{"gene":"ALKAL2","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":2015,"finding":"ALKAL2 (FAM150B/AUG-α) is a ligand for ALK receptor tyrosine kinase. It binds ALK with high affinity and activates ALK in cells with subnanomolar potency. ALKAL2 also binds and activates LTK. In contrast, ALKAL1 (FAM150A/AUG-β) is specific for LTK and only weakly binds ALK. ALKAL2 stimulates transformation of NIH/3T3 cells expressing ALK and induces IL-3-independent growth of Ba/F3 cells expressing ALK.","method":"Binding assays, cell-based activation assays, NIH/3T3 transformation assay, Ba/F3 IL-3-independent growth assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays (binding, phosphorylation, transformation, IL-3-independence), replicated concept in companion paper (PMID:26418745)","pmids":["26630010"],"is_preprint":false},{"year":2015,"finding":"FAM150A (ALKAL1) and FAM150B (ALKAL2) are potent activating ligands for human ALK. They bind the extracellular domain of ALK and activate wild-type ALK as well as drive 'superactivation' of neuroblastoma-associated gain-of-function ALK mutants.","method":"Binding assays to ALK extracellular domain, cell-based ALK phosphorylation assays, superactivation assays with neuroblastoma ALK mutants","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding and functional activation assays, multiple ALK variants tested, independently replicated by PMID:26630010","pmids":["26418745"],"is_preprint":false},{"year":2014,"finding":"FAM150A and FAM150B (ALKAL2) were identified as ligands for the orphan receptor LTK by screening 3,191 extracellular proteins. FAM150A binds LTK extracellular domain with high affinity (KD = 28 pM) and stimulates LTK phosphorylation in a ligand-dependent manner.","method":"Large-scale extracellular proteome signaling screen, binding affinity measurement (KD), LTK phosphorylation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional screen with direct binding quantification, confirmed ligand-dependent receptor activation","pmids":["25331893"],"is_preprint":false},{"year":2017,"finding":"In zebrafish, ALKAL2 orthologs (aug-α1 and aug-α2) are essential for embryonic iridophore development and adult body coloration. These effects are mediated entirely through Ltk and not Alk, establishing a physiological link between ALKAL2 ligands and Ltk-driven neural crest-derived cell differentiation.","method":"Zebrafish genetic knockdown/knockout, epistasis with ltk-deficient zebrafish, phenotypic analysis of iridophore patterning","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis using multiple ligand knockdowns and receptor-deficient zebrafish, clear cell-type-specific phenotype","pmids":["29078341"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM, NMR, and X-ray crystallography reveal the mechanism of ALK activation by ALKAL2: ALKAL2 is a dimeric ligand that drives ALK dimerization. The ALK extracellular region undergoes a pronounced ligand-induced rearrangement and adopts an orientation parallel to the membrane surface, further stabilized by ligand-membrane interaction. ALK-ECR domain architecture and the receptor-ligand complex geometry are defined at atomic resolution.","method":"Cryo-electron microscopy, NMR spectroscopy, X-ray crystallography","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic structures determined by three independent structural methods (cryo-EM, NMR, X-ray crystallography) in one study","pmids":["34819673"],"is_preprint":false},{"year":2021,"finding":"X-ray crystallography reveals that ALKAL2 is a monomeric three-helix bundle cytokine. Its binding to ALK elicits a dimeric assembly with two-fold symmetry that tents a single cytokine molecule proximal to the cell membrane. The cytokine-binding segment of ALK comprises a permuted TNF-like module bracing a glycine-rich subdomain. The membrane-proximal EGF-like domain dictates the apparent cytokine preference of ALK.","method":"X-ray crystallography, structure-function mutagenesis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structures with functional validation by mutagenesis, published concurrently with Reshetnyak et al. 2021","pmids":["34646012"],"is_preprint":false},{"year":2021,"finding":"ALKAL2 overexpression in mice drives ALK tyrosine kinase inhibitor-sensitive neuroblastoma in the absence of ALK mutation, demonstrating that ALKAL2 ligand alone (autocrine/paracrine signaling) is sufficient to potentiate MYCN-driven neuroblastoma progression.","method":"Transgenic mouse model (ALKAL2 overexpression), ALK TKI treatment (in vivo), tumor burden assessment","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic model with pharmacological validation using clinical ALK inhibitors","pmids":["33411331"],"is_preprint":false},{"year":2017,"finding":"ALK mutations L1198F and G1201E originally described as constitutively activating in anaplastic thyroid cancer are not ligand-independent. ALK-L1198F is activated by ALKAL2 (FAM150B) in a ligand-dependent manner similar to wild-type ALK. ALK-G1201E shows only very weak activation by ALKAL2, most likely due to impaired protein stability.","method":"In vitro cell culture phosphorylation assays, biochemical analysis, Drosophila in vivo assays","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple assay systems (cell-based, biochemical, Drosophila), single laboratory","pmids":["28030793"],"is_preprint":false},{"year":2022,"finding":"ALKAL2 is expressed in TRPV1+ peptidergic nociceptors during inflammation or injury. Nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn. Depletion of ALKAL2 in DRG or ALK inhibition reversed thermal hyperalgesia and mechanical allodynia, establishing ALKAL2/ALK as a central regulator of nociceptor sensitization.","method":"Coculture expression system, nociceptor excitability assay, neurite outgrowth assay, intrathecal/intraplantar injection, ALK phosphorylation (Western blot), DRG-specific ALKAL2 knockdown, pharmacological ALK inhibition (crizotinib, lorlatinib), behavioral pain assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vitro and in vivo