microRNA-889 is downregulated by histone deacetylase inhibitors and confers resistance to natural killer cytotoxicity in hepatocellular carcinoma cells

Haitao Xie, Qiugui Zhang, Hui Zhou, Jun Zhou, Ji Zhang, Yan Jiang, Jinghong Wang, Xianglin Meng, Leping Zeng, Xiaoxin Jiang

Major histocompatibility complex class I chain-related gene B (MICB) is expressed on tumor cells and participates in natural killer (NK) cell-mediated antitumor immune response through engagement with the NKG2D receptor. This study was undertaken to identify novel microRNA (miRNA) regulators of MICB and clarify their functions in NK cell-mediated cytotoxicity to hepatocellular carcinoma (HCC) cells. Bioinformatic analysis and luciferase reporter assay were conducted to search for MICB-targeting miRNAs. Overexpression and knockdown experiments were performed to determine the roles of candidate miRNAs in the susceptibility of HCC cells to NK lysis. miR-889 was identified as a novel MICB-targeting miRNA and overexpression of miR-889 significantly inhibited the mRNA and protein expression of MICB in HepG2 and SMMC7721 HCC cells. miR-889 expression had a negative correlation with MICB mRNA levels in HCC specimens (r = -0.392, P = 0.0146). NK cell-mediated cytotoxicity was reduced in miR-889-overexpressing HCC cells, which was reversed by restoration of MICB expression. In contrast, knockdown of miR-889 led to more pronounced NK cell-mediated lysis in HCC cells. HCC cells exposed to the histone deacetylase (HDAC) inhibitor sodium valproate showed downregulation of miR-889. Enforced expression of miR-889 prevented the upregulation of MICB and enhancement of NK cell-mediated lysis by HDAC inhibitors. In conclusion, miR-889 upregulation attenuates the susceptibility of HCC cells to NK lysis and represents a potential target for improving NK cell-based antitumor therapies.