{"gene":"ALKAL1","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":2014,"finding":"ALKAL1 (FAM150A) binds the extracellular domain of leukocyte tyrosine kinase (LTK) with high affinity (KD = 28 pM) and stimulates LTK phosphorylation in a ligand-dependent manner, establishing it as a functional ligand for LTK.","method":"Functional signaling screen of 3,191 extracellular proteins, binding affinity measurements, LTK phosphorylation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct binding assay with KD quantification, functional phosphorylation assay, large-scale screen with only two hits, replicated by multiple subsequent labs","pmids":["25331893"],"is_preprint":false},{"year":2015,"finding":"ALKAL1 (FAM150A/AUG-β) is specific for LTK and only weakly binds ALK, establishing a ligand hierarchy: ALKAL2 (FAM150B/AUG-α) activates both ALK and LTK, while ALKAL1 preferentially activates LTK.","method":"Detailed binding experiments using cells expressing ALK or LTK, receptor activation assays, NIH/3T3 transformation and Ba/F3 IL-3-independent growth assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal cell-based binding and functional assays, replicated across labs","pmids":["26630010"],"is_preprint":false},{"year":2015,"finding":"ALKAL1 (FAM150A) and ALKAL2 (FAM150B) are potent activating ligands for human ALK that bind to the extracellular domain of ALK and can drive 'superactivation' of activated ALK mutants from neuroblastoma.","method":"In vitro cell culture binding and activation assays, functional superactivation assays with neuroblastoma ALK mutants","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding and activation assays, independently replicated by multiple labs","pmids":["26418745"],"is_preprint":false},{"year":2017,"finding":"In zebrafish, ALKAL1 (aug-β) ligand is essential for iridophore development, and this function is mediated specifically through Ltk (not Alk); aug-α2 and aug-β are required for iridophore formation in the adult eye.","method":"Zebrafish genetic knockout/deficiency models, phenotypic analysis of iridophore patterning in embryonic and adult fish, epistasis with Ltk-deficient zebrafish","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function in vivo with defined cellular phenotype and epistasis placing ALKAL1 upstream of Ltk","pmids":["29078341"],"is_preprint":false},{"year":2017,"finding":"ALK-L1198F mutation (identified in anaplastic thyroid cancer) is not constitutively active but is activated by ALKAL1 (FAM150A/AUG-β) ligand in a ligand-dependent manner similar to wild-type ALK; ALK-G1201E shows only very weak activation by ALKAL1, likely due to impaired protein stability.","method":"In vitro cell culture biochemical assays, Drosophila in vivo analyses, ALK inhibitor sensitivity assays","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple model systems (in vitro + Drosophila) in single lab, functional activation assays","pmids":["28030793"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM, NMR, and X-ray crystallography reveal that ALKAL1 acts as a monomeric ligand that induces ALK dimerization with 2:1 stoichiometry (one cytokine per two receptors), while ALKAL2 can act as a dimeric ligand enabling 2:2 assemblies; ALKAL1 causes the ALK extracellular region to undergo a pronounced ligand-induced rearrangement adopting an orientation parallel to the membrane surface, further stabilized by ligand-membrane interaction.","method":"Cryo-electron microscopy, NMR, X-ray crystallography, structural analysis of human ALK-ALKAL1/2 complexes","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic-resolution structures by three complementary structural methods in a single rigorous study","pmids":["34819673"],"is_preprint":false},{"year":2021,"finding":"X-ray crystal structures show ALKAL1 and ALKAL2 are monomeric three-helix bundle cytokines; their binding to ALK and LTK elicits dimeric 2:1 assemblies (one cytokine tenting two receptors) with two-fold symmetry proximal to the cell membrane; the membrane-proximal EGF-like domain of ALK dictates apparent cytokine preference between ALK and LTK.","method":"X-ray crystallography of ALK/LTK extracellular domains in complex with ALKAL1 and ALKAL2, structure-function mutagenesis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structures with functional validation, independently consistent with Reshetnyak et al. 