FRAT1

FRAT1 is a positive regulator of canonical Wnt/β-catenin signaling that acts as a substrate-selective inhibitor of GSK-3. FRAT1 is recruited to a quaternary complex with Dishevelled, Axin, and GSK-3β—a process facilitated by CKIε-mediated phosphorylation of Dvl and by LRP5 at the plasma membrane—where its GSK-3-binding domain (FRATtide) competitively displaces GSK-3 from Axin, selectively blocking phosphorylation of β-catenin and Axin without affecting priming-dependent substrates such as glycogen synthase (PMID:10428961, PMID:10481074, PMID:12556519, PMID:15699046). This leads to β-catenin stabilization, nuclear accumulation, and TCF/LEF-dependent transcription of targets including c-Myc; FRAT1 activity is negatively regulated by PKA phosphorylation at Ser188 and post-transcriptionally by miR-34a-3p and miR-3648 (PMID:16982607, PMID:18498136, PMID:28340489, PMID:36153370). Originally identified as a proto-oncogene cooperating with Pim1 and Myc in murine lymphomagenesis, FRAT1 overexpression promotes tumor progression in multiple cancer contexts, while single-gene knockout mice are viable due to functional redundancy with Frat3 (PMID:9034327, PMID:10534617, PMID:10557087).

1. 1997 High

   The initial discovery of Frat1 established it as a proto-oncogene that cooperates with Pim1 and Myc to accelerate lymphomagenesis, but its molecular mechanism was unknown.

   Evidence Retroviral insertional mutagenesis and proviral tagging in Eμ-Myc/Pim1 transgenic mice

   PMID:9034327

   Open questions at the time

   • No molecular target or binding partner identified
   • Mechanism of oncogenic cooperation with Pim1/Myc undefined
2. 1999 High

   Three concurrent studies revealed that FRAT1 functions within Wnt signaling by forming a quaternary complex with Dvl, Axin, and GSK-3, using a defined peptide domain (FRATtide) to competitively displace GSK-3 from Axin and selectively block β-catenin/Axin phosphorylation without affecting priming-dependent GSK-3 substrates—establishing FRAT1 as a substrate-selective GSK-3 inhibitor.

   Evidence Reciprocal co-immunoprecipitation of quaternary complex, FRATtide competitive binding and in vitro kinase assays with multiple GSK-3 substrates, Xenopus axis duplication assays, LEF-1 reporters

   PMID:10428961 PMID:10481074

   Open questions at the time

   • Upstream signal connecting Wnt receptor activation to FRAT1 recruitment unresolved
   • Structural basis of FRATtide–GSK-3 interaction not yet determined
3. 1999 High

   Loss-of-function and gain-of-function mouse models showed that Frat1 is dispensable for normal development due to redundancy with Frat3, but its overexpression causes glomerulosclerosis and accelerates lymphomagenesis, confirming its oncogenic potential in vivo.

   Evidence Frat1-knockout mice (gene targeting), Frat1-overexpressing transgenics, bitransgenic crosses with Pim1

   PMID:10534617 PMID:10557087

   Open questions at the time

   • Frat1/Frat3 double knockout not yet generated to test pathway-level requirement
   • Tissue-specific contributions of Frat family members unclear
4. 2003 High

   CKIε was identified as the kinase that phosphorylates Dvl-1 to enhance Dvl–Frat1 complex formation, linking Wnt3a receptor activation to the mechanism by which FRAT1 is recruited into the destruction complex.

   Evidence Co-immunoprecipitation with Dvl-1 deletion mutants, CKIε RNAi knockdown, Wnt3a-stimulated β-catenin accumulation assays

   PMID:12556519

   Open questions at the time

   • Whether CKIε is the sole kinase regulating this interaction not excluded
   • Quantitative contribution of CKIε-dependent FRAT1 recruitment versus other Wnt-induced events unknown
5. 2005 High

   The Wnt co-receptor LRP5 was identified as an additional FRAT1-binding partner that recruits FRAT1 to the plasma membrane upon Wnt3a stimulation, placing FRAT1 at the receptor complex and linking it to Axin degradation.

