Progenitor genotyping reveals a complex clonal architecture in a subset of CALR-mutated myeloproliferative neoplasms.
The identification of acquired CALR mutations in patients with essential thrombocythaemia (ET) or myelofibrosis (MF) has meant that disease-initiating mutations can now be detected in about 90% of all patients with a myeloproliferative neoplasm (MPN). Here, we show that only those CALR mutations that cause a +1 frameshift, thereby altering the carboxy-terminus of calreticulin, promote cytokine independence in vitro; in-frame deletions were not functional, and are unlikely to be the pathogenetic mutation underlying some MPN cases. Expression of the thrombopoietin receptor, MPL, was also necessary for factor-independence. Although the CALR mutations are considered to occur only in JAK2 V617F-negative cases and in a heterozygous state, progenitor genotyping revealed that this is not always true. Notably, CALR mutation-positive MPNs can be polyclonal: in one case, two distinct CALR mutation-positive subpopulations could be identified; in another, separate populations of JAK2 V617F-positive and CALR-mutated cells were present. Mitotic recombination involving chromosome 19 in a third instance resulted in the emergence of a CALR mutation-homozygous subclone. Collectively, our studies demonstrate that occasional patients with CALR mutation-positive ET or MF carry other MPN-initiating genetic mutations (including JAK2 V617F), acquire "secondary mutations" before or after the CALR mutation, or evolve over time to being CALR mutation-homozygous.
The University of Queensland Diamantina Institute, University of Queensland, Translational Research Institute, Brisbane, Australia.
Sarah
S
Martin
The University of Queensland Diamantina Institute, University of Queensland, Translational Research Institute, Brisbane, Australia.
Casey M
CM
Wright
The University of Queensland Diamantina Institute, University of Queensland, Translational Research Institute, Brisbane, Australia.
Linda M
0000-0003-0334-1479
LM
Scott
D000483:Alleles; D000818:Animals; D037282:Calreticulin / Q000737:chemistry / Q000235:genetics*; D002460:Cell Line; D002888:Chromosomes, Human, Pair 19; D060965:Clonal Evolution; D016207:Cytokines / Q000378:metabolism; D004252:DNA Mutational Analysis; D005260:Female; D056726:Genetic Association Studies; D018740:Genetic Heterogeneity; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009154:Mutation; D009196:Myeloproliferative Disorders / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D011995:Recombination, Genetic
D037282:Calreticulin; D016207:Cytokines


MPL

; 
JAK2
; CALR mutation; clonal evolution; myeloproliferative neoplasm