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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The gene E2A on chromosome 19 is involved in recurrent chromosomal rearrangements associated with pediatric acute lymphoblastic leukemia. The resulting fusion of 5' E2A sequences with 3' portions of other genes leads to the expression of two well-characterized fusion proteins: E2A-PBX1 and E2A-HLF. Since the E2A, PBX1 and HLF proteins all appear to function as transcription factors, it appears likely that the oncogenic fusion proteins contribute to leukemia development by causing abnormal transcriptional regulation of key target genes. Furthermore, since the E2A portion of the fusion proteins contains transcriptional activation domains, and the PBX1 and HLF portions contain DNA binding domains, leukemogenesis may be due, at least in part, to excessive transcriptional induction of target genes defined by PBX1 or HLF. However, recent findings suggest that this model is simplistic and possibly incorrect. In this article, I review the evidence pertaining to leukemogenesis by the well-characterized E2A-fusion proteins and consider its mechanistic implications.
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PMID:E2A basic helix-loop-helix transcription factors in human leukemia. 1270 34

Multiple genes have been shown to be independently hypermethylated in lymphoid malignancies. We report here on the extent of concurrent methylation of E-cadherin, Dap-kinase, O(6)MGMT, p73, p16, p15 and p14 in 129 pediatric ALL cases. While most of these genes demonstrated methylation in a proportion of cases, O(6)MGMT, p16 and p14 were infrequently methylated (11, 7 and 3%, respectively). Methylation of at least one gene was found in the vast majority (83%) of cases. To determine the extent and concordance of methylation we calculated a methylation index (MI=number of methylated genes/number of studied genes) for each sample. The average MI was 0.28, corresponding to 2/7 methylated genes. MI was correlated with standard prognostic factors, including immunophenotype, age, sex, WBC and presence of specific translocations (TEL-AML1, BCR-ABL, E2A-PBX1 or MLL-AF4). We determined that children >/=10 years old and children presenting with high WBC (>/=50 x 10(9)/l) both associated with a higher MI (P<0.01 and <0.05, respectively). T-ALLs demonstrated a lower MI (median=0.17) than precursor B ALLs (median=0.28). Among the different molecular subgroups, MLL-ALLs had the highest MI (mean=0.35), while ALLs carrying the t(1;19) had the lowest MI (mean=0.07). The most common epigenetic lesion in childhood ALL was methylation of E-cadherin (72%) independent of the molecular subtype or other clinicopathological factors.
Leukemia 2003 Sep
PMID:Concurrent methylation of multiple genes in childhood ALL: Correlation with phenotype and molecular subgroup. 1297 Jul 85

Notch and basic helix-loop-helix E2A pathways specify cell fate and regulate neoplastic transformation in a variety of cell types. Whereas Notch enhances tumorigenesis, E2A suppresses it. However, whether and how Notch and E2A interact functionally in an integrative mechanism for regulating neoplastic transformation remains to be understood. It has been shown that Notch3-induced T-cell leukaemia is abrogated by the inactivation of pTalpha/pre-T-cell antigen receptor (pre-TCR). We report here that Notch3-induced transcriptional activation of pTalpha/pre-TCR is responsible for the downregulation of E2A DNA binding and transcriptional activity. Further, the E2A messenger RNA and protein levels remain unaltered but the E2A inhibitor Id1 expression is augmented in thymocytes and T lymphoma cells derived from Notch3 transgenic mice. The increase in Id1 expression is achieved by pre-TCR-induced extracellular-signalling-regulated kinase 1/2. These observations support a model in which the upregulation of pre-TCR signalling seems to be the prerequi-site for Notch3-induced inhibition of E2A, thus leading to the development of lymphoma in Notch3 transgenic mice.
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PMID:Pre-TCR-triggered ERK signalling-dependent downregulation of E2A activity in Notch3-induced T-cell lymphoma. 1456 27

