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)

Telomestatin is a potent G-quadruplex ligand that interacts with the 3' telomeric overhang, leading to its degradation, and induces a delayed senescence and apoptosis of cancer cells. POT1 and TRF2 were recently identified as specific telomere-binding proteins involved in telomere capping and t-loop maintenance and whose interaction with telomeres is modulated by telomestatin. We show here that the treatment of HT1080 human tumor cells by telomestatin induces a rapid decrease of the telomeric G-overhang and of the double-stranded telomeric repeats. Telomestatin treatment also provokes a strong decrease of POT1 and TRF2 from their telomere sites, suggesting that the ligand triggers the uncapping of the telomere ends. The effect of the ligand is associated with an increase of the gamma-H2AX foci, one part of them colocalizing at telomeres, thus indicating the occurrence of a DNA damage response at the telomere, but also the presence of additional DNA targets for telomestatin. Interestingly, the expression of GFP-POT1 in HT1080 cells increases both telomere and G-overhang length. As compared with HT1080 cells, HT1080GFP-POT1 cells presented a resistance to telomestatin treatment characterized by a protection to the telomestatin-induced growth inhibition and the G-overhang shortening. This protection is related to the initial G-overhang length rather than to its degradation rate and is overcome by increased telomestatin concentration. Altogether these results suggest that telomestatin induced a telomere dysfunction in which G-overhang length and POT1 level are important factors but also suggest the presence of additional DNA sites of action for the ligand.
J Biol Chem 2006 Dec 15
PMID:Telomestatin-induced telomere uncapping is modulated by POT1 through G-overhang extension in HT1080 human tumor cells. 1705 May 46

The presence of internal tandem duplications (ITD) mutations in the FMS-like tyrosine kinase 3 (FLT3) receptor influences the risk of relapse in acute myeloid leukaemia (AML). We have investigated DNA repair in FLT3-ITD and wild-type (WT) cells. Using the comet assay, we have demonstrated that the FLT3 inhibitor PKC412 significantly inhibits repair of DNA damage in the MV4-11-FLT3-ITD cell line and FLT3-ITD patient samples but not in the HL-60-FLT3-WT cell line or FLT3-WT patient samples. Following the discovery that transcript levels of the DNA repair gene RAD51 are significantly correlated with FLT3 transcript levels in FLT3-ITD patients, we further investigated the role of RAD51 in FLT3-ITD-AML. The reduction in DNA repair in PKC412-treated FLT3-ITD cells was shown to be associated with downregulation of RAD51 mRNA and protein expression and correlates with the maintenance of phosphorylated H2AX levels, implying that PKC412 inhibits the homologous recombination double-strand break repair pathway in FLT3-ITD cells. Using FLT3-short interfering RNA (siRNA), we also demonstrated that genetic silencing of FLT3 results in RAD51 downregulation in FLT3-ITD cells but not in FLT3-WT cells. This work suggests that the use of FLT3 inhibitors such as PKC412 may reverse the drug-resistant phenotype of FLT3-ITD-AML cells by inhibiting repair of chemotherapy-induced genotoxic damage and thereby reduce the risk of disease relapse.
Leukemia 2006 Dec
PMID:DNA repair contributes to the drug-resistant phenotype of primary acute myeloid leukaemia cells with FLT3 internal tandem duplications and is reversed by the FLT3 inhibitor PKC412. 1706 94

Histone deacetylases (HDAC) have been identified as therapeutic targets due to their regulatory function in DNA structure and organization. LBH589 is a novel inhibitor of class I and II HDACs. We studied the effect of LBH589 and ionizing radiation (IR) on DNA repair in two human non-small cell lung cancer (NSCLC) cell lines (H23 and H460). gamma-H2AX foci present at DNA double-strand breaks (DSBs) were detected in the nuclei following 3 Gy irradiation for up to 6 hours. LBH589 administered before irradiation increased the duration of gamma-H2AX foci beyond 24 hours. Furthermore, radiation alone induced translocation of HDAC4 to the nucleus. In contrast, treatment with LBH589 followed by irradiation resulted in HDAC4 confinement to the cytoplasm, indicating that HDAC inhibition affects the nuclear localization of HDAC4. The findings that LBH589 confines HDAC4 to the cytoplasm and increases the duration of gamma-H2AX foci in irradiated cell lines suggest that HDAC4 participates in DNA damage signaling following IR. Annexin-propidium iodide flow cytometry assays, cell morphology studies, and cleaved caspase-3 Western blot analysis revealed a synergistic effect of LBH589 with IR in inducing apoptosis. Clonogenic survival showed a greater than additive effect when LBH589 was administered before irradiation compared with irradiation alone. In vivo tumor volume studies showed a growth delay of 20 days with combined treatment compared with 4 and 2 days for radiation or LBH589 alone. This study identifies HDAC4 as a biomarker of LBH589 activity and recognizes the ability of LBH589 to sensitize human NSCLC to radiation-induced DNA DSBs.
Cancer Res 2006 Dec 01
PMID:Histone deacetylase (HDAC) inhibitor LBH589 increases duration of gamma-H2AX foci and confines HDAC4 to the cytoplasm in irradiated non-small cell lung cancer. 1714 76

