JAK2 V617F in myeloid disorders: What do we know now, and where are we headed?

Clonal haematopoiesis - a novel entity that modifies pathological processes in elderly

Progress in the development of new sequencing techniques with wider accessibility and higher sensitivity of the protocol of deciphering genome particularities led to the discovery of a new phenomenon - clonal haematopoiesis. It is characterized by the presence in the bloodstream of elderly people a minor clonal population of cells with mutations in certain genes, but without any sign of disease related to the hematopoietic system. Here we will review this recent advancement in the field of clonal haematopoiesis and how it may affect the disease's development in old age.

The role of JAK inhibitors in hematopoietic cell transplantation

The Janus Kinase (JAK)/Signal Transducers and Activators of Transcription (STAT) pathway is essential for both the regulation of hematopoiesis and the control of inflammation. Disruption of this pathway can lead to inflammatory and malignant disease processes. JAK inhibitors, designed to control the downstream effects of pro-inflammatory and pro-angiogenic cytokines, have been successfully used in pre-clinical models and clinical studies of patients with autoimmune diseases, hematologic malignancies, and the hematopoietic cell transplantation (HCT) complication graft versus host disease (GVHD). In the last decade, JAK inhibitors Ruxolitinib, Fedratinib, and most recently Pacritinib have been United States Federal Drug Administration (FDA) approved for the treatment of myelofibrosis (MF). Ruxolitinib was also recently approved for the treatment of steroid refractory acute as well as chronic GVHD; JAK inhibitors are currently under evaluation in the pre-HCT setting in MF and for the prevention of GVHD. This review will focus on the role of JAK inhibitors in the treatment of hematologic malignancies, the potential function of pre-HCT JAK inhibitors in patients with MF, and the role of JAK inhibitors in the prevention and treatment of acute and chronic GVHD.

JAK2S523L, a novel gain-of-function mutation in a critical autoregulatory residue in JAK2V617F- MPNs

The SH2-JH2 linker domain of JAK2 has been implicated in the negative regulation of JAK2 activity. In 2 patients with myeloproliferative neoplasms (MPNs), we identified and characterized the novel JAK2 mutation S523L, which occurs in a key residue in the linker region. In 1 case, acquisition of JAK2S523L was associated with thrombocytosis and bone marrow megakaryocytic hyperplasia, and there were no other somatic alterations in this patient. The second patient with JAK2S523Lmutation presented with increased hematocrit and had concurrent mutations in RUNX1 and BCORL1. Consistent with the genetic and clinical data, expression of JAK2S523L causes interleukin-3-independent growth in Ba/F3 cells transduced with the erythropoietin receptor by constitutively active Jak2/Stat5 signaling.

JAK2 V617F, MPL W515L and JAK2 Exon 12 Mutations in Chinese Patients with Primary Myelofibrosis

OBJECTIVE

JAK2 V617F, MPL W515L and JAK2 exon 12 mutations are novel acquired mutations that induce constitutive cytokine-independent activation of the JAK-STAT pathway in myeloproliferative disorders (MPD). The discovery of these mutations provides novel mechanism for activation of signal transduction in hematopoietic malignancies. This research was to investigate their prevalence in Chinese patients with primary myelofibrosis (PMF).

METHODS

We introduced allele-specific PCR (AS-PCR) combined with sequence analysis to simultaneously screen JAK2 V617F, MPL W515L and JAK2 exon 12 mutations in 30 patients with PMF.

RESULTS

Fifteen PMF patients (50.0%) carried JAK2 V617F mutation, and only two JAK2 V617F-negative patients (6.7%) harbored MPL W515L mutation. None had JAK2 exon 12 mutations. Furthermore, these three mutations were not detected in 50 healthy controls.

CONCLUSION

MPL W515L and JAK2 V617F mutations existed in PMF patients but JAK2 exon 12 mutations not. JAK2 V617F and MPL W515L and mutations might contribute to the primary molecular pathogenesis in patients with PMF.

Etiology of thrombocytosis in a general medicine population: analysis of 801 cases with emphasis on infectious causes

BACKGROUND

The clinical importance of an elevated platelet count is often overlooked, particularly as a diagnostic clue to the presence of an underlying infection. We sought to better describe the relationship between thrombocytosis and inflammatory conditions, with a focus on infectious causes.

METHODS

We retrospectively reviewed 801 sequential cases of thrombocytosis (platelet count > 500 × 10(9)/L) at a tertiary care hospital.

