Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P16104 (H2AX)
 3,930 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The development of genomic instability is a hallmark of high-risk human papillomavirus (HPV) associated cervical carcinogenesis. We have previously shown that the HPV-16 E7 oncoprotein rapidly subverts mitotic fidelity by inducing abnormal centrosome numbers and multipolar mitotic spindles. Here we report that expression of HPV-16 E6 and E7 independently results in various mitotic abnormalities. HPV-16 E6 and E7 were each associated with unaligned or lagging chromosomal material, indicating relaxation of spindle checkpoint control. Moreover, by overwhelming checkpoint control mechanisms that may prevent cells with multiple spindle poles to enter anaphase, expression of HPV-16 E6 and E7 leads to a small but significant number of cells with altered polarity at later stages of the cell division process. In addition to changes that have the potential to give rise to numerical chromosome imbalances, we discovered that expression of HPV-16 E7 could trigger anaphase bridge formation to an extent similar to that of high-risk HPV E6. Anaphase bridges typically develop after chromosomal breaks and alterations of chromosomal structure. Further investigation of mechanisms by which HPV-16 E6 and E7 contribute to the destabilization of the host cell genome revealed that both high-risk HPV oncoproteins induce DNA damage. Moreover, expression of HPV-16 E7 was associated with an increased number of cells exhibiting nuclear foci of phosphorylated histone H2AX as well as activation of cell cycle checkpoints triggered by DNA repair. Our results therefore suggest that HPV oncoproteins are a source for both numerical and structural chromosome instability during HPV-associated carcinogenesis.
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PMID:The human papillomavirus type 16 E6 and E7 oncoproteins independently induce numerical and structural chromosome instability. 1246 Sep 29

Acidic pH plays an important role in various pathophysiological states and has been demonstrated to be carcinogenic in animal models. Recent studies have also implicated acidic pH in the development of preneoplastic Barrett's esophagus in human. However, little is known about the molecular mechanism underlying acidic pH-induced carcinogenesis. In the current study, we show that acidic pH, like the topoisomerase II (TOP2) poison VP-16 (demethylepipodophyllotoxin ethylidene-beta-D-glucoside), induces tumors in 9,10-dimethyl-1,2-benzanthracene(DMBA)-initiated mice. The following studies in tissue culture models have suggested that acidic pH acts like a TOP2 poison to induce TOP2-mediated DNA damage: (i) acidic pH induces TOP2-dependent DNA damage signals as evidenced by up-regulation of p53 and Ser-139 phosphorylation of H2AX [a substrate for ataxia telangiectasia mutated (ATM)ATM and Rad3-related (ATR) kinases]; (ii) acidic pH-induced cytotoxicity in tumor cells is reduced in TOP2-deficient cells; (iii) acidic pH increases the mutation frequency of the hypoxanthine phosphoribosyl transferase (HPRT) gene in a TOP2-dependent manner; and (iv) acidic pH induces reversible TOP2-mediated DNA strand breaks in vitro. We discuss the possibility that TOP2-mediated DNA damage may contribute to acidic pH-induced carcinogenesis.
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PMID:Acidic pH induces topoisomerase II-mediated DNA damage. 1269 9

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is one of the dietary carcinogens. At the initial step in the carcinogenic process, its exocyclic amino group is metabolically activated to the hydroxyamino derivative by the cytochrome P450 (CYP) 1A and 1B subfamily and then form DNA adducts, which are considered to be the main cause of DNA damage during the carcinogenic process. On the other hand, our previous study has shown that Trp-P-1 exhibits cytotoxicity to primary cultured rat hepatocytes, via induction of caspase-9-dependent apoptosis without being metabolized by CYP 1A1. In the present study, we investigated what type of DNA damage would be involved in the induction of apoptosis induced by Trp-P-1. When RL-34 cells derived from normal rat liver were treated with a high (30 microM) concentration of Trp-P-1, apoptotic events such as the loss of cell viability, nuclear condensation and the activation of caspase-3 were observed. In these apoptotic cells, intracellular topoisomerase I activity was inhibited and histone H2AX phosphorylation, which occurs after introduction of DNA double-strand breaks (DSBs), was observed in the early phase of the apoptosis. On the other hand, treatment with a non-apoptotic concentration (1 microM) of Trp-P-1 increased the formation of 8-hydroxy-2'-deoxyguanosine. The formation of DNA adducts was detected at almost the same level in both cells exposed to the apoptotic and non-apoptotic concentrations of Trp-P-1. These results indicate that Trp-P-1-induced apoptosis was triggered by DNA DSBs through the inhibition of topoisomerase I but not the formation of DNA adducts.
Carcinogenesis 2004 Jul
PMID:3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) triggers apoptosis by DNA double-strand breaks caused by inhibition of topoisomerase I. 1497 28

