miR-329 regulates the sensitivity of 5-FU in chemotherapy of colorectal cancer by targeting E2F1

Colorectal cancer (CRC) is a common digestive system malignancy with high morbidity and mortality. Accumulating studies have shown that miRNAs play a critical role in the progression of CRC. Here, we explored the effect of miR-329 and its target gene on the sensitivity of 5-fluorouracil (5-FU) in the chemotherapy of CRC. RT-qPCR was utilized to determine the expression of miR-329 in cancer tissues, adjacent tissues and cells. CCK-8 and Transwell assays were introduced to detect the role of miR-329 overexpression in cell viability and invasion. Luciferase reporter assay was performed to verify that E2F1 was a direct target of miR-329. Protein expression of E2F1 was accessed by western blot analysis. The expression level of miR-329 was decreased in CRC tissues and tumor tissues at stage III+IV with lymph node metastasis, and the patients' total survival time was positively associated with the expression of miR-329. Overexpression of miR-329 significantly attenuated the viability and invasiveness of tumor cells. The viability of drug-resistant cells was markedly higher than that of non-resistant cells under the same dose of 5-FU treatment. The expression of miR-329 in tumor cells was negatively associated with drug sensitivity. Luciferase reporter assay showed that E2F1 was the direct target of miR-329. Besides, the expression of E2F1 protein in drug-resistant cells was remarkably higher than that in the non-resistant cells, while the overexpression of miR-329 significantly decreased the expression of E2F1 protein. E2F1 overexpression increased cell viability, but overexpression of both E2F1 and miR-329 in turn decreased cell viability. miR-329 expression is reduced in CRC, and overexpression of miR-329 promotes the sensitivity of 5-FU in the chemotherapy of CRC by degrading the target gene E2F1.