{"gene":"CALR","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2013,"finding":"Somatic CALR mutations in exon 9 generate a +1 base-pair frameshift producing a mutant protein with a novel C-terminal. Mutant calreticulin was observed in the endoplasmic reticulum without increased cell-surface or Golgi accumulation, consistent with ER retention despite loss of normal C-terminal sequence.","method":"Exome sequencing, immunofluorescence, flow cytometry, phylogenetic clonal analysis","journal":"The New England journal of medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (exome sequencing, immunofluorescence, flow cytometry) in a large discovery cohort, independently replicated by contemporaneous studies","pmids":["24325359"],"is_preprint":false},{"year":2016,"finding":"Mutant CALR (but not wild-type CALR) preferentially associates with the thrombopoietin receptor c-MPL bound to JAK2, activating JAK2 phosphorylation and downstream signaling to drive cytokine-independent cell growth. The mutant-specific C-terminus interferes with the P-domain of CALR, allowing the N-domain to interact with c-MPL, explaining the gain-of-function. c-MPL is required for mutant CALR-induced TPO-independent megakaryopoiesis.","method":"Co-immunoprecipitation, cytokine-independent growth assays in UT-7/TPO cells, JAK2 inhibitor treatment, iPSC-derived hematopoietic stem cell differentiation, domain mutagenesis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, functional rescue/inhibition experiments, multiple orthogonal methods including mutagenesis and cell-line and iPSC models","pmids":["26817954"],"is_preprint":false},{"year":2022,"finding":"A monoclonal antibody (4D7) directed against the neoepitope encoded by CALR frameshift mutations selectively binds cells co-expressing mutant CALR and TpoR (MPL), blocks JAK-STAT signalling, TPO-independent proliferation, and megakaryocyte differentiation by disrupting binding of CALR dimers to TpoR. It inhibited proliferation of patient samples and prolonged survival in xenograft models.","method":"Monoclonal antibody development, cell-based proliferation assays, JAK-STAT signalling readouts, xenograft bone marrow models","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays (signalling, proliferation, differentiation, in vivo xenograft) with mechanistic blocking experiments","pmids":["35156745"],"is_preprint":false},{"year":2016,"finding":"Expression of CALR del52 and ins5 mutants in zebrafish caused mpl-dependent thrombocytosis and JAK-STAT signalling activation; morpholino knockdown of mpl (but not epor or csf3r) significantly attenuated these effects, demonstrating that mutant CALR activates JAK-STAT signalling through an mpl-dependent mechanism in vivo.","method":"Zebrafish transgenic expression, morpholino knockdown epistasis, JAK inhibitor treatment (ruxolitinib, fedratinib), hematopoietic progenitor quantification","journal":"Blood cancer journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis (morpholino knockdown of mpl vs. epor vs. csf3r), pharmacological inhibition, replicated mechanistic conclusion across multiple CALR mutant types","pmids":["27716741"],"is_preprint":false},{"year":2015,"finding":"CALR type 1 (52-bp deletion) and type 2 (5-bp insertion) mutations produce mutant proteins with significantly different isoelectric points. Type 1 mutations caused abnormal cytosolic calcium signals in cultured megakaryocytes (absent in type 2), suggesting that type 1 mutations markedly impair the calcium-binding activity of calreticulin's C-terminal, whereas type 2 mutations do so to a lesser degree.","method":"Calcium flux measurements in cultured megakaryocytes, isoelectric point prediction, clinical correlation of mutation subtype","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct calcium flux assay in cultured cells with multiple mutation subtypes, but single lab and limited mechanistic follow-up","pmids":["26449662"],"is_preprint":false},{"year":2019,"finding":"Mice harboring a Calr del19 frameshift mutation (analogous to human mutants, losing KDEL motif and generating positively charged C-terminal amino acids) exhibited only mild thrombocytosis. The murine CALR del19 mutant had weaker ability to combine with murine MPL than human CALR del52 mutant, resulting in very weak STAT5 activation downstream, indicating that loss of KDEL and positively charged C-terminal amino acids alone are insufficient for full MPL binding and ET development.","method":"CRISPR/Cas9 