miR-25 targets TNF-related apoptosis inducing ligand (TRAIL) death receptor-4 and promotes apoptosis resistance in cholangiocarcinoma

MicroRNA expression is altered in a variety of human cancers, with some microRNAs exhibiting increased expression levels and others reduced amounts compared to non tumor samples (1). Functionally, microRNAs contribute to many processes, including oncogenesis, angiogenesis, cell death, and metastasis. Thus, the control of microRNA levels in cancer cells, as well as their particular protein targets, is an active area of investigation. Among the microRNAs known to be dysregulated in disease states, miR-25 is expressed at altered levels in a number of cancers. miR-25 is 22 nucleotides in length, hosted by the minichromosome maintenance protein-7 (MCM7) gene, and transcribed as part of the mir-106b~25 polycistron. Examples of miR-25 dysregulation include its upregulation in pediatric brain tumors of multiple histological classifications (2), prostate carcinoma (3), gastric adenocarcinoma (4), and epidermal growth factor receptor-positive lung adenocarcinoma (5). In the liver, miR-25 is elevated in hepatocellular carcinoma cell lines (6, 7) and human hepatocellular carcinoma samples (8, 9), and was among the microRNAs shown to be overexpressed in intrahepatic cholangiocarcinoma (10). Further, exposure to tamoxifen, a known inducer of liver cancer, increased hepatic miR-25 expression in rats (11). Notably, elevated miR-25 levels are not universally associated with a worse disease course, for instance in acute myelogenous leukemia (12). Therefore, the particular functional effect of elevated microRNA quantities cannot necessarily be generalized from one tumor type to another. Cholangiocarcinoma represents the second most common primary hepatobiliary cancer (13) and is resistant to apoptosis mediated by TRAIL, a major player in the extrinsic death pathway (14). Similar to other tumors, cholangiocarcinoma paradoxically expresses TRAIL (15-17) and, therefore, may rely on strong cellular survival signals for tumor development. We report a role for miR-25 in regulating apoptotic signaling in cholangiocarcinoma cell lines and human tumor samples. Increased miR-25 repressed Death Receptor-4 (DR4) protein expression protecting cells from TRAIL-induced death, and this effect was reversed on antagonism of miR-25.