title: Calreticulin mutation does not contribute to disease progression in essential thrombocythemia by inhibiting phagocytosis.
abstract: Somatic mutations of calreticulin (CALR) have been observed in many cases of essential thrombocythemia (ET) or primary myelofibrosis that harbor non-mutated Janus kinase 2 (JAK2). CALR mainly localizes within the endoplasmic reticulum lumen, but a small fraction of the total CALR pool is distributed over the cell surface. Cell surface CALR is known to transduce prophagocytic "eat me" signals to macrophages and acts as one of the important regulators for macrophage engulfment. In this study, we attempted to clarify whether mutant CALR may affect the threshold for macrophage engulfment and play an integral role in the pathogenesis of CALR-mutated ET. First, we compared the surface expression levels of CALR on hematopoietic stem and progenitor cells (HSPCs) and mature blood cells in patients with myeloproliferative neoplasms and found that the surface expression of mutant CALR did not change. Next, we compared the threshold for macrophage phagocytosis of each HSPC fraction and mature blood cells and found no significant change in the efficiency of macrophage engulfment. Our data suggest that CALR mutation does not affect sensitivity to phagocytosis by macrophages. Finally, we analyzed the phosphorylation statuses of molecules downstream of JAK2 at each HSPC level in patients with ET and found that CALR mutations activated the JAK-STAT pathway in a manner similar to that associated with JAK2 mutations. These results indicate that mutant CALR causes myeloproliferation because of the activation of JAK-STAT pathway and not by the inhibition of phagocytosis, which is similar to the myeloproliferation caused by JAK2 V617F mutation.
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Daitoku
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Katsuto
authors.initials: K
authors.lastname: Takenaka
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Takuji
authors.initials: T
authors.lastname: Yamauchi
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Ayano
authors.initials: A
authors.lastname: Yurino
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Jinnouchi
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nunomura
authors.affiliation: Department of Hematology, Hamanomachi Hospital, Fukuoka, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Eto
authors.affiliation: Department of Hematology, Hara-Sanshin Hospital, Fukuoka, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kamimura
authors.affiliation: Department of Hematology, Japan Community Health Care Organization Kyushu Hospital, Fukuoka, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Higuchi
authors.affiliation: Department of Hematology, National Hospital Organization Kyushu Medical Center, Fukuoka, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Harada
authors.affiliation: Department of Hematology, Hamanomachi Hospital, Fukuoka, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Saito
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Miyamoto
authors.affiliation: Center for Cellular and Molecular Medicine, Kyushu University Hospital, Fukuoka, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Iwasaki
authors.affiliation: Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan; Center for Cellular and Molecular Medicine, Kyushu University Hospital, Fukuoka, Japan. Electronic address: akashi@med.kyushu-u.ac.jp.
authors.forename: Koichi
authors.initials: K
authors.lastname: Akashi
mesh_terms: D015415:Biomarkers; D051928:CD47 Antigen / Q000378:metabolism; D037282:Calreticulin / Q000235:genetics* / Q000378:metabolism; D016022:Case-Control Studies; D002462:Cell Membrane / Q000378:metabolism; D018450:Disease Progression; D006412:Hematopoietic Stem Cells; D006801:Humans; D016130:Immunophenotyping; D053614:Janus Kinase 2 / Q000235:genetics; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D009154:Mutation; D010587:Phagocytosis / Q000235:genetics* / Q000276:immunology*; D010766:Phosphorylation; D011087:Polycythemia Vera / Q000175:diagnosis / Q000235:genetics / Q000276:immunology; D053628:Receptors, Thrombopoietin / Q000235:genetics; D015398:Signal Transduction; D013920:Thrombocythemia, Essential / Q000175:diagnosis / Q000235:genetics* / Q000276:immunology*
chemical_list: D015415:Biomarkers; D051928:CD47 Antigen; D037282:Calreticulin; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D053614:Janus Kinase 2