Certain hexavalent chromium [Cr(VI)] compounds are implicated as occupational respiratory carcinogens. Cr(VI) induces a broad spectrum of DNA damage, but Cr(VI)-induced DNA double-strand breaks (DSBs) have not been reported. Previously we found that Cr(VI) activates the ataxia telangiectasia mutated (ATM) kinase. ATM is activated specifically in response to DSBs. Therefore, the objective of this study was to investigate DSB induction by Cr(VI) exposure with the overarching hypothesis that S phase-dependent DSBs are produced by Cr(VI) exposure. To test this hypothesis, normal human fibroblasts were treated with either Cr(VI) or neocarzinostatin (NCS). DSBs were analyzed by both comet assay under neutral conditions, which detects primarily DNA DSBs, and phosphorylation of histone H2AX (gamma-H2AX) and the resultant formation of nuclear foci, which are considered to be indicative of DSBs. Induction of DSBs was observed after Cr(VI) exposure, however, the Cr(VI)-induced DSBs were abrogated by G(1) synchronization. Furthermore, our data showed that Cr(VI)-induced DSBs were only observed in the S phase population, whereas no significant DSBs were observed in Cr(VI)-treated G(1) synchronized cells. In contrast, NCS-induced DSBs were equally distributed in all cell cycle phases in both asynchronous and G(1) synchronized cells. Moreover, Cr(VI)-induced gamma-H2AX foci formation was restricted to PCNA-positive cells, whereas NCS-induced gamma-H2AX foci formed in both PCNA-positive and PCNA-negative cells. These results indicate that Cr(VI)-induced DSBs are S phase-dependent. Finally, our data showed that Cr(VI)-induced gamma-H2AX production was significantly decreased in ATM(-/-) cells compared with ATM(+/+) cells. Taken together, these results suggest that Cr(VI)-induced activation of ATM involves the formation of S phase-dependent DSBs. Examining the mechanism of Cr(VI)-induced DSBs will aid in understanding the interrelated mechanisms of Cr(VI) toxicity and carcinogenesis.
Carcinogenesis 2004 Nov
PMID:Generation of S phase-dependent DNA double-strand breaks by Cr(VI) exposure: involvement of ATM in Cr(VI) induction of gamma-H2AX. 1528 80

DNA damage that is not repaired with high fidelity can lead to chromosomal aberrations or mitotic cell death. To date, it is unclear what factors control the ultimate fate of a cell receiving low levels of DNA damage (i.e. survival at the risk of increased mutation or cell death). We investigated whether DNA damage could be introduced into human cells at a level and frequency that could evade detection by cellular sensors of DNA damage. To achieve this, we exposed cells to equivalent doses of ionizing radiation delivered at either a high dose rate (HDR) or a continuous low dose rate (LDR). We observed reduced activation of the DNA damage sensor ataxia-telangiectasia mutated (ATM) and its downstream target histone H2A variant (H2AX) following LDR compared with HDR exposures in both cancerous and normal human cells. This lack of DNA damage signaling was associated with increased amounts of cell killing following LDR exposures. Increased killing by LDR radiation has been previously termed the "inverse dose rate effect," an effect for which no clear molecular processes have been described. These LDR effects could be abrogated by the preactivation of ATM or simulated in HDR-treated cells by inhibiting ATM function. These data are the first to demonstrate that DNA damage introduced at a reduced rate does not activate the DNA damage sensor ATM and that failure to activate ATM-associated repair pathways contributes to the increased lethality of continuous LDR radiation exposures. This inactivation may reflect one strategy by which cells avoid accumulating mutations as a result of error-prone DNA repair and may have a broad range of implications for carcinogenesis and, potentially, the clinical treatment of solid tumors.
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PMID:Evasion of early cellular response mechanisms following low level radiation-induced DNA damage. 1537 58

