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Results for “Cell Cycle Checkpoints”

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PubMed2000

Differential toxicities of anticancer agents among DNA repair and checkpoint mutants of Saccharomyces cerevisiae.

Most cytotoxic anticancer agents damage DNA directly, interfere with DNA metabolism or chromosome segregation, and are particularly toxic in dividing cells. Although a considerable amount of information on the mechanisms of action of these agents is available, the molecular bases for selective tumor cell killing by chemotherapy are largely unknown. Many genetic alterations found in sporadic and hereditary cancers affect functions in DNA repair and cell cycle control and result in sensitivity to DNA damaging agents. We have therefore set out to determine the effects of these cancer mutations on sensitivity or resistance to various chemotherapeutic agents. Because most of the affected genes are well conserved among eukaryotes, we have carried out a comprehensive analysis of a panel of isogenic yeast strains, each defective in a particular DNA repair or cell cycle checkpoint function, for sensitivity to the Food and Drug Administration-approved cytotoxic anticancer agents. Widely different toxicity profiles were observed for 23 agents and X-rays, indicating that the type of DNA repair and cell cycle checkpoint mutations in individual tumors could strongly influence the outcome of a particular chemotherapeutic regimen.

Antimetabolites, Antineoplastic↗

PubMed2000

The human checkpoint protein hRad17 interacts with the PCNA-like proteins hRad1, hHus1, and hRad9.

DNA damage activates cell cycle checkpoints that prevent progression through the cell cycle. In yeast, the DNA damage checkpoint response is regulated by a series of genes that have mammalian homologs, including rad1, rad9, hus1, and rad17. On the basis of sequence homology, yeast and human Rad1, Rad9, and Hus1 protein homologs are predicted to structurally resemble the sliding clamp PCNA. Likewise, Rad17 homologs have extensive homology with replication factor C (RFC) subunits (p36, p37, p38, p40, and p140), which form a clamp loader for PCNA. These observations predict that Rad1, Hus1, and Rad9 might interact with Rad17 as a clamp-clamp loader pair during the DNA damage response. In this report, we demonstrate that endogenous human Rad17 (hRad17) interacts with the PCNA-related checkpoint proteins hRad1, hRad9, and hHus1. Mutational analysis of hRad1 and hRad17 demonstrates that this interaction has properties similar to the interaction between RFC and PCNA, a well characterized clamp-clamp loader pair. Moreover, we show that DNA damage affects the association of hRad17 with the clamp-like checkpoint proteins. Collectively, these data provide the first experimental evidence that hRad17 interacts with the PCNA-like proteins hRad1, hHus1, and hRad9 in manner similar to the interaction between RFC and PCNA.

Cell Cycle↗

PubMed2001

Bisimidazoacridones induce a potent cytostatic effect in colon tumor cells that sensitizes them to killing by UCN-01.

PURPOSE: To determine the ability of WMC26, a prototypic bisimidazoacridone (BIA), to induce apoptosis in sensitive colon adenocarcinoma cells and to advance the hypothesis that cancer cells that are growth-arrested by WMC26 are predisposed to undergo apoptotic death by abrogators of cell cycle checkpoints. METHODS: The antiproliferative activity of WMC26 was examined in detail by a 4-day MTT assay, cell counting, BrdU incorporation and a two-color LIVE/DEAD assay. To detect apoptosis a number of established techniques were used, including gel electrophoresis, flow cytometry, and confocal laser microscopy of treated cells. The activity of senescence-associated beta-galactosidase in treated cells was also analyzed. RESULTS: WMC26, at physiological concentrations, induced complete and longlasting growth arrest of HCT116 cells in culture but did not trigger cell death. The growth-arrested cells (blocked at G1 and G2/M cell cycle checkpoints) did not synthesize DNA but were metabolically active and had intact plasma membranes. Although they resembled the senescence-like phenotype reported to be induced by treatment with some antitumor agents, the cells did not express senescence-associated beta-galactosidase, an indicator of the senescence-like state. Treatment of WMC26 growth-arrested cells with 1 microM UCN-01, an abrogator of the G2/M checkpoint, caused a very rapid (1 h) change in morphology and cell death within 72 h. CONCLUSIONS: BIAs do not induce apoptosis in sensitive colon tumor cells. They are highly cytostatic but only marginally toxic to the cells even at concentrations 100-fold higher than those sufficient for complete growth arrest. In this respect WMC26 differs from some other DNA-interacting antitumor agents that produce cell growth arrest at low concentrations but are toxic at higher doses. The complete growth arrest induced by WMC26 in colon cancer cells sensitized them to apoptotic death induced by UCN-01. This finding suggests that a combination of WMC26 and cyclin-dependent kinase inhibitors may be an attractive treatment method for colon cancer that utilizes the highly tumor-selective activity of WMC26.

