{"gene":"FAT4","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2008,"finding":"Fat4 is required for oriented cell divisions and tubule elongation during kidney development; loss of Fat4 disrupts planar cell polarity (PCP) signaling, leading to cystic kidney disease. Fat4 genetically interacts with the PCP genes Vangl2 and Fjx1 in cyst formation, and Fat4 represses Fjx1 expression, indicating conservation of Fat signaling from Drosophila to vertebrates.","method":"Genetic loss-of-function (Fat4 knockout mice), genetic epistasis with Vangl2 and Fjx1, gene expression analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype, genetic epistasis across multiple genes, replicated in multiple developmental contexts","pmids":["18604206"],"is_preprint":false},{"year":2011,"finding":"Dchs1 and Fat4 function as a ligand-receptor pair during murine development; they are predominantly expressed in mesenchymal cells, and mutation of either gene increases protein staining for the other. They regulate planar cell polarity, kidney growth and branching, and cell survival in multiple organs including the ear, kidney, skeleton, intestine, heart and lung.","method":"Gene-targeted mutation (Dchs1 knockout mice), comparison with Fat4 mutants, double mutant analysis, antibody staining","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal single and double mutant analysis across multiple organs, protein staining, independently consistent with Drosophila pathway","pmids":["21303848"],"is_preprint":false},{"year":2013,"finding":"Mutations in FAT4 (and its ligand DCHS1) lead to periventricular neuronal heterotopia; reducing Dchs1 or Fat4 in mouse neuroepithelium increased progenitor cell numbers and reduced differentiation into neurons. These effects were countered by concurrent knockdown of Yap, placing FAT4 upstream of YAP in the Hippo signaling pathway during neurogenesis.","method":"Loss-of-function in mouse embryonic neuroepithelium (knockdown), Yap concurrent knockdown (epistasis), human genetic mutation identification","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via concurrent Yap knockdown rescue, defined cellular phenotype, human mutations identified","pmids":["24056717"],"is_preprint":false},{"year":2014,"finding":"Fat4 and Dchs1 are expressed in complementary gradients and are required intrinsically within facial branchiomotor (FBM) neurons and extrinsically within the neuroepithelium for collective tangential neuronal migration and PCP. Fat-PCP and Fz-PCP regulate FBM neuron migration along orthogonal axes. Disruption of Dchs1 gradients by mosaic inactivation alters FBM neuron polarity and migration, implying that PCP is regulated via gradients of Fat4 and Dchs1 expression.","method":"Conditional and mosaic knockout mice, live imaging, PCP analysis, genetic epistasis","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — tissue-specific and mosaic KO with defined cellular polarity and migration phenotype, orthogonal axis epistasis established","pmids":["24998526"],"is_preprint":false},{"year":2015,"finding":"FAT4 acts non-autonomously in the renal stroma to control nephron progenitors. Loss of Yap from cap mesenchyme (CM) in Fat4-null mice does not reduce the expanded CM, indicating FAT4 regulates the CM independently of YAP. Excess progenitors in Fat4 mutants are dependent on Six2. Dchs1 and its paralogue Dchs2 function partially redundantly to regulate nephron progenitor numbers. FAT4 in the stroma binds to DCHS1/2 in the CM to restrict progenitor self-renewal.","method":"Tissue-specific conditional knockouts, Six2−/−;Fat4−/− double mutants, electron microscopy, gene expression analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — tissue-specific KO, genetic epistasis with Six2 and Yap, multiple orthogonal methods","pmids":["26116661"],"is_preprint":false},{"year":2015,"finding":"Fat4 and Dchs1 are implicated in signaling between stromal and cap mesenchyme cell layers in the kidney; Dchs1 protein is polarized within cap mesenchyme cells, accumulating at the interface with stromal cells, consistent with direct interaction with a stromal protein (Fat4). Dchs1 acts as a Fat4 receptor for stromal signaling essential for kidney development.","method":"Dchs1 conditional knockout mice, antibody staining of genetic mosaics revealing polarized Dchs1 protein localization, phenotypic comparison with Fat4 mutants","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — polarized protein localization in genetic mosaics, conditional KO with defined phenotype, consistent with ligand-receptor model","pmids":["26116666"],"is_preprint":false},{"year":2015,"finding":"Fat1 and Fat4 interact genetically to regulate neural tube closure, neural progenitor proliferation, and apical constriction. Fat1 and Fat4 bind different sets of actin-regulating and junctional proteins. In vitro data suggest that Fat1 and Fat4 form cis-heterodimers, providing a mechanism for bringing together their diverse interactors.","method":"Fat1 and Fat4 mouse knockouts, in utero electroporation, proteomic analysis, in vitro binding assays","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic interaction, proteomic analysis, in vitro cis-heterodimer data in single lab","pmids":["26209645"],"is_preprint":false},{"year":2016,"finding":"Dchs1-Fat4 PCP pathway controls cell orientation in the early skeletal condensation to define the shape and dimensions of the mouse sternum. This involves cell intercalation along differential Dchs1-Fat4 activity. Fat4 and Dchs1 establish polarized cell behavior intrinsically within the mesenchyme.","method":"Fat4 and Dchs1 knockout mice, cell orientation analysis in skeletal condensations","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular polarity phenotype, single lab","pmids":["27145737"],"is_preprint":false},{"year":2016,"finding":"Fat4 and Dchs1 regulate vertebral development through control of cell proliferation in the early sclerotome, independently of Yap and Taz; analysis of Fat4;Yap and Fat4;Taz double mutants and expression of transcriptional target Ctgf indicates this is a Yap/Taz-independent mechanism of Fat4-Dchs1 signaling.","method":"Fat4−/− and Dchs1−/− knockout mice, Fat4;Yap and Fat4;Taz double mutants, Ctgf expression analysis","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — double mutant epistasis, defined cellular phenotype, single lab","pmids":["27381226"],"is_preprint":false},{"year":2016,"finding":"Fat4 suppression leads to increased phosphorylated Yap and nuclear accumulation of Yap in gastric cancer cells, promoting proliferation, migration, and cell cycle progression. Re-expression of full-length Fat4 decreases phosphorylated Yap and inhibits cell cycle progression. Fat4 reduction also leads to accumulation of cytoplasmic β-catenin via loss of restraint on cytoplasmic Yap.","method":"Fat4-shRNA knockdown, Fat4 overexpression, western blotting, cell proliferation and migration assays","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — knockdown and rescue with protein-level readouts, single lab, two methods","pmids":["26575609"],"is_preprint":false},{"year":2017,"finding":"In the mouse heart, Fat4 modulates Hippo signaling to restrict cardiomyocyte growth and proliferation. Fat4 is not required for canonical activation of Hippo kinases but sequesters Amotl1 out of the nucleus; nuclear translocation of Amotl1 is accompanied by Yap1 to promote cardiomyocyte proliferation. Amotl1 is identified as a mammalian intermediate for non-canonical Hippo signaling downstream of Fat4.","method":"Fat4 mutant mouse myocardium analysis, Yap1 transcriptional activity assay, nuclear fractionation, co-localization studies","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined phenotype, mechanistic dissection of canonical vs non-canonical Hippo, identification of novel intermediate Amotl1","pmids":["28239148"],"is_preprint":false},{"year":2017,"finding":"Dachsous1-Fat4 signaling is required specifically for lymphatic