RESULTS

Essential thrombocythemia was the most common cause of primary thrombocytosis, and these patients were more likely to have extreme (> 800 × 10(9)/L) and prolonged (> 1 month) thrombocytosis. Secondary thrombocytosis was more common than primary, with infectious causes accounting for nearly half the cases. Demographic factors associated with an infectious etiology included inpatient status, quadriplegia/paraplegia, an indwelling prosthesis, dementia and diabetes. Clinical and laboratory characteristics associated with an infectious cause of thrombocytosis included fever, tachycardia, weight loss, hypoalbuminemia, neutrophilia, leukocytosis and anemia. Patients with thrombocytosis secondary to infection had a more rapid normalization of platelet count, but higher risk of dying, than those with secondary, non-infectious causes.

CONCLUSIONS

Infection is a common cause of thrombocytosis and should be considered in patients with comorbidities that increase risk of infection and when clinical and/or laboratory data support an infectious etiology. Thrombocytosis may have prognostic implications as a clinical parameter.

Sensitive detection and quantification of the JAK2V617F allele by real-time PCR blocking wild-type amplification by using a peptide nucleic acid oligonucleotide

A single G-to-T missense mutation in the gene for the JAK2 tyrosine kinase, leading to a V617F amino acid substitution, is commonly found in several myeloproliferative neoplasms. Reliable quantification of this mutant allele is of increasing clinical and therapeutic interest in predicting and diagnosing this group of neoplasms. Because JAK2V617F is somatically acquired and may be followed by loss of heterozygosity, the percentage of mutant versus wild-type DNA in blood can vary between 0% and almost 100%. Therefore, we developed a real-time PCR assay for detection and quantification of the low-to-high range of the JAK2V617F allele burden. To allow the assay to meet these criteria, amplification of the wild-type JAK2 was blocked with a peptide nucleic acid oligonucleotide. JAK2V617F patient DNA diluted in JAK2 wild-type DNA could be amplified linearly from 0.05% to 100%, with acceptable reproducibility of quantification. The sensitivity of the assay was 0.05% (n = 3 of 3). In 9 of 100 healthy blood donors, a weak positive/background signal was observed in DNA isolated from blood, corresponding to approximately 0.01% JAK2V617F allele. In one healthy individual, we observed this signal in duplicate. The clinical relevance of this finding is not clear. By inhibiting amplification of the wild-type allele, we developed a sensitive and linear real-time PCR assay to detect and quantify JAK2V617F.

Monitoring of minimal residual disease in patients with core binding factor acute myeloid leukemia and the impact of C-KIT, FLT3, and JAK2 mutations on clinical outcome

Mutational analysis of C-KIT, fms-like tyrosine kinase 3 (FLT3), and JAK2 genes was performed in 60 patients with core binding factor acute myeloid leukemia (CBF-AML). Patients reaching molecular remission had lower incidence of relapse and better overall survival (OS) than those not achieving molecular remission (p = 0.008 and 0.044, respectively). The overall incidence of C-KIT mutations was 33.3%, FLT3/internal tandem duplication (ITD) 6.6%, FLT3(D835) 10.0% and JAK2(V617F) mutations 3.3%. C-KIT mutations did not predict for clinical/molecular relapse (p = 0.33). OS of patients with C-KIT mutations was identical to patients without them when all patients with CBF-AML were analyzed together (p = 0.58). When AML1/ETO-positive patients were evaluated separately, OS in C-KIT-mutated patients was slightly inferior to unmutated ones (p = 0.14). Patients with CBF-AML with a mutated C-KIT gene were also more prone to extramedullary disease (p = 0.08). Of six patients harboring various FLT3(D835) mutations, four (66.7%) relapsed, whereas among 43 cases without these mutations, 16 relapses (37%) were observed (p = 0.08). Our results on minimal residual disease, C-KIT, and FLT3/ITDs are in line with previous studies. Surprisingly, a possible role for FLT3(D835) mutations was noted in addition. These results need validation in even larger patient cohorts than ours. For routine clinical practice, it may be meaningful to screen for C-KIT mutations in AML1/ETO-positive patients, as well as for FLT3(D835) mutations in CBF-AML.

