Quantitative relationship between functionally active telomerase and major telomerase components (hTERT and hTR) in acute leukaemia cells

Functionally active telomerase is affected at various steps including transcriptional and post-transcriptional levels of major telomerase components (hTR and human telomerase reverse transcriptase (hTERT)). We therefore developed a rapid and sensitive method to quantify hTERT and its splicing variants as well as the hTR by a Taqman real-time reverse transcriptase–polymerase chain reaction to determine whether their altered expression may contribute to telomere attrition in vivo or not. Fresh leukaemia cells obtained from 38 consecutive patients were used in this study. The enzymatic level of telomerase activity measured by TRAP assay was generally associated with the copy numbers of full-length hTERT+α+β mRNA (P=0.0024), but did not correlate with hTR expression (P=0.6753). In spite of high copy numbers of full-length hTERT mRNA, telomerase activity was low in some cases correlating with low copy numbers of hTR, raising the possibility that alteration of the hTR : hTERT ratio may affect functionally active telomerase activity in vivo. The spliced nonactive hTERT mRNA tends to be lower in patients with high telomerase activity, suggesting that this epiphenomenon may play some role in telomerase regulation. An understanding of the complexities of telomerase gene regulation in biologically heterogeneous leukaemia cells may offer new therapeutic approaches to the treatment of acute leukaemia

Transcriptional profiling of Epstein–Barr virus (EBV) genes and host cellular genes in nasal NK/T-cell lymphoma and chronic active EBV infection

Nasal NK/T-cell lymphoma is an aggressive subtype of non-Hodgkin lymphoma (NHL) that is closely associated with Epstein–Barr virus (EBV). The clonal expansion of EBV-infected NK or T cells is also seen in patients with chronic active EBV (CAEBV) infection, suggesting that two diseases might share a partially similar mechanism by which EBV affects host cellular gene expression. To understand the pathogenesis of EBV-associated NK/T-cell lymphoproliferative disorders (LPD) and design new therapies, we employed a novel EBV DNA microarray to compare patterns of EBV expression in six cell lines established from EBV-associated NK/T-cell LPD. We found that expression of BZLF1, which encodes the immediate-early gene product Zta, was expressed in SNK/T cells and the expression levels were preferentially high in cell lines from CAEBV infection. We also analyzsd the gene expression patterns of host cellular genes using a human oligonucleotide DNA microarray. We identified a subset of pathogenically and clinically relevant host cellular genes, including TNFRSF10D, CDK2, HSPCA, IL12A as a common molecular biological properties of EBV-associated NK/T-cell LPD and a subset of genes, such as PDCD4 as a putative contributor for disease progression. This study describes a novel approach from the aspects of viral and host gene expression, which could identify novel therapeutic targets in EBV-associated NK/T-cell LPD

The C allele of JAK2 rs4495487 is an additional candidate locus that contributes to myeloproliferative neoplasm predisposition in the Japanese population

<p>Abstract</p> <p>Background</p> <p>Polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) are myeloproliferative neoplasms (MPNs) characterized in most cases by a unique somatic mutation, <it>JAK2 </it>V617F. Recent studies revealed that <it>JAK2 </it>V617F occurs more frequently in a specific <it>JAK2 </it>haplotype, named <it>JAK2 </it>46/1 or GGCC haplotype, which is tagged by rs10974944 (C/G) and/or rs12343867 (T/C). This study examined the impact of single nucleotide polymorphisms (SNPs) of the <it>JAK2 </it>locus on MPNs in a Japanese population.</p> <p>Methods</p> <p>We sequenced 24 <it>JAK2 </it>SNPs in Japanese patients with PV. We then genotyped 138 MPN patients (33 PV, 96 ET, and 9 PMF) with known <it>JAK2 </it>mutational status and 107 controls for a novel SNP, in addition to two SNPs known to be part of the 46/1 haplotype (rs10974944 and rs12343867). Associations with risk of MPN were estimated by odds ratios and their 95% confidence intervals using logistic regression.</p> <p>Results</p> <p>A novel locus, rs4495487 (T/C), with a mutated T allele was significantly associated with PV. Similar to rs10974944 and rs12343867, rs4495487 in the <it>JAK2 </it>locus is significantly associated with <it>JAK2</it>-positive MPN. Based on the results of SNP analysis of the three <it>JAK2 </it>locus, we defined the "GCC genotype" as having at least one minor allele in each SNP (G allele in rs10974944, C allele in rs4495487, and C allele in rs12343867). The GCC genotype was associated with increased risk of both <it>JAK2 </it>V617F-positive and <it>JAK2 </it>V617F-negative MPN. In ET patients, leukocyte count and hemoglobin were significantly associated with <it>JAK2 </it>V617F, rather than the GCC genotype. In contrast, none of the <it>JAK2 </it>V617F-negative ET patients without the GCC genotype had thrombosis, and splenomegaly was frequently seen in this subset of ET patients. PV patients without the GCC genotype were significantly associated with high platelet count.</p> <p>Conclusions</p> <p>Our results indicate that the C allele of <it>JAK2 </it>rs4495487, in addition to the 46/1 haplotype, contributes significantly to the occurrence of <it>JAK2 </it>V617F-positive and <it>JAK2 </it>V617F-negative MPNs in the Japanese population. Because lack of the GCC genotype represents a distinct clinical-hematological subset of MPN, analyzing <it>JAK2 </it>SNPs and quantifying <it>JAK2 </it>V617F mutations will provide further insights into the molecular pathogenesis of MPN.</p

