FZD1

FZD1 is a cell-surface Wnt receptor that binds multiple Wnt ligands and cooperates with LRP5/6 co-receptors to activate canonical Wnt/β-catenin signaling, driving cytoplasmic β-catenin stabilization and nuclear translocation (PMID:15923619, PMID:42256303). It engages distinct Wnt ligands in different contexts: Wnt7b together with LRP5 (PMID:15923619), Wnt5b together with LRP6 to drive renal fibroblast activation under hypoxia (PMID:42256303), and Wnt7B in complexes facilitated by SULF1 (PMID:42140034). A recurrent functional output of FZD1-driven Wnt/β-catenin signaling is transactivation of the drug transporter MDR1/P-glycoprotein, and FZD1 silencing reduces nuclear β-catenin, lowers MDR1/ABCB1 expression, and restores chemosensitivity across neuroblastoma and breast cancer models (PMID:19421142, PMID:22484497). In multidrug-resistant cells FZD1 additionally signals through a non-canonical PKCδ/AP-1 pathway to control AP-1 target genes and ABCB1 expression (PMID:24814288). FZD1 signaling is restrained by LRP1, which sequesters FZD1 and disrupts its FZD1-LRP6 co-receptor complex independently of receptor internalization (PMID:14739301). FZD1 abundance is tightly regulated at multiple levels: cis-regulatory promoter polymorphisms create Egr1 and E2F1 binding sites that elevate promoter activity (PMID:18715140, PMID:20051274); MBD2a activates and SIRT2-mediated H3K27 deacetylation represses the promoter (PMID:33402389, PMID:41485500); and mRNA levels are set by miR-135b targeting of the 3'-UTR (PMID:27643554) and by stabilizing RNA-binding proteins RBM38 and the m6A-reader IGF2BP3 (PMID:34893109, PMID:40706743). Genetically, FZD1 is required for normal female fertility in mice, where Fzd1-null females show subfertility and blunted ovulatory induction of oocyte and cumulus cell genes (PMID:22954793).

1. 2004 Medium

   Established that FZD1-mediated canonical Wnt signaling is subject to negative regulation by a co-receptor competitor, defining a mechanism of pathway restraint at the receptor complex.

   Evidence Co-IP, reporter assays, and endocytosis-defective LRP1 mutants in transfected cells

   PMID:14739301

   Open questions at the time

   • Physiological context of LRP1-FZD1 antagonism not defined
   • Stoichiometry of FZD1-LRP6 complex disruption not resolved
2. 2005 Medium

   Identified a specific Wnt ligand (Wnt7b) that binds FZD1 and showed it selectively activates the canonical rather than non-canonical pathway with LRP5, defining FZD1 ligand specificity.

   Evidence Cell-surface binding assay and canonical vs non-canonical reporter assays in transfected cells

   PMID:15923619

   Open questions at the time

   • No structural basis for Wnt7b-FZD1 binding
   • Single ligand tested for pathway selectivity
3. 2009 Medium

   Linked FZD1 to a cancer phenotype by showing its upregulation sustains Wnt/β-catenin signaling and MDR1 expression to drive chemoresistance, framing FZD1 as a resistance effector.

   Evidence shRNAmir knockdown with nuclear β-catenin and MDR1 readouts in neuroblastoma cells

   PMID:19421142

   Open questions at the time

   • Upstream cause of FZD1 upregulation in resistant cells not defined
   • Direct β-catenin occupancy of MDR1 promoter not shown
4. 2009 Medium

   Resolved a cis-regulatory determinant of FZD1 expression by showing a promoter polymorphism creates an Egr1 binding site with allele-specific transcriptional output.

   Evidence Promoter reporter assay and EMSA for Egr1 binding in osteoblast-like cell lines

   PMID:18715140

   Open questions at the time

   • In vivo relevance of the polymorphism not established
   • Egr1-driven FZD1 induction signal not defined
5. 2010 Medium

   Extended the cis-regulatory model by identifying a second polymorphism creating an E2F1 site and a haplotype with higher promoter activity.

