Recent research has illuminated the significant role of tumor-intrinsic programmed cell death ligand 1 (PD-L1) regulates tumor progression independently of the immune system. For immunotherapy and targeted therapy, PD-L1 expression is related to the tumor response and overall survival of head and neck squamous cell carcinoma (HNSCC) patients during anti-PD-1/PD-L1 immunotherapy. However, its effect on EGF-mediated metastasis and chemotherapy in HNSCC under lipid-enriched conditions remains unclear.

Investigating the impact of ANGPTL4, PTX3, and PD-L1 on HNSCC progression, we analyzed the gene expression signatures in four phenotypic classes of HNSCC (atypical, basal, classical, and mesenchymal), as analyzed through the Gene Expression Profiling Interactive Analysis version 2 (GEPIA2) database. To clarify the molecular mechanism regulating PD-L1 expression in EGF-treated cells, inhibitors of MAPK/ERK and NF-κB were used, followed by examining mRNA, protein, and promoter activity of PD-L1. The metastatic regulators, such as epithelial-mesenchymal transition (EMT) markers, ANGPTL4, and PTX3, were also examined in cells. The in vitro trans-well migration and invasion assays and in vivo extravasation assay were applied to study the role of PD-L1 in HNSCC metastasis. The apoptotic and spheroid formation assays were used to further study the impact of gefitinib and PD-L1 on the cell viability in cisplatin-treated HNSCC cells.

Our study showed a significant increase in PD-L1 expression in EGF-treated HNSCC cell lines. We determined that EGF-induced transcriptional activation of PD-L1 relies on ERK and NF-κB activation and ANGPTL4 expression. Importantly, depleting PD-L1 reduced EGF-induced expression of EMT markers, resulting in inhibition of migration, invasion, and anoikis resistance. Moreover, the enhancement of EGF-induced anoikis resistance and metastasis by oleic acid (OA) was diminished in PD-L1-knockdown cells. The combination of EGF and OA (EGF/OA)-induced cell metastasis and anoikis resistance were disrupted when treated with gefitinib. Although the EGF/OA attenuated cisplatin-induced apoptosis, only gefitinib, but not PD-L1 knockdown, restored sensitivity to cisplatin treatment. These findings suggest that intrinsic PD-L1 is essential for EGF- and lipid-induced cell metastasis but is not correlated to chemoresistance.

Targeting both EGFR and PD-L1 may provide a promising therapeutic strategy for managing metastatic HNSCC with cisplatin resistance and dysregulated lipid metabolism.