FBXL12

UniProt ID: Q9NXK8
Organism: Homo sapiens
Review Status: COMPLETE
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Gene Description

FBXL12 (F-box/LRR-repeat protein 12; FBL12) is a substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex. Its N-terminal F-box motif binds SKP1, linking it to the CUL1-RBX1 catalytic core, and its leucine-rich repeats confer substrate selectivity, so that SCF(FBXL12) directs substrate-specific (often K48-linked) polyubiquitination and proteasomal degradation. Several physiological substrates have been defined in distinct cellular programs, with substrate selection frequently gated by substrate phosphorylation. SCF(FBXL12) degrades calcium/calmodulin-dependent protein kinase I (CAMK1; acceptor Lys59), which lowers CAMK1-driven p27 phosphorylation, disrupts cyclin D1/CDK4 complex assembly, and triggers G1 cell-cycle arrest in lung epithelia. It targets the cyclin-dependent kinase inhibitors p57KIP2/CDKN1C (TGF-beta1-induced, phosphorylation-dependent turnover linked to osteoblast differentiation) and CDKN1B/p27 (Lys165 acceptor; degraded together with SCF(FBXL1)/SKP2 downstream of pre-TCR and Notch signaling to license the proliferative burst of thymocyte beta-selection). It promotes CHK1-phosphorylation-dependent degradation of chromatin-associated FANCD2 to support replication-fork recovery and cancer-cell survival under replication stress, and degrades the aldehyde dehydrogenases ALDH3A1/ALDH3A2 to permit trophoblast differentiation during placental development. An SCF complex containing FBXL12 also mediates DNA-damage-induced K48-linked ubiquitination and removal of the NHEJ factor Ku80 from DNA ends (shown in Xenopus extracts, with conservation to human inferred). FBXL12 acts in both the cytoplasm (where it co-localizes with CAMK1) and the nucleus/chromatin (FANCD2, Ku80). Many of its catalogued interactions derive from high-throughput proteomic screens and are not established functional substrates.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0005515 protein binding
IPI
PMID:18660753
A new ubiquitin ligase involved in p57KIP2 proteolysis regul...
KEEP AS NON CORE
Summary: Interactions with CDKN1C/p57KIP2 (P49918) and SKP1 (P63208) from the study showing SCF(FBL12) directly ubiquitinates p57KIP2. Bare protein binding is uninformative.
Reason: Records functionally important substrate (CDKN1C) and SKP1 interactions, but bare protein binding is uninformative per curation guidelines; the substrate relationship is captured by the catabolic-process annotations.
Supporting Evidence:
PMID:18660753
FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
GO:0005515 protein binding
IPI
PMID:21163940
Interactome mapping suggests new mechanistic details underly...
KEEP AS NON CORE
Summary: Interaction with RNF32 (Q9H0A6) from an Alzheimer's-disease interactome map. Bare protein binding is uninformative.
Reason: High-throughput interaction of uncertain functional significance; bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; Q9H0A6: RNF32; NbExp=2; IntAct=EBI-719790, EBI-724829;
GO:0005515 protein binding
IPI
PMID:25416956
A proteome-scale map of the human interactome network.
KEEP AS NON CORE
Summary: High-throughput interactions (e.g. DOCK8, LNX1) from a proteome-scale interactome. Bare protein binding is uninformative.
Reason: High-throughput interactions of uncertain functional significance; bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; Q8TBB1: LNX1; NbExp=3; IntAct=EBI-719790, EBI-739832;
GO:0005515 protein binding
IPI
PMID:27705803
A High-Density Map for Navigating the Human Polycomb Complex...
KEEP AS NON CORE
Summary: Interaction with SKP1 (P63208) from a Polycomb complexome map. Bare protein binding is uninformative.
Reason: Records the FBXL12-SKP1 association required for SCF assembly, but bare protein binding is uninformative; captured by the ubiquitin ligase complex annotation.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;
GO:0005515 protein binding
IPI
PMID:32296183
A reference map of the human binary protein interactome.
KEEP AS NON CORE
Summary: Interactions (GEMIN4, SKP1) from a binary interactome reference map. Bare protein binding is uninformative.
Reason: High-throughput interactions; bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; P57678: GEMIN4; NbExp=3; IntAct=EBI-719790, EBI-356700;
GO:0005515 protein binding
IPI
PMID:33961781
Dual proteome-scale networks reveal cell-specific remodeling...
KEEP AS NON CORE
Summary: Interaction with SKP1 (P63208) from a cell-specific proteome-scale interactome. Bare protein binding is uninformative.
Reason: High-throughput SKP1 interaction; bare protein binding is uninformative and is subsumed by the ubiquitin ligase complex annotation.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;
GO:0005515 protein binding
IPI
PMID:40205054
Multimodal cell maps as a foundation for structural and func...
KEEP AS NON CORE
Summary: Interaction with SKP1 (P63208) from a multimodal cell-map genomics study. Bare protein binding is uninformative.
Reason: High-throughput SKP1 interaction; bare protein binding is uninformative.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;
GO:0000151 ubiquitin ligase complex
IEA
GO_REF:0000107
ACCEPT
Summary: Ortholog-based electronic assignment of ubiquitin ligase complex membership, consistent with FBXL12 being an SCF substrate-recognition subunit.
Reason: Correct core cellular component; FBXL12 assembles into SCF(FBXL12). A more specific SCF complex term would be preferable.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005737 cytoplasm
IEA
GO_REF:0000120
ACCEPT
Summary: Combined automated electronic assignment of cytoplasmic localization, consistent with the cytosolic Reactome annotations.
Reason: Plausible localization for a cytosolic SCF substrate receptor; consistent with TAS cytosol annotations.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0016567 protein ubiquitination
IEA
GO_REF:0000041
ACCEPT
Summary: UniPathway-derived general protein ubiquitination process, consistent with FBXL12's role in substrate ubiquitination.
Reason: Correct but generic; the SCF-dependent catabolic process term better captures the role. Supported by direct ubiquitination of p57KIP2.
Supporting Evidence:
PMID:18660753
FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
GO:0031146 SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
NAS
PMID:33234069
The FBXL family of F-box proteins: variations on a theme.
ACCEPT
Summary: ComplexPortal author statement that FBXL12 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 p57KIP2 degradation (PMID:18660753).
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0051726 regulation of cell cycle
NAS
PMID:33234069
The FBXL family of F-box proteins: variations on a theme.
KEEP AS NON CORE
Summary: ComplexPortal author statement linking FBXL12 to cell-cycle regulation, consistent with degradation of the CDK inhibitors p57KIP2/CDKN1C and CDKN1B/p27 and of CAMK1 (G1 arrest; thymocyte beta-selection proliferation).
Reason: Supported downstream regulatory role (via CAMK1, p57KIP2/CDKN1C and CDKN1B/p27 turnover) but a generic process distinct from the core substrate-receptor activity.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
disruption of cyclin D1/CDK4 complex assembly which results in G1 cell cycle arrest in lung epithelia
file:human/FBXL12/FBXL12-deep-research-falcon.md
SCF-Fbxl12 promoted **K48-linked polyubiquitination** of Cdkn1b, with a key ubiquitination site identified at **K165**; Cdkn1b(K165R) strongly reduced polyubiquitination
GO:0005829 cytosol
TAS
Reactome:R-HSA-8952618
KEEP AS NON CORE
Summary: Reactome curation of cytosolic localization within generic CRL1/NEDD8-cycle reactions. Plausible localization, though derived from pathway context.
Reason: Generic CRL-cycle pathway annotation (NEDD8 transfer); reflects the shared cytosolic CRL machinery rather than FBXL12-specific function.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-8952620
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic CRL1 NEDD8-binding reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-8955241
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic CAND1/CRL reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-8955289
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic COMMD/CAND1/CRL reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-8956040
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic COP9-signalosome deneddylation reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-8956200
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic DCUN1D3/CRL1 reaction.
Reason: Generic CRL-cycle pathway annotation; reflects shared cytosolic CRL machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-983140
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic E2-to-substrate ubiquitin-transfer reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-983147
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic E3-release reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-983156
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic substrate-polyubiquitination reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:0005829 cytosol
TAS
Reactome:R-HSA-983157
KEEP AS NON CORE
Summary: Reactome cytosolic localization within a generic E3-substrate-E2 interaction reaction.
Reason: Generic ubiquitination pathway annotation; reflects shared cytosolic machinery.
Supporting Evidence:
file:human/FBXL12/FBXL12-uniprot.txt
Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
GO:1990756 ubiquitin-like ligase-substrate adaptor activity
IDA
PMID:18660753
A new ubiquitin ligase involved in p57KIP2 proteolysis regul...
NEW
Summary: Proposed core molecular function. As the LRR substrate-recognition subunit of SCF(FBXL12), FBXL12 selects substrates such as p57KIP2/CDKN1C (and CAMK1) for SCF-dependent ubiquitination. This more informative MF term is not in the GOA.
Reason: Captures the precise molecular function of FBXL12 as an SCF substrate-recognition adaptor, more informative than the bare protein binding annotations.
Supporting Evidence:
PMID:18660753
FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner

Core Functions

Substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex that selects (frequently phosphorylation-gated) substrates, including the CDK inhibitors p57KIP2/CDKN1C and CDKN1B/p27 and the kinase CAMK1, for SCF-dependent polyubiquitination and proteasomal degradation.