knock-in mouse model, in vitro binding assays (murine mutant CALR vs. murine MPL), STAT5 phosphorylation assays","journal":"Blood cancer journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knock-in mouse model with biochemical binding and signalling readouts, single lab, mechanistically informative negative/partial result","pmids":["30926777"],"is_preprint":false},{"year":2021,"finding":"Patient-derived iPSCs carrying CALR ins5 or del52 mutations showed enhanced megakaryopoiesis and accelerated megakaryocytic development in a thrombopoietin-independent manner. CRISPR/Cas9 repair of the mutation rescued myeloperoxidase deficiency in granulocytic cells. Mechanistically, differentially regulated pathways including hypoxia signaling were identified in mutated versus unmutated megakaryocytes.","method":"Patient-derived iPSC generation, CRISPR/Cas9 mutation repair, directed megakaryocyte differentiation, transcriptomic pathway analysis","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic iPSC correction by CRISPR confirms causality, multiple differentiation readouts, single lab","pmids":["34678208"],"is_preprint":false},{"year":2021,"finding":"A transgenic murine model with conditional expression of human mutant CALR exon 9 (del52) from the endogenous murine Calr locus developed essential thrombocythemia-like phenotype with thrombocytosis, megakaryocytosis, splenomegaly, and anemia. Mutant CALR stem cells showed proliferative advantage, and anti-human mutCALR monoclonal antibody treatment lowered platelet and stem cell counts, confirming mutant CALR as the functional driver.","method":"Conditional knock-in transgenic mouse model, bone marrow transplantation, monoclonal antibody treatment, flow cytometry, transcriptome profiling of HSCs","journal":"American journal of hematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo conditional knock-in model with transplantation and antibody intervention, single lab","pmids":["33761144"],"is_preprint":false},{"year":2024,"finding":"In 32D myeloid progenitor cells, CALR ins5 and del52 mutations (with MPL) showed elevated cytosolic Ca2+ during store depletion compared to CALR-WT/MPL cells upon TPO stimulation. However, key Ca2+ signaling components PLCγ-1 and IP3R were NOT hyper-activated in CALR-mutated cells (unlike JAK2-V617F cells), indicating that CALR mutations affect Ca2+ dynamics through a different mechanism than JAK2-V617F.","method":"Fura-2 AM intracellular Ca2+ measurements, store-operated calcium entry (SOCE) assays, phospho-western blotting for PLCγ-1 and IP3R, growth inhibition and apoptosis assays","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct Ca2+ flux measurements with multiple CALR mutant cell lines, mechanistically informative comparison, single lab","pmids":["38509561"],"is_preprint":false},{"year":2001,"finding":"The 52 kDa SSA/Ro protein (encoded by CALR alias locus) interacts with the deubiquitinating enzyme UnpEL via yeast two-hybrid and mammalian two-hybrid assays. This interaction required the full-length 52Ro (containing leucine zipper) but not the alternative splice form 52β (lacking leucine zipper). Co-transfection of 52Ro and UnpEL caused marked redistribution of UnpEL subcellular localization in human cardiocytes and other cell lines, suggesting 52Ro may be involved in the ubiquitin pathway via its RING finger domain.","method":"Yeast two-hybrid screen of fetal heart cDNA library, mammalian two-hybrid confirmation, subcellular colocalization by cotransfection/immunofluorescence in cardiocytes, HEK293, and COS-1 cells","journal":"The international journal of biochemistry & cell biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — two-hybrid and cotransfection localization data, single lab, no biochemical ubiquitination assay performed; note this paper appears to be about TRIM21/Ro52 (SSA1), not CALR","pmids":["11461834"],"is_preprint":false}],"current_model":"CALR (calreticulin) functions as an ER-resident chaperone whose oncogenic frameshift mutations (most commonly a 52-bp deletion or 5-bp insertion in exon 9) generate a novel positively-charged C-terminus that enables the mutant protein to aberrantly bind and constitutively activate the thrombopoietin receptor MPL at the cell surface, recruiting JAK2 and triggering JAK-STAT signalling to drive cytokine-independent myeloproliferation; the degree of disruption to calreticulin's native calcium-binding C-terminal domain (more severe in type 1 than type 2 mutations) further modulates the disease phenotype."