Project description:Familial essential thrombocythemia features the acquisition of somatic mutations and an evolution similar to the sporadic form of the disease. Here we report two patients-father and daughter-with essential thrombocythemia who displayed a heterogeneous pattern of somatic mutations. The JAK2 V617F mutation was found in the daughter, while the father harbored the MPL W515L mutation. This case report may constitute further proof that in familial essential thrombocythemia there are other, still undefined, constitutional, inherited genetic factors predisposing to the acquisition of various somatic mutations (e.g., JAK2 V617F and MPL).
Project description:BackgroundIt has been discovered that Janus kinase 2 (JAK2) exon12 mutations lead to the polycythemia vera (PV) phenotype, while somatic mutations of calreticulin (CALR) are associated with essential thrombocythemia (ET) or primary myelofibrosis. In this article, we report a case of ET with coexistence of JAK2 exon12 and CALR mutations. The objective of this study was to elucidate the pathogenicity mechanism of a JAK2 exon12 mutation (JAK2N533S) and the role of the coexistence of mutations on the hematological phenotype.MethodsWe designed a colony analysis of tumor cells obtained from this patient, and attempted to identify mutant genes using DNA from hair follicles. Mutation impairment prediction and conservative analysis were conducted to predict the mutation impairment and structure of JAK2N533S. In addition, we conducted a functional analysis of JAK2N533S by constructing Ba/F3 cell models.ResultsThree distinct tumor subclones, namely JAK2N533Shet+/CALRtype1het +, JAK2N533Shet+/CALR wt, and JAK2N533Shet+/CALRtype1hom +, were identified from the 17 selected erythroid and 21 selected granulocyte colonies. The analysis of hair follicles yielded positive results for JAK2N533S. According to the bioinformatics analysis, JAK2N533S may exert only a minor effect on protein function. Functional studies showed that JAK2N533S did not have a significant effect on the proliferation of Ba/F3 cells in the absence of interleukin-3 (IL-3), similar to wild-type JAK2. Notably, there were no increased phosphorylation levels of JAK2-downstream signaling proteins, including signal transducer and activator of transcription 3 (STAT3) and STAT5, in Ba/F3 cells harboring the JAK2N533S.ConclusionOur study revealed that the JAK2N533Shet+/CALRtype1het+ subclone was linked to a significant expansion advantage in this patient, indicating that it may contribute to the development of the ET phenotype. We further demonstrated that JAK2N533S, as a noncanonical JAK2 exon12 mutation, is a germline mutation that may not exert an effect on cell proliferation and protein function. These results and the present body of available data imply that certain noncanonical JAK2 mutations are not gain-of-function mutations leading to the development of myeloproliferative neoplasms.
Project description:In this study, we explored the transcriptome of hematopoietic stem cells (HSCs) and megakaryocyte-erythroid progenitors (MEPs) in JAK2 V617F+ PV and ET and found that distinctive gene expression patterns within MPN subtypes begin at the HSC stage. HSCs from ET exhibited prominent megakaryocyte (Mk)-lineage priming. The differentially expressed genes (DEGs) indicated that cellular processes and signaling pathways in HSCs and MEPs from healthy donors (HDs), PV and ET patients are differentially modulated
Project description:The JAK2 V617F mutation is found in most patients with a myeloproliferative neoplasm and is sufficient to produce a myeloproliferative phenotype in murine retroviral transplantation or transgenic models. However, several lines of evidence suggest that disease phenotype is influenced by the level of mutant JAK2 signaling, and we have therefore generated a conditional knock-in mouse in which a human JAK2 V617F is expressed under the control of the mouse Jak2 locus. Human and murine Jak2 transcripts are expressed at similar levels, and mice develop modest increases in hemoglobin and platelet levels reminiscent of human JAK2 V617F-positive essential thrombocythemia. The phenotype is transplantable and accompanied by increased terminal erythroid and megakaryocyte differentiation together with increased numbers of clonogenic progenitors, including erythropoietin-independent erythroid colonies. Unexpectedly, JAK2(V617F) mice develop reduced numbers of lineage(-)Sca-1(+)c-Kit(+) cells, which exhibit increased DNA damage, reduced apoptosis, and reduced cell cycling. Moreover, competitive bone marrow transplantation studies demonstrated impaired hematopoietic stem cell function in JAK2(V617F) mice. These results suggest that the chronicity of human myeloproliferative neoplasms may reflect a balance between impaired hematopoietic stem cell function and the accumulation of additional mutations.
Project description:The aim of the study was to evaluate selected angiogenic factors in patients with essential thrombocythemia (ET) depending on JAK2V617F, calreticulin gene (CALR) and myeloproliferative leukemia virus oncogene (MPL) mutations. Sixty ET patients and 20 healthy volunteers were enrolled in the study. The following tests were performed: vascular endothelial growth factor- A (VEGF-A), soluble vascular endothelial growth factor receptor-1 (sVEGFR-1),soluble vascular endothelial growth factor receptor-2 (sVEGFR-2), platelet-derived growth factor( PDGF-BB), and stromal-derived factor-1α (SDF-1α). We observed an increased PDGF-BB level in patients with ET compared to the controls. Patients with CALR mutation had significantly higher concentration of PDGF-BB and lower concentration of SDF-1α than patients with JAK2V617F mutation. High concentration of PDGF-BB and low concentration of SDF-1α in patients with CALR(+) ET may indicate a contribution of these chemokines in disturbed Ca2+ metabolism in platelets.
Project description:Janus-activated kinase 2 (JAK2) mutations are common in myeloproliferative disorders; however, although they are detected in virtually all polycythemia vera patients, they are found in approximately 50% of essential thrombocythemia (ET) patients, suggesting that converging pathways/abnormalities underlie the onset of ET. Recently, the chromosomal translocation 3;21, leading to the fusion gene AML1/MDS1/EVI1 (AME), was observed in an ET patient. After we forced the expression of AME in the bone marrow (BM) of C57BL/6J mice, all the reconstituted mice died of a disease with symptoms similar to ET with a latency of 8 to 16 months. Peripheral blood smears consistently showed an elevated number of dysplastic platelets with anisocytosis, degranulation, and giant size. Although the AME-positive mice did not harbor Jak2 mutations, the BM of most of them had significantly higher levels of activated Stat3 than the controls. With combined biochemical and biological assays we found that AME binds to the Stat3 promoter leading to its up-regulation. Signal transducers and activators of transcription 3 (STAT3) analysis of a small group of ET patients shows that in about half of the patients, there is STAT3 hyperactivation independently of JAK2 mutations, suggesting that the hyperactivation of STAT3 by JAK2 mutations or promoter activation may be a critical step in development of ET.