methods, loss-of-function with specific phenotypic readout, pharmacological validation","pmids":["35608912"],"is_preprint":false},{"year":2024,"finding":"ALK activation by ALKAL2 ligand results in stabilization of SLC3A2 protein levels via regulation of the MARCH11 E3 ligase, which controls SLC3A2 ubiquitination. Stimulation of ALK with ALKAL2 increases SLC3A2 protein levels, while ALK inhibition leads to decreased SLC3A2 expression and protein stability. SLC3A2 and ALK physically interact in neuroblastoma cells.","method":"BioID proximity labeling, Co-immunoprecipitation, ALK stimulation with ALKAL2, ALK inhibitor (lorlatinib) treatment, SLC3A2 knockdown, ubiquitination assay, Western blot","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (BioID, Co-IP, stimulation/inhibition assays), single laboratory","pmids":["38858548"],"is_preprint":false},{"year":2021,"finding":"ALK activation in response to ALKAL2 ligand results in rapid phosphorylation of the RET receptor tyrosine kinase in neuroblastoma cells, placing RET as a downstream target of ALK-ALKAL2 signaling.","method":"ALKAL2 ligand stimulation of neuroblastoma cells, RET phosphorylation analysis (Western blot)","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct ligand stimulation experiment showing substrate phosphorylation, single laboratory, limited methodological detail in abstract","pmids":["33921066"],"is_preprint":false},{"year":2022,"finding":"In CMS1 colorectal cancer cells, ALKAL2 and ALK mRNA are co-amplified, and CMS1 cells display constitutively phosphorylated ALK signaling primarily through the AKT axis. ALK inhibition (using clinical ALK inhibitors) disrupts this autocrine ALKAL2-ALK loop, inhibiting proliferation, inducing apoptosis, enhancing cell-cell adhesion, and reducing tumor growth in patient-derived organoids and xenografts.","method":"ALK phosphorylation analysis, ALK inhibitor treatment (2D/3D cell cultures, PDOs, xenografts), ALKAL2/ALK copy number analysis, in vivo tumor imaging","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple model systems (cell lines, organoids, xenografts) with pharmacological intervention, single laboratory","pmids":["35351152"],"is_preprint":false},{"year":2025,"finding":"Neuronal ALKAL2 is upregulated at early stages of colitis-associated colorectal cancer (CAC) and activates ALK signaling in the colonic mucosa. Treatment of colonic organoids with exogenous ALKAL2 triggered ALK activation. In vivo ALK inhibition at colitis onset reduced tumor burden by ~90%. Chemogenetic activation of TRPV1+ nociceptors exacerbated tumor growth, while silencing these neurons reduced it, establishing a TRPV1+/ALKAL2/ALK axis driving CAC progression.","method":"Mouse CAC model, colonic organoid stimulation with recombinant ALKAL2, ALK inhibitor (lorlatinib) treatment in vivo, DREADD-mediated neuronal activation/silencing, tumor burden quantification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vivo methods (pharmacological, chemogenetic), organoid validation, specific mechanistic pathway established","pmids":["40493183"],"is_preprint":false},{"year":2024,"finding":"LPA (lysophosphatidic acid) enhances ALK phosphorylation and potentiates ALK activation by ALKAL2 (FAM150B) in neuroblastoma cells, indicating crosstalk between LPA receptor signaling and the ALKAL2/ALK axis.","method":"ALK phosphorylation assay (Western blot), LPA+ALKAL2 co-stimulation, ALK inhibitors (NPV-TAE684, alectinib), ALK siRNA knockdown","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct co-stimulation experiments with pharmacological and genetic loss-of-function validation, single laboratory","pmids":["38927035"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM reanalysis reveals that both 2:1 (two receptor : one ligand) and 2:2 (two receptor : two ligand) stoichiometric complexes of ALK-ALKAL2 exist. The 2:1 ALK-ALKAL2 complex was resolved to 3.2 Å, consistent with the 2:1 stoichiometry also seen in ALK-ALKAL2 and LTK-ALKAL1 crystal structures, establishing that ALK dimerization can be driven by a single ALKAL2 molecule.","method":"Cryo-EM data reanalysis, 3D reconstruction with orientation rebalancing, structural comparison with X-ray crystallography","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — high-resolution structural method (cryo-EM at 3.2 Å), single reanalysis study, consistent with existing crystal structures","pmids":["40208865"],"is_preprint":false},{"year":2026,"finding":"Both Fam150b (ALKAL2) and Alk are expressed in the paraventricular nucleus (PVN) of the mouse hypothalamus, including in CRH-containing neurons, but Fam150b and Alk are not co-expressed in the same cells. During inflammation-associated stress, Fam150b (but not Alk) mRNA expression in the PVN increases in a mifepristone-sensitive (glucocorticoid-dependent) manner.","method":"Single-cell RNA-seq, multiplexed in situ hybridization, glucocorticoid receptor antagonist (mifepristone) treatment","journal":"Journal of neuroendocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal spatial transcriptomic methods, pharmacological intervention establishing glucocorticoid regulation, single laboratory","pmids":["41856795"],"is_preprint":false},{"year":2025,"finding":"Spatial transcriptomics of neuroblastoma tissue identified adrenocortical-like stromal cells expressing ALKAL2 that are predicted and experimentally shown to communicate with neighboring ALK-expressing cancer cells, suggesting a paracrine ALKAL2/ALK signaling axis in neuroblastoma. A developmental pattern of adrenal medulla-specific ALK expression and adrenocortical-specific ALKAL2 expression was demonstrated.","method":"Spatial transcriptomics (Visium) on FFPE neuroblastoma samples, experimental validation of predicted interactions, developmental expression pattern analysis","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — spatial transcriptomics with experimental validation, two patient samples, single laboratory","pmids":["40778592"],"is_preprint":false}],"current_model":"ALKAL2 (FAM150B/AUG-α) is a secreted cytokine ligand that binds the extracellular domain of the receptor tyrosine kinase ALK (and, with lower specificity, LTK), inducing ALK dimerization and transphosphorylation through a mechanism—structurally resolved by cryo-EM, NMR, and X-ray crystallography—in which one or two ALKAL2 molecules bridge two ALK ectodomains oriented parallel to the membrane; downstream, ALK-ALKAL2 signaling activates AKT and ERK pathways, phosphorylates RET, and stabilizes SLC3A2 via MARCH11-mediated ubiquitination, with physiological roles in iridophore differentiation (via Ltk in zebrafish), nociceptor sensitization and pain, hypothalamic energy/stress regulation, and pathological roles in driving neuroblastoma (potentiating MYCN-amplified tumors), colorectal cancer, and colitis-associated colorectal cancer progression."