CAPZ, but not canonical autophagy, regulates the endosomal-exosomal trafficking of plasma membrane PD-L1

Abstract

Programmed death-ligand 1 (PD-L1) undergoes continuous endocytosis and intracellular trafficking that regulate its degradation, recycling, and exosomal release. Although PD-L1 internalization is known to depend on RAB5-mediated endocytosis, whether canonical autophagy contributes to its subsequent endosomal trafficking remains unclear. Here we show that the endosomal and exosomal trafficking of cell surface PD-L1 occurs independently of the canonical autophagy machinery. Genetic disruption of core autophagy components, including LC3B, ATG4B, ATG5, and ATG7, did not impair trafficking of internalized PD-L1 to early endosomes, multivesicular bodies, late endosomes, or extracellular vesicles. Pharmacologic inhibition of autophagosome-lysosome fusion enhanced accumulation of PD-L1 within RAB5-and CD63-positive compartments, but this effect persisted in cells lacking LC3B, ATG5, or ATG7, indicating that PD-L1 trafficking through the endosomal-exosomal pathway does not require canonical autophagy. Instead, we identify the actin-capping protein CAPZ as a key regulator of an endosomal maturation checkpoint that controls PD-L1 sorting. Loss of CAPZ impaired progression of PD-L1 from early to late endosomal compartments, reduced PD-L1 incorporation into multivesicular bodies and extracellular vesicles, and redirected PD-L1 toward RAB11-dependent recycling, resulting in increased plasma membrane PD-L1 abundance. These findings establish that PD-L1 membrane fate is determined by CAPZ-dependent endosomal maturation rather than canonical autophagy and identify endosomal trafficking machinery as a critical regulator of immune checkpoint distribution.