Molecular Pathogenesis Of Myeloproliferative Disorders Research Articles

Molecular pathogenesis of myeloproliferative disorders

Molecular pathogenesis of myeloproliferative disorders

The analysis of JAK2 and MPL mutations and JAK2 single nucleotide polymorphisms in MPN patients by MassARRAY assay

Recent studies have shown that JAK2 V617F, MPL W515L/K and JAK2 exon 12 mutations underlie the major molecular pathogenesis of myeloproliferative disorders (MPN). Allele-Specific Polymerase Chain Reaction (AS-PCR), direct sequencing and MassARRAY assay were used to ascertain the real prevalence of these mutations and the influence of genetic susceptibility in Chinese MPN patients. The positive rate of JAK2 V617F in polycythaemia vera (PV), essential thrombocythaemia (ET) and primary myelofibrosis (PMF) was 82.0%, 36.6% and 51.1% respectively. One ET patient and two PMF patients harboured the MPL W515L mutation and three PV patients harboured JAK2 exon 12 mutations. All of these patients were confirmed as JAK2 V617F negative. Clinical data demonstrated that PV patients with JAK2 exon 12 mutations were younger, had higher haemoglobin levels and white blood cell counts than PV patients with JAK2 V617F. In addition, through analysis of 4 polymorphic loci of JAK2 gene, no significant difference of distribution frequency was found among PV, ET and PMF patients. Distribution frequency of haplotype also was not significantly different among PV, ET and PMF patients. We conclude that JAK2 V617F is a major molecular pathogenesis in Chinese MPN patients. MPL W515L mutation and JAK2 exon 12 mutations can also be found in JAK2 V617F negative MPN patients.

The Analysis of JAK2 and MPL Mutation as Well as JAK2 SNPs in MPN Patients by MassARRAY Assay.

Abstract 4989 IntroductionRecent studies have shown that JAK2 V617F, MPL W515L/K and JAK2 exon 12 mutations underlie the major molecular pathogenesis of myeloproliferative disorders (MPN). MethodsTo ascertain the real prevalence of these mutations and the influence of genetic susceptibility in Chinese MPN patients, we applied Allele-Specific Polymerase Chain Reaction (AS-PCR), directly sequencing and MassARRAY assay into our study. ResultsThe positive rate of JAK2 V617F in polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) was 82.0%, 36.6% and 51.1% individually. We also found one ET patient, two PMF patients harboring MPL W515L mutation, and three PV patients harboring JAK2 exon 12 mutations. All of these patients were confirmed as JAK2 V617F negative. Moreover, clinical data demonstrated that PV patients with JAK2 exon 12 mutations had higher hemoglobin and lower age as well as WBC than PV patients with JAK2 V617F. In addition, through analysis of 4 polymorphic loci of JAK2 gene, no significant difference of distribution frequency was found among PV, ET and PMF patients. Distribution frequency of haplotype was not found to have significant difference among PV, ET and PMF patients either. ConclusionWe conclude that JAK2 V617F is major molecular pathogenesis in Chinese MPN patients. MPL W515L mutation and JAK2 exon 12 mutations can also be found in JAK2 V617F negative MPN patients. DisclosuresNo relevant conflicts of interest to declare.

Lnk inhibits myeloproliferative disorder-associated JAK2 mutant, JAK2V617F

The JAK2 mutation JAK2V617F is found frequently in patients with myeloproliferative disorders (MPD) and transforms hematopoietic cells to cytokine-independent proliferation when expressed with specific cytokine receptors. The Src homology 2 (SH2) and pleckstrin homology (PH) domain-containing adaptor protein Lnk (SH2B3) is a negative regulator of hematopoietic cytokine signaling. Here, we show that Lnk is a potent inhibitor of JAK2V617F constitutive activity. Lnk down-regulates JAK2V617F-mediated signaling and transformation in hematopoietic Ba/F3-erythropoietin receptor cells. Furthermore, in CFU assays, Lnk-deficient murine bone marrow cells are significantly more sensitive to transformation by JAK2V617F than wild-type (WT) cells. Lnk, through its SH2 and PH domains, interacts with WT and mutant JAK2 and is phosphorylated by constitutively activated JAK2V617F. Finally, we found that Lnk levels are high in CD34(+) hematopoietic progenitors from MPD patients and that Lnk expression is induced following JAK2 activation. Our data suggest that JAK2V617F is susceptible to endogenous negative-feedback regulation, providing new insights into the molecular pathogenesis of MPD.