2021","pmids":["34646012"],"is_preprint":false},{"year":2025,"finding":"Reanalysis of cryo-EM data confirms that both 2:1 and 2:2 ALK-ALKAL2 stoichiometric assemblies coexist in the same dataset; a 3.2 Å structure of the 2:1 ALK-ALKAL2 complex was resolved, reconciling ALK and LTK receptor dimerization modes and directly showing that LTK-ALKAL1 and ALK-ALKAL2 can share a common 2:1 receptor dimerization mode.","method":"Cryo-EM reanalysis (cryoSPARC particle rebalancing, RELION 3D refinement with Blush regularization) of deposited EMPIAR-10930 data","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — high-resolution structural analysis, single reanalysis study but with rigorous computational methods","pmids":["40208865"],"is_preprint":false},{"year":2019,"finding":"ALKAL1 (FAM150A) ligand is necessary for ALK activation in BRAF inhibitor-resistant melanoma; ALK activates the PI3K/AKT pathway to confer BRAFi resistance.","method":"Phospho-RTK array, FAM150A knockdown/overexpression, PI3K/AKT pathway analysis in cell culture and mouse xenograft models","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional knockdown with pathway readout and in vivo validation, single lab","pmids":["31229894"],"is_preprint":false},{"year":2021,"finding":"ALKAL1 silencing inhibits tumorigenesis, metastasis, and invasion of colorectal cancer cells via suppression of the Sonic Hedgehog (SHH) signaling pathway, which is essential for ALKAL1-induced migration.","method":"siRNA gene silencing, in vitro migration/invasion assays, in vivo tumor assays, GSEA, Western blotting, luciferase reporter assays for SHH pathway","journal":"Journal of Cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with pathway reporter validation in vitro and in vivo, single lab","pmids":["33391411"],"is_preprint":false},{"year":2024,"finding":"ALKAL1 is a target gene of aryl hydrocarbon receptor (AhR) in MerTK+ macrophages and facilitates MerTK phosphorylation, resulting in heightened phagocytic activity and polarization toward an immunosuppressive phenotype in the melanoma tumor microenvironment.","method":"Single-cell RNA sequencing, adoptive transfer experiments, mechanistic studies with AhR antagonist, phosphorylation assays","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mechanistic assays including in vivo adoptive transfer and phosphorylation readout, single lab","pmids":["39365866"],"is_preprint":false}],"current_model":"ALKAL1 (FAM150A/AUG-β) is a small monomeric three-helix bundle cytokine that acts as an activating ligand preferentially for LTK (and weakly for ALK), binding with picomolar affinity to induce receptor extracellular domain rearrangement and dimerization in a 2:1 (ligand:receptor dimer) stoichiometry proximal to the cell membrane, thereby activating downstream signaling pathways including PI3K/AKT and SHH; in vivo, ALKAL1 is physiologically required for Ltk-mediated iridophore development in zebrafish, and in pathological contexts it promotes cancer progression, BRAFi resistance, and nociceptor sensitization through ALK/LTK activation."},"narrative":{"mechanistic_narrative":"ALKAL1 (FAM150A/AUG-β) is a secreted cytokine that functions as a high-affinity activating ligand for the receptor tyrosine kinase LTK, binding its extracellular domain with picomolar affinity (KD = 28 pM) to drive ligand-dependent receptor phosphorylation [PMID:25331893]. It establishes a defined ligand hierarchy in which ALKAL1 preferentially activates LTK while only weakly engaging the related receptor ALK, in contrast to ALKAL2 which activates both [PMID:26630010]; nonetheless ALKAL1 can bind and activate the ALK extracellular domain, including superactivating oncogenic ALK mutants [PMID:26418745, PMID:28030793]. Structurally, ALKAL1 is a monomeric three-helix bundle cytokine that induces receptor dimerization with a 2:1 (ligand:receptor dimer) stoichiometry, tenting two receptors together and triggering a pronounced ligand-induced rearrangement of the receptor extracellular region into an orientation parallel to and stabilized against the membrane surface; the membrane-proximal EGF-like domain of the receptor dictates ALK-versus-LTK preference [PMID:34819673, PMID:34646012]. Physiologically, ALKAL1 is required in vivo for iridophore development in zebrafish, acting specifically through Ltk rather than Alk [PMID:29078341]. In pathological settings, ALKAL1 promotes ALK-driven