SEARCH · Search PubMed

Results for “Genome Instability”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55Linked to original sources

PubMed1994

Alterations of (CA)n DNA repeats and tumor suppressor genes in human gastric cancer.

We have examined whether alterations of simple (CA)n DNA repeats, as observed in human colon cancers, occur during human gastric carcinogenesis and whether such alterations reflect genomic instability that could lead to other genetic changes. A total of 22 gastric cancer samples were analyzed: 15 well or moderately differentiated adenocarcinomas, 6 signet-ring cell carcinomas, and 1 poorly differentiated adenocarcinoma. When (CA)n repeat sequences were examined at 10 loci, one adenocarcinoma showed a loss of repeat sequences at five loci, three adenocarcinomas gained a repeat at one locus, and one adenocarcinoma had new, repeated sequences at five loci. Three samples showed mutations in the p53 gene, two in exon 5 (both GC to AT transition at a CpG dinucleotide) and one in exon 7 (AT to GC transition). Only one sample with a p53 mutation also showed altered (CA)n repeats. A putative tumor suppressor gene, connexin 32, was not altered as assessed by single-strand conformation polymorphism analysis. These results suggest that genomic instability revealed by (CA)n repeat changes does not seem to contribute to induction of point mutations in p53 or connexin 32 genes but may participate in loss of heterozygosity at APC/MCC loci. The results are consistent with the hypothesis that different mechanisms are involved in the gain and loss of (CA)n repeats.

Adenocarcinoma↗

PubMed2001

Elevated breast cancer risk in irradiated BALB/c mice associates with unique functional polymorphism of the Prkdc (DNA-dependent protein kinase catalytic subunit) gene.

Female BALB/c mice are unusually radiosensitive and more susceptible than C57BL/6 and other tested inbred mice to ionizing radiation (IR)-induced mammary tumors. This breast cancer susceptibility is correlated with elevated susceptibility for mammary cell transformation and genomic instability following irradiation. In this study, we report the identification of two BALB/c strain-specific polymorphisms in the coding region of Prkdc, the gene encoding the DNA-dependent protein kinase catalytic subunit, which is known to be involved in DNA double-stranded break repair and post-IR signal transduction. First, we identified an A --> G transition at base 11530 resulting in a Met --> Val conversion at codon 3844 (M3844V) in the phosphatidylinositol 3-kinase domain upstream of the scid mutation (Y4046X). Second, we identified a C --> T transition at base 6418 resulting in an Arg --> Cys conversion at codon 2140 (R2140C) downstream of the putative leucine zipper domain. This unique PrkdcBALB variant gene is shown to be associated with decreased DNA-dependent protein kinase catalytic subunit activity and with increased susceptibility to IR-induced genomic instability in primary mammary epithelial cells. The data provide the first evidence that naturally arising allelic variation in a mouse DNA damage response gene may associate with IR response and breast cancer risk.

Amino Acid Sequence↗

PubMed2003

The constitutional t(17;22): another translocation mediated by palindromic AT-rich repeats.

We have demonstrated that the breakpoints of the constitutional t(11;22) are located at palindromic AT-rich repeats (PATRRs) on 11q23 and 22q11. As a mechanism for this recurrent translocation, we proposed that the PATRR forms a cruciform structure that induces the genomic instability leading to the rearrangement. A patient with neurofibromatosis type 1 (NF1) had previously been found to have a constitutional t(17;22) disrupting the NF1 gene on 17q11. We have localized the breakpoint on 22q11 within the 22q11-specific low-copy repeat where the breakpoints of the constitutional t(11;22)s reside, implying a similar palindrome-mediated mechanism for generation of the t(17;22). The NF1 gene contains a 195-bp PATRR within intron 31. We have isolated the junction fragments from both the der(17) and the der(22). The breakpoint on 17q11 is close to the center of the PATRR. A published breakpoint of an additional NF1-afflicted patient with a constitutional t(17;22) is also located close to the center of the same PATRR. Our data lend additional support to the hypothesis that PATRR-mediated genomic instability can lead to a variety of translocations.

Base Sequence↗

PubMed2003

Werner's syndrome protein is phosphorylated in an ATR/ATM-dependent manner following replication arrest and DNA damage induced during the S phase of the cell cycle.

