Pivotal role of long non-coding ribonucleic acid-X-inactive specific transcript in regulating immune checkpoint programmed death ligand 1 through a shared pathway between miR-194-5p and miR-155-5p in hepatocellular carcinoma

Anti-programmed death therapy has thrust immunotherapy into the spotlight. However, such therapy has a modest response in hepatocellular carcinoma (HCC). Epigenetic immunomodulation is a suggestive combinatorial therapy with immune checkpoint blockade. Non-coding ribonucleic acid (ncRNA) driven regulation is a major mechanism of epigenetic modulation. Given the wide range of ncRNAs that co-opt in programmed cell-death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) regulation, and based on the literature, we hypothesized that miR-155-5p, miR-194-5p and long non-coding RNAs (lncRNAs) X-inactive specific transcript (XIST) and MALAT-1 are involved in a regulatory upstream pathway for PD-1/PD-L1. Recently, nutraceutical therapeutics in cancers have received increasing attention. Thus, it is interesting to study the impact of oleuropein on the respective study key players. To explore potential upstream regulatory ncRNAs for the immune checkpoint PD-1/PD-L1. Bioinformatics tools including microrna.org and lnCeDB software were adopted to detect targeting of miR-155-5p, miR-194-5p and lncRNAs XIST and MALAT-1 to PD-L1 mRNA, respectively. In addition, Diana tool was used to predict targeting of both aforementioned miRNAs to lncRNAs XIST and MALAT-1. HCC and normal tissue samples were collected for scanning of PD-L1, XIST and MALAT-1 expression. To study the interaction among miR-155-5p, miR-194-5p, lncRNAs XIST and MALAT-1, as well as PD-L1 mRNA, a series of transfections of the Huh-7 cell line was carried out. Bioinformatics software predicted that miR-155-5p and miR-194-5p can target PD-L1, MALAT-1 and XIST. MALAT-1 and XIST were predicted to target PD-L1 mRNA. PD-L1 and XIST were significantly upregulated in 23 HCC biopsies compared to healthy controls; however, MALAT-1 was barely detected. MiR-194 induced expression elevated the expression of PD-L1, XIST and MALAT-1. However, overexpression of miR-155-5p induced the upregulation of PD-L1 and XIST, while it had a negative impact on MALAT-1 expression. Knockdown of XIST did have an impact on PD-L1 expression; however, following knockdown of the negative regulator of X-inactive specific transcript (TSIX), PD-L1 expression was elevated, and abolished MALAT-1 activity. Upon co-transfection of miR-194-5p with siMALAT-1, PD-L1 expression was elevated. Co-transfection of miR-194-5p with siXIST did not have an impact on PD-L1 expression. Upon co-transfection of miR-194 with siTSIX, PD-L1 expression was upregulated. I