Alternative titles; symbols
HGNC Approved Gene Symbol: MDC1
Cytogenetic location: 6p21.33 Genomic coordinates (GRCh38) : 6:30,699,807-30,717,281 (from NCBI)
The MDC1 protein contains a forkhead homology-associated (FHA) domain and 2 BRCA1 (113705) C-terminal motifs (BRCTs) and is required for the intra-S-phase DNA damage checkpoint (Goldberg et al., 2003).
Shang et al. (2003) identified nuclear factor with BRCT domains protein-1 (NFBD1) as a mammalian homolog of S. cerevisiae Rad9.
By randomly sequencing cDNAs obtained from the human myeloid cell line KG-1, Nagase et al. (1996) cloned MDC1, which they called KIAA0170. The deduced MDC1 protein contains 2,089 amino acids. Northern blot analysis showed that MDC1 is ubiquitously expressed.
Goldberg et al. (2003) identified MDC1 as a binding partner for the MRE11 complex (see MRE11; 600814). They determined that the MDC1 protein has a predicted molecular mass of 226.5 kD. It contains an FHA domain at its N terminus and 2 BRCTs at its C terminus. The central region of MDC1 has 19 consecutive repeats of an approximately 40-amino acid motif.
Stewart et al. (2003) reported that MDC1 contains a large S/TQ cluster domain encompassing its N-terminal half. The central region of MDC1 has a large proline/serine/threonine-rich repeat domain.
Goldberg et al. (2003) showed that, in response to ionizing radiation, MDC1 was hyperphosphorylated in an ATM (607585)-dependent manner and rapidly relocalized to nuclei foci containing the MRE11 complex, phosphorylated histone H2AX (601772), and TP53BP1 (605230). Downregulation of MDC1 expression by small interfering RNA yielded a radioresistant DNA synthesis phenotype and prevented ionizing radiation-induced focus formation by the MRE11 complex. However, downregulation of MDC1 did not abolish the ionizing radiation-induced phosphorylation of NBS1 (602667), CHK2 (604373), and SMC1 (300040), or the degradation of CDC25A (116947). Furthermore, overexpression of the MDC1 FHA domain interfered with focus formation by MDC1 itself and by the MRE11 complex, and it induced a radioresistant DNA synthesis phenotype. Goldberg et al. (2003) concluded 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.
Stewart et al. (2003) showed that MDC1 works with H2AX to promote recruitment of repair proteins to the site of DNA breaks and controls damage-induced cell-cycle arrest checkpoints. MDC1 formed foci that colocalized extensively with gamma-H2AX foci within minutes after exposure to ionizing radiation. H2AX was required for MDC1 foci formation, and MDC1 formed complexes with phosphorylated H2AX. Peptides containing the phosphorylated site on H2AX bound MDC1 in a phosphorylation-dependent manner. Stewart et al. (2003) used small interfering RNA to show that cells lacking MDC1 were sensitive to ionizing radiation and that MDC1 controlled the formation of damaged-induced TP53BP1, BRCA1 (113705), and MRN (MRE11, RAD50 (604040), NBS1, i.e., the MRE11 complex) foci, in part by promoting efficient H2AX phosphorylation. In addition, cells lacking MDC1 failed to activate the intra-S phase and G2/M phase cell cycle checkpoints properly after exposure to ionizing radiation, and this failure was associated with the inability to regulate CHK1 (603078) properly.
Lou et al. (2003) found that MDC1 localized to sites of DNA breaks and associated with CHK2 after DNA damage. This association was mediated by the MDC1 FHA domain and the phosphorylated thr68 of CHK2. MDC1 was phosphorylated in an ATM/CHK2-dependent manner after DNA damage, suggesting that MDC1 may function in the ATM/CHK2 pathway. Consistent with this hypothesis, suppression of MDC1 expression resulted in defective S-phase checkpoint and reduced apoptosis in response to DNA damage, which could be restored by expression of wildtype MDC1, but not by MDC1 with a deleted FHA domain. Suppression of MDC1 expression resulted in decreased p53 (191170) stabilization in response to DNA damage. Lou et al. (2003) concluded that MDC1 is recruited through its FHA domain to the activated CHK2 and has a critical role in CHK2-mediated DNA damage responses.
