Investigating the Role of DSS1 in Homologous Recombination DNA Repair

Background: To investigate the effects ionizing radiation has on the DNA damage and repair process, research is being performed on the human osteosarcoma cell line U2OS-DRGFP. We specifically studied DSS1, a small relatively acidic protein that plays a key role in DNA double-strand break (DSB) repair via homologous recombination repair (HRR). From the U2OS-direct repeat green fluorescent protein (DRGFP) parental line, 35 sub-clonal isolates were derived. The derivative cell lines consisted of 12 wild type DSS1, 11 mutant DSS1, and 12 cMyc expressing cell lines. Methods: Using Western blot analysis the expression levels of the endogenous and ectopic DSS1 protein was determined and compared with clonal isolates and parental U2OS-DRGFP cells. Ionizing radiation tests were performed on cell lines to test the effectiveness of HRR in ectopic, wild type, and mutant DSS1 cell lines. Cells were exposed to high levels of ionizing radiation (8Gy) to induce DSBs and study the role of DSS1 in the HRR process. Results: Cells expressing ectopic (mutant) DSS1 were able to perform HRR repair as assessed by fluorescent activated cell sorting (FACS) and the DRGFP assay. Conclusion: DSS1 is an important mediator of the HRR pathway. However, individuals expressing a mutation in DSS1 are still able to perform DNA repair that may result from unidentified co-mediating proteins. While, individuals that do not express DSS1 are unable to perform HRR, resulting in a higher chance of cancer or disease.