Glioblastoma (GBM) is a highly aggressive primary brain tumor that shows intratumoral heterogeneity at the cellular and molecular level. Activation of programmed death receptor 1 (PD-1) interaction with its ligand PD-L1 is a well-known mechanism requisite for immune evasion deployed by malignant tumors including GBM. Herein, we set out to dissect the mechanism explaining the regulation of PD-L1 gene expression in GBM. The clinical samples consisted of 37 GBM tissues and 18 normal brain tissues. GBM cell model was treated by microRNA (miRNA) inhibitor, DNA constructs, and siRNAs. Assays of CCK-8 and Transwell insert were employed to assess the survival, migratory and invasive ability of GBM cell model. The immunosuppressive factor production, T cell apoptosis, and T cell cytotoxicity to GBM cells were evaluated in the co-culture system. GBM exhibited more miR-10b-5p abundance than normal at both tissue and cellular level. Suppression of miR-10b-5p weakened the ability of GBM cell model to survive, migrate, and invade, decreased the release of immunosuppressive factors, reduced T cell apoptosis, and strengthened the T cell cytotoxicity to GBM cell model. MiR-10b-5p conferred a negative control of Ten-eleven translocation 2 (TET2) that was downregulated in GBM. The functions of miR-10b-5p on GBM cell aggressiveness and immune evasion were mediated by TET2. TET2 recruited histone deacetylases HDAC1 and HDAC2 into the PD-L1 promoter region thus inhibiting its transcription. The study demonstrated the importance of miR-10b-5p-mediated repression of TET2 in PD-L1-driven immune evasion and their potential for immunotherapeutic targeting in GBM.
Keywords: PD-L1; TET2; glioblastoma; immune evasion; miR-10b-5p.