Glycosylation and stabilization of programmed death ligand-1 suppresses T-cell activity.

Extracellular interaction between programmed death ligand-1 (PD-L1) and programmed cell death protein-1 (PD-1) leads to tumour-associated immune escape. Here we show that the immunosuppression activity of PD-L1 is stringently modulated by ubiquitination and N-glycosylation. We show that glycogen synthase kinase 3β (GSK3β) interacts with PD-L1 and induces phosphorylation-dependent proteasome degradation of PD-L1 by β-TrCP. In-depth analysis of PD-L1 N192, N200 and N219 glycosylation suggests that glycosylation antagonizes GSK3β binding. In this regard, only non-glycosylated PD-L1 forms a complex with GSK3β and β-TrCP. We also demonstrate that epidermal growth factor (EGF) stabilizes PD-L1 via GSK3β inactivation in basal-like breast cancer. Inhibition of EGF signalling by gefitinib destabilizes PD-L1, enhances antitumour T-cell immunity and therapeutic efficacy of PD-1 blockade in syngeneic mouse models. Together, our results link ubiquitination and glycosylation pathways to the stringent regulation of PD-L1, which could lead to potential therapeutic strategies to enhance cancer immune therapy efficacy.

M.-C.H. received sponsored research agreement from STCube Pharmaceuticals Inc. through MD Anderson Cancer Center. C.-W.L., S.-O.L. and M.-C.H. are inventors on patent applications under review: Dual function antibodies specific to glycosylated PD-L1 and methods of use thereof, 2016, No. 62/314,652. Combination treatments directed toward programmed death ligand-1 (PD-LI) positive cancers, 2016, No. 62/316,178. Antibodies specific to glycosylated PD-L1 and methods of use thereof, 2016, No. PCT/US16/24691. The remaining authors declare no competing financial interests.