Knockdown of METTL5 inhibits the Myc pathway to downregulate PD-L1 expression and inhibits immune escape of hepatocellular carcinoma cells

The incidence of hepatocellular carcinoma (HCC) is raised annually, which causes a great harm to people's health. This research aimed to investigate the influence and mechanism of methyltransferase-like 5 (METTL5) in HCC. According to The Cancer Genome Atlas (TCGA) database, METTL5 levels and prognosis was analyzed in HCC. Next, in HCC tissues and cells, METTL5 expression was examined via quantitative real-time polymerase chain reaction (qRT-PCR). Biological behaviors of HCC cells were assessed by Cell Counting Kit-8 (CCK-8), colony formation, transwell and flow cytometry assays. Gene Set Enrichment Analysis (GSEA) was applied to predict METTL5 related pathway. The possible binding sites of programmed cell death 1 ligand 1 (PD-L1) and myelocytomatosis viral oncogene (Myc) was predicted by JASPAR database. Western blot was utilized to test the change of PD-L1 and Myc pathway related proteins [cellular (c)-Myc, chaperonin containing TCP1 subunit 2 (CCT2) and chromobox protein homolog 3 (CBX3)]. In HCC tissues and cells, METTL5 expression was increased. High METTL5 expression was associated with poor prognosis. Knockdown of METTL5 inhibited HCC cell proliferation and invasion, induced cell apoptosis and reduced the expression of PD-L1, c-Myc, CCT2 and CBX3. The bind between PD-L1 and the Myc promoter in HCC cells was confirmed using Chip and luciferase reporter assays. Moreover, the influences of knockdown of METTL5 on PD-L1 expression and HCC cell biological behaviors were reversed by overexpression of Myc. Knockdown of METTL5 inhibited PD-L1 expression and malignant cell behavior of HCC through inhibiting the Myc pathway.