Bim and Mcl-1 exert key roles in regulating JAK2V617F cell survival

Background

The JAK2^V617F mutation plays a major role in the pathogenesis of myeloproliferative neoplasms and is found in the vast majority of patients suffering from polycythemia vera and in roughly every second patient suffering from essential thrombocythemia or from primary myelofibrosis. The V617F mutation is thought to provide hematopoietic stem cells and myeloid progenitors with a survival and proliferation advantage. It has previously been shown that activated JAK2 promotes cell survival by upregulating the anti-apoptotic STAT5 target gene Bcl-xL. In this study, we have investigated the role of additional apoptotic players, the pro-apoptotic protein Bim as well as the anti-apoptotic protein Mcl-1.

Methods

Pharmacological inhibition of JAK2/STAT5 signaling in JAK2^V617F mutant SET-2 and MB-02 cells was used to study effects on signaling, cell proliferation and apoptosis by Western blot analysis, WST-1 proliferation assays and flow cytometry. Cells were transfected with siRNA oligos to deplete candidate pro- and anti-apoptotic proteins. Co-immunoprecipitation assays were performed to assess the impact of JAK2 inhibition on complexes of pro- and anti-apoptotic proteins.

Results

Treatment of JAK2^V617F mutant cell lines with a JAK2 inhibitor was found to trigger Bim activation. Furthermore, Bim depletion by RNAi suppressed JAK2 inhibitor-induced cell death. Bim activation following JAK2 inhibition led to enhanced sequestration of Mcl-1, besides Bcl-xL. Importantly, Mcl-1 depletion by RNAi was sufficient to compromise JAK2^V617F mutant cell viability and sensitized the cells to JAK2 inhibition.

Conclusions

We conclude that Bim and Mcl-1 have key opposing roles in regulating JAK2^V617F cell survival and propose that inactivation of aberrant JAK2 signaling leads to changes in Bim complexes that trigger cell death. Thus, further preclinical evaluation of combinations of JAK2 inhibitors with Bcl-2 family antagonists that also tackle Mcl-1, besides Bcl-xL, is warranted to assess the therapeutic potential for the treatment of chronic myeloproliferative neoplasms.

JAK2 exon 14 deletion in patients with chronic myeloproliferative neoplasms

Background

The JAK2 V617F mutation in exon 14 is the most common mutation in chronic myeloproliferative neoplasms (MPNs); deletion of the entire exon 14 is rarely detected. In our previous study of >10,000 samples from patients with suspected MPNs tested for JAK2 mutations by reverse transcription-PCR (RT-PCR) with direct sequencing, complete deletion of exon 14 (Δexon14) constituted <1% of JAK2 mutations. This appears to be an alternative splicing mutation, not detectable with DNA-based testing.

Methodology/Principal Findings

We investigated the possibility that MPN patients may express the JAK2 Δexon14 at low levels (<15% of total transcript) not routinely detectable by RT-PCR with direct sequencing. Using a sensitive RT-PCR–based fluorescent fragment analysis method to quantify JAK2 Δexon14 mRNA expression relative to wild-type, we tested 61 patients with confirmed MPNs, 183 with suspected MPNs (93 V617F-positive, 90 V617F-negative), and 46 healthy control subjects. The Δexon14 variant was detected in 9 of the 61 (15%) confirmed MPN patients, accounting for 3.96% to 33.85% (mean  = 12.04%) of total JAK2 transcript. This variant was also detected in 51 of the 183 patients with suspected MPNs (27%), including 20 of the 93 (22%) with V617F (mean [range] expression  = 5.41% [2.13%–26.22%]) and 31 of the 90 (34%) without V617F (mean [range] expression  = 3.88% [2.08%–12.22%]). Immunoprecipitation studies demonstrated that patients expressing Δexon14 mRNA expressed a corresponding truncated JAK2 protein. The Δexon14 variant was not detected in the 46 control subjects.

Conclusions/Significance

These data suggest that expression of the JAK2 Δexon14 splice variant, leading to a truncated JAK2 protein, is common in patients with MPNs. This alternatively spliced transcript appears to be more frequent in MPN patients without V617F mutation, in whom it might contribute to leukemogenesis. This mutation is missed if DNA rather than RNA is used for testing.

