PD-L1 alteration in lung cancer affects tumorigenicity lung tumors

Cancer immunotherapy has focused on inhibitors of checkpoint proteins, such as Programmed Death Ligand 1 (PD-L1). Unlike RAS-mutated lung cancers, EGFR mutant tumors have generally low response to immunotherapy. Because treatment outcomes vary by EGFR allele, we assumed that intrinsic and microenvironmental factors are involved. Among all non-immunological signaling pathways we surveyed in patients' datasets, EGFR signaling best associated with high PD-L1. Correspondingly, active EGFRs stabilized PD-L1's transcripts and depleting PD-L1 severely inhibited EGFR-driven tumorigenicity and metastasis in mice. The underlying mechanisms involve recruitment of phospholipase C-g1 (PLC-g1) to a cytoplasmic motif of PD-L1, which enhances PLC-g1 activation by EGFR. Once stimulated, PLC-g1 activates calcium flux, RHO GTPases and protein kinase C, which promotes an aggressive phenotype. Furthermore, anti-PD-L1 antibodies can inhibit these intrinsic functions of PD-L1. Our results portray PD-L1 as a molecular amplifier of EGFR signaling and lay the foundation for understanding resistance of EGFR+ tumors to immunotherapy. Overall design: PC9ER cells either overexpressing PDL1 or inhibition of si-PDL1 total RNA seq profiles.