Human RKO cells LC-MSMS (gel-based proteomics)

Tumor cells evade T cell-mediated immunosurveillance via the interaction between programmed death-1 (PD-1) ligand 1 (PD-L1) on tumor cells and PD-1 on T cells. Strategies disrupting PD-1/PD-L1 have shown clinical benefits in various cancers. However, the limited response rate prompts us to investigate the molecular regulation of PD-L1. Here we identify trafficking protein particle complex subunit 4 (TRAPPC4), a major player in vesicular trafficking, as a crucial PD-L1 regulator. TRAPPC4 interacts with PD-L1 in recycling endosomes, promoting RAB11-mediated recycling of PD-L1, and acting as a scaffold between PD-L1 and RAB11, thus replenishing its distribution on the tumor cell surface.