Here we document the role of MDC1 (mediator of DNA damage checkpoint 1) in the detection and repair of human and mouse telomeres rendered dysfunctional through inhibition of TRF2. Consistent with its role in promoting DNA damage foci, MDC1 knockdown affected the formation of telomere dysfunction-induced foci (TIFs), diminishing the accumulation of phosphorylated ATM, 53BP1, Nbs1, and to a lesser extent, gamma-H2AX. In addition to this effect on TIFs, the rate of nonhomologous end-joining (NHEJ) of dysfunctional telomeres was significantly decreased when MDC1 itself or its recruitment to chromatin was inhibited. MDC1 appeared to promote a step in the NHEJ pathway after the removal of the 3' telomeric overhang. The acceleration of NHEJ was unlikely to be due to increased presence of 53BP1 and Mre11 in TIFs, since knockdown of neither factor affected telomere fusions. Furthermore, relevant cell cycle effectors (Chk2, p53, and p21) of the ATM kinase pathway were unaffected and there was no change in the rate of cell cycle progression. We propose that the binding of MDC1 to gamma-H2AX directly affects NHEJ in a manner that is independent of the ATM-dependent cell cycle arrest pathway.
Genes Dev 2006 Dec 01
PMID:MDC1 accelerates nonhomologous end-joining of dysfunctional telomeres. 1715 42

The mechanisms of the medium-mediated bystander response induced by gamma-rays in non-irradiated TK6 cells were investigated. Cell cultures were irradiated and the culture medium discarded immediately after irradiation and replaced with a fresh one. In cells incubated with conditioned medium from irradiated cells (CM), a significant decrease in cell viability and cloning efficiency was observed, together with a significant increase in apoptosis, also in directly irradiated cells. To examine whether bystander apoptosis involved the extrinsic pathway, an inhibitor of caspase-8 was added to CM cultures, which significantly decreased apoptosis to control levels. The addition to CM of ROS scavengers, Cu-Zn superoxide dismutase and N-acetylcysteine did not affect the induction of apoptosis. To assess whether CM treatment activates a DNA damage response, also the formation of gamma-H2AX foci, as markers of double-strand breaks and their colocalisation with 53-binding protein 1 (53BP1) and the protein mutated in the Nijmegen breakage syndrome 1 (NBS1) was analysed. In cultures treated for 2h with CM, 9-11% of cells showed gamma-H2AX foci, which partially or totally lacked colocalisation with 53BP1 and NBS1 foci. About 85% of irradiated cells were positive for gamma-H2AX foci, which colocalised with 53BP1 and NBS1 proteins. At 24h from irradiation, very few irradiated cells retained foci, fitting DNA repair kinetics. The number of foci-positive bystander cells also decreased to background values 24h after CM incubation. Our results suggest that irradiated TK6 cells release into the medium some soluble factors, not ROS, which are responsible for the cytotoxic effects induced in bystander cells. In our experimental system, the role of ROS appeared to be of minor importance in inducing cell mortality, but probably critical in activating the DNA damage response in the responsive fraction of bystander cells.
Mutat Res 2007 Dec 01
PMID:Bystander response in human lymphoblastoid TK6 cells. 1766 38

The detrimental effects of preconceptional paternal exposure to the alkylating anticancer agent, cyclophosphamide, include aberrant epigenetic programming, dysregulated zygotic gene activation, and abnormalities in the offspring that are transmitted to the next generation. The adverse developmental consequences of genomic instabilities transmitted via the spermatozoon emphasize the need to elucidate the mechanisms by which the early embryo recognizes DNA damage in the paternal genome. Little information exists on DNA damage detection in the zygote. We assessed the impact of paternal cyclophosphamide exposure on phosphorylated H2AX (gammaH2AX) and poly(ADP-ribose) polymerase-1(PARP-1), biomarkers of DNA damage, to determine the capacity in the rat zygote to recognize genomic damage and initiate a response to DNA lesions. An amplified biphasic gammaH2AX response was triggered in the paternal pronucleus in zygotes sired by drug-treated males; the maternal genome was not affected. PARP-1 immunoreactivity was substantially elevated in both parental genomes, coincident with the second phase of gammaH2AX induction in embryos sired by cyclophosphamide-exposed spermatozoa. Thus, paternal exposure to a DNA damaging agent rapidly activates signals implemental for DNA damage recognition in the zygote. Inefficient repair of DNA lesions may lead to persistent alterations of the histone code and chromatin integrity, resulting in aberrant embryogenesis. We propose that the response of the early embryo to disturbances in spermatozoal genomic integrity plays a vital role in determining its outcome.
Toxicol Sci 2007 Dec
PMID:DNA damage recognition in the rat zygote following chronic paternal cyclophosphamide exposure. 1787 95