Werner's syndrome (WS) is an autosomal recessive disorder, characterized at the cellular level by genomic instability in the form of variegated translocation mosaicism and extensive deletions. Individuals with WS prematurely develop multiple age-related pathologies and exhibit increased incidence of cancer. WRN, the gene defective in WS, encodes a 160-kDa protein (WRN), which has 3'-5'exonuclease, DNA helicase and DNA-dependent ATPase activities. WRN-defective cells are hypersensitive to certain genotoxic agents that cause replication arrest and/or double-strand breaks at the replication fork, suggesting a pivotal role for WRN in the protection of the integrity of the genoma during the DNA replication process. Here, we show that WRN is phosphorylated through an ATR/ATM dependent pathway in response to replication blockage. However, we provide evidence that WRN phosphorylation is not essential for its subnuclear relocalization after replication arrest. Finally, we show that WRN and ATR colocalize after replication fork arrest, suggesting that WRN and the ATR kinase collaborate to prevent genome instability during the S phase.

Ataxia Telangiectasia Mutated Proteins↗

PubMed2007

A mild mutator phenotype arises in a mouse model for malignancies associated with neurofibromatosis type 1.

Defects in genes that control DNA repair, proliferation, and apoptosis can increase genomic instability, and thus promote malignant progression. Although most tumors that arise in humans with neurofibromatosis type 1 (NF1) are benign, these individuals are at increased risk for malignant peripheral nerve sheath tumors (MPNST). To characterize additional mutations required for the development of MPNST from benign plexiform neurofibromas, we generated a mouse model for these tumors by combining targeted null mutations in Nf1 and p53, in cis. CisNf1+/-; p53+/- mice spontaneously develop PNST, and these tumors exhibit loss-of-heterozygosity at both the Nf1 and p53 loci. Because p53 has well-characterized roles in the DNA damage response, DNA repair, and apoptosis, and because DNA repair genes have been proposed to act as modifiers in NF1, we used the cisNf1+/-; p53+/- mice to determine whether a mutator phenotype arises in NF1-associated malignancies. To quantitate spontaneous mutant frequencies (MF), we crossed the Big Blue mouse, which harbors a lacI transgene, to the cisNf1+/-; p53+/- mice, and isolated genomic DNA from both tumor and normal tissues in compound heterozygotes and wild-type siblings. Many of the PNST exhibited increased mutant frequencies (MF=4.70) when compared to normal peripheral nerve and brain (MF=2.09); mutations occurred throughout the entire lacI gene, and included base substitutions, insertions, and deletions. Moreover, the brains, spleens, and livers of these cisNf1+/-; p53+/- animals exhibited increased mutant frequencies when compared to tissues from wild-type littermates. We conclude that a mild mutator phenotype arises in the tumors and tissues of cisNf1+/-; p53+/- mice, and propose that genomic instability influences NF1 tumor progression and disease severity.

Animals↗

PubMed2026

RADX protects against intestinal inflammation by restraining IFI16-mediated innate immunity.

Genomic instability is increased in patients with inflammatory bowel disease (IBD), yet whether it contributes directly to disease pathogenesis remains unclear. Here, we identify RADX, a structural antagonist to RAD51 and a key regulator of replication fork stability, as a critical suppressor of intestinal inflammation by limiting innate immune sensing of replication-associated DNA damage. RADX deficiency exacerbates experimental colitis, with macrophages serving as the principal mediators of this phenotype. Mechanistically, RADX competes with the DNA sensor IFI16 for binding to single-stranded DNA (ssDNA). Loss of RADX promotes ssDNA accumulation, triggering IFI16-dependent activation of NF-κB signaling and inflammasome assembly, thereby driving intestinal inflammation. Consistent with these findings, two RADX variants identified in patients with IBD associate with reduced RADX protein expression, increased DNA damage signaling, and elevated IL-1β levels. Pharmacological inhibition of RAD51 with RI-1 alleviated colitis in both wild-type and Radx-deficient mice. Together, these findings establish a mechanistic link between genome instability and intestinal inflammation, identify a RADX-IFI16 checkpoint that restrains pathogenic innate immune activation, and nominate modulation of replication stress as a therapeutic strategy for IBD.

Animals↗

PubMed1996

Induction of circles of heterogeneous sizes in carcinogen-treated cells: two-dimensional gel analysis of circular DNA molecules.