valve morphogenesis; valve endothelial cells are disoriented and fail to form proper valve leaflets in Fat4 or Dachsous1 mutant mice. Dachsous1 is polarized to membrane protrusions and cellular junctions of valve endothelial cells in vivo and in vitro.","method":"Fat4 and Dachsous1 mutant mice, Lifeact-GFP imaging of actin dynamics, in vitro and in vivo immunostaining of Dchs1 localization","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined valve phenotype, polarized protein localization shown in vivo, single lab","pmids":["28705793"],"is_preprint":false},{"year":2017,"finding":"Fat4-Ds1 complexes accumulate on cell boundaries in a threshold-like manner and exhibit dramatically slower dynamics than unbound Fat4 and Ds1, providing evidence for a localized feedback mechanism based on enhanced stability of Fat4-Ds1 complexes. Co-expression of Fat4 and Ds1 in the same cells is sufficient to induce polarization of Fat4-Ds1 complexes.","method":"Synthetic biology platform in mammalian cells expressing human Fat4 and Ds1, live-cell imaging of complex dynamics and FRAP","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Moderate — quantitative live imaging reconstitution with biophysical measurements, single lab but multiple orthogonal methods","pmids":["28826487"],"is_preprint":false},{"year":2019,"finding":"FAT4 interacts with RET through extracellular cadherin repeats and perturbs the assembly of the RET-GFRA1-GDNF complex, thereby reducing RET signaling. Loss of Fat4 causes abnormal ureteric budding and excessive RET signaling; removal of one copy of the RET ligand Gdnf rescues Fat4−/− kidney development. FAT4 acts non-autonomously to regulate RET signaling.","method":"Fat4 knockout mice, conditional knockout analyses, co-immunoprecipitation of FAT4-RET interaction, Gdnf heterozygous rescue epistasis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP of FAT4-RET interaction, genetic rescue epistasis, conditional KO non-autonomous mechanism established","pmids":["30853441"],"is_preprint":false},{"year":2019,"finding":"FAT4 regulates EMT and autophagy in colorectal cancer cells in part via the PI3K-AKT/mTOR and PI3K-AKT/GSK-3β signaling pathways; FAT4 promotes autophagy and inhibits EMT through PI3K activity regulation.","method":"FAT4 overexpression and knockdown, western blotting for PI3K/AKT pathway components, transwell assays, xenograft model","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway inference from western blot without direct biochemical mechanism","pmids":["30832706"],"is_preprint":false},{"year":2019,"finding":"Dchs1-Fat4 signaling is essential for osteoblast differentiation; loss of Dchs1-Fat4 signaling increases Yap-Tead activity in osteoprogenitors, and Yap is required for proliferation in these cells. Taz is expressed in more-committed Runx2-expressing osteoblasts, and Taz-Tead activity is unaffected in Dchs1/Fat4 mutants. Yap and Taz differentially regulate Runx2 transcriptional activity, and the activity of Yap-Runx2 and Taz-Runx2 complexes is altered in Dchs1/Fat4 mutant osteoblasts.","method":"Dchs1 and Fat4 mutant mice, YAP and TAZ knockouts, reporter assays for Tead and Runx2 activity","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic mutants, epistasis, reporter assays for transcriptional complexes, multiple orthogonal methods","pmids":["31358536"],"is_preprint":false},{"year":2019,"finding":"FAT4 silencing in endometrial cancer decreases phosphorylation of LATS1/2 and YAP while increasing YAP nuclear translocation, consistent with Hippo pathway suppression. Co-immunoprecipitation confirmed direct binding of FAT4 and the deubiquitinating enzyme USP51. USP51 knockdown decreases FAT4 protein level while USP51 overexpression increases FAT4 protein level, indicating USP51 is required for FAT4 stability.","method":"FAT4 knockdown and overexpression, shRNA for USP51, PCR array, co-immunoprecipitation, western blotting","journal":"American journal of translational research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP confirms FAT4-USP51 interaction, bidirectional regulation of FAT4 stability shown, single lab","pmids":["31217854"],"is_preprint":false},{"year":2020,"finding":"GLI2 (a Hedgehog transcriptional effector) directly activates atypical cadherin and PCP genes including Fat4; Fat4 and Dchs1 are critical for villus formation in gut development. The Fat4-Dchs1 axis acts in parallel to the core-Vangl2 PCP axis to control mesenchymal cell clustering. WNT5A guides oriented cell migration of PDGFRα+ mesenchymal cells via PCP.","method":"GLI2 targetome analysis, Fat4 and Dchs1 knockout mice, Vangl2 PCP-mutant mice, genetic interaction studies, live light-sheet fluorescence microscopy of cultured PDGFRα+ cells","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple knockout models, genetic epistasis with Vangl2, live imaging, GLI2 targetome establishing upstream regulation","pmids":["32155439"],"is_preprint":false},{"year":2020,"finding":"FAT4 functions in a lymphatic endothelial cell-autonomous manner to control cell polarity in response to flow and is required for lymphatic vessel morphogenesis. FAT4 is a target gene of GATA2, a transcriptional regulator of lymphatic vascular development.","method":"Fat4 conditional knockout (cell-autonomous analysis), flow-dependent polarity assays, GATA2 target gene identification","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-autonomous conditional KO with defined polarity phenotype, GATA2 transcriptional target validation, single lab","pmids":["32182215"],"is_preprint":false},{"year":2023,"finding":"The co-crystal structure of human Fat4 (EC domains 1-4) and Dachsous1 (Dchs1) establishes the molecular basis for Fat-Dachsous heterophilic interactions. The binding interface is extended along EC domains 1-4 of each protein. Fat4-Dchs1 affinity is among the highest reported for cadherin superfamily members, attributed to an extensive network of salt bridges not present in structurally similar protocadherin homodimers. Extracellular phosphorylation modifications may directly modulate Fat-Dachsous binding by introducing charged contacts across the interface.","method":"Co-crystal structure determination, biophysical affinity measurements, structural modeling of phosphorylation effects","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — co-crystal structure with biophysical validation, mechanistic basis for heterophilic interaction established","pmids":["36797229"],"is_preprint":false},{"year":2023,"finding":"FAT4 overexpression binds β-catenin and antagonizes its nuclear localization, promoting phosphorylation and degradation of β-catenin by the destruction complex (AXIN1, APC, GSK3β, CK1). This suppresses STT3A-mediated PD-L1 N-glycosylation, causing PD-L1 ER accumulation and polyubiquitination-dependent degradation, thereby reducing immune evasion in cervical cancer.","method":"FAT4 overexpression, Co-IP of FAT4-β-catenin interaction, functional assays for PD-L1 glycosylation and ubiquitination, immunodeficient and immunocompetent xenograft models","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of FAT4-β-catenin, multiple downstream readouts, in vivo validation, single lab","pmids":["37658376"],"is_preprint":false},{"year":2024,"finding":"IL-32 interacts with FAT4 and MST1/2 proteins (identified by immunoprecipitation and mass spectrometry); elevation of IL-32 enhances its interactions with FAT4 and MST1/2, prompting MST1/2 phosphorylation and activating the Hippo/YAP signaling pathway, causing matrix metabolism disorder in nucleus pulposus cells.","method":"Immunoprecipitation and mass spectrometry, lentiviral FAT4 knockdown, western blotting for MST1/2 phosphorylation and YAP, rat in vivo model","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — IP-MS identification of IL-32-FAT4-MST1/2 complex, functional FAT4 knockdown, single lab","pmids":["39178518"],"is_preprint":false},{"year":2025,"finding":"The intracellular domain (ICD) of