},"narrative":{"mechanistic_narrative":"ALKAL2 (FAM150B/AUG-α) is a secreted cytokine ligand that activates the receptor tyrosine kinases ALK and LTK, controlling neural crest-derived cell differentiation, nociceptor sensitization, and tumor progression [PMID:26630010, PMID:25331893, PMID:29078341]. It binds the extracellular region of ALK with subnanomolar potency and activates wild-type ALK as well as superactivating neuroblastoma-associated gain-of-function ALK mutants, while binding LTK with high affinity (KD = 28 pM); ALKAL1, by contrast, is LTK-specific [PMID:26630010, PMID:26418745, PMID:25331893]. Structurally, ALKAL2 is a three-helix-bundle cytokine that bridges two ALK ectodomains, driving a pronounced ligand-induced rearrangement in which the receptor adopts an orientation parallel to the membrane and is further stabilized by ligand-membrane contacts; the cytokine-binding ALK segment is a permuted TNF-like module and the membrane-proximal EGF-like domain dictates cytokine preference, with both 2:1 and 2:2 receptor:ligand stoichiometries observed [PMID:34819673, PMID:34646012, PMID:40208865]. Downstream, ALK-ALKAL2 signaling drives AKT and ERK activation, transphosphorylates the RET receptor, and stabilizes SLC3A2 by regulating MARCH11-mediated ubiquitination [PMID:38858548, PMID:33921066, PMID:35351152]. Physiologically, ALKAL2 orthologs are essential for zebrafish iridophore development via Ltk, mediate TRPV1+ nociceptor sensitization and pain through ALK, and are upregulated in hypothalamic PVN neurons during stress in a glucocorticoid-dependent manner [PMID:29078341, PMID:35608912, PMID:41856795]. Pathologically, autocrine/paracrine ALKAL2 is sufficient to potentiate MYCN-driven neuroblastoma in the absence of ALK mutation, sustains an autocrine ALKAL2-ALK loop in CMS1 colorectal cancer, and drives a neuronal TRPV1+/ALKAL2/ALK axis promoting colitis-associated colorectal cancer [PMID:33411331, PMID:35351152, PMID:40493183].","teleology":[{"year":2014,"claim":"Establishing the identity of the ligand for the orphan receptor LTK answered what activates this receptor and revealed the FAM150/ALKAL family as RTK ligands.","evidence":"Large-scale extracellular proteome signaling screen with KD measurement and LTK phosphorylation assay","pmids":["25331893"],"confidence":"High","gaps":["Did not establish ALKAL2's relationship to ALK","No structural basis for receptor recognition"]},{"year":2015,"claim":"Identifying ALKAL2 as a high-affinity activating ligand for ALK answered what physiological ligand drives ALK and showed it activates both wild-type and oncogenic mutant ALK.","evidence":"Binding assays, cell-based ALK phosphorylation/transformation assays, Ba/F3 IL-3-independent growth, superactivation of neuroblastoma ALK mutants (two independent studies)","pmids":["26630010","26418745"],"confidence":"High","gaps":["Mechanism of dimerization not resolved","Downstream signaling effectors not defined"]},{"year":2017,"claim":"Genetic epistasis in zebrafish established the first in vivo physiological role of ALKAL2 ligands, acting through Ltk rather than Alk in neural crest-derived iridophores.","evidence":"Zebrafish knockdown/knockout, epistasis with ltk-deficient fish, iridophore patterning phenotypes","pmids":["29078341"],"confidence":"High","gaps":["Mammalian developmental role not addressed","Receptor selectivity determinants unknown"]},{"year":2017,"claim":"Re-examining ALK mutants previously called constitutively active showed some remain ligand-dependent, clarifying that ALKAL2 governs activation of certain disease-associated ALK variants.","evidence":"Cell-based phosphorylation assays, biochemical analysis, Drosophila in vivo assays","pmids":["28030793"],"confidence":"Medium","gaps":["Single laboratory","Structural basis for differential mutant responsiveness not defined"]},{"year":2021,"claim":"Atomic structures resolved the long-standing question of how ALKAL2 activates ALK, showing a cytokine-driven dimerization with the receptor reoriented parallel to the membrane.","evidence":"Cryo-EM, NMR, and X-ray crystallography; crystallography plus structure-function mutagenesis (two concurrent studies)","pmids":["34819673","34646012"],"confidence":"High","gaps":["Stoichiometry (2:1 vs 2:2) not fully reconciled at the time","Conformational dynamics in cells not captured"]},{"year":2021,"claim":"Transgenic ALKAL2 overexpression established that ligand availability alone, without ALK mutation, is sufficient to potentiate MYCN-driven neuroblastoma and is TKI-sensitive.","evidence":"Transgenic mouse model with in vivo ALK TKI treatment and tumor burden assessment","pmids":["33411331"],"confidence":"High","gaps":["Source of ligand in human tumors not defined here","Downstream effectors of tumor potentiation not mapped"]},{"year":2021,"claim":"Demonstrating ALKAL2-induced RET phosphorylation expanded the downstream signaling map of the ALK-ALKAL2 axis in neuroblastoma.","evidence":"ALKAL2 ligand stimulation of neuroblastoma cells with RET phosphorylation readout","pmids":["33921066"],"confidence":"Medium","gaps":["Limited methodological detail","Functional consequence of RET phosphorylation not established"]},{"year":2022,"claim":"Defining ALKAL2 expression in TRPV1+ nociceptors and