Adenocarcinoma↗

PubMed2002

BCR/ABL regulates response to DNA damage: the role in resistance to genotoxic treatment and in genomic instability.

BCR/ABL regulates cell proliferation, apoptosis, differentiation and adhesion. In addition, BCR/ABL can induce resistance to cytostatic drugs and irradiation by modulation of DNA repair mechanisms, cell cycle checkpoints and Bcl-2 protein family members. Upon DNA damage BCR/ABL not only enhances reparation of DNA lesions (e.g. homologous recombination repair), but also prolongs activation of cell cycle checkpoints (e.g. G2/M) providing more time for repair of otherwise lethal lesions. Moreover, by modification of anti-apoptotic members of the Bcl-2 family (e.g. upregulation of Bcl-x(L)) BCR/ABL provides a cytoplasmic 'umbrella' protecting mitochondria from the 'rain' of apoptotic signals coming from the damaged DNA in the nucleus, thus preventing release of cytochrome c and activation of caspases. The unrepaired and/or aberrantly repaired (but not lethal) DNA lesions resulting from spontaneous and/or drug-induced damage can accumulate in BCR/ABL-transformed cells leading to genomic instability and malignant progression of the disease. Inhibition of BCR/ABL kinase activity by STI571 (Gleevec, imatinib mesylate) reverses drug resistance and, in combination with standard chemotherapeutics can exert strong anti-leukemia effect.

Antineoplastic Agents↗

PubMed2001

Cell cycle in the fucus zygote parallels a somatic cell cycle but displays a unique translational regulation of cyclin-dependent kinases.

In eukaryotic cells, the basic machinery of cell cycle control is highly conserved. In particular, many cellular events during cell cycle progression are controlled by cyclin-dependent kinases (CDKs). The cell cycle in animal early embryos, however, differs substantially from that of somatic cells or yeasts. For example, cell cycle checkpoints that ensure that the sequence of cell cycle events is correct have been described in somatic cells and yeasts but are largely absent in embryonic cells. Furthermore, the regulation of CDKs is substantially different in the embryonic and somatic cells. In this study, we address the nature of the first cell cycle in the brown alga Fucus, which is evolutionarily distant from the model systems classically used for cell cycle studies in embryos. This cycle consists of well-defined G1, S, G2, and M phases. The purine derivative olomoucine inhibited CDKs activity in vivo and in vitro and induced different cell cycle arrests, including at the G1/S transition, suggesting that, as in somatic cells, CDKs tightly control cell cycle progression. The cell cycle of Fucus zygotes presented the other main features of a somatic cell cycle, such as a functional spindle assembly checkpoint that targets CDKs and the regulation of the early synthesis of two PSTAIRE CDKs, p32 and p34, and the associated histone H1 kinase activity as well as the regulation of CDKs by tyrosine phosphorylation. Surprisingly, the synthesis after fertilization of p32 and p34 was translationally regulated, a regulation not described previously for CDKs. Finally, our results suggest that the activation of mitotic CDKs relies on an autocatalytic amplification mechanism.

Animals↗

PubMed2000

Role for ATM in DNA damage-induced phosphorylation of BRCA1.

The human genetic disorder ataxia-telangiectasia is characterized by immunodeficiency, progressive cerebellar ataxia, radiosensitivity, cell cycle checkpoint defects, and cancer predisposition. The gene product [ataxia-telangiectasia mutation (ATM)] mutated in this syndrome is a component of the DNA damage detection pathway. Loss of ATM function in human and mouse cells causes defects in DNA repair and cell cycle checkpoint control and, not surprisingly, humans and mice with compromised ATM function are prone to cancers. An excess of breast cancer in the relatives of ataxia-telangiectasia patients has also been reported by epidemiological studies. Predisposition to breast and ovarian cancers is also observed in women with germline mutations in BRCA1, a tumor suppressor gene. BRCA1 is a nuclear protein with a cell cycle-regulated expression pattern and is hyperphosphorylated in response to DNA-damaging agents. Here we show that rapid ionizing radiation-induced in vivo phosphorylation of BRCA1 requires the presence of functional ATM protein. Furthermore, we show that ATM interacts with BRCA1, and this association is enhanced by radiation. We also demonstrate that BRCA1 is a substrate of ATM kinase in vitro and in vivo. Using phospho-specific antibodies against serines 1387, 1423, and 1457 of BRCA1, we demonstrate radiation-induced, ATM-dependent phosphorylation of BRCA1 at these sites. These findings show that BRCA1 is regulated by an ATM-dependent mechanism as a part of the cellular response to DNA damage. This interaction between ATM and BRCA1 argues in favor of the involvement of particular aspects of ATM function in breast cancer predisposition.