Supporting Evidence:
  • PMID:18660753
    FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
  • file:human/FBXL12/FBXL12-uniprot.txt
    Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex

As the SCF(FBXL12) substrate receptor, promotes CHK1-phosphorylation-dependent proteasomal degradation of chromatin-associated FANCD2, clearing replication-stalled FANCD2 to support replication-fork recovery and cancer-cell survival under replication stress.

Supporting Evidence:
  • file:human/FBXL12/FBXL12-deep-research-falcon.md
    FANCD2 becomes a substrate of SCF^FBXL12 following **CHK1-dependent phosphorylation**, creating a phosphodegron that triggers FBXL12-dependent turnover, thereby helping clear "chromatin-trapped" FANCD2 at stalled forks and enabling replication restart

References

Gene Ontology annotation based on UniPathway vocabulary mapping
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
Combined Automated Annotation using Multiple IEA Methods
A new ubiquitin ligase involved in p57KIP2 proteolysis regulates osteoblast cell differentiation.
  • FBL12/FBXL12 forms an SCF(FBL12) complex and directly ubiquitinates p57KIP2/CDKN1C in a phosphorylation-dependent manner downstream of TGF-beta1, regulating osteoblast differentiation.
Interactome mapping suggests new mechanistic details underlying Alzheimer's disease.
A proteome-scale map of the human interactome network.
A High-Density Map for Navigating the Human Polycomb Complexome.
A reference map of the human binary protein interactome.
The FBXL family of F-box proteins: variations on a theme.
Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
Multimodal cell maps as a foundation for structural and functional genomics.
Fbxl12 triggers G1 arrest by mediating degradation of calmodulin kinase I.
  • FBXL12 mediates polyubiquitination and proteasomal degradation of CAMK1, disrupting cyclin D1/CDK4 complex assembly and causing G1 cell-cycle arrest in lung epithelia.
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/FBXL12/FBXL12-deep-research-falcon.md
Falcon deep research report for human FBXL12
  • FBXL12 is an SCF (SKP1-CUL1-RBX1) substrate-recognition subunit whose biology is best defined by its substrates in different cellular programs, including FANCD2, CaMKI, ALDH3A1/2, and CDKN1B/p27.
    "SCF substrate-recognition subunit that drives ubiquitin-dependent remodeling of protein abundance (often proteasomal degradation) for specific substrates in distinct biological programs: replication stress recovery (FANCD2), cell-cycle gating (CaMKI; CDKN1B/p27), and differentiation programs (ALDH3A1/2)."
  • Human SCF(FBXL12) promotes CHK1-phosphorylation-dependent proteasomal degradation of chromatin-associated FANCD2 to enable replication-fork recovery and cancer-cell survival under replication stress.
    "FANCD2 becomes a substrate of SCF^FBXL12 following **CHK1-dependent phosphorylation**, creating a phosphodegron that triggers FBXL12-dependent turnover, thereby helping clear "chromatin-trapped" FANCD2 at stalled forks and enabling replication restart"
  • SCF(FBXL12) targets ALDH3A1 and ALDH3A2 for ubiquitin-dependent degradation, which is essential for trophoblast differentiation during placental development.
    "SCF^FBXL12 targets **ALDH3A1 and ALDH3A2** for ubiquitin-dependent degradation and that this is **essential for trophoblast differentiation** and proper placental development"
  • SCF(FBXL12) directly K48-polyubiquitinates CDKN1B/p27 (acceptor K165) to license the proliferative burst of thymocyte beta-selection downstream of pre-TCR and Notch signaling.
    "SCF-Fbxl12 promoted **K48-linked polyubiquitination** of Cdkn1b, with a key ubiquitination site identified at **K165**; Cdkn1b(K165R) strongly reduced polyubiquitination"
  • An SCF complex containing Fbxl12 mediates DNA-damage-induced ubiquitination of Ku80 and its removal from DNA ends (Xenopus extracts, human conservation inferred).
    "an **SCF complex containing Fbxl12** was required for **DNA damage-induced Ku80 ubiquitylation**, removal from DNA ends, and subsequent degradation"

Suggested Questions for Experts

Q: What is the complete physiological substrate repertoire of SCF(FBXL12), and what degron/phosphodegron features (e.g. CHK1, CK2, TGF-beta-driven) does its LRR domain recognize across substrates?

Q: How is FBXL12 partitioned between cytoplasmic (CAMK1) and nuclear/chromatin (FANCD2, Ku80, p27) substrate pools, and what determines context-specific substrate choice in cell cycle, replication stress, development, and immunity?

Suggested Experiments

Experiment: Reconstitute SCF(FBXL12)-mediated ubiquitination in vitro with purified SKP1-CUL1-RBX1-FBXL12, an E2, and phosphorylated versus unphosphorylated substrates (p57KIP2, CAMK1, CDKN1B/p27, CHK1-phosphorylated FANCD2) to define the phosphodegron requirement and map ubiquitination sites.

Experiment: Perform quantitative ubiquitinome/proteome profiling in FBXL12-knockout versus control cells (including replication-stressed cancer models and differentiating trophoblast/thymocyte systems) to define the endogenous substrate landscape and validate the cell-cycle, replication-stress, and developmental consequences.

Deep Research

Falcon

(FBXL12-deep-research-falcon.md)
Research report: Functional annotation of human **FBXL12** (UniProt **Q9NXK8**; *Homo sapiens*) Falcon Edison Scientific Literature 26 citations 2 artifacts 2026-06-13T06:06:56.522988

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: Functional annotation of human FBXL12 (UniProt Q9NXK8; Homo sapiens)

0. Gene/protein identity verification (mandatory)

The literature retrieved in this analysis consistently refers to FBXL12 (also written Fbl12/Fbxl12) as an F-box and leucine-rich repeat (LRR) protein that functions as a substrate-recognition subunit within SCF (SKP1–CUL1–RBX1–F-box) ubiquitin E3 ligase complexes, matching the UniProt description provided (Q9NXK8; “F-box/LRR-repeat protein 12”). This identity is supported by multiple independent mechanistic studies that explicitly assign FBXL12 to SCF complexes and demonstrate substrate recognition and ubiquitin-dependent turnover of specific proteins (FANCD2, CaMKI, ALDH3A1/2, CDKN1B/p27), with pathway roles in replication stress, cell-cycle control, development, and immune differentiation (brunner2023fbxl12degradesfancd2 pages 5-6, mallampalli2013fbxl12triggersg1 pages 5-6, nishiyama2015fbxl12‐mediateddegradationof pages 5-6, zhao2019notchandthe pages 6-7).

1. Key concepts and definitions (current understanding)

1.1 SCF ubiquitin ligases and F-box proteins

SCF complexes are cullin-RING ubiquitin ligases (CRLs) in which the F-box protein is the substrate receptor: it binds SKP1 via the F-box motif and binds substrate proteins via additional interaction domains (here, LRRs), thereby enabling RBX1-associated E2 enzymes to build ubiquitin chains on the substrate for downstream signaling—often proteasomal degradation. In the context of FBXL12, multiple studies directly demonstrate F-box dependence for SCF assembly and substrate ubiquitination (e.g., FBXL12 ΔF mutants fail to ubiquitinate substrates) (zhao2019notchandthe pages 3-4, nishiyama2015fbxl12‐mediateddegradationof pages 5-6, postow2013anscfcomplex pages 1-3).