Fat4 is required for trans-endocytosis of Dchs1 into Fat4-expressing cells and for boundary accumulation of Fat4/Dchs1 complexes. The Fat4 ICD controls the internalization rate of Fat4/Dchs1 complexes. Actin polymerization is required for accumulation of Fat4/Dchs1 complexes at boundaries.","method":"Quantitative live imaging of Fat4 ICD deletion mutants, FRAP, actin polymerization inhibition, mammalian cell expression system","journal":"Biophysical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative live imaging with deletion mutants and pharmacological inhibition, single lab, mechanistic dissection of ICD function","pmids":["39955614"],"is_preprint":false},{"year":2025,"finding":"UBE4B directly binds to and ubiquitinates FAT4, leading to its proteasomal degradation. Tandem Mass Tag (TMT) proteomics revealed FAT4 as a downstream target of UBE4B; UBE4B inhibits autophagy in gastric cancer cells by mediating FAT4 ubiquitination and degradation.","method":"Co-IP, TMT quantitative proteomics, western blot, transmission electron microscopy, UBE4B knockdown/overexpression","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and proteomics establishing UBE4B-FAT4 interaction, ubiquitination confirmed, single lab","pmids":["40701960"],"is_preprint":false},{"year":2026,"finding":"FAT4 directly interacts with YAP (shown by co-immunoprecipitation) and retains YAP in the cytoplasm, blocking its nuclear translocation, independently of the canonical Hippo phosphorylation cascade (LATS1/2-mediated). FAT4 knockdown promotes nuclear translocation of YAP without altering canonical phosphorylation.","method":"Co-immunoprecipitation of FAT4-YAP, FAT4 knockdown, nuclear fractionation, zebrafish and mouse in vivo models","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of direct FAT4-YAP interaction, non-canonical mechanism supported by phosphorylation analysis, single lab","pmids":["42023818"],"is_preprint":false},{"year":2015,"finding":"FAT4 functions as a tumor suppressor in gastric cancer by modulating Wnt/β-catenin signaling; knockdown of FAT4 promotes growth and invasion via activation of Wnt/β-catenin signaling and induces EMT.","method":"FAT4 siRNA knockdown in gastric cancer cell lines, western blotting for Wnt/β-catenin pathway components, xenograft model in vivo","journal":"British journal of cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway activity inferred from western blot without direct binding evidence","pmids":["26633557"],"is_preprint":false}],"current_model":"FAT4 is a large transmembrane atypical cadherin that forms high-affinity heterophilic complexes with its ligand DCHS1/Dachsous1 (co-crystal structure resolved for EC domains 1–4), acting as a planar cell polarity (PCP) signaling receptor in multiple tissues; it functions upstream of the Hippo pathway by sequestering Amotl1 and directly binding YAP to retain it in the cytoplasm (independent of canonical LATS1/2 phosphorylation), represses Fjx1 expression, interacts with the RET receptor tyrosine kinase through its extracellular cadherin repeats to fine-tune RET-GFRA1-GDNF complex assembly, binds β-catenin to promote its destruction-complex-mediated degradation, and is regulated post-translationally by ubiquitination (via UBE4B) and stabilization (via USP51); its intracellular domain controls Fat4/Dchs1 complex internalization and boundary accumulation, while upstream Hedgehog/GLI2 signaling transcriptionally activates FAT4 and GATA2 regulates it in lymphatic endothelium."},"narrative":{"mechanistic_narrative":"FAT4 is a large transmembrane atypical cadherin that functions as a planar cell polarity (PCP) receptor governing oriented cell division, tissue growth, and progenitor behavior across multiple developing organs including kidney, ear, skeleton, heart, gut, brain, and lymphatic vasculature [PMID:18604206, PMID:21303848, PMID:24056717]. It acts as the receptor for the ligand DCHS1 (Dachsous1, partially redundant with DCHS2), forming high-affinity heterophilic complexes whose structural basis lies in an extended binding interface across EC domains 1–4 stabilized by an extensive salt-bridge network [PMID:36797229]; FAT4 and DCHS1 are expressed in complementary gradients and accumulate as polarized complexes at cell boundaries through a threshold-like, self-stabilizing feedback mechanism [PMID:28826487, PMID:26116666], with the FAT4 intracellular domain driving trans-endocytosis of DCHS1 and actin-dependent boundary accumulation [PMID:39955614]. FAT4 acts upstream of the Hippo pathway largely through non-canonical routes: it restrains YAP nuclear translocation by directly binding YAP and by sequestering the intermediate Amotl1 in the cytoplasm, independent of canonical LATS1/2 phosphorylation, thereby limiting cardiomyocyte, neural progenitor, and osteoprogenitor proliferation [PMID:28239148, PMID:42023818, PMID:24056717, PMID:31358536], while in several developmental and cancer contexts it also regulates progenitor self-renewal and cell proliferation entirely independently of YAP/TAZ [PMID:26116661, PMID:27381226]. FAT4 additionally tunes RET–GFRA1–GDNF receptor tyrosine kinase signaling non-autonomously through its extracellular cadherin repeats during ureteric budding [PMID:30853441], promotes β-catenin destruction-complex-mediated degradation [PMID:37658376], and represses Fjx1 [PMID:18604206]. FAT4 expression is controlled upstream by Hedgehog effector GLI2 and by GATA2 in lymphatic endothelium [PMID:32155439, PMID:32182215], and FAT4 protein abundance is set post-translationally by USP51-mediated stabilization and UBE4B-mediated ubiquitination and degradation [PMID:31217854, PMID:40701960]. Loss-of-function FAT4 mutations cause periventricular neuronal heterotopia in humans [PMID:24056717], and FAT4 behaves as a tumor suppressor whose loss activates YAP and Wnt/β-catenin signaling [PMID:26575609, PMID:37658376].","teleology":[{"year":2008,"claim":"Established that vertebrate Fat4 is a PCP signaling component, answering whether Drosophila Fat signaling is conserved and linking it to oriented cell division and tissue morphogenesis.","evidence":"Fat4 knockout mice with genetic epistasis against Vangl2 and Fjx1 and gene expression analysis in kidney","pmids":["18604206"],"confidence":"High","gaps":["Molecular ligand of Fat4 not yet identified","Downstream effector pathway not defined","Mechanism of Fjx1 repression unknown"]},{"year":2011,"claim":"Identified DCHS1 as the Fat4 ligand-receptor partner, answering what molecule FAT4 engages and showing reciprocal protein-level dependence across many organs.","evidence":"Dchs1 knockout, Fat4/Dchs1 double mutant analysis and reciprocal antibody staining in mice","pmids":["21303848"],"confidence":"High","gaps":["Direct physical binding not biochemically demonstrated","Structural basis of interaction unknown","Intracellular signaling output not defined"]},{"year":2013,"claim":"Placed FAT4 upstream of YAP in the Hippo pathway during neurogenesis and tied FAT4 mutation to a human brain malformation.","evidence":"Mouse neuroepithelium knockdown with concurrent Yap rescue and human mutation identification","pmids":["24056717"],"confidence":"High","gaps":["Mechanism connecting FAT4 to YAP not resolved","Canonical vs non-canonical Hippo link unclear"]},{"year":2014,"claim":"Showed PCP is encoded by graded Fat4/Dchs1 expression and operates on an axis orthogonal to Frizzled-PCP, clarifying how directional information is established.","evidence":"Conditional and mosaic knockout mice with live imaging of facial branchiomotor neuron migration","pmids":["24998526"],"confidence":"High","gaps":["Molecular readout of gradient sensing unknown","Intracellular polarity machinery not identified"]},{"year":2015,"claim":"Resolved that FAT4 controls progenitor self-renewal non-autonomously via stromal-to-mesenchyme signaling, and notably can do so independently of YAP, revealing a YAP-independent branch.","evidence":"Tissue-specific conditional