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

MLL, involved in many chromosomal translocations associated with acute myeloid and lymphoid leukemia, has >50 known partner genes with which it is able to form in-frame fusions. Characterizing important downstream target genes of MLL and of MLL fusion proteins may provide rational therapeutic strategies for the treatment of MLL-associated leukemia. We explored downstream target genes of the most prevalent MLL fusion protein, MLL-AF4. To this end, we developed inducible MLL-AF4 fusion cell lines in different backgrounds. Overexpression of MLL-AF4 does not lead to increased proliferation in either cell line, but rather, cell growth was slowed compared with similar cell lines inducibly expressing truncated MLL. We found that in the MLL-AF4-induced cell lines, the expression of the cyclin-dependent kinase inhibitor gene CDKN1B was dramatically changed at both the RNA and protein (p27kip1) levels. In contrast, the expression levels of CDKN1A (p21) and CDKN2A (p16) were unchanged. To explore whether CDKN1B might be a direct target of MLL and of MLL-AF4, we used chromatin immunoprecipitation (ChIP) assays and luciferase reporter gene assays. MLL-AF4 binds to the CDKN1B promoter in vivo and regulates CDKN1B promoter activity. Further, we confirmed CDKN1B promoter binding by ChIP in MLL-AF4 as well as in MLL-AF9 leukemia cell lines. Our results suggest that CDKN1B is a downstream target of MLL and of MLL-AF4, and that, depending on the background cell type, MLL-AF4 inhibits or activates CDKN1B expression. This finding may have implications in terms of leukemia stem cell resistance to chemotherapy in MLL-AF4 leukemias.
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PMID:The MLL fusion gene, MLL-AF4, regulates cyclin-dependent kinase inhibitor CDKN1B (p27kip1) expression. 1616 1

Strong expression of at least one of the three D-type cyclins is common in human cancers. While the cyclin D1 and D3 genes (CCND1 and CCND3) are recurrently involved in genomic rearrangements, especially in B-cell lymphoid neoplasias, no clear involvement of the cyclin D2 gene (CCND2) has been reported to date. Here, we identified chromosomal translocations targeting the CCND2 locus at 12p13, and the T-cell receptor beta (TCRB) or the TCRA/D loci in T-cell acute lymphoblastic leukemias (T-ALLs). Expression analysis demonstrated dramatic cyclin D2 overexpression in the translocated cases (n=3) compared to other T-ALLs (total, n=89). In order to evaluate dysregulation in T-ALL with respect to normal T-cell differentiation, we analyzed CCND2 expression in normal purified human thymic subpopulations. CCND2 levels were downregulated through progression from the early stages of human T-cell differentiation, further suggesting that the massive and sustained expression in the CCND2-rearranged T-ALL cases was oncogenic. Association with other oncogene expression (TAL1, HOXAs, or TLX3/HOX11L2), NOTCH1 activating mutations, and/or CDKN2A/p16/ARF deletion, showed that cyclin D2 dysregulation could contribute to multi-event oncogenesis in various T-ALL groups. This report is the first clear evidence of a direct involvement of cyclin D2 in human cancer due to recurrent somatic genetic alterations.
Leukemia 2006 Jan
PMID:Cyclin D2 dysregulation by chromosomal translocations to TCR loci in T-cell acute lymphoblastic leukemias. 1627 38

Ninety consecutive patients with acute promyelocytic leukaemia were investigated for promoter methylation of CDKN2B (alias p15) and CDKN2A (alias p16) in disease relapse and progression. CDKN2B methylation was significantly more frequent at first relapse (30/36, 83%) than at presentation (48/77, 62%) (P=0.025), while CDKN2A methylation appeared unaffected. Both acquisition and loss of CDKN2B methylation happened at relapse, with acquisition more frequent. No significant increase in CDKN2B and CDKN2A methylation occurred at more advanced relapses. At first or subsequent relapses, owing to highly effective salvage by arsenic trioxide, CDKN2B methylation did not impact on event-free survival or overall survival.
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PMID:Serial studies of methylation of CDKN2B and CDKN2A in relapsed acute promyelocytic leukaemia treated with arsenic trioxide. 1635 40