Arsenic compounds, which are well-documented human carcinogens, are now used in cancer therapy. Knowledge of the mechanism by which arsenic exerts its toxicity may help in designing a more effective regimen for therapy. In this study, we showed that arsenite could induce prominent mitotic arrest in CGL-2 cells and demonstrated the presence of damaged DNA in arsenite-arrested mitotic cells. We then explored why these cells with arsenite-induced DNA damage were arrested at mitosis instead of G2 stage. When synchronized CGL-2 cells were treated with arsenite at stage G1, S or G2, all progressed into, and arrested at, the mitotic stage and contained damaged DNA, as demonstrated by the appearance of the DNA double-strand break marker, phosphorylated histone H2A.X (gamma-H2AX). Since X-irradiation induced G2 arrest in CGL-2 cells, these cells clearly have a functional G2 DNA damage checkpoint. However, treatment of X-irradiated CGL-2 cells with arsenite resulted in a decrease in G2 cells and an increase in mitotic cells, suggesting that arsenite may inhibit activation of the G2 DNA damage checkpoint and thus allow cells with damaged DNA to proceed from G2 into mitosis. Immunoblot analysis confirmed that arsenite treatment reduced the X-irradiation-induced phosphorylation of both ataxia-telangiectasia, mutated at serine 1981 and Cdc25C at serine 216, events which are crucial for G2 checkpoint activation and G2 arrest. Moreover, a higher frequency of apoptotic cells is observed in mitotic CGL-2 cells arrested by arsenite than those arrested by nocodazole or taxol. Our results show that the combined effects of arsenite in inducing DNA damages, inhibiting the activation of G2 checkpoint, and arresting cells with damaged DNA in the mitotic stage may subsequently enhance the induction of apoptosis in arsenite-arrested mitotic CGL-2 cells.
Carcinogenesis 2005 Jan
PMID:Arsenite induces prominent mitotic arrest via inhibition of G2 checkpoint activation in CGL-2 cells. 1547 1

Norethindrone is a commonly used drug for contraception and hormone replacement therapy, whose carcinogenic potential is still controversial. We applied a novel and particularly sensitive method to screen for DNA damage with special attention to double-strand breaks (DSBs) and identified norethindrone to be likely genotoxic and therefore potentially mutagenic: a p53-reporter assay served as a first, high-throughput screening method and was followed by the immunofluorescent detection of phosphorylated H2AX as a sensitive assay for the presence of DSBs. Norethindrone at concentrations of 2-100 microg/ml activated p53 and phosphorylated H2AX specifically and in a dose-dependent manner. No p53 activation or H2AX phosphorylation was detected using a panel of structurally/functionally related drugs. The overall amount of DNA damage induced by norethindrone was low as compared with etoposide and ionizing radiation. Consistently, norethindrone treatment did not cause a cell cycle arrest. DSBs were not detected with the neutral comet assay, a less sensitive method for DSB assessment than H2AX phosphorylation. Our findings in the p53-reporter and gamma-H2AX assays could not be ascribed to common DSB-causing artifacts in standard genotoxicity screening, including drug precipitation, high cytotoxicity levels and increased apoptosis. Therefore, our study suggests that norethindrone induces DSBs in our experimental setting, both complementing and adding a new aspect to the existing literature on the genotoxic potential of norethindrone. As the effective concentrations of norethindrone used in our assays were approximately 100- to 1000-fold higher than therapeutical doses, the significance of these findings with regard to human exposure still remains to be determined.
Carcinogenesis 2005 Oct
PMID:Novel genotoxicity assays identify norethindrone to activate p53 and phosphorylate H2AX. 1590 98

