This project is a continuation of projects Z01 CM 06380-03 RO and ZOI CM 06365-06 RO, which were initiated in the Radiation Oncology Br., C.O.P., D.C.T., N.C.I. Both of the former projects dealt with the study of stress responses in mammalian cells. The first project involved the isolation and characterization of DNA-damage-inducible (DDI) genes. The second project involved the study of heat-shock genes, which are currently being used as a model for more general stress response genes that are not specific for DNA damage. In bacteria and yeast, many of the genes important in the cellular response to DNA damage are induced by such damage. Until recently, evidence for such specific responses to genotoxic stress in mammalian cells was not definitive. Our group has been in the forefront in demonstrating that certain genes in mammalian cells can be specifically induced by specific types of DNA damage and that SOS-like responses exist in mammalian cells. Using specialized cloning procedures which we developed, cDNA clones for more than 20 novel DDI genes have been isolated and sequenced. Based on sequence analysis and other studies, we have evidence that at least one encodes a nucleic acid binding protein and that a second may play a role in DNA replication. Five of our DDI genes were found to be coordinately induced by either DNA damage or inhibition of cell growth. There is good evidence in both bacteria and eukaryotes that inhibition of cell growth after DNA damage can have a protective effect; e.g., one of the SOS genes is a growth arrest gene. In collaboration with D. Nebert, we have found that these genes were coordinately overexpressed in a mouse mutant which may provide insight into their regulation. Two of these genes have been sequenced and newly-described regulatory regions have been identified and partially characterized; antibodies to one of the proteins have been developed in collaboration with N. Holbrook. In collaboration with G. Stark, I. Hickson, and L. Barrows, expression of our DDI transcripts in DNA repair mutants has been investigated. Several examples of both increased and decreased expression in the mutant cells has been observed.
