Fig. 3

Pharmacological inhibition of ERK1/2 promotes PD-L1 degradation via autophagy induction. A ERK inhibition by ERKi in different concentrations (0.5, 1.0, 2.0, 4.0 μM) in HuCCT1 and RBE cells induced the conversion of LC3-I to LC3-II. B Representative images of positive staining of LC3 (green) and DAPI (blue) was determined by immunofluorescence in HuCCT1 and RBE cells treated by ERKi (4 μM) for 24 h. (Scar bar, 20 μm). C Western blotting analysis of ERK, p-ERK, PD-L1, p62/SQSTMQ1 and LC3-I/II after the treatment of ERKi alone or a combination of ERKi and autophagy inhibitors, including chloroquine (CQ, 5 μM) or 3-methyladenine (3-MA, 5 μM) in HuCCT1 and RBE cells for 24 h. D Western blotting analysis of ERK, p-ERK, PD-L1, p62/SQSTMQ1 and LC3-I/II upon the autophagy inhibiting by knocking down ATG7 in HuCCT1 and RBE cells with or without ERKi pretreatment. The knockdown efficacies of ATG7 were verified. The conversion of LC3-I to LC3-II was reduced. E–F Representative images of positive staining of PD-L1 (red), LC3-II (green) and DAPI (blue) was determined by immunofluorescence after treatment of ERKi alone or a combination of ERKi and CQ(5 μM) or 3-MA(5 μM) in HuCCT1 and RBE cells for 24 h (Scale bar, 150 μm)