Bone marrow morphologic features in polycythemia vera with JAK2 exon 12 mutations

The diagnosis of polycythemia vera (PV) requires the integration of clinical and laboratory findings, bone marrow morphologic features, and JAK2 analysis. JAK2(V617F) (exon 14) mutation is found in 95% of PV cases. Functionally similar mutations in JAK2 exon 12 have also been described, but a thorough bone marrow study has not been done. We identified 7 PV cases with exon 12 mutations; all had hypercellular bone marrow with erythroid hyperplasia. Small, atypical megakaryocytes predominated; atypical megakaryocyte lobation and abnormal chromatin distribution was identified in all cases. Rare clusters of megakaryocytes could be found but were typically subtle. Because JAK2 exon 12-positive PV cases lack the classic myeloproliferative morphologic features, bone marrow samples from the patients may be difficult to classify as myeloproliferative neoplasms. Clinically suspected PV with low serum erythropoietin and absent JAK2(V617F), together with the bone marrow findings of erythroid hyperplasia and subtle megakaryocytic atypia, should prompt an evaluation for an exon 12 mutation.

Plasma levels of JAK2 mRNA in patients with chronic myeloproliferative diseases with and without V617F mutation: implications for prognosis and disease biology

The association of V617F JAK2 expression levels with disease behavior has not been studied in patients with nonchronic myelogenous leukemia (CML) myeloproliferative disease (MPD). We found plasma levels of total JAK2 mRNA to be higher in patients with non-CML MPD (n=175) than in CML patients (n=45) and normal controls (n=58) (each P<0.001). Overall survival was studied in 68 patients and showed positive correlation with levels of total and mutant JAK2 mRNA in patients with the V617F mutation, but not those without the mutation. These findings suggest that total JAK2 expression levels play a role in the biology of the disease in V617F-positive patients, and a therapy aiming at downmodulating the expression of the total JAK2 mRNA should be considered. In conclusion, we studied JAK2 total and V6217F mutant mRNA levels in plasma. We show high levels of JAK2 expression in MPD patients and these levels correlate with survival.

Prodromal myeloproliferative neoplasms: the 2008 WHO classification

The concept of prodromal chronic myeloproliferative neoplasms has been endorsed by the WHO classification implicating a stepwise evolution of disease. Histology of the bone marrow (BM) and borderline to mildly expressed clinical features play a pivotal role for diagnosing prefibrotic-early primary myelofibrosis. By lowering the platelet count for essential thrombocythemia and regarding BM morphology, early manifestations are tackled. Pre-polycythemic stages of polycythemia vera with a low hemoglobin level at onset are diagnosed by positive JAK2V617F mutation status, a low erythropoietin value, and characteristic BM features. The revised WHO classification incorporates hematological, morphological, and molecular-genetic parameters to generate a consensus-based working diagnosis.

Design and evaluation of a real-time PCR assay for quantification of JAK2 V617F and wild-type JAK2 transcript levels in the clinical laboratory

The somatic mutation JAK2 V617F is associated with BCR-ABL1-negative myeloproliferative neoplasms. Detection of this mutation aids diagnosis of these neoplasms, and quantification of JAK2 V617F may provide a method to monitor response to therapy. For these reasons, we designed a clinical assay that uses allele-specific PCR and real-time detection with hydrolysis probes for the quantification of JAK2 V617F, wild-type JAK2, and GAPDH transcripts. Mutant and wild-type JAK2 were quantified by using external plasmid standards that contain the relevant JAK2 V617F or JAK2 sequence, respectively. We tested 55 peripheral blood specimens from patients with suspected myeloproliferative neoplasms and 55 peripheral blood specimens from patients not known to have myeloproliferative neoplasms. Low-level, nonspecific amplification was detected in reactions containing a high copy number of plasmid standards and in specimens from patients not known to have myeloproliferative neoplasms, necessitating the use of a laboratory-established mutant to wild-type cutoff. The limit of detection established by using cell line dilutions is 0.1%, and this method identified three JAK2 V617F-positive patients who were not detected by a less sensitive method. The assay characteristics and our initial evaluation indicate this method can be used for the detection and quantification of JAK2 V617F, which should be useful for diagnosis of myeloproliferative neoplasms and potentially for monitoring minimal residual disease in future trials of therapies targeted to myeloproliferative neoplasms.

Comparison of JAK2V617F mutation assessment employing different molecular diagnostic techniques

BACKGROUND

The JAK2(V617F) mutation is present in the majority of patients with polycythaemia vera and in approximately half of patients with essential thrombocythaemia and primary myelofibrosis. In this study we compare the results of JAK2(V617F) mutation detection using three different molecular techniques in the same group of patients affected by essential thrombocythaemia.

PATIENTS AND METHODS

The JAK2 mutation was investigated with a qualitative method in 115 consecutive outpatients with a diagnosis of essential thrombocythaemia made according to WHO 2001 criteria. In 48/115 (41.7%) the allele burden was also evaluated with two different qualitative methods, of which one was a method developed in-house and the other was a commercially available method.