1.2 Functional definition for FBXL12

Across contexts, the best-supported primary molecular function for human FBXL12 is:
- SCF substrate-recognition subunit that drives ubiquitin-dependent remodeling of protein abundance (often proteasomal degradation) for specific substrates in distinct biological programs: replication stress recovery (FANCD2), cell-cycle gating (CaMKI; CDKN1B/p27), and differentiation programs (ALDH3A1/2). (brunner2023fbxl12degradesfancd2 pages 5-6, mallampalli2013fbxl12triggersg1 pages 3-4, nishiyama2015fbxl12‐mediateddegradationof pages 5-6, zhao2019notchandthe pages 6-7)

2. Evidence-based biological functions, pathways, and localization

Process/Pathway Proposed FBXL12 molecular role Direct substrate(s) and ubiquitin linkage if known Key experimental evidence (assays/models) Subcellular context Publication (year, journal) and URL/DOI
Replication stress recovery / Fanconi anemia signaling / cancer cell survival SCF^FBXL12 substrate receptor that recognizes chromatin-associated, CHK1-phosphorylated FANCD2 and promotes its proteasomal turnover to enable fork recovery FANCD2; polyubiquitylation reported, linkage not specified in the extracted text; interaction with FANCI also detected siRNA imaging screen; DNA fiber assays; neutral comet assays; co-IP; chromatin fractionation; CUL1 IP-MS; FBXL12 KO/rescue; MG132 rescue; FANCD2 phosphodegron analysis; viability assays in breast cancer cells Primarily chromatin / replication forks; nuclear foci; chromatin-associated FANCD2 degradation Brunner et al., 2023, Molecular Cell — https://doi.org/10.1016/j.molcel.2023.07.026 (brunner2023fbxl12degradesfancd2 pages 5-6, brunner2023fbxl12degradesfancd2 pages 1-3, brunner2023fbxl12degradesfancd2 pages 3-5)
DNA double-strand break response / NHEJ factor removal SCF-Fbxl12 adaptor recruiting Cul1-Skp1 complex to DSB-bound Ku for damage-induced ubiquitylation and removal from DNA Ku80; heavily K48-linked polyubiquitylation reported in Xenopus extract system Xenopus egg extract DNA-bead assays modeling DSBs; immunodepletion of Fbxl12/Cul1; dominant-negative Cul1; chromatin binding and release assays; F-box mutant analysis DSB-associated chromatin; recruited in a Ku-dependent manner to DNA ends Postow & Funabiki, 2013, Cell Cycle — https://doi.org/10.4161/cc.23408 (Xenopus mechanism; conservation to human FBXL12 inferred) (postow2013anscfcomplex pages 3-4, postow2013anscfcomplex pages 1-3, postow2013anscfcomplex pages 7-9)
G1 cell-cycle control / lung epithelial signaling SCF^FBXL12 substrate receptor promoting ubiquitin-proteasome degradation of CaMKI, thereby reducing p27 phosphorylation, disrupting cyclin D1/CDK4 assembly, and inducing G1 arrest CaMKI; polyubiquitylation shown; K59 identified as a critical acceptor site on CaMKI; linkage not specified Co-IP and pull-down; CHX chase; MG132 sensitivity; in vivo and in vitro ubiquitylation with purified SCF components; CaMKI lysine mutants (K59R/K110R); BrdU/flow cytometry; immunostaining FBXL12 and CaMKI co-localize mainly in cytoplasm; downstream effect includes nuclear retention/mislocalization of p27 Mallampalli et al., 2013, Cellular Signalling — https://doi.org/10.1016/j.cellsig.2013.05.012 (mallampalli2013fbxl12triggersg1 pages 9-10, mallampalli2013fbxl12triggersg1 pages 4-5, mallampalli2013fbxl12triggersg1 pages 5-6, mallampalli2013fbxl12triggersg1 pages 3-4, mallampalli2013fbxl12triggersg1 pages 6-7, mallampalli2013fbxl12triggersg1 pages 1-2)
Trophoblast differentiation / placental development SCF^FBXL12 substrate receptor driving ubiquitin-dependent degradation of ALDH3 to permit trophoblast stem-cell differentiation ALDH3A1 and ALDH3A2; direct ubiquitylation shown in vitro and in cells; linkage not specified Differential proteomics (DiPIUS/LC-MS/MS); reciprocal co-IP; in vivo and in vitro ubiquitylation; shRNA depletion; CHX chase; ALDEFLUOR activity assay; Fbxl12 knockout mice; TSC differentiation and gossypol rescue Placental junctional zone; trophoblast stem/differentiating cells Nishiyama et al., 2015, STEM CELLS — https://doi.org/10.1002/stem.2088 (nishiyama2015fbxl12‐mediateddegradationof pages 9-10, nishiyama2015fbxl12‐mediateddegradationof pages 2-3, nishiyama2015fbxl12‐mediateddegradationof pages 1-2, nishiyama2015fbxl12‐mediateddegradationof pages 5-6, nishiyama2015fbxl12‐mediateddegradationof pages 3-5)
Thymocyte β-selection proliferation / pre-TCR and Notch signaling SCF-Fbxl12 substrate receptor acting with SCF-Fbxl1 to degrade Cdkn1b/p27 downstream of pre-TCR and Notch-driven transcriptional induction CDKN1B/p27; K48-linked polyubiquitylation; major ubiquitination site K165 Conditional mouse knockout (Lck-Cre Fbxl12^fl/fl); anti-CD3 induction; OP9-DL1/DL4 cultures; HEK293T overexpression/ubiquitylation assays; MG132; genetic rescue by Cdkn1b deletion; cell-cycle profiling DN/DP thymocytes; nuclear/cellular p27 turnover context in developing thymocytes Zhao et al., 2019, Nature Immunology — https://doi.org/10.1038/s41590-019-0469-z (zhao2019notchandthe pages 4-5, zhao2019notchandthe pages 10-11, zhao2019notchandthe pages 6-7, zhao2019notchandthe pages 3-4, zhao2019notchandthe pages 1-2, zhao2019notchandthe pages 5-6, zhao2019notchandthe pages 2-3)
Targeted protein degradation (TPD) platform potential Candidate broad-acting proximity-dependent degrader when forcibly recruited to heterologous substrates; role here is application-oriented rather than endogenous biology Not a defined endogenous substrate in this review excerpt; tested across 10 model substrates with different localizations Human ORFeome/proximity-dependent (de)stabilization screens using eGFP-ABI1 reporter, anti-GFP nanobody or PYL1/ABI1 dimerization, eGFP/BFP ratio readout; focused ligase screen Activity reported across substrates with varied subcellular localizations Hermanns & Hofmann, 2024, Signal Transduction and Targeted Therapy — https://doi.org/10.1038/s41392-024-01884-3 (summarizing screen results that included FBXL12) (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
General family annotation / baseline localization F-box + leucine-rich repeat SCF substrate-recognition subunit; exact substrate spectrum still incomplete Reported substrates/interactors across literature: ALDH3, Ku80, CaMKI, p21; linkage varies by substrate and is often unspecified in summaries Review synthesis of primary studies Cytoplasm and nucleus listed in review table Tekcham et al., 2020, Theranostics — https://doi.org/10.7150/thno.42735 (tekcham2020fboxproteinsand pages 4-6, tekcham2020fboxproteinsand pages 11-12)

Table: This table summarizes the strongest published functional annotation evidence for human FBXL12, organized by pathway, substrate, mechanism, localization, and study. It is useful for quickly distinguishing well-supported endogenous roles from broader translational or screening-based observations.

2.1 Replication stress tolerance via turnover of FANCD2 (2023–present)

A recent and mechanistically detailed study demonstrated that human SCF^FBXL12 promotes proteasomal degradation of FANCD2 to support replication recovery and survival under high replication stress (brunner2023fbxl12degradesfancd2 pages 1-3, brunner2023fbxl12degradesfancd2 pages 5-6). FBXL12 was identified as required for replication recovery (siRNA imaging screen) and then linked to a mechanism in which FBXL12 physically associates with SCF core components and Fanconi anemia proteins (FANCD2/FANCI), with interaction and regulation enriched in chromatin fractions (brunner2023fbxl12degradesfancd2 pages 5-6).

Mechanistic model: FANCD2 becomes a substrate of SCF^FBXL12 following CHK1-dependent phosphorylation, creating a phosphodegron that triggers FBXL12-dependent turnover, thereby helping clear “chromatin-trapped” FANCD2 at stalled forks and enabling replication restart (brunner2023fbxl12degradesfancd2 pages 1-3, brunner2023fbxl12degradesfancd2 pages 3-5). Functional phenotypes upon FBXL12 loss included replication-fork defects and increased DNA damage signaling (e.g., increased pan-γH2AX staining and CHK1 phosphorylation in some contexts), with strong viability dependencies in replication-stressed cancer models (brunner2023fbxl12degradesfancd2 pages 3-5, brunner2023fbxl12degradesfancd2 pages 5-6).

Visual evidence from this study shows the authors’ graphical model and quantitative DNA-fiber/viability/correlation analyses supporting the SCF^FBXL12–FANCD2 replication-stress axis (brunner2023fbxl12degradesfancd2 media dd0726f7, brunner2023fbxl12degradesfancd2 media 52998111).