knockouts, Six2;Fat4 and Yap epistasis, and polarized Dchs1 localization in genetic mosaics","pmids":["26116661","26116666"],"confidence":"High","gaps":["Identity of the YAP-independent effector unknown","How stromal FAT4 transmits a signal across cell layers unresolved"]},{"year":2015,"claim":"Implicated FAT4 as a tumor suppressor acting through Wnt/β-catenin, extending its role beyond development to cancer.","evidence":"FAT4 siRNA knockdown in gastric cancer cells with pathway western blots and xenografts","pmids":["26633557"],"confidence":"Low","gaps":["Pathway activity inferred from western blot without direct binding evidence","No mechanism linking FAT4 to the β-catenin destruction complex shown"]},{"year":2016,"claim":"Distinguished FAT4 functional outputs that are YAP/TAZ-independent and proposed cis-heterodimerization with FAT1, broadening the interactor repertoire.","evidence":"Fat4/Fat1 and Fat4;Yap/Fat4;Taz double mutants, proteomics, and in vitro binding assays","pmids":["26209645","27145737","27381226"],"confidence":"Medium","gaps":["FAT1-FAT4 cis-heterodimer not confirmed in vivo","Effectors of the YAP/TAZ-independent branch not identified"]},{"year":2017,"claim":"Defined a non-canonical Hippo mechanism whereby FAT4 sequesters Amotl1 in the cytoplasm to restrict proliferation, identifying a mammalian intermediate downstream of FAT4.","evidence":"Fat4 mutant myocardium with nuclear fractionation, co-localization, and YAP transcriptional assays","pmids":["28239148"],"confidence":"High","gaps":["Direct FAT4-Amotl1 binding not structurally defined","How extracellular FAT4 engagement controls Amotl1 localization unclear"]},{"year":2017,"claim":"Provided biophysical evidence that Fat4-Dchs1 complexes self-stabilize and polarize, establishing the molecular feedback underlying boundary accumulation.","evidence":"Synthetic reconstitution of human Fat4/Ds1 in mammalian cells with live imaging and FRAP, plus lymphatic valve mutant analysis","pmids":["28826487","28705793"],"confidence":"High","gaps":["Molecular determinant of slowed complex dynamics not defined","Link from complex stability to downstream signaling unresolved"]},{"year":2019,"claim":"Identified RET as a direct FAT4 extracellular partner, showing FAT4 fine-tunes RET-GFRA1-GDNF receptor tyrosine kinase signaling beyond PCP/Hippo.","evidence":"Co-IP of FAT4-RET, conditional knockouts, and Gdnf heterozygous genetic rescue in kidney","pmids":["30853441"],"confidence":"High","gaps":["Structural basis of FAT4-RET interaction unknown","Whether DCHS1 engagement modulates RET binding untested"]},{"year":2019,"claim":"Tied FAT4 protein stability to deubiquitination and linked FAT4 loss to differential YAP/TAZ-Runx2 transcriptional output, adding post-translational and tissue-specific regulatory layers.","evidence":"Co-IP of FAT4-USP51 with bidirectional stability assays in endometrial cancer, and Dchs1/Fat4 mutants with Tead/Runx2 reporters in osteoblasts","pmids":["31217854","31358536","30832706"],"confidence":"High","gaps":["USP51 deubiquitination site on FAT4 not mapped","PI3K-AKT/mTOR link to FAT4 inferred only from western blot"]},{"year":2020,"claim":"Placed FAT4 transcriptionally downstream of Hedgehog/GLI2 and GATA2, defining how FAT4 expression is induced in gut and lymphatic contexts.","evidence":"GLI2 targetome and Fat4/Dchs1/Vangl2 mutants in gut; cell-autonomous Fat4 conditional knockout and GATA2 target validation in lymphatics","pmids":["32155439","32182215"],"confidence":"High","gaps":["Direct GLI2/GATA2 binding to the FAT4 locus in each tissue not all mapped","How flow is transduced to FAT4-dependent polarity unresolved"]},{"year":2023,"claim":"Delivered the atomic structure of the Fat4-Dchs1 interface, explaining the unusually high heterophilic affinity and a route for phosphoregulation.","evidence":"Co-crystal structure of human Fat4 EC1-4 with Dchs1 and biophysical affinity measurements","pmids":["36797229"],"confidence":"High","gaps":["Functional impact of extracellular phosphorylation on binding not tested in vivo","Full-length complex architecture beyond EC1-4 unknown"]},{"year":2023,"claim":"Mechanistically connected FAT4 to β-catenin destruction-complex-mediated degradation and a downstream immune-evasion axis in cancer.","evidence":"FAT4 overexpression with Co-IP of FAT4-β-catenin and PD-L1 glycosylation/ubiquitination assays in cervical cancer xenografts","pmids":["37658376"],"confidence":"Medium","gaps":["Direct FAT4-β-catenin binding interface not mapped","Single lab, requires independent confirmation"]},{"year":2024,"claim":"Demonstrated FAT4 can participate in IL-32-driven canonical Hippo activation via MST1/2, contrasting with its non-canonical roles elsewhere.","evidence":"IP-MS identification of IL-32-FAT4-MST1/2 complex and FAT4 knockdown in nucleus pulposus cells with a rat model","pmids":["39178518"],"confidence":"Medium","gaps":["Direct FAT4-MST1/2 binding not validated reciprocally","Reconciliation with non-canonical FAT4-Hippo activity unresolved"]},{"year":2025,"claim":"Defined the FAT4 intracellular domain as the driver of Dchs1 trans-endocytosis and actin-dependent boundary accumulation, explaining how the receptor enforces polarized complex distribution.","evidence":"Quantitative live imaging of Fat4 ICD deletion mutants with FRAP and actin polymerization inhibition; plus UBE4B Co-IP/proteomics establishing FAT4 ubiquitination and degradation","pmids":["39955614","40701960"],"confidence":"Medium","gaps":["ICD motifs mediating endocytosis not mapped","UBE4B ubiquitination sites on FAT4 undefined"]},{"year":2026,"claim":"Showed FAT4 directly binds YAP to retain it in the cytoplasm independently of LATS1/2 phosphorylation, consolidating a direct non-canonical Hippo control mechanism.","evidence":"Co-IP of FAT4-YAP, knockdown, nuclear fractionation in zebrafish and mouse models","pmids":["42023818"],"confidence":"Medium","gaps":["FAT4-YAP binding interface not mapped","How a transmembrane cadherin physically contacts cytoplasmic YAP unclear"]},{"year":null,"claim":"How a single extracellular Fat4-Dchs1 engagement event is transduced into the diverse intracellular outputs—non-canonical YAP/Amotl1 sequestration, YAP/TAZ-independent proliferation control, RET modulation, and β-catenin degradation—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking ligand binding to the multiple downstream branches","Tissue determinants selecting canonical vs non-canonical Hippo output unknown","Direct intracellular interaction interfaces (YAP, Amotl1, β-catenin) not structurally defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,5,19]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13,24,10]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,11,12]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[22]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,1,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,10,24]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,9,20]}],"complexes":["Fat4-Dchs1 heterophilic complex"],"partners":["DCHS1","YAP1","AMOTL1","RET","CTNNB1","USP51","UBE4B","FAT1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6V0I7","full_name":"Protocadherin Fat 4","aliases":["Cadherin family member 14","FAT tumor suppressor homolog 4","Fat-like cadherin protein FAT-J"],"length_aa":4981,"mass_kda":542.7,"function":"Cadherins are calcium-dependent cell adhesion proteins. 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Fat4 genetically interacts with the PCP genes Vangl2 and Fjx1 in cyst formation, and Fat4 represses Fjx1 expression, indicating conservation of Fat signaling from Drosophila to vertebrates.