PD-L1 knockout increased EGFR and p-EGFRY1068 proteins by autophagy inhibition and proteasome induction

Yen-Cheng Lin (林彥丞) 1, Ya-Chun Yu 1, Rou-Hsin Wang 1,2, Jui-I Chao 1,2,3

1 Department of Biological Science and Technology, National Yang Ming Chiao Tung University

2 Institute of Molecular Medicine and Bioengineering, National Yang Ming Chiao Tung University

3 Center For Intelligent Drug Systems and Smart Bio-devices, National Yang Ming Chiao Tung University  

Programmed death-ligand 1 (PD-L1) is one of the immunocheck point protein, which inhibiting T cell receptor (TCR) signaling through interacting with programmed-death 1 (PD-1) protein enriched on the membrane of T cells. Studies have pointed out that epidermal growth factor receptor (EGFR) protein modulated PD-L1 protein expression by regulating PI3K/AKT pathway and RAS/ERK pathway. In this study, we demonstrated that PD-L1 could reversely negatively regulate EGFR protein expression in human non-small cell lung cancer (NSCLC) cells. Immunoblot analysis and immunofluorescent staining revealed that knockout of PD-L1 protein significantly increased EGFR and phosphorylated p-EGFRY1068 protein expression level. The decrease of EGFR induced by neo-protein synthsis inhibitor cycloheximide (CHX) was not mediated by PD-L1 protein. However, treatment of autophagy inhibitor chloroquine (CQ) dramatically increased EGFR protein accumulation in the PD-L1 normal cells but PD-L1 knockout cells. And treatment of proteasome inhibitor MG132 increased EGFR accumulation much more in the PD-L1 knockout cells. These findings indicated that PD-L1 improved EGFR degradation by autophagy pathway, while proteasome-ubiquitin system (UPS) was activated under PD-L1 knockout condition. Our study innovatively discovered that knockout of PD-L1 increased EGFR and phosphorylated p-EGFRY1068 protein expression level through defective autophagy activity. UPS was activated to modulate EGFR protein level in the PD-L1 knockout cells.