBXL15
findings:
- statement: FBXL15 is the substrate-recognition adaptor of an SCF (SKP1-CUL1-RBX1/Roc1) E3 ligase that confers target specificity for K48-like degradative ubiquitination and proteasomal turnover, rather than catalyzing ubiquitin transfer itself.
supporting_text: >-
Its primary molecular function is as a **substrate-recognition adaptor**
that confers target specificity to an **SCF-type RING E3 ligase**, thereby
promoting **K48-like degradative ubiquitination** and **proteasomal turnover**
of the recruited substrate(s).
- statement: SCF(FBXL15)-mediated SMURF1 degradation maps primarily to SMURF1 WW-HECT linker lysine K357, with K355 secondary.
supporting_text: >-
K357 identified as the primary residue and K355 as a secondary residue for
FBXL15-mediated degradation; a K355/K357 double mutant attenuates ubiquitination
and stabilizes SMURF1
- statement: By counteracting the BMP-inhibitor SMURF1, FBXL15 is required for full BMP/SMAD transcriptional output, including BMP-2-stimulated induction of the target genes ID1 and SMAD6.
supporting_text: >-
FBXL15 knockdown reduces BMP-2-stimulated signaling outputs, including reduced
BRE reporter activity and decreased induction of BMP/Smad target genes ID1 and
SMAD6 by qRT-PCR
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
Falcon synthesis is built almost entirely on Cui et al. 2011 (EMBO J;
PMID:21572392, already the core reference here) plus 2024 induced-proximity
degrader screens and DEGRONOPEDIA; cross-checked against UniProt and
PMID:21572392. Refines the SMURF1 degron mapping (K357/K355) and the BMP/SMAD
target-gene readout (ID1, SMAD6); no new GOA terms added.
core_functions:
- description: Substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex that selects the HECT-type ubiquitin ligase SMURF1 (and related SMURF2/WWP2) for SCF-dependent polyubiquitination and proteasomal degradation.
molecular_function:
id: GO:1990756
label: ubiquitin-like ligase-substrate adaptor activity
locations:
- id: GO:0005737
label: cytoplasm
supported_by:
- reference_id: PMID:21572392
supporting_text: FBXL15, through its leucine-rich repeat domain, specifically recognizes the large subdomain within the N-lobe of the Smurf1 HECT domain
directly_involved_in:
- id: GO:0031146
label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
- description: Positive regulator of BMP signaling that controls the abundance of the BMP-inhibitory HECT ligase SMURF1, thereby influencing dorsal/ventral pattern formation during development and bone mass maintenance.
molecular_function:
id: GO:1990756
label: ubiquitin-like ligase-substrate adaptor activity
locations:
- id: GO:0005737
label: cytoplasm
supported_by:
- reference_id: PMID:21572392
supporting_text: FBXL15 positively regulates BMP signalling in mammalian cells
directly_involved_in:
- id: GO:0030513
label: positive regulation of BMP signaling pathway
proposed_new_terms: []
suggested_questions:
- question: Beyond SMURF1/SMURF2/WWP2, does SCF(FBXL15) have additional substrates, and what degron does its LRR recognize on the HECT N-lobe?
- question: Is the reported G2/M transition role (GO:0000086) a genuine SCF(FBXL15) function, and if so which substrate mediates it?
suggested_experiments:
- description: Reconstitute SCF(FBXL15)-mediated ubiquitination of SMURF1 in vitro with purified SKP1-CUL1-RBX1-FBXL15 and an E2 to confirm direct ubiquitination and map the WW-HECT linker lysines (e.g. K355/K357).
- description: Generate FBXL15-knockout cells/animals and measure SMURF1 levels, BMP/SMAD signaling output, bone mineralization, and any cell-cycle (G2/M) phenotypes to test the breadth of FBXL15 function.