The outcome for children with acute lymphoblastic leukemia (ALL) has improved dramatically with current therapy resulting in an event free survival exceeding 75% for most patients. However significant challenges remain including developing better methods to predict which patients can be cured with less toxic treatment and which ones will benefit from augmented therapy. In addition, 25% of patients fail therapy and novel treatments that are focused on undermining specifically the leukemic process are needed urgently. In Section I, Dr. Carroll reviews current approaches to risk classification and proposes a system that incorporates well-established clinical parameters, genetic lesions of the blast as well as early response parameters. He then provides an overview of emerging technologies in genomics and proteomics and how they might lead to more rational, biologically based classification systems. In Section II, Drs. Mary Relling and Stella Davies describe emerging findings that relate to host features that influence outcome, the role of inherited germline variation. They highlight technical breakthroughs in assessing germline differences among patients. Polymorphisms of drug metabolizing genes have been shown to influence toxicity and the best example is the gene thiopurine methyltransferase (TPMT) a key enzyme in the metabolism of 6-mercaptopurine. Polymorphisms are associated with decreased activity that is also associated with increased toxicity. The role of polymorphisms in other genes whose products play an important role in drug metabolism as well as cytokine genes are discussed. In Sections III and IV, Drs. James Downing and Cheryl Willman review their findings using gene expression profiling to classify ALL. Both authors outline challenges in applying this methodology to analysis of clinical samples. Dr. Willman describes her laboratory's examination of infant leukemia and precursor B-ALL where unsupervised approaches have led to the identification of inherent biologic groups not predicted by conventional morphologic, immunophenotypic and cytogenetic variables. Dr. Downing describes his results from a pediatric ALL expression database using over 327 diagnostic samples, with 80% of the dataset consisting of samples from patients treated on a single institutional protocol. Seven distinct leukemia subtypes were identified representing known leukemia subtypes including: BCR-ABL, E2A-PBX1, TEL-AML1, rearrangements in the MLL gene, hyperdiploid karyotype (i.e., > 50 chromosomes), and T-ALL as well as a new leukemia subtype. A subset of genes have been identified whose expression appears to be predictive of outcome but independent verification is needed before this type of analysis can be integrated into treatment assignment. Chemotherapeutic agents kill cancer cells by activating apoptosis, or programmed cell death. In Section V, Dr. John Reed describes major apoptotic pathways and the specific role of key proteins in this response. The expression level of some of these proteins, such as BCL2, BAX, and caspase 3, has been shown to be predictive of ultimate outcome in hematopoietic tumors. New therapeutic approaches that modulate the apoptotic pathway are now available and Dr. Reed highlights those that may be applicable to the treatment of childhood ALL.
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PMID:Pediatric acute lymphoblastic leukemia. 1463 79

In childhood acute lymphoblastic leukaemia (ALL), cytogenetics play an important role in diagnosis, allocation of treatment and prognosis. Conventional cytogenetic analysis, involving mainly karyotyping in our experience, has not been successful in a large proportion of cases due to inadequate metaphase spreads and poor chromosome morphology. Our aim is to develop a highly sensitive and specific method to screen simultaneously for the four most frequent fusion transcripts resulting from specific chromosomal translocations, namely, both the CML- and ALLtype BCR-ABL transcripts of t(9;22), E2A-PBX1 transcript of t(1;19), the MLL-AF4 transcript of t(4;11) and TEL-AML1 (also termed ETV6-CBFA2) of the cryptic t(12;21). A multiplex reverse transcription polymerase chain reaction protocol (RT-PCR) was developed and tested out on archival bone marrow samples and leukaemia cell lines. In all samples with a known translocation detected by cytogenetic techniques, the same translocation was identified by the multiplex-PCR assay. Multiplex RT-PCR assay is an effective, sensitive, accurate and cost-effective diagnostic tool which can improve our ability to accurately and rapidly risk-stratify patients with childhood ALL.
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PMID:Validation of a multiplex RT-PCR assay for screening significant oncogene fusion transcripts in children with acute lymphoblastic leukaemia. 1502 55

Chromosome aberrations are frequently observed in precursor-B-acute lymphoblastic leukemias (ALL) and T-cell acute lymphoblastic leukemias (T-ALL). These translocations can form leukemia-specific chimeric fusion proteins or they can deregulate expression of an (onco)gene, resulting in aberrant expression or overexpression. Detection of chromosome aberrations is an important tool for risk classification. We developed rapid and sensitive split-signal fluorescent in situ hybridization (FISH) assays for six of the most frequent chromosome aberrations in precursor-B-ALL and T-ALL. The split-signal FISH approach uses two differentially labeled probes, located in one gene at opposite sites of the breakpoint region. Probe sets were developed for the genes TCF3 (E2A) at 19p13, MLL at 11q23, ETV6 at 12p13, BCR at 22q11, SIL-TAL1 at 1q32 and TLX3 (HOX11L2) at 5q35. In normal karyotypes, two colocalized green/red signals are visible, but a translocation results in a split of one of the colocalized signals. Split-signal FISH has three main advantages over the classical fusion-signal FISH approach, which uses two labeled probes located in two genes. First, the detection of a chromosome aberration is independent of the involved partner gene. Second, split-signal FISH allows the identification of the partner gene or chromosome region if metaphase spreads are present, and finally it reduces false-positivity.
Leukemia 2004 May
PMID:Split-signal FISH for detection of chromosome aberrations in acute lymphoblastic leukemia. 1504 5

