TRAF6 Knockout Cell Line (A549)

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.

TNF receptor-associated factor 6 (TRAF6)-BECN1 signaling axis plays a pivotal role in autophagy induction through ubiquitination of BECN1, thereby inducing lung cancer migration and invasion in response to toll-like receptor 4 (TLR4) stimulation. Herein, we provide novel molecular and cellular mechanisms involved in the negative effect of ubiquitin-specific peptidase 15 (USP15) on lung cancer progression. Clinical data of the TCGA and primary non-small cell lung cancer (NSCLC) patients (n = 41) revealed that the expression of USP15 was significantly downregulated in lung cancer patients. Importantly, USP15-knockout (USP15KO) A549 and USP15KO H1299 lung cancer cells generated with CRISPR-Cas9 gene-editing technology showed increases in cancer migration and invasion with enhanced autophagy induction in response to TLR4 stimulation. In addition, biochemical studies revealed that USP15 interacted with BECN1, but not with TRAF6, and induced deubiquitination of BECN1, thereby attenuating autophagy induction. Notably, in primary NSCLC patients (n = 4) with low expression of USP15, 10 genes (CCNE1, MMP9, SFN, UBE2C, CCR2, FAM83A, ETV4, MYO7A, MMP11, and GSDMB) known to promote lung cancer progression were significantly upregulated, whereas 10 tumor suppressor genes (FMO2, ZBTB16, FCN3, TCF21, SFTPA1B, HPGD, SOSTDC1, TMEM100, GDF10, and WIF1) were downregulated, providing clinical relevance of the functional role of USP15 in lung cancer progression. Taken together, our data demonstrate that USP15 can negatively regulate the TRAF6-BECN1 signaling axis for autophagy induction. Thus, USP15 is implicated in lung cancer progression.

Thioredoxin-interacting protein (TXNIP) functions as a tumor suppressor, but its role in lung cancer remains poorly defined. This study identifies TXNIP as a negative regulator of TNF receptor-associated factor 6 (TRAF6)-mediated NF-κB activation and autophagy, key pathways in tumor progression. TXNIP directly binds TRAF6 via its C-terminal arrestin domain, inhibiting TRAF6 dimerization and auto-ubiquitination. This, in turn, reduces ubiquitination of downstream targets TGF-β-activated kinase 1 and beclin 1 (BECN1), thereby suppressing NF-κB signaling and autophagic activity. TXNIP expression is significantly reduced in lung adenocarcinoma and lung squamous cell carcinoma, as demonstrated by public datasets and patient tissue analysis. Gene set enrichment analysis shows that non-small cell lung cancer patients with TXNIP and TRAF6 expression exhibit increased metastasis-associated gene signatures and poorer survival outcomes. Functionally, -knockout lung cancer cells show enhanced TRAF6 and BECN1 ubiquitination, increased LC3 puncta, and elevated NF-κB activity and cytokine production after TLR3/4 stimulation. These cells also display increased proliferation, migration, invasion, and colony formation in vitro across multiple lung cancer cell lines (A549 and H1299). Collectively, this study highlights TXNIP as a critical suppressor of TRAF6-driven oncogenic pathways in lung cancer, suggesting that its downregulation contributes to disease progression through enhanced TLR-induced signaling.