BRAF-inhibitor resistance in melanoma via the PI3K/AKT pathway [PMID:31229894], drives colorectal cancer migration, invasion, and metastasis through Sonic Hedgehog signaling [PMID:33391411], and, as an AhR target gene in MerTK+ macrophages, facilitates MerTK phosphorylation to promote phagocytosis and an immunosuppressive tumor microenvironment [PMID:39365866].","teleology":[{"year":2014,"claim":"Identified the orphan-receptor ligand for LTK, answering what activates this receptor tyrosine kinase and defining ALKAL1 as a bona fide functional ligand.","evidence":"Large-scale functional signaling screen of 3,191 extracellular proteins with binding affinity and LTK phosphorylation assays","pmids":["25331893"],"confidence":"High","gaps":["Did not resolve binding stoichiometry or structural mode of receptor engagement","Downstream signaling pathways not delineated"]},{"year":2015,"claim":"Established the receptor selectivity of ALKAL1 versus ALKAL2, clarifying which receptor each ligand preferentially activates and resolving a ligand hierarchy across ALK and LTK.","evidence":"Cell-based binding and receptor activation assays plus NIH/3T3 transformation and Ba/F3 IL-3-independent growth assays","pmids":["26630010","26418745"],"confidence":"High","gaps":["Structural basis of differential ALK/LTK preference not yet defined","Physiological relevance of weak ALK binding by ALKAL1 unclear"]},{"year":2017,"claim":"Demonstrated an in vivo physiological role, showing ALKAL1 is genetically required for iridophore development through Ltk, placing the ligand upstream of a specific receptor in a defined developmental process.","evidence":"Zebrafish genetic loss-of-function models with iridophore phenotyping and epistasis against Ltk-deficient fish","pmids":["29078341"],"confidence":"High","gaps":["Mammalian developmental role not addressed","Downstream signaling from Ltk in iridophores not mapped"]},{"year":2017,"claim":"Showed ALKAL1 can activate cancer-associated ALK mutants in a ligand-dependent manner, distinguishing ligand-dependent from constitutively active oncogenic mutations.","evidence":"In vitro biochemical assays and Drosophila in vivo analyses with ALK inhibitor sensitivity testing","pmids":["28030793"],"confidence":"Medium","gaps":["Single-lab study across model systems","Clinical relevance in thyroid cancer patients not established"]},{"year":2021,"claim":"Resolved the structural mechanism of receptor activation, defining ALKAL1 as a monomeric cytokine that drives 2:1 receptor dimerization and a membrane-proximal extracellular rearrangement, and identifying the determinant of receptor preference.","evidence":"Cryo-EM, NMR, and X-ray crystallography of human ALK/LTK extracellular complexes with structure-function mutagenesis","pmids":["34819673","34646012"],"confidence":"High","gaps":["Full-length transmembrane/intracellular activation step not captured","Dynamics of membrane stabilization in cells not directly observed"]},{"year":2019,"claim":"Linked ALKAL1 to therapy resistance, showing it is necessary for ALK activation driving BRAF-inhibitor resistance via PI3K/AKT.","evidence":"Phospho-RTK arrays, FAM150A knockdown/overexpression, and PI3K/AKT readouts in melanoma cell culture and mouse xenografts","pmids":["31229894"],"confidence":"Medium","gaps":["Single-lab study","Whether effect is LTK- or ALK-mediated not fully resolved"]},{"year":2021,"claim":"Connected ALKAL1 to a distinct oncogenic pathway, showing its tumor-promoting activity in colorectal cancer depends on Sonic Hedgehog signaling.","evidence":"siRNA silencing with migration/invasion assays, in vivo tumor assays, GSEA, and SHH luciferase reporters","pmids":["33391411"],"confidence":"Medium","gaps":["Mechanistic link between receptor activation and SHH pathway not defined","Single-lab study"]},{"year":2024,"claim":"Revealed an immune-microenvironment role, showing ALKAL1 is an AhR target in macrophages that promotes MerTK phosphorylation and immunosuppressive polarization.","evidence":"Single-cell RNA-seq, adoptive transfer, AhR antagonist studies, and phosphorylation assays in melanoma models","pmids":["39365866"],"confidence":"Medium","gaps":["Direct ALKAL1-MerTK binding not demonstrated","Single-lab study"]},{"year":2025,"claim":"Reconciled competing receptor dimerization models, confirming that LTK-ALKAL1 and ALK-ALKAL2 share a common 2:1 dimerization mode and that 2:1 and 