Comparison of AluI-induced frequencies of dicentrics and translocations in human lymphocytes by chromosome painting.
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It has been shown repeatedly that following irradiation of human lymphocytes in the G0 stage, more translocations are induced than dicentrics. To check the role of DNA double-strand breaks (DSB) alone for the induction of symmetrical and asymmetrical chromosome aberrations, the frequencies of induced exchange aberrations by the restriction enzyme AluI were analyzed. The enzyme was introduced into cells using the pellet pipetting technique. Frequencies of induced translocations and dicentrics were determined using a chromosome painting assay with chromosome-specific DNA libraries for chromosomes 1, 4 and X (representing 16.8% of the human genome). The number of translocations detected was approximately 3-fold higher than the number of dicentrics, indicating that the increased frequency of translocations compared with dicentrics found in irradiated human lymphocytes does not result from DNA lesions other than DSB but from differential processing of DSB. (+info)
Genetic pathway to recurrent chromosome translocations in murine lymphoma involves V(D)J recombinase.
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Chromosome translocations involving antigen receptor loci are a genetic hallmark of non-Hodgkin's lymphomas in humans. Most commonly, these translocations result in juxtaposition of the immunoglobulin heavy-chain (IgH) locus with one of several cellular proto-oncogenes, leading to deregulated oncogene expression. The V(D)J recombinase, which mediates physiologic rearrangements of antigen receptor genes, may play a mechanistic role in some lymphoma translocations, although evidence is indirect. A high incidence of B-lineage lymphomas has been observed in mice with severe combined immunodeficiency (SCID) and p53-null mutations. We show that these tumors are characteristic of the pro-B-cell stage of development and that they harbor recurrent translocations involving chromosomes 12 and 15. Fluorescence in situ hybridization (FISH) shows retention of IgH sequences on the derivative chromosome 12, implying that breakpoints involve the IgH locus. Pro-B-cell lymphomas were suppressed in SCID p53(-/-) mice by a Rag-2-null mutation, demonstrating that DNA breaks generated during V(D)J recombination are required for oncogenic transformation, and suggesting that t(12;15) arise during attempted IgH rearrangement in pro-B cells. These studies indicate that the oncogenic potential inherent in antigen receptor diversification is controlled in vivo by efficient rejoining of DNA ends generated during V(D)J recombination and an intact cellular response to DNA damage. (+info)
Cancer-specific chromosome alterations in the constitutive fragile region FRA3B.
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We have sequenced 870 kilobases of the FHIT/FRA3B locus, from FHIT intron 3 to intron 7. The locus is AT rich (61.5%) and Alu poor (6. 2%), and it apparently does not harbor other genes. In a detailed analysis of the 308-kilobase region between FHIT exon 5 and the telomeric end of intron 3, a region known to encompass a human papillomavirus-16 integration site and two clusters of aphidicolin-induced chromosome 3p14.2 breakpoints, we have precisely mapped 10 deletion and translocation endpoints in cancer-derived cell lines relative to positions of specific repetitive elements, regions of high genome flexibility and aphidicolin-induced breakpoints. Conclusions are (i) that aphidicolin-induced breakpoint clusters fall close to high-flexibility sequences, suggesting that these sequences contribute directly to aphidicolin-induced fragility; (ii) that 9 of the 10 FHIT allelic deletions in cancer cell lines resulted in loss of exons, with 7 deletion endpoints near long interspersed nuclear elements or long terminal repeat elements; and (iii) that cancer-specific deletions encompass multiple high-flexibility genomic regions, suggesting that fragile breaks may occur at these regions, whereas repair of the breaks involves homologous pairing of flanking sequences with concomitant deletion of the damaged fragile sequence. (+info)
Gain of chromosome arm 17q and adverse outcome in patients with neuroblastoma.
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BACKGROUND: Gain of genetic material from chromosome arm 17q (gain of segment 17q21-qter) is the most frequent cytogenetic abnormality of neuroblastoma cells. This gain has been associated with advanced disease, patients who are > or =1 year old, deletion of chromosome arm 1p, and amplification of the N-myc oncogene, all of which predict an adverse outcome. We investigated these associations and evaluated the prognostic importance of the status of chromosome 17. METHODS: We compiled molecular cytogenetic analyses of chromosome 17 in primary neuroblastomas in 313 patients at six European centers. Clinical and survival information were collected, along with data on 1p, N-myc, and ploidy. RESULTS: Unbalanced gain of segment 17q21-qter was found in 53.7 percent of the tumors, whereas the chromosome was normal in 46.3 percent. The gain of 17q was characteristic of advanced tumors and of tumors in children > or =1 year of age and was strongly associated with the deletion of 1p and amplification of N-myc. No tumor showed amplification of N-myc in the absence of either deletion of 1p or gain of 17q. Gain of 17q was a significant predictive factor for adverse outcome in univariate analysis. Among the patients with this abnormality, overall survival at five years was 30.6 percent (95 percent confidence interval, 21 to 40 percent), as compared with 86.0 percent (95 percent confidence interval, 78 to 91 percent) among those with normal 17q status. in multivariate analysis, gain of 17q was the most powerful prognostic factor, followed by the presence of stage 4 disease and deletion of 1p (hazard ratios, 3.4, 2.3, and 1.9, respectively). CONCLUSIONS: Gain of chromosome segment 17q21-qter is an important prognostic factor in children with neuroblastoma. (+info)
Complete remission of t(11;17) positive acute promyelocytic leukemia induced by all-trans retinoic acid and granulocyte colony-stimulating factor.
