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)

Nijmegen breakage syndrome is a recessive genetic disorder, characterized by elevated sensitivity to ionizing radiation, chromosome instability and high frequency of malignancies. Since cellular features partly overlap with those of ataxia-telangiectasia (A-T), NBS was long considered an A-T clinical variant. NBS1, the product of the gene underlying the disease, contains three functional regions: the forkhead-associated (FHA) domain and BRCA1 C-terminus (BRCT) domain at the N-terminus, several SQ motifs (consensus phosphorylation sites by ATM and ATR kinases) at a central region and MRE11-binding region at the C-terminus. NBS1 forms a multimeric complex with hMRE11/hRAD50 nuclease at the C-terminus and recruits or retains them at the vicinity of sites of DNA damage by direct binding to histone H2AX, which is phosphorylated by ATM in response to DNA damage. The combination of the FHA/BRCT domains has a crucial role for the binding of NBS1 to H2AX. Thereafter, the NBS1 complex proceeds to rejoin double-strand breaks predominantly by homologous recombination repair in vertebrates, while it also might be involved in suppression of inter-chromosomal recombination even for V(D)J recombination. These processes collaborate with cell cycle checkpoints to facilitate DNA repair, while defects of these checkpoints in NBS cells are partial in nature. A possible explanation for these moderate defects are the redundancy of multiple checkpoint regulations in vertebrates, or the modulator role of NBS1, in which NBS1 amplifies ATM activation by accumulation of the MRN complex at damaged sites. This molecular link of NBS1 to ATM may explain the phenotypic similarity of NBS to A-T.
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PMID:NBS1 and its functional role in the DNA damage response. 1527 70

Bloom's syndrome is a rare autosomal recessive genetic disorder characterized by chromosomal aberrations, genetic instability, and cancer predisposition, all of which may be the result of abnormal signal transduction during DNA damage recognition. Here, we show that BLM is an intermediate responder to stalled DNA replication forks. BLM colocalized and physically interacted with the DNA damage response proteins 53BP1 and H2AX. Although BLM facilitated physical interaction between p53 and 53BP1, 53BP1 was required for efficient accumulation of both BLM and p53 at the sites of stalled replication. The accumulation of BLM/53BP1 foci and the physical interaction between them was independent of gamma-H2AX. The active Chk1 kinase was essential for both the accurate focal colocalization of 53BP1 with BLM and the consequent stabilization of BLM. Once the ATR/Chk1- and 53BP1-mediated signal from replicational stress is received, BLM functions in multiple downstream repair processes, thereby fulfilling its role as a caretaker tumor suppressor.
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PMID:Functional interaction between BLM helicase and 53BP1 in a Chk1-mediated pathway during S-phase arrest. 1536 58

In eukaryotic cells, DNA double strand breaks (DSBs) cause the prompt phosphorylation of serine 139 at the carboxy terminus of histone H2AX to generate gamma-H2AX, detectable by Western blotting or immunofluorescence. The consensus sequence at the phosphorylation site implicates the phosphatidylinositol 3-like family of protein kinases in H2AX phosphorylation. It remains open whether ATM (ataxia telangiectasia mutated) is the major H2AX kinase, or whether other members of the family, such as DNA-PK (DNA dependent protein kinase) or ATR (ATM and Rad3 related), contribute in a functionally complementary manner. To address this question, we measured global H2AX phosphorylation in cell lysates and foci formation in individual cells of either wild type or mutant (ATM or DNA-PK) genetic background. Normal global phosphorylation kinetics is observed after irradiation in cells defective either in ATM or DNA-PK alone, suggesting a complementary contribution to H2AX phosphorylation. This is further supported by the observation that initial H2AX phosphorylation is delayed when both kinases are inhibited by wortmannin, as well as when ATM is inhibited by caffeine in DNA-PK deficient cells. However, robust residual global phosphorylation is detectable under all conditions of genetic or chemical inhibition suggesting the function of additional kinases, such as ATR. Treatment with wortmannin, caffeine, or UCN-01 produces a strong DNA-PK dependent late global hyperphosphorylation of H2AX, uncoupled from DNA DSB rejoining and compatible with an inhibition of late steps in DNA DSB processing. Evaluation of gamma-H2AX foci formation confirms the major conclusions made on the basis of global H2AX phosphorylation, but also points to differences particularly several hours after exposure to IR. The results in aggregate implicate DNA-PK, ATM and possibly other kinases in H2AX phosphorylation. The functional significance and the mechanisms of coordination in space and time of these multiple inputs require further investigation.
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PMID:Complex H2AX phosphorylation patterns by multiple kinases including ATM and DNA-PK in human cells exposed to ionizing radiation and treated with kinase inhibitors. 1538 85