2:2 assemblies coexist.","evidence":"Cryo-EM reanalysis of deposited EMPIAR-10930 data with particle rebalancing and Blush-regularized refinement","pmids":["40208865"],"confidence":"Medium","gaps":["Single computational reanalysis","Functional consequence of coexisting stoichiometries in cells not tested"]},{"year":null,"claim":"How ALKAL1 receptor activation mechanistically couples to the divergent downstream programs (PI3K/AKT, SHH, MerTK) and the mammalian physiological function of the ligand remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mammalian developmental loss-of-function phenotype reported in the corpus","Mechanistic link from receptor dimerization to SHH and MerTK pathways undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,2,5,6]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,5,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,8,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,9,10]}],"complexes":[],"partners":["LTK","ALK"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6UXT8","full_name":"ALK and LTK ligand 1","aliases":["Augmentor beta","AUG-beta"],"length_aa":129,"mass_kda":14.3,"function":"Cytokine that acts as a physiological ligand for receptor tyrosine kinase LTK, leading to its activation (PubMed:25331893, PubMed:26418745, PubMed:26630010, PubMed:34646012, PubMed:34819673). Monomeric ALKAL1 binds to LTK, leading to LTK homodimerization and activation (PubMed:34646012, PubMed:34819673). In contrast to ALKAL2, does not act as a potent physiological ligand for ALK (PubMed:26418745, PubMed:34646012)","subcellular_location":"Secreted; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q6UXT8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ALKAL1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ALKAL1","total_profiled":1310},"omim":[{"mim_id":"619671","title":"ALK AND LTK LIGAND 2; ALKAL2","url":"https://www.omim.org/entry/619671"},{"mim_id":"619670","title":"ALK AND LTK LIGAND 1; ALKAL1","url":"https://www.omim.org/entry/619670"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"gallbladder","ntpm":2.2},{"tissue":"thyroid gland","ntpm":2.2},{"tissue":"urinary bladder","ntpm":1.5}],"url":"https://www.proteinatlas.org/search/ALKAL1"},"hgnc":{"alias_symbol":["UNQ9433","AUGB"],"prev_symbol":["FAM150A"]},"alphafold":{"accession":"Q6UXT8","domains":[{"cath_id":"-","chopping":"68-129","consensus_level":"medium","plddt":80.0637,"start":68,"end":129}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXT8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXT8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXT8-F1-predicted_aligned_error_v6.png","plddt_mean":67.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ALKAL1","jax_strain_url":"https://www.jax.org/strain/search?query=ALKAL1"},"sequence":{"accession":"Q6UXT8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UXT8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UXT8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXT8"}},"corpus_meta":[{"pmid":"2082185","id":"PMC_2082185","title":"5'-Heterogeneity in human 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affinity measurements, LTK phosphorylation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct binding assay with KD quantification, functional phosphorylation assay, large-scale screen with only two hits, replicated by multiple subsequent labs\",\n      \"pmids\": [\"25331893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ALKAL1 (FAM150A/AUG-β) is specific for LTK and only weakly binds ALK, establishing a ligand hierarchy: ALKAL2 (FAM150B/AUG-α) activates both ALK and LTK, while ALKAL1 preferentially activates LTK.\",\n      \"method\": \"Detailed binding experiments using cells expressing ALK or LTK, receptor activation assays, NIH/3T3 transformation and Ba/F3 IL-3-independent growth assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal cell-based binding and functional assays, replicated across labs\",\n      \"pmids\": [\"26630010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ALKAL1 (FAM150A) and ALKAL2 (FAM150B) are potent activating ligands for human ALK that bind to the extracellular domain of ALK and can drive 'superactivation' of activated ALK mutants from neuroblastoma.