MicroRNA-197 influences 5-fluorouracil resistance via thymidylate synthase in colorectal cancer

The response rate of first-line fluoropyrimidine-based regimens for metastatic colorectal cancer (mCRC) is generally less than 50 %. The down-regulation of miR-197 in colorectal cancer cells after exposure to 5-fluorouracil might be related to the mechanism of resistance to fluoropyrimidine-based chemotherapy. So we investigated the regulatory mechanism of miR-197 on 5-FU sensitivity. Dual luciferase reporter gene construct and dual luciferase reporter assay were used to identify the target of miR-197. TYMS expression was evaluated by immunohistochemistry staining. 5-Fu resistance of colorectal cancer cell lines was detected by MTS assay. The expression of miR-197 was detected by real time PCR. A luciferase assay and western blot analysis confirmed that miR-197 directly binds to and negatively regulates TYMS expression. Overexpressing miR-197 could increase the sensitivity of colorectal cancer cells to 5-fluorouracil (5-FU). The expression of miR-197 negatively correlated with TYMS expression in cancerous tissues from patients with stage IV colorectal cancer. miR-197 mediates the response of colorectal cancer cells to 5-FU by regulating TYMS expression.