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)

Induction of apoptosis is pivotal for eliminating cells with damaged DNA or deregulated proliferation. We show that tumor suppressor ARF and ATM/ATR kinase pathways cooperate in the induction of apoptosis in response to elevated expression of c-myc, beta-catenin or human papilloma virus E7 oncogenes. Overexpression of oncogenes leads to the formation of phosphorylated H2AX foci, induction of Rad51 protein levels and ATM/ATR-dependent phosphorylation of p53. Inhibition of ATM/ATR kinases abolishes both induction of Rad51 and phosphorylation of p53, and remarkably reduces the level of apoptosis induced by co-expression of oncogenes and ARF. However, the induction of apoptosis is downregulated in p53-/- cells and does not depend on activities of ATM/ATR kinases, indicating that efficient induction of apoptosis by oncogene activation depends on coordinated action of ARF and ATM/ATR pathways in the regulation of p53.
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PMID:ARF and ATM/ATR cooperate in p53-mediated apoptosis upon oncogenic stress. 1600 68

Atypical retinoids are potent inducers of apoptosis, but activation of the apoptotic pathway seems to be independent of retinoid receptors. Previous studies with a novel adamantyl retinoid, ST1926, have shown that apoptosis induction is associated with an early genotoxic stress. To better understand the relevance of these events, we have selected a subline of the H460 lung carcinoma cell line resistant to ST1926. Resistant cells exhibited cross-resistance to a related molecule, CD437, but not cross-resistance to agents with different mechanisms of action. In spite of a lack of defects in intracellular drug accumulation, induction of DNA strand breaks in resistant cells required exposure to a substantially higher concentration, which was consistent with the degree of resistance. At drug concentrations causing a similar antiproliferative effect (IC80) and a comparable extent of DNA lesions in sensitive and resistant cells, the apoptotic response was a delayed and less marked event in resistant cells, thus indicating a reduced susceptibility to apoptosis. In spite of recognition of DNA lesions in resistant cells, as supported by phosphorylation of p53 and histone H2AX, resistant cells exhibited no activation of the mitochondrial pathways of apoptosis. Following exposure to equitoxic drug concentrations, only sensitive cells exhibited a typical stress/DNA damage response, with activation of the S-phase checkpoint. The cellular resistance to ST1926 reflects alterations responsible for a reduced generation of DNA lesions and for an enhanced tolerance of the genotoxic stress, resulting in lack of activation of the intrinsic pathway of apoptosis. The defective DNA damage response, accompanied by a reduced susceptibility to apoptosis in resistant cells, provides further support to the involvement of genotoxic stress as a critical event in mediating apoptosis induction by ST1926.
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PMID:Development of resistance to the atypical retinoid, ST1926, in the lung carcinoma cell line H460 is associated with reduced formation of DNA strand breaks and a defective DNA damage response. 1602 46

2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC) is a nucleoside analogue with a novel mechanism of action that is currently being evaluated in clinical trials. Incorporation of CNDAC triphosphate into DNA and extension during replication leads to single-strand breaks directly caused by beta-elimination. These breaks, or the lesions that arise from further processing, cause cells to arrest in G2. The purpose of this investigation was to define the molecular basis for G2 checkpoint activation and to delineate the sequelae of its abrogation. Cell lines derived from diverse human tissues underwent G2 arrest after CNDAC treatment, suggesting a common mechanism of response to the damage created. CNDAC-induced G2 arrest was instituted by activation of the Chk1-Cdc25C-Cdk1/cyclin B checkpoint pathway. Neither Chk2, p38, nor p53 was required for checkpoint activation. Inhibition of Chk1 kinase with 7-hydroxystaurosporine (UCN-01) abrogated the checkpoint pathway as indicated by dephosphorylation of checkpoint proteins and progression of cells through mitosis and into G1. Cell death was first evident in hematologic cell lines after G1 entry. As indicated by histone H2AX phosphorylation, DNA damage initiated by CNDAC incorporation was transformed into double-strand breaks when ML-1 cells arrested in G2. Some breaks were manifested as chromosomal aberrations when the G2 checkpoint of CNDAC-arrested cells was abrogated by UCN-01 but also in a minor population of cells that escaped to mitosis during treatment with CNDAC alone. These findings provide a mechanistic rationale for the design of new strategies, combining CNDAC with inhibitors of cell cycle checkpoint regulation in the therapy of hematologic malignancies.
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PMID:Molecular basis for G2 arrest induced by 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine and consequences of checkpoint abrogation. 1606 71

