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 ATM protein kinase mediates a rapid induction of cellular responses to DNA double strand breaks (DSBs). ATM kinase activity is enhanced immediately after exposure of cells to DSB-inducing agents, but no changes in its amount or subcellular location following that activation have been reported. We speculated that some of the ATM molecules associate with sites of DSBs, while the rest of the nuclear ATM pool remains in the nucleoplasm, masking detection of the damage-associated ATM fraction. Using detergent extraction to remove nucleoplasmic proteins, we show here that immediately following induction of DSBs, a fraction of the ATM pool becomes resistant to extraction and is detected in nuclear aggregates. Colocalization of the retained ATM with the phosphorylated form of histone H2AX (gamma-H2AX) and with foci of the Nbs1 protein suggests that ATM associates with sites of DSBs. The striking correlation between the appearance of retained ATM and of gamma-H2AX, and the rapid association of a fraction of ATM with gamma-H2AX foci, are consistent with a major role for ATM in the early detection of DSBs and subsequent induction of cellular responses.
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PMID:Nuclear retention of ATM at sites of DNA double strand breaks. 1145 56

Mre11 complex promotes repair of DNA double-strand breaks (DSBs). Xenopus Mre11 (X-Mre11) has been cloned, and its role in DNA replication and DNA damage checkpoint studied in cell-free extracts. DSBs stimulate the phosphorylation and 3'-5' exonuclease activity of X-Mre11 complex. This induced phosphorylation is ATM independent. Phosphorylated X-Mre11 is found associated with replicating nuclei. X-Mre11 complex is required to yield normal DNA replication products. Genomic DNA replicated in extracts immunodepleted of X-Mre11 complex accumulates DSBs as demonstrated by TUNEL assay and reactivity to phosphorylated histone H2AX antibodies. In contrast, the ATM-dependent DNA damage checkpoint that blocks DNA replication initiation is X-Mre11 independent. These results strongly suggest that the function of X-Mre11 complex is to repair DSBs that arise during normal DNA replication, thus unraveling a critical link between recombination-dependent repair and DNA replication.
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PMID:Mre11 protein complex prevents double-strand break accumulation during chromosomal DNA replication. 1151 67

A very early step in the response of mammalian cells to DNA double-strand breaks is the phosphorylation of histone H2AX at serine 139 at the sites of DNA damage. Although the phosphatidylinositol 3-kinases, DNA-PK (DNA-dependent protein kinase), ATM (ataxia telangiectasia mutated), and ATR (ATM and Rad3-related), have all been implicated in H2AX phosphorylation, the specific kinase involved has not yet been identified. To definitively identify the specific kinase(s) that phosphorylates H2AX in vivo, we have utilized DNA-PKcs-/- and Atm-/- cell lines and mouse embryonic fibroblasts. We find that H2AX phosphorylation and nuclear focus formation are normal in DNA-PKcs-/- cells and severely compromised in Atm-/- cells. We also find that ATM can phosphorylate H2AX in vitro and that ectopic expression of ATM in Atm-/- fibroblasts restores H2AX phosphorylation in vivo. The minimal H2AX phosphorylation in Atm-/- fibroblasts can be abolished by low concentrations of wortmannin suggesting that DNA-PK, rather than ATR, is responsible for low levels of H2AX phosphorylation in the absence of ATM. Our results clearly establish ATM as the major kinase involved in the phosphorylation of H2AX and suggest that ATM is one of the earliest kinases to be activated in the cellular response to double-strand breaks.
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PMID:ATM phosphorylates histone H2AX in response to DNA double-strand breaks. 1157 Dec 74

H2AX, a member of the histone H2A family, is rapidly phosphorylated in response to ionizing radiation. This phosphorylation, at an evolutionary conserved C-terminal phosphatidylinositol 3-OH-kinase-related kinase (PI3KK) motif, is thought to be critical for recognition and repair of DNA double strand breaks. Here we report that inhibition of DNA replication by hydroxyurea or ultraviolet irradiation also induces phosphorylation and foci formation of H2AX. These phospho-H2AX foci colocalize with proliferating cell nuclear antigen (PCNA), BRCA1, and 53BP1 at the arrested replication fork in S phase cells. This response is ATR-dependent but does not require ATM or Hus1. Our findings suggest that, in addition to its role in the recognition and repair of double strand breaks, H2AX also participates in the surveillance of DNA replication.
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PMID:Histone H2AX is phosphorylated in an ATR-dependent manner in response to replicational stress. 1167 49

