| Description |
Within the context of a multicellular organism, accumulation of genetic mutations can lead to tumor formation. In order to avoid such deleterious events, each cell is equipped with a series of DNA damage sensors and repair systems to deal with the DNA lesions that can lead to such mutations. Joined to these repair systems are additional cellular responses, such as cell cycle arrest, providing the cell time for repair, or if need be, apoptosis, removing a cell from the population if the repair systems are not sufficient to deal with the DNA damage. The deleterious effects of deficiencies in components of the repair and cell response pathways are evident in the human diseases associated with inherited and spontaneous mutations in genes encoding these factors. This dissertation attempts to elucidate the specific roles of certain components of the DNA mismatch repair (MMR) and DNA double strand break (DSB) repair systems. In addition, we examined the link between their role in repair and other cellular responses to DNA damage. Employing a CHO model system, the role of mammalian MSH3, with respect to its function in mismatch repair, was studied. In agreement with studies of the human homolog, and the lack of disease associated with its mutation, we found no consistent link between the loss of MSH3 and the common cellular phenotypes associated with MMR deficiency. The MMR deficient HCT116 colon tumor cell line demonstrates the characteristics of a NMR deficient cell line, presumably due to the specific deficiency of the MMR protein hMLH1. Employing an inducible hMLH1 expression system, we were able to correct the MMR deficiency phenotype of this tumor line and, interestingly, only a small amount of hMLH1 expression was necessary for complementation. Finally, we studied the role of the Rad51 paralog XRCC3 in the homologous recombination associated DSB repair system. Employing a CHO model system, we found that despite the expected increase in sensitivity to camptothecin, a DNA double-strand break inducing agent, the XRCC3 deficient cell line irs1SF had a reduced apoptotic response. This suggests a link between the processes of homologous recombination and induction of apoptosis. |