Ataxia Telangiectasia↗

PubMed1998

Splitting the ATM: distinct repair and checkpoint defects in ataxia-telangiectasia.

Ataxia-telangiectasia (A-T) is an autosomal recessive human disorder that, because of its multisystem nature, is of interest to scientists and clinicians from many disciplines. A-T patients have defects in the neurological and immune systems, telangiectasia in the eyes and face, and are, in addition, cancer-prone and radiation-sensitive. A-T cell lines have a range of diverse phenotypes including sensitivity to ionizing radiation and defects in cell-cycle checkpoint control. The ATM protein is a member of the PI 3-kinase-like superfamily, and it has been widely accepted that A-T cells represent mammalian cell-cycle checkpoint mutants and that the radiation sensitivity is a consequence of this defect. However, several lines of evidence suggest that A-T cells have distinct repair and checkpoint defects. A-T cells therefore appear to harbour dual checkpoint/repair defects. Here, we review the evidence supporting this contention and consider its implications for an analysis of the A-T phenotype.

Animals↗

PubMed2000

Chk1 is an essential kinase that is regulated by Atr and required for the G(2)/M DNA damage checkpoint.

Chk1, an evolutionarily conserved protein kinase, has been implicated in cell cycle checkpoint control in lower eukaryotes. By gene disruption, we show that CHK1 deficiency results in a severe proliferation defect and death in embryonic stem (ES) cells, and peri-implantation embryonic lethality in mice. Through analysis of a conditional CHK1-deficient cell line, we demonstrate that ES cells lacking Chk1 have a defective G(2)/M DNA damage checkpoint in response to gamma-irradiation (IR). CHK1 heterozygosity modestly enhances the tumorigenesis phenotype of WNT-1 transgenic mice. We show that in human cells, Chk1 is phosphorylated on serine 345 (S345) in response to UV, IR, and hydroxyurea (HU). Overexpression of wild-type Atr enhances, whereas overexpression of the kinase-defective mutant Atr inhibits S345 phosphorylation of Chk1 induced by UV treatment. Taken together, these data indicate that Chk1 plays an essential role in the mammalian DNA damage checkpoint, embryonic development, and tumor suppression, and that Atr regulates Chk1.

Alleles↗

PubMed2003

Human T-cell leukemia virus-I tax oncoprotein functionally targets a subnuclear complex involved in cellular DNA damage-response.

The virally encoded oncoprotein Tax has been implicated in HTLV-1-mediated cellular transformation. The exact mechanism by which this protein contributes to the oncogenic process is not known. However, it has been hypothesized that Tax induces genomic instability via repression of cellular DNA repair. We examined the effect of de novo Tax expression upon the cell cycle, because appropriate activation of cell cycle checkpoints is essential to a robust damage-repair response. Upon induction of tax expression, Jurkat T-cells displayed a pronounced accumulation in G2/M that was reversible by caffeine. We examined the G2-specific checkpoint signaling response in these cells and found activation of the ATM/chk2-mediated pathway, whereas the ATR/chk1-mediated response was unaffected. Immunoprecipitation with anti-chk2 antibody results in co-precipitation of Tax demonstrating a direct interaction of Tax with a chk2-containing complex. We also show that Tax targets a discrete nuclear site and co-localizes with chk2 and not chk1. This nuclear site, previously identified as Tax Speckled Structures (TSS), also contains the early damage response factor 53BP1. The recruitment of 53BP1 to TSS is dependent upon ATM signaling and requires expression of Tax. Specifically, Tax expression induces redistribution of diffuse nuclear 53BP1 to the TSS foci. Taken together these data suggest that the TSS describe a unique nuclear site involved in DNA damage recognition, repair response, and cell cycle checkpoint activation. We suggest that association of Tax with this multifunctional subnuclear site results in disruption of a subset of the site-specific activities and contributes to cellular genomic instability.

