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)

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

To counteract the continuous exposure of cells to agents that damage DNA, cells have evolved complex regulatory networks called checkpoints to sense DNA damage and coordinate DNA replication, cell-cycle arrest and DNA repair. It has recently been shown that the histone H2A variant H2AX specifically controls the recruitment of DNA repair proteins to the sites of DNA damage. Here we identify a novel BRCA1 carboxy-terminal (BRCT) and forkhead-associated (FHA) domain-containing protein, MDC1 (mediator of DNA damage checkpoint protein 1), which works with H2AX to promote recruitment of repair proteins to the sites of DNA breaks and which, in addition, controls damage-induced cell-cycle arrest checkpoints. MDC1 forms foci that co-localize extensively with gamma-H2AX foci within minutes after exposure to ionizing radiation. H2AX is required for MDC1 foci formation, and MDC1 forms complexes with phosphorylated H2AX. Furthermore, this interaction is phosphorylation dependent as peptides containing the phosphorylated site on H2AX bind MDC1 in a phosphorylation-dependent manner. We have shown by using small interfering RNA (siRNA) that cells lacking MDC1 are sensitive to ionizing radiation, and that MDC1 controls the formation of damage-induced 53BP1, BRCA1 and MRN foci, in part by promoting efficient H2AX phosphorylation. In addition, cells lacking MDC1 also fail to activate the intra-S phase and G2/M phase cell-cycle checkpoints properly after exposure to ionizing radiation, which was associated with an inability to regulate Chk1 properly. These results highlight a crucial role for MDC1 in mediating transduction of the DNA damage signal.
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PMID:MDC1 is a mediator of the mammalian DNA damage checkpoint. 1260 5

NFBD1/MDC1 (mediator of DNA damage checkpoint 1) is a nuclear factor with an amino-terminal FHA (forkhead-associated) domain and a tandem repeat of BRCT (breast cancer susceptibility gene-1 carboxyl terminus) domains. We have previously shown that NFBD1 is an early participant in DNA damage signaling pathways and that ionizing radiation-induced nuclear foci (IRIF) of NFBD1 colocalize with several DNA checkpoint signaling and repair factors. We report here that NFBD1 physically associates with ATM, p53, components of the MRE11-RAD50-NBS1 (MRN) complex, and gamma-H2AX. An overexpressed FHA domain-containing fragment of NFBD1 binds to endogenous NFBD1 and components of the MRN complex, but not to gamma-H2AX. This fragment interferes with IRIF formation by endogenous NFBD1, MRE11, or NBS1. A BRCT domain-containing fragment of NFBD1 binds to gamma-H2AX and 53BP1, but not to components of the MRN complex, and abolishes IRIF formation by NFBD1, MRE11, NBS1, 53BP1, CHK2 phospho-T68, gamma-H2AX, and possible ATM/ATR substrates recognized by anti-phospho-SQ/TQ antibody. These results suggest that NFBD1 is an ATM/ATR-dependent organizer that recruits DNA checkpoint signaling and repair proteins to the sites of DNA damage.
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PMID:NFBD1/MDC1 regulates ionizing radiation-induced focus formation by DNA checkpoint signaling and repair factors. 1451 63

Most human somatic cells can undergo only a limited number of population doublings in vitro. This exhaustion of proliferative potential, called senescence, can be triggered when telomeres--the ends of linear chromosomes-cannot fulfil their normal protective functions. Here we show that senescent human fibroblasts display molecular markers characteristic of cells bearing DNA double-strand breaks. These markers include nuclear foci of phosphorylated histone H2AX and their co-localization with DNA repair and DNA damage checkpoint factors such as 53BP1, MDC1 and NBS1. We also show that senescent cells contain activated forms of the DNA damage checkpoint kinases CHK1 and CHK2. Furthermore, by chromatin immunoprecipitation and whole-genome scanning approaches, we show that the chromosome ends of senescent cells directly contribute to the DNA damage response, and that uncapped telomeres directly associate with many, but not all, DNA damage response proteins. Finally, we show that inactivation of DNA damage checkpoint kinases in senescent cells can restore cell-cycle progression into S phase. Thus, we propose that telomere-initiated senescence reflects a DNA damage checkpoint response that is activated with a direct contribution from dysfunctional telomeres.
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PMID:A DNA damage checkpoint response in telomere-initiated senescence. 1460 68

