Article

A Gain-of-Function Mutation of JAK2 in Myeloproliferative Disorders

University of Pavia, Ticinum, Lombardy, Italy
New England Journal of Medicine (Impact Factor: 55.87). 05/2005; 352(17):1779-90. DOI: 10.1056/NEJMoa051113
Source: PubMed

ABSTRACT

Polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis are clonal myeloproliferative disorders arising from a multipotent progenitor. The loss of heterozygosity (LOH) on the short arm of chromosome 9 (9pLOH) in myeloproliferative disorders suggests that 9p harbors a mutation that contributes to the cause of clonal expansion of hematopoietic cells in these diseases.
We performed microsatellite mapping of the 9pLOH region and DNA sequencing in 244 patients with myeloproliferative disorders (128 with polycythemia vera, 93 with essential thrombocythemia, and 23 with idiopathic myelofibrosis).
Microsatellite mapping identified a 9pLOH region that included the Janus kinase 2 (JAK2) gene. In patients with 9pLOH, JAK2 had a homozygous G-->T transversion, causing phenylalanine to be substituted for valine at position 617 of JAK2 (V617F). All 51 patients with 9pLOH had the V617F mutation. Of 193 patients without 9pLOH, 66 were heterozygous for V617F and 127 did not have the mutation. The frequency of V617F was 65 percent among patients with polycythemia vera (83 of 128), 57 percent among patients with idiopathic myelofibrosis (13 of 23), and 23 percent among patients with essential thrombocythemia (21 of 93). V617F is a somatic mutation present in hematopoietic cells. Mitotic recombination probably causes both 9pLOH and the transition from heterozygosity to homozygosity for V617F. Genetic evidence and in vitro functional studies indicate that V617F gives hematopoietic precursors proliferative and survival advantages. Patients with the V617F mutation had a significantly longer duration of disease and a higher rate of complications (fibrosis, hemorrhage, and thrombosis) and treatment with cytoreductive therapy than patients with wild-type JAK2.
A high proportion of patients with myeloproliferative disorders carry a dominant gain-of-function mutation of JAK2.

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Available from: Andreas Buser, Aug 25, 2014
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    • "MPNs provide a window into cancer early during its ontogeny and give insights into the processes that regulate genome stability during malignant clonal evolution. The most common recurrent lesion in MPN patients is an activating V617F mutation in the JAK2 non-receptor tyrosine kinase (JAK2V617F) that causes hyperactive JAK-STAT signaling and confers a capacity for cytokine-independent growth (Baxter et al., 2005; James et al., 2005; Kralovics et al., 2005; Levine et al., 2005). Recently, a growing body of work has suggested that JAK2V617F is associated with increased DNA damage: (1) increased numbers of gH2Ax-marked double-strand breaks (DSBs) have been detected in Ba/F3 pro-B cells overexpressing JAK2V617F (Marty et al., 2013) and in lineage-negative , Sca1-positive, c-Kit-positive (LSK) cells (enriched for hematopoietic stem cell [HSC] activity) from 6-month-old JAK2V617F-heterozygous knockin mice (Li et al., 2010); (2) JAK2V617F expression is associated with increased levels of DNA-damaging reactive oxygen species (Marty et al., 2013); (3) RAD51-positive foci indicative of increased DSB repair have been observed in CD34+ hematopoietic cells obtained from JAK2V617F-positive MPN patients (Plo et al., 2008); and (4) JAK2V617F expression in both human diploid fibroblasts and primary erythroblasts from MPN patients leads to higher rates of stalled replication forks, with improper processing of stalled replication intermediates representing a potential source of DSBs (Chen et al., 2014). "
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    ABSTRACT: JAK2V617F is the most common oncogenic lesion in patients with myeloproliferative neoplasms (MPNs). Despite the ability of JAK2V617F to instigate DNA damage in vitro, MPNs are nevertheless characterized by genomic stability. In this study, we address this paradox by identifying the DNA helicase RECQL5 as a suppressor of genomic instability in MPNs. We report increased RECQL5 expression in JAK2V617F-expressing cells and demonstrate that RECQL5 is required to counteract JAK2V617F-induced replication stress. Moreover, RECQL5 depletion sensitizes JAK2V617F mutant cells to hydroxyurea (HU), a pharmacological inducer of replication stress and the most common treatment for MPNs. Using single-fiber chromosome combing, we show that RECQL5 depletion in JAK2V617F mutant cells impairs replication dynamics following HU treatment, resulting in increased double-stranded breaks and apoptosis. Cumulatively, these findings identify RECQL5 as a critical regulator of genome stability in MPNs and demonstrate that replication stress-associated cytotoxicity can be amplified specifically in JAK2V617F mutant cells through RECQL5-targeted synthetic lethality.
    Full-text · Article · Dec 2015 · Cell Reports
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    • "The robust induction of AIM2, a key component of the pathway, was confirmed by qRT-PCR, suggesting that AIM2 may be a downstream effector of JAK2V617F and may play a role in the development of myelofibrosis (discussed below). Consistent with previous reports in a murine cell line[22,23], the expression of JAK2V617F promotes STAT activation and subsequent cytokine-independent growthin the lower panel. V5-tagged JAK2V617F induction was observed by immunoblotting analysis (upper panel). "
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    ABSTRACT: The gain-of-function mutation JAK2V617F is frequently found in Philadelphia-chromosome-negative myeloproliferative neoplasm (MPN) patients. However, the tumorigenic properties of JAK2V617F have mostly been characterized in in vivo and in vitro murine models due to the lack of appropriate human cell lines. Using the multipotent hematologic cell line UT-7/GM, we established D9, a novel human cell line that expresses JAK2V617F upon tetracycline addition. We assessed cellular differentiation in UT-7/GM cells when JAK2V617F was induced, and we used microarrays to analyze changes in mRNA expression caused by JAK2V617F. Using the human D9 cell line, we demonstrated that the induction of JAK2V617F leads to cytokine-independent cell growth with increased STAT activation and erythroid differentiation, mimicking the characteristics observed in polycythemia vera, making it a suitable in vitro model for studying this disorder. Interestingly, JAK2V617F-dependent erythroid cell differentiation was blocked when GM-CSF was added to the culture, suggesting that the GM-CSF pathway antagonizes JAK2V617F-induced erythroid cell differentiation. Our microarray analysis identified several genes involved in inflammasome activation, such as AIM2, IL1B, and CASP1, which were significantly up-regulated in JAK2V617F-induced cells. The observed inflammasome activation following JAK2V617F induction is consistent with a recent report demonstrating the involvement of IL1B in myelofibrosis development in a JAK2V617F model mouse. These results indicate that the D9 cell line should be useful for characterizing the signaling pathways downstream of JAK2V617F, allowing for the identification of effector molecules that contribute to the development of MPN.
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    • "Mutations in the JAK2 gene are thought to underlie the development of polycythemia vera (PV) [3], essential thrombocythemia (ET), and primary myelofibrosis (PMF) [4] [5] [6]. Indeed, ≥95% of PV patients, and half or more of ET and PMF patients, harbor the JAK2V617F mutation [7]. "
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