Carrier Proteins↗

PubMed1999

G1 checkpoint protein and p53 abnormalities occur in most invasive transitional cell carcinomas of the urinary bladder.

The G1 cell cycle checkpoint regulates entry into S phase for normal cells. Components of the G1 checkpoint, including retinoblastoma (Rb) protein, cyclin D1 and p16INK4a, are commonly altered in human malignancies, abrogating cell cycle control. Using immunohistochemistry, we examined 79 invasive transitional cell carcinomas of the urinary bladder treated by cystectomy, for loss of Rb or p16INK4a protein and for cyclin D1 overexpression. As p53 is also involved in cell cycle control, its expression was studied as well. Rb protein loss occurred in 23/79 cases (29%); it was inversely correlated with loss of p16INK4a, which occurred in 15/79 cases (19%). One biphenotypic case, with Rb+p16- and Rb-p16+ areas, was identified as well. Cyclin D1 was overexpressed in 21/79 carcinomas (27%), all of which retained Rb protein. Fifty of 79 tumours (63%) showed aberrant accumulation of p53 protein; p53 staining did not correlate with Rb, p16INK4a, or cyclin D1 status. Overall, 70% of bladder carcinomas showed abnormalities in one or more of the intrinsic proteins of the G1 checkpoint (Rb, p16INK4a and cyclin D1). Only 15% of all bladder carcinomas (12/79) showed a normal phenotype for all four proteins. In a multivariate survival analysis, cyclin D1 overexpression was linked to less aggressive disease and relatively favourable outcome. In our series, Rb, p16INK4a and p53 status did not reach statistical significance as prognostic factors. In conclusion, G1 restriction point defects can be identified in the majority of bladder carcinomas. Our findings support the hypothesis that cyclin D1 and p16INK4a can cooperate to dysregulate the cell cycle, but that loss of Rb protein abolishes the G1 checkpoint completely, removing any selective advantage for cells that alter additional cell cycle proteins.

Aged↗

PubMed2001

The Ataxia telangiectasia gene product is required for oxidative stress-induced G1 and G2 checkpoint function in human fibroblasts.

Ataxia telangiectasia (AT) is an autosomal recessive disorder characterized by neuronal degeneration accompanied by ataxia, telangiectasias, acute cancer predisposition, and sensitivity to ionizing radiation (IR). Cells from individuals with AT show unusual sensitivity to IR, severely attenuated cell cycle checkpoint functions, and poor p53 induction in response to IR compared with normal human fibroblasts (NHFs). The gene mutated in AT (ATM) has been cloned, and its product, pATM, has IR-inducible kinase activity. The AT phenotype has been suggested to be a consequence, at least in part, of an inability to respond appropriately to oxidative damage. To test this hypothesis, we examined the ability of NHFs and AT dermal fibroblasts to respond to t-butyl hydroperoxide and IR treatment. AT fibroblasts exhibit, in comparison to NHFs, increased sensitivity to the toxicity of t-butyl hydroperoxide, as measured by colony-forming efficiency assays. Unlike NHFs, AT fibroblasts fail to show G(1) and G(2) phase checkpoint functions or to induce p53 in response to t-butyl hydroperoxide. Treatment of NHFs with t-butyl hydroperoxide activates pATM-associated kinase activity. Our results indicate that pATM is involved in responding to certain aspects of oxidative damage and in signaling this information to downstream effectors of the cell cycle checkpoint functions. Our data further suggest that some of the pathologies seen in AT could arise as a consequence of an inability to respond normally to oxidative damage.

Adolescent↗

PubMed1998

Molecular mechanisms of DNA double strand break repair.

DNA double-strand breaks (DSBs) are major threats to the genomic integrity of cells. If not taken care of properly, they can cause chromosome fragmentation, loss and translocation, possibly resulting in carcinogenesis. Upon DSB formation, cell-cycle checkpoints are triggered and multiple DSB repair pathways can be activated. Recent research on the Nijmegen breakage syndrome, which predisposes patients to cancer, suggests a direct link between activation of cell-cycle checkpoints and DSB repair. Furthermore, the biochemical activities of proteins involved in the two major DSB repair pathways, homologous recombination and DNA end-joining, are now beginning to emerge. This review discusses these new findings and their implications for the mechanisms of DSB repair.

Animals↗

PubMed2003

The Drosophila chk2 gene loki is essential for embryonic DNA double-strand-break checkpoints induced in S phase or G2.

