Research

The main interests of our lab are cell-cycle control and checkpoint regulation in humans. To maintain health humans must renew and replace cells throughout life. To achieve this, individual cells must replicate and segregate their genomes accurately and efficiently. However many problems, in the form of damaged DNA or blocks in the replication process, are encountered during the process. When damaged DNA is encountered it needs to be repaired, and cell cycle progression needs to be suspended until the damage has been fixed. Checkpoints are the signal transduction pathways that slow or delay cell cycle progression in the presence of damaged DNA. Loss of proper checkpoint control is associated with increased sensitivity to radiation, genomic instability and the occurrence of cancer. Coordination of cell cycle checkpoints and DNA repair are especially important following genotoxic radiation or chemotherapy, when unusually high loads of DNA damage are sustained. Thus, loss of checkpoint control has profound implications not only for the development of cancer but also for determining the effectiveness of treatment.

Earlier work form our lab showed that inhibitory phosphorylation of the cyclin-dependent kinase, Cdc2, is needed to delay cell cycle progression in response to blocked replication or damaged DNA. Thus, our attention focused on the kinases and phosphatases that control the inhibitory phosphorylation of Cdc2. We found that the G2 checkpoint involves inactivation of the mitosis inducing phosphatase Cdc25. Two kinases that phosphorylate and inactivate Cdc25 in vitro have been identified. One of them, Cds1, is activated in response to g-irradiation. Cds1 is activated by ATM: a gene that is mutated in the cancer prone disorder Ataxia Telangiectasia. Our ongoing studies of Cds1 and other checkpoint proteins are aimed at determining exactly how checkpoint kinases are regulated, and how they control cell-cycle responses. A link between a checkpoint kinase and a DNA repair process was suggested by the finding that Cds1 physically interacts with a human homologue of the DNA damage and replication stress tolerance protein Mus81. Mus81 is has homology to the XPF-family of endonucleases. Human Mus81-associated endonuclease resolves Holliday junctions in vitro, suggesting that Mus81 is required to deal with aberrant DNA structures that arise during DNA replication.

Our efforts continue to focus on the processes by which human cells protect themselves from damaged and incompletely replicated DNA. A combination of cell biology, molecular biology, biochemistry and genetics is being used to detail interactions between known components of the DNA damage response pathway, and to identify novel components of these pathways. We are excited by the potential this research has for improving the treatment of human disease.