Extrachromosomal circular DNA molecules are associated with genomic instability, and circles containing inverted repeats were suggested to be the early amplification products. Here we present for the first time the use of neutral-neutral two-dimensional (2D) gel electrophoresis as a technique for the identification, isolation, and characterization of heterogeneous populations of circular molecules. Using this technique, we demonstrated that in N-methyl-N'-nitro-N-nitrosoguanidine-treated simian virus 40-transformed Chinese hamster cells (CO60 cells), the viral sequences are amplified as circular molecules of various sizes. The supercoiled circular fraction was isolated and was shown to contain molecules with inverted repeats. 2D gel analysis of extrachromosomal DNA from CHO cells revealed circular molecules containing highly repetitive DNA which are similar in size to the simian virus 40-amplified molecules. Moreover, enhancement of the amount of circular DNA was observed upon N-methyl-N'-nitro-N-nitrosoguanidine treatment of CHO cells. The implications of these findings regarding the processes of gene amplification and genomic instability and the possible use of the 2D gel technique to study these phenomena are discussed.

Animals↗

PubMed1995

Astrocytes derived from p53-deficient mice provide a multistep in vitro model for development of malignant gliomas.

Loss or mutation of p53 is thought to be an early event in the malignant transformation of many human astrocytic tumors. To better understand the role of p53 in their growth and transformation, we developed a model employing cultured neonatal astrocytes derived from mice deficient in one (p53 +/-) or both (p53 -/-) p53 alleles, comparing them with wild-type (p53 +/+) cells. Studies of in vitro and in vivo growth and transformation were performed, and flow cytometry and karyotyping were used to correlate changes in growth with genomic instability. Early-passage (EP) p53 -/- astrocytes achieved higher saturation densities and had more rapid growth than EP p53 +/- and +/+ cells. The EP p53 -/- cells were not transformed, as they were unable to grow in serum-free medium or in nude mice. With continued passaging, p53 -/- cells exhibited a multistep progression to a transformed phenotype. Late-passage p53 -/- cells achieved saturation densities 50 times higher than those of p53 +/+ cells and formed large, well-vascularized tumors in nude mice. p53 +/- astrocytes exhibited early loss of the remaining wild-type p53 allele and then evolved in a manner phenotypically similar to p53 -/- astrocytes. In marked contrast, astrocytes retaining both wild-type p53 alleles never exhibited a transformed phenotype and usually senesced after 7 to 10 passages. Dramatic alterations in ploidy and karyotype occurred and were restricted to cells deficient in wild-type p53 following repeated passaging. The results of these studies suggest that loss of wild-type p53 function promotes genomic instability, accelerated growth, and malignant transformation in astrocytes.

Animals↗

PubMed2005

Biologic behavior of microsatellite-unstable colorectal cancer and treatment with 5-fluorouracil.

Colorectal cancers develop as a consequence of genomic instability. Microsatellite instability is involved in the genesis of about 15% of sporadic colorectal cancers and in most hereditary non-polyposis cancers. High frequency MSI has been associated with a favorable prognosis, however it is not clear whether this is because MSI-H tumors are inherently less aggressive or because they are more sensitive to chemotherapy. Chemotherapy with a combination of 5-fluorouracil and leukovorin or levamizole has been the standard of care for high risk stage II and stage III CRC; it is also used in stage IV CRC. Several in vitro studies have shown that colon cancer cell lines displaying MSI-H are less responsive to fluorouracil than microsatellite-stable cell lines. Human studies, all of them retrospective, yielded conflicting results. The selection of patients with CRC for 5-FU treatment has been based so far on the stage of the tumor rather than the biology of the tumor. Although surgical staging is highly predictive of survival, there are indications that the form of genomic instability within a patient's colorectal tumor has clinical implications, with and without 5-FU treatment. This review suggests that patients with MSI-H colorectal tumors may not benefit from 5-FU-based chemotherapy and can avoid its potential side effects (nausea, diarrhea, stomatitis, dermatitis, alopecia, and neurologic symptoms) that occur in half the treated patients. If confirmed by future prospective randomized controlled studies, these findings would indicate that microsatellite-instability testing should be conducted routinely and the results used to direct rational adjuvant chemotherapy in colon cancer.

Antimetabolites, Antineoplastic↗

PubMed2003

Telomere length study in celiac disease.

