FRAT2

FRAT2 is a positive regulator of Wnt/β-catenin signaling that acts as a GSK3β-binding adaptor, with its acidic and proline-rich domains required for pathway activation, as shown by its ability to induce secondary axis formation in Xenopus (PMID:11237732). It binds GSK3β and Dishevelled and localizes to both cytosol and nucleus (PMID:12095675, PMID:15073180), and rather than simply inhibiting the kinase it selectively enhances GSK3β-mediated phosphorylation of primed substrates such as tau while sparing unprimed substrates; FRAT2 is itself a GSK3β substrate, defining a reciprocal kinase–adaptor relationship (PMID:15522877). FRAT2 is a comparatively weak activator of canonical β-catenin/TCF signaling, consistent with a partly divergent GSK3β function (PMID:15073180), and in leukemia it links MLL fusion oncogenes to Rac GTPase activation through a GSK3- and DVL-dependent mechanism, where Frat2 loss reduces Rac activity and abrogates MLL-driven leukemogenesis (PMID:23074275). FRAT2 physically associates with its paralog FRAT1 and is required for FRAT1-driven cancer cell invasion (PMID:36153370), while its activity is negatively constrained by TMEM98, which binds FRAT2 and lowers its protein levels to dampen β-catenin/TCF signaling (PMID:31961879).

1. 2001 High

   Established FRAT2 as a positive Wnt-pathway regulator and mapped the protein domains needed for that activity, addressing whether FRAT2 functions in Wnt signal transduction at all.

   Evidence Xenopus axis duplication assay with domain-deletion FRAT2 mutants and cDNA sequence analysis

   PMID:11237732

   Open questions at the time

   • Did not identify the direct molecular partner mediating activation
   • Mechanism downstream of the acidic/proline-rich domains undefined
2. 2002 Medium

   Identified the physical partners of FRAT2 within the Wnt machinery, answering which signaling proteins FRAT2 engages.

   Evidence Co-immunoprecipitation of GSK-3 and Dishevelled and subcellular localization in transfected COS-1 cells

   PMID:12095675

   Open questions at the time

   • Binding inferred from overexpression without reciprocal endogenous validation
   • Functional consequence of nuclear localization not dissected
3. 2004 High

   Resolved whether FRAT2 is a core canonical Wnt component or a divergent GSK3β effector, and revealed FRAT2 as a phosphoprotein.

   Evidence Co-IP for GSK3β binding, β-catenin/TCF reporter side-by-side with Frat1/Frat3, and phosphorylation detection in 293T cells

   PMID:15073180

   Open questions at the time

   • Kinase responsible for Frat2 phosphorylation not pinned down here
   • Nature of the divergent GSK3β pathway unspecified
4. 2004 High

   Defined the biochemical mechanism of FRAT2 action on GSK3β — substrate-priming-dependent enhancement — rather than simple kinase inhibition.

   Evidence In vitro kinase assays with recombinant proteins, co-IP, and primed/unprimed phospho-substrate (including tau) readouts with site-specific antibodies

   PMID:15522877

   Open questions at the time

   • Physiological substrates beyond tau not enumerated
   • Structural basis of priming selectivity unresolved
5. 2012 High

   Connected FRAT2 to oncogenic Rac signaling, establishing its requirement for MLL-fusion leukemogenesis through a GSK3/DVL-dependent route.

   Evidence Frat knockout mouse hematopoietic progenitors, retroviral MLL-fusion transformation, direct Rac activity assays, GSK3/DVL epistasis, and in vivo leukemia model

   PMID:23074275

   Open questions at the time

   • Molecular link from FRAT2/GSK3/DVL to specific Rac GEFs unknown
   • Whether β-catenin is involved in the Rac arm not resolved
6. 2020 Medium

   Identified a negative regulator of FRAT2, answering how FRAT2 protein levels and downstream Wnt output are constrained.

   Evidence Co-IP of TMEM98 with FRAT2, FRAT2 protein-level quantification, β-catenin/TCF reporter assay, and TMEM98 trafficking assays

   PMID:31961879

   Open questions at the time

   • Mechanism by which TMEM98 lowers FRAT2 levels (degradation vs. stability) not defined
   • Single lab without independent replication
7. 2022 Medium

   Demonstrated FRAT1–FRAT2 heteromeric interaction and a microRNA control point, placing FRAT2 as a required effector of FRAT1-driven cancer invasion.

   Evidence Co-IP of FRAT1 with FRAT2, miR-3648 luciferase targeting, siRNA knockdown rescue, and invasion assays in vitro and in vivo

   PMID:36153370

   Open questions at the time

   • Whether the FRAT1–FRAT2 complex acts through GSK3β in this context not tested
   • Stoichiometry and functional role of the heterocomplex undefined

• How FRAT2 partitions between its canonical β-catenin/TCF, divergent GSK3β, and Rac-activating functions, and how these are coordinated by partner availability and post-translational control, remains unresolved.
• No structure of FRAT2 bound to GSK3β or DVL
• Endogenous regulation of FRAT2 phosphorylation not characterized
• Determinants selecting canonical vs. Rac outputs unknown