Cell cycle checkpoints are signal transduction pathways that control the order and timing of cell cycle transitions, ensuring that critical events are completed before the occurrence of the next cell cycle transition. The Chk2 family of kinases is known to play a central role in mediating the cellular responses to DNA damage or DNA replication blocks in various organisms. Here we show through a phylogenetic study that the Drosophila melanogaster serine/threonine kinase Loki is the homolog of the yeast Mek1p, Rad53p, Dun1p, and Cds1 proteins as well as the human Chk2. Functional analyses allowed us to conclude that, in flies, chk2 is involved in monitoring double-strand breaks (DSBs) caused by irradiation during S and G2 phases. In this process it plays an essential role in inducing a cell cycle arrest in embryonic cells. Our results also show that, in contrast to C. elegans chk2, Drosophila chk2 is not essential for normal meiosis and recombination, and it also appears to be dispensable for the MMS-induced DNA damage checkpoint and the HU-induced DNA replication checkpoint during larval development. In addition, Drosophila chk2 does not act at the same cell cycle phases as its yeast homologs, but seems rather to be involved in a pathway similar to the mammalian one, which involves signaling through the ATM/Chk2 pathway in response to genotoxic insults. As mutations in human chk2 were linked to several cancers, these similarities point to the usefulness of the Drosophila model system.

Animals↗

PubMed1999

Disruption of mRad50 causes embryonic stem cell lethality, abnormal embryonic development, and sensitivity to ionizing radiation.

The Mre11/Rad50 protein complex functions in diverse aspects of the cellular response to double-strand breaks (DSBs), including the detection of DNA damage, the activation of cell cycle checkpoints, and DSB repair. Whereas genetic analyses in Saccharomyces cerevisiae have provided insight regarding DSB repair functions of this highly conserved complex, the implication of the human complex in Nijmegen breakage syndrome reveals its role in cell cycle checkpoint functions. We established mRad50 mutant mice to examine the role of the mammalian Mre11/Rad50 protein complex in the DNA damage response. Early embryonic cells deficient in mRad50 are hypersensitive to ionizing radiation, consistent with a role for this complex in the repair of ionizing radiation-induced DSBs. However, the null mrad50 mutation is lethal in cultured embryonic stem cells and in early developing embryos, indicating that the mammalian Mre11/Rad50 protein complex mediates functions in normally growing cells that are essential for viability.

Animals↗

PubMed1996

Molecular and cellular responses to DNA damage in a murine pituitary adenoma cell line.

Loss of cell cycle control and the inability of the cell to repair DNA at cell cycle checkpoints results in the propagation of genetic lesions which ultimately leads to cancer. To further our understanding of these pathways in pituitary tumorigenesis, we have investigated the effects of DNA damage by gamma radiation in a murine pituitary adenoma (AtT20) cell line with attention to cell cycle checkpoint responses, the induction of apoptosis, and the expression of known regulators of these processes. Irradiated cells exhibited characteristic morphologic changes of apoptosis beginning at 24 h, which included cell shrinkage, chromatin condensation, and cytoplasmic vacuolization, yet the ability to exclude trypan blue was retained for several days. DNA fragmentation could be demonstrated by ethidium bromide staining beginning at 24 h post-irradiation. By propidium iodide staining and flow cytometry, irradiated cells demonstrated G1 and G2 arrest at 24 h, followed at 48 h by a shift to a sub-G1 position of the apoptotic cell population. The G1 arrest coincided with an induction of p53 protein by Western blot analysis which peaked at 4 h post-radiation and persisted beyond 48 h. Expression of c-myc in irradiated cells was found to progressively decrease at 12, 24, and 48 h. Basal expression of the bcl-2 gene in AtT20 cells was found to be 15-fold higher than in normal mouse pituitary by RNase protection assay. Bcl-2 mRNA and protein levels, however, remained unchanged at 24 and 48 h following gamma-irradiation, suggesting that apoptosis occurs independently of bcl-2 gene expression in these cells following this stimulus, as reported in other cell types. We conclude that AtT20 cells undergo G1 and G2 arrest following DNA damage and that a significant proportion of cells then undergo apoptosis. The G1 arrest at 24 h is concurrent with a strong induction of p53 protein, while c-myc expression progressively diminishes. Bcl-2 is highly expressed in this cell line. The absence of variation in bcl-2 expression during apoptosis could be related to its high basal level in these cells.

Adenoma↗

PubMed2001

Perturbation of cell cycle regulators in Peyronie's disease.