OBJECTIVES: Telomeres are important structures that are critical for maintaining chromosomal integrity and cell surveillance. The aim of this study was to analyze telomere length in patients with celiac disease (CD), a multifactorial disorder with a strong genetic component that exhibits genomic instability and cancer predisposition, particularly T-cell lymphomas. METHODS: Telomere length measured by telomere restriction fragments (TRF) was studied in small intestinal biopsy (SIB) samples and peripheral blood lymphocytes (PBL) from 20 untreated CD patients, distributed according to the clinical form as four asymptomatic, five monosymptomatic, and 11 polysymptomatic individuals. We also analyzed TRF from normal peripheral blood lymphocytes and normal biopsy samples as normal controls. RESULTS: TRF evaluation showed a significant telomere shortening in SIB samples from CD patients (4.21 +/- 0.29 Kb) compared to PBL from the same individuals (9.17 +/- 0.35 Kb) (p < 0.0001), independently of clinical form. Mean TRF peak values from normal biopsy samples were significantly higher (8.33 +/- 0.38 Kb) than those observed in CD biopsy samples (p < 0.001). No differences between TRF values in CD-PBL and normal peripheral blood lymphocytes (8.89 +/- 0.37Kb) were found. CONCLUSIONS: Our findings in patients with CD, a disorder in which the gluten-induced mucosal injury could accelerate telomere shortening, would increase the process of end-to-end fusions resulting in chromosomal changes, supports the hypothesis that genomic instability and telomere reduction may play a role in the cancer predisposition observed in these patients.

Adult↗

PubMed2001

Inverted repeats as genetic elements for promoting DNA inverted duplication: implications in gene amplification.

Inverted repeats are important genetic elements for genome instability. In the current study we have investigated the role of inverted repeats in a DNA rearrangement reaction using a linear DNA substrate. We show that linear DNA substrates with terminal inverted repeats can efficiently transform Escherichia coli. The transformation products contain circular inverted dimers in which the DNA sequences between terminal inverted repeats are duplicated. In contrast to the recombination/rearrangement product of circular DNA substrates, which is exclusively one particular form of the inverted dimer, the rearrangement products of the linear DNA substrate consist of two isomeric forms of the inverted dimer. Escherichia coli mutants defective in RecBCD exhibit much reduced transformation efficiency, suggesting a role for RecBCD in the protection rather than destruction of these linear DNA substrates. These results suggest a model in which inverted repeats near the ends of a double-strand break can be processed by a helicase/exonuclease to form hairpin caps. Processing of hairpin capped DNA intermediates can then yield inverted duplications. Linear DNA substrates containing terminal inverted repeats can also be converted into inverted dimers in COS cells, suggesting conservation of this type of genome instability from bacteria to mammalian cells.

Animals↗

PubMed1998

Analysis of centrosome abnormalities and angiogenesis in epidermal-targeted p53172H mutant and p53-knockout mice after chemical carcinogenesis: evidence for a gain of function.

We previously developed a transgenic mouse model that expresses in the epidermis a murine p53172R-->H mutant (p53m) under the control of a human keratin-1-based vector (HK1.p53m). In contrast to mice with wild-type p53 and p53-knockout mice, HK1.p53m mice exhibit increased susceptibility to chemical carcinogenesis, with greatly accelerated benign papilloma formation, malignant conversion, and metastasis. In the study presented here, we examined the expression pattern of several differentiation markers and observed that p53m tumors exhibited a less differentiated phenotype than tumors elicited in non-transgenic mice. Metastasis in p53m tumors was also associated with a poorly differentiated phenotype. To determine whether genomic instability was associated with a putative gain-of-function role for this p53m, in situ examination of centrosomes was performed in HK1.p53m and equivalent p53-null papillomas. In contrast to HK1.p53m papillomas, which had centrosome abnormalities at high frequencies (75% of cells contained more than three centrosomes/cell), p53-null tumors exhibited few abnormal centrosomes (4% of cells contained more than three centrosomes/cell). To determine whether angiogenesis played a role in the rapid progression of p53m tumors, the expression of vascular endothelial growth factor, a promoter of angiogenesis, and thrombospondin-1, an inhibitor of angiogenesis, was examined in tumors derived from either p53m or p53-knockout mice. Regardless of their p53 status (wild type, p53m, p53-/-), all of the papillomas exhibited similar levels of vascular endothelial growth factor expression and decreased expression of thrombospondin-1 as did normal epidermis. In addition, tumors from different p53 genotypes showed a similar density of blood vessels. Because p53 status did not appear to play an overt role in angiogenesis, these data suggest that p53m accelerates tumorigenesis primarily by exerting a gain of function associated with genomic instability.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2002

Micronuclei, nucleoplasmic bridges and nuclear buds induced in folic acid deficient human lymphocytes-evidence for breakage-fusion-bridge cycles in the cytokinesis-block micronucleus assay.