\",\n      \"method\": \"In vitro cell culture binding and activation assays, functional superactivation assays with neuroblastoma ALK mutants\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding and activation assays, independently replicated by multiple labs\",\n      \"pmids\": [\"26418745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In zebrafish, ALKAL1 (aug-β) ligand is essential for iridophore development, and this function is mediated specifically through Ltk (not Alk); aug-α2 and aug-β are required for iridophore formation in the adult eye.\",\n      \"method\": \"Zebrafish genetic knockout/deficiency models, phenotypic analysis of iridophore patterning in embryonic and adult fish, epistasis with Ltk-deficient zebrafish\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function in vivo with defined cellular phenotype and epistasis placing ALKAL1 upstream of Ltk\",\n      \"pmids\": [\"29078341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ALK-L1198F mutation (identified in anaplastic thyroid cancer) is not constitutively active but is activated by ALKAL1 (FAM150A/AUG-β) ligand in a ligand-dependent manner similar to wild-type ALK; ALK-G1201E shows only very weak activation by ALKAL1, likely due to impaired protein stability.\",\n      \"method\": \"In vitro cell culture biochemical assays, Drosophila in vivo analyses, ALK inhibitor sensitivity assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple model systems (in vitro + Drosophila) in single lab, functional activation assays\",\n      \"pmids\": [\"28030793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM, NMR, and X-ray crystallography reveal that ALKAL1 acts as a monomeric ligand that induces ALK dimerization with 2:1 stoichiometry (one cytokine per two receptors), while ALKAL2 can act as a dimeric ligand enabling 2:2 assemblies; ALKAL1 causes the ALK extracellular region to undergo a pronounced ligand-induced rearrangement adopting an orientation parallel to the membrane surface, further stabilized by ligand-membrane interaction.\",\n      \"method\": \"Cryo-electron microscopy, NMR, X-ray crystallography, structural analysis of human ALK-ALKAL1/2 complexes\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic-resolution structures by three complementary structural methods in a single rigorous study\",\n      \"pmids\": [\"34819673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"X-ray crystal structures show ALKAL1 and ALKAL2 are monomeric three-helix bundle cytokines; their binding to ALK and LTK elicits dimeric 2:1 assemblies (one cytokine tenting two receptors) with two-fold symmetry proximal to the cell membrane; the membrane-proximal EGF-like domain of ALK dictates apparent cytokine preference between ALK and LTK.\",\n      \"method\": \"X-ray crystallography of ALK/LTK extracellular domains in complex with ALKAL1 and ALKAL2, structure-function mutagenesis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structures with functional validation, independently consistent with Reshetnyak et al. 2021\",\n      \"pmids\": [\"34646012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Reanalysis of cryo-EM data confirms that both 2:1 and 2:2 ALK-ALKAL2 stoichiometric assemblies coexist in the same dataset; a 3.2 Å structure of the 2:1 ALK-ALKAL2 complex was resolved, reconciling ALK and LTK receptor dimerization modes and directly showing that LTK-ALKAL1 and ALK-ALKAL2 can share a common 2:1 receptor dimerization mode.\",\n      \"method\": \"Cryo-EM reanalysis (cryoSPARC particle rebalancing, RELION 3D refinement with Blush regularization) of deposited EMPIAR-10930 data\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution structural analysis, single reanalysis study but with rigorous computational methods\",\n      \"pmids\": [\"40208865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ALKAL1 (FAM150A) ligand is necessary for ALK activation in BRAF inhibitor-resistant melanoma; ALK activates the PI3K/AKT pathway to confer BRAFi resistance.\",\n      \"method\": \"Phospho-RTK array, FAM150A knockdown/overexpression, PI3K/AKT pathway analysis in cell culture and mouse xenograft models\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional knockdown with pathway readout and in vivo validation, single lab\",\n      \"pmids\": [\"31229894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ALKAL1 silencing inhibits tumorigenesis, metastasis, and invasion of colorectal cancer cells via suppression of the Sonic Hedgehog (SHH) signaling pathway, which is essential for ALKAL1-induced migration.