2.2 DNA double-strand break response: Ku80 ubiquitylation/removal (mechanistic evidence; conservation inferred)

FBXL12 has also been implicated in DNA damage responses through targeting of Ku80, a key DNA end-binding factor in NHEJ. In a Xenopus egg extract system screening F-box proteins, an SCF complex containing Fbxl12 was required for DNA damage-induced Ku80 ubiquitylation, removal from DNA ends, and subsequent degradation (postow2013anscfcomplex pages 3-4, postow2013anscfcomplex pages 1-3). Ku80 was reported to undergo heavy K48-linked polyubiquitylation in this DSB context, consistent with proteasome-directed turnover (postow2013anscfcomplex pages 1-3).

Quantitative/biophysical context included in the study: Ku’s DNA-binding affinity was cited as Kd ~2 nM, and Ku concentration in human cells was estimated at ~300 nM, emphasizing the need for active mechanisms to remove Ku from DNA ends after repair initiation (postow2013anscfcomplex pages 1-3).

2.3 Cell-cycle control via CaMKI degradation and disruption of cyclin D1/CDK4 assembly (2013)

In lung epithelial cell models, FBXL12 (Fbxl12) was shown to mediate ubiquitin–proteasome degradation of CaMKI, causing G1 arrest via a mechanistic cascade involving p27 phosphorylation/localization and cyclin D1/CDK4 complex assembly (mallampalli2013fbxl12triggersg1 pages 1-2, mallampalli2013fbxl12triggersg1 pages 5-6). Direct biochemical evidence includes:
- In vitro ubiquitination of CaMKI using purified SCF components (CUL1/SKP1/RBX1 plus Fbxl12), E1, E2, and ubiquitin (mallampalli2013fbxl12triggersg1 pages 3-4).
- Identification of a key acceptor site: CaMKI K59R exhibited extended half-life and resistance to Fbxl12-driven degradation, supporting K59 as functionally important for ubiquitination-dependent turnover (mallampalli2013fbxl12triggersg1 pages 4-5).
- Proteasome dependence: MG132 stabilized CaMKI, whereas leupeptin did not (mallampalli2013fbxl12triggersg1 pages 3-4).

Subcellular context: Fbxl12 and CaMKI were reported to co-localize in the cytoplasm (mallampalli2013fbxl12triggersg1 pages 3-4). Downstream, p27 became predominantly nuclear when Fbxl12 was overexpressed, consistent with loss of CaMKI-driven p27 phosphorylation controlling p27 compartmentalization (mallampalli2013fbxl12triggersg1 pages 5-6).

Quantitative data example: flow cytometry readouts showed markedly lower S-phase percentages in Fbxl12 conditions compared with CaMKI overexpression across time points (S% values reported in the text/figures, e.g., Fbxl12 ~5.9–8.1 vs CaMKI up to ~40.2) consistent with G1 arrest (mallampalli2013fbxl12triggersg1 pages 6-7).

2.4 Placental development and trophoblast differentiation via ALDH3A1/2 degradation (2015)

A study in trophoblast stem cell (TSC) models and Fbxl12 knockout mice established that SCF^FBXL12 targets ALDH3A1 and ALDH3A2 for ubiquitin-dependent degradation and that this is essential for trophoblast differentiation and proper placental development (nishiyama2015fbxl12‐mediateddegradationof pages 1-2, nishiyama2015fbxl12‐mediateddegradationof pages 5-6). Evidence included:
- Reciprocal co-IP showing specific interaction of endogenous FBXL12 with ALDH3A1/2 (nishiyama2015fbxl12‐mediateddegradationof pages 5-6).
- In vivo and in vitro ubiquitination assays demonstrating SCF^FBXL12-dependent ubiquitination of ALDH3A1, requiring canonical ubiquitination components (E1 Uba1, E2 UbcH5C, ubiquitin) and the SCF complex (nishiyama2015fbxl12‐mediateddegradationof pages 2-3, nishiyama2015fbxl12‐mediateddegradationof pages 5-6).
- Functional causality: ALDH3A1 overexpression phenocopied FBXL12 deficiency, while ALDH inhibition (gossypol) partially rescued differentiation marker expression (e.g., Tpbpa) (nishiyama2015fbxl12‐mediateddegradationof pages 5-6).

Quantitative developmental outcomes included significant differences in embryo/newborn weights (p < .01) and marker gene expression changes (p < .01, Student’s t-test) associated with Fbxl12 loss (nishiyama2015fbxl12‐mediateddegradationof pages 9-10, nishiyama2015fbxl12‐mediateddegradationof pages 10-13).

2.5 Thymocyte β-selection: pre-TCR/Notch coordination and CDKN1B/p27 ubiquitination (2019)

In thymocyte development, SCF^Fbxl12 was shown to promote β-selection-associated proliferation by targeting the CDK inhibitor Cdkn1b (p27) for proteasomal degradation, in coordination with a related SCF complex containing Fbxl1 (zhao2019notchandthe pages 1-2, zhao2019notchandthe pages 6-7). Key mechanistic evidence includes:
- In cell-based ubiquitination assays, SCF-Fbxl12 promoted K48-linked polyubiquitination of Cdkn1b, with a key ubiquitination site identified at K165; Cdkn1b(K165R) strongly reduced polyubiquitination (zhao2019notchandthe pages 6-7, zhao2019notchandthe pages 3-4).
- F-box dependence: an Fbxl12 ΔF mutant abolished Cdkn1b polyubiquitination (zhao2019notchandthe pages 3-4).
- In vivo genetics: conditional Fbxl12 deletion (Lck-Cre Fbxl12^fl/fl) increased Cdkn1b abundance and reduced cycling populations; importantly, Cdkn1b deletion rescued T cell development defects, supporting Cdkn1b as the principal relevant substrate in this developmental context (zhao2019notchandthe pages 4-5, zhao2019notchandthe pages 5-6).

Quantitative examples: reducing Fbxl1/Fbxl12 dosage by ~50% (compound heterozygotes) caused a ~twofold increase in Cdkn1b and significantly attenuated cycling/proliferation (zhao2019notchandthe pages 10-11). The authors also contextualize β-selection as involving a large proliferative burst (estimated 100–200-fold expansion) and show that Fbxl12 contributes to enabling this expansion by relieving Cdkn1b-mediated cell-cycle inhibition (zhao2019notchandthe pages 1-2).

3. Recent developments (prioritizing 2023–2024)

3.1 FBXL12 as a replication-stress dependency and potential therapeutic node (2023)

The 2023 Molecular Cell study positions FBXL12 as a component of replication-stress tolerance, especially in Cyclin E-driven contexts, where FBXL12 loss exacerbates replication-fork defects and compromises survival (brunner2023fbxl12degradesfancd2 pages 3-5, brunner2023fbxl12degradesfancd2 pages 5-6). This provides a specific, mechanistically grounded hypothesis for how FBXL12 may contribute to tumor fitness under oncogene-induced replication stress.

3.2 FBXL12 in targeted protein degradation (TPD) screens (2024)

A 2024 review of proximity-dependent (de)stabilization screening highlights FBXL12 among top candidate effectors that can destabilize multiple recruited substrates with different subcellular localizations (assayed via eGFP/BFP ratiometric reporters and recruitment by nanobody or chemical dimerization), consistent with interest in FBXL12 as a potential E3 recruiter in induced-proximity degrader technologies (hermanns2024proximitydependentprotein(de)stabilization pages 1-2).

4. Current applications and real-world implementations

4.1 Cancer biology: replication stress, DNA damage responses, and drug sensitivity

FBXL12’s role in clearing FANCD2 from chromatin under replication stress suggests that manipulating this axis could modulate cancer vulnerabilities tied to replication stress and fork recovery (brunner2023fbxl12degradesfancd2 pages 1-3, brunner2023fbxl12degradesfancd2 pages 3-5). In this framework, FBXL12 has been linked to drug-response phenotypes in replication-stressed cancer contexts (including sensitization patterns reported with WEE1 inhibition in the primary study) (brunner2023fbxl12degradesfancd2 pages 1-3, brunner2023fbxl12degradesfancd2 pages 5-6).

4.2 TPD/induced proximity engineering

The proximity-screen literature suggests FBXL12 can act as a relatively “broad” destabilizer when artificially recruited to targets, which is conceptually relevant to the development of molecular glues or bifunctional degraders that harness specific E3 ligases (hermanns2024proximitydependentprotein(de)stabilization pages 1-2).

4.3 Disease associations (genetics/functional genomics)

Open Targets reports disease associations for FBXL12 including osteoarthritis (knee/hip), bronchial disease, neurodegenerative disease, and skeletal system abnormalities, based on curated evidence connected to PubMed records (PMIDs 34031600 and 39024449 listed in the Open Targets evidence view) (OpenTargets Search: -FBXL12). These associations are not, by themselves, mechanistic proof; rather, they indicate where human genetics/functional-genomics signals have implicated FBXL12 and may motivate deeper mechanistic follow-up.