Cell cycle arrest in response to environmental effects can lead to DNA breaks. We investigated whether inhibition of DNA replication during the initiation step can lead to DNA damage and characterised a cell-cycle-arrest point at the replication initiation step before the establishment of active replication forks. This arrest can be elicited by the iron chelators mimosine, ciclopirox olamine or 2,2'-bipyridyl, and can be reversed by the removal of the drugs or the addition of excess iron. Iron depletion induces DNA double-strand breaks in treated cells, and activates a DNA damage response that results in focal phosphorylation of histone H2AX, focal accumulation of replication protein A (RPA) and ATR (ATM and Rad3-related kinase), and activation of CHK1 kinase. Abrogation of the checkpoint response does not abolish the cell cycle arrest before the establishment of active DNA replication forks. DNA breaks appear concomitantly with the arrival of cells at the arrest point and persist upon release from the cell cycle block. We conclude that DNA double-strand breaks are the consequence, and not the cause, of cell cycle arrest during the initiation step of DNA replication by iron chelation.
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PMID:Cell cycle arrest at the initiation step of human chromosomal DNA replication causes DNA damage. 1545 44

In mammalian spermatogenesis, the X and Y chromosomes are transcriptionally silenced during the pachytene stage of meiotic prophase (meiotic sex chromosome inactivation, MSCI), forming a condensed chromatin domain termed the sex or XY body. The nucleosomal core histone H2AX is phosphorylated within the XY chromatin domain just prior to MSCI, and it has been hypothesized that this triggers the chromatin condensation and transcriptional repression. Here, we show that the kinase ATR localizes to XY chromatin at the onset of MSCI and that this localization is disrupted in mice with a mutant form of the tumor suppressor protein BRCA1. In the mutant pachytene cells, ATR is usually present at nonsex chromosomal sites, where it colocalizes with aberrant sites of H2AX phosphorylation; in these cells, there is MSCI failure. In rare pachytene cells, ATR does locate to XY chromatin, H2AX is then phosphorylated, a sex body forms, and MSCI ensues. These observations highlight an important role for BRCA1 in recruiting the kinase ATR to XY chromatin at the onset of MSCI and provide compelling evidence that it is ATR that phosphorylates H2AX and triggers MSCI.
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PMID:BRCA1, histone H2AX phosphorylation, and male meiotic sex chromosome inactivation. 1558 57

It has been established that telomere-dependent replicative senescence of human fibroblasts is stress-dependent. First, it was shown that telomere shortening, which is a major contributor to telomere uncapping, is stress-dependent to a significant degree. Second, the signalling pathway connecting telomere uncapping and replicative senescence appears to be the same as the one that is activated by DNA damage: uncapped telomeres activate signalling cascades involving the protein kinases ATM, ATR and, possibly, DNA-PK. Furthermore, phosphorylation of histone H2A.X facilitates the formation of DNA damage foci around uncapped telomeres, and this in turn activates downstream kinases Chk1 and Chk2 and, eventually, p53. It appears that this signalling pathway has to be maintained in order to keep cells in a senescent state. Thus, cellular senescence can be regarded as a permanently maintained DNA damage response state. This suggests that antibodies against DNA damage foci components might be useful markers for senescent cells in vivo.
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PMID:Human cell senescence as a DNA damage response. 1561 Jul 69

Common fragile sites have been involved in neoplastic transformation, although their molecular basis is still poorly understood. Here, we demonstrate that inhibition of the SMC1 by RNAi is sufficient to induce fragile site expression. By investigating normal, ATM- and ATR-deficient cell lines, we provide evidence that the contribution of SMC1 in preventing the collapse of stalled replication fork is an Atr-dependent pathway. Using a fluorescent antibody specific for gamma-H2AX, we show that very rare discrete nuclear foci appear 1 and 2 h after exposure to aphidicolin and/or RNAi-SMC1, but became more numerous and distinct after longer treatment times. In this context, fragile sites might be viewed as an in vitro phenomenon originating from double-strand breaks formed because of a stalled DNA replication that lasted too long to be managed by physiological rescue acting through the Atr/Smc1 axis. We propose that in vivo, following an extreme replication block, rare cells could escape checkpoint mechanisms and enter mitosis with a defect in genome assembly, eventually leading to neoplastic transformation.
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PMID:SMC1 involvement in fragile site expression. 1564 Feb 46

