Tumor-intrinsic PD-L1 drives lung cancer progression in response to TLR stimulation by promoting autophagy through the TRAF6– BECN1 signaling axis

Abstract

Background Programmed death-ligand 1 (PD-L1, CD274) is well known for its immunosuppressive function within the tumor microenvironment; however, its tumor cell–intrinsic roles remain incompletely characterized. Emerging evidence suggests that PD-L1 may regulate oncogenic processes beyond immune evasion. This study aimed to define the intrinsic functions of PD-L1 in non–small cell lung cancer (NSCLC), with a focus on autophagy and metastasis-related signaling pathways. Methods Integrated transcriptomic analyses of patient-derived NSCLC specimens were performed to evaluate associations between CD274 expression and oncogenic gene signatures. CRISPR–Cas9–mediated knockout and plasmid-driven overexpression of PD-L1 were conducted in H460 and A549 cell lines to assess proliferation, migration, clonogenicity, and 3D spheroid growth. Molecular interactions among PD-L1, TRAF6, and BECN1 were examined through immunoprecipitation and ubiquitination assays. Autophagy induction was evaluated by LC3 lipidation and autophagosome formation under Toll-like receptor ( TLR) stimulation. The functional relevance of PD-L1 in metastasis was further assessed using xenograft models. Results Clinical transcriptomic analyses demonstrated that CD274 upregulation correlates with enrichment of cancer progression, proliferation, and autophagy-associated gene sets in NSCLC. PD-L1 knockout markedly reduced cell proliferation, migration, clonogenicity, and 3D spheroid formation, whereas its overexpression enhanced these oncogenic phenotypes. Mechanistically, PD-L1 physically interacted with TRAF6 and BECN1, promoting TRAF6 dependent BECN1 ubiquitination and TLR-induced autophagy. PD-L1 depletion suppressed TLR-driven LC3 lipidation, autophagosome formation, and epithelial–mesenchymal transition (EMT), while PD-L1 overexpression augmented autophagy and EMT responses. In vivo, PD-L1-deficient lung cancer cells displayed diminished tumor growth and reduced metastatic potential in xenograft models. Conclusions This study identifies PD-L1 as a previously unrecognized intrinsic driver of NSCLC progression through activation of the TLR–TRAF6–BECN1 autophagy axis and promotion of EMT. Beyond its canonical role in immune evasion, PD-L1 functions as a dual-regulator of tumorigenesis by coordinating autophagy-dependent oncogenic processes. These findings provide novel mechanistic insight and support the therapeutic rationale for targeting PD-L1 not only as an immune checkpoint but also as a key modulator of cancer cell–intrinsic signaling in NSCLC.