title: Activation of the thrombopoietin receptor by mutant calreticulin in CALR-mutant myeloproliferative neoplasms.
abstract: Recurrent somatic mutations of calreticulin (CALR) have been identified in patients harboring myeloproliferative neoplasms; however, their role in tumorigenesis remains elusive. Here, we found that the expression of mutant but not wild-type CALR induces the thrombopoietin (TPO)-independent growth of UT-7/TPO cells. We demonstrated that c-MPL, the TPO receptor, is required for this cytokine-independent growth of UT-7/TPO cells. Mutant CALR preferentially associates with c-MPL that is bound to Janus kinase 2 (JAK2) over the wild-type protein. Furthermore, we demonstrated that the mutant-specific carboxyl terminus portion of CALR interferes with the P-domain of CALR to allow the N-domain to interact with c-MPL, providing an explanation for the gain-of-function property of mutant CALR. We showed that mutant CALR induces the phosphorylation of JAK2 and its downstream signaling molecules in UT-7/TPO cells and that this induction was blocked by JAK2 inhibitor treatment. Finally, we demonstrated that c-MPL is required for TPO-independent megakaryopoiesis in induced pluripotent stem cell-derived hematopoietic stem cells harboring the CALR mutation. These findings imply that mutant CALR activates the JAK2 downstream pathway via its association with c-MPL. Considering these results, we propose that mutant CALR promotes myeloproliferative neoplasm development by activating c-MPL and its downstream pathway.
authors.affiliation: Department of Transfusion Medicine and Stem Cell Regulation.
authors.forename: Marito
authors.initials: M
authors.lastname: Araki
authors.affiliation: Department of Hematology.
authors.forename: Yinjie
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Hematology, Research Institute for Disease of Old Age.
authors.forename: Nami
authors.initials: N
authors.lastname: Masubuchi
authors.affiliation: Department of Hematology.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Hironaka
authors.affiliation: Department of Hematology.
authors.forename: Hiraku
authors.initials: H
authors.lastname: Takei
authors.affiliation: Department of Transfusion Medicine and Stem Cell Regulation.
authors.forename: Soji
authors.initials: S
authors.lastname: Morishita
authors.affiliation: Department of Hematology, Center for Genomic and Regenerative Medicine, and.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Mizukami
authors.affiliation: Department of Hematology, Leading Center for the Development and Research of Cancer Medicine, Juntendo University Graduate School of Medicine, Tokyo, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Kan
authors.affiliation: Department of Hematology.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Shirane
authors.affiliation: Department of Hematology.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Edahiro
authors.affiliation: Department of Hematology.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Sunami
authors.affiliation: Department of Transfusion Medicine and Stem Cell Regulation.
authors.forename: Akimichi
authors.initials: A
authors.lastname: Ohsaka
authors.affiliation: Department of Hematology.
authors.forename: Norio
authors.initials: N
authors.lastname: Komatsu
mesh_terms: D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D057809:HEK293 Cells; D019337:Hematologic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000401:mortality; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000378:metabolism / Q000473:pathology; D053614:Janus Kinase 2 / Q000378:metabolism; D009196:Myeloproliferative Disorders / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D053628:Receptors, Thrombopoietin / Q000235:genetics / Q000378:metabolism*; D034061:Thrombopoiesis / Q000235:genetics; D013926:Thrombopoietin / Q000378:metabolism
chemical_list: C576483:CALR protein, human; D037282:Calreticulin; D009363:Neoplasm Proteins; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin; C507924:JAK2 protein, human; D053614:Janus Kinase 2