   Evidence Yeast two-hybrid screen with LRP5 cytoplasmic domain, reciprocal co-IP, dominant-negative Dvl rescue, TCF reporter assays

   PMID:15699046

   Open questions at the time

   • Whether LRP6 similarly recruits FRAT1 not tested
   • Relative importance of LRP5- versus Dvl-mediated FRAT1 recruitment not quantified
6. 2006 High

   PKA was shown to phosphorylate FRAT1 at Ser188 downstream of β-adrenergic receptor signaling, identifying the first negative regulatory modification of FRAT1 that inhibits its ability to activate β-catenin-dependent transcription.

   Evidence In vitro PKA kinase assay, Ser188 mutagenesis, norepinephrine stimulation of endogenous β-adrenergic receptors, TCF reporter assays

   PMID:16982607

   Open questions at the time

   • How Ser188 phosphorylation mechanistically disrupts FRAT1 function (altered GSK-3 binding vs. localization vs. stability) not resolved
   • Physiological contexts where PKA–FRAT1 crosstalk operates in vivo not defined
7. 2008 Medium

   FRAT1 was shown to drive nuclear β-catenin accumulation and cancer cell growth through TCF-dependent c-Myc expression, directly linking FRAT1's GSK-3 inhibitory mechanism to a specific transcriptional output in human cancer cells.

   Evidence Stable FRAT1 overexpression and RNAi in esophageal squamous cell carcinoma cells, GSK-3β and dominant-negative TCF4 rescue, c-Myc functional assays

   PMID:18498136

   Open questions at the time

   • Whether c-Myc is the critical or sole effector of FRAT1-driven proliferation not established genome-wide
   • Contribution of FRAT1 to Wnt-independent GSK-3 functions in cancer unexplored
8. 2014 Medium

   NDRG1 was identified as an upstream positive regulator of FRAT1 expression that prevents GSK-3β from joining the Axin1–APC–CK1 destruction complex, revealing a regulatory input that tunes FRAT1-dependent β-catenin stabilization at the plasma membrane.

   Evidence NDRG1/FRAT1 siRNA knockdown, co-IP of GSK-3β–Axin1, Western blotting for phospho-β-catenin, subcellular fractionation

   PMID:24829151

   Open questions at the time

   • Mechanism by which NDRG1 upregulates FRAT1 (transcriptional vs. post-translational) not determined
   • Single-lab finding not independently replicated
9. 2017 Medium

   miR-34a-3p was validated as a direct post-transcriptional repressor of FRAT1, establishing a microRNA-mediated regulatory layer on FRAT1 expression.

   Evidence Dual luciferase 3′UTR reporter with binding-site mutagenesis in meningioma cells

   PMID:28340489

   Open questions at the time

   • Physiological relevance of miR-34a-3p–FRAT1 axis beyond meningioma not shown
   • Whether miR-34a-3p regulation of FRAT1 is sufficient to modulate Wnt output in vivo untested
10. 2022 Medium

    FRAT1 was found to physically interact with FRAT2 and to be co-targeted with FRAT2 by miR-3648, which forms a negative feedback loop with c-Myc, revealing coordinated regulation of FRAT family members and a Wnt–c-Myc–miRNA circuit.

    Evidence Co-immunoprecipitation of FRAT1–FRAT2, siRNA rescue of FRAT1-driven invasion, luciferase reporter for miR-3648 targeting, ChIP for c-Myc at miR-3648 promoter in gastric cancer cells

    PMID:36153370

    Open questions at the time

    • Functional significance of FRAT1–FRAT2 heterodimerization for GSK-3 inhibition not tested biochemically
    • Single-lab finding in gastric cancer; generalizability to other tissues unknown

• Key unresolved questions include the structural basis of FRATtide–GSK-3 selectivity, the in vivo requirement for the entire FRAT gene family in Wnt signaling (no Frat1/Frat3 double knockout reported), and the relative contributions of LRP5-, Dvl-, and NDRG1-mediated FRAT1 recruitment in physiological Wnt activation.
• No high-resolution structure of full-length FRAT1 in complex with GSK-3 or Axin
• Frat1/Frat3 double knockout mouse not reported
• Quantitative modeling of FRAT1's contribution relative to other GSK-3 inhibitory mechanisms in the Wnt pathway lacking