Ultraviolet (UV) irradiation produces DNA photoproducts that are blocks to DNA replication by normal replicative polymerases. A specialized, damage-specific, distributive polymerase, Pol H or Pol h, that is the product of the hRad30A gene, is required for replication past these photoproducts. This polymerase is absent from XP variant (XP-V) cells that must employ other mechanisms to negotiate blocks to DNA replication. These mechanisms include the use of alternative polymerases or recombination between sister chromatids. Replication forks arrested by UV damage in virus transformed XP-V cells degrade into DNA double strand breaks that are sites for recombination, but in normal cells arrested forks may be protected from degradation by p53 protein. These breaks are sites for binding a protein complex, hMre11/hRad50/Nbs1, that colocalizes with H2AX and PCNA, and can be visualized as immunofluorescent foci. The protein complexes need phosphorylation to activate their DNA binding capacity. Incubation of UV irradiated XP-V cells with the irreversible kinase inhibitor wortmannin, however, increased the yield of Mre11 focus-positive cells. One interpretation of this observation is that two classes of kinases are involved after UV irradiation. One would be a wortmannin-resistant kinase that phosphorylates the Mre11 complex. The other would be a wortmannin-sensitive kinase that phosphorylates and activates the p53/large T in SV40 transformed XP-V cells. The sensitive class corresponds to the PI3-kinases of ATM, ATR, and DNA-PK, but the resistant class remains to be identified. Alternatively, the elevated yield of Mre11 foci positive cells following wortmannin treatment may reflect an overall perturbation to the signaling cascades regulated by wortmannin-sensitive PI3 related kinases. In this scenario, wortmannin could compromise damage inducible-signaling pathways that maintain the stability of stalled forks, resulting in a further destabilization of stalled forks that then degrade, with the formation of DNA double strand breaks.
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PMID:DNA replication arrest in XP variant cells after UV exposure is diverted into an Mre11-dependent recombination pathway by the kinase inhibitor wortmannin. 1245 48

NFBD1/KIAA0170 is a nuclear factor with an N-terminal FHA (forkhead-associated) domain and a tandem repeat of BRCT (breast cancer susceptibility gene-1 C terminus) domains, both of which are present in a number of proteins involved in DNA repair and/or DNA damage signaling pathways. We have investigated the association of NFBD1 with DNA damage responses. We found that the NFBD1 transcript is abundant in the testis relative to other tissues. NFBD1 is a chromatin-associated protein and is modified in G(2)/M phase or after DNA damage. NFBD1 phosphorylation in response to ionizing radiation (IR) was ATM-dependent. NFBD1 exhibited diffuse nuclear staining in the majority of untreated cells analyzed by indirect immunofluorescence and formed discrete nuclear foci after exposure to IR, UV radiation, and hydroxyurea treatment. IR induced NFBD1 foci within 1 min. The foci colocalized with gamma-H2AX foci, which have been previously shown to localize at sites of DNA double-strand breaks. IR-induced NFBD1 foci also colocalized with 53BP1 and MRE11/RAD50 foci. Taken together, these results suggest that NFBD1 is a mediator of DNA damage-dependent signaling.
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PMID:NFBD1/KIAA0170 is a chromatin-associated protein involved in DNA damage signaling pathways. 1249 69

The ATR kinase phosphorylates both p53 and Chk1 in response to extreme hypoxia (oxygen concentrations of less than 0.02%). In contrast to ATR, loss of ATM does not affect the phosphorylation of these or other targets in response to hypoxia. However, hypoxia within tumors is often transient and is inevitably followed by reoxygenation. We hypothesized that ATR activity is induced under hypoxic conditions because of growth arrest and ATM activity increases in response to the oxidative stress of reoxygenation. Using the comet assay to detect DNA damage, we find that reoxygenation induced significant amounts of DNA damage. Two ATR/ATM targets, p53 serine 15 and histone H2AX, were both phosphorylated in response to hypoxia in an ATR-dependent manner. These phosphorylations were then maintained in response to reoxygenation-induced DNA damage in an ATM-dependent manner. The reoxygenation-induced p53 serine 15 phosphorylation was inhibited by the addition of N-acetyl-l-cysteine (NAC), indicating that free radical-induced DNA damage was mediated by reactive oxygen species. Taken together these data implicate both ATR and ATM as critical roles in the response of hypoxia and reperfusion in solid tumors.
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PMID:ATR/ATM targets are phosphorylated by ATR in response to hypoxia and ATM in response to reoxygenation. 1251 69