We have validated the analysis of nucleoplasmic bridges (NPBs) and nuclear buds as biomarkers of genomic instability within the cytokinesis-block micronucleus assay in long-term lymphocyte cultures. Lymphocytes from 20 subjects were cultured in medium containing 12-120 nM folic acid for 9 days. Binucleate cells were scored for micronuclei (MN), NPBs and nuclear budding on day nine after 24h incubation in the presence of the cytokinesis inhibitor cytochalasin-B. Folic acid concentration was correlated significantly (P<0.0001) and negatively (r=-0.63 to -0.74) with all these markers of chromosome damage. Chromosome damage was minimised at 60-120 nM folic acid, which is greater than the concentration of folate normally observed in plasma (<30 nM). Current evidence suggests that (a) NPBs originate from dicentric chromosomes in which the centromeres have been pulled to the opposite poles of the cell at anaphase and are therefore, indicative of chromosome rearrangement and (b) that the nuclear budding process is the mechanism by which cells remove amplified DNA and is therefore a marker of gene amplification. The strong correlation between micronucleus formation, nuclear budding and NPBs (r=0.75-0.77, P<0.001) is supportive of the hypothesis that folic acid deficiency causes genomic instability and gene amplification by the initiation of breakage-fusion-bridge (BFB) cycles. These results also suggest that the CBMN assay may be a useful model for the study of the BFB cycle which may be one of the key mechanisms for the hypermutability phenotype required for the rapid evolution of cancer cells.

Cell Division↗

PubMed2000

Misregulation of gene expression in primary fibroblasts lacking poly(ADP-ribose) polymerase.

Poly(ADP-ribose) polymerase (PARP) is implicated in the maintenance of genomic integrity, given that inhibition or depletion of this enzyme increases genomic instability in cells exposed to genotoxic agents. We previously showed that immortalized fibroblasts derived from PARP(-/-) mice exhibit an unstable tetraploid population, and partial chromosomal gains and losses in PARP(-/-) mice and immortalized fibroblasts are accompanied by changes in the expression of p53, Rb, and c-Jun, as well as other proteins. A tetraploid population has also now been detected in primary fibroblasts derived from PARP(-/-) mice. Oligonucleotide microarray analysis was applied to characterize more comprehensively the differences in gene expression between asynchronously dividing primary fibroblasts derived from PARP(-/-) mice and their wild-type littermates. Of the 11,000 genes monitored, 91 differentially expressed genes were identified. The loss of PARP results in down-regulation of the expression of several genes involved in regulation of cell cycle progression or mitosis, DNA replication, or chromosomal processing or assembly. PARP deficiency also up-regulates genes that encode extracellular matrix or cytoskeletal proteins that are implicated in cancer initiation or progression or in normal or premature aging. These results provide insight into the mechanism by which PARP deficiency impairs mitotic function, thereby resulting in the genomic alterations and chromosomal abnormalities as well as in altered expression of genes that may contribute to genomic instability, cancer, and aging.

Animals↗

PubMed1997

Selective elimination of human lymphoid cells with unstable chromosome aberrations by p53-dependent apoptosis.

Alterations in p53 expression are associated with genomic instability, presumably because loss of p53 leads to an inability to eliminate damaged and therefore potentially unstable cells by apoptosis or by induced cell cycle block. We tested this hypothesis by examining the influence of apoptosis on X-ray-induced chromosome aberration frequency in two isogenic human B-lymphoblastoid cell lines; TK6, which is sensitive to the induction of apoptosis, and WI-L2-NS, a p53 mutant resistant to apoptosis induction. While TK6 was more sensitive than WI-L2-NS cells to the cytotoxic effects of X-rays, it showed fewer induced chromosome aberrations. Inhibition of apoptosis in TK6 cells with phorbol 12-myristate 13-acetate (PMA) resulted in X-ray-induced aberration frequencies similar in magnitude to WI-L2-NS. The results support the hypothesis that apoptosis acts to selectively remove damaged cells. The reduction in aberration frequency associated with apoptosis was seen primarily for unstable types of aberrations; acentric chromosome fragments and dicentric chromosomes. There was no effect on the induced frequency of balanced translocations, the stable counterpart to dicentrics. The failure to remove cells with unstable types of aberrations is consistent with the genomic instability that accompanies loss of p53 activity.