},"narrative":{"mechanistic_narrative":"CALR encodes calreticulin, an endoplasmic reticulum-resident protein in which recurrent somatic +1 frameshift mutations in exon 9 (most commonly a 52-bp deletion or 5-bp insertion) generate a novel positively-charged C-terminus while preserving ER retention [PMID:24325359]. This mutant protein acquires a pathogenic gain of function: it preferentially binds the thrombopoietin receptor c-MPL complexed with JAK2, driving JAK2 phosphorylation and cytokine-independent proliferation, with the mutant-specific C-terminus disrupting the CALR P-domain so the N-domain engages c-MPL [PMID:26817954]. This MPL-dependent activation of JAK-STAT signalling underlies mutant CALR-driven megakaryopoiesis and thrombocytosis in vivo, as demonstrated by mpl-knockdown epistasis in zebrafish and by knock-in mouse models that recapitulate an essential thrombocythemia-like phenotype [PMID:27716741, PMID:33761144]. Receptor engagement requires both loss of the native KDEL motif and the positively-charged residues yet is not fully explained by them alone, since a murine del19 mutant binds MPL weakly and produces only mild disease [PMID:30926777]. The neoepitope is therapeutically actionable: a monoclonal antibody against the mutant C-terminus selectively disrupts CALR-dimer binding to TpoR, blocking signalling, proliferation, and differentiation [PMID:35156745]. Distinct from the classical chaperone calcium-buffering role, type 1 (del52) mutations impair the C-terminal calcium-binding activity more severely than type 2 (ins5), correlating with altered cytosolic calcium signalling [PMID:26449662].","teleology":[{"year":2013,"claim":"Established that recurrent exon 9 +1 frameshift mutations define a molecular class of myeloproliferative neoplasm, producing a mutant calreticulin with a novel C-terminus that nonetheless remains ER-retained.","evidence":"Exome sequencing with immunofluorescence and flow cytometry in a patient discovery cohort","pmids":["24325359"],"confidence":"High","gaps":["Did not define the gain-of-function mechanism","Did not identify the receptor partner"]},{"year":2015,"claim":"Addressed whether mutation subtypes differ biochemically, showing type 1 mutations impair C-terminal calcium binding more severely than type 2 and alter megakaryocyte calcium signalling.","evidence":"Calcium flux measurements in cultured megakaryocytes with isoelectric point prediction and clinical correlation","pmids":["26449662"],"confidence":"Medium","gaps":["Single lab","Causal link between altered calcium and disease phenotype not established","Mechanism connecting calcium dysregulation to MPL signalling unresolved"]},{"year":2016,"claim":"Identified the oncogenic gain-of-function: mutant CALR specifically binds the JAK2-bound thrombopoietin receptor c-MPL through its N-domain to drive cytokine-independent growth.","evidence":"Co-immunoprecipitation, cytokine-independent growth assays in UT-7/TPO cells, JAK2 inhibition, iPSC differentiation, and domain mutagenesis","pmids":["26817954"],"confidence":"High","gaps":["Stoichiometry and structural basis of CALR-MPL engagement not resolved","Did not establish requirement in vivo"]},{"year":2016,"claim":"Demonstrated in vivo genetic dependence on MPL, showing mutant CALR-induced thrombocytosis and JAK-STAT activation require mpl but not other cytokine receptors.","evidence":"Zebrafish transgenic expression with morpholino knockdown epistasis (mpl vs epor vs csf3r) and JAK inhibitor treatment","pmids":["27716741"],"confidence":"High","gaps":["Zebrafish hematopoiesis may differ from mammalian","Did not address chronic disease evolution"]},{"year":2019,"claim":"Clarified that loss of KDEL and acquisition of positively-charged C-terminal residues are necessary but not sufficient for full MPL binding, refining the structural requirements for oncogenic activity.","evidence":"CRISPR/Cas9 knock-in mouse (Calr del19) with in vitro binding and STAT5 phosphorylation assays","pmids":["30926777"],"confidence":"Medium","gaps":["Species differences confound interpretation","Exact sequence features required for high-affinity MPL binding not defined"]},{"year":2021,"claim":"Confirmed causality in human cells and an authentic in vivo disease model, with isogenic CRISPR correction and a conditional knock-in mouse recapitulating essential thrombocythemia.","evidence":"Patient-derived iPSCs with CRISPR repair and directed megakaryocyte differentiation; conditional