Effects of HsRad51 Overexpression on Cell Proliferation, Cell Cycle Progression, and Apoptosis

Flygare, Jenny; Fält, Susann; Ottervald, Jan; Castro, Juan; Dackland, Åsa-Lena; Hellgren, Dennis; Wennborg, Anders

doi:10.1006/excr.2001.5265

Cited by 52 publications

(47 citation statements)

References 45 publications

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“…[76][77][78][79] Elevated levels of Rad51 detected in multiple tumor cell types may contribute to genomic instability by stimulating recombination between short repetitive elements and homologous sequences. 76,78,80 Expression of Rad51 is predictive of B-cell chronic lymphocytic leukemia patient response to nitrogen mustards, 81,82 as well as small-cell lung cancer cell sensitivity to Thus, the ability to modulate damage sensor and repair proteins will impact the ability of the CD34 ϩ subpopulation to protect against illegitimate repair of etoposide-induced DNA damage and potentially oncogenic rearrangements. This system can be used to determine the relative importance of repair proteins in the maintenance of genome stability following exposure of CD34 ϩ cells to chemotherapeutic regimens that include etoposide.…”

Section: Discussionmentioning

confidence: 99%

Therapy-related acute myeloid leukemia–like MLL rearrangements are induced by etoposide in primary human CD34+ cells and remain stable after clonal expansion

Libura

Slater

Felix

et al. 2005

Blood

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Rearrangements involving the MLL gene on chromosome band 11q23 are a hallmark of therapy-related acute myeloid leukemias following treatment with topoisomerase II poisons including etoposide. Therapy-related and de novo genomic translocation breakpoints cluster within a well-characterized 8.3-kb fragment of MLL. Repair of etoposidestabilized DNA topoisomerase II covalent complexes may initiate MLL rearrangements observed in patients. We used a culture system of primary human hematopoietic CD34 ؉ cells and inverse polymerase chain reaction to characterize the spectrum of stable genomic rearrangements promoted by etoposide exposure originating within an MLL translocation hotspot in therapy-related leukemia. Alterations to the region were observed at a readily detectable frequency in etoposidetreated cells. Illegitimate repair events after minimal repair included MLL tandem duplications and translocations, with minor populations of deletions or insertions. In stably repaired cells that proliferated for 10 to 14 days, the significant majority of illegitimate events were MLL IntroductionGenome integrity is controlled by multiple damage surveillance pathways, cell-cycle checkpoints, and repair mechanisms. [1][2][3] Despite these safeguards, illegitimate repair of chromosomal doublestrand breaks (DSBs), such as those produced by chemotherapy agents that target topoisomerase II (topo II), can promote chromosomal rearrangements and, ultimately, tumorigenesis. Topo II is an essential cellular enzyme that catalyzes changes in DNA topology via its cleavage-religation equilibrium. Topo II-targeted drugs that are poisons of this enzyme stabilize topo II-DNA covalent complexes, most often by decreasing the rate of religation in a dose-dependent manner. Disruption of the cleavage-religation reaction results in accumulation of DSBs, p53 activation, and induction of apoptosis or repair. 4,5 Chromosomal DSBs are potent inducers of recombination, stimulating the exchange of homologous sequences between 2 DNA duplexes 1000-fold 6-8 not only between sister chromatids, but also between homologs, and sequence repeats on heterologous chromosomes. 9-12 DSBs may be repaired by homologous recombination or nonhomologous end joining (NHEJ), and both repair mechanisms have been associated with chromosomal translocations, a hallmark of leukemias, lymphomas, and soft-tissue sarcomas. [13][14][15] There is clear evidence that exposure to chemotherapy or irradiation can result in subsequent development of therapy-related leukemias, which occur in 1% to 15% of patients exposed to DNA-damaging agents in anticancer regimens. 16,17 Exposure to topo II poisons such as etoposide is predominantly associated with therapy-related leukemias characterized by rearrangements of the MLL gene on chromosome band 11q23. 16 MLL spans 100 kb, encodes a 430-kDa protein homologous to the Drosophila trithorax gene, and has important functions in embryogenesis and hematopoiesis. 18,19 Mixed-lineage leukemia (MLL) is a critical transcriptional regulator and numerous tr...

