| Category | Specific finding | Evidence type/assay | Key details | Source |
|---|---|---|---|---|
| complex | FBXW8 is the substrate-recognition F-box/WD40 subunit of a CUL7-based SCF-like E3 ligase | Review synthesis of biochemical/genetic studies | Complex includes SKP1, FBXW8, CUL7, RBX1/ROC1; WD40 region implicated in substrate binding | Sarikas 2008, *Cell Cycle* (Oct 2008). DOI: https://doi.org/10.4161/cc.7.20.6922 (pqac-00000001) |
| complex | FBXW8 is one of the very few F-box proteins reported to partner with CUL7 | Review of primary studies | C-terminal WD40 repeats mediate substrate recognition; reported CUL7/FBXW8 substrates include cyclin D1, IRS1, HPK1, GRASP65, MRFAP1 | Shi 2020, *Oncogenesis* (Oct 2020). DOI: https://doi.org/10.1038/s41389-020-00276-w (pqac-00000003, pqac-00000005) |
| partner | FBXW8 bridges CUL1 and CUL7 complexes | Co-immunoprecipitation, domain mapping, knockout mouse biochemistry | F-box/Skp1-dependent binding to CUL1; central/C-terminal FBXW8 regions bind CUL7 independently of canonical F-box interaction | Tsunematsu 2006, *Molecular and Cellular Biology* (Aug 2006). DOI: https://doi.org/10.1128/mcb.00595-06 (pqac-00000008, pqac-00000037) |
| complex | FBXW8 is essential for CUL1-CUL7 complex formation | Biochemistry in knockout tissues/cells | Proposed Rbx1-Cul1-Skp1-Fbxw8-Cul7-Rbx1 assembly; CUL7 stabilizes FBXW8 protein | Tsunematsu 2006, *Molecular and Cellular Biology* (Aug 2006). DOI: https://doi.org/10.1128/mcb.00595-06 (pqac-00000008, pqac-00000034) |
| complex | CRL7^FBXW8 is an atypical multi-cullin E3 in which CUL7 recruits substrate while neddylated CUL1-RBX1 provides catalytic activity | Cryo-EM structure and reconstituted biochemistry | CUL7 binds FBXW8 in an F-box-independent mode; CRL7^FBXW8 alone lacks auto-neddylation/ubiquitination activity; catalytic coupling occurs to CUL1-RBX1 | Hopf 2022, *Nature Structural & Molecular Biology* (Aug 2022). DOI: https://doi.org/10.1038/s41594-022-00815-6 (pqac-00000002, pqac-00000007) |
| substrate | Cyclin D1 is an FBXW8 substrate | Co-IP, in vitro ubiquitination, siRNA knockdown, pulse-chase, fractionation/immunofluorescence | Recognition requires ERK/MAPK-mediated Thr286 phosphorylation; cyclin D1 D-domain (aa179-193) supports phosphorylation; degradation occurs mainly in cytoplasm during S phase | Okabe 2006, *PLoS ONE* (Dec 2006). DOI: https://doi.org/10.1371/journal.pone.0000128 (pqac-00000009, pqac-00000011, pqac-00000012, pqac-00000014, pqac-00000016) |
| regulation | FBXW8-dependent cyclin D1 turnover is MAPK/ERK regulated | ERK2 kinase assay, MEK inhibitor, phospho-specific immunoblot, pulse-chase | U0126 reduces Thr286 phosphorylation and extends cyclin D1 half-life from 22.5 min to 54.6 min | Okabe 2006, *PLoS ONE* (Dec 2006). DOI: https://doi.org/10.1371/journal.pone.0000128 (pqac-00000014, pqac-00000015) |
| localization | FBXW8 is predominantly cytoplasmic in G1/S in the cyclin D1 system | V5-tagged expression, cell fractionation, immunofluorescence | Spatial separation explains timing: FBXW8 cytoplasmic, cyclin D1 nuclear in G1 then exported in S phase for degradation | Okabe 2006, *PLoS ONE* (Dec 2006). DOI: https://doi.org/10.1371/journal.pone.0000128 (pqac-00000009, pqac-00000011, pqac-00000012) |