RESULTS

The JAK2(V617F) mutation was detected by the qualitative method in 81/115 (69.6%) of the patients. Among the 48/115 patients in whom all three methods were applied, the qualitative method detected the mutation in 38 (79%). According to the quantitative method developed in-house, the mutation was present in 35/48 (73%) of the patients: of these, 2/35 (5.7%) patients were homozygous for the JAK2(V617F) mutation. The commercial quantitative method showed the mutation in 37/48 (77%) patients: of these, 9/37 (18%) patients were homozygous. Three of the 13 patients in whom no mutation was detected by the in-house method were positive for the JAK2(V617F) according to the commercial method. In one patient the search for the JAK2(V617F) mutation was positive with the in-house method but negative with the commercial kit.

CONCLUSION

Detection of the JAK2(V617F) mutation may depend on the molecular technique used. Considering that detection of this mutation will not only have a diagnostic value, but also a role in treatment given the development of JAK2(V617F) pathway inhibiting drugs, indications on a reference molecular diagnostic technique for JAK2(V617F) assessment and quantification of its allele burden from a panel of experts are warranted.

Structural effects of clinically observed mutations in JAK2 exons 13-15: comparison with V617F and exon 12 mutations

Background

The functional relevance of many of the recently detected JAK2 mutations, except V617F and exon 12 mutants, in patients with chronic myeloproliferative neoplasia (MPN) has been significantly overlooked. To explore atomic-level explanations of the possible mutational effects from those overlooked mutants, we performed a set of molecular dynamics simulations on clinically observed mutants, including newly discovered mutations (K539L, R564L, L579F, H587N, S591L, H606Q, V617I, V617F, C618R, L624P, whole exon 14-deletion) and control mutants (V617C, V617Y, K603Q/N667K).

Results

Simulation results are consistent with all currently available clinical/experimental evidence. The simulation-derived putative interface, not possibly obtained from static models, between the kinase (JH1) and pseudokinase (JH2) domains of JAK2 provides a platform able to explain the mutational effect for all mutants, including presumably benign control mutants, at the atomic level.

Conclusion

The results and analysis provide structural bases for mutational mechanisms of JAK2, may advance the understanding of JAK2 auto-regulation, and have the potential to lead to therapeutic approaches. Together with recent mutation profiling results demonstrating the breadth of clinically observed JAK2 mutations, our findings suggest that molecular testing/diagnostics of JAK2 should extend beyond V617F and exon 12 mutations, and perhaps should encompass most of the pseudo-kinase domain-coding region.

Philadelphia chromosome-negative chronic myeloproliferative disease

Session 2 of the 2007 Workshop of the Society for Hematopathology/European Association for Haematopathology was focused on Philadelphia chromosome-negative chronic myeloproliferative diseases (Ph- MPDs), recently termed chronic myeloproliferative neoplasms. The presented and submitted cases highlighted some important issues and also impending problems associated with the diagnosis and classification. Cases included predominantly rare entities like chronic eosinophilic leukemia and related disorders, chronic neutrophilic leukemia, and others with specific genetic abnormalities that allowed molecularly targeted therapy. In this context, the distinctive role of a positive JAK2(V617F) mutation for the diagnosis of Ph- MPD was underscored, including entities with a low allele burden and the discrimination from reactive disorders (autoimmune myelofibrosis, reactive thrombocytosis). Although novel genetic and molecular approaches have significantly improved the way we classify Ph- MPD, a combined clinicopathologic approach, including representative bone marrow specimens, still remains the yardstick for diagnosis.

Mechanisms of constitutive activation of Janus kinase 2-V617F revealed at the atomic level through molecular dynamics simulations

BACKGROUND

The tyrosine kinase Janus kinase 2 (JAK2) is important in triggering nuclear translocation and regulation of target genes expression through signal transducer and activator of transcription pathways. The valine-to-phenylalanine mutation at amino acid 617 (V617F), which results in the deregulation of JAK2, has been implicated in the oncogenesis of chronic myeloproliferative disease. However, both the mechanism of JAK2 autoinhibition and the mechanism of V617F constitutive activation remain unclear.

METHOD

In this work, the authors used molecular dynamics simulation techniques to establish plausible mechanisms of JAK2 autoinhibition and V617F constitutive activation at the atomic level.

