Elevated Expression of ERCC6 Confers Resistance to 5-Fluorouracil and Is Associated with Poor Patient Survival in Colorectal Cancer.

Excision repair cross-complementation (ERCC) enzymes are key members of the nucleotide excision repair pathway. Dysregulation of ERCC family members has been shown to be involved in chemoresistance in several malignancies. However, the function of ERCC6 in regulating chemo response has not been evaluated in colorectal cancer (CRC). We stably knocked down ERCC6 expression using short hairpin RNA (shRNA) in HCT116 and DLD1 human colon cancer cell lines, followed by chemosensitivity assay. In vivo chemosensitizing effects of ERCC6 were examined in xenograft experiments. Downregulation of ERCC6 conferred sensitivity to 5-fluorouracil (5-FU) in HCT116 and DLD1 cells. Stable knockdown of ERCC6 significantly enhanced antitumor activity of 5-FU in HCT116 xenograft mouse model. ERCC6 was upregulated in CRC tissues compared to matched noncancerous adjacent tissues and was also upregulated in patients who were resistant to 5-FU treatment. In addition, high expression of ERCC6 was associated with poor overall survival in CRC patients with or without receiving 5-FU therapy. Elevated expression of ERCC6 contributes to chemoresistance in CRC cells. Low ERCC6 expression is associated with better chemo response and survival in CRC patients. Therefore, this protein represents a novel therapeutic target for improvement of chemotherapeutic efficacy and predictive biomarker for patient survival.