Human leukemia-derived cell lines containing characteristic chromosomal translocations and inversions have been instrumental in identifying fusion genes implicated in the pathogenesis of the corresponding leukemia. Although chimeric fusion genes usually provide early and essential steps in the development of leukemia, they are not in themselves sufficient, requiring additional genetic events. The nature of these secondary, cooperating genetic events is not known. The advent of genome wide microarray-based methods for assessing copy number changes made it possible to search for cytogenetically invisible regions of chromosome imbalance. We used BAC microarrays with a resolution of 1 Mb to determine whether cryptic regions of deletion or gain were associated with specific leukemia-associated fusion genes in a series of cell lines. To complement the array analysis, we also applied 24-color karyotyping by M-FISH. This revealed cryptic chromosomal translocations and regions of loss or gain in all the cell lines studied. The chromosomal origin of previously unidentified marker chromosomes was revealed. In all cases, chromosomes described as monosomic were shown to be involved in unbalanced translocations with concurrent loss and/or gain of chromosomal material. The extent of these amplified and deleted regions was more accurately defined. Finally, small regions of deletion and amplification, often including genes known to be involved in leukemia progression (for example MYC, TP53, CDKN2A, and KIT), were identified.
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PMID:Array CGH of fusion gene-positive leukemia-derived cell lines reveals cryptic regions of genomic gain and loss. 1652 83

Gross cytogenetic anomalies are traditionally being used as diagnostic, prognostic and therapeutic markers in the clinical management of cancer, including childhood acute lymphoblastic leukemia (ALL). Recently, it has become increasingly clear that genetic lesions driving tumorigenesis frequently occur at the submicroscopic level and, consequently, escape standard cytogenetic observations. Therefore, we profiled the genomes of 40 childhood ALLs at high resolution. We detected multiple de novo genetic lesions, including gross aneuploidies and segmental gains and losses, some of which were subtle and affected single genes. Many of these lesions involved recurrent (partially) overlapping deletions and duplications, containing various established leukemia-associated genes, such as ETV6, RUNX1 and MLL. Importantly, the most frequently affected genes were those controlling G1/S cell cycle progression (e.g. CDKN2A, CDKN1B and RB1), followed by genes associated with B-cell development. The latter group includes microdeletions of the B-lineage transcription factors PAX5, EBF, E2-2 and IKZF1 (Ikaros), as well as genes with other established roles in B-cell development, that is RAG1 and RAG2, FYN, PBEF1 or CBP/PAG. The fact that we frequently encountered multiple lesions affecting genes involved in cell cycle regulation and B-cell differentiation strongly suggests that both these processes need to be targeted independently and simultaneously to trigger ALL development.
Leukemia 2007 Jun
PMID:High-resolution genomic profiling of childhood ALL reveals novel recurrent genetic lesions affecting pathways involved in lymphocyte differentiation and cell cycle progression. 1744 27

Single-nucleotide polymorphism (SNP) array analysis was performed using the 10K GeneChip array on a series of 26 paired follicular lymphoma (FL) and transformed-FL (t-FL) biopsies and the lymphoma cell lines SCI-1, DoHH2 and RL2261. Regions of acquired homozygosity were detected in 43/52 (83%) primary specimens with a mean of 1.7 and 3.0 aberrations in the FL and t-FL, respectively. A notable feature was the occurrence of recurring sites of acquired uniparental disomy (aUDP) on 6p, 9p, 12q and 17p in cell lines and primary samples. Homozygosity of 9p and 17p arose predominantly in t-FL and in three cases rendered the cell homozygous for a pre-existing mutation of either CDKN2A or TP53. These data suggest that mutation precedes mitotic recombination, which leads to the removal of the remaining wild-type allele. In all, 18 cases exhibited abnormalities in both FL and t-FL samples. In 10 cases blocks of homozygosity were detected in FL that were absent in the subsequent t-FL sample. These differences support the notion that FL and t-FL may arise in a proportion of patients by divergence from a common malignant ancestor cell rather than by clonal evolution from an antecedent FL.
Leukemia 2007 Jul
PMID:Genome-wide detection of recurring sites of uniparental disomy in follicular and transformed follicular lymphoma. 1749 76