RESULTS

In wild-type JAK2, the activation loop of JAK2-homology domain 1 (JH1) is pulled toward the JH1/JH2 interface through interactions with key residues of JH2, especially S591, F595, and V617, and stabilizes the inactivated form of JH1. In the case of V617F, through the aromatic ring-ring stacking interaction, F617 blocks the interaction of JH1 the activation loop, S591, and F595, thus causing the JH1 activation loop to move back to its activated form.

CONCLUSIONS

The current results indicated that this simulation-derived mechanism of JAK2 autoregulation is consistent with current available experimental evidence and may lead to a deeper understanding of JAK2 and other kinase systems that are regulated by pseudokinases.

The saga of JAK2 mutations and translocations in hematologic disorders: pathogenesis, diagnostic and therapeutic prospects, and revised World Health Organization diagnostic criteria for myeloproliferative neoplasms

JAK2 is a tyrosine kinase involved in cytokine signaling. The JAK2V617F point mutation, first described in 2005, results in constitutive activation of JAK2 and is now widely used as a diagnostic marker for Philadelphia chromosome negative myeloproliferative neoplasms. In recent years, more novel JAK2 mutations and fusion genes have been discovered in myeloproliferative neoplasms and other hematologic malignancies. This review aims to summarize the discovery and use of the JAK2V617F point mutation, other novel JAK2 mutations, and JAK2 translocations in diagnosing myeloproliferative neoplasms, acute myeloid leukemia, and acute lymphoid leukemia. JAK2 mutation testing is addressed, including the sensitivity and specificity of the different JAK2 mutation testing methods, clinical indications for use, and the use of quantitative JAK2 mutation testing for routine pathologic diagnosis, prognosis, and monitoring response to therapy. The relationship of JAK2 mutation to endogenous erythroid colony formation, thrombopoietin receptor mutation, polycythemia rubra vera-1 overexpression, and thrombopoietin receptor underexpression in myeloproliferative neoplasms are explored. Also discussed are the JAK2 inhibitors for clinical trials. Finally, the advantages of the newly proposed World Health Organization classification for myeloproliferative neoplasms are reviewed.

A potential role for HSP90 inhibitors in the treatment of JAK2 mutant-positive diseases as demonstrated using quantitative flow cytometry

The V617F mutation of the JAK2 tyrosine kinase is found in a majority of patients with myeloproliferative disorders. Flow cytometry assays for quantitation of phosphorylated and total protein for JAK2, STAT5, and heat shock proteins (HSPs) were developed to facilitate the study of the JAK/STAT pathway. A cell line homozygous for V617F (HEL) was treated with inhibitors of JAK2 tyrosine kinase activity and the HSP90 inhibitor 17-AAG. 17-AAG reduced HSP90 levels, but increased HSP70 levels. Phospho-STAT5, total STAT5, and total AKT levels were also reduced by 17-AAG treatment. Further, phospho-JAK2, total JAK2, and cell viability were reduced to a greater extent by 17-AAG than by the pan-JAK kinase family inhibitor JKII or the JAK2-specific inhibitor AG490, and these inhibitors failed to synergize with 17-AAG. Flow-cytometry-based assays for JAK/STAT signaling pathway and HSPs are likely to have broad clinical utility for monitoring patients with abnormalities in the JAK2 pathway.

Cl-IB-MECA inhibits human erythropoiesis

Candidate drugs are being sought for the suppression of human erythropoiesis. Cl-IB-MECA [2-chloro-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide] is a derivative of adenosine that inhibits the growth of leukaemic cell lines. To determine the effects of Cl-IB-MECA upon erythropoiesis, studies were performed by using an ex vivo culture system of primary human CD34+ cells. Cl-IB-MECA suppressed erythroblast growth and maturation at doses >/=50 mumol/l through a mechanism of cell cycle inhibition and accumulation of cells in the G1/G0 phase. These findings demonstrate that Cl-IB-MECA inhibits human erythropoiesis, and suggest that further consideration of this drug is warranted for patients with erythrocytosis or polycythemia syndromes.

