title: Mdc1 modulates the interaction between TopBP1 and the MRN complex during DNA damage checkpoint responses.
abstract: TopBP1 has been identified as a direct activator of ATR and interacts with the Nbs1 subunit of the Mre11-Rad50-Nbs1 (MRN) complex in egg extracts in a checkpoint-regulated manner. In this study, we show that Mdc1 associates with both TopBP1 and Nbs1 in egg extracts and human cells. We cloned a cDNA encoding the full-length version of Xenopus Mdc1. The association between Mdc1 and TopBP1 involves the first pair of BRCT repeats in TopBP1. The N-terminal region (161-230) of Mdc1 is required for this binding. The interaction between Mdc1 and Nbs1 involves the two tandem BRCT repeats of Nbs1. Functional studies with mutated forms of Mdc1, TopBP1, and Nbs1 indicate that the BRCT-dependent association of these proteins is critical for a normal checkpoint response to DSBs. TopBP1 cannot interact with Nbs1 in Mdc1-depleted egg extracts, suggesting that Mdc1 connects TopBP1 and Nbs1 together. These findings suggest that Mdc1 is a crucial mediator of the DNA damage checkpoint response.
authors: Department of Health Sciences and Technology, Samsung Advanced Institute for Health Sciences and Technology, Sungkyunkwan University, Seoul 135-710, Republic of Korea; Samsung Biomedical Research Institute, Research Institute for Future Medicine, Samsung Medical Center, Seoul 135-710, Republic of Korea.
authors: Seung Ho
authors: SH
authors: Choi
authors: Department of Health Sciences and Technology, Samsung Advanced Institute for Health Sciences and Technology, Sungkyunkwan University, Seoul 135-710, Republic of Korea; Samsung Biomedical Research Institute, Research Institute for Future Medicine, Samsung Medical Center, Seoul 135-710, Republic of Korea. Electronic address: hyoo@skku.edu.
authors: Hae Yong
authors: HY
authors: Yoo
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002457:Cell Extracts / Q000737:chemistry; D045744:Cell Line, Tumor; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D000076228:MRE11 Homologue Protein; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D010063:Ovum / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D002457:Cell Extracts; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C000620293:Mdc1 protein, Xenopus; C510917:Mre11 protein, Xenopus; D046912:Multiprotein Complexes; C511600:NBN protein, Xenopus; C542167:Rad50 protein, Xenopus; C509993:TopBP1 protein, Xenopus; D025521:Tumor Suppressor Proteins; D029867:Xenopus Proteins; D000076228:MRE11 Homologue Protein; D045643:DNA Repair Enzymes
keywords: DNA damage checkpoint; MRN complex; Mdc1; Nbs1; TopBP1