knock-in mouse with transplantation, antibody treatment, and HSC transcriptomics","pmids":["34678208","33761144"],"confidence":"Medium","gaps":["Single-lab models","Hypoxia and other dysregulated pathways not mechanistically linked to MPL signalling","Stem cell proliferative advantage mechanism incompletely defined"]},{"year":2022,"claim":"Validated the mutant neoepitope as a therapeutic target by showing an antibody that disrupts CALR-dimer binding to TpoR blocks signalling and tumor growth.","evidence":"Monoclonal antibody (4D7) with cell-based proliferation, JAK-STAT readouts, patient samples, and xenograft models","pmids":["35156745"],"confidence":"High","gaps":["Did not resolve whether dimerization is obligatory for receptor activation in all mutant types","Clinical efficacy not addressed"]},{"year":2024,"claim":"Distinguished the calcium-signalling consequences of CALR mutation from JAK2-V617F, showing elevated cytosolic calcium during store depletion without hyperactivation of PLCγ-1 or IP3R.","evidence":"Fura-2 calcium measurements, SOCE assays, and phospho-western blotting in 32D myeloid progenitor cells","pmids":["38509561"],"confidence":"Medium","gaps":["Mechanism producing altered calcium dynamics not identified","Functional contribution of calcium changes to myeloproliferation unclear","Single lab"]},{"year":null,"claim":"The structural basis of mutant CALR-MPL complex assembly and the contribution of calcium dysregulation to disease phenotype remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No atomic-resolution structure of the mutant CALR-MPL-JAK2 complex","Causal link between C-terminal calcium-binding loss and clinical phenotype not established","Mechanism connecting altered cytosolic calcium to JAK-STAT output unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,3]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["MPL","JAK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P27797","full_name":"Calreticulin","aliases":["CRP55","Calregulin","Endoplasmic reticulum resident protein 60","ERp60","HACBP","grp60"],"length_aa":417,"mass_kda":48.1,"function":"Calcium-binding chaperone that promotes folding, oligomeric assembly and quality control in the endoplasmic reticulum (ER) via the calreticulin/calnexin cycle. This lectin interacts transiently with almost all of the monoglucosylated glycoproteins that are synthesized in the ER (PubMed:7876246). Interacts with the DNA-binding domain of NR3C1 and mediates its nuclear export (PubMed:11149926). Involved in maternal gene expression regulation. May participate in oocyte maturation via the regulation of calcium homeostasis (By similarity). Present in the cortical granules of non-activated oocytes, is exocytosed during the cortical reaction in response to oocyte activation and might participate in the block to polyspermy (By similarity)","subcellular_location":"Endoplasmic reticulum lumen; Cytoplasm, cytosol; Secreted, extracellular space, extracellular matrix; Cell surface; Sarcoplasmic reticulum lumen; Cytoplasmic vesicle, secretory vesicle, Cortical granule; Cytolytic granule","url":"https://www.uniprot.org/uniprotkb/P27797/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CALR","classification":"Not Classified","n_dependent_lines":21,"n_total_lines":1208,"dependency_fraction":0.0173841059602649},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":0.2},{"gene":"COPA","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CALR","total_profiled":1310},"omim":[{"mim_id":"620096","title":"RING FINGER PROTEIN 185; RNF185","url":"https://www.omim.org/entry/620096"},{"mim_id":"617122","title":"C1QTNF9B ANTISENSE RNA 1; C1QTNF9BAS1","url":"https://www.omim.org/entry/617122"},{"mim_id":"616604","title":"CHROMOSOME 14q32 DUPLICATION SYNDROME, 700-KB","url":"https://www.omim.org/entry/616604"},{"mim_id":"616499","title":"TRANSMEMBRANE PROTEIN 203; TMEM203","url":"https://www.omim.org/entry/616499"},{"mim_id":"613638","title":"CHROMOSOME 19p13.13 DELETION SYNDROME","url":"https://www.omim.org/entry/613638"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CALR"},"hgnc":{"alias_symbol":["RO","SSA","cC1qR","CRT","FLJ26680","CALR1"],"prev_symbol":[]},"alphafold":{"accession":"P27797","domains":[{"cath_id":"2.60.120.200","chopping":"20-205_304-353","consensus_level":"high","plddt":97.2311,"start":20,"end":353}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P27797","model_url":"https://alphafold.ebi.ac.uk/files/AF-P27797-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P27797-F1-predicted_aligned_error_v6.png","plddt_mean":89.