Cyclin-dependent kinases (Cdk) promote cell proliferation, are often deregulated in human cancers, and are targets of ongoing cancer chemotherapy trials. We show here that Cdk activity is also required in human cells to maintain function of the Chk1 pathway, a key component of the response to DNA damage or stalled replication. Chk1 expression was markedly reduced in primary fibroblasts and U2OS osteogenic sarcoma cells by treatment with small molecule Cdk inhibitors or induction of a dominant-negative mutant of Cdk2. The findings of decreased Chk1 activity and accumulation of Cdc25A, a protein targeted for degradation by Chk1, confirmed that Chk1 function was impaired. Furthermore, Cdk inhibition triggered a DNA damage response, characterized by the accumulation of activated forms of ATM and Chk2 as well as nuclear foci containing phosphorylated substrates of ATM/ATR, including histone H2AX (gammaH2AX). Time course experiments showed that the bulk of ATM activation followed Chk1 down-regulation. Chk1 RNA interference combined with partial inhibition of DNA replication was sufficient to evoke the DNA damage response. Conversely, ectopic expression of Chk1 blunted induction of gammaH2AX foci by Cdk inhibitors, indicating that Chk1 down-regulation was necessary to elicit the full phenotype. Finally, both Cdk and Chk1 inhibitors enhanced the cytotoxity of etoposide, a DNA-damaging agent. These results define a pathway through which Cdk inhibition can mediate DNA damage and potentially enhance the efficacy of extant cancer chemotherapies.
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PMID:Cdk inhibition in human cells compromises chk1 function and activates a DNA damage response. 1570 74

Budding yeast Rad9 (scRad9) plays a central role in mediating Mec1-dependent phosphorylation by recruiting its downstream substrates. The human scRad9 orthologues 53BP1 and NFBD1 associate with ionizing radiation-induced foci (IRIF) at sites of DNA repair. RNAi-based gene silencing of 53BP1 or NFBD1 has shown impaired phosphorylation of SQ/TQ [ataxia-telangiectasia mutated/ATM and Rad3-related (ATM/ATR) substrates] at IRIF, intra-S, and G(2)-M checkpoints and has thereby revealed essential roles for 53BP1 and NFBD1 in the DNA damage signaling pathway. Whether 53BP1 and NFBD1 are required for activation of kinases and/or for recruitment of substrates at IRIF, however, is not clear. Here we show that both 53BP1 and NFBD1 are required for recruitment of ATR to DNA damage sites, as well as for ATR-dependent phosphorylation in response to DNA damage. NFBD1 is not required for ssDNA generation at DNA damage sites and is not recruited by replication protein A (RPA)-coated ssDNA. We therefore show that recruitment of NFBD1 and/or 53BP1, the factors downstream of H2AX, is independent of ssDNA generation and RPA coating, whereas both ssDNA and RPA coating play key roles in regulation of the ATR-dependent pathway. These novel findings help clarify where NFBD1 functions in DNA damage early responses.
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PMID:NFBD1/Mdc1 mediates ATR-dependent DNA damage response. 1573 98

The histone variant H2AX is rapidly phosphorylated at the sites of DNA double-strand breaks (DSBs). This phosphorylated H2AX (gamma-H2AX) is involved in the retention of repair and signaling factor complexes at sites of DNA damage. The dependency of this phosphorylation on the various PI3K-related protein kinases (in mammals, ataxia telangiectasia mutated and Rad3-related [ATR], ataxia telangiectasia mutated [ATM], and DNA-PKCs) has been a subject of debate; it has been suggested that ATM is required for the induction of foci at DSBs, whereas ATR is involved in the recognition of stalled replication forks. In this study, using Arabidopsis as a model system, we investigated the ATR and ATM dependency of the formation of gamma-H2AX foci in M-phase cells exposed to ionizing radiation (IR). We find that although the majority of these foci are ATM-dependent, approximately 10% of IR-induced gamma-H2AX foci require, instead, functional ATR. This indicates that even in the absence of DNA replication, a distinct subset of IR-induced damage is recognized by ATR. In addition, we find that in plants, gamma-H2AX foci are induced at only one-third the rate observed in yeasts and mammals. This result may partly account for the relatively high radioresistance of plants versus yeast and mammals.
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PMID:Ionizing radiation-dependent gamma-H2AX focus formation requires ataxia telangiectasia mutated and ataxia telangiectasia mutated and Rad3-related. 1577 50


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