FBXL15

UniProt ID: Q9H469
Organism: Homo sapiens
Review Status: COMPLETE
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Gene 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 Review

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

Core Functions

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.

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

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.

Supporting Evidence:
  • PMID:21572392
    FBXL15 positively regulates BMP signalling in mammalian cells

References

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
Gene Ontology annotation based on UniPathway vocabulary mapping
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
SCFFBXL¹⁵ regulates BMP signalling by directing the degradation of HECT-type ubiquitin ligase Smurf1.
  • 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).
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
file:human/FBXL15/FBXL15-deep-research-falcon.md
Falcon deep research report for human FBXL15
  • 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.
    "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)."
  • SCF(FBXL15)-mediated SMURF1 degradation maps primarily to SMURF1 WW-HECT linker lysine K357, with K355 secondary.
    "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"
  • 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.
    "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"

Suggested Questions for Experts

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?

Suggested Experiments

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.

Deep Research

Falcon

(FBXL15-deep-research-falcon.md)
Research report: Human **FBXL15** (UniProt **Q9H469**; gene **FBXL15**; synonym **FBXO37**)—functional annotation Falcon Edison Scientific Literature 18 citations 2 artifacts 2026-06-13T06:08:09.914067

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 FBXL15 (UniProt Q9H469; gene FBXL15; synonym FBXO37)—functional annotation

0. Target verification (critical identity check)

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)

1. Key concepts and definitions (current understanding)

1.1 FBXL proteins and SCF ubiquitin ligases

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)

1.2 What “molecular function” means for FBXL15

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)

2. Established molecular functions, substrates, and pathway roles (best-supported biology)

2.1 Core mechanistic finding: FBXL15 targets SMURF1 (and SMURF2) for ubiquitination and degradation

Substrate: SMURF1 (HECT-type E3 ligase; Nedd4 family)

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)

Substrate extension: SMURF2

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)

Substrate mapping / specificity determinants

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)

2.2 Pathway role: positive regulation of BMP (and broader TGF-β family) signaling

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)

Authoritative synthesis / expert framing

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)

2.3 Subcellular localization (what is known vs. not well supported)

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)

3. Recent developments (prioritizing 2023–2024)

3.1 2024: FBXL15 highlighted as a candidate ligase/adaptor for induced-proximity targeted protein degradation (TPD)

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)

3.2 2024: Evidence that FBXL15 itself is proteasome-regulated and influenced by terminal degron context (methodological but informative)

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)

4. Current applications and real-world implementations

4.1 Mechanism-informed applications: manipulating BMP signaling by modulating SMURF1 stability

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.

4.2 Technology application (2024): FBXL15 as a potential “recruitable” effector for targeted protein degradation platforms

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)

5. Disease relevance, genetics, and translational signals (strength of evidence)

5.1 Database-level associations (low confidence based on available output)

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)

5.2 Cancer context (expert synthesis rather than direct FBXL15 clinical evidence)

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)

6. Evidence-centric summary (what is known vs. uncertain)

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.

High-confidence conclusions (direct experimental support)

  1. FBXL15 is an SCF substrate receptor that assembles with Skp1/Cul1/Roc1 and drives substrate ubiquitination leading to proteasomal degradation. (cui2011scffbxl15regulatesbmp pages 5-6)
  2. SMURF1 is a direct substrate of SCF(FBXL15); FBXL15 promotes SMURF1 ubiquitination in vivo and in vitro and decreases SMURF1 stability in an SCF-dependent manner. (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6)
  3. FBXL15-mediated SMURF1 degradation requires SMURF1 linker lysines K355 and K357, with K357 highlighted as primary in the reported mapping. (cui2011scffbxl15regulatesbmp pages 6-7)
  4. FBXL15 positively regulates BMP signaling outputs (BRE reporter; ID1/SMAD6 induction), consistent with suppression of SMURF-mediated pathway inhibition. (cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp media 37c24d2f)

Moderate-confidence extensions

  • FBXL15 can ubiquitinate SMURF2 (reported in the same mechanistic study), suggesting broader control of SMURF/Nedd4 family HECT ligases. (cui2011scffbxl15regulatesbmp pages 8-9)

Uncertain / incomplete areas (insufficient direct evidence in retrieved texts)

  • Endogenous subcellular localization: only secondary annotation of “cytoplasmic” was retrieved; primary localization studies were not captured in the extracted texts. (tekcham2020fboxproteinsand pages 11-12)
  • Human disease causality: Open Targets suggests weak associations without supporting literature links in the retrieved output; no definitive genotype–phenotype or mechanistic disease study for FBXL15 was identified here. (OpenTargets Search: -FBXL15)

7. Key visual evidence

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 (URLs and publication dates)

  • Cui Y. et al. “SCF^FBXL15 regulates BMP signalling by directing the degradation of HECT-type ubiquitin ligase Smurf1.” The EMBO Journal (2011-07). https://doi.org/10.1038/emboj.2011.155 (cui2011scffbxl15regulatesbmp pages 6-7, cui2011scffbxl15regulatesbmp pages 5-6, cui2011scffbxl15regulatesbmp pages 8-9, cui2011scffbxl15regulatesbmp pages 1-2, cui2011scffbxl15regulatesbmp media 37c24d2f)
  • Hermanns T., Hofmann K. “Proximity-dependent protein (de)stabilization: screening the human ORFeome for protein degraders and stabilizers.” Signal Transduction and Targeted Therapy (2024-07; Research Highlight). https://doi.org/10.1038/s41392-024-01884-3 (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
  • Poirson J. et al. “Proteome-scale discovery of protein degradation and stabilization effectors.” Nature (2024-03). https://doi.org/10.1038/s41586-024-07224-3 (supplement excerpt) (poirson2024proteomescalediscoveryof pages 1-2)
  • Szulc N.A. et al. “DEGRONOPEDIA: a web server for proteome-wide inspection of degrons.” Nucleic Acids Research (2024-04). https://doi.org/10.1093/nar/gkae238 (szulc2024degronopediaaweb pages 7-8)
  • Randle S.J., Laman H. “F-box protein interactions with the hallmark pathways in cancer.” Seminars in Cancer Biology (2016-02). https://doi.org/10.1016/j.semcancer.2015.09.013 (randle2016fboxproteininteractions pages 9-11)
  • Tekcham D.S. et al. “F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects.” Theranostics (2020-03). https://doi.org/10.7150/thno.42735 (table annotation including cytoplasmic localization and SMURF1 substrate listing) (tekcham2020fboxproteinsand pages 11-12)
  • Open Targets Platform: FBXL15 disease associations (tool output; no literature links in retrieved rows). (OpenTargets Search: -FBXL15)