The Mre11 complex undergoes dramatic relocalization in the nuclei of gamma-irradiated and replicating human cells. In this study, we examined Mre11 complex localization and chromatin association in synchronous cultures to examine the molecular determinants of relocalization. The data indicate that the complex is deposited on chromatin in an S phase-specific manner. Mre11 complex chromatin association in S phase was resistant to detergent extraction, in contrast to that in gamma-irradiated cells. The complex exhibits extensive colocalization with proliferating cell nuclear antigen throughout S phase, and chromatin loading is enhanced by replication fork stalling, suggesting that the replication fork is a site of Mre11 complex chromatin loading. This is supported by the observation that the complex localized to single-stranded DNA arising in hydroxyurea-treated cells. Although the Mre11 complex appears to function as a DNA damage sensor, limited colocalization with Brca1 or gamma-H2AX was observed, arguing that neither DNA damage nor gamma-H2AX is required for Mre11 complex chromatin loading. These data provide a potential molecular basis for promotion of sister chromatid association and recombination by the Mre11 complex as well as for ATM-Mre11 complex-dependent activation of cell cycle checkpoints.
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PMID:DNA replication-dependent nuclear dynamics of the Mre11 complex. 1255 60

MRE11, RAD50 and NBS1 form a highly conserved protein complex (the MRE11 complex) that is involved in the detection, signalling and repair of DNA damage. We identify MDC1 (KIAA0170/NFBD1), a protein that contains a forkhead-associated (FHA) domain and two BRCA1 carboxy-terminal (BRCT) domains, as a binding partner for the MRE11 complex. We show that, in response to ionizing radiation, MDC1 is hyperphosphorylated in an ATM-dependent manner, and rapidly relocalizes to nuclear foci that also contain the MRE11 complex, phosphorylated histone H2AX and 53BP1. Downregulation of MDC1 expression by small interfering RNA yields a radio-resistant DNA synthesis (RDS) phenotype and prevents ionizing radiation-induced focus formation by the MRE11 complex. However, downregulation of MDC1 does not abolish the ionizing radiation-induced phosphorylation of NBS1, CHK2 and SMC1, or the degradation of CDC25A. Furthermore, we show that overexpression of the MDC1 FHA domain interferes with focus formation by MDC1 itself and by the MRE11 complex, and induces an RDS phenotype. These findings reveal that MDC1-mediated focus formation by the MRE11 complex at sites of DNA damage is crucial for the efficient activation of the intra-S-phase checkpoint.
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PMID:MDC1 is required for the intra-S-phase DNA damage checkpoint. 1260 3

53BP1 participates in the cellular response to DNA damage. Like many proteins involved in the DNA damage response, 53BP1 becomes hyperphosphorylated after radiation and colocalizes with phosphorylated H2AX in megabase regions surrounding the sites of DNA strand breaks. However, it is not yet clear whether the phosphorylation status of 53BP1 determines its localization or vice versa. In this study we mapped a region upstream of the 53BP1 C terminus that is required and sufficient for the recruitment of 53BP1 to these DNA break areas. In vitro assays revealed that this region binds to phosphorylated but not unphosphorylated H2AX. Moreover, using H2AX-deficient cells reconstituted with wild-type or a phosphorylation-deficient mutant of H2AX, we have shown that phosphorylation of H2AX at serine 140 is critical for efficient 53BP1 foci formation, implying that a direct interaction between 53BP1 and phosphorylated H2AX is required for the accumulation of 53BP1 at DNA break sites. On the other hand, radiation-induced phosphorylation of the 53BP1 N terminus by the ATM (ataxia-telangiectasia mutated) kinase is not essential for 53BP1 foci formation and takes place independently of 53BP1 redistribution. Thus, these two damage-induced events, hyperphosphorylation and relocalization of 53BP1, occur independently in the cell.
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PMID:Accumulation of checkpoint protein 53BP1 at DNA breaks involves its binding to phosphorylated histone H2AX. 1269 68


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