The chronic myeloproliferative disorders and mutation of JAK2: Dameshek's 54 year old speculation comes of age

In 1951, William Dameshek speculated on the common origin of the chronic myeloproliferative disorders--polycythemia vera (PV), essential thrombocythemia (ET), chronic idiopathic myelofibrosis (IMF), and chronic myelogenous leukemia (CML). Subsequent work suggested that all arose from the hematopoietic stem cell. About 20 years ago the oncogene responsible for CML, bcr-abl, was identified, and more recently the mutant genes that cause hypereosinophilic syndrome and systemic mast cell disorder have been discovered. However, until very recently, the origin of PV, ET, and IMF have defied molecular explanation. In 2005, four separate groups working on tyrosine kinase signal transduction reported a gain-of-function, valine-to-phenyalanine, mutation at position 617 in the JH2 domain of the Janus kinase (JAK) 2 cytoplasmic tyrosine kinase. This mutation requires the presence of the erythropoietin, thrombopoietin, or granulocyte-colony stimulating factor receptor/s for function, the mutation leads to functional hyperactivity and appears responsible for hematopoietic growth factor hypersensitivity, the most characteristic finding in these disorders. Virtually all patients with PV and substantial proportions of those with ET and IMF have now been shown to harbor this mutation. The mutant kinase appears to be a useful diagnostic test for myeloproliferative disorders and may have prognostic value. Future research will undoubtedly focus on the development of specific inhibitors as therapeutic agents as well as answering a number of questions that remain regarding the role of signal intensity, genotypic and phenotypic expression and the possible involvement of additional as yet unidentified mutations in these disorders.

Cytogenetic and molecular aspects of Philadelphia negative chronic myeloproliferative disorders: clinical implications

Chronic myeloproliferative disorders (CMPD) are clonal disorders of the hematopoietic stem cell. The myeloid lineage shows increased proliferation with effective maturation, while peripheral leukocytosis, thrombocytosis or elevated red blood cell mass are found. In Philadelphia negative CMPD recurrent cytogenetic abnormalities occur, but no specific abnormality has been defined to date. The spectrum of cytogenetic aberrations is heterogeneous ranging from numerical gains and losses to structural changes including unbalanced translocations. The most common chromosomal abnormalities are 20q-, 13q-, 12p-, +8, +9, partial duplication of 1q, balanced translocations involving 8p11 and gains in 9p. Cytogenetic analysis of CMPD by conventional or molecular techniques has an important role in establishing the diagnosis of a malignant disease, adding also more information for disease outcome. Molecular studies may detect the possible role of candidate genes implicated in the neoplastic process, addressing new molecular target therapies. FIP1L1/PDGFRalpha rearrangements, as well as alterations of PDGFRbeta or FGFR1 gene have been found to be associated with specific types of CMPD. Recently, a novel somatic mutation, JAK2V617F, has been reported in most of the polycthemia vera (PV) patients, as well as in a lower percentage in essential thrombocythemia (ET) or idiopathic myelofibrosis (IMF) patients. This finding represents the most important advance in understanding of the molecular mechanisms underlined the pathogenesis of CMPD, contributing to the classification and management of patients.

Role of the activating mutation Val617Phe of Janus kinase 2 gene in myeloproliferative diseases and significance of its detection

The Val617Phe point mutation of Janus kinase 2 gene is believed to participate in the pathogenesis of myeloproliferative syndrome characterised by the clonal alteration of hematopoetic stem cells. According to current results, the frequency of Val617Phe activating mutation is around 80% in polycythaemia vera, 35% in essential thrombocythaemia, and 50% in chronic idiopathic myelofibrosis. The diagnoses of polycythaemia vera, essential thrombocythaemia and idiopathic myelofibrosis were so far based on the exclusion of secondary factors as well as bone marrow biopsy histology. The goal of the present work was to establish simple molecular genetic techniques for the routine testing of Janus kinase 2 gene Val617Phe mutation, and to compare the clinical phenotypes of Val617Phe mutation positive and negative myeloproliferative syndromes. We employed the allele specific polymerase chain technique for detection of Val617Phe mutation in 252 patients with myeloproliferative syndrome. We measured Val617Phe frequency as 85,4% (117/137) in polycytaemia vera, 56,6% (56/99) in essential thrombocythaemia, and 87,5% (14/16) in idiopathic myelofibrosis. We found significantly elevated hemoglobin levels and white blood cell counts (measured at the time of diagnosis) in Val617Phe-positive polycythaemia vera and essential thrombocythaemia patient groups compared to Val617Phe-negative patients. However, the frequencies of splenomegaly and other complications (thrombosis, bleeding, transformation to acute leukemia) were not significantly different between the mutation-positive and negative groups. In conclusion, the non-invasive mutation analysis of the Janus kinase 2 Val617Phe is suitable for routine laboratory application and helps the differential diagnosis of myeloproliferative syndrome. Althought the exact role of Val617Phe mutation testing has not yet been identified on the basis of a broad professional consensus, the testing is suggested in cases of erythrocytoses and thrombocytoses of unknown origin.