References

  1. (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.

  2. (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.

  3. (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.

  4. (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.

  5. (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.

  6. (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.

  7. (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.

  8. (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.

  9. (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.

  10. (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.

  11. (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.

  12. (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.

  13. (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.

Artifacts

Citations

  1. randle2016fboxproteininteractions pages 9-11
  2. tekcham2020fboxproteinsand pages 11-12
  3. poirson2024proteomescalediscoveryof pages 1-2
  4. szulc2024degronopediaaweb pages 7-8
  5. https://doi.org/10.1038/s41392-024-01884-3
  6. https://doi.org/10.1038/s41586-024-07224-3
  7. https://doi.org/10.1093/nar/gkae238
  8. https://doi.org/10.1038/emboj.2011.155
  9. https://doi.org/10.1038/emboj.2011.155;
  10. https://doi.org/10.1016/j.semcancer.2015.09.013
  11. https://doi.org/10.1038/s41392-024-01884-3;
  12. https://doi.org/10.7150/thno.42735
  13. https://doi.org/10.1038/emboj.2011.155,
  14. https://doi.org/10.1016/j.semcancer.2015.09.013,
  15. https://doi.org/10.7150/thno.42735,
  16. https://doi.org/10.1038/s41392-024-01884-3,
  17. https://doi.org/10.1038/s41586-024-07224-3,
  18. https://doi.org/10.1093/nar/gkae238,

📚 Additional Documentation

Pn Notes

(FBXL15-pn-notes.md)

FBXL15 PN Consistency Notes

  • Generated: 2026-06-18
  • Project: PROTEOSTASIS
  • Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
  • UniProt: Q9H469
  • 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: 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/core annotation action counts: ACCEPT: 8; KEEP_AS_NON_CORE: 16; NEW: 1; UNDECIDED: 1

PN Consistency Summary

  • Consistency: Strong. Falcon, review YAML, and PN mapping agree FBXL15 (FBXO37) is the SCF(FBXL15) substrate receptor that degrades the HECT ligase SMURF1 (also SMURF2/WWP2), positively regulating BMP signaling (PMID:21572392, IDA-rich). Falcon refines the SMURF1 degron (K357/K355) and BMP readout (ID1/SMAD6) — consistent. One internal caveat handled well: the IMP G2/M annotation (GO:0000086) is left UNDECIDED because the abstract foregrounds BMP, not cell cycle — correct per "don't overrule curators" guidance.
  • PN story / NEW pressure: PN asserts generic adaptor MF (GO:1990756, verified real). GOA carries only 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.
  • Evidence alignment: PN reference only "15340381/rev" (placeholder); review does not cite it. Review centers on PMID:21572392 (primary, full text) + falcon. Benign divergence.
  • Verdict: CONSISTENT / ACCEPT mapping. No edits required; NEW(GO:1990756) pattern correctly applied; substrate validated; G2/M UNDECIDED appropriately conservative.

Full Consistency Review

  • UniProt: Q9H469 · 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; F-box+LRR subtype/type no_mapping; class context_only / too_broad / GO:0061630; branch no_mapping.
  • Consistency: Strong. Falcon, review YAML, and PN mapping agree FBXL15 (FBXO37) is the SCF(FBXL15) substrate receptor that degrades the HECT ligase SMURF1 (also SMURF2/WWP2), positively regulating BMP signaling (PMID:21572392, IDA-rich). Falcon refines the SMURF1 degron (K357/K355) and BMP readout (ID1/SMAD6) — consistent. One internal caveat handled well: the IMP G2/M annotation (GO:0000086) is left UNDECIDED because the abstract foregrounds BMP, not cell cycle — correct per "don't overrule curators" guidance.
  • PN story / NEW pressure: PN asserts generic adaptor MF (GO:1990756, verified real). GOA carries only 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.
  • Mapping strategy: Gene does not change the node. Catalysis correctly excluded from sub-nodes (RBX1 RING). SMURF1 is a validated substrate (LRR recognizes HECT N-lobe) → adaptor MF grounded, not orphan. PN-projected GO:1990756 matches review core_functions MF exactly. Note: substrate is itself a HECT E3, so this is an E3-degrades-E3 node — does not change mapping.
  • Evidence alignment: PN reference only "15340381/rev" (placeholder); review does not cite it. Review centers on PMID:21572392 (primary, full text) + falcon. Benign divergence.
  • Verdict: CONSISTENT / ACCEPT mapping. No edits required; NEW(GO:1990756) pattern correctly applied; substrate validated; G2/M UNDECIDED appropriately conservative.

PN Dossier Context

  • review_batch: proteostasis-batch-2026-06-13
  • review_yaml: genes/human/FBXL15/FBXL15-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: Q9H469
  • In branches: UPS
  • Signature domains: IPR001810
  • Auxiliary domains: IPR001611, 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: 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.