Background: Colorectal cancer (CRC) is the third commonly diagnosed cancer with a high risk of death. After curative surgery, 40% of patients will have metastases or develop recurrence. Therefore, chemotherapy is significantly responsible as the major therapy method. However, chemoresistance is found in almost all metastatic patients and remains a critical obstacle to curing CRC.
Materials and methods: Cell viability is analyzed by sulforhodamine B staining assay. The nonhomologous end joining (NHEJ) repair ability of each cell line was determined by NHEJ reporter assay. mRNA expression levels of NHEJ factors are detected by real-time quantitative polymerase chain reaction. The protein expression levels were observed by western blot assay.
Results: Our study found that 5-florouracil (5-Fu) and oxaliplatin (OXA)-resistant HCT116 and LS174T cells showed upregulated efficiency of DNA double-strand repair pathway NHEJ. We then identified that the NHEJ key factor XLF is responsible for the chemoresistance and XLF deficiency sensitizes CRC cells to 5-Fu and OXA significantly.
Conclusion: Our research first demonstrates that the NHEJ pathway, especially its key factor XLF, significantly contributes to chemoresistance in CRC.
Keywords: XLF, nonhomologous end joining, 5-florouracil, oxaliplatin, chemoresistance, colorectal cancer