JAK2 V617F is a rare finding in de novo acute myeloid leukemia, but STAT3 activation is common and remains unexplained

Signal transducer and activator of transcription (STAT) proteins are phosphorylated and activated by Janus kinases (JAKs). Recently, several groups identified a recurrent somatic point mutation constitutively activating the hematopoietic growth factor receptor-associated JAK2 tyrosine kinase in diverse chronic myeloid disorders - most commonly classic myeloproliferative disorders (MPD), especially polycythemia vera. We hypothesized that the JAK2 V617F mutation might also be present in samples from patients with acute myeloid leukemia (AML), especially erythroleukemia (AML-M6) or megakaryoblastic leukemia (AML-M7), where it might mimic erythropoietin or thrombopoietin signaling. First, we documented STAT3 activation by immunoblotting in AML-M6 and other AML subtypes. Immunoperoxidase staining confirmed phosphorylated STAT3 in malignant myeloblasts (21% of cases, including all AML-M3 samples tested). We then analyzed genomic DNA from 162 AML, 30 B-cell lymphoma, and 10 chronic lymphocytic leukemia (CLL) samples for JAK2 mutations, and assayed a subset for SOCS1 and FLT3 mutations. Janus kinase2 V617F was present in 13/162 AML samples (8%): 10/13 transformed MPD, and three apparent de novo AML (one of 12 AML-M6, one of 24 AML-M7, and one AML-M2 - all mixed clonality). FLT3 mutations were present in 5/32 (16%), while SOCS1 mutations were totally absent. Lymphoproliferative disorder samples were both JAK2 and SOCS1 wild type. Thus, while JAK2 V617F is uncommon in de novo AML and probably does not occur in lymphoid malignancy, unexplained STAT3 activation is common in AML. Janus kinase2 extrinsic regulators and other proteins in the JAK-STAT pathway should be interrogated to explain frequent STAT activation in AML.

JAK2 V617F in myeloid disorders: molecular diagnostic techniques and their clinical utility: a paper from the 2005 William Beaumont Hospital Symposium on Molecular Pathology

In early 2005, several groups of investigators studying myeloid malignancies described a novel somatic point mutation (V617F) in the conserved autoinhibitory pseudokinase domain of the Janus kinase 2 (JAK2) protein, which plays an important role in normal hematopoietic growth factor signaling. The V617F mutation is present in blood and marrow from a large proportion of patients with classic BCR/ABL-negative chronic myeloproliferative disorders and of a few patients with other clonal hematological diseases such as myelodysplastic syndrome, atypical myeloproliferative disorders, and acute myeloid leukemia. The JAK2 V617F mutation causes constitutive activation of the kinase, with deregulated intracellular signaling that mimics continuous hematopoietic growth factor stimulation. Within 7 months of the first electronic publication describing this new mutation, clinical molecular diagnostic laboratories in the United States and Europe began offering JAK2 mutation testing on a fee-for-service basis. Here, I review the various techniques used by research groups and clinical laboratories to detect the genetic mutation underlying JAK2 V617F, including fluorescent dye chemistry sequencing, allele-specific polymerase chain reaction (PCR), real-time PCR, DNA-melting curve analysis, pyrosequencing, and others. I also discuss diagnostic sensitivity, performance, and other practical concerns relevant to the clinical laboratorian in addition to the potential diagnostic utility of JAK2 mutation tests.

The role of Janus kinases in haemopoiesis and haematological malignancy

The production of blood cells is regulated by a number of protein growth factors and cytokines that influence cell survival, proliferation and differentiation. Many of these molecules bind to cell surface receptors, which belong to a family of closely related cytokine receptors that lack intrinsic catalytic activity but are intimately associated with tyrosine kinases of the Janus kinase (JAK) family. Ligand binding induces the activation of JAKs, which sit at the apex of a signalling cascade in which a key role is played by members of the signal transducers and activators of transcription (STAT) group. Congenital deficiencies in JAK-STAT signalling are associated with immunodeficiency states and acquired activating mutations and translocations are involved in the pathophysiology of haematological malignancy. The latter findings have raised hopes that drugs that target aberrant JAK-STAT signalling may be useful for the treatment of human disease.