We found examples of both of these categories in published and previously unpublished MPL exon 10 sequencing data from MPN patients, demonstrating that some, if not all of the new mutations reported here represent likely drivers or modifiers of myeloproliferative disease.
These mutations include JAK2, CALR and MPL mutations as the main disease drivers, mutations driving clonal expansion, and mutations that contribute to progression of chronic MPNs to myelodysplasia and acute leukemia.
Mutations in <i>CALR</i> observed in myeloproliferative neoplasms (MPN) were recently shown to be pathogenic via their interaction with MPL and the subsequent activation of the Janus Kinase - Signal Transducer and Activator of Transcription (JAK-STAT) pathway.
<b>Expert Opinion</b>: Altogether, we believe that MPL is an important, but challenging, therapeutic target in MPNs that requires novel strategies to interrupt the specific conformational changes induced by each mutation or pathologic interaction without compromising the key functions of wild type MPL.
Since its discovery in 2013, we now have a more precise understanding of how mutant CALR, an endoplasmic reticulum chaperone protein, activates the JAK/STAT signaling pathway via a pathogenic binding interaction with the thrombopoietin receptor, MPL, to induce MPN.
Since association with MPL is required for the oncogenicity of mutant CALR, we propose a model in which the constitutive activation of the MPL downstream pathway by mutant CALR multimers induces the development of MPN.
The association between the <i>JAK2</i> haplotype<sup>GGCC_46/1</sup> and mutations in other genes, such as thrombopoietin receptor (<i>MPL</i>) and calreticulin (<i>CALR</i>), or the association with triple negative MPN, is still controversial.
This study explored the relationship between mutations in the Janus kinase 2 gene ( JAK2), MPL, and the calreticulin gene ( CALR) in Uygur and Han Chinese patients with BCR-ABL fusion gene-negative MPN and corresponding clinical features.
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.
Somatic mutations in JAK2, MPL and CALR are recurrently identified in most of the cases with Philadelphia chromosome negative myeloproliferative neoplasms (MPNs).
It has recently been shown that mutant CALR constitutively activates the thrombopoietin receptorMPL and, thus, plays a causal role in the development of MPNs.
JAK2, CALR, MPL and triple-negative mutational status has a direct impact on symptom severity and disease burden assessed by MPN10 score in myeloproliferative neoplasms (MPNs).
The discovery of the activating Janus kinase (JAK)2<sup>V617F</sup> mutation in 2005 in most patients with the classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) spurred intense interest in research into these disorders, culminating in the identification of activating mutations in MPL in 2006 and indels in the gene encoding calreticulin (CALR) in 2013, thus providing additional mechanistic explanations for the universal activation of JAK-signal transducer and activator of transcription (JAK-STAT) observed in these conditions, and the success of the JAK1/2 inhibitor ruxolitinib, which first received regulatory approval in 2011.
Mutations in the ER chaperone calreticulin (CALR) are common in myeloproliferative neoplasm (MPN) patients, activate the thrombopoietin receptor (MPL), and mediate constitutive JAK/STAT signaling.
MPN driver mutations (JAK2, CALR, MPL) are somatically acquired also in familial cases, so a genetic predisposition to acquire one of the MPN driver mutations would be inherited, even though the causative germline mutations underlying familial MPN remain largely unknown.
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.
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).
Expression of mutant CALR in murine or human haematopoietic cell lines was accompanied by myeloproliferative leukemia protein (MPL)-dependent activation of MAPK signalling, and MPN patients with CALR mutations showed increased MAPK activity in CD34 cells, platelets and megakaryocytes.