\",\n      \"method\": \"siRNA gene silencing, in vitro migration/invasion assays, in vivo tumor assays, GSEA, Western blotting, luciferase reporter assays for SHH pathway\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with pathway reporter validation in vitro and in vivo, single lab\",\n      \"pmids\": [\"33391411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ALKAL1 is a target gene of aryl hydrocarbon receptor (AhR) in MerTK+ macrophages and facilitates MerTK phosphorylation, resulting in heightened phagocytic activity and polarization toward an immunosuppressive phenotype in the melanoma tumor microenvironment.\",\n      \"method\": \"Single-cell RNA sequencing, adoptive transfer experiments, mechanistic studies with AhR antagonist, phosphorylation assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mechanistic assays including in vivo adoptive transfer and phosphorylation readout, single lab\",\n      \"pmids\": [\"39365866\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ALKAL1 (FAM150A/AUG-β) is a small monomeric three-helix bundle cytokine that acts as an activating ligand preferentially for LTK (and weakly for ALK), binding with picomolar affinity to induce receptor extracellular domain rearrangement and dimerization in a 2:1 (ligand:receptor dimer) stoichiometry proximal to the cell membrane, thereby activating downstream signaling pathways including PI3K/AKT and SHH; in vivo, ALKAL1 is physiologically required for Ltk-mediated iridophore development in zebrafish, and in pathological contexts it promotes cancer progression, BRAFi resistance, and nociceptor sensitization through ALK/LTK activation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ALKAL1 (FAM150A/AUG-β) is a secreted cytokine that functions as a high-affinity activating ligand for the receptor tyrosine kinase LTK, binding its extracellular domain with picomolar affinity (KD = 28 pM) to drive ligand-dependent receptor phosphorylation [#0]. It establishes a defined ligand hierarchy in which ALKAL1 preferentially activates LTK while only weakly engaging the related receptor ALK, in contrast to ALKAL2 which activates both [#1]; nonetheless ALKAL1 can bind and activate the ALK extracellular domain, including superactivating oncogenic ALK mutants [#2, #4]. Structurally, ALKAL1 is a monomeric three-helix bundle cytokine that induces receptor dimerization with a 2:1 (ligand:receptor dimer) stoichiometry, tenting two receptors together and triggering a pronounced ligand-induced rearrangement of the receptor extracellular region into an orientation parallel to and stabilized against the membrane surface; the membrane-proximal EGF-like domain of the receptor dictates ALK-versus-LTK preference [#5, #6]. Physiologically, ALKAL1 is required in vivo for iridophore development in zebrafish, acting specifically through Ltk rather than Alk [#3]. In pathological settings, ALKAL1 promotes ALK-driven BRAF-inhibitor resistance in melanoma via the PI3K/AKT pathway [#8], drives colorectal cancer migration, invasion, and metastasis through Sonic Hedgehog signaling [#9], and, as an AhR target gene in MerTK+ macrophages, facilitates MerTK phosphorylation to promote phagocytosis and an immunosuppressive tumor microenvironment [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified the orphan-receptor ligand for LTK, answering what activates this receptor tyrosine kinase and defining ALKAL1 as a bona fide functional ligand.\",\n      \"evidence\": \"Large-scale functional signaling screen of 3,191 extracellular proteins with binding affinity and LTK phosphorylation assays\",\n      \"pmids\": [\"25331893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve binding stoichiometry or structural mode of receptor engagement\", \"Downstream signaling pathways not delineated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established the receptor selectivity of ALKAL1 versus ALKAL2, clarifying which receptor each ligand preferentially activates and resolving a ligand hierarchy across ALK and LTK.\",\n      \"evidence\": \"Cell-based binding and receptor activation assays plus NIH/3T3 transformation and Ba/F3 IL-3-independent growth assays\",\n      \"pmids\": [\"26630010\", \"26418745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of differential ALK/LTK preference not yet defined\", \"Physiological relevance of weak ALK binding by ALKAL1 unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated an in vivo physiological role, showing ALKAL1 is genetically required for iridophore development through Ltk, placing the ligand upstream of a specific receptor in a defined developmental process.