title: Calreticulin mutants in mice induce an MPL-dependent thrombocytosis with frequent progression to myelofibrosis.
abstract: Frameshift mutations in the calreticulin (CALR) gene are seen in about 30% of essential thrombocythemia and myelofibrosis patients. To address the contribution of the CALR mutants to the pathogenesis of myeloproliferative neoplasms, we engrafted lethally irradiated recipient mice with bone marrow cells transduced with retroviruses expressing these mutants. In contrast to wild-type CALR, CALRdel52 (type I) and, to a lesser extent, CALRins5 (type II) induced thrombocytosis due to a megakaryocyte (MK) hyperplasia. Disease was transplantable into secondary recipients. After 6 months, CALRdel52-, in contrast to rare CALRins5-, transduced mice developed a myelofibrosis associated with a splenomegaly and a marked osteosclerosis. Monitoring of virus-transduced populations indicated that CALRdel52 leads to expansion at earlier stages of hematopoiesis than CALRins5. However, both mutants still specifically amplified the MK lineage and platelet production. Moreover, a mutant deleted of the entire exon 9 (CALRdelex9) did not induce a disease, suggesting that the oncogenic property of CALR mutants was related to the new C-terminus peptide. To understand how the CALR mutants target the MK lineage, we used a cell-line model and demonstrated that the CALR mutants, but not CALRdelex9, specifically activate the thrombopoietin (TPO) receptor (MPL) to induce constitutive activation of Janus kinase 2 and signal transducer and activator of transcription 5/3/1. We confirmed in c-mpl- and tpo-deficient mice that expression of Mpl, but not of Tpo, was essential for the CALR mutants to induce thrombocytosis in vivo, although Tpo contributes to disease penetrance. Thus, CALR mutants are sufficient to induce thrombocytosis through MPL activation.
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Caroline
authors.initials: C
authors.lastname: Marty
authors.affiliation: Signal Transduction and Molecular Hematology Unit, Ludwig Institute for Cancer Research, Brussels, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels, Belgium; and.
authors.forename: Christian
authors.initials: C
authors.lastname: Pecquet
authors.affiliation: CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.
authors.forename: Harini
authors.initials: H
authors.lastname: Nivarthi
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Mira
authors.initials: M
authors.lastname: El-Khoury
authors.affiliation: Signal Transduction and Molecular Hematology Unit, Ludwig Institute for Cancer Research, Brussels, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels, Belgium; and.
authors.forename: Ilyas
authors.initials: I
authors.lastname: Chachoua
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Micheline
authors.initials: M
authors.lastname: Tulliez
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Villeval
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Hana
authors.initials: H
authors.lastname: Raslova
authors.affiliation: CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Kralovics
authors.affiliation: Signal Transduction and Molecular Hematology Unit, Ludwig Institute for Cancer Research, Brussels, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels, Belgium; and.
authors.forename: Stefan N
authors.initials: SN
authors.lastname: Constantinescu
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: Isabelle
authors.initials: I
authors.lastname: Plo
authors.affiliation: INSERM, Unité Mixte de Recherche (UMR) 1170, Villejuif, France; Université Paris-Saclay, UMR 1170, Villejuif, France; Gustave Roussy, UMR 1170, Villejuif, France;
authors.forename: William
authors.initials: W
authors.lastname: Vainchenker
mesh_terms: D000818:Animals; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D016368:Frameshift Mutation; D054643:INDEL Mutation; D053614:Janus Kinase 2 / Q000235:genetics / Q000378:metabolism; D008533:Megakaryocytes / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008817:Mice, Mutant Strains; D055728:Primary Myelofibrosis / Q000209:etiology / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D053628:Receptors, Thrombopoietin / Q000235:genetics / Q000378:metabolism*; D013922:Thrombocytosis / Q000150:complications / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
chemical_list: D037282:Calreticulin; C481270:Mpl protein, mouse; D053628:Receptors, Thrombopoietin; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2