   Evidence Promoter reporter assay, EMSA, and bioinformatics in osteoblast-like cells

   PMID:20051274

   Open questions at the time

   • Endogenous E2F1 control of FZD1 not demonstrated
   • Functional consequence on bone biology not tested
6. 2012 Medium

   Generalized the FZD1-Wnt/β-catenin-MDR1 resistance axis to breast cancer and confirmed it controls cytoplasmic and nuclear β-catenin and P-glycoprotein.

   Evidence siRNA knockdown with β-catenin fractionation Western blot and drug sensitivity assays in MCF-7/ADM cells

   PMID:22484497

   Open questions at the time

   • Ligand driving the signaling not identified
   • Mechanism of MDR1 transactivation not directly shown
7. 2012 High

   Defined an in vivo physiological requirement for FZD1 in female fertility, distinguishing it from being the sole ovarian WNT4 receptor.

   Evidence Fzd1-null mouse model with microarray and cumulus-oocyte complex gene expression analysis

   PMID:22954793

   Open questions at the time

   • Ovarian Wnt ligand for FZD1 not identified
   • Pathway (canonical vs non-canonical) in fertility not resolved
8. 2014 Medium

   Revealed a non-canonical FZD1 output, showing FZD1 drives a PKCδ/AP-1 cascade controlling ABCB1 and drug efflux, broadening FZD1 signaling beyond β-catenin.

   Evidence shRNA knockdown, pharmacological inhibition, and drug pump-out assays in MES-SA/Dx5 cells

   PMID:24814288

   Open questions at the time

   • Link between FZD1 and PKCδ activation not biochemically defined
   • Relationship to canonical β-catenin branch unclear
9. 2016 Medium

   Added post-transcriptional regulation of FZD1 by identifying direct miR-135b targeting of its 3'-UTR with consequences for chemoresistance.

   Evidence Dual-luciferase 3'-UTR reporter, miR-135b mimic, and RT-qPCR in lung cancer cells

   PMID:27643554

   Open questions at the time

   • Endogenous miR-135b regulation of FZD1 in vivo not shown
   • Other 3'-UTR regulators not surveyed
10. 2021 Medium

    Identified RNA-stability control of FZD1 by RBM38 and a CpG-island promoter activation mechanism via MBD2a, expanding the regulatory layers controlling FZD1 abundance.

    Evidence RIP-qPCR and actinomycin D decay assays (RBM38); CpG-island binding and splice-variant manipulation with EMT/metastasis assays (MBD2a)

    PMID:33402389 PMID:34893109

    Open questions at the time

    • RBM38 effect tested in a single cell model
    • MBD2a/MBD2c balance regulation in vivo not defined
11. 2025 Medium

    Connected m6A RNA modification to FZD1 by showing IGF2BP3 stabilizes FZD1 transcripts in an m6A-dependent manner and promotes FZD1/FZD7 heterodimerization to sustain stemness and chemoresistance.

    Evidence RNA binding and m6A analysis, IGF2BP3/RBM15 knockdown, and β-catenin translocation/FACS in TNBC

    PMID:40706743

    Open questions at the time

    • FZD1/FZD7 heterodimer functional stoichiometry not resolved
    • Direct m6A sites on FZD1 not mapped
12. 2026 Medium

    Identified new modulators of FZD1 signaling: SULF1 (stabilized by JOSD1) facilitating Wnt7B-FZD1 complex formation, SIRT2-mediated H3K27 deacetylation repressing FZD1 transcription, and FZD1/LRP6 acting as a Wnt5b co-receptor in fibrosis.

    Evidence Co-IP and ubiquitination assays (SULF1/JOSD1); ChIP and rescue/xenograft (SIRT2); Wnt5b knockdown, exosome isolation, and hypoxia mouse model (Wnt5b)

    PMID:41485500 PMID:42140034 PMID:42256303

    Open questions at the time

    • Mechanism by which SULF1 promotes Wnt7B-FZD1 complex not structurally defined
    • Tissue-specificity of each regulatory input not integrated

• How FZD1 selects between canonical β-catenin and non-canonical PKCδ/AP-1 outputs, and the structural basis of its ligand and co-receptor complexes, remain unresolved.
• No structural model of FZD1-Wnt-LRP complexes
• Determinants of canonical vs non-canonical branch choice unknown
• Normal physiological Wnt ligands for FZD1 in most tissues undefined