its ALK-dependent pain phenotype established a physiological neuronal role in nociceptor sensitization.","evidence":"Coculture, excitability/neurite assays, intrathecal/intraplantar ALKAL2, DRG-specific knockdown, ALK inhibitors, behavioral pain assays","pmids":["35608912"],"confidence":"High","gaps":["Intracellular signaling in nociceptors not fully traced","Long-term consequences of axis activation not addressed"]},{"year":2022,"claim":"Identifying co-amplified ALKAL2/ALK and an autocrine AKT-driven loop in CMS1 colorectal cancer extended the oncogenic relevance of the axis beyond neuroblastoma.","evidence":"ALK phosphorylation/copy-number analysis, ALK inhibitors in 2D/3D cultures, PDOs and xenografts","pmids":["35351152"],"confidence":"Medium","gaps":["Single laboratory","Mechanism of co-amplification selection not defined"]},{"year":2024,"claim":"Linking ALK-ALKAL2 signaling to SLC3A2 stabilization via MARCH11 identified a new effector arm controlling protein stability downstream of the axis.","evidence":"BioID, Co-IP, ALKAL2 stimulation/ALK inhibition, ubiquitination assay, knockdown","pmids":["38858548"],"confidence":"Medium","gaps":["Single laboratory","Functional importance of SLC3A2 stabilization for tumor phenotype not quantified"]},{"year":2024,"claim":"Showing LPA potentiates ALKAL2-driven ALK activation revealed crosstalk between lysophospholipid signaling and the ALKAL2/ALK axis.","evidence":"Co-stimulation phosphorylation assays, ALK inhibitors and siRNA knockdown","pmids":["38927035"],"confidence":"Medium","gaps":["Mechanism of LPA potentiation unresolved","Single laboratory"]},{"year":2025,"claim":"Cryo-EM reanalysis reconciled receptor:ligand stoichiometry, showing both 2:1 and 2:2 complexes exist and that a single ALKAL2 can drive ALK dimerization.","evidence":"Cryo-EM reanalysis at 3.2 Å with orientation rebalancing and comparison to crystal structures","pmids":["40208865"],"confidence":"Medium","gaps":["Functional difference between 2:1 and 2:2 signaling outputs unknown","Single reanalysis study"]},{"year":2025,"claim":"Establishing a neuronal TRPV1+/ALKAL2/ALK axis in colitis-associated colorectal cancer connected nociceptor-derived ligand to tumor progression and identified ALK inhibition as a potent intervention.","evidence":"Mouse CAC model, colonic organoid stimulation, in vivo ALK inhibition, DREADD chemogenetic neuronal manipulation, tumor burden quantification","pmids":["40493183"],"confidence":"High","gaps":["Human CAC relevance not directly tested","Signaling within mucosal target cells not detailed"]},{"year":2025,"claim":"Spatial transcriptomics localized ALKAL2 to adrenocortical-like stromal cells adjacent to ALK-expressing neuroblastoma cells, defining a paracrine source of ligand in tumors.","evidence":"Visium spatial transcriptomics on FFPE neuroblastoma, interaction validation, developmental expression analysis","pmids":["40778592"],"confidence":"Medium","gaps":["Two patient samples only","Functional contribution of paracrine ligand to tumor growth not quantified"]},{"year":2026,"claim":"Defining glucocorticoid-dependent ALKAL2 upregulation in hypothalamic PVN neurons established a physiological role in energy/stress regulation distinct from receptor co-expression.","evidence":"Single-cell RNA-seq, multiplexed in situ hybridization, mifepristone treatment","pmids":["41856795"],"confidence":"Medium","gaps":["Lack of ALK/ALKAL2 co-expression leaves the signaling target cell undefined","Behavioral/physiological consequence not established"]},{"year":null,"claim":"How distinct receptor:ligand stoichiometries, downstream effector arms (RET, SLC3A2, AKT/ERK), and tissue-specific ligand sources are integrated into context-specific physiological versus pathological outcomes remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking complex stoichiometry to signaling output","Mammalian developmental role of ALKAL2 not defined","Determinants of physiological versus oncogenic outcomes unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,2,4,5]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,8,12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,4,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,11,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,16]}],"complexes":["ALK-ALKAL2 receptor-ligand complex","LTK-ALKAL2 receptor-ligand complex"],"partners":["ALK","LTK","RET","SLC3A2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6UX46","full_name":"ALK and LTK ligand 2","aliases":["Augmentor alpha","AUG-alpha"],"length_aa":152,"mass_kda":16.9,"function":"Cytokine that acts as a physiological ligand for receptor tyrosine kinases LTK and ALK, leading to their activation (PubMed:26418745, PubMed:26630010, PubMed:30061385, PubMed:33411331, PubMed:34646012, PubMed:34819673). Cytokine-binding is sufficient to activate LTK (PubMed:34646012). In contrast, ALKAL2-driven activation of ALK is coupled with heparin-binding to ALK (PubMed:34646012). Stimulation of ALK signaling is involved in neural development and regulation of energy expenditure (PubMed:34646012, PubMed:34819673)","subcellular_location":"Secreted; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q6UX46/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ALKAL2","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/ALKAL2","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 many","driving_tissues":[{"tissue":"adrenal gland","ntpm":212.1}],"url":"https://www.proteinatlas.org/search/ALKAL2"},"hgnc":{"alias_symbol":["AUGA"],"prev_symbol":["FAM150B"]},"alphafold":{"accession":"Q6UX46","domains":[{"cath_id":"-","chopping":"92-150","consensus_level":"high","plddt":88.7624,"start":92,"end":150}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UX46","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UX46-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UX46-F1-predicted_aligned_error_v6.png","plddt_mean":70.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ALKAL2","jax_strain_url":"https://www.jax.org/strain/search?query=ALKAL2"},"sequence":{"accession":"Q6UX46","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UX46.