\",\n      \"method\": \"Genetic loss-of-function (Fat4 knockout mice), genetic epistasis with Vangl2 and Fjx1, gene expression analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype, genetic epistasis across multiple genes, replicated in multiple developmental contexts\",\n      \"pmids\": [\"18604206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Dchs1 and Fat4 function as a ligand-receptor pair during murine development; they are predominantly expressed in mesenchymal cells, and mutation of either gene increases protein staining for the other. They regulate planar cell polarity, kidney growth and branching, and cell survival in multiple organs including the ear, kidney, skeleton, intestine, heart and lung.\",\n      \"method\": \"Gene-targeted mutation (Dchs1 knockout mice), comparison with Fat4 mutants, double mutant analysis, antibody staining\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal single and double mutant analysis across multiple organs, protein staining, independently consistent with Drosophila pathway\",\n      \"pmids\": [\"21303848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mutations in FAT4 (and its ligand DCHS1) lead to periventricular neuronal heterotopia; reducing Dchs1 or Fat4 in mouse neuroepithelium increased progenitor cell numbers and reduced differentiation into neurons. These effects were countered by concurrent knockdown of Yap, placing FAT4 upstream of YAP in the Hippo signaling pathway during neurogenesis.\",\n      \"method\": \"Loss-of-function in mouse embryonic neuroepithelium (knockdown), Yap concurrent knockdown (epistasis), human genetic mutation identification\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via concurrent Yap knockdown rescue, defined cellular phenotype, human mutations identified\",\n      \"pmids\": [\"24056717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Fat4 and Dchs1 are expressed in complementary gradients and are required intrinsically within facial branchiomotor (FBM) neurons and extrinsically within the neuroepithelium for collective tangential neuronal migration and PCP. Fat-PCP and Fz-PCP regulate FBM neuron migration along orthogonal axes. Disruption of Dchs1 gradients by mosaic inactivation alters FBM neuron polarity and migration, implying that PCP is regulated via gradients of Fat4 and Dchs1 expression.\",\n      \"method\": \"Conditional and mosaic knockout mice, live imaging, PCP analysis, genetic epistasis\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — tissue-specific and mosaic KO with defined cellular polarity and migration phenotype, orthogonal axis epistasis established\",\n      \"pmids\": [\"24998526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FAT4 acts non-autonomously in the renal stroma to control nephron progenitors. Loss of Yap from cap mesenchyme (CM) in Fat4-null mice does not reduce the expanded CM, indicating FAT4 regulates the CM independently of YAP. Excess progenitors in Fat4 mutants are dependent on Six2. Dchs1 and its paralogue Dchs2 function partially redundantly to regulate nephron progenitor numbers. FAT4 in the stroma binds to DCHS1/2 in the CM to restrict progenitor self-renewal.\",\n      \"method\": \"Tissue-specific conditional knockouts, Six2−/−;Fat4−/− double mutants, electron microscopy, gene expression analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — tissue-specific KO, genetic epistasis with Six2 and Yap, multiple orthogonal methods\",\n      \"pmids\": [\"26116661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Fat4 and Dchs1 are implicated in signaling between stromal and cap mesenchyme cell layers in the kidney; Dchs1 protein is polarized within cap mesenchyme cells, accumulating at the interface with stromal cells, consistent with direct interaction with a stromal protein (Fat4). Dchs1 acts as a Fat4 receptor for stromal signaling essential for kidney development.\",\n      \"method\": \"Dchs1 conditional knockout mice, antibody staining of genetic mosaics revealing polarized Dchs1 protein localization, phenotypic comparison with Fat4 mutants\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — polarized protein localization in genetic mosaics, conditional KO with defined phenotype, consistent with ligand-receptor model\",\n      \"pmids\": [\"26116666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Fat1 and Fat4 interact genetically to regulate neural tube closure, neural progenitor proliferation, and apical constriction. Fat1 and Fat4 bind different sets of actin-regulating and junctional proteins. In vitro data suggest that Fat1 and Fat4 form cis-heterodimers, providing a mechanism for bringing together their diverse interactors.\",\n      \"method\": \"Fat1 and Fat4 mouse knockouts, in utero electroporation, proteomic analysis, in vitro binding assays\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic interaction, proteomic analysis, in vitro cis-heterodimer data in single lab\",\n      \"pmids\": [\"26209645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Dchs1-Fat4 PCP pathway controls cell orientation in the early skeletal condensation to define the shape and dimensions of the mouse sternum. This involves cell intercalation along differential Dchs1-Fat4 activity. Fat4 and Dchs1 establish polarized cell behavior intrinsically within the mesenchyme.\",\n      \"method\": \"Fat4 and Dchs1 knockout mice, cell orientation analysis in skeletal condensations\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular polarity phenotype, single lab\",\n      \"pmids\": [\"27145737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fat4 and Dchs1 regulate vertebral development through control of cell proliferation in the early sclerotome, independently of Yap and Taz; analysis of Fat4;Yap and Fat4;Taz double mutants and expression of transcriptional target Ctgf indicates this is a Yap/Taz-independent mechanism of Fat4-Dchs1 signaling.\",\n      \"method\": \"Fat4−/− and Dchs1−/− knockout mice, Fat4;Yap and Fat4;Taz double mutants, Ctgf expression analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — double mutant epistasis, defined cellular phenotype, single lab\",\n      \"pmids\": [\"27381226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fat4 suppression leads to increased phosphorylated Yap and nuclear accumulation of Yap in gastric cancer cells, promoting proliferation, migration, and cell cycle progression. Re-expression of full-length Fat4 decreases phosphorylated Yap and inhibits cell cycle progression. Fat4 reduction also leads to accumulation of cytoplasmic β-catenin via loss of restraint on cytoplasmic Yap.\",\n      \"method\": \"Fat4-shRNA knockdown, Fat4 overexpression, western blotting, cell proliferation and migration assays\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — knockdown and rescue with protein-level readouts, single lab, two methods\",\n      \"pmids\": [\"26575609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In the mouse heart, Fat4 modulates Hippo signaling to restrict cardiomyocyte growth and proliferation. Fat4 is not required for canonical activation of Hippo kinases but sequesters Amotl1 out of the nucleus; nuclear translocation of Amotl1 is accompanied by Yap1 to promote cardiomyocyte proliferation. Amotl1 is identified as a mammalian intermediate for non-canonical Hippo signaling downstream of Fat4.\",\n      \"method\": \"Fat4 mutant mouse myocardium analysis, Yap1 transcriptional activity assay, nuclear fractionation, co-localization studies\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined phenotype, mechanistic dissection of canonical vs non-canonical Hippo, identification of novel intermediate Amotl1\",\n      \"pmids\": [\"28239148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Dachsous1-Fat4 signaling is required specifically for lymphatic valve morphogenesis; valve endothelial cells are disoriented and fail to form proper valve leaflets in Fat4 or Dachsous1 mutant mice. Dachsous1 is polarized to membrane protrusions and cellular junctions of valve endothelial cells in vivo and in vitro.