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CALR","jax_strain_url":"https://www.jax.org/strain/search?query=CALR"},"sequence":{"accession":"P27797","fasta_url":"https://rest.uniprot.org/uniprotkb/P27797.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P27797/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P27797"}},"corpus_meta":[{"pmid":"24325359","id":"PMC_24325359","title":"Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2.","date":"2013","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/24325359","citation_count":1430,"is_preprint":false},{"pmid":"24366362","id":"PMC_24366362","title":"JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes.","date":"2013","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/24366362","citation_count":472,"is_preprint":false},{"pmid":"24402162","id":"PMC_24402162","title":"CALR vs JAK2 vs MPL-mutated or triple-negative myelofibrosis: clinical, cytogenetic and molecular comparisons.","date":"2014","source":"Leukemia","url":"https://pubmed.ncbi.nlm.nih.gov/24402162","citation_count":437,"is_preprint":false},{"pmid":"18162766","id":"PMC_18162766","title":"Sessile serrated adenoma (SSA) vs. traditional serrated adenoma (TSA).","date":"2008","source":"The American journal of surgical pathology","url":"https://pubmed.ncbi.nlm.nih.gov/18162766","citation_count":246,"is_preprint":false},{"pmid":"26817954","id":"PMC_26817954","title":"Activation of the thrombopoietin receptor by mutant calreticulin in CALR-mutant myeloproliferative neoplasms.","date":"2016","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/26817954","citation_count":240,"is_preprint":false},{"pmid":"26449662","id":"PMC_26449662","title":"Differential clinical effects of different mutation subtypes in CALR-mutant myeloproliferative neoplasms.","date":"2015","source":"Leukemia","url":"https://pubmed.ncbi.nlm.nih.gov/26449662","citation_count":219,"is_preprint":false},{"pmid":"1985094","id":"PMC_1985094","title":"Protein heterogeneity in the human Ro/SSA ribonucleoproteins. 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Mutant calreticulin was observed in the endoplasmic reticulum without increased cell-surface or Golgi accumulation, consistent with ER retention despite loss of normal C-terminal sequence.\",\n      \"method\": \"Exome sequencing, immunofluorescence, flow cytometry, phylogenetic clonal analysis\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (exome sequencing, immunofluorescence, flow cytometry) in a large discovery cohort, independently replicated by contemporaneous studies\",\n      \"pmids\": [\"24325359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mutant CALR (but not wild-type CALR) preferentially associates with the thrombopoietin receptor c-MPL bound to JAK2, activating JAK2 phosphorylation and downstream signaling to drive cytokine-independent cell growth. The mutant-specific C-terminus interferes with the P-domain of CALR, allowing the N-domain to interact with c-MPL, explaining the gain-of-function. c-MPL is required for mutant CALR-induced TPO-independent megakaryopoiesis.\",\n      \"method\": \"Co-immunoprecipitation, cytokine-independent growth assays in UT-7/TPO cells, JAK2 inhibitor treatment, iPSC-derived hematopoietic stem cell differentiation, domain mutagenesis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, functional rescue/inhibition experiments, multiple orthogonal methods including mutagenesis and cell-line and iPSC models\",\n      \"pmids\": [\"26817954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A monoclonal antibody (4D7) directed against the neoepitope encoded by CALR frameshift mutations selectively binds cells co-expressing mutant CALR and TpoR (MPL), blocks JAK-STAT signalling, TPO-independent proliferation, and megakaryocyte differentiation by disrupting binding of CALR dimers to TpoR. It inhibited proliferation of patient samples and prolonged survival in xenograft models.\",\n      \"method\": \"Monoclonal antibody development, cell-based proliferation assays, JAK-STAT signalling readouts, xenograft bone marrow models\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays (signalling, proliferation, differentiation, in vivo xenograft) with mechanistic blocking experiments\",\n      \"pmids\": [\"35156745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Expression of CALR del52 and ins5 mutants in zebrafish caused mpl-dependent thrombocytosis and JAK-STAT signalling activation; morpholino knockdown of mpl (but not epor or csf3r) significantly attenuated these effects, demonstrating that mutant CALR activates JAK-STAT signalling through an mpl-dependent mechanism in vivo.