Advances in the molecular characterization of Philadelphia-negative chronic myeloproliferative disorders

The identification and characterization of somatic disease alleles have greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies investigating the role of activated tyrosine kinase signaling in the Philadelphia chromosome negative myeloproliferative disorders. Previously identified tyrosine kinase mutations in chronic myeloid leukemia and other myeloproliferative disorders suggested the possibility that polycythemia vera, essential thrombocythemia and primary myelofibrosis are also caused by activated tyrosine kinases. Recent studies identified an activating mutation in the JAK2 tyrosine kinase (JAK2V617F) in most patients with polycythemia vera and in approximately half of those with essential thrombocythemia and primary myelofibrosis. More recently, activating mutations in the thrombopoietin receptor and in JAK2 exon 12 have been identified in JAK2V617F negative myeloproliferative disorders. The discovery of activated tyrosine kinases in the majority of patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis has diagnostic and pathogenetic implications. Subsequent studies are needed to elucidate the cause of myeloproliferative disorders without known disease alleles and to determine if inhibition of JAK2 signaling has therapeutic efficacy in the treatment of polycythemia vera, essential thrombocythemia and primary myelofibrosis.

Advances in molecular diagnostics of myeloproliferative disorders

Incremental advances in the molecular pathogenesis of myeloproliferative disorders (MPDs) have had a substantial impact on clinical practice in terms of both diagnosis and treatment. An array of novel molecular methods are being developed and integrated into the current battery of tests for diagnosis and monitoring of treatment response. Primarily, subjective clinico-histologic approaches to diagnosis are being replaced by more objective semimolecular diagnostic algorithms. Furthermore, identification of disease-specific molecular markers has facilitated the development of small-molecule drugs for targeted therapy. This review provides an overview of MPDs with emphasis on molecular diagnostic tests and their incorporation into contemporary diagnostic and therapeutic algorithms.

JAK-2 mutations and their relevance to myeloproliferative disease

The identification of the JAK2V617F allele greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies offering new genetic, biochemical, and functional insight into the role of JAK2V617F in the pathogenesis of these disorders. JAK2V617F mutations are present in almost all patients with polycythemia vera, and in approximately half of those with essential thrombocytosis and myelofibrosis. JAK2V617F has constitutive tyrosine kinase activity, and is able to transform hematopoietic cells and activate JAK-STAT signaling when co-expressed with homodimeric type I cytokine receptors. Murine bone marrow transplant experiments demonstrate that JAK2V617F is sufficient for the development of polycythemia vera in recipient mice. These results suggested that JAK-STAT pathway activation might contribute to the pathogenesis of JAK2-negative myeloproliferative disorders, and led to the discovery of an activating mutation in the thrombopoietin receptor in JAK2-negative myelofibrosis and essential thrombocytosis. The discovery of the JAK2V617F allele represents an important advance in our understanding of the molecular pathogenesis of myeloproliferative disorders, though many questions remain regarding the role of a single allele in three clinically distinct disorders, the mechanism of activation of JAK2V617F, and the pathogenesis of JAK2-negative myeloproliferative disorders.

Beyond chronic myelogenous leukemia: potential role for imatinib in Philadelphia-negative myeloproliferative disorders.

The myeloproliferative disorders (MPDs) are chronic malignant conditions originating from the clonal expansion of a multipotential hematopoietic stem cell. These diseases include polycythemia vera (PV), essential thrombocythenia, atypical chronic myeloid leukemia, idiopathic hypereosinophilic syndrome (HES), agnogenic myeloid metaplasia with myelofibrosis, and others. Receptor tyrosine kinases-the platelet-derived growth factor receptors (PDGFRs) and c-Kit-and their respective ligands have been implicated in the pathogenesis of MPDs. For example, a constitutively activated PDGFR fusion tyrosine kinase (FIP1L1-PDGFRA) was identified in some patients with HES, a disease characterized by sustained overproduction of eosinophils that has been classified by the World Health Organization as a chronic subtype of the MPDs. Imatinib is a selective inhibitor of PDGFRs, c-Kit, Abl and Arg protein-tyrosine kinases, as well as Bcr-Abl, the oncogenic tyrosine kinase that causes chronic myeloid leukemia. The efficacy of imatinib in treating HES, systemic mast cell disease, chronic myelomonocytic leukemia associated with PDGFRbeta fusion genes, and (to a lesser extent) PV and idiopathic myelofibrosis was reviewed from institutional experience and a review of the literature. In 3 studies that involved 11 patients with PV, 10 patients had reductions in phlebotomy with imatinib. Eight studies of 42 patients with HES indicated that 70% achieved complete hematologic remissions with imatinib. Four studies of 6 patients with MPD indicated responses with imatinib in 5 patients. Insight into the molecular pathogenesis of MPDs will improve the definitions of different disease categories and suggests that signal transduction inhibition is likely to be an increasingly important treatment option in the future.