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 |
Loading supporting content…
Download this section (compressed HTML)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.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)