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Title: Identification and analysis of DNA repair pathways that contribute to the survival of cells after nucleoside analogue treatment in Schizossacharomyces pombe
Author: Gasasira Uwamahoro, Marie-Fabrice
Awarding Body: Bangor University
Current Institution: Bangor University
Date of Award: 2013
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Nucleoside analogues (NA) are a group of anti-cancer drugs that are widely used in cancer therapy. It is therefore important to understand the cellular responses to these drugs in order to improve therapy. In this PhD project, I have used the amenable model, Schizosaccharomyces pombeto study DNA repair mechanisms that are involved in cell survival to two of the most widely used anti-cancer nucleoside analogues, Gemcitabine (GemC) and Cytarabine (AraC). Screening of a genome wide gene deletion library and analysis of specific DNA repair mutants strongly suggested a role of DNA repair mechanisms in survival of cells to GemC and AraC treatment. Identified gene products that may play a role in the survival to the two drugs include the multifunctional MRN (Mrn11-Rad50-Nbs1)-Ctp1CtIPcomplex, nucleotide excision repair (NER) recognition factors Rhp41-Rhp42XPCand Rhp14XPAand 5` incision nuclease Swi10ERCC1, and base excision repair (BER) abasic site endonuclease Apn2APE1and the glycosylase Nth1NTH1. However, while most members of the NER pathway were required for survival, the 3` incision nuclease Rad13XPGmutant was not sensitive to GemC and AraC indicating that the nuclease is not involved in survival to NA treatment and suggesting an unorthodox role of the NER in the repair of DNA lesions induced by NAs. Post-replication repair (PRR) DNA polymerase Rev3REV3and mismatch repair (MMR) exonuclease Exo1EXO1mutants were also not sensitive to GemC and AraC, suggesting that the gene products are not involved in cell survival. Interestingly, mutants in the PRR PCNA ubiquitinating factor Rhp18RAD18and the BER nuclease Rad2FEN-1 showed a slight resistance in comparison to WT. This resistance was significantly increased when the BER uracil glycosylase Ung1UNG1and the MMR proteins Mlh1MLH1, Msh2MSH2and Msh6MSH6were absent suggesting that the presence of the gene products might enhance drug activity. In addition to the role of DNA repair mechanisms, analysis of the genome wide deletion library suggested a role of several genome maintenance mechanisms in the response to GemC. These include the DNA damage and DNA replication checkpoints, telomere maintenance and chromatin remodelling. Results in this thesis suggest that the genetic background of patients plays a pivotal role in the response to NA therapies as for examples patients with mutations in the MMR repair pathway may be more resistant rendering the therapy less effective.
Supervisor: Hartsuiker, Edgar Sponsor: North West Cancer Research Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available