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UX46/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UX46"}},"corpus_meta":[{"pmid":"9873038","id":"PMC_9873038","title":"Sequence-specific DNA cleavage by 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It binds ALK with high affinity and activates ALK in cells with subnanomolar potency. ALKAL2 also binds and activates LTK. In contrast, ALKAL1 (FAM150A/AUG-β) is specific for LTK and only weakly binds ALK. ALKAL2 stimulates transformation of NIH/3T3 cells expressing ALK and induces IL-3-independent growth of Ba/F3 cells expressing ALK.\",\n      \"method\": \"Binding assays, cell-based activation assays, NIH/3T3 transformation assay, Ba/F3 IL-3-independent growth assay\",\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 functional assays (binding, phosphorylation, transformation, IL-3-independence), replicated concept in companion paper (PMID:26418745)\",\n      \"pmids\": [\"26630010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FAM150A (ALKAL1) and FAM150B (ALKAL2) are potent activating ligands for human ALK. They bind the extracellular domain of ALK and activate wild-type ALK as well as drive 'superactivation' of neuroblastoma-associated gain-of-function ALK mutants.\",\n      \"method\": \"Binding assays to ALK extracellular domain, cell-based ALK phosphorylation assays, superactivation assays with neuroblastoma ALK mutants\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding and functional activation assays, multiple ALK variants tested, independently replicated by PMID:26630010\",\n      \"pmids\": [\"26418745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"FAM150A and FAM150B (ALKAL2) were identified as ligands for the orphan receptor LTK by screening 3,191 extracellular proteins. FAM150A binds LTK extracellular domain with high affinity (KD = 28 pM) and stimulates LTK phosphorylation in a ligand-dependent manner.\",\n      \"method\": \"Large-scale extracellular proteome signaling screen, binding affinity measurement (KD), LTK phosphorylation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional screen with direct binding quantification, confirmed ligand-dependent receptor activation\",\n      \"pmids\": [\"25331893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In zebrafish, ALKAL2 orthologs (aug-α1 and aug-α2) are essential for embryonic iridophore development and adult body coloration. These effects are mediated entirely through Ltk and not Alk, establishing a physiological link between ALKAL2 ligands and Ltk-driven neural crest-derived cell differentiation.\",\n      \"method\": \"Zebrafish genetic knockdown/knockout, epistasis with ltk-deficient zebrafish, phenotypic analysis of iridophore patterning\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis using multiple ligand knockdowns and receptor-deficient zebrafish, clear cell-type-specific phenotype\",\n      \"pmids\": [\"29078341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM, NMR, and X-ray crystallography reveal the mechanism of ALK activation by ALKAL2: ALKAL2 is a dimeric ligand that drives ALK dimerization. The ALK extracellular region undergoes a pronounced ligand-induced rearrangement and adopts an orientation parallel to the membrane surface, further stabilized by ligand-membrane interaction. ALK-ECR domain architecture and the receptor-ligand complex geometry are defined at atomic resolution.\",\n      \"method\": \"Cryo-electron microscopy, NMR spectroscopy, X-ray crystallography\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic structures determined by three independent structural methods (cryo-EM, NMR, X-ray crystallography) in one study\",\n      \"pmids\": [\"34819673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"X-ray crystallography reveals that ALKAL2 is a monomeric three-helix bundle cytokine. Its binding to ALK elicits a dimeric assembly with two-fold symmetry that tents a single cytokine molecule proximal to the cell membrane. The cytokine-binding segment of ALK comprises a permuted TNF-like module bracing a glycine-rich subdomain. The membrane-proximal EGF-like domain dictates the apparent cytokine preference of ALK.\",\n      \"method\": \"X-ray crystallography, structure-function mutagenesis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structures with functional validation by mutagenesis, published concurrently with Reshetnyak et al. 2021\",\n      \"pmids\": [\"34646012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ALKAL2 overexpression in mice drives ALK tyrosine kinase inhibitor-sensitive neuroblastoma in the absence of ALK mutation, demonstrating that ALKAL2 ligand alone (autocrine/paracrine signaling) is sufficient to potentiate MYCN-driven neuroblastoma progression.\",\n      \"method\": \"Transgenic mouse model (ALKAL2 overexpression), ALK TKI treatment (in vivo), tumor burden assessment\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic model with pharmacological validation using clinical ALK inhibitors\",\n      \"pmids\": [\"33411331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ALK mutations L1198F and G1201E originally described as constitutively activating in anaplastic thyroid cancer are not ligand-independent. ALK-L1198F is activated by ALKAL2 (FAM150B) in a ligand-dependent manner similar to wild-type ALK. ALK-G1201E shows only very weak activation by ALKAL2, most likely due to impaired protein stability.\",\n      \"method\": \"In vitro cell culture phosphorylation assays, biochemical analysis, Drosophila in vivo assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple assay systems (cell-based, biochemical, Drosophila), single laboratory\",\n      \"pmids\": [\"28030793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ALKAL2 is expressed in TRPV1+ peptidergic nociceptors during inflammation or injury. Nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn. Depletion of ALKAL2 in DRG or ALK inhibition reversed thermal hyperalgesia and mechanical allodynia, establishing ALKAL2/ALK as a central regulator of nociceptor sensitization.