Shang et al. (2003) showed that NFBD1 is a 250-kD nuclear protein containing a forkhead-associated motif at its N terminus, 2 BRCT motifs at its C terminus, and 13 internal repetitions of a 41-amino acid sequence. Five minutes after gamma-irradiation, NFBD1 formed nuclear foci that colocalized with the phosphorylated form of H2AX and CHK2, 2 phosphorylation events involved in early DNA damage response. NFBD1 foci were also detected in response to camptothecin, etoposide, and methylmethanesulfonate treatments. Deletion of the forkhead-associated motif or the internal repeats of NFBD1 had no effect on DNA damage-induced NFBD1 foci formation. Conversely, deletion of the BRCT motifs abrogated damage-induced NFBD1 foci. Ectopic expression of the BRCT motifs reduced damage-induced NFBD1 foci and compromised phosphorylated CHK2- and phosphorylated H2AX-containing foci. Shang et al. (2003) concluded that NFBD1, like BRCA1 and TP53BP1, participates in the early response to DNA damage.
By examining immunoglobulin heavy chain (see 147100) class switch recombination in mouse B-lymphocytes deficient in H2ax, Atm, 53bp1, or Mdc1, Franco et al. (2006) determined that these factors promote end joining and thereby prevent DNA double-strand breaks from progressing into chromosomal breaks and translocations.
Dimitrova and de Lange (2006) found that MDC1 had a role in detection and repair of human and mouse telomeres rendered dysfunctional through inhibition of TRF2 (TERF2; 602027). MDC1 knockdown affected the formation of telomere dysfunction-induced foci, diminishing accumulation of phosphorylated ATM, TP53BP1, NBS1, and, to a lesser extent, gamma-H2AX. In addition, inhibition of MDC1 itself or of its recruitment to chromatin significantly decreased the rate of nonhomologous end-joining of dysfunctional telomeres. MDC1 appeared to promote a step in the nonhomologous end-joining pathway after removal of the 3-prime telomeric overhang.
Kolas et al. (2007) determined that the ubiquitin ligase RNF8 (611685) mediates ubiquitin conjugation and 53BP1 (605230) and BRCA1 (113705) focal accumulation at sites of DNA lesions. Moreover, Kolas et al. (2007) established that MDC1 recruits RNF8 through phosphodependent interactions between the RNF8 forkhead-associated domain and motifs in MDC1 that are phosphorylated by the DNA damage-activated protein kinase ataxia telangiectasia mutated (ATM; 607585). They showed that depletion of the E2 enzyme UBC13 (603679) impairs 53BP1 recruitment to sites of damage, which suggests that it cooperates with RNF8. RNF8 was shown to promote the G(2)/M DNA damage checkpoint and resistance to ionizing radiation. Kolas et al. (2007) concluded that their results demonstrated how the DNA damage response is orchestrated by ATM-dependent phosphorylation of MDC1 and RNF8-mediated ubiquitination.
Pei et al. (2011) found that H4K20 methylation actually increases locally upon the induction of double-strand breaks and that methylation of H4K20 at double-strand breaks is mediated by the histone methyltransferase MMSET (602952) in mammals. Downregulation of MMSET significantly decreases H4K20 methylation at double-strand breaks and the subsequent accumulation of 53BP1. Furthermore, Pei et al. (2011) found that the recruitment of MMSET to double-strand breaks requires the gamma-H2AX (601772)-MDC1 pathway; specifically, the interaction between the MDC1 BRCT domain and phosphorylated ser102 of MMSET. Thus, Pei et al. (2011) proposed that a pathway involving gamma-H2AX-MDC1-MMSET regulates the induction of H4K20 methylation on histones around double-strand breaks, which, in turn, facilitates 53BP1 recruitment.
By analysis of human/rodent hybrid cell lines, Nagase et al. (1996) mapped the MDC1 gene to chromosome 6.