\",\n      \"method\": \"Fat4 and Dachsous1 mutant mice, Lifeact-GFP imaging of actin dynamics, in vitro and in vivo immunostaining of Dchs1 localization\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined valve phenotype, polarized protein localization shown in vivo, single lab\",\n      \"pmids\": [\"28705793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Fat4-Ds1 complexes accumulate on cell boundaries in a threshold-like manner and exhibit dramatically slower dynamics than unbound Fat4 and Ds1, providing evidence for a localized feedback mechanism based on enhanced stability of Fat4-Ds1 complexes. Co-expression of Fat4 and Ds1 in the same cells is sufficient to induce polarization of Fat4-Ds1 complexes.\",\n      \"method\": \"Synthetic biology platform in mammalian cells expressing human Fat4 and Ds1, live-cell imaging of complex dynamics and FRAP\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — quantitative live imaging reconstitution with biophysical measurements, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"28826487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FAT4 interacts with RET through extracellular cadherin repeats and perturbs the assembly of the RET-GFRA1-GDNF complex, thereby reducing RET signaling. Loss of Fat4 causes abnormal ureteric budding and excessive RET signaling; removal of one copy of the RET ligand Gdnf rescues Fat4−/− kidney development. FAT4 acts non-autonomously to regulate RET signaling.\",\n      \"method\": \"Fat4 knockout mice, conditional knockout analyses, co-immunoprecipitation of FAT4-RET interaction, Gdnf heterozygous rescue epistasis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP of FAT4-RET interaction, genetic rescue epistasis, conditional KO non-autonomous mechanism established\",\n      \"pmids\": [\"30853441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FAT4 regulates EMT and autophagy in colorectal cancer cells in part via the PI3K-AKT/mTOR and PI3K-AKT/GSK-3β signaling pathways; FAT4 promotes autophagy and inhibits EMT through PI3K activity regulation.\",\n      \"method\": \"FAT4 overexpression and knockdown, western blotting for PI3K/AKT pathway components, transwell assays, xenograft model\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway inference from western blot without direct biochemical mechanism\",\n      \"pmids\": [\"30832706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Dchs1-Fat4 signaling is essential for osteoblast differentiation; loss of Dchs1-Fat4 signaling increases Yap-Tead activity in osteoprogenitors, and Yap is required for proliferation in these cells. Taz is expressed in more-committed Runx2-expressing osteoblasts, and Taz-Tead activity is unaffected in Dchs1/Fat4 mutants. Yap and Taz differentially regulate Runx2 transcriptional activity, and the activity of Yap-Runx2 and Taz-Runx2 complexes is altered in Dchs1/Fat4 mutant osteoblasts.\",\n      \"method\": \"Dchs1 and Fat4 mutant mice, YAP and TAZ knockouts, reporter assays for Tead and Runx2 activity\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic mutants, epistasis, reporter assays for transcriptional complexes, multiple orthogonal methods\",\n      \"pmids\": [\"31358536\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FAT4 silencing in endometrial cancer decreases phosphorylation of LATS1/2 and YAP while increasing YAP nuclear translocation, consistent with Hippo pathway suppression. Co-immunoprecipitation confirmed direct binding of FAT4 and the deubiquitinating enzyme USP51. USP51 knockdown decreases FAT4 protein level while USP51 overexpression increases FAT4 protein level, indicating USP51 is required for FAT4 stability.\",\n      \"method\": \"FAT4 knockdown and overexpression, shRNA for USP51, PCR array, co-immunoprecipitation, western blotting\",\n      \"journal\": \"American journal of translational research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP confirms FAT4-USP51 interaction, bidirectional regulation of FAT4 stability shown, single lab\",\n      \"pmids\": [\"31217854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GLI2 (a Hedgehog transcriptional effector) directly activates atypical cadherin and PCP genes including Fat4; Fat4 and Dchs1 are critical for villus formation in gut development. The Fat4-Dchs1 axis acts in parallel to the core-Vangl2 PCP axis to control mesenchymal cell clustering. WNT5A guides oriented cell migration of PDGFRα+ mesenchymal cells via PCP.\",\n      \"method\": \"GLI2 targetome analysis, Fat4 and Dchs1 knockout mice, Vangl2 PCP-mutant mice, genetic interaction studies, live light-sheet fluorescence microscopy of cultured PDGFRα+ cells\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple knockout models, genetic epistasis with Vangl2, live imaging, GLI2 targetome establishing upstream regulation\",\n      \"pmids\": [\"32155439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FAT4 functions in a lymphatic endothelial cell-autonomous manner to control cell polarity in response to flow and is required for lymphatic vessel morphogenesis. FAT4 is a target gene of GATA2, a transcriptional regulator of lymphatic vascular development.\",\n      \"method\": \"Fat4 conditional knockout (cell-autonomous analysis), flow-dependent polarity assays, GATA2 target gene identification\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-autonomous conditional KO with defined polarity phenotype, GATA2 transcriptional target validation, single lab\",\n      \"pmids\": [\"32182215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The co-crystal structure of human Fat4 (EC domains 1-4) and Dachsous1 (Dchs1) establishes the molecular basis for Fat-Dachsous heterophilic interactions. The binding interface is extended along EC domains 1-4 of each protein. Fat4-Dchs1 affinity is among the highest reported for cadherin superfamily members, attributed to an extensive network of salt bridges not present in structurally similar protocadherin homodimers. Extracellular phosphorylation modifications may directly modulate Fat-Dachsous binding by introducing charged contacts across the interface.\",\n      \"method\": \"Co-crystal structure determination, biophysical affinity measurements, structural modeling of phosphorylation effects\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — co-crystal structure with biophysical validation, mechanistic basis for heterophilic interaction established\",\n      \"pmids\": [\"36797229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FAT4 overexpression binds β-catenin and antagonizes its nuclear localization, promoting phosphorylation and degradation of β-catenin by the destruction complex (AXIN1, APC, GSK3β, CK1). This suppresses STT3A-mediated PD-L1 N-glycosylation, causing PD-L1 ER accumulation and polyubiquitination-dependent degradation, thereby reducing immune evasion in cervical cancer.\",\n      \"method\": \"FAT4 overexpression, Co-IP of FAT4-β-catenin interaction, functional assays for PD-L1 glycosylation and ubiquitination, immunodeficient and immunocompetent xenograft models\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of FAT4-β-catenin, multiple downstream readouts, in vivo validation, single lab\",\n      \"pmids\": [\"37658376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IL-32 interacts with FAT4 and MST1/2 proteins (identified by immunoprecipitation and mass spectrometry); elevation of IL-32 enhances its interactions with FAT4 and MST1/2, prompting MST1/2 phosphorylation and activating the Hippo/YAP signaling pathway, causing matrix metabolism disorder in nucleus pulposus cells.\",\n      \"method\": \"Immunoprecipitation and mass spectrometry, lentiviral FAT4 knockdown, western blotting for MST1/2 phosphorylation and YAP, rat in vivo model\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — IP-MS identification of IL-32-FAT4-MST1/2 complex, functional FAT4 knockdown, single lab\",\n      \"pmids\": [\"39178518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The intracellular domain (ICD) of Fat4 is required for trans-endocytosis of Dchs1 into Fat4-expressing cells and for boundary accumulation of Fat4/Dchs1 complexes. The Fat4 ICD controls the internalization rate of Fat4/Dchs1 complexes. Actin polymerization is required for accumulation of Fat4/Dchs1 complexes at boundaries.