In pro-B cell acute lymphoblastic leukemia (ALL), expression of the E2A-HLF fusion gene as a result of t(17;19)(q22;p13) is associated with poor prognosis, hypercalcemia, and hemorrhagic complications. We previously reported that the E2A-HLF fusion protein protects interleukin-3 (IL-3)-dependent lymphoid cells from apoptosis caused by cytokine starvation. Here, we report that annexin II, a surface phospholipid-binding protein and one of the proposed causes of the hemorrhagic complications of acute promyelocytic leukemia (APL), is also implicated in t(17;19)+ ALL. Annexin II was expressed at high levels in APL cells and in each of 4 t(17;19)+ leukemia cell lines, and annexin II expression was induced by enforced expression of E2A-HLF in leukemia cells. In IL-3-dependent cells, we found that annexin II expression was regulated by IL-3 mainly by Ras pathways, including Ras/phosphatidylinositol 3-kinase pathways. Moreover, E2A-HLF increased annexin II expression in IL-3-dependent cells in the absence of the cytokine. These findings indicate that E2A-HLF induces annexin II by substituting for cytokines that activate downstream pathways of Ras.
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PMID:Regulation of annexin II by cytokine-initiated signaling pathways and E2A-HLF oncoprotein. 1507 Jul 1

The E4BP4 basic leucine zipper (bZIP) transcription factor is regulated by interleukin-3 (IL-3) in pro-B cells and has been reported to promote survival of the murine IL-3-dependent pro-B cell lines, FL5.12 and Baf-3. The E2A-HLF oncoprotein arises from a t(17;19) translocation in childhood pro-B cell acute lymphoblastic leukaemia and acts as an anti-apoptotic factor in FL5.12 and Baf-3 cells. To assess the functions of E2A-HLF and E4BP4 in cell survival, a tetracycline-inducible system was established in Baf-3 cells to express E4BP4 or E2A-HLF. Upon IL-3 withdrawal, expression of E2A-HLF conferred resistance to apoptosis whereas overexpression of E4BP4 did not. E4BP4 and E2A-HLF both recognized the same DNA sequence in reporter gene assays, but had opposite effects on transcription. E2A-HLF acts as a transcriptional activator and E4BP4 as a transcriptional repressor. Furthermore, E4BP4 is a downstream transcriptional target of E2A-HLF. Our data suggests that the overexpression of E4BP4 is unable to block apoptosis induced by IL-3 withdrawal and that the expression of E2A-HLF does not replace the function of E4BP4 in mediating survival.
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PMID:E4BP4 expression is regulated by the t(17;19)-associated oncoprotein E2A-HLF in pro-B cells. 1514 70

Activation of the basic-helix-loop-helix (bHLH) gene TAL1 (or SCL) is a frequent gain-of-function mutation in T cell acute lymphoblastic leukemia (T-ALL). To provide genetic evidence that tal1/scl induces leukemia by interfering with E47 and HEB, we expressed tal1/scl in an E2A or HEB heterozygous background. These mice exhibit disease acceleration and perturbed thymocyte development due to repression of E47/HEB target genes. In tal1/scl thymocytes, we find the corepressor mSin3A bound to the CD4 enhancer, whereas an E47/HEB/p300 complex is detected in wild-type thymocytes. Furthermore, tal1/scl tumors are sensitive to pharmacologic inhibition of HDAC and undergo apoptosis. These data demonstrate that tal1/scl induces leukemia by repressing E47/HEB and suggest that HDAC inhibitors may prove efficacious in T-ALL patients who express TAL1/SCL.
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PMID:TAL1/SCL induces leukemia by inhibiting the transcriptional activity of E47/HEB. 1519 61

Notch signaling is required for normal T cell development. However, Notch expression must be precisely regulated as constitutive Notch signaling leads to T cell lymphomas. Recent evidence has provided insights into potential mechanisms of Notch-mediated lymphomagenesis and its relationship to T cell development. The evidence suggests that Notch likely interacts with several important cellular pathways and can cooperate with other oncogenes during lymphomagenesis. In particular, Notch appears to modulate pre-TCR signaling, inhibit the E2A pathway, and in murine leukemia models, frequently cooperates with Myc, E2A-PBX and dominant negative Ikaros dysregulation. This review will present current knowledge in these areas and explore theories on Notch-mediated T cell lymphomagenesis.
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PMID:Notch and T cell malignancy. 1528 58


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