Downregulation of cyclin-dependent kinase 8 by microRNA-148a suppresses proliferation and invasiveness of papillary thyroid carcinomas.

MicroRNAs (miRNAs) are important gene regulators that play key roles in tumor genesis. In this study, we investigate the role of miR-148a in the development of papillary thyroid cancer (PTC). Data from the cancer genome atlas (TCGA) indicate that miR-148a is downregulated in PTC tissues; we also find that miR-148a is downregulated in tissue samples from PTC patients and PTC cell lines. Overexpression of miR-148a significantly suppresses PTC cell proliferation, migration and invasiveness in vitro, and inhibits tumor growth in vivo as well. We have identified the cyclin-dependent kinase 8 (CDK8) gene as a direct target of miR-148a using the online software packages TargetScan and miRanda. Overexpression of miR-148a significantly represses CDK8 expression by directly targeting the 3'-untranslated region (3'-UTR) of the CDK8 gene in PTC tissues and cell lines; overexpression of CDK8 reverses the inhibitory effects of miR-148a on PTC cell growth, migration and invasiveness. Taken together, our results indicate that miR-148a functions as a tumor suppressor in PTC by repressing CDK8 expression.