Cancer cells are characterised by the loss of controls over cell division and over the induction of cell death or apoptosis. Through understanding the molecular mechanisms of these controls we may improve existing therapies and identify targets for novel and more specific anti-cancer drugs. Our group mainly studies mechanisms working at the level of post-translational regulation, through reversible protein phosphorylation and protein complex assembly. Much of our work uses cell-free systems that reproduce biochemical processes in vitro under conditions similar to those in intact cells. We are currently investigating three control mechanisms:
- Regulation of caspase activation by Bcl-2 family proteins and cell signalling pathways.
An important event during apoptosis is the activation of caspases, a family of highly specific proteases that cleave a limited number of key proteins to bring about the biochemical and morphological changes that lead to cell death and engulfment by other cells. Resistance to the induction of apoptosis contributes to the development of cancer and may determine the susceptibility of cancer cells to cell-killing drugs and radiation. We are studying the biochemical mechanisms controlling caspase activation. We are investigating the pro- and anti-apoptotic proteins of the Bcl-2 family. We are also studying proteins that interact directly with caspases and the role of reversible phosphorylation regulated by cell signalling pathways.
- Regulation of mitosis by checkpoints.
Entry into mitosis requires the activation of a protein kinase complex consisting of the Cdc2 catalytic subunit bound to a regulatory cyclin B subunit. Checkpoint mechanisms that control the activation of Cdc2/cyclin B in response to DNA damage or arrest of DNA replication can be reconstituted in cell extracts. The Chk1 and Chk2 protein kinases play important roles in restraining mitosis by phosphorylating and inactivating the Cdc25C phosphatase required for the dephosphorylation and activation of Cdc2/cyclin B. Upstream of Chk1 and Chk2 are the ATR and ATM kinases. We are investigating the control of these pathways in Xenopus egg extracts and human cells by determining the regulation of components by phosphorylation and protein interactions. Inhibition of the enzymes involved in these pathways or disruption of their molecular interactions may be a useful strategy to sensitise cancer cells to therapies that damage DNA.
- Role of the Ran GTPase in the cell division cycle.
We are studying the functions of Ran, a GTPase of the Ras superfamily that is involved in the regulation of nuclear structure and function during the cell division cycle. During interphase, Ran controls the transport of proteins and nucleic acids between the nucleus and the cytoplasm. During cell division, Ran controls the assembly of the mitotic spindle and nuclear envelope formation at the end of mitosis. Ran has also been implicated in the operation of checkpoints controlling entry into mitosis as well as progression through S-phase. Defects in the functions of Ran may result in abnormal mitosis, contributing to the genetic instability that characterises many cancer cells. We are characterising proteins that regulate Ran and we are investigating its interactions with the cell cycle machinery and checkpoint pathways.