| substrate | IRS1 is a CUL7/FBXW8 target in insulin/IGF signaling | Primary mechanistic study summarized in review | Ubiquitin-dependent degradation of IRS1; linked to mTOR/S6K-dependent serine phosphorylation and negative feedback on signaling | Xu 2008, *Molecular Cell* (May 2008), summarized by Sarikas 2008, *Cell Cycle* (Oct 2008). DOI: https://doi.org/10.1016/j.molcel.2008.03.009; https://doi.org/10.4161/cc.7.20.6922 (pqac-00000001, pqac-00000007) |
| substrate | HPK1 is a CUL7/FBXW8 substrate | Interaction screen, IP/IB, MG132 rescue, knockdown, proliferation assays | Degradation is proteasome-dependent and requires HPK1 kinase activity/autophosphorylation; PP4 antagonizes FBXW8 action via HPK1 Thr355 dephosphorylation | Wang 2014, *Journal of Biological Chemistry* (Feb 2014). DOI: https://doi.org/10.1074/jbc.M113.520106 (pqac-00000013) |
| regulation | HPK1 stability is controlled by a phosphorylation-sensitive FBXW8 mechanism | Phosphatase and mutational analysis | Thr355 is a key PP4-controlled site through which CUL7/FBXW8 regulates HPK1 turnover | Wang 2014, *Journal of Biological Chemistry* (Feb 2014). DOI: https://doi.org/10.1074/jbc.M113.520106 (pqac-00000013) |
| substrate | MRFAP1 is an FBXW8 substrate during mitotic exit | IP-proteomics, co-IP, co-localization, ubiquitination assay, half-life analysis | Cul7/FBXW8 promotes MRFAP1 degradation during anaphase-telophase; FBXW8 overexpression increases polyubiquitination and knockdown prolongs half-life | Li 2017, *Oncotarget* (Oct 2017). DOI: https://doi.org/10.18632/oncotarget.21843 (pqac-00000010) |
| localization | In the MRFAP1 study, FBXW8 is mainly cytoplasmic with limited nuclear signal | Immunofluorescence co-localization | MRFAP1 is mainly nuclear; overlap supports substrate engagement near mitotic transition | Li 2017, *Oncotarget* (Oct 2017). DOI: https://doi.org/10.18632/oncotarget.21843 (pqac-00000010) |
| substrate | ATGL is a newly defined FBXW8 substrate in metabolic regulation | siRNA screen, co-IP, ubiquitination assay, organelle fractionation, mouse liver genetics | Golgi-localized CUL7-FBXW8 directly interacts with ATGL and mediates K48-linked polyubiquitylation/proteasomal degradation | Ding 2024, *Nature Cell Biology* (Apr 2024). DOI: https://doi.org/10.1038/s41556-024-01386-y (pqac-00000019, pqac-00000021, pqac-00000024, pqac-00000038) |
| regulation | FBXW8 Golgi recruitment is controlled by Golgi PtdIns4P and intracellular glucose | Cell biology, phosphoinositide perturbation, localization assays | FBXW8 has a polybasic N-terminal region binding Golgi PtdIns4P; glucose deprivation lowers Golgi PtdIns4P, reduces FBXW8/CUL7 assembly at Golgi, stabilizes ATGL, and increases lipolysis | Ding 2024, *Nature Cell Biology* (Apr 2024). DOI: https://doi.org/10.1038/s41556-024-01386-y (pqac-00000017, pqac-00000019, pqac-00000022, pqac-00000038) |
| localization | FBXW8 functions at the Golgi in the ATGL pathway | Immunofluorescence, Golgi fractionation, model figure | Golgi PtdIns4P recruits FBXW8/CUL7; ATGL localizes to Golgi and is ubiquitinated there before turnover | Ding 2024, *Nature Cell Biology* (Apr 2024). DOI: https://doi.org/10.1038/s41556-024-01386-y (pqac-00000021, pqac-00000024, pqac-00000038) |