\",\n      \"method\": \"Quantitative live imaging of Fat4 ICD deletion mutants, FRAP, actin polymerization inhibition, mammalian cell expression system\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative live imaging with deletion mutants and pharmacological inhibition, single lab, mechanistic dissection of ICD function\",\n      \"pmids\": [\"39955614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"UBE4B directly binds to and ubiquitinates FAT4, leading to its proteasomal degradation. Tandem Mass Tag (TMT) proteomics revealed FAT4 as a downstream target of UBE4B; UBE4B inhibits autophagy in gastric cancer cells by mediating FAT4 ubiquitination and degradation.\",\n      \"method\": \"Co-IP, TMT quantitative proteomics, western blot, transmission electron microscopy, UBE4B knockdown/overexpression\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and proteomics establishing UBE4B-FAT4 interaction, ubiquitination confirmed, single lab\",\n      \"pmids\": [\"40701960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FAT4 directly interacts with YAP (shown by co-immunoprecipitation) and retains YAP in the cytoplasm, blocking its nuclear translocation, independently of the canonical Hippo phosphorylation cascade (LATS1/2-mediated). FAT4 knockdown promotes nuclear translocation of YAP without altering canonical phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation of FAT4-YAP, FAT4 knockdown, nuclear fractionation, zebrafish and mouse in vivo models\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of direct FAT4-YAP interaction, non-canonical mechanism supported by phosphorylation analysis, single lab\",\n      \"pmids\": [\"42023818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FAT4 functions as a tumor suppressor in gastric cancer by modulating Wnt/β-catenin signaling; knockdown of FAT4 promotes growth and invasion via activation of Wnt/β-catenin signaling and induces EMT.\",\n      \"method\": \"FAT4 siRNA knockdown in gastric cancer cell lines, western blotting for Wnt/β-catenin pathway components, xenograft model in vivo\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway activity inferred from western blot without direct binding evidence\",\n      \"pmids\": [\"26633557\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FAT4 is a large transmembrane atypical cadherin that forms high-affinity heterophilic complexes with its ligand DCHS1/Dachsous1 (co-crystal structure resolved for EC domains 1–4), acting as a planar cell polarity (PCP) signaling receptor in multiple tissues; it functions upstream of the Hippo pathway by sequestering Amotl1 and directly binding YAP to retain it in the cytoplasm (independent of canonical LATS1/2 phosphorylation), represses Fjx1 expression, interacts with the RET receptor tyrosine kinase through its extracellular cadherin repeats to fine-tune RET-GFRA1-GDNF complex assembly, binds β-catenin to promote its destruction-complex-mediated degradation, and is regulated post-translationally by ubiquitination (via UBE4B) and stabilization (via USP51); its intracellular domain controls Fat4/Dchs1 complex internalization and boundary accumulation, while upstream Hedgehog/GLI2 signaling transcriptionally activates FAT4 and GATA2 regulates it in lymphatic endothelium.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FAT4 is a large transmembrane atypical cadherin that functions as a planar cell polarity (PCP) receptor governing oriented cell division, tissue growth, and progenitor behavior across multiple developing organs including kidney, ear, skeleton, heart, gut, brain, and lymphatic vasculature [#0, #1, #2]. It acts as the receptor for the ligand DCHS1 (Dachsous1, partially redundant with DCHS2), forming high-affinity heterophilic complexes whose structural basis lies in an extended binding interface across EC domains 1–4 stabilized by an extensive salt-bridge network [#19]; FAT4 and DCHS1 are expressed in complementary gradients and accumulate as polarized complexes at cell boundaries through a threshold-like, self-stabilizing feedback mechanism [#12, #5], with the FAT4 intracellular domain driving trans-endocytosis of DCHS1 and actin-dependent boundary accumulation [#22]. FAT4 acts upstream of the Hippo pathway largely through non-canonical routes: it restrains YAP nuclear translocation by directly binding YAP and by sequestering the intermediate Amotl1 in the cytoplasm, independent of canonical LATS1/2 phosphorylation, thereby limiting cardiomyocyte, neural progenitor, and osteoprogenitor proliferation [#10, #24, #2, #15], while in several developmental and cancer contexts it also regulates progenitor self-renewal and cell proliferation entirely independently of YAP/TAZ [#4, #8]. FAT4 additionally tunes RET–GFRA1–GDNF receptor tyrosine kinase signaling non-autonomously through its extracellular cadherin repeats during ureteric budding [#13], promotes β-catenin destruction-complex-mediated degradation [#20], and represses Fjx1 [#0]. FAT4 expression is controlled upstream by Hedgehog effector GLI2 and by GATA2 in lymphatic endothelium [#17, #18], and FAT4 protein abundance is set post-translationally by USP51-mediated stabilization and UBE4B-mediated ubiquitination and degradation [#16, #23]. Loss-of-function FAT4 mutations cause periventricular neuronal heterotopia in humans [#2], and FAT4 behaves as a tumor suppressor whose loss activates YAP and Wnt/β-catenin signaling [#9, #20].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that vertebrate Fat4 is a PCP signaling component, answering whether Drosophila Fat signaling is conserved and linking it to oriented cell division and tissue morphogenesis.\",\n      \"evidence\": \"Fat4 knockout mice with genetic epistasis against Vangl2 and Fjx1 and gene expression analysis in kidney\",\n      \"pmids\": [\"18604206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular ligand of Fat4 not yet identified\", \"Downstream effector pathway not defined\", \"Mechanism of Fjx1 repression unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified DCHS1 as the Fat4 ligand-receptor partner, answering what molecule FAT4 engages and showing reciprocal protein-level dependence across many organs.\",\n      \"evidence\": \"Dchs1 knockout, Fat4/Dchs1 double mutant analysis and reciprocal antibody staining in mice\",\n      \"pmids\": [\"21303848\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical binding not biochemically demonstrated\", \"Structural basis of interaction unknown\", \"Intracellular signaling output not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed FAT4 upstream of YAP in the Hippo pathway during neurogenesis and tied FAT4 mutation to a human brain malformation.\",\n      \"evidence\": \"Mouse neuroepithelium knockdown with concurrent Yap rescue and human mutation identification\",\n      \"pmids\": [\"24056717\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting FAT4 to YAP not resolved\", \"Canonical vs non-canonical Hippo link unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed PCP is encoded by graded Fat4/Dchs1 expression and operates on an axis orthogonal to Frizzled-PCP, clarifying how directional information is established.\",\n      \"evidence\": \"Conditional and mosaic knockout mice with live imaging of facial branchiomotor neuron migration\",\n      \"pmids\": [\"24998526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular readout of gradient sensing unknown\", \"Intracellular polarity machinery not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved that FAT4 controls progenitor self-renewal non-autonomously via stromal-to-mesenchyme signaling, and notably can do so independently of YAP, revealing a YAP-independent branch.