The Effect of X rays on the Expression of Mismatch Repair Genes and Proteins in Lynch Syndrome Associated Human Colorectal Cancer Cell Lines

This study investigated whether therapeutic doses of X rays can affect the expression of mismatch repair (MMR) genes and proteins using Lynch syndrome-associated human colorectal cancer cell lines. MMR-deficient cell lines (HCT116, SW48, LoVo) and an MMR-proficient control cell line (HT29) were exposed to X rays [a 2 Gy dose or 2 Gy daily for five consecutive days (10 Gy)]. Reverse transcription quantitative real-time PCR (RT-qPCR) and Western blotting were used to detect the radiation-induced changes in the expression of RNAs and proteins, respectively. RT-qPCR revealed that MLH1 and MSH6 genes were stably expressed regardless of the MMR status of the cell line and the radiation dose. In contrast, the MSH2 gene was either up-regulated or down-regulated after 2 Gy or 10 Gy or both. The expression of PMS2 increased after 10 Gy irradiation in all MMR-deficient cell lines, even though the data were not statistically significant compared to other doses, except for the LoVo cell line. Protein expression analysed using Western blotting demonstrated that MLH1 protein expression was stable, whereas the expression of MSH2 was significantly affected by radiation exposure in both MLH1-deficient cell lines. No correlation between the expression of RNA and protein could be identified. In conclusion, radiation may have significantly differential effects on MMR RNA and protein expression when different cell lines, doses, and specific genes are considered.