\",\n      \"method\": \"Coculture expression system, nociceptor excitability assay, neurite outgrowth assay, intrathecal/intraplantar injection, ALK phosphorylation (Western blot), DRG-specific ALKAL2 knockdown, pharmacological ALK inhibition (crizotinib, lorlatinib), behavioral pain assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vitro and in vivo methods, loss-of-function with specific phenotypic readout, pharmacological validation\",\n      \"pmids\": [\"35608912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ALK activation by ALKAL2 ligand results in stabilization of SLC3A2 protein levels via regulation of the MARCH11 E3 ligase, which controls SLC3A2 ubiquitination. Stimulation of ALK with ALKAL2 increases SLC3A2 protein levels, while ALK inhibition leads to decreased SLC3A2 expression and protein stability. SLC3A2 and ALK physically interact in neuroblastoma cells.\",\n      \"method\": \"BioID proximity labeling, Co-immunoprecipitation, ALK stimulation with ALKAL2, ALK inhibitor (lorlatinib) treatment, SLC3A2 knockdown, ubiquitination assay, Western blot\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (BioID, Co-IP, stimulation/inhibition assays), single laboratory\",\n      \"pmids\": [\"38858548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ALK activation in response to ALKAL2 ligand results in rapid phosphorylation of the RET receptor tyrosine kinase in neuroblastoma cells, placing RET as a downstream target of ALK-ALKAL2 signaling.\",\n      \"method\": \"ALKAL2 ligand stimulation of neuroblastoma cells, RET phosphorylation analysis (Western blot)\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct ligand stimulation experiment showing substrate phosphorylation, single laboratory, limited methodological detail in abstract\",\n      \"pmids\": [\"33921066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In CMS1 colorectal cancer cells, ALKAL2 and ALK mRNA are co-amplified, and CMS1 cells display constitutively phosphorylated ALK signaling primarily through the AKT axis. ALK inhibition (using clinical ALK inhibitors) disrupts this autocrine ALKAL2-ALK loop, inhibiting proliferation, inducing apoptosis, enhancing cell-cell adhesion, and reducing tumor growth in patient-derived organoids and xenografts.\",\n      \"method\": \"ALK phosphorylation analysis, ALK inhibitor treatment (2D/3D cell cultures, PDOs, xenografts), ALKAL2/ALK copy number analysis, in vivo tumor imaging\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple model systems (cell lines, organoids, xenografts) with pharmacological intervention, single laboratory\",\n      \"pmids\": [\"35351152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Neuronal ALKAL2 is upregulated at early stages of colitis-associated colorectal cancer (CAC) and activates ALK signaling in the colonic mucosa. Treatment of colonic organoids with exogenous ALKAL2 triggered ALK activation. In vivo ALK inhibition at colitis onset reduced tumor burden by ~90%. Chemogenetic activation of TRPV1+ nociceptors exacerbated tumor growth, while silencing these neurons reduced it, establishing a TRPV1+/ALKAL2/ALK axis driving CAC progression.\",\n      \"method\": \"Mouse CAC model, colonic organoid stimulation with recombinant ALKAL2, ALK inhibitor (lorlatinib) treatment in vivo, DREADD-mediated neuronal activation/silencing, tumor burden quantification\",\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 in vivo methods (pharmacological, chemogenetic), organoid validation, specific mechanistic pathway established\",\n      \"pmids\": [\"40493183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LPA (lysophosphatidic acid) enhances ALK phosphorylation and potentiates ALK activation by ALKAL2 (FAM150B) in neuroblastoma cells, indicating crosstalk between LPA receptor signaling and the ALKAL2/ALK axis.\",\n      \"method\": \"ALK phosphorylation assay (Western blot), LPA+ALKAL2 co-stimulation, ALK inhibitors (NPV-TAE684, alectinib), ALK siRNA knockdown\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct co-stimulation experiments with pharmacological and genetic loss-of-function validation, single laboratory\",\n      \"pmids\": [\"38927035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM reanalysis reveals that both 2:1 (two receptor : one ligand) and 2:2 (two receptor : two ligand) stoichiometric complexes of ALK-ALKAL2 exist. The 2:1 ALK-ALKAL2 complex was resolved to 3.2 Å, consistent with the 2:1 stoichiometry also seen in ALK-ALKAL2 and LTK-ALKAL1 crystal structures, establishing that ALK dimerization can be driven by a single ALKAL2 molecule.\",\n      \"method\": \"Cryo-EM data reanalysis, 3D reconstruction with orientation rebalancing, structural comparison with X-ray crystallography\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution structural method (cryo-EM at 3.2 Å), single reanalysis study, consistent with existing crystal structures\",\n      \"pmids\": [\"40208865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Both Fam150b (ALKAL2) and Alk are expressed in the paraventricular nucleus (PVN) of the mouse hypothalamus, including in CRH-containing neurons, but Fam150b and Alk are not co-expressed in the same cells. During inflammation-associated stress, Fam150b (but not Alk) mRNA expression in the PVN increases in a mifepristone-sensitive (glucocorticoid-dependent) manner.\",\n      \"method\": \"Single-cell RNA-seq, multiplexed in situ hybridization, glucocorticoid receptor antagonist (mifepristone) treatment\",\n      \"journal\": \"Journal of neuroendocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal spatial transcriptomic methods, pharmacological intervention establishing glucocorticoid regulation, single laboratory\",\n      \"pmids\": [\"41856795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Spatial transcriptomics of neuroblastoma tissue identified adrenocortical-like stromal cells expressing ALKAL2 that are predicted and experimentally shown to communicate with neighboring ALK-expressing cancer cells, suggesting a paracrine ALKAL2/ALK signaling axis in neuroblastoma. A developmental pattern of adrenal medulla-specific ALK expression and adrenocortical-specific ALKAL2 expression was demonstrated.