The cellular response to DNA damage involves extensive interaction with and manipulation of chromatin. This includes the detection and repair of the DNA lesion, but there are also transcriptional responses to DNA damage, involving the up- or down-regulation of numerous genes. Therefore changes to chromatin structure, including covalent modification of histone proteins, are known to occur during DNA-damage responses. One of the most well characterized DNA-damage-responsive chromatin modification events is the phosphorylation of the SQ motif found in the C-terminal tail of histone H2A or the H2AX variant in higher eukaryotes. In the budding yeast, a number of additional residues in this region of histone H2A that contribute to the cellular response to DNA damage have been identified, providing an insight into the nature and complexity of the DNA-damage histone code.
Biochem Soc Trans 2007 Dec
PMID:The contribution of the budding yeast histone H2A C-terminal tail to DNA-damage responses. 1803 Dec 58

Carbon nanotubes (CNTs) have shown promise as an important new class of multifunctional building blocks and innovative tools in a large variety of applications, ranging from nanocomposite materials through nanoelectronics to biomedical devices. Because of their unusual one-dimensional hollow nanostructure and unique physicochemical properties, CNTs are particularly useful as novel drug delivery tools and imaging agents. However, such biomedical applications will not be realized if there is no proper assessment of the potential hazards of CNTs to humans and other biological systems. Although a few reports on the cytotoxicity of CNTs have been published, very little is known about the toxicity at the molecular level, or genotoxicity, of CNTs in mammalian cells. We have for the first time assessed the DNA damage response to multiwalled carbon nanotubes (MWNTs) in mouse embryonic stem (ES) cells. We found that MWNTs can accumulate and induce apoptosis in mouse ES cells and activate the tumor suppressor protein p53 within 2 h of exposure. Furthermore, we also observed increased expression of two isoforms of base excision repair protein 8-oxoguanine-DNA glycosylase 1 (OGG1), double strand break repair protein Rad 51, phosphorylation of H2AX histone at serine 139, and SUMO modification of XRCC4 following the treatment with MWNTs. A mutagenesis study using an endogenous molecular marker, adenine phosphoribosyltransferase (Aprt), showed that MWNTs increased the mutation frequency by 2-fold compared with the spontaneous mutation frequency in mouse ES cells. These results suggest that careful scrutiny of the genotoxicity of nanomaterials is needed even for those materials, like multiwalled carbon nanotubes, that have been previously demonstrated to have limited or no toxicity at the cellular level.
Nano Lett 2007 Dec
PMID:DNA damage induced by multiwalled carbon nanotubes in mouse embryonic stem cells. 1804 46

Defects in the detection and repair of DNA double-strand breaks (DSBs) have been causatively linked to tumourigenesis. Moreover, inhibition of DNA damage responses (DDR) can increase the efficacy of cancer therapies that rely on generation of damaged DNA. DDR must occur within the context of chromatin, and there have been significant advances in recent years in understanding how the modulation and manipulation of chromatin contribute to this activity. One particular covalent modification of a histone variant--the phosphorylation of H2AX--has been investigated in great detail and has been shown to have important roles in DNA DSB responses and in preventing tumourigenesis. These studies are reviewed here in the context of their relevance to cancer therapy and diagnostics. In addition, there is emerging evidence for contributions by proteins involved in mediating higher order structure to DNA DSB responses. The contributions of a subset of these proteins--linker histones and high-mobility group box (HMGB) proteins--to DDR and their potential significance in tumourigenesis are discussed.
Oncogene 2007 Dec 10
PMID:Chromatin structure and DNA double-strand break responses in cancer progression and therapy. 1806 89

Camptothecin (CPT) analogues are powerful anticancer agents but are chemically unstable due to their alpha-hydroxylactone six-membered E-ring structure, which is essential for trapping topoisomerase I (Top1)-DNA cleavage complexes. To stabilize the E-ring, CPT keto analogues with a five-membered E-ring lacking the oxygen of the lactone ring (S38809 and S39625) have been synthesized. S39625 has been selected for advanced preclinical development based on its promising activity in tumor models. Here, we show that both keto analogues are active against purified Top1 and selective against Top1 in yeast and human cancer cells. The keto analogues show improved cytotoxicity toward colon, breast, and prostate cancer cells and leukemia cells compared with CPT. The drug-induced Top1-DNA cleavage complexes induced by the keto analogues show remarkable persistence both with purified Top1 and in cells following 1-h drug treatments. Moreover, we find that S39625 is not a substrate for either the ABCB1 (multidrug resistance-1/P-glycoprotein) or ABCG2 (mitoxantrone resistance/breast cancer resistance protein) drug efflux transporters, which sets S39625 apart from the clinically used CPT analogues topotecan or SN-38 (active metabolite of irinotecan). Finally, we show that nanomolar concentrations of S38809 or S39625 induce intense and persistent histone gamma-H2AX. The chemical stability of the keto analogues and the ability of S39625 to produce high levels of persistent Top1-DNA cleavage complex and its potent antiproliferative activity against human cancer cell lines make S39625 a promising new anticancer drug candidate. Histone gamma-H2AX could be used as a biomarker for the upcoming clinical trials of S39625.
Mol Cancer Ther 2007 Dec
PMID:Novel E-ring camptothecin keto analogues (S38809 and S39625) are stable, potent, and selective topoisomerase I inhibitors without being substrates of drug efflux transporters. 1808 16


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