| application | The Golgi PtdIns4P-CUL7-FBXW8-ATGL axis is actionable in steatosis/MASH models | Mouse genetics, pharmacology, ex vivo human liver perfusion | Genetic/pharmacologic modulation reduced hepatic triglycerides and improved steatosis; UCB9608 increased ATGL and improved steatotic phenotypes, including in an ex vivo human steatotic liver graft | Ding 2024, *Nature Cell Biology* (Apr 2024). DOI: https://doi.org/10.1038/s41556-024-01386-y (pqac-00000017, pqac-00000018, pqac-00000023) |
| substrate | FBXW8 targets a viral protein, the PDCoV nucleocapsid (N), as an antiviral effector | Co-IP, GST pull-down, CHX chase, ubiquitination assays, inhibitor studies | FBXW8 directly binds PDCoV N via its F-box-dependent interaction and shortens N half-life | Ji 2024, *Frontiers in Immunology* (Nov 2024). DOI: https://doi.org/10.3389/fimmu.2024.1457255 (pqac-00000025, pqac-00000027, pqac-00000030) |
| regulation | FBXW8 catalyzes K48-linked ubiquitination of PDCoV N but routes it to selective autophagy rather than proteasomes | Ubiquitin linkage mutants, autophagy receptor analysis, pharmacologic inhibitors | K48-linked chains decorate a lysine-rich KR motif in N; NDP52 recognizes ubiquitinated N; 3-MA/chloroquine block degradation whereas MG132 does not | Ji 2024, *Frontiers in Immunology* (Nov 2024). DOI: https://doi.org/10.3389/fimmu.2024.1457255 (pqac-00000025, pqac-00000027, pqac-00000028) |
| localization | PDCoV infection induces FBXW8 cytoplasmic relocalization | Infection model, promoter analysis, cell imaging | NF-κB/p65 activates FBXW8 expression and infection drives cytoplasmic redistribution consistent with antiviral targeting of PDCoV N | Ji 2024, *Frontiers in Immunology* (Nov 2024). DOI: https://doi.org/10.3389/fimmu.2024.1457255 (pqac-00000025, pqac-00000026, pqac-00000030) |
| phenotype | FBXW8 is essential for placental development and fetal growth in mouse models | Knockout mouse genetics, placental histology | Loss causes intrauterine growth retardation, small placentas, reduced spongiotrophoblast/labyrinth abnormalities; placental defect depends on fetal genotype | Tsunematsu 2006, *Molecular and Cellular Biology* (Aug 2006). DOI: https://doi.org/10.1128/mcb.00595-06 (pqac-00000034, pqac-00000036) |
| phenotype | FBXW8 contributes to developmental size control downstream of CRL7 | Review of developmental/cardiac studies | Fbxw8-null mice are small but viable to adulthood, milder than Cul7-null lethality; supports FBXW8 as one, but not all, CRL7 effector arms | Zambrano-Carrasco 2024, *Cells* (Jan 2024). DOI: https://doi.org/10.3390/cells13030235 (pqac-00000031, pqac-00000033) |
| application | FBXW8/CRL7 is of translational interest but not yet a mature direct drug target | Expert review analysis | Suggested relevance in cancer, metabolism, development, and targeted modulation of neddylation/CRLs; no FBXW8-specific therapy established | Jeong 2023, *Experimental & Molecular Medicine* (Oct 2023); Shi 2020, *Oncogenesis* (Oct 2020). DOI: https://doi.org/10.1038/s12276-023-01087-w; https://doi.org/10.1038/s41389-020-00276-w (pqac-00000032) |


*Table: This table compiles experimentally supported functional annotation for human FBXW8/Q8N3Y1 across complex assembly, substrates, regulation, localization, phenotypes, and translational relevance. It is useful as a source-linked summary of what is firmly established versus emerging, especially for recent 2024 metabolic and antiviral findings.*