\",\n      \"method\": \"Zebrafish transgenic expression, morpholino knockdown epistasis, JAK inhibitor treatment (ruxolitinib, fedratinib), hematopoietic progenitor quantification\",\n      \"journal\": \"Blood cancer journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis (morpholino knockdown of mpl vs. epor vs. csf3r), pharmacological inhibition, replicated mechanistic conclusion across multiple CALR mutant types\",\n      \"pmids\": [\"27716741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CALR type 1 (52-bp deletion) and type 2 (5-bp insertion) mutations produce mutant proteins with significantly different isoelectric points. Type 1 mutations caused abnormal cytosolic calcium signals in cultured megakaryocytes (absent in type 2), suggesting that type 1 mutations markedly impair the calcium-binding activity of calreticulin's C-terminal, whereas type 2 mutations do so to a lesser degree.\",\n      \"method\": \"Calcium flux measurements in cultured megakaryocytes, isoelectric point prediction, clinical correlation of mutation subtype\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct calcium flux assay in cultured cells with multiple mutation subtypes, but single lab and limited mechanistic follow-up\",\n      \"pmids\": [\"26449662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mice harboring a Calr del19 frameshift mutation (analogous to human mutants, losing KDEL motif and generating positively charged C-terminal amino acids) exhibited only mild thrombocytosis. The murine CALR del19 mutant had weaker ability to combine with murine MPL than human CALR del52 mutant, resulting in very weak STAT5 activation downstream, indicating that loss of KDEL and positively charged C-terminal amino acids alone are insufficient for full MPL binding and ET development.\",\n      \"method\": \"CRISPR/Cas9 knock-in mouse model, in vitro binding assays (murine mutant CALR vs. murine MPL), STAT5 phosphorylation assays\",\n      \"journal\": \"Blood cancer journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knock-in mouse model with biochemical binding and signalling readouts, single lab, mechanistically informative negative/partial result\",\n      \"pmids\": [\"30926777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Patient-derived iPSCs carrying CALR ins5 or del52 mutations showed enhanced megakaryopoiesis and accelerated megakaryocytic development in a thrombopoietin-independent manner. CRISPR/Cas9 repair of the mutation rescued myeloperoxidase deficiency in granulocytic cells. Mechanistically, differentially regulated pathways including hypoxia signaling were identified in mutated versus unmutated megakaryocytes.\",\n      \"method\": \"Patient-derived iPSC generation, CRISPR/Cas9 mutation repair, directed megakaryocyte differentiation, transcriptomic pathway analysis\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic iPSC correction by CRISPR confirms causality, multiple differentiation readouts, single lab\",\n      \"pmids\": [\"34678208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A transgenic murine model with conditional expression of human mutant CALR exon 9 (del52) from the endogenous murine Calr locus developed essential thrombocythemia-like phenotype with thrombocytosis, megakaryocytosis, splenomegaly, and anemia. Mutant CALR stem cells showed proliferative advantage, and anti-human mutCALR monoclonal antibody treatment lowered platelet and stem cell counts, confirming mutant CALR as the functional driver.\",\n      \"method\": \"Conditional knock-in transgenic mouse model, bone marrow transplantation, monoclonal antibody treatment, flow cytometry, transcriptome profiling of HSCs\",\n      \"journal\": \"American journal of hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional knock-in model with transplantation and antibody intervention, single lab\",\n      \"pmids\": [\"33761144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In 32D myeloid progenitor cells, CALR ins5 and del52 mutations (with MPL) showed elevated cytosolic Ca2+ during store depletion compared to CALR-WT/MPL cells upon TPO stimulation. However, key Ca2+ signaling components PLCγ-1 and IP3R were NOT hyper-activated in CALR-mutated cells (unlike JAK2-V617F cells), indicating that CALR mutations affect Ca2+ dynamics through a different mechanism than JAK2-V617F.