Azacitidine and decitabine are cytidine analogues that inhibit DNA methylation, and are used to treat myeloid haematological malignancies. Hydroxycarbamide (HC) (also known as hydroxyurea), a ribonucleotide reductase (RR) inhibitor, blocks the conversion of ribonucleotides to deoxyribonucleotides, and is also used to treat leukaemia and sickle-cell disease. Azacitidine is a ribonucleoside and decitabine is a deoxyribonucleoside; therefore, we hypothesized that inhibition of RR by HC would be antagonistic to azacitidine and synergistic to decitabine. HL-60 and T24 cancer cell lines were treated with azacitidine or decitabine in combination with HC and DNA methylation of LRE1, MAGEA1 and CDKN2A was quantitatively measured by bisulphite-polymerase chain reaction pyrosequencing. Surprisingly, we found that HC blocked the ability of both azacitidine and decitabine to inhibit DNA methylation and this antagonistic effect was attributable to the arrest of the cell cycle induced by HC. However, this antagonism could be avoided with sequential treatment of HC followed by azacitidine or decitabine. This data suggest that concurrent combination of HC blocks the ability of azacitidine and decitabine to inhibit DNA methylation and therefore these drugs should be used sequentially.
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PMID:Hydroxycarbamide in combination with azacitidine or decitabine is antagonistic on DNA methylation inhibition. 1768 55

Previously, several individuals with X-linked SCID (SCID-X1) were treated by gene therapy to restore the missing IL-2 receptor gamma (IL2RG) gene to CD34+ BM precursor cells using gammaretroviral vectors. While 9 of 10 patients were successfully treated, 4 of the 9 developed T cell leukemia 31-68 months after gene therapy. In 2 of these cases, blast cells contained activating vector insertions near the LIM domain-only 2 (LMO2) proto-oncogene. Here, we report data on the 2 most recent adverse events, which occurred in patients 7 and 10. In patient 10, blast cells contained an integrated vector near LMO2 and a second integrated vector near the proto-oncogene BMI1. In patient 7, blast cells contained an integrated vector near a third proto-oncogene,CCND2. Additional genetic abnormalities in the patients' blast cells included chromosomal translocations, gain-of-function mutations activating NOTCH1, and copy number changes, including deletion of tumor suppressor gene CDKN2A, 6q interstitial losses, and SIL-TAL1 rearrangement. These findings functionally specify a genetic network that controls growth in T cell progenitors. Chemotherapy led to sustained remission in 3 of the 4 cases of T cell leukemia, but failed in the fourth. Successful chemotherapy was associated with restoration of polyclonal transduced T cell populations. As a result, the treated patients continued to benefit from therapeutic gene transfer.
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PMID:Insertional oncogenesis in 4 patients after retrovirus-mediated gene therapy of SCID-X1. 1868 85

Children with Down syndrome (DS) have a greatly increased risk of acute megakaryoblastic leukemia (AMKL) and acute lymphoblastic leukemia (ALL). Both DS-AMKL and the related transient myeloproliferative disorder (TMD) have GATA1 mutations as obligatory, early events. To identify mutations contributing to leukemogenesis in DS-ALL, we undertook sequencing of candidate genes, including FLT3, RAS, PTPN11, BRAF, and JAK2. Sequencing of the JAK2 pseudokinase domain identified a specific, acquired mutation, JAK2R683, in 12 (28%) of 42 DS-ALL cases. Functional studies of the common JAK2R683G mutation in murine Ba/F3 cells showed growth factor independence and constitutive activation of the JAK/STAT signaling pathway. High-resolution SNP array analysis of 9 DS-ALL cases identified additional submicroscopic deletions in key genes, including ETV6, CDKN2A, and PAX5. These results infer a complex molecular pathogenesis for DS-ALL leukemogenesis, with trisomy 21 as an initiating or first hit and with chromosome aneuploidy, gene deletions, and activating JAK2 mutations as complementary genetic events.
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PMID:Specific JAK2 mutation (JAK2R683) and multiple gene deletions in Down syndrome acute lymphoblastic leukemia. 1934 9

Studies of loss of heterozygosity (LOH) play an important role in cancer research. In this paper, we developed a two-step procedure to examine LOH by comparing unpaired tumour and normal samples. In the first step we determined which chromosomes significantly differ between the two sets of samples by using nonparametric procedures. We then used the biplot data visualisation technique and homozygosity intensity estimates to determine the regions of these chromosomes that required further examination. We illustrated our method by examining 22 autosomes in samples of 95 normal controls and 14 acute lymphoblastic leukaemia patients. The genomewide scan of LOH with the Affymetrix Human Mapping 100K Set successfully identified the important tumour suppressor gene, CDKN2A, whose deletion was validated by quantitative polymerase chain reaction in multiple patients of this study.
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PMID:Nonparametric estimation of LOH using Affymetrix SNP genotyping arrays for unpaired samples. 1898 37


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