5′-UTR and 3′-UTR Regulation of MICB Expression in Human Cancer Cells by Novel microRNAs

The treatment of cancer through the induction of natural killer group 2, member D (NKG2D) ligands is of interest, but understanding of mechanisms controlling expression of individual ligand is limited. The major histocompatibility complex (MHC) class I chain related protein B (MICB) is a member of NKG2D ligands. We aimed to investigate the role of 3'-untranslated (3'-UTR) and 5'-untranslated regions (5'-UTR) in post-transcriptional regulation of MICB. Nine novel microRNAs (miRNAs) predicted to interact with 3'-UTR and 5'-UTR using TargetScan, RNAhybrid and miBridge were identified. Their regulation of 3'-UTR, 5'-UTR and both 3'- and 5'-UTR sequences of MICB were indicated by the reduction of luciferase activities of luciferase reporter constructs. Mutations of miRNA binding sites at 3'- and 5'-UTRs resulted in increased luciferase activities confirming the regulation of nine candidate miRNAs. In addition, overexpression of candidate miRNAs also down-regulated the expression of reporter constructs. Consequently, the overexpression and inhibition of candidate miRNAs lead to the decreased and increased. MICB protein expressions on the cells tested, respectively. This study has identified a new role of miRNAs in regulation of MICB expression via both 3'-UTR and 5'-UTR sequences applicable for cancer immunotherapy.