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.
| 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
|
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?
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.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The 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).
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).
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)
| 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.
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).
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).
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).
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).
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).
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.
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).
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).
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).
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.
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).
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).
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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(postow2013anscfcomplex pages 3-4): Lisa Postow and Hironori Funabiki. An scf complex containing fbxl12 mediates dna damage-induced ku80 ubiquitylation. Cell Cycle, 12:587-595, Feb 2013. URL: https://doi.org/10.4161/cc.23408, doi:10.4161/cc.23408. This article has 82 citations and is from a peer-reviewed journal.
(postow2013anscfcomplex pages 7-9): Lisa Postow and Hironori Funabiki. An scf complex containing fbxl12 mediates dna damage-induced ku80 ubiquitylation. Cell Cycle, 12:587-595, Feb 2013. URL: https://doi.org/10.4161/cc.23408, doi:10.4161/cc.23408. This article has 82 citations and is from a peer-reviewed journal.
(mallampalli2013fbxl12triggersg1 pages 9-10): Rama K. Mallampalli, Leah Kaercher, Courtney Snavely, Roopa Pulijala, Bill B. Chen, Tiffany Coon, Jing Zhao, and Marianna Agassandian. Fbxl12 triggers g1 arrest by mediating degradation of calmodulin kinase i. Cellular signalling, 25 10:2047-59, Oct 2013. URL: https://doi.org/10.1016/j.cellsig.2013.05.012, doi:10.1016/j.cellsig.2013.05.012. This article has 29 citations and is from a peer-reviewed journal.
(mallampalli2013fbxl12triggersg1 pages 4-5): Rama K. Mallampalli, Leah Kaercher, Courtney Snavely, Roopa Pulijala, Bill B. Chen, Tiffany Coon, Jing Zhao, and Marianna Agassandian. Fbxl12 triggers g1 arrest by mediating degradation of calmodulin kinase i. Cellular signalling, 25 10:2047-59, Oct 2013. URL: https://doi.org/10.1016/j.cellsig.2013.05.012, doi:10.1016/j.cellsig.2013.05.012. This article has 29 citations and is from a peer-reviewed journal.
(mallampalli2013fbxl12triggersg1 pages 6-7): Rama K. Mallampalli, Leah Kaercher, Courtney Snavely, Roopa Pulijala, Bill B. Chen, Tiffany Coon, Jing Zhao, and Marianna Agassandian. Fbxl12 triggers g1 arrest by mediating degradation of calmodulin kinase i. Cellular signalling, 25 10:2047-59, Oct 2013. URL: https://doi.org/10.1016/j.cellsig.2013.05.012, doi:10.1016/j.cellsig.2013.05.012. This article has 29 citations and is from a peer-reviewed journal.
(mallampalli2013fbxl12triggersg1 pages 1-2): Rama K. Mallampalli, Leah Kaercher, Courtney Snavely, Roopa Pulijala, Bill B. Chen, Tiffany Coon, Jing Zhao, and Marianna Agassandian. Fbxl12 triggers g1 arrest by mediating degradation of calmodulin kinase i. Cellular signalling, 25 10:2047-59, Oct 2013. URL: https://doi.org/10.1016/j.cellsig.2013.05.012, doi:10.1016/j.cellsig.2013.05.012. This article has 29 citations and is from a peer-reviewed journal.
(nishiyama2015fbxl12‐mediateddegradationof pages 9-10): 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.
(nishiyama2015fbxl12‐mediateddegradationof pages 2-3): 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.
(nishiyama2015fbxl12‐mediateddegradationof pages 1-2): 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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
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.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.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.This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
id: 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.