The phytochemical indole-3-carbinol (I3C), from cruciferous vegetables such as broccoli, has been shown to elicit a potent anti-proliferative response in human breast cancer cell lines. Treatment of the immortalized human mammary epithelial cell line MCF10A with I3C induced a G1 cell cycle arrest, elevated p53 tumor suppressor protein levels and stimulated expression of downstream transcriptional target, p21. I3C treatment also elevated p53 levels in several breast cancer cell lines that express mutant p53. I3C did not arrest MCF10A cells stably transfected with dominant-negative p53, establishing a functional requirement for p53. Cell fractionation and immunolocalization studies revealed a large fraction of stabilized p53 protein in the nucleus of I3C-treated MCF10A cells. With I3C treatment, phosphatidyl-inositol-3-kinase family member ataxia telangiectasia-mutated (ATM) was phosphorylated, as were its substrates p53, CHK2 and BRCA1. Phosphorylation of p53 at the N-terminus has previously been shown to disrupt the interaction between p53 and its ubiquitin ligase, MDM2, and therefore stabilizing p53. Coimmunoprecipitation analysis revealed that I3C reduced by 4-fold the level of MDM2 protein that associated with p53. The p53-MDM2 interaction and absence of p21 production were restored in cells treated with I3C and the ATM inhibitor wortmannin. Significantly, I3C does not increase the number of 53BP1 foci or H2AX phosphorylation, indicating that ATM is activated independent of DNA double-strand breaks. Taken together, our results demonstrate that I3C activates ATM signaling through a novel pathway to stimulate p53 phosphorylation and disruption of the p53-MDM2 interaction, which releases p53 to induce the p21 CDK inhibitor and a G1 cell cycle arrest.
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PMID:Indole-3-carbinol activates the ATM signaling pathway independent of DNA damage to stabilize p53 and induce G1 arrest of human mammary epithelial cells. 1615 27

A variant of histone H2A, H2AX, is phosphorylated on Ser139 in response to DNA double-strand breaks (DSBs), and clusters of the phosphorylated form of H2AX (gamma-H2AX) in nuclei of DSB-induced cells show foci at breakage sites. Here, we show phosphorylation of H2AX in a cell cycle-dependent manner without any detectable DNA damage response. Western blot and immunocytochemical analyses with the anti-gamma-H2AX antibody revealed that H2AX is phosphorylated at M phase in HeLa cells. In ataxia-telangiectasia cells lacking ATM kinase activity, gamma-H2AX was scarcely detectable in the mitotic chromosomes, suggesting involvement of ATM in M-phase phosphorylation of H2AX. Single-cell gel electrophoresis assay and Western blot analysis with the anti-phospho-p53 (Ser15) antibody indicated that H2AX in human M-phase cells is phosphorylated independently of DSB and DNA damage signaling. Even in the absence of DNA damage, phosphorylation of H2AX in normal cell cycle progression may contribute to maintenance of genomic integrity.
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PMID:Phosphorylation of histone H2AX at M phase in human cells without DNA damage response. 1615 2

Mitotic catastrophe occurs as a result of the uncoupling of the onset of mitosis from the completion of DNA replication, but precisely how the ensuing lethality is regulated or what signals are involved is largely unknown. We demonstrate here the essential role of the ATM/ATR-p53 pathway in mitotic catastrophe from premature mitosis. Chk1 deficiency resulted in a premature onset of mitosis because of abnormal activation of cyclin B-Cdc2 and led to the activation of caspases 3 and 9 triggered by cytoplasmic release of cytochrome c. This deficiency was associated with foci formation by the phosphorylated histone, H2AX (gammaH2AX), specifically at S phase. Ectopic expression of Cdc2AF, a mutant that cannot be phosphorylated at inhibitory sites, also induced premature mitosis and foci formation by gammaH2AX at S phase in both embryonic stem cells and HCT116 cells. Depletion of ATM and ATR protected against cell death from premature mitosis. p53-deficient cells were highly resistant to lethality from premature mitosis as well. Our results therefore suggest that ATM/ATR-p53 is required for mitotic catastrophe that eliminates cells escaping Chk1-dependent mitotic regulation. Loss of this function might be important in mammalian tumorigenesis.
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PMID:Depletion of Chk1 leads to premature activation of Cdc2-cyclin B and mitotic catastrophe. 1615 83

