FZD8

FZD8 is a seven-transmembrane Frizzled family receptor that transduces canonical Wnt/β-catenin signaling in diverse developmental and disease contexts, including corticogenesis, bone remodeling, cancer stem cell maintenance, and inflammatory joint disease. A human-accelerated regulatory enhancer (HARE5) contacts the FZD8 promoter and drives accelerated neural progenitor cell-cycle kinetics during neocortical development, while p53 directly binds the FZD8 promoter to repress its transcription (PMID:25702574, PMID:28602974). FZD8 protein stability is regulated by USP14-mediated deubiquitination, and FZD8 mRNA levels are controlled by ALKBH1-dependent m7G methylation as well as by multiple miRNAs (miR-100, miR-375) that directly target the FZD8 3′-UTR to attenuate downstream β-catenin, survivin, and TCF/LEF output (PMID:40318610, PMID:41274478, PMID:26537584, PMID:25619565). In cancer, FZD8 operates downstream of c-Met/ERK/c-Fos signaling to sustain Wnt/β-catenin activation, promoting chemoresistance, invasion, and metastasis in breast, prostate, and head-and-neck carcinomas (PMID:25320014, PMID:23445611).

1. 2013 Medium

   Establishing that FZD8 is a functionally relevant Wnt receptor in cancer stem-like cells: FZD8 knockdown in triple-negative breast cancer tumor-initiating cells reduced β-catenin and survivin levels, linking FZD8-driven Wnt signaling to chemoresistance.

   Evidence siRNA knockdown with Western blot and in vivo xenograft imaging in TNBC cells

   PMID:23445611

   Open questions at the time

   • No structural basis for FZD8–Wnt ligand selectivity determined
   • Contribution of other Frizzled receptors in the same cells not ruled out
2. 2014 Medium

   Placing FZD8 within a defined upstream signaling cascade: c-Met was shown to upregulate FZD8 via ERK/c-Fos, and FZD8 overexpression rescued β-catenin signaling when c-Met was inhibited, establishing a linear c-Met→ERK→c-Fos→FZD8→β-catenin pathway.

   Evidence siRNA/pharmacologic inhibition with ectopic FZD8 rescue in HNSCC cancer stem-like cells and xenografts

   PMID:25320014

   Open questions at the time

   • Whether c-Fos directly binds the FZD8 promoter was not shown by ChIP
   • Generalizability beyond HNSCC stem cells unknown
3. 2015 High

   Demonstrating that a human-accelerated enhancer (HARE5) physically contacts the FZD8 promoter and that its human-specific sequence accelerates neural progenitor cell cycle and increases brain size, linking FZD8 expression regulation to human cortical evolution.

   Evidence Chromosome conformation capture (3C) in mouse embryonic neocortex plus transgenic mice comparing human vs. chimpanzee HARE5-driven Fzd8 expression

   PMID:25702574

   Open questions at the time

   • Which Wnt ligands are relevant in the developing neocortex not identified
   • Downstream effectors beyond β-catenin not dissected
4. 2015 Medium

   Identifying miRNA-mediated post-transcriptional regulation of FZD8: miR-100 and miR-375 were validated as direct FZD8 3′-UTR targeting miRNAs that suppress Wnt/β-catenin output in breast cancer and synovial fibroblasts, respectively.

   Evidence Luciferase reporter assays, Western blot, migration/invasion assays (miR-100 in breast cancer); luciferase reporter plus stabilized β-catenin epistasis (miR-375 in arthritis fibroblasts)

   PMID:25619565 PMID:26537584

   Open questions at the time

   • Physiological miRNA levels and relevance in vivo not established
   • Cooperative or redundant miRNA targeting of FZD8 not tested
5. 2017 Medium

   Revealing transcriptional repression of FZD8 by p53: ChIP demonstrated direct p53 binding to the FZD8 promoter, and FZD8 overexpression promoted prostate cancer invasion and bone metastasis through Wnt/β-catenin, linking loss of p53 tumor suppression to FZD8 derepression.

   Evidence ChIP assay, overexpression/silencing, in vivo bone metastasis model in prostate cancer cells

   PMID:28602974

   Open questions at the time

   • Whether p53 mutations found in patient tumors correlate with FZD8 upregulation not shown
   • Specific p53 response element in FZD8 promoter not mapped
6. 2023 Medium

   Developing FZD8-selective blocking tools: structure-guided design of an FZD8-specific antibody (sF8_AG6) demonstrated that FZD8-mediated Wnt signaling can be selectively inhibited at the receptor level.

   Evidence Structural determination of antibody–FZD8 CRD complex and cell-based Wnt reporter assays

   PMID:37926311

   Open questions at the time

   • In vivo efficacy of the blocking antibody not tested
   • Whether antibody discriminates FZD8 from FZD5 in physiological contexts unknown
7. 2025 Medium

   Defining post-translational and epitranscriptomic control of FZD8 protein and mRNA: USP14 was shown to deubiquitinate and stabilize FZD8 protein, while ALKBH1-mediated m7G demethylation of FZD8 mRNA suppresses its expression, each with rescue experiments confirming FZD8 as the critical effector of Wnt/β-catenin output.

   Evidence Co-IP, GST pull-down, ubiquitination assay with rescue (USP14–FZD8); RIP-qPCR, m7G-MeRIP-qPCR with transcriptome sequencing and in vivo rescue (ALKBH1–FZD8)

   PMID:40318610 PMID:41274478

   Open questions at the time

   • Specific ubiquitin linkage type on FZD8 not determined
   • Whether m7G methylation affects FZD8 mRNA stability vs. translation not distinguished
   • Each interaction demonstrated by a single laboratory

• The identity of preferred Wnt ligand(s) for FZD8 in physiological contexts, the co-receptor requirements (e.g., LRP5/6 dependency), and the structural basis for ligand-induced FZD8 activation remain incompletely resolved in the primary literature.
• No Wnt ligand selectivity profiling for FZD8 in the discovery timeline
• Co-receptor dependency not directly tested
• Full-length FZD8 structure in active/inactive conformations unavailable