H2AX phosphorylation is an early step in the response to DNA damage. It is widely accepted that ATM (ataxia telangiectasia mutated protein) phosphorylates H2AX in response to DNA double-strand breaks (DSBs). Whether DNA-dependent protein kinase (DNA-PK) plays any role in this response is unclear. Here, we show that H2AX phosphorylation after exposure to ionizing radiation (IR) occurs to similar extents in human fibroblasts and in mouse embryo fibroblasts lacking either DNA-PK or ATM but is ablated in ATM-deficient cells treated with LY294002, a drug that specifically inhibits DNA-PK. Additionally, we show that inactivation of both DNA-PK and ATM is required to ablate IR-induced H2AX phosphorylation in chicken cells. We confirm that H2AX phosphorylation induced by DSBs in nonreplicating cells is ATR (ataxia telangiectasia and Rad3-related protein) independent. Taken together, we conclude that under most normal growth conditions, IR-induced H2AX phosphorylation can be carried out by ATM and DNA-PK in a redundant, overlapping manner. In contrast, DNA-PK cannot phosphorylate other proteins involved in the checkpoint response, including chromatin-associated Rad17. However, by phosphorylating H2AX, DNA-PK can contribute to the presence of the damage response proteins MDC1 and 53BP1 at the site of the DSB.
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PMID:ATM and DNA-PK function redundantly to phosphorylate H2AX after exposure to ionizing radiation. 1505 90

Disruption of the mechanisms that regulate cell-cycle checkpoints, DNA repair, and apoptosis results in genomic instability and the development of cancer in multicellular organisms. The protein kinases ATM and ATR, as well as their downstream substrates Chk1 and Chk2, are central players in checkpoint activation in response to DNA damage. Histone H2AX, ATRIP, as well as the BRCT-motif-containing molecules 53BP1, MDC1, and BRCA1 function as molecular adapters or mediators in the recruitment of ATM or ATR and their targets to sites of DNA damage. The increased chromosomal instability and tumor susceptibility apparent in mutant mice deficient in both p53 and either histone H2AX or proteins that contribute to the nonhomologous end-joining mechanism of DNA repair indicate that DNA damage checkpoints play a pivotal role in tumor suppression.
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PMID:DNA damage tumor suppressor genes and genomic instability. 1510 99

Mammalian ATR and ATM checkpoint kinases modulate chromatin structures near DNA breaks by phosphorylating a serine residue in the carboxy-terminal tail SQE motif of histone H2AX. Histone H2A is similarly regulated in Saccharomyces cerevisiae. The phosphorylated forms of H2AX and H2A, known as gamma-H2AX and gamma-H2A, are thought to be important for DNA repair, although their evolutionarily conserved roles are unknown. Here, we investigate gamma-H2A in the fission yeast Schizosaccharomyces pombe. We show that formation of gamma-H2A redundantly requires the ATR/ATM-related kinases Rad3 and Tel1. Mutation of the SQE motif to AQE (H2A-AQE) in the two histone H2A genes caused sensitivity to a wide range of genotoxic agents, increased spontaneous DNA damage, and impaired checkpoint maintenance. The H2A-AQE mutations displayed a striking synergistic interaction with rad22Delta (Rad52 homolog) in ionizing radiation (IR) survival. These phenotypes correlated with defective phosphorylation of the checkpoint proteins Crb2 and Chk1 and a failure to recruit large amounts of Crb2 to damaged DNA. Surprisingly, the H2A-AQE mutations substantially suppressed the IR hypersensitivity of crb2Delta cells by a mechanism that required the RecQ-like DNA helicase Rqh1. We propose that gamma-H2A modulates checkpoint and DNA repair through large-scale recruitment of Crb2 to damaged DNA. This function correlates with evidence that gamma-H2AX regulates recruitment of several BRCA1 carboxyl terminus domain-containing proteins (NBS1, 53BP1, MDC1/NFBD1, and BRCA1) in mammals.
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PMID:Histone H2A phosphorylation controls Crb2 recruitment at DNA breaks, maintains checkpoint arrest, and influences DNA repair in fission yeast. 1522 25