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The combined use of retinoic acid and chemotherapy has led to an important improvement of cure rates in acute promyelocytic leukemia. Retinoic acid forces terminal maturation of the malignant cells and this application represents the first generally accepted differentiation-based therapy in leukemia. Unfortunately, similar approaches have failed in other types of hematological malignancies suggesting that the applicability is limited to this specific subgroup of patients. This has been endorsed by the notorious lack of response in acute promyelocytic leukemia bearing the variant t(11;17) translocation. Based on the reported synergistic effects of retinoic acid and the hematopoietic growth factor granulocyte colony-stimulating factor (G-CSF), we studied maturation of t(11;17) positive leukemia cells using several combinations of retinoic acid and growth factors. In cultures with retinoic acid or G-CSF the leukemic cells did not differentiate into mature granulocytes, but striking granulocytic differentiation occurred with the combination of both agents. At relapse, the patient was treated with retinoic acid and G-CSF before reinduction chemotherapy. With retinoic acid and G-CSF treatment alone, complete granulocytic maturation of the leukemic cells occurred in vivo, followed by a complete cytogenetical and hematological remission. Bone marrow and blood became negative in fluorescense in situ hybridization analysis and semi-quantitative polymerase chain reaction showed a profound reduction of promyelocytic leukemia zinc finger-retinoic acid receptor-alpha fusion transcripts. This shows that t(11;17) positive leukemia cells are not intrinsically resistant to retinoic acid, provided that the proper costimulus is administered. These observations may encourage the investigation of combinations of all-trans retinoic acid and hematopoietic growth factors in other types of leukemia. (+info)
t(1;2)(q21;p23) and t(2;3)(p23;q21): two novel variant translocations of the t(2;5)(p23;q35) in anaplastic large cell lymphoma.
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Cytogenetic investigations in two cases of anaplastic large cell lymphoma (ALCL) showed novel variants of the classical (2;5)(p23;q35) translocation, namely a t(1;2)(q21;p23) and a t(2;3)(p23;q21). The tumor cells in both cases gave positive immunohistochemical labeling for ALK protein (with both monoclonal and polyclonal antibodies), demonstrating that these translocations induce aberrant expression of this kinase and suggesting that genes other than NPM can activate the ALK gene in ALCL. These two cases were shown by an in vitro kinase assay to express ALK kinases (104 kD and 97 kD, respectively), which differed in size from the classical NPM-ALK fusion product (80 kD). Moreover, ALK expression was confined to the cytoplasm of the tumor cells in each case, supporting the hypothesis that the observed nuclear localization of NPM-ALK in classical ALCL is not the site of oncogenic activity of the ALK kinase. (+info)
Preimplantation genetic diagnosis and sperm analysis by fluorescence in-situ hybridization for the most common reciprocal translocation t(11;22).
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In this study we describe the pre-clinical development and clinical application of preimplantation genetic diagnosis (PGD) by fluorescence in-situ hybridization (FISH) for two non-related carriers (one male and one female) of the most common balanced reciprocal translocation: t(11;22)(q25;q12). For the couple with the female carrier, enumeration of the sex chromosomes in the embryos was also indicated (husband: 47,XXY karyotype). Four-colour FISH analysis was performed on six blastomeres from three embryos. No embryo transfer was possible because all the embryos were unbalanced. Three PGD cycles, with two-colour FISH, were carried out for the couple with the male translocation carrier. A total of 35 embryos were biopsied and diagnosed by FISH; nine out of the 35 embryos (25. 7%) were normal and seven of them were transferred (two embryos from the first and four from the third cycle), six out of 35 embryos (17%) were unbalanced, three out of 35 embryos (5.7%) were triploid or polyploid, 10 out of 35 embryos (28.6%) were mosaic and seven out of 35 embryos (20%) were chaotic. Diagnosis failed in 2.9% of the embryos. The spermatozoa of the male carrier were also analysed using three-colour FISH. Only 29.1% of the sperm cells seemed to be balanced or normal. By choosing probes lying on both sides of the breakpoints and by using a combination of sub-telomeric or locus-specific probes and centromeric probes, the use of three-colour FISH enabled detection of all the imbalances in sperm and/or cleavage-stage embryos in the patients. This may improve risk assessment and genetic counselling in the future for translocation carriers. (+info)
Inhibitors of histone deacetylase relieve ETO-mediated repression and induce differentiation of AML1-ETO leukemia cells.
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The (8;21) translocation, found in 12% of acute myeloid leukemia (AML), creates the chimeric fusion product, AML1-ETO. Previously, we demonstrated that the ETO moiety recruits a transcription repression complex that includes the histone deacetylase (HDAC1) enzyme. Here, we used inhibitors of HDAC1 to study the pathophysiology of AML1-ETO. Both the potent inhibitor, trichostatin (TSA), and the well-known but less specific inhibitor, phenylbutyrate (PB), could partially reverse ETO-mediated transcriptional repression. PB was also able to induce partial differentiation of the AML1-ETO cell line, Kasumi-1. With the intention of developing a clinically useful protocol, we combined PB with a number of other agents that induced differentiation and apoptosis of Kasumi-1 cells. In summary, transcriptional repression mediated by AML1-ETO appears to play a mechanistic role in the t(8;21) AML, and relief of repression using agents such as PB (alone or in combination) may prove to be therapeutically useful. (+info)