5. Expert synthesis and analysis

5.1 A unifying functional model

Across diverse tissues and pathways, the most coherent model is that FBXL12 acts as a modular substrate receptor, and its biological “function” is best defined by its substrates in each context:
- In replication stress: FBXL12 limits persistence of chromatin-associated FANCD2 to facilitate fork recovery (brunner2023fbxl12degradesfancd2 pages 1-3).
- In G1 control: FBXL12 restricts CaMKI abundance, impacting p27 phosphorylation/localization and cyclin D/CDK4 complexing (mallampalli2013fbxl12triggersg1 pages 5-6, mallampalli2013fbxl12triggersg1 pages 3-4).
- In developmental differentiation: FBXL12 reduces ALDH3A1/2 levels to permit trophoblast differentiation and placental morphogenesis (nishiyama2015fbxl12‐mediateddegradationof pages 5-6, nishiyama2015fbxl12‐mediateddegradationof pages 9-10).
- In thymocyte development: FBXL12 directly ubiquitinates p27 (Cdkn1b) with K48 chains to enable proliferative expansion at β-selection (zhao2019notchandthe pages 6-7, zhao2019notchandthe pages 1-2).

5.2 Localization: primarily intracellular, with nucleus–cytoplasm partitioning depending on substrate biology

Experimental localization evidence is substrate/context dependent. FBXL12 and CaMKI co-localize in the cytoplasm (mallampalli2013fbxl12triggersg1 pages 3-4), whereas FANCD2 regulation is described as occurring in chromatin/replication-fork proximity with nuclear foci (brunner2023fbxl12degradesfancd2 pages 5-6). Reviews also summarize FBXL12 as present in cytoplasm and nucleus, consistent with multiple compartments and roles (tekcham2020fboxproteinsand pages 11-12).

6. Key statistics and data highlights (from recent and authoritative studies)

  • Replication stress (2023): FBXL12 depletion increases stalled forks and new origin firing (DNA fiber assays) and compromises cancer cell viability under replication stress; visualized quantitative panels and correlation analyses are provided in the primary study figures (brunner2023fbxl12degradesfancd2 media 52998111, brunner2023fbxl12degradesfancd2 media b9665031).
  • NHEJ context: Ku DNA-binding affinity Kd ~2 nM; Ku cellular concentration ~300 nM (background quantitative context supporting need for active Ku removal) (postow2013anscfcomplex pages 1-3).
  • Thymocyte β-selection: ~50% reduction in Fbxl1/Fbxl12 dosage leads to ~2-fold increase in Cdkn1b and reduced cycling; β-selection proliferative burst estimated 100–200-fold expansion (zhao2019notchandthe pages 10-11, zhao2019notchandthe pages 1-2).
  • Placental development: Fbxl12 deficiency associated with statistically significant developmental phenotypes including embryo/newborn weight differences (p < .01) and trophoblast marker expression differences (p < .01) (nishiyama2015fbxl12‐mediateddegradationof pages 9-10, nishiyama2015fbxl12‐mediateddegradationof pages 10-13).

7. Reference URLs (most central sources)

  • Brunner et al. Molecular Cell (published Oct 2023): https://doi.org/10.1016/j.molcel.2023.07.026 (brunner2023fbxl12degradesfancd2 pages 1-3)
  • Hermanns & Hofmann Signal Transduction and Targeted Therapy (published Jul 2024): https://doi.org/10.1038/s41392-024-01884-3 (hermanns2024proximitydependentprotein(de)stabilization pages 1-2)
  • Zhao et al. Nature Immunology (published Aug 2019): https://doi.org/10.1038/s41590-019-0469-z (zhao2019notchandthe pages 1-2)
  • Nishiyama et al. STEM CELLS (published Nov 2015): https://doi.org/10.1002/stem.2088 (nishiyama2015fbxl12‐mediateddegradationof pages 1-2)
  • Mallampalli et al. Cellular Signalling (published Oct 2013): https://doi.org/10.1016/j.cellsig.2013.05.012 (mallampalli2013fbxl12triggersg1 pages 1-2)
  • Postow & Funabiki Cell Cycle (published Feb 2013): https://doi.org/10.4161/cc.23408 (postow2013anscfcomplex pages 1-3)

8. Limitations of this synthesis

Some assertions about FBXL12 in DNA DSB repair (Ku80) are supported by strong biochemical evidence in Xenopus extracts with human ortholog inference, but direct confirmation in human cells was not retrieved in the current evidence set (postow2013anscfcomplex pages 1-3). Additionally, disease associations from Open Targets provide hypothesis-generating links rather than validated mechanisms (OpenTargets Search: -FBXL12).

References

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  19. (nishiyama2015fbxl12‐mediateddegradationof pages 3-5): Masaaki Nishiyama, Akihiro Nita, Kanae Yumimoto, and Keiichi I. Nakayama. Fbxl12‐mediated degradation of aldh3 is essential for trophoblast differentiation during placental development. STEM CELLS, 33:3327-3340, Nov 2015. URL: https://doi.org/10.1002/stem.2088, doi:10.1002/stem.2088. This article has 20 citations and is from a highest quality peer-reviewed journal.

  20. (zhao2019notchandthe pages 4-5): Bin Zhao, Kogulan Yoganathan, LiQi Li, Jan Y. Lee, Juan Carlos Zúñiga-Pflücker, and Paul E. Love. Notch and the pre-tcr coordinate thymocyte proliferation by induction of the scf subunits fbxl1 and fbxl12. Aug 2019. URL: https://doi.org/10.1038/s41590-019-0469-z, doi:10.1038/s41590-019-0469-z. This article has 42 citations and is from a highest quality peer-reviewed journal.

  21. (zhao2019notchandthe pages 10-11): Bin Zhao, Kogulan Yoganathan, LiQi Li, Jan Y. Lee, Juan Carlos Zúñiga-Pflücker, and Paul E. Love. Notch and the pre-tcr coordinate thymocyte proliferation by induction of the scf subunits fbxl1 and fbxl12. Aug 2019. URL: https://doi.org/10.1038/s41590-019-0469-z, doi:10.1038/s41590-019-0469-z. This article has 42 citations and is from a highest quality peer-reviewed journal.

  22. (zhao2019notchandthe pages 1-2): Bin Zhao, Kogulan Yoganathan, LiQi Li, Jan Y. Lee, Juan Carlos Zúñiga-Pflücker, and Paul E. Love. Notch and the pre-tcr coordinate thymocyte proliferation by induction of the scf subunits fbxl1 and fbxl12. Aug 2019. URL: https://doi.org/10.1038/s41590-019-0469-z, doi:10.1038/s41590-019-0469-z. This article has 42 citations and is from a highest quality peer-reviewed journal.

  23. (zhao2019notchandthe pages 5-6): Bin Zhao, Kogulan Yoganathan, LiQi Li, Jan Y. Lee, Juan Carlos Zúñiga-Pflücker, and Paul E. Love. Notch and the pre-tcr coordinate thymocyte proliferation by induction of the scf subunits fbxl1 and fbxl12. Aug 2019. URL: https://doi.org/10.1038/s41590-019-0469-z, doi:10.1038/s41590-019-0469-z. This article has 42 citations and is from a highest quality peer-reviewed journal.

  24. (zhao2019notchandthe pages 2-3): Bin Zhao, Kogulan Yoganathan, LiQi Li, Jan Y. Lee, Juan Carlos Zúñiga-Pflücker, and Paul E. Love. Notch and the pre-tcr coordinate thymocyte proliferation by induction of the scf subunits fbxl1 and fbxl12. Aug 2019. URL: https://doi.org/10.1038/s41590-019-0469-z, doi:10.1038/s41590-019-0469-z. This article has 42 citations and is from a highest quality peer-reviewed journal.

  25. (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.

  26. (tekcham2020fboxproteinsand pages 4-6): 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.

  27. (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.

  28. (brunner2023fbxl12degradesfancd2 media dd0726f7): Andrä Brunner, Qiuzhen Li, Samuele Fisicaro, Alexandros Kourtesakis, Johanna Viiliäinen, Henrik J. Johansson, Vijaya Pandey, Adarsh K. Mayank, Janne Lehtiö, James A. Wohlschlegel, Charles Spruck, Juha K. Rantala, Lukas M. Orre, and Olle Sangfelt. Fbxl12 degrades fancd2 to regulate replication recovery and promote cancer cell survival under conditions of replication stress. Oct 2023. URL: https://doi.org/10.1016/j.molcel.2023.07.026, doi:10.1016/j.molcel.2023.07.026. This article has 18 citations and is from a highest quality peer-reviewed journal.