The protein MDC1/NFBD1 contains a forkhead-associated (FHA) domain and two BRCA1 carboxyl-terminal (BRCT) domains. It interacts with several proteins involved in DNA damage repair and checkpoint signalling, and is phosphorylated in response to DNA damage and during mitosis. Upon treatment of cultured human cells with DNA damaging agents, MDC1/NFBD1 translocates to sites of DNA lesions, where it collaborates with other proteins and with phosphorylated histone H2AX to mediate the accumulation of checkpoint and repair factors into nuclear foci. Down-regulation of MDC1/NFBD1 expression levels by small interfering RNA (siRNA) renders cells hyper-sensitive to DNA damaging agents and leads to defects in cell cycle checkpoint activation and apoptosis. Thus, MDC1/NFBD1 appears to be a key regulator of the DNA damage response in mammalian cells.
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PMID:MDC1/NFBD1: a key regulator of the DNA damage response in higher eukaryotes. 1527 81

Cellular functions of the NimA-related mammalian kinase Nek1 have not been demonstrated to date. Here we show that Nek1 is involved early in the DNA damage response induced by ionizing radiation (IR) and that Nek1 is important for cells to repair and recover from DNA damage. When primary or transformed cells are exposed to IR, Nek1 kinase activity is increased within 4 minutes, and Nek1 expression is up-regulated shortly thereafter and sustained for hours. At the same early time frame after IR that its kinase activity is highest, a portion of Nek1 redistributes in cells from cytoplasm to discrete nuclear foci at sites of DNA double-strand breaks. There it colocalizes with gamma-H2AX and NFBD1/MDC1, two key proteins involved very early in the response to IR-induced DNA double-strand breaks. Finally, Nek1-deficient fibroblasts are much more sensitive to the effects of IR-induced DNA damage than otherwise identical fibroblasts expressing Nek1. These results suggest that Nek1 may function as a kinase early in the DNA damage response pathway.
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PMID:NIMA-related protein kinase 1 is involved early in the ionizing radiation-induced DNA damage response. 1560 34

STAT-1 plays a role in mediating stress responses to various stimuli and has also been implied to be a tumour suppressor. Here, we report that STAT-1-deficient cells have defects both in intra-S-phase and G2-M checkpoints in response to DNA damage. Interestingly, STAT-1-deficient cells showed reduced Chk2 phosphorylation on threonine 68 (Chk2(-T68)) following DNA damage, suggesting that STAT-1 might function in the ATM-Chk2 pathway. Moreover, the defects in Chk2(-T68) phosphorylation in STAT-1-deficient cells also correlated with reduced degradation of Cdc25A compared with STAT-1-expressing cells after DNA damage. We also show that STAT-1 is required for ATM-dependent phosphorylation of NBS1 and p53 but not for BRCA1 or H2AX phosphorylation following DNA damage. Expression levels of BRCT mediator/adaptor proteins MDC1 and 53BP1, which are required for ATM-mediated pathways, are reduced in cells lacking STAT-1. Enforced expression of MDC1 into STAT-1-deficient cells restored ATM-mediated phosphorylation of downstream substrates. These results imply that STAT-1 plays a crucial role in the DNA-damage-response by regulating the expression of 53BP1 and MDC1, factors known to be important for mediating ATM-dependent checkpoint pathways.
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PMID:STAT-1 facilitates the ATM activated checkpoint pathway following DNA damage. 2572 97


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