Tumor-expressing PD-L1 regulates NT5E expression through MAPK/ERK pathway in triple-negative breast cancer.

OBJECTIVES: While programmed cell death 1 (PD-1) inhibitors have improved cancer treatment, the function and mechanisms of programmed cell death ligand 1 (PD-L1), particularly when expressed by cancer cells, remain unclear. This study aims to explore the role of PD-L1 within breast cancer cells and identify key