MicroRNA-23a Antisense Enhances 5-Fluorouracil Chemosensitivity Through APAF-1/Caspase-9 Apoptotic Pathway in Colorectal Cancer Cells

ABSTRACT Current literature provided information that alteration in microRNA expression impacted sensitivity or resistance of certain tumor types to anticancer treatment, including the possible intracellular pathways. The microRNA‐23a (miR‐23a)‐regulated apoptosis in response to the 5‐fluorouracil (5‐FU)‐induced mitochondria‐mediated apoptotic pathway was determined in this study. The miR‐23a expression in 5‐FU‐treated and untreated colon cancer cells and tissues was assessed using real‐time PCR analysis. To determine the function of miR‐23a in the regulation of 5‐FU‐induced apoptosis, cell‐proliferation, cytotoxicity, and apoptosis analyses were performed. Dual luciferase reporter assay was used to identify the apoptosis‐related target gene for miR‐23a. The activity of caspases‐3, ‐7, and ‐9 were also assessed in miR‐23a antisense and 5‐FU treated tumor cells. A xenograft tumor model was established to evaluate the biological relevance of altered miR‐23a expression to the 5‐FU‐based chemotherapy in vivo. We found that the expression of miR‐23a was increased and the level of apoptosis‐activating factor‐1 (APAF‐1) was decreased in 5‐FU‐treated colon cancer cells compared to untreated cells. The activation of the caspases‐3 and 7 was increased in miR‐23a antisense and 5‐FU‐treated colon cancer cells compared to negative control. APAF‐1, as a target gene of miR‐23a, was identified and miR‐23a antisense‐induced increase in the activation of caspase‐9 was observed. The overexpression of miR‐23a antisense up‐regulated the 5‐FU induced apoptosis in colon cancer cells. However, the miR‐23a knockdown did not increase the antitumor effect of 5‐FU in xenograft model of colon cancer. This study shows that miR‐23a antisense enhanced 5‐FU‐induced apoptosis in colorectal cancer cells through the APAF‐1/caspase‐9 apoptotic pathway. J. Cell. Biochem. 115: 772–784, 2014. © 2013 Wiley Periodicals, Inc.