\",\n      \"evidence\": \"Zebrafish genetic loss-of-function models with iridophore phenotyping and epistasis against Ltk-deficient fish\",\n      \"pmids\": [\"29078341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian developmental role not addressed\", \"Downstream signaling from Ltk in iridophores not mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed ALKAL1 can activate cancer-associated ALK mutants in a ligand-dependent manner, distinguishing ligand-dependent from constitutively active oncogenic mutations.\",\n      \"evidence\": \"In vitro biochemical assays and Drosophila in vivo analyses with ALK inhibitor sensitivity testing\",\n      \"pmids\": [\"28030793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study across model systems\", \"Clinical relevance in thyroid cancer patients not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolved the structural mechanism of receptor activation, defining ALKAL1 as a monomeric cytokine that drives 2:1 receptor dimerization and a membrane-proximal extracellular rearrangement, and identifying the determinant of receptor preference.\",\n      \"evidence\": \"Cryo-EM, NMR, and X-ray crystallography of human ALK/LTK extracellular complexes with structure-function mutagenesis\",\n      \"pmids\": [\"34819673\", \"34646012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length transmembrane/intracellular activation step not captured\", \"Dynamics of membrane stabilization in cells not directly observed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Linked ALKAL1 to therapy resistance, showing it is necessary for ALK activation driving BRAF-inhibitor resistance via PI3K/AKT.\",\n      \"evidence\": \"Phospho-RTK arrays, FAM150A knockdown/overexpression, and PI3K/AKT readouts in melanoma cell culture and mouse xenografts\",\n      \"pmids\": [\"31229894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Whether effect is LTK- or ALK-mediated not fully resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected ALKAL1 to a distinct oncogenic pathway, showing its tumor-promoting activity in colorectal cancer depends on Sonic Hedgehog signaling.\",\n      \"evidence\": \"siRNA silencing with migration/invasion assays, in vivo tumor assays, GSEA, and SHH luciferase reporters\",\n      \"pmids\": [\"33391411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between receptor activation and SHH pathway not defined\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed an immune-microenvironment role, showing ALKAL1 is an AhR target in macrophages that promotes MerTK phosphorylation and immunosuppressive polarization.\",\n      \"evidence\": \"Single-cell RNA-seq, adoptive transfer, AhR antagonist studies, and phosphorylation assays in melanoma models\",\n      \"pmids\": [\"39365866\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ALKAL1-MerTK binding not demonstrated\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reconciled competing receptor dimerization models, confirming that LTK-ALKAL1 and ALK-ALKAL2 share a common 2:1 dimerization mode and that 2:1 and 2:2 assemblies coexist.\",\n      \"evidence\": \"Cryo-EM reanalysis of deposited EMPIAR-10930 data with particle rebalancing and Blush-regularized refinement\",\n      \"pmids\": [\"40208865\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single computational reanalysis\", \"Functional consequence of coexisting stoichiometries in cells not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ALKAL1 receptor activation mechanistically couples to the divergent downstream programs (PI3K/AKT, SHH, MerTK) and the mammalian physiological function of the ligand remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mammalian developmental loss-of-function phenotype reported in the corpus\", \"Mechanistic link from receptor dimerization to SHH and MerTK pathways undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 2, 5, 6]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 5, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 9, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"LTK\", \"ALK\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}