\",\n      \"method\": \"Fura-2 AM intracellular Ca2+ measurements, store-operated calcium entry (SOCE) assays, phospho-western blotting for PLCγ-1 and IP3R, growth inhibition and apoptosis assays\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct Ca2+ flux measurements with multiple CALR mutant cell lines, mechanistically informative comparison, single lab\",\n      \"pmids\": [\"38509561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The 52 kDa SSA/Ro protein (encoded by CALR alias locus) interacts with the deubiquitinating enzyme UnpEL via yeast two-hybrid and mammalian two-hybrid assays. This interaction required the full-length 52Ro (containing leucine zipper) but not the alternative splice form 52β (lacking leucine zipper). Co-transfection of 52Ro and UnpEL caused marked redistribution of UnpEL subcellular localization in human cardiocytes and other cell lines, suggesting 52Ro may be involved in the ubiquitin pathway via its RING finger domain.\",\n      \"method\": \"Yeast two-hybrid screen of fetal heart cDNA library, mammalian two-hybrid confirmation, subcellular colocalization by cotransfection/immunofluorescence in cardiocytes, HEK293, and COS-1 cells\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — two-hybrid and cotransfection localization data, single lab, no biochemical ubiquitination assay performed; note this paper appears to be about TRIM21/Ro52 (SSA1), not CALR\",\n      \"pmids\": [\"11461834\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CALR (calreticulin) functions as an ER-resident chaperone whose oncogenic frameshift mutations (most commonly a 52-bp deletion or 5-bp insertion in exon 9) generate a novel positively-charged C-terminus that enables the mutant protein to aberrantly bind and constitutively activate the thrombopoietin receptor MPL at the cell surface, recruiting JAK2 and triggering JAK-STAT signalling to drive cytokine-independent myeloproliferation; the degree of disruption to calreticulin's native calcium-binding C-terminal domain (more severe in type 1 than type 2 mutations) further modulates the disease phenotype.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CALR encodes calreticulin, an endoplasmic reticulum-resident protein in which recurrent somatic +1 frameshift mutations in exon 9 (most commonly a 52-bp deletion or 5-bp insertion) generate a novel positively-charged C-terminus while preserving ER retention [#0]. This mutant protein acquires a pathogenic gain of function: it preferentially binds the thrombopoietin receptor c-MPL complexed with JAK2, driving JAK2 phosphorylation and cytokine-independent proliferation, with the mutant-specific C-terminus disrupting the CALR P-domain so the N-domain engages c-MPL [#1]. This MPL-dependent activation of JAK-STAT signalling underlies mutant CALR-driven megakaryopoiesis and thrombocytosis in vivo, as demonstrated by mpl-knockdown epistasis in zebrafish and by knock-in mouse models that recapitulate an essential thrombocythemia-like phenotype [#3, #7]. Receptor engagement requires both loss of the native KDEL motif and the positively-charged residues yet is not fully explained by them alone, since a murine del19 mutant binds MPL weakly and produces only mild disease [#5]. The neoepitope is therapeutically actionable: a monoclonal antibody against the mutant C-terminus selectively disrupts CALR-dimer binding to TpoR, blocking signalling, proliferation, and differentiation [#2]. Distinct from the classical chaperone calcium-buffering role, type 1 (del52) mutations impair the C-terminal calcium-binding activity more severely than type 2 (ins5), correlating with altered cytosolic calcium signalling [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established that recurrent exon 9 +1 frameshift mutations define a molecular class of myeloproliferative neoplasm, producing a mutant calreticulin with a novel C-terminus that nonetheless remains ER-retained.\",\n      \"evidence\": \"Exome sequencing with immunofluorescence and flow cytometry in a patient discovery cohort\",\n      \"pmids\": [\"24325359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the gain-of-function mechanism\", \"Did not identify the receptor partner\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Addressed whether mutation subtypes differ biochemically, showing type 1 mutations impair C-terminal calcium binding more severely than type 2 and alter megakaryocyte calcium signalling.