\",\n      \"method\": \"Spatial transcriptomics (Visium) on FFPE neuroblastoma samples, experimental validation of predicted interactions, developmental expression pattern analysis\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — spatial transcriptomics with experimental validation, two patient samples, single laboratory\",\n      \"pmids\": [\"40778592\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ALKAL2 (FAM150B/AUG-α) is a secreted cytokine ligand that binds the extracellular domain of the receptor tyrosine kinase ALK (and, with lower specificity, LTK), inducing ALK dimerization and transphosphorylation through a mechanism—structurally resolved by cryo-EM, NMR, and X-ray crystallography—in which one or two ALKAL2 molecules bridge two ALK ectodomains oriented parallel to the membrane; downstream, ALK-ALKAL2 signaling activates AKT and ERK pathways, phosphorylates RET, and stabilizes SLC3A2 via MARCH11-mediated ubiquitination, with physiological roles in iridophore differentiation (via Ltk in zebrafish), nociceptor sensitization and pain, hypothalamic energy/stress regulation, and pathological roles in driving neuroblastoma (potentiating MYCN-amplified tumors), colorectal cancer, and colitis-associated colorectal cancer progression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ALKAL2 (FAM150B/AUG-\\u03b1) is a secreted cytokine ligand that activates the receptor tyrosine kinases ALK and LTK, controlling neural crest-derived cell differentiation, nociceptor sensitization, and tumor progression [#0, #2, #3]. It binds the extracellular region of ALK with subnanomolar potency and activates wild-type ALK as well as superactivating neuroblastoma-associated gain-of-function ALK mutants, while binding LTK with high affinity (KD = 28 pM); ALKAL1, by contrast, is LTK-specific [#0, #1, #2]. Structurally, ALKAL2 is a three-helix-bundle cytokine that bridges two ALK ectodomains, driving a pronounced ligand-induced rearrangement in which the receptor adopts an orientation parallel to the membrane and is further stabilized by ligand-membrane contacts; the cytokine-binding ALK segment is a permuted TNF-like module and the membrane-proximal EGF-like domain dictates cytokine preference, with both 2:1 and 2:2 receptor:ligand stoichiometries observed [#4, #5, #14]. Downstream, ALK-ALKAL2 signaling drives AKT and ERK activation, transphosphorylates the RET receptor, and stabilizes SLC3A2 by regulating MARCH11-mediated ubiquitination [#9, #10, #11]. Physiologically, ALKAL2 orthologs are essential for zebrafish iridophore development via Ltk, mediate TRPV1+ nociceptor sensitization and pain through ALK, and are upregulated in hypothalamic PVN neurons during stress in a glucocorticoid-dependent manner [#3, #8, #15]. Pathologically, autocrine/paracrine ALKAL2 is sufficient to potentiate MYCN-driven neuroblastoma in the absence of ALK mutation, sustains an autocrine ALKAL2-ALK loop in CMS1 colorectal cancer, and drives a neuronal TRPV1+/ALKAL2/ALK axis promoting colitis-associated colorectal cancer [#6, #11, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Establishing the identity of the ligand for the orphan receptor LTK answered what activates this receptor and revealed the FAM150/ALKAL family as RTK ligands.\",\n      \"evidence\": \"Large-scale extracellular proteome signaling screen with KD measurement and LTK phosphorylation assay\",\n      \"pmids\": [\"25331893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish ALKAL2's relationship to ALK\", \"No structural basis for receptor recognition\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying ALKAL2 as a high-affinity activating ligand for ALK answered what physiological ligand drives ALK and showed it activates both wild-type and oncogenic mutant ALK.\",\n      \"evidence\": \"Binding assays, cell-based ALK phosphorylation/transformation assays, Ba/F3 IL-3-independent growth, superactivation of neuroblastoma ALK mutants (two independent studies)\",\n      \"pmids\": [\"26630010\", \"26418745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of dimerization not resolved\", \"Downstream signaling effectors not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Genetic epistasis in zebrafish established the first in vivo physiological role of ALKAL2 ligands, acting through Ltk rather than Alk in neural crest-derived iridophores.\",\n      \"evidence\": \"Zebrafish knockdown/knockout, epistasis with ltk-deficient fish, iridophore patterning phenotypes\",\n      \"pmids\": [\"29078341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian developmental role not addressed\", \"Receptor selectivity determinants unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Re-examining ALK mutants previously called constitutively active showed some remain ligand-dependent, clarifying that ALKAL2 governs activation of certain disease-associated ALK variants.\",\n      \"evidence\": \"Cell-based phosphorylation assays, biochemical analysis, Drosophila in vivo assays\",\n      \"pmids\": [\"28030793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single laboratory\", \"Structural basis for differential mutant responsiveness not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Atomic structures resolved the long-standing question of how ALKAL2 activates ALK, showing a cytokine-driven dimerization with the receptor reoriented parallel to the membrane.\",\n      \"evidence\": \"Cryo-EM, NMR, and X-ray crystallography; crystallography plus structure-function mutagenesis (two concurrent studies)\",\n      \"pmids\": [\"34819673\", \"34646012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry (2:1 vs 2:2) not fully reconciled at the time\", \"Conformational dynamics in cells not captured\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Transgenic ALKAL2 overexpression established that ligand availability alone, without ALK mutation, is sufficient to potentiate MYCN-driven neuroblastoma and is TKI-sensitive.