on-homologous end joining (NHEJ) and homologous recombination (HR) are pathways that repair DNA double-strand breaks (DSBs). In Saccharomyces cerevisiae, the repair of these breaks is influenced by histone acetylation. Therefore, we tested mammalian cells deleted for NHEJ (Ku80 or DNA Ligase IV) or altered for HR (breast cancer associated gene, Brca2, or Bloom's syndrome, Blm) for sensitivity to trichostatin A (TSA), a histone deacetylase inhibitor that is being investigated as an anti-cancer therapeutic. We show that cells mutated for Ku80 (ku80-/-) or DNA Ligase IV (lig 4-/-), but not cells mutated for Brca2 (brca2lex1/lex2) or Blm (blm(tm3Brd/tm4Brd)), are hypersensitive to TSA in a dose-dependent manner. TSA-induced toxicity stimulates apoptosis and cell cycle checkpoint responses independent of p53, but does not increase phosphorylated histone H2AX (-H2AX) as compared with a clastogenic agent, camptothecin, indicating that the quantity of DSBs is not the primary cause of TSA-induced cell death. In addition, we show that potential anti-cancer drugs (LY-294002 and vanillin) that inhibit the family of phosphatidylinositol 3 kinases that include the NHEJ protein, DNA-PKCS act in synergy with TSA to reduce the viability of HeLa cells in tissue culture presenting the possibility of using the two drugs in combination to treat cancer.
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PMID:Non-homologous end joining, but not homologous recombination, enables survival for cells exposed to a histone deacetylase inhibitor. 1617 81

p53 binding protein 1 (53BP1) is a putative DNA damage sensor that accumulates at sites of double-strand breaks (DSBs) in a manner dependent on histone H2AX. Here we show that the loss of one or both copies of 53BP1 greatly accelerates lymphomagenesis in a p53-null background, suggesting that 53BP1 and p53 cooperate in tumor suppression. A subset of 53BP1-/- p53-/- lymphomas, like those in H2AX-/- p53-/- mice, were diploid and harbored clonal translocations involving antigen receptor loci, indicating misrepair of DSBs during V(D)J recombination as one cause of oncogenic transformation. Loss of a single 53BP1 allele compromised genomic stability and DSB repair, which could explain the susceptibility of 53BP1+/- mice to tumorigenesis. In addition to structural aberrations, there were high rates of chromosomal missegregation and accumulation of aneuploid cells in 53BP1-/- p53+/+ and 53BP1-/- p53-/- tumors as well as in primary 53BP1-/- splenocytes. We conclude that 53BP1 functions as a dosage-dependent caretaker that promotes genomic stability by a mechanism that preserves chromosome structure and number.
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PMID:53BP1 cooperates with p53 and functions as a haploinsufficient tumor suppressor in mice. 1626 Jun 21

Juglone (5-hydroxy-1,4-naphtoquinone) is a natural toxin produced by walnut trees. In this study we show that juglone differentially reduces viability of human cells in culture. Normal fibroblast were found to be especially sensitive to juglone and lost viability primarily through a rapid apoptotic and necrotic response. This response may have been triggered by DNA damage since juglone induced a rapid and strong phosphorylation of H2AX in all phases of the cell cycle. Furthermore, juglone inhibits mRNA synthesis in human fibroblasts in a dose-dependent manner. Surprisingly, juglone caused a drastic reduction of the basal level of p53 in human fibroblasts and this loss could not be fully rescued by proteasome and calpain I inhibitors. However, when cells were pretreated with UV light or ionizing radiation, juglone was not able to reduce the cellular levels of activated p53. Our results show that juglone has multiple effects on cells such as the induction of DNA damage, inhibition of transcription, reduction of p53 protein levels and the induction of cell death.
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PMID:The natural toxin juglone causes degradation of p53 and induces rapid H2AX phosphorylation and cell death in human fibroblasts. 1627 20

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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