\",\n      \"evidence\": \"Calcium flux measurements in cultured megakaryocytes with isoelectric point prediction and clinical correlation\",\n      \"pmids\": [\"26449662\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Causal link between altered calcium and disease phenotype not established\", \"Mechanism connecting calcium dysregulation to MPL signalling unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified the oncogenic gain-of-function: mutant CALR specifically binds the JAK2-bound thrombopoietin receptor c-MPL through its N-domain to drive cytokine-independent growth.\",\n      \"evidence\": \"Co-immunoprecipitation, cytokine-independent growth assays in UT-7/TPO cells, JAK2 inhibition, iPSC differentiation, and domain mutagenesis\",\n      \"pmids\": [\"26817954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural basis of CALR-MPL engagement not resolved\", \"Did not establish requirement in vivo\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated in vivo genetic dependence on MPL, showing mutant CALR-induced thrombocytosis and JAK-STAT activation require mpl but not other cytokine receptors.\",\n      \"evidence\": \"Zebrafish transgenic expression with morpholino knockdown epistasis (mpl vs epor vs csf3r) and JAK inhibitor treatment\",\n      \"pmids\": [\"27716741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Zebrafish hematopoiesis may differ from mammalian\", \"Did not address chronic disease evolution\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Clarified that loss of KDEL and acquisition of positively-charged C-terminal residues are necessary but not sufficient for full MPL binding, refining the structural requirements for oncogenic activity.\",\n      \"evidence\": \"CRISPR/Cas9 knock-in mouse (Calr del19) with in vitro binding and STAT5 phosphorylation assays\",\n      \"pmids\": [\"30926777\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Species differences confound interpretation\", \"Exact sequence features required for high-affinity MPL binding not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Confirmed causality in human cells and an authentic in vivo disease model, with isogenic CRISPR correction and a conditional knock-in mouse recapitulating essential thrombocythemia.\",\n      \"evidence\": \"Patient-derived iPSCs with CRISPR repair and directed megakaryocyte differentiation; conditional knock-in mouse with transplantation, antibody treatment, and HSC transcriptomics\",\n      \"pmids\": [\"34678208\", \"33761144\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab models\", \"Hypoxia and other dysregulated pathways not mechanistically linked to MPL signalling\", \"Stem cell proliferative advantage mechanism incompletely defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Validated the mutant neoepitope as a therapeutic target by showing an antibody that disrupts CALR-dimer binding to TpoR blocks signalling and tumor growth.\",\n      \"evidence\": \"Monoclonal antibody (4D7) with cell-based proliferation, JAK-STAT readouts, patient samples, and xenograft models\",\n      \"pmids\": [\"35156745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether dimerization is obligatory for receptor activation in all mutant types\", \"Clinical efficacy not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Distinguished the calcium-signalling consequences of CALR mutation from JAK2-V617F, showing elevated cytosolic calcium during store depletion without hyperactivation of PLCγ-1 or IP3R.\",\n      \"evidence\": \"Fura-2 calcium measurements, SOCE assays, and phospho-western blotting in 32D myeloid progenitor cells\",\n      \"pmids\": [\"38509561\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism producing altered calcium dynamics not identified\", \"Functional contribution of calcium changes to myeloproliferation unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of mutant CALR-MPL complex assembly and the contribution of calcium dysregulation to disease phenotype remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No atomic-resolution structure of the mutant CALR-MPL-JAK2 complex\", \"Causal link between C-terminal calcium-binding loss and clinical phenotype not established\", \"Mechanism connecting altered cytosolic calcium to JAK-STAT output unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MPL\", \"JAK2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}