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Section: Discussionmentioning

confidence: 99%

Therapy-related acute myeloid leukemia–like MLL rearrangements are induced by etoposide in primary human CD34+ cells and remain stable after clonal expansion

Libura

Slater

Felix

et al. 2005

Blood

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“…These authors have also indicated that basal RAD51 gene expression correlates negatively with micronuclei induction in irradiated blood cells, and the level of Rad51 can partly explain the individual sensitivity to IR assessed by radiation-induced micronuclei. A 10-fold overexpression of Rad51 in HT1080 fibrosarcoma cell line has resulted in decreased plating efficiency and growth rate, in a dose-dependent manner with regard to the degree of overexpression (Flygare et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

Normal expression of DNA repair proteins, hMre11, Rad50 and Rad51 but protracted formation of Rad50 containing foci in X-irradiated skin fibroblasts from radiosensitive cancer patients

Djuzenova¹,

Mühl²,

Schakowski³

et al. 2004

Br J Cancer

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About 5% of oncology patients treated by radiation therapy develop acute or late radiotoxic effects whose molecular mechanisms remain poorly understood. In this study, we evaluated the potential role of DNA repair proteins in the hypersensitivity of cancer patients to radiation therapy. The expression levels and focal nuclear distribution of DNA repair proteins, hMre11, Rad50 and Rad51 were investigated in skin fibroblasts strains derived from cancer patients with adverse early skin reaction to radiotherapy using Western blot and foci immunofluorescence techniques, respectively. Cells from cancer patients with normal reaction to radiotherapy as well as cells from apparently healthy subjects served as controls. Cellular radiosensitivity after in vitro irradiation was assessed by the clonogenic survival assay. The clonogenic survival assay and Western blot analysis of the DNA repair proteins did not reveal any abnormalities in cellular radiosensitivity in vitro and in protein expression levels or their migration patterns in the fibroblasts derived from cancer patients with hypersensitive reaction to radiotherapy. In contrast, in vitro irradiated cells from radiosensitive patients exhibited a significantly higher number of nuclei with focally concentrated Rad50 protein than in both control groups. The observed alteration of the distribution of radiation-induced Rad50 foci in cells derived from cancer patients with acute side reactions to radiotherapy might contribute to their radiation therapy outcome. These data suggest the usefulness of the Rad50 foci analysis for predicting clinical response of cancer patients to radiotherapy.

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“…Deregulations of Rad51 expression, both inhibition and elevated expression, compromises integrity of the genome. First reports came from immortalized cell lines and tumor cells in which elevated expression of Rad51 was associated with an aberrant recombination between short repetitive elements and homologous sequences (Xia et al, 1997;Flygare et al, 2001;Raderschall et al, 2002). Further analyses indicated elevated Rad51 protein levels in cells from chronic myelogenous leukemia (CML), and even higher Rad51 expression in cells from the blast crisis -stage of the disease characterized by a profound genome instability (Slupianek et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

Impaired homologous recombination DNA repair and enhanced sensitivity to DNA damage in prostate cancer cells exposed to anchorage-independence

Wang

Trojanek

et al. 2005

Oncogene

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During metastases, cancer cells are temporarily exposed to the condition in which interactions with extracellular environment can be restricted (anchorage-independence). We demonstrate that the sensitivity of prostate cancer cell lines, DU145 and PC-3, to genotoxic treatment (cisplatin and c-irradiation) increased several folds when cells were forced to grow in anchorage-independence. This enhanced drug sensitivity was associated with a severe impairment of homologous recombination-directed DNA repair (HRR). The mechanism involves Rad51, which is the major enzymatic component of HRR. The protein level of Rad51 and its recruitment to DNA double-strand breaks (DSBs) were both attenuated. Rad51 deficiency in anchorage-independence was not associated with Rad51 promoter activity, and was not compensated by a constitutive overexpression of Rad51 cDNA. Instead, Rad51 protein level and its ability to colocalize with DSBs were restored in the presence of proteosome inhibitors, or when cells from the suspension cultures were allowed reattachment. Presented results indicate that anchorageindependence sensitizes prostate cancer cells to genotoxic agents; however, it also attenuates faithful component of DNA repair by targeting stability of Rad51. This temporal attenuation of HRR may contribute to the accumulation mutations after DNA damage, and possibly the selection of new adaptations in cells, which survived genotoxic treatment.

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Effects of HsRad51 Overexpression on Cell Proliferation, Cell Cycle Progression, and Apoptosis

Cited by 52 publications

References 45 publications

Therapy-related acute myeloid leukemia–like MLL rearrangements are induced by etoposide in primary human CD34+ cells and remain stable after clonal expansion

Therapy-related acute myeloid leukemia–like MLL rearrangements are induced by etoposide in primary human CD34+ cells and remain stable after clonal expansion

Normal expression of DNA repair proteins, hMre11, Rad50 and Rad51 but protracted formation of Rad50 containing foci in X-irradiated skin fibroblasts from radiosensitive cancer patients

Impaired homologous recombination DNA repair and enhanced sensitivity to DNA damage in prostate cancer cells exposed to anchorage-independence

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