MicroRNA-155-5p suppresses PD-L1 expression in lung adenocarcinoma.

MiR-155-5p is a key oncogenic microRNA that maintains immune homeostasis and mediates cross-talk between inflammation and tumorigenesis. High expression of programmed death ligand-1 (PD-L1) also plays an important role in immune tolerance in tumors. The present study aimed to explore the relationship between miR-155-5p and PD-L1 in lung adenocarcinoma (LUAD) cells A549 and H1650. The expression levels of miR-155-5p and PD-L1 in LUAD patients were detected by a quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and mimics of miR-155-5p were used to model increased expression in A549 or H1650 cells. After 24 h, we measured levels of PD-L1 by qRT-PCR, western blotting and flow cytometry. In addition, we identified two sites in the PD-L1 3'-UTR (5'-AGCAUUA-3' and 5'-GCAUUAA-3') that can be bound by miR-155-5p using TargetScan (http://www.targetscan.org). Compared to normal tissue, miR-155-5p was overexpressed in tumor tissue (P = 0.0456), whereas the expression of PD-L1 was not significantly different (P = 0.1349). The expression levels of miR-155-5p and PD-L1 were negatively correlated (r = -0.6409, P = 0.0459 and r = -0.7544, P = 0.0117). Exogenous overexpression of miR-155-5p decreased the mRNA, total protein and membrane protein expression levels of PD-L1 both in A549 and H1650 cells (P < 0.05). Taken together, our data suggest that miR-155-5p may suppress the expression of PD-L1 in LUAD.