Background: PD-L1 and PD-L2 are PD-1 ligands (PD-Ls). PD-Ls over-expression is associated with poor prognosis in hepatocellular carcinoma (HCC). However, little is known about how PD-Ls expression is regulated. Here, we investigated the involvement of lncRNA-microRNA network in the regulation of PD-Ls in HCC.
Methods: The expression of PD-Ls, PCED1B-AS1 and hsa-miR-194-5p was measured in 45 pairs of HCC samples. The interaction between PCED1B-AS1 and hsa-miR-194-5p was measured by microRNA pull down and in vitro binding assay. The effects of PCED1B-AS1 knockdown and over-expression on hsa-miR-194-5p and PD-Ls expression were investigated in HCC cell lines. Immunosuppression was evaluated in co-culture of HCC cell line and human T cells. Exosomes were isolated from HCC cells and their effects on receipt cells were investigated. Tumor behaviors were evaluated by in vitro and in vivo assays.
Results: PD-L1 expression was highly correlated with PD-L2 expression in HCC. PCED1B-AS1 and hsa-miR-194-5p expression was up-regulated in HCC. PCED1B-AS1 was positively correlated with PD-Ls but negatively correlated hsa-miR-194-5p in HCC. These correlations were cross-validated by TCGA-LIHC dataset. PCED1B-AS1 interacted with hsa-mir-194-5p which inhibited PD-Ls expression. PCED1B-AS1 enhanced the expression of PD-Ls via sponging hsa-mir-194-5p. PCED1B-AS1-induced PD-Ls-mediated immunosuppression in co-cultured T cells. HCC cells released PCED1B-AS1 containing exosomes and the exosomal PCED1B-AS1 enhanced PD-Ls expression in receipt HCC cells while inhibited receipt T cells and macrophages. Blood exosomal PCED1B-AS1 was correlated with HCC PD-Ls expression. Finally, PCED1B-AS1 promoted cell proliferation, colony formation and in vivo tumor formation in xenografted nude mice while inhibited apoptosis.
Conclusions: PCED1B-AS1 enhances the expression and function of PD-Ls via sponging hsa-miR-194-5p to induce immunosuppression in HCC.
Keywords: Exosome; Hepatocellular carcinoma; Immune checkpoint; Immunosuppression; PCED1B-AS1; PD-L1; PD-L2; lncRNA; miR-194-5p; microRNA.