\",\n      \"evidence\": \"Tissue-specific conditional knockouts, Six2;Fat4 and Yap epistasis, and polarized Dchs1 localization in genetic mosaics\",\n      \"pmids\": [\"26116661\", \"26116666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the YAP-independent effector unknown\", \"How stromal FAT4 transmits a signal across cell layers unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Implicated FAT4 as a tumor suppressor acting through Wnt/β-catenin, extending its role beyond development to cancer.\",\n      \"evidence\": \"FAT4 siRNA knockdown in gastric cancer cells with pathway western blots and xenografts\",\n      \"pmids\": [\"26633557\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Pathway activity inferred from western blot without direct binding evidence\", \"No mechanism linking FAT4 to the β-catenin destruction complex shown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Distinguished FAT4 functional outputs that are YAP/TAZ-independent and proposed cis-heterodimerization with FAT1, broadening the interactor repertoire.\",\n      \"evidence\": \"Fat4/Fat1 and Fat4;Yap/Fat4;Taz double mutants, proteomics, and in vitro binding assays\",\n      \"pmids\": [\"26209645\", \"27145737\", \"27381226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FAT1-FAT4 cis-heterodimer not confirmed in vivo\", \"Effectors of the YAP/TAZ-independent branch not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined a non-canonical Hippo mechanism whereby FAT4 sequesters Amotl1 in the cytoplasm to restrict proliferation, identifying a mammalian intermediate downstream of FAT4.\",\n      \"evidence\": \"Fat4 mutant myocardium with nuclear fractionation, co-localization, and YAP transcriptional assays\",\n      \"pmids\": [\"28239148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct FAT4-Amotl1 binding not structurally defined\", \"How extracellular FAT4 engagement controls Amotl1 localization unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided biophysical evidence that Fat4-Dchs1 complexes self-stabilize and polarize, establishing the molecular feedback underlying boundary accumulation.\",\n      \"evidence\": \"Synthetic reconstitution of human Fat4/Ds1 in mammalian cells with live imaging and FRAP, plus lymphatic valve mutant analysis\",\n      \"pmids\": [\"28826487\", \"28705793\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinant of slowed complex dynamics not defined\", \"Link from complex stability to downstream signaling unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified RET as a direct FAT4 extracellular partner, showing FAT4 fine-tunes RET-GFRA1-GDNF receptor tyrosine kinase signaling beyond PCP/Hippo.\",\n      \"evidence\": \"Co-IP of FAT4-RET, conditional knockouts, and Gdnf heterozygous genetic rescue in kidney\",\n      \"pmids\": [\"30853441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FAT4-RET interaction unknown\", \"Whether DCHS1 engagement modulates RET binding untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Tied FAT4 protein stability to deubiquitination and linked FAT4 loss to differential YAP/TAZ-Runx2 transcriptional output, adding post-translational and tissue-specific regulatory layers.\",\n      \"evidence\": \"Co-IP of FAT4-USP51 with bidirectional stability assays in endometrial cancer, and Dchs1/Fat4 mutants with Tead/Runx2 reporters in osteoblasts\",\n      \"pmids\": [\"31217854\", \"31358536\", \"30832706\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"USP51 deubiquitination site on FAT4 not mapped\", \"PI3K-AKT/mTOR link to FAT4 inferred only from western blot\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Placed FAT4 transcriptionally downstream of Hedgehog/GLI2 and GATA2, defining how FAT4 expression is induced in gut and lymphatic contexts.\",\n      \"evidence\": \"GLI2 targetome and Fat4/Dchs1/Vangl2 mutants in gut; cell-autonomous Fat4 conditional knockout and GATA2 target validation in lymphatics\",\n      \"pmids\": [\"32155439\", \"32182215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct GLI2/GATA2 binding to the FAT4 locus in each tissue not all mapped\", \"How flow is transduced to FAT4-dependent polarity unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Delivered the atomic structure of the Fat4-Dchs1 interface, explaining the unusually high heterophilic affinity and a route for phosphoregulation.\",\n      \"evidence\": \"Co-crystal structure of human Fat4 EC1-4 with Dchs1 and biophysical affinity measurements\",\n      \"pmids\": [\"36797229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional impact of extracellular phosphorylation on binding not tested in vivo\", \"Full-length complex architecture beyond EC1-4 unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mechanistically connected FAT4 to β-catenin destruction-complex-mediated degradation and a downstream immune-evasion axis in cancer.\",\n      \"evidence\": \"FAT4 overexpression with Co-IP of FAT4-β-catenin and PD-L1 glycosylation/ubiquitination assays in cervical cancer xenografts\",\n      \"pmids\": [\"37658376\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FAT4-β-catenin binding interface not mapped\", \"Single lab, requires independent confirmation\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated FAT4 can participate in IL-32-driven canonical Hippo activation via MST1/2, contrasting with its non-canonical roles elsewhere.\",\n      \"evidence\": \"IP-MS identification of IL-32-FAT4-MST1/2 complex and FAT4 knockdown in nucleus pulposus cells with a rat model\",\n      \"pmids\": [\"39178518\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FAT4-MST1/2 binding not validated reciprocally\", \"Reconciliation with non-canonical FAT4-Hippo activity unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined the FAT4 intracellular domain as the driver of Dchs1 trans-endocytosis and actin-dependent boundary accumulation, explaining how the receptor enforces polarized complex distribution.\",\n      \"evidence\": \"Quantitative live imaging of Fat4 ICD deletion mutants with FRAP and actin polymerization inhibition; plus UBE4B Co-IP/proteomics establishing FAT4 ubiquitination and degradation\",\n      \"pmids\": [\"39955614\", \"40701960\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ICD motifs mediating endocytosis not mapped\", \"UBE4B ubiquitination sites on FAT4 undefined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed FAT4 directly binds YAP to retain it in the cytoplasm independently of LATS1/2 phosphorylation, consolidating a direct non-canonical Hippo control mechanism.\",\n      \"evidence\": \"Co-IP of FAT4-YAP, knockdown, nuclear fractionation in zebrafish and mouse models\",\n      \"pmids\": [\"42023818\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FAT4-YAP binding interface not mapped\", \"How a transmembrane cadherin physically contacts cytoplasmic YAP unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single extracellular Fat4-Dchs1 engagement event is transduced into the diverse intracellular outputs—non-canonical YAP/Amotl1 sequestration, YAP/TAZ-independent proliferation control, RET modulation, and β-catenin degradation—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking ligand binding to the multiple downstream branches\", \"Tissue determinants selecting canonical vs non-canonical Hippo output unknown\", \"Direct intracellular interaction interfaces (YAP, Amotl1, β-catenin) not structurally defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 5, 19]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 10]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13, 24, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 11, 12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 1, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 10, 24]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 9, 20]}\n    ],\n    \"complexes\": [\"Fat4-Dchs1 heterophilic complex\"],\n    \"partners\": [\"DCHS1\", \"YAP1\", \"AMOTL1\", \"RET\", \"CTNNB1\", \"USP51\", \"UBE4B\", \"FAT1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}