Lou et al. (2006) found that Mdc1 -/- mice were born at the expected mendelian frequency, but they showed a phenotype similar to that of H2ax -/- mice, including growth retardation, male infertility, immune defects, chromosome instability, DNA repair defects, and radiation sensitivity. In the absence of Mdc1, many downstream Atm signaling events were defective following DNA damage. Lou et al. (2006) concluded that MDC1 is a signal amplifier of the ATM pathway that is vital in controlling proper DNA damage response and maintaining genomic stability.
Dimitrova, N., de Lange, T. MDC1 accelerates nonhomologous end-joining of dysfunctional telomeres. Genes Dev. 20: 3238-3243, 2006. [PubMed: 17158742] [Full Text: https://doi.org/10.1101/gad.1496606]
Franco, S., Gostissa, M., Zha, S., Lombard, D. B., Murphy, M. M., Zarrin, A. A., Yan, C., Tepsuporn, S., Morales, J. C., Adams, M. M., Lou, Z., Bassing, C. H., Manis, J. P., Chen, J., Carpenter, P. B., Alt, F. W. H2AX prevents DNA breaks from progressing to chromosome breaks and translocations. Molec. Cell 21: 201-214, 2006. [PubMed: 16427010] [Full Text: https://doi.org/10.1016/j.molcel.2006.01.005]
Goldberg, M., Stucki, M., Falck, J., D'Amours, D., Rahman, D., Pappin, D., Bartek, J., Jackson, S. P. MDC1 is required for the intra-S-phase DNA damage checkpoint. Nature 421: 952-956, 2003. [PubMed: 12607003] [Full Text: https://doi.org/10.1038/nature01445]
Kolas, N. K., Chapman, J. R., Nakada, S., Ylanko, J., Chahwan, R., Sweeney, F. D., Panier, S., Mendez, M., Wildenhain, J., Thomson, T. M., Pelletier, L., Jackson, S. P., Durocher, D. Orchestration of the DNA-damage response by the RNF8 ubiquitin ligase. Science 318: 1637-1640, 2007. [PubMed: 18006705] [Full Text: https://doi.org/10.1126/science.1150034]
Lou, Z., Minter-Dykhouse, K., Franco, S., Gostissa, M., Rivera, M. A., Celeste, A., Manis, J. P., van Deursen, J., Nussenzweig, A., Paull, T. T., Alt, F. W., Chen, J. MDC1 maintains genomic stability by participating in the amplification of ATM-dependent DNA damage signals. Molec. Cell 21: 187-200, 2006. [PubMed: 16427009] [Full Text: https://doi.org/10.1016/j.molcel.2005.11.025]
Lou, Z., Minter-Dykhouse, K., Wu, X., Chen, J. MDC1 is coupled to activated CHK2 in mammalian DNA damage response pathways. Nature 421: 957-961, 2003. [PubMed: 12607004] [Full Text: https://doi.org/10.1038/nature01447]
Nagase, T., Seki, N., Ishikawa, K., Tanaka, A., Nomura, N. Prediction of the coding sequences of unidentified human genes. V. The coding sequences of 40 new genes (KIAA0161-KIAA0200) deduced by analysis of cDNA clones from human cell line KG-1. DNA Res. 3: 17-24, 1996. [PubMed: 8724849] [Full Text: https://doi.org/10.1093/dnares/3.1.17]
Pei, H., Zhang, L., Luo, K., Qin, Y., Chesi, M., Fei, F., Bergsagel, P. L., Wang, L., You, Z., Lou, Z. MMSET regulates histone H4K20 methylation and 53BP1 accumulation at DNA damage sites. Nature 470: 124-128, 2011. [PubMed: 21293379] [Full Text: https://doi.org/10.1038/nature09658]
Shang, Y. L., Bodero, A. J., Chen, P.-L. NFBD1, a novel nuclear protein with signature motifs of FHA and BRCT, and an internal 41-amino acid repeat sequence, is an early participant in DNA damage response. J. Biol. Chem. 278: 6323-6329, 2003. [PubMed: 12475977] [Full Text: https://doi.org/10.1074/jbc.M210749200]
Stewart, G. S., Wang, B., Bignell, C. R., Taylor, A. M. R., Elledge, S. J. MDC1 is a mediator of the mammalian DNA damage checkpoint. Nature 421: 961-966, 2003. [PubMed: 12607005] [Full Text: https://doi.org/10.1038/nature01446]