title: Mediator of DNA damage checkpoint 1 (MDC1) regulates mitotic progression.
abstract: Human mediator of DNA damage checkpoint 1 (hMDC1) is an essential component of the cellular response to DNA double strand breaks. Recently, hMDC1 has been shown to associate with a subunit of the anaphase-promoting complex/cyclosome (APC/C) (Coster, G., Hayouka, Z., Argaman, L., Strauss, C., Friedler, A., Brandeis, M., and Goldberg, M. (2007) J. Biol. Chem. 282, 32053-32064), a key regulator of mitosis, suggesting a possible role for hMDC1 in controlling normal cell cycle progression. Here, we extend this work to show that hMDC1 regulates normal metaphase-to-anaphase transition through its ability to bind directly to the APC/C and modulate its E3 ubiquitin ligase activity. In support of a role for hMDC1 in controlling mitotic progression, depletion of hMDC1 by small interfering RNA results in a metaphase arrest that appears to be independent of both BubR1-dependent signaling pathways and ATM/ATR activation. Mitotic cells lacking hMDC1 exhibit markedly reduced levels of APC/C activity characterized by reduced levels of Cdc20, and a failure of Cdc20 to bind the APC/C and CREB-binding protein. We suggest therefore that hMDC1 functionally regulates the normal metaphase-to-anaphase transition by modulating the Cdc20-dependent activation of the APC/C.
authors.affiliation: Cancer Research-United Kingdom Institute for Cancer Sciences, University of Birmingham Medical School, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Kelly
authors.initials: K
authors.lastname: Townsend
authors.forename: Helen
authors.initials: H
authors.lastname: Mason
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Blackford
authors.forename: Edward S
authors.initials: ES
authors.lastname: Miller
authors.forename: J Ross
authors.initials: JR
authors.lastname: Chapman
authors.forename: Garry G
authors.initials: GG
authors.lastname: Sedgwick
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Barone
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Turnell
authors.forename: Grant S
authors.initials: GS
authors.lastname: Stewart
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000705:Anaphase; D064173:Anaphase-Promoting Complex-Cyclosome; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting / Q000379:methods; D008677:Metaphase; D008856:Microscopy, Fluorescence / Q000379:methods; D008938:Mitosis; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D043743:Ubiquitin-Protein Ligase Complexes / Q000737:chemistry; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; C413163:MDC1 protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D015534:Trans-Activators; C577488:CDC20 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases