DNA mismatch repair, genome stability and tumorigenesis

A germline heterozygous alteration of any one of the human DNA mismatch repair (MMR) genes, MSH2, MLH1, MSH6, PMS2 and PMS1 has been associated with hereditary non-polyposis colorectal cancer (HNPCC).; Mice homozygous deficient for one of the MMR genes develop T-cell thymic lymphomas. I have evaluated the role of MMR in several cellular processes leading to the development of tissue-specific tumorigenesis. This thesis characterizes the genetic instability in the murine MMR deficient tumours and furthers our understanding of how tumorigenesis arises by (i) molecular characterization of Msh2 deficient murine lymphomas; (ii) analysis of chromosomal instability in Msh2 deficient murine lymphomas as well as in a human cell-line lacking MSH2; (iii) investigation of the involvement of MMR in telomere function; (iv) investigation of a role for MMR in centrosome stability; and (v) the generation of a novel mouse model to study HNPCC tumorigenesis.; I performed spectral karyotype analysis (SKY) on mouse tumours and SKY analysis of a cell line derived from a rare human patient deficient for MSH2, showed translocations and rearrangements. These results represent the first successful characterization of chromosomal instability in MMR deficient tumorigenesis. My results show that microsatellite instability (MSI+) as well as chromosomal instability (CIN) can co-exist and contribute to tumorigenesis.; Using immunofluorescence techniques I assayed the stability of centrosomal proteins in the absence of MMR in MEFs. For the first time I've shown that hyperamplification of centrosome proteins occurs in the absence of MMR and may account for the increase in aneuploidy that I've observed in MMR deficient MEFs.; I created a novel animal model. I bred Msh2-/- and Msh6-/- mice to athymic nude mice. This animal model will allow us to further study the role of MMR proteins in the development of T and B-cells.; In conclusion, this thesis helps expand our understanding of the multi-functional roles that the MMR proteins have within a cell by identifying new areas, such as telomere regulation, T and B-cell development and centrosome regulation where mammalian MMR is required. Thus, in the absence of MMR, tumorigenesis arises from a combination of effects, underscoring the importance of MMR in neoplasia.