SomaticCALRMutations in Myeloproliferative Neoplasms with NonmutatedJAK2

Abstract

BACKGROUND Somatic mutations in the Janus kinase 2 gene (JAK2) occur in many myeloproliferative neoplasms, but the molecular pathogenesis of myeloproliferative neoplasms with nonmutated JAK2 is obscure, and the diagnosis of these neoplasms remains a challenge. METHODS We performed exome sequencing of samples obtained from 151 patients with myeloproliferative neoplasms. The mutation status of the gene encoding calreticulin (CALR) was assessed in an additional 1345 hematologic cancers, 1517 other cancers, and 550 controls. We established phylogenetic trees using hematopoietic colonies. We assessed calreticulin subcellular localization using immunofluorescence and flow cytometry. RESULTS Exome sequencing identified 1498 mutations in 151 patients, with medians of 6.5, 6.5, and 13.0 mutations per patient in samples of polycythemia vera, essential thrombocythemia, and myelofibrosis, respectively. Somatic CALR mutations were found in 70 to 84% of samples of myeloproliferative neoplasms with nonmutated JAK2, in 8% of myelodysplasia samples, in occasional samples of other myeloid cancers, and in none of the other cancers. A total of 148 CALR mutations were identified with 19 distinct variants. Mutations were located in exon 9 and generated a +1 base-pair frameshift, which would result in a mutant protein with a novel C-terminal. Mutant calreticulin was observed in the endoplasmic reticulum without increased cell-surface or Golgi accumulation. Patients with myeloproliferative neoplasms carrying CALR mutations presented with higher platelet counts and lower hemoglobin levels than patients with mutated JAK2. Mutation of CALR was detected in hematopoietic stem and progenitor cells. Clonal analyses showed CALR mutations in the earliest phylogenetic node, a finding consistent with its role as an initiating mutation in some patients. CONCLUSIONS Somatic mutations in the endoplasmic reticulum chaperone CALR were found in a majority of patients with myeloproliferative neoplasms with nonmutated JAK2. (Funded by the Kay Kendall Leukaemia Fund and others.)

Understanding deregulated cellular and molecular dynamics in the haematopoietic stem cell niche to develop novel therapeutics for bone marrow fibrosis

“…PMF refers to BCR‐ABL1 ‐negative MPN, and is a clonal disorder of haematopoiesis arising in the haematopoietic stem cell (HSC) 2. The majority of patients with PMF carry mutations that activate JAK–STAT signalling; 60% harbour the JAK2V617F mutation, approximately 30% carry a calreticulin (CALR) mutation, and 8% carry a myeloproliferative leukaemia virus oncogene ( MPL ) mutation 3, 4, 5, 6, 7, 8. PMF is the most aggressive of the three classic MPNs, and is associated with significantly shortened survival 9, 10.…”

N‐methyl‐d‐aspartate receptor mediated calcium influx supports in vitro differentiation of normal mouse megakaryocytes but proliferation of leukemic cell lines

“…The contribution from intracellular calcium ions (Ca 2+ ) to megakaryocytic differentiation remains poorly understood but is an area of active research due to the discovery that 30% of patients with essential thrombocythaemia (ET) and primary myelofibrosis (PMF) harbor mutations in the CALR gene that encodes calreticulin 10, 11. Calreticulin is highly expressed in megakaryocytes and buffers Ca 2+ in the endoplasmic reticulum (ER) 12, 13.…”

CALR and ASXL1 mutations-based molecular prognostication in primary myelofibrosis: an international study of 570 patients

“…4 JAK2 or MPL mutations are found in 50-70% of patients with PMF or essential thrombocythemia (ET) and calreticulin (CALR) mutations account for the majority of the remaining cases; 5,6 in strictly World Health Organization-defined disease, CALR mutations were seen in 49% of ET and 74% of PMF patients not expressing mutant JAK2 or MPL. 7,8 In ET, CALR mutations correlated with male sex, younger age, lower leukocyte count, lower hemoglobin level and higher platelet count 8 and in PMF with younger age, higher platelet count and lower incidences of anemia, leukocytosis and spliceosome mutations.…”