MRC National Institute for Medical Research, London
Science for Health
Identifying proteins that deal with DNA damage
11 February 2010
DNA is constantly damaged both by factors outside our bodies (such as ultraviolet rays from sunlight) and by factors from within (such as reactive oxygen species produced during metabolism). DNA damage can lead to malfunctioning of genes, and persistent DNA damage can result in developmental disorders or the development of cancer. To ensure proper DNA repair, cells are equipped with an evolutionarily conserved DNA damage checkpoint, which stops proliferation and activates DNA repair mechanisms. Intriguingly, this DNA damage checkpoint responds to DNA damage throughout the cell cycle, except during mitosis.
Steve Smerdon (pictured) in NIMR's Division of Molecular Structure, working with collaborators in USA, Canada and London, has studied how cells dismantle their DNA damage checkpoint during mitosis to allow cell division to proceed even if there is damaged DNA present. Using the observation that kinases phosphorylate their substrates on evolutionarily conserved, kinase-specific sequence motifs, they have used a combined computational and experimental approach to predict and verify key proteins involved in mitotic checkpoint inactivation. They showed that the checkpoint scaffold protein 53BP1 is phosphorylated by the mitotic kinases Cdk1 and Polo-like kinase-1 (Plk1). Furthermore, they found that Plk1 can inactivate the checkpoint kinase Chk2, which is downstream of 53BP1. Plk1 is shown to be a key mediator of mitotic checkpoint inactivation, as cells that cannot activate Plk1 fail to properly dismantle the DNA damage checkpoint during mitosis and instead show DNA damage-induced Chk2 kinase activation.
Our results strengthen a role for 53BP1 as a checkpoint regulator and indicate that 53BP1 functions as a binding platform for Plk1 during the checkpoint recovery process. In addition to constituting a mechanism for silencing an activated DNA damage checkpoint, the Cdk1-Plk1-53BP1 feedback loop may be a more general means to prevent activation of the DNA damage checkpoint during mitosis.
Immortalized proliferating cells are believed to have increased replication stress and elevated levels of associated DNA damage. The DNA damage checkpoint, therefore, was shown to form a barrier against malignant transformation. Feedback mechanisms, in which mitotic kinases can silence DNA damage checkpoints, may thus explain why Plk1 and Aurora A are frequently overexpressed in cancers and may form a rationale for including inhibitors of such mitotic kinases during cancer treatment.
Steve Smerdon
Original article
The research findings are published in full in:
van Vugt MA, Gardino AK, Linding R, Ostheimer GJ, Reinhardt HC, Ong SE, Tan CS, Miao H, Keezer SM, Li J, Pawson T, Lewis TA, Carr SA, Smerdon SJ, Brummelkamp TR, Yaffe MB. (2010)
A mitotic phosphorylation feedback network connects Cdk1, Plk1, 53BP1, and Chk2 to inactivate the G2/M DNA damage checkpoint
PLoS Biology, 8(1):e1000287. Full-text
© MRC National Institute for Medical Research
The Ridgeway, Mill Hill, London NW7 1AA
Top of page