Finally, it was demonstrated, in a Ba/F3 cell model, that increased calreticulin expression was directly linked to <i>JAK2V617F</i> and could be regulated by JAK2 kinase inhibitors.<b>Implications:</b> In conclusion, these results reveal proteome alterations in MPN granulocytes depending on the phenotype and genotype of patients, highlighting new oncogenic mechanisms associated with <i>JAK2</i> mutations and overexpression of calreticulin.<i></i>.
Mutations in JAK2, MPL and CALR genes have been identified in the majority of myeloproliferative neoplasm (MPN) patients, and patients negative for these three mutations are the so-called triple-negative (TN) MPN.
Chronic myeloproliferative neoplasms (MPN) characteristically arise from a somatic mutation in the pluripotent hematopoietic stem cell, and most common recurring mutations are in the JAK2, CALR, and cMPL genes.
The driver mutations JAK2V617F, MPLW515L/K and CALR influence disease phenotype of myeloproliferative neoplasms (MPNs) and might sustain a condition of chronic inflammation.
Somatic mutations of Janus kinase 2 (JAK2V617F), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) are the major clonal molecules that drive the pathogenesis of myeloproliferative neoplasms (MPN).
Although the role of mutated CALR in the development of MPNs has begun to be clarified, there are still no data available on the function of wild-type (WT) CALR during physiological hematopoiesis.
Moreover, the combination of BMN673, ruxolitinib, and hydroxyurea was highly effective in vivo against JAK2(V617F)<sup>+</sup> murine MPN-like disease and also against JAK2(V617F)<sup>+</sup>, CALR(del52)<sup>+</sup>, and MPL(W515L)<sup>+</sup> primary MPN xenografts.
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.
Lay summary: Mutations of the CALR gene are detected in 0 to 2% of patients with SVT, thus the utility of systematic CALR mutation testing to diagnose MPN is questionable.
As a whole, these data support the model that CALR-mutated ET could be considered as a distinct disease entity from JAK2V617F-positive MPNs and may provide the molecular basis supporting the different clinical features of these patients.
PNA-based FMCA for detecting common JAK2, MPL, and CALR mutations is a rapid, simple, and sensitive technique in BCR-ABL1-negative MPNs with >10% mutant allele at the time of initial diagnosis.
The results from gene expression and chromatin occupancy analysis have focused on the JAK-STAT pathway activated in both JAK2 V617F- and CALR-mutated MPN patient groups, although a more complete analysis is needed to be performed in MKs.
The combination of laboratory testing for the detection of JAK2, CALR, and MPL mutations is necessary to improve the diagnosis and classification of BCR-ABL1-negative MPN.
Erythroid staining for pSTAT5 was seen exclusively in "triple-negative (TN)" cases lacking JAK2 V617F, MPL, and CALR mutations (P=0.006, TN vs. other genotypes), and pSTAT5 staining in megakaryocyte nuclei was seen in 2 TN cases. pSTAT5 staining in TN MPN suggests that other unknown abnormalities in this pathway may contribute to the pathogenesis of these cases.
We model calreticulin (CALR) mutations in murine interleukin-3 (mIL-3) dependent pro-B (Ba/F3) cells by delivery of single guide RNAs (sgRNAs) targeting the endogenous Calr locus in the specific region where insertion and/or deletion (indel) CALR mutations occur in patients with myeloproliferative neoplasms (MPN), a type of blood cancer.
Mutations of JAK2V617F, JAK2 exon 12, MPL W515L/K and CALR were analysed in 439 Argentinean patients with BCR-ABL1-negative MPN, including 176 polycythemia vera (PV), 214 essential thrombocythemia (ET) and 49 primary myelofibrosis (PMF).
Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by stem cell-derived clonal myeloproliferation that is often but not always accompanied by JAK2, CALR, or MPL mutations; additional disease features include bone marrow stromal reaction including reticulin fibrosis, abnormal cytokine expression, anemia, hepatosplenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, leukemic progression, and shortened survival.
Our findings support the possibility of coexisting JAK2 V617F and CALR mutations and stress the importance of further molecular screening in MPN patients with low allele frequencies of JAK2 V617F.