Quantitative assay for the detection of the V617F variant in the Janus kinase 2 (JAK2) gene using the Luminex xMAP technology

<p>Abstract</p> <p>Background</p> <p>The availability of clinically valid biomarkers contribute to improve the diagnosis and clinical management of diseases. A valine-to-phenylalanine substitution at position 617 (V617F) in the Janus kinase 2 (JAK2) gene has been recently associated with key signaling abnormalities in the transduction of haemopoietic growth-factor receptors and is now considered as a useful clinical marker of myeloproliferative neoplasms. Several methods have recently been reported to detect the JAK2 V617F point mutation and show variable sensitivity.</p> <p>Methods</p> <p>Using the Luminex xMAP technology, we developed a quantitative assay to detect the JAK2V617F variant. The method was based on polymerase chain reaction (PCR) followed by hybridization to specific probes coupled with internally dyed microspheres. The assay comprises 3 steps: genomic DNA extraction, end point PCR reaction, direct hybridization of PCR fragments and quantification. It has been tested with different sources of nucleic acid.</p> <p>Results</p> <p>Applied to whole blood samples, this quantitative assay showed a limit of detection of 2%. A highly sensitive allele-specific primer extension reaction performed in parallel allowed to validate the results and to identify the specimens with values below 2%.</p> <p>Conclusion</p> <p>Direct hybridization assay using the Luminex xMAP technology allows sensitive quantification of JAK2V617F from blood spots. It is simple and can be easily performed in a clinical setting.</p

Telomere and telomerase in stem cells

Telomeres, guanine-rich tandem DNA repeats of the chromosomal end, provide chromosomal stability, and cellular replication causes their loss. In somatic cells, the activity of telomerase, a reverse transcriptase that can elongate telomeric repeats, is usually diminished after birth so that the telomere length is gradually shortened with cell divisions, and triggers cellular senescence. In embryonic stem cells, telomerase is activated and maintains telomere length and cellular immortality; however, the level of telomerase activity is low or absent in the majority of stem cells regardless of their proliferative capacity. Thus, even in stem cells, except for embryonal stem cells and cancer stem cells, telomere shortening occurs during replicative ageing, possibly at a slower rate than that in normal somatic cells. Recently, the importance of telomere maintenance in human stem cells has been highlighted by studies on dyskeratosis congenital, which is a genetic disorder in the human telomerase component. The regulation of telomere length and telomerase activity is a complex and dynamic process that is tightly linked to cell cycle regulation in human stem cells. Here we review the role of telomeres and telomerase in the function and capacity of the human stem cells

The implication of identifying JAK2V617F in myeloproliferative neoplasms and myelodysplastic syndromes with bone marrow fibrosis

The myeloproliferative neoplasms (MPN) and myelodysplastic syndromes (MDS) occasionally demonstrate overlapping morphological features including hypercellularity, mild/nonspecific dysplastic changes and variable bone marrow fibrosis. Thus, when the associated bone marrow fibrosis results in a suboptimal specimen for morphological evaluation, the descriptive diagnosis “fibrotic marrow with features indeterminate for MDS versus MPN” is often applied. The JAK2V617F mutation was recently shown to be frequently identified in MPN, but it is rarely present in other myeloid disorders. However, the diagnostic utility of JAK2V617F screening in hypercellular bone marrow specimens with fibrosis has not been previously investigated. Using a real-time polymerase chain reaction melting-curve assay capable of detecting JAK2V617F in archived fixed materials, we retrospectively studied JAK2V617F in 45 cases with fibrotic hypercellular bone marrow at initial presentation, including 19 cases initially described as “with features indeterminate for MDS versus MPN”. These 19 cases were reclassified into more specific categories of MDS (n = 14) or MPN (n = 5) based on the availability of subsequent clinical data and/or bone marrow examinations. The JAK2V617F allele was identified in 17 out of 18 BCR/ABL gene-negative MPN cases with marrow fibrosis, whereas only wild-type alleles were identified in the remaining non-MPN cases. Importantly, JAK2V617F alleles were seen in all five cases of “with features indeterminate for MDS versus MPN” at initial presentation that were later determined to be MPN, but they were absent in the 14 cases later determined to be MDS. Our results suggest that JAK2V617F allele evaluation can be a useful ancillary test for discriminating MDS from MPN in specimens with bone marrow fibrosis