Apoptosis-Independent Reduction of Programmed Death Ligand-1 Levels by Boningmycin Through AMPK-Mediated Endoplasmic Reticulum-Associated Protein Degradation in Human Tumor Cells

Abstract Boningmycin (BON), a new member of the bleomycin family, exhibits highly potent activity against tumor cells in vitro and in vivo. It remains unclear if BON can affect the protein levels of programmed death ligand-1 (PD-L1) in a manner similar to that of other antitumor agents. Potent inhibition of cell survival by BON was observed in non-small-cell lung cancer NCI-H460 cells and sarcoma HT1080 cells. Apoptosis-independent reduction of PD-L1 was observed after exposure to BON. Furthermore, BON-treatment increased AMP-activated protein kinase phosphorylation, however, this increase was suppressed by treatment with specific inhibitor (compound C) or RNAi-mediated knockdown of AMPKα. BON-induced PD-L1 reduction is mediated by the endoplasmic reticulum-associated degradation pathway. Its mode of action is similar to that of metformin on the PD-L1 protein. In conclusion, it is firstly reported that BON can decrease PD-L1 protein levels through the AMPK activated endoplasmic reticulum- associated degradation pathway.