\",\n      \"evidence\": \"Transgenic mouse model with in vivo ALK TKI treatment and tumor burden assessment\",\n      \"pmids\": [\"33411331\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of ligand in human tumors not defined here\", \"Downstream effectors of tumor potentiation not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating ALKAL2-induced RET phosphorylation expanded the downstream signaling map of the ALK-ALKAL2 axis in neuroblastoma.\",\n      \"evidence\": \"ALKAL2 ligand stimulation of neuroblastoma cells with RET phosphorylation readout\",\n      \"pmids\": [\"33921066\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Limited methodological detail\", \"Functional consequence of RET phosphorylation not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defining ALKAL2 expression in TRPV1+ nociceptors and its ALK-dependent pain phenotype established a physiological neuronal role in nociceptor sensitization.\",\n      \"evidence\": \"Coculture, excitability/neurite assays, intrathecal/intraplantar ALKAL2, DRG-specific knockdown, ALK inhibitors, behavioral pain assays\",\n      \"pmids\": [\"35608912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Intracellular signaling in nociceptors not fully traced\", \"Long-term consequences of axis activation not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying co-amplified ALKAL2/ALK and an autocrine AKT-driven loop in CMS1 colorectal cancer extended the oncogenic relevance of the axis beyond neuroblastoma.\",\n      \"evidence\": \"ALK phosphorylation/copy-number analysis, ALK inhibitors in 2D/3D cultures, PDOs and xenografts\",\n      \"pmids\": [\"35351152\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single laboratory\", \"Mechanism of co-amplification selection not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking ALK-ALKAL2 signaling to SLC3A2 stabilization via MARCH11 identified a new effector arm controlling protein stability downstream of the axis.\",\n      \"evidence\": \"BioID, Co-IP, ALKAL2 stimulation/ALK inhibition, ubiquitination assay, knockdown\",\n      \"pmids\": [\"38858548\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single laboratory\", \"Functional importance of SLC3A2 stabilization for tumor phenotype not quantified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showing LPA potentiates ALKAL2-driven ALK activation revealed crosstalk between lysophospholipid signaling and the ALKAL2/ALK axis.\",\n      \"evidence\": \"Co-stimulation phosphorylation assays, ALK inhibitors and siRNA knockdown\",\n      \"pmids\": [\"38927035\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of LPA potentiation unresolved\", \"Single laboratory\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM reanalysis reconciled receptor:ligand stoichiometry, showing both 2:1 and 2:2 complexes exist and that a single ALKAL2 can drive ALK dimerization.\",\n      \"evidence\": \"Cryo-EM reanalysis at 3.2 \\u00c5 with orientation rebalancing and comparison to crystal structures\",\n      \"pmids\": [\"40208865\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional difference between 2:1 and 2:2 signaling outputs unknown\", \"Single reanalysis study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Establishing a neuronal TRPV1+/ALKAL2/ALK axis in colitis-associated colorectal cancer connected nociceptor-derived ligand to tumor progression and identified ALK inhibition as a potent intervention.\",\n      \"evidence\": \"Mouse CAC model, colonic organoid stimulation, in vivo ALK inhibition, DREADD chemogenetic neuronal manipulation, tumor burden quantification\",\n      \"pmids\": [\"40493183\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human CAC relevance not directly tested\", \"Signaling within mucosal target cells not detailed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Spatial transcriptomics localized ALKAL2 to adrenocortical-like stromal cells adjacent to ALK-expressing neuroblastoma cells, defining a paracrine source of ligand in tumors.\",\n      \"evidence\": \"Visium spatial transcriptomics on FFPE neuroblastoma, interaction validation, developmental expression analysis\",\n      \"pmids\": [\"40778592\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Two patient samples only\", \"Functional contribution of paracrine ligand to tumor growth not quantified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defining glucocorticoid-dependent ALKAL2 upregulation in hypothalamic PVN neurons established a physiological role in energy/stress regulation distinct from receptor co-expression.\",\n      \"evidence\": \"Single-cell RNA-seq, multiplexed in situ hybridization, mifepristone treatment\",\n      \"pmids\": [\"41856795\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Lack of ALK/ALKAL2 co-expression leaves the signaling target cell undefined\", \"Behavioral/physiological consequence not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct receptor:ligand stoichiometries, downstream effector arms (RET, SLC3A2, AKT/ERK), and tissue-specific ligand sources are integrated into context-specific physiological versus pathological outcomes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking complex stoichiometry to signaling output\", \"Mammalian developmental role of ALKAL2 not defined\", \"Determinants of physiological versus oncogenic outcomes unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 2, 4, 5]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 8, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 4, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 11, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 16]}\n    ],\n    \"complexes\": [\n      \"ALK-ALKAL2 receptor-ligand complex\",\n      \"LTK-ALKAL2 receptor-ligand complex\"\n    ],\n    \"partners\": [\n      \"ALK\",\n      \"LTK\",\n      \"RET\",\n      \"SLC3A2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}