Ionizing radiation can lead to a variety of deleterious effects in humans, most importantly to the induction of cancer. DNA double-strand breaks (DSBs) are among the most significant genetic lesions introduced by ionizing radiation that can initiate carcinogenesis. We have enumerated gamma-H2AX foci as a measure for DSBs in lymphocytes from individuals undergoing computed tomography examination of the thorax and/or the abdomen. The number of DSBs induced by computed tomography examination was found to depend linearly on the dose-length product, a radiodiagnostic unit that is proportional to both the local dose delivered and the length of the body exposed. Analysis of lymphocytes sampled up to 1 day postirradiation provided kinetics for the in vivo loss of gamma-H2AX foci that correlated with DSB repair. Interestingly, in contrast to results obtained in vitro, normal individuals repair DSBs to background levels. A patient who had previously shown severe side effects after radiotherapy displayed levels of gamma-H2AX foci at various sampling times postirradiation that were several times higher than those of normal individuals. Gamma-H2AX and pulsed-field gel electrophoresis analysis of fibroblasts obtained from this patient confirmed a substantial DSB repair defect. Additionally, these fibroblasts showed significant in vitro radiosensitivity. These data show that the in vivo induction and repair of DSBs can be assessed in individuals exposed to low radiation doses, adding a further dimension to DSB repair studies and providing the opportunity to identify repair-compromised individuals after diagnostic irradiation procedures.
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PMID:In vivo formation and repair of DNA double-strand breaks after computed tomography examinations. 1595 3

Bystander effects induced by low dose of ionizing radiation have been shown to widely exist in many cell types and may have a significant impact on radiation risk assessment. Though many studies have been reported on this phenomenological observation, the mechanisms underlying this process are not clear, especially on the questions of how soon after irradiation the bystander effects can be initiated and how far this bystander signal can be propagated once it is started. DNA double-strand breaks (DSBs) induced by ionizing radiation or carcinogenic chemicals can be visualized in situ using gamma-H2AX immunofluorescent staining. Our previous studies have shown that in situ visualization of DSBs could be used to assess irradiation-induced extranuclear/extracellular (bystander) effect at an early stage after irradiation. In the present studies, we used this method to investigate the time and spatial effects of damage signals on unirradiated bystander cells. The results showed that increased DSBs in irradiated and unirradiated bystander areas could be visualized 2 min after radiation and reached its maximum 30 min after radiation. The average levels of DSB formation at 30 min post-1cGy irradiation in the irradiated and unirradiated bystander areas were 3-fold and 2-fold higher than those of the sham-irradiated control cells, respectively. Afterwards, the formation of DSBs declined with incubation time and remained steady for at least 6 h at a level that was statistically higher than their controls. The results also showed that the bystander signal derived from irradiated cells could be transferred to anywhere in the dish and the percentage of DSBs in the unirradiated bystander cells was not dependent on the dose delivered. Moreover, the fraction of DSB positive cells in unirradiated bystander areas showed a time-dependent increase based on its distance to the irradiated area at very early stage post-irradiation. Both lindane and DMSO significantly suppressed the yield of DSBs in the cells of unirradiated bystander areas, which suggest that gap junctional intercellular communication and reactive oxygen species played important roles in the induction of the bystander effects, both in irradiated and unirradiated bystander areas.
Carcinogenesis 2006 Feb
PMID:The time and spatial effects of bystander response in mammalian cells induced by low dose radiation. 1615 Aug 94

Despite a clear link between ataxia-telangiectasia mutated (ATM)-dependent phosphorylation of p53 and cell cycle checkpoint control, the intracellular biology and subcellular localization of p53 phosphoforms during the initial sensing of DNA damage is poorly understood. Using G0-G1 confluent primary human diploid fibroblast cultures, we show that endogenous p53, phosphorylated at Ser15 (p53Ser15), accumulates as discrete, dose-dependent and chromatin-bound foci within 30 minutes following induction of DNA breaks or DNA base damage. This biologically distinct subpool of p53Ser15 is ATM dependent and resistant to 26S-proteasomal degradation. p53Ser15 colocalizes and coimmunoprecipitates with gamma-H2AX with kinetics similar to that of biochemical DNA double-strand break (DNA-dsb) rejoining. Subnuclear microbeam irradiation studies confirm p53Ser15 is recruited to sites of DNA damage containing gamma-H2AX, ATM(Ser1981), and DNA-PKcs(Thr2609) in vivo. Furthermore, studies using isogenic human and murine cells, which express Ser15 or Ser18 phosphomutant proteins, respectively, show defective nuclear foci formation, decreased induction of p21WAF, decreased gamma-H2AX association, and altered DNA-dsb kinetics following DNA damage. Our results suggest a unique biology for this p53 phosphoform in the initial steps of DNA damage signaling and implicates ATM-p53 chromatin-based interactions as mediators of cell cycle checkpoint control and DNA repair to prevent carcinogenesis.
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PMID:Evidence for the direct binding of phosphorylated p53 to sites of DNA breaks in vivo. 1632 27


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