Peyronie's disease is a fibromatosis of the tunica albuginea, characterized by development of a plaque consisting primarily of collagen. It has been suggested that trauma to the erect penis is the inciting event. More recent research has focused on the cellular events leading to the dysregulated wound healing and plaque formation. Previous work has shown chromosomal aneusomies and this combined with an increased S-phase in plaque derived cell cultures suggests a perturbation in the cell cycle in this condition. The p53 protein has been shown to be an important cell cycle regulator and pro-apoptotic factor. Aberrant p53 function leading to cell immortalization and proliferation has been implicated in several human malignancies. We hypothesized that abnormal p53 function may explain the high proliferative ability of fibroblasts derived from Peyronie's plaques. This study was undertaken to study the presence and function of p53 and its downstream elements (p21, mdm-2) in Peyronie's disease cell cultures. Plaque-derived fibroblasts have been established in culture and characterized. These cells and control neonatal foreskin fibroblasts were subjected to 5 Gy of gamma radiation to induce DNA damage. After fixation, antibodies to p53 and its transcriptional elements were used to stain irradiated and non-irradiated cells and levels of p53, p21 and mdm-2 were quantified using combined immunofluorescence and flow cytometry. Non-irradiated plaque fibroblasts demonstrated the presence of p53, p21 and mdm-2 at baseline. In control foreskin fibroblasts no p53 or mdm-2 were detectable at baseline. In irradiated foreskin-derived cells significant changes in all elements were demonstrated indicating a fully functional p53 pathway and cell cycle checkpoint system in these cells. In contrast, plaque-derived cells showed no such alterations in levels of cell cycle regulators following irradiation. This is highly suggestive of an aberration of the p53 pathway in plaque-derived fibroblasts. Peyronie's plaque-derived fibroblasts demonstrated stabilization and defunctionalization of p53 protein combined with appropriate responses of its transcriptional elements. These findings may explain the high cell proliferation rates in these cells and suggests a role for perturbation of the p53 pathway in the pathogenesis of Peyronie's disease.

Cell Cycle↗

PubMed1998

A human homologue of the Schizosaccharomyces pombe rad1+ checkpoint gene encodes an exonuclease.

In the fission yeast Schizosaccharomyces pombe the rad1(+) gene is required for both the DNA damage-dependent and the DNA replication-dependent cell cycle checkpoints. We have identified a human homologue of the S. pombe rad1(+) gene, designated Hrad1, as well as a mouse homologue: Mrad1. Two Hrad1 alternative splice variants with different open reading frames have been identified; one codes for a long form, Hrad1A, and the other encodes a short form because of N-terminal truncation, Hrad1B. Hrad1A has 60% identity to the S. pombe rad1+ sequence at the DNA level and 49% identity and 72% similarity at the amino acid level. Northern blot analysis indicates elevated levels of expression in testis and cancer cell lines. Chromosomal localization by fluorescence in situ hybridization indicates that Hrad1 is located on chromosome 5p13. 2-13.3. This region is subject to loss of heterozygosity in several human cancers. Hrad1 also shares homology with the Saccharomyces cerevisiae RAD17 and Ustilago maydis REC1 proteins. REC1 has previously been characterized as a 3' --> 5' exonuclease with a C-terminal domain essential for cell cycle checkpoint function. We have expressed and purified polyhistidine-tagged fusions of Hrad1A and Hrad1B and show that HisHrad1A has 3' --> 5' exonuclease activity, whereas HisHrad1B lacks such activity. The biological functions of the two proteins remain to be determined.

Alternative Splicing↗

PubMed1998

The hMre11/hRad50 protein complex and Nijmegen breakage syndrome: linkage of double-strand break repair to the cellular DNA damage response.

Nijmegen breakage syndrome (NBS) is an autosomal recessive disorder characterized by increased cancer incidence, cell cycle checkpoint defects, and ionizing radiation sensitivity. We have isolated the gene encoding p95, a member of the hMre11/hRad50 double-strand break repair complex. The p95 gene mapped to 8q21.3, the region that contains the NBS locus, and p95 was absent from NBS cells established from NBS patients. p95 deficiency in these cells completely abrogates the formation of hMre11/hRad50 ionizing radiation-induced foci. Comparison of the p95 cDNA to the NBS1 cDNA indicated that the p95 gene and NBS1 are identical. The implication of hMre11/hRad50/p95 protein complex in NBS reveals a direct molecular link between DSB repair and cell cycle checkpoint functions.

Acid Anhydride Hydrolases↗