Burke, Daniel J.
Professor, Biochemistry and Molecular Genetics
- PhD, , John Hopkins University
PO Box 800733
Jordan Hall, Jordan 6014A
Biochemistry, Bioinformatics and Genomics, Cell and Developmental Biology, Genetics, Microbiology
Regulation of mitosis
My lab studies a mitotic regulatory system that is essential in maintaining genomic stability and preventing tumor progression in certain types of cancers. We are studying the "spindle checkpoint" in the budding yeast Saccharomyces cerevisiae using a combination of genetics, cell biology, molecular biology, biochemistry and molecular genetics. The spindle checkpoint prevents cells from entering anaphase if even a single chromosome is detached from the spindle. Many of the yeast genes that constitute the spindle checkpoint have been identified. There are mammalian homologs of each, and recent evidence suggests that mutations in some of these genes are responsible for genomic instability that accompanies tumor progression in a variety of cancer cells. Therefore, this mitotic checkpoint is evolutionarily conserved and is vital for maintaining genomic stability in organisms from yeast to humans.
We have used classical yeast genetics to determine that cell cycle arrest via the checkpoint is induced when kinetochore function is impaired. This suggests that yeast cells monitor kinetochore attachment to the spindle and arrest cell division when attachments are incomplete. Recently we have cloned mammalian homologs of three of the yeast genes and shown that the checkpoint proteins are localized to the kinetochore. This suggests a provocative model where localizing checkpoint proteins to the kinetochore may be required to sense that chromosomes are detached from the spindle and may be an important aspect of generating the inhibitory mitotic signal.
We are interested in determining the role that the kinetochore plays in spindle checkpoint function. We have mapped the sites of interaction within the kinetochore and determined that checkpoint function is dependent on a subset of kinetochore proteins. We are also investigating the molecular basis for kinetochore-microtubule interactions. We have identified kinetochore mutants that are defective in attaching chromosomes to the mitotic spindle. We are using a genetic approach to identify and characterize the genes responsible to elucidate the molecular mechanisms responsible for this critical event in the cell cycle. We are also continuing our genetic analysis of the spindle checkpoint by looking for new genes required for checkpoint function. We are using a dominant mutant that activates the spindle checkpoint as a starting point to identify recessive mutants that eliminate checkpoint function. We are also using the dominant mutant to identify new genes required to turn off the checkpoint when cells enter anaphase.
The long-term goal is to have a complete molecular description of the checkpoint in both yeast and human cells. Some anti-cancer chemotherapies employ compounds like taxol, that inhibit cell division by activating the spindle checkpoint. We have developed a strain for high throughput screening of chemical compounds that inhibit key regulatory components of the cell cycle. We are using strains that have temperature sensitive mutations in cell cycle genes and looking for synthetic interactions that compromise the growth of the cells. We are beginning with cdc20 mutants, because Cdc20 is the target of the spindle checkpoint. Our goal is to find compounds, like taxol that are potent anti-cancer agents. We have obtained the complete set of deletion mutants of every ORF in the yeast genome and have completed a genome-wide screen for sensitivity to anti-tubulin drugs. This kind of approach should provide novel targets for combination treatments to sensitize cancer cells to chemotherapeutic agents. Finally, we are developing new approaches to genome-wide screens to identify new genes that interact with the spindle checkpoint and the response to this important class of anti-cancer drugs.