Apoptosis↗

PubMed1996

Cancer of the microsatellite mutator phenotype.

This review focuses on the genomic instability underlying the microsatellite mutator phenotype (MMP) pathway for cancer. MMP was discovered by the application of DNA fingerprinting by Arbitrarily Primed PCR (AP-PCR) to the analysis of somatic genetic alterations in colon tumors. The unbiased nature of AP-PCR permitted to infer, from the mobility shifts observed in some fingerprint bands, the accumulation by a subset of colon tumors of hundreds of thousands of somatic mutations in simple repeated sequences or microsatellites. We deduced that this enormous agglomeration of clonal mutations was due to the previous occurrence of 'mutator mutations' in DNA replication or repair factors leading to a decreased fidelity of replication. These mutator mutations appeared to be the remote cause for the development of these MMP tumors, whose existence unmistakably validated the hypothesis of 'cancer as a mutator phenotype'. Since these original observations, rapid progress has occurred in the field. The mutator mutations were identified as those occurring in members of the DNA mismatch repair gene family, which are also associated with hereditary non-polyposis colorectal cancer (HN-PCC). In this review I discuss the experimental approach that allowed the discovery of MMP and the features of the genomic instability of these tumors. I also review recent developments that affect the understanding of the role of the mismatch repair mutator mutations in the unfolding of MMP during carcinogenesis.

Colorectal Neoplasms, Hereditary Nonpolyposis↗

PubMed1995

The pattern of mutations induced by neocarzinostatin and methyl methanesulfonate in the ataxia telangiectasia-like Chinese hamster cell line V-E5.

The Chinese hamster cell line V-E5 is a mutant cell line isolated from V79 cells. The phenotypic characteristics of V-E5 strongly resemble those of cells from patients suffering from the genomic instability syndrome ataxia telangiectasia. In order to further characterize the mutant cell line and to get insight into the underlying genetic defect we compared the clastogenic and mutagenic effects of neocarzinostatin (NCS) and methyl methanesulfonate (MMS) in V-E5 and V79 wild-type cells (V79-LE). V-E5 cells were 2-3 times more sensitive to the cytotoxic effect of NCS or MMS. The clastogenic action of NCS was characterized by the predominant induction of chromosome breaks and dicentrics in both cell lines, whereas MMS mainly induced chromatid-type aberrations. The frequency of mutations induced by NCS as well as MMS was slightly enhanced in V-E5 cells compared to V79 cells treated with the same dose. However, the mutant cell line was found to be hypomutable when considering the same survival level as in the parental cell line. Molecular analysis of mutants induced by NCS revealed a high frequency of total deletions of the hprt gene in both cell lines. In contrast, among MMS-induced mutations only 11% deletion mutations were found in V79-LE, whereas in V-E5 MMS-induced deletions were seen in 52% of the hprt-deficient mutants. These results are discussed with respect to a possible relation between genomic instability, cell cycle control and mutational spectra.

Animals↗

PubMed1998

Delayed DNA damage associated with mitotic catastrophe following X-irradiation of HeLa S3 cells.

Partial loss of the radiation G2/M checkpoint is thought to be an early event in cell immortalization. One of the attributes of immortalized cell lines is an increase in susceptibility to induction of genomic instability by clastogenic agents. Recently we have shown that in irradiated HeLa cells cell cycle delays in late S and G2 lead to overaccumulation of cyclin B1 and that enhanced intracellular levels of this positive regulator of the cell cycle is correlated with cyclin-dependent kinase activation, spontaneous premature chromosome condensation and subsequent mitotic catastrophe occurring following irradiation. Previous studies have shown that spontaneous premature chromosome condensation and mitotic catastrophe are independent of apoptosis. This report shows that 40 h following X-irradiation of HeLa S3 cells, and subsequent to mitotic catastrophe, DNA strand breaks appear which are chemically distinct from those initially produced by ionizing radiation. This delayed damage is recognized by terminal transferase and thus involves generation of free 3'-OH ends. Pulse field gel electrophoresis analysis of DNA size distributions shows that DNA fragments of approximately 40 kbp and smaller are produced. As strand breaks produced as a direct result of irradiation are generally repaired within a few hours after exposure to X-rays at the doses used, these results describe a novel mechanism for generation of DNA damage occurring a day or more following irradiation. These results may be pertinent to the understanding of mechanisms underlying the delayed lethal effects of irradiation and may provide an initiating mechanism for radiation-induced genomic instability.

Cell Nucleus↗