Yeast checkpoint controls and relevance to cancer.

Checkpoint controls arrest cells with defects in DNA replication or DNA damage. For several reasons, checkpoint controls may be relevant to ontogeny and treatment of cancer. Firstly, mutations in two human genes, TP53 and ATM, give rise to cellular defects in cell cycle checkpoints and are associated with cancer. Secondly, although checkpoint defects potentially render the cell damage sensitive, they may do so only in combination with other defects in the cell's response to damage. Therefore, manipulation of checkpoint defects, requiring a description of normal and mutant pathways, will be required for this type of therapeutic approach. Those pathways are being described in yeast cells. In budding yeast, the study of checkpoint genes has led to the view that these genes have many roles in the cellular responses to DNA damage, including roles in arrest in multiple stages of cell cycle, in transcriptional induction of repair genes, in DNA repair itself and additionally some undefined role in DNA replication. The checkpoint pathways and proteins that carry out these responses may consist of sensor proteins that detect damage, signaller proteins that transduce an inhibitory signal and target proteins that are altered to arrest cell division (or cause other changes in cell behaviour). Yeast genes that may act at each step have been identified, leading to a working model of checkpoint pathways. An initial step in the pathway may involve the processing of damage to an intermediate that signals arrest and acts in DNA repair. Human checkpoint pathways may have defects in processing damage as well.