  29. (brunner2023fbxl12degradesfancd2 media 52998111): Andrä Brunner, Qiuzhen Li, Samuele Fisicaro, Alexandros Kourtesakis, Johanna Viiliäinen, Henrik J. Johansson, Vijaya Pandey, Adarsh K. Mayank, Janne Lehtiö, James A. Wohlschlegel, Charles Spruck, Juha K. Rantala, Lukas M. Orre, and Olle Sangfelt. Fbxl12 degrades fancd2 to regulate replication recovery and promote cancer cell survival under conditions of replication stress. Oct 2023. URL: https://doi.org/10.1016/j.molcel.2023.07.026, doi:10.1016/j.molcel.2023.07.026. This article has 18 citations and is from a highest quality peer-reviewed journal.

  30. (nishiyama2015fbxl12‐mediateddegradationof pages 10-13): Masaaki Nishiyama, Akihiro Nita, Kanae Yumimoto, and Keiichi I. Nakayama. Fbxl12‐mediated degradation of aldh3 is essential for trophoblast differentiation during placental development. STEM CELLS, 33:3327-3340, Nov 2015. URL: https://doi.org/10.1002/stem.2088, doi:10.1002/stem.2088. This article has 20 citations and is from a highest quality peer-reviewed journal.

  31. (OpenTargets Search: -FBXL12): Open Targets Query (-FBXL12, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

  32. (brunner2023fbxl12degradesfancd2 media b9665031): Andrä Brunner, Qiuzhen Li, Samuele Fisicaro, Alexandros Kourtesakis, Johanna Viiliäinen, Henrik J. Johansson, Vijaya Pandey, Adarsh K. Mayank, Janne Lehtiö, James A. Wohlschlegel, Charles Spruck, Juha K. Rantala, Lukas M. Orre, and Olle Sangfelt. Fbxl12 degrades fancd2 to regulate replication recovery and promote cancer cell survival under conditions of replication stress. Oct 2023. URL: https://doi.org/10.1016/j.molcel.2023.07.026, doi:10.1016/j.molcel.2023.07.026. This article has 18 citations and is from a highest quality peer-reviewed journal.

Artifacts

Citations

  1. postow2013anscfcomplex pages 1-3
  2. zhao2019notchandthe pages 3-4
  3. zhao2019notchandthe pages 10-11
  4. zhao2019notchandthe pages 1-2
  5. tekcham2020fboxproteinsand pages 11-12
  6. zhao2019notchandthe pages 6-7
  7. postow2013anscfcomplex pages 3-4
  8. postow2013anscfcomplex pages 7-9
  9. zhao2019notchandthe pages 4-5
  10. zhao2019notchandthe pages 5-6
  11. zhao2019notchandthe pages 2-3
  12. tekcham2020fboxproteinsand pages 4-6
  13. https://doi.org/10.1016/j.molcel.2023.07.026
  14. https://doi.org/10.4161/cc.23408
  15. https://doi.org/10.1016/j.cellsig.2013.05.012
  16. https://doi.org/10.1002/stem.2088
  17. https://doi.org/10.1038/s41590-019-0469-z
  18. https://doi.org/10.1038/s41392-024-01884-3
  19. https://doi.org/10.7150/thno.42735
  20. https://doi.org/10.1016/j.molcel.2023.07.026,
  21. https://doi.org/10.1016/j.cellsig.2013.05.012,
  22. https://doi.org/10.1002/stem.2088,
  23. https://doi.org/10.1038/s41590-019-0469-z,
  24. https://doi.org/10.4161/cc.23408,
  25. https://doi.org/10.1038/s41392-024-01884-3,
  26. https://doi.org/10.7150/thno.42735,

📚 Additional Documentation

Pn Notes

(FBXL12-pn-notes.md)

FBXL12 PN Consistency Notes

  • Generated: 2026-06-18
  • Project: PROTEOSTASIS
  • Scope: PN consistency rereview against local AIGR review and available deep-research artifacts
  • UniProt: Q9NXK8
  • 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: FBXL12 (F-box/LRR-repeat protein 12; FBL12) is a substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex. Its N-terminal F-box motif binds SKP1, linking it to the CUL1-RBX1 catalytic core, and its leucine-rich repeats confer substrate selectivity, so that SCF(FBXL12) directs substrate-specific (often K48-linked) polyubiquitination and proteasomal degradation. Several physiological substrates have been defined in distinct cellular programs, with substrate selection frequently gated by substrate phosphorylation. SCF(FBXL12) degrades calcium/calmodulin-dependent protein kinase I (CAMK1; acceptor Lys59), which lowers CAMK1-driven p27 phosphorylation, disrupts cyclin D1/CDK4 complex assembly, and triggers G1 cell-cycle arrest in lung epithelia. It targets the cyclin-dependent kinase inhibitors p57KIP2/CDKN1C (TGF-beta1-induced, phosphorylation-dependent turnover linked to osteoblast differentiation) and CDKN1B/p27 (Lys165 acceptor; degraded together with SCF(FBXL1)/SKP2 downstream of pre-TCR and Notch signaling to license the proliferative burst of thymocyte beta-selection). It promotes CHK1-phosphorylation-dependent degradation of chromatin-associated FANCD2 to support replication-fork recovery and cancer-cell survival under replication stress, and degrades the aldehyde dehydrogenases ALDH3A1/ALDH3A2 to permit trophoblast differentiation during placental development. An SCF complex containing FBXL12 also mediates DNA-damage-induced K48-linked ubiquitination and removal of the NHEJ factor Ku80 from DNA ends (shown in Xenopus extracts, with conservation to human inferred). FBXL12 acts in both the cytoplasm (where it co-localizes with CAMK1) and the nucleus/chromatin (FANCD2, Ku80). Many of its catalogued interactions derive from high-throughput proteomic screens and are not established functional substrates.
  • Existing/core annotation action counts: ACCEPT: 4; KEEP_AS_NON_CORE: 18; NEW: 1

PN Consistency Summary

  • Consistency: Strong. Deep research (falcon, marked VERIFIED here, cross-checked vs UniProt + cached PMID:18660753), review, PN annotation, and node mapping agree FBXL12 is the SCF(FBXL12) receptor with multiple substrates (p57KIP2/CDKN1C validated IDA PMID:18660753; CAMK1 PMID:23707388; plus falcon leads FANCD2, p27/CDKN1B-K165, ALDH3A1/2, Ku80). No contradictions.
  • PN story / NEW pressure: PN asserts the generic adaptor MF. FBXL12 GOA has NO MF beyond protein binding. The review adds GO:1990756 as action: NEW (IDA, PMID:18660753) — the batch-correct call, matching the PN-projected new_to_goa term. BPs (SCF catabolism, regulation of cell cycle) already captured. Conclusion: adaptor MF correctly ADDED as NEW; no over-reach.
  • Evidence alignment: PN cites only "15340381/rev"; review uses gene-specific primaries (18660753, 23707388, 33234069) + falcon leads. No overlap with the PN placeholder; review evidence richer. Benign divergence.
  • Verdict: CONSISTENT / ACCEPT mapping. Correct NEW→GO:1990756 application with a validated substrate anchor. No edits required.

Full Consistency Review

  • UniProt: Q9NXK8 · batch: proteostasis-batch-2026-06-13 · review status: COMPLETE
  • PN placement: UPS|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box|LRR ; PN-node mapping: group-level mapped / ok_for_propagation_to_go / GO:1990756; class context_only / too_broad / GO:0061630.
  • Consistency: Strong. Deep research (falcon, marked VERIFIED here, cross-checked vs UniProt + cached PMID:18660753), review, PN annotation, and node mapping agree FBXL12 is the SCF(FBXL12) receptor with multiple substrates (p57KIP2/CDKN1C validated IDA PMID:18660753; CAMK1 PMID:23707388; plus falcon leads FANCD2, p27/CDKN1B-K165, ALDH3A1/2, Ku80). No contradictions.
  • PN story / NEW pressure: PN asserts the generic adaptor MF. FBXL12 GOA has NO MF beyond protein binding. The review adds GO:1990756 as action: NEW (IDA, PMID:18660753) — the batch-correct call, matching the PN-projected new_to_goa term. BPs (SCF catabolism, regulation of cell cycle) already captured. Conclusion: adaptor MF correctly ADDED as NEW; no over-reach.
  • Mapping strategy: Gene does not change the node. Status/scope right; PN-projected GO:1990756 equals the review MF (not broader/narrower). Has a PMID-validated substrate (p57KIP2 IDA) — canonical receptor, NOT an orphan. Cytoplasmic + nuclear/chromatin dual localization is gene-specific and rightly outside the shared node mapping.
  • Evidence alignment: PN cites only "15340381/rev"; review uses gene-specific primaries (18660753, 23707388, 33234069) + falcon leads. No overlap with the PN placeholder; review evidence richer. Benign divergence.
  • Verdict: CONSISTENT / ACCEPT mapping. Correct NEW→GO:1990756 application with a validated substrate anchor. No edits required.

PN Dossier Context

  • review_batch: proteostasis-batch-2026-06-13
  • review_yaml: genes/human/FBXL12/FBXL12-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: Q9NXK8
  • In branches: UPS
  • Signature domains: IPR001810
  • Auxiliary domains: IPR032675
  • PN references (titles):
    • 15340381 / rev
  • PN-node mapping records (path + ancestors):
    • [subtype] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box|LRR
      status=no_mapping scope= GO=[]
      rationale: Reviewed as a narrower substrate-receptor, adaptor, domain, or family subdivision already covered by the curated parent adaptor/receptor mapping. No additional direct GO mapping is needed at this node.
    • [type] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor|F-box
      status=no_mapping scope= GO=[]
      rationale: Reviewed as a narrower substrate-receptor, adaptor, domain, or family subdivision already covered by the curated parent adaptor/receptor mapping. No additional direct GO mapping is needed at this node.
    • [group] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases|Cul1 substrate receptor
      status=mapped scope=ok_for_propagation_to_go GO=[GO:1990756 ubiquitin-like ligase-substrate adaptor activity]
      rationale: This PN group captures substrate receptors/adaptors for cullin/UBL ligase systems. The shared GO molecular-function target is ubiquitin-like ligase-substrate adaptor activity.
    • [class] Ubiquitin Proteasome System|E3 ubiquitin and UBL ligases
      status=context_only scope=too_broad_to_propagate GO=[GO:0061630 ubiquitin protein ligase activity]
      rationale: This class is a genuine E3-ligase context, but its descendants include catalytic ligases, cullin scaffolds, substrate receptors, adaptors, cofactors, regulators, and UBL modifier systems. A class-level propagation would over-annotate.
    • [branch] Ubiquitin Proteasome System
      status=no_mapping scope= GO=[]
      rationale: Reviewed as the top-level UPS branch. It is a project taxonomy umbrella rather than a direct GO assertion; UPS propagation must come from manually curated child nodes.

Projected GO annotations (1)

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

Note

This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.

📄 View Raw YAML

id: Q9NXK8
gene_symbol: FBXL12
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  FBXL12 (F-box/LRR-repeat protein 12; FBL12) is a substrate-recognition
  subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex. Its N-terminal
  F-box motif binds SKP1, linking it to the CUL1-RBX1 catalytic core, and its
  leucine-rich repeats confer substrate selectivity, so that SCF(FBXL12) directs
  substrate-specific (often K48-linked) polyubiquitination and proteasomal
  degradation. Several physiological substrates have been defined in distinct
  cellular programs, with substrate selection frequently gated by substrate
  phosphorylation. SCF(FBXL12) degrades calcium/calmodulin-dependent protein
  kinase I (CAMK1; acceptor Lys59), which lowers CAMK1-driven p27 phosphorylation,
  disrupts cyclin D1/CDK4 complex assembly, and triggers G1 cell-cycle arrest in
  lung epithelia. It targets the cyclin-dependent kinase inhibitors p57KIP2/CDKN1C
  (TGF-beta1-induced, phosphorylation-dependent turnover linked to osteoblast
  differentiation) and CDKN1B/p27 (Lys165 acceptor; degraded together with
  SCF(FBXL1)/SKP2 downstream of pre-TCR and Notch signaling to license the
  proliferative burst of thymocyte beta-selection). It promotes
  CHK1-phosphorylation-dependent degradation of chromatin-associated FANCD2 to
  support replication-fork recovery and cancer-cell survival under replication
  stress, and degrades the aldehyde dehydrogenases ALDH3A1/ALDH3A2 to permit
  trophoblast differentiation during placental development. An SCF complex
  containing FBXL12 also mediates DNA-damage-induced K48-linked ubiquitination
  and removal of the NHEJ factor Ku80 from DNA ends (shown in Xenopus extracts,
  with conservation to human inferred). FBXL12 acts in both the cytoplasm (where
  it co-localizes with CAMK1) and the nucleus/chromatin (FANCD2, Ku80). Many of
  its catalogued interactions derive from high-throughput proteomic screens and
  are not established functional substrates.
alternative_products:
- name: '1'
  id: Q9NXK8-1
- name: '2'
  id: Q9NXK8-2
  sequence_note: VSP_008859
existing_annotations:
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:18660753
  qualifier: enables
  review:
    summary: Interactions with CDKN1C/p57KIP2 (P49918) and SKP1 (P63208) from the study showing SCF(FBL12) directly ubiquitinates p57KIP2. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records functionally important substrate (CDKN1C) and SKP1 interactions, but bare protein binding is uninformative per curation guidelines; the substrate relationship is captured by the catabolic-process annotations.
    supported_by:
    - reference_id: PMID:18660753
      supporting_text: FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:21163940
  qualifier: enables
  review:
    summary: Interaction with RNF32 (Q9H0A6) from an Alzheimer's-disease interactome map. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput interaction of uncertain functional significance; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; Q9H0A6: RNF32; NbExp=2; IntAct=EBI-719790, EBI-724829;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: High-throughput interactions (e.g. DOCK8, LNX1) from a proteome-scale interactome. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput interactions of uncertain functional significance; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; Q8TBB1: LNX1; NbExp=3; IntAct=EBI-719790, EBI-739832;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27705803
  qualifier: enables
  review:
    summary: Interaction with SKP1 (P63208) from a Polycomb complexome map. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the FBXL12-SKP1 association required for SCF assembly, but bare protein binding is uninformative; captured by the ubiquitin ligase complex annotation.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: Interactions (GEMIN4, SKP1) from a binary interactome reference map. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput interactions; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; P57678: GEMIN4; NbExp=3; IntAct=EBI-719790, EBI-356700;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: Interaction with SKP1 (P63208) from a cell-specific proteome-scale interactome. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput SKP1 interaction; bare protein binding is uninformative and is subsumed by the ubiquitin ligase complex annotation.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: Interaction with SKP1 (P63208) from a multimodal cell-map genomics study. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput SKP1 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: 'Q9NXK8; P63208: SKP1; NbExp=11; IntAct=EBI-719790, EBI-307486;'
- term:
    id: GO:0000151
    label: ubiquitin ligase complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: part_of
  review:
    summary: Ortholog-based electronic assignment of ubiquitin ligase complex membership, consistent with FBXL12 being an SCF substrate-recognition subunit.
    action: ACCEPT
    reason: Correct core cellular component; FBXL12 assembles into SCF(FBXL12). A more specific SCF complex term would be preferable.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: Combined automated electronic assignment of cytoplasmic localization, consistent with the cytosolic Reactome annotations.
    action: ACCEPT
    reason: Plausible localization for a cytosolic SCF substrate receptor; consistent with TAS cytosol annotations.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- 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 FBXL12's role in substrate ubiquitination.
    action: ACCEPT
    reason: Correct but generic; the SCF-dependent catabolic process term better captures the role. Supported by direct ubiquitination of p57KIP2.
    supported_by:
    - reference_id: PMID:18660753
      supporting_text: FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
- term:
    id: GO:0031146
    label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
  evidence_type: NAS
  original_reference_id: PMID:33234069
  qualifier: involved_in
  review:
    summary: ComplexPortal author statement that FBXL12 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 p57KIP2 degradation (PMID:18660753).
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0051726
    label: regulation of cell cycle
  evidence_type: NAS
  original_reference_id: PMID:33234069
  qualifier: involved_in
  review:
    summary: ComplexPortal author statement linking FBXL12 to cell-cycle regulation, consistent with degradation of the CDK inhibitors p57KIP2/CDKN1C and CDKN1B/p27 and of CAMK1 (G1 arrest; thymocyte beta-selection proliferation).
    action: KEEP_AS_NON_CORE
    reason: Supported downstream regulatory role (via CAMK1, p57KIP2/CDKN1C and CDKN1B/p27 turnover) but a generic process distinct from the core substrate-receptor activity.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: disruption of cyclin D1/CDK4 complex assembly which results in G1 cell cycle arrest in lung epithelia
    - reference_id: file:human/FBXL12/FBXL12-deep-research-falcon.md
      supporting_text: >-
        SCF-Fbxl12 promoted **K48-linked polyubiquitination** of Cdkn1b, with a key
        ubiquitination site identified at **K165**; Cdkn1b(K165R) strongly reduced
        polyubiquitination
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8952618
  qualifier: located_in
  review:
    summary: Reactome curation of cytosolic localization within generic CRL1/NEDD8-cycle reactions. Plausible localization, though derived from pathway context.
    action: KEEP_AS_NON_CORE
    reason: Generic CRL-cycle pathway annotation (NEDD8 transfer); reflects the shared cytosolic CRL machinery rather than FBXL12-specific function.
    supported_by:
    - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8952620
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8955241
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8955289
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8956040
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-8956200
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-983140
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-983147
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-983156
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-983157
  qualifier: located_in
  review:
    summary: Reactome 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/FBXL12/FBXL12-uniprot.txt
      supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
- term:
    id: GO:1990756
    label: ubiquitin-like ligase-substrate adaptor activity
  evidence_type: IDA
  original_reference_id: PMID:18660753
  qualifier: enables
  review:
    summary: Proposed core molecular function. As the LRR substrate-recognition subunit of SCF(FBXL12), FBXL12 selects substrates such as p57KIP2/CDKN1C (and CAMK1) for SCF-dependent ubiquitination. This more informative MF term is not in the GOA.
    action: NEW
    reason: Captures the precise molecular function of FBXL12 as an SCF substrate-recognition adaptor, more informative than the bare protein binding annotations.
    supported_by:
    - reference_id: PMID:18660753
      supporting_text: FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
references:
- id: GO_REF:0000041
  title: Gene Ontology annotation based on UniPathway vocabulary mapping
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:18660753
  title: A new ubiquitin ligase involved in p57KIP2 proteolysis regulates osteoblast
    cell differentiation.
  findings:
  - statement: FBL12/FBXL12 forms an SCF(FBL12) complex and directly ubiquitinates p57KIP2/CDKN1C in a phosphorylation-dependent manner downstream of TGF-beta1, regulating osteoblast differentiation.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified (EMBO Rep 2008), full text available; establishes p57KIP2/CDKN1C as a direct SCF(FBXL12) substrate.
- id: PMID:21163940
  title: Interactome mapping suggests new mechanistic details underlying Alzheimer's
    disease.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of a bare protein binding (RNF32) annotation.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of bare protein binding annotations.
- id: PMID:27705803
  title: A High-Density Map for Navigating the Human Polycomb Complexome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput complexome map; source of an SKP1 interaction (bare protein binding).
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Binary interactome reference map; source of bare protein binding annotations.
- id: PMID:33234069
  title: 'The FBXL family of F-box proteins: variations on a theme.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Review of the FBXL family; basis for the ComplexPortal NAS SCF-catabolic-process and cell-cycle annotations.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of an SKP1 interaction (bare protein binding).
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput cell-map genomics; source of an SKP1 interaction (bare protein binding).
- id: PMID:23707388
  title: Fbxl12 triggers G1 arrest by mediating degradation of calmodulin kinase I.
  findings:
  - statement: FBXL12 mediates polyubiquitination and proteasomal degradation of CAMK1, disrupting cyclin D1/CDK4 complex assembly and causing G1 cell-cycle arrest in lung epithelia.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cited in UniProt FUNCTION as the source of the CAMK1-degradation role (Cell Signal 2013); not in the publications cache, so supporting quotes for this claim are drawn from the UniProt entry.
- 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/FBXL12/FBXL12-deep-research-falcon.md
  title: Falcon deep research report for human FBXL12
  findings:
  - statement: FBXL12 is an SCF (SKP1-CUL1-RBX1) substrate-recognition subunit whose biology is best defined by its substrates in different cellular programs, including FANCD2, CaMKI, ALDH3A1/2, and CDKN1B/p27.
    supporting_text: >-
      SCF substrate-recognition subunit that drives ubiquitin-dependent remodeling
      of protein abundance (often proteasomal degradation) for specific substrates
      in distinct biological programs: replication stress recovery (FANCD2),
      cell-cycle gating (CaMKI; CDKN1B/p27), and differentiation programs (ALDH3A1/2).
  - statement: Human SCF(FBXL12) promotes CHK1-phosphorylation-dependent proteasomal degradation of chromatin-associated FANCD2 to enable replication-fork recovery and cancer-cell survival under replication stress.
    supporting_text: >-
      FANCD2 becomes a substrate of SCF^FBXL12 following **CHK1-dependent
      phosphorylation**, creating a phosphodegron that triggers FBXL12-dependent
      turnover, thereby helping clear "chromatin-trapped" FANCD2 at stalled forks
      and enabling replication restart
  - statement: SCF(FBXL12) targets ALDH3A1 and ALDH3A2 for ubiquitin-dependent degradation, which is essential for trophoblast differentiation during placental development.
    supporting_text: >-
      SCF^FBXL12 targets **ALDH3A1 and ALDH3A2** for ubiquitin-dependent degradation
      and that this is **essential for trophoblast differentiation** and proper
      placental development
  - statement: SCF(FBXL12) directly K48-polyubiquitinates CDKN1B/p27 (acceptor K165) to license the proliferative burst of thymocyte beta-selection downstream of pre-TCR and Notch signaling.
    supporting_text: >-
      SCF-Fbxl12 promoted **K48-linked polyubiquitination** of Cdkn1b, with a key
      ubiquitination site identified at **K165**; Cdkn1b(K165R) strongly reduced
      polyubiquitination
  - statement: An SCF complex containing Fbxl12 mediates DNA-damage-induced ubiquitination of Ku80 and its removal from DNA ends (Xenopus extracts, human conservation inferred).
    supporting_text: >-
      an **SCF complex containing Fbxl12** was required for **DNA damage-induced
      Ku80 ubiquitylation**, removal from DNA ends, and subsequent degradation
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Falcon synthesis cross-checked against UniProt (CAMK1 FUNCTION; CDKN1C IntAct)
      and the cached PMID:18660753 (p57KIP2). Additional substrate axes (FANCD2 /
      Brunner 2023 Mol Cell; ALDH3A1-2 / Nishiyama 2015 Stem Cells; CDKN1B-p27 /
      Zhao 2019 Nat Immunol; Ku80 / Postow 2013 Cell Cycle) are reported via
      author-year DOIs not in the PMID cache, so treated as leads but drawn from
      peer-reviewed primary studies; not added as new GOA terms.
core_functions:
- description: Substrate-recognition subunit of an SCF (SKP1-CUL1-RBX1) E3 ubiquitin ligase complex that selects (frequently phosphorylation-gated) substrates, including the CDK inhibitors p57KIP2/CDKN1C and CDKN1B/p27 and the kinase CAMK1, for SCF-dependent polyubiquitination and proteasomal degradation.
  molecular_function:
    id: GO:1990756
    label: ubiquitin-like ligase-substrate adaptor activity
  locations:
  - id: GO:0005829
    label: cytosol
  - id: GO:0005634
    label: nucleus
  supported_by:
  - reference_id: PMID:18660753
    supporting_text: FBL12 formed an SCF(FBL12) complex and directly ubiquitinated p57(KIP2) in a phosphorylation-dependent manner
  - reference_id: file:human/FBXL12/FBXL12-uniprot.txt
    supporting_text: Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex
  directly_involved_in:
  - id: GO:0031146
    label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
- description: As the SCF(FBXL12) substrate receptor, promotes CHK1-phosphorylation-dependent proteasomal degradation of chromatin-associated FANCD2, clearing replication-stalled FANCD2 to support replication-fork recovery and cancer-cell survival under replication stress.
  molecular_function:
    id: GO:1990756
    label: ubiquitin-like ligase-substrate adaptor activity
  locations:
  - id: GO:0005634
    label: nucleus
  supported_by:
  - reference_id: file:human/FBXL12/FBXL12-deep-research-falcon.md
    supporting_text: >-
      FANCD2 becomes a substrate of SCF^FBXL12 following **CHK1-dependent
      phosphorylation**, creating a phosphodegron that triggers FBXL12-dependent
      turnover, thereby helping clear "chromatin-trapped" FANCD2 at stalled forks
      and enabling replication restart
  directly_involved_in:
  - id: GO:0031146
    label: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process
proposed_new_terms: []
suggested_questions:
- question: What is the complete physiological substrate repertoire of SCF(FBXL12), and what degron/phosphodegron features (e.g. CHK1, CK2, TGF-beta-driven) does its LRR domain recognize across substrates?
- question: How is FBXL12 partitioned between cytoplasmic (CAMK1) and nuclear/chromatin (FANCD2, Ku80, p27) substrate pools, and what determines context-specific substrate choice in cell cycle, replication stress, development, and immunity?
suggested_experiments:
- description: Reconstitute SCF(FBXL12)-mediated ubiquitination in vitro with purified SKP1-CUL1-RBX1-FBXL12, an E2, and phosphorylated versus unphosphorylated substrates (p57KIP2, CAMK1, CDKN1B/p27, CHK1-phosphorylated FANCD2) to define the phosphodegron requirement and map ubiquitination sites.
- description: Perform quantitative ubiquitinome/proteome profiling in FBXL12-knockout versus control cells (including replication-stressed cancer models and differentiating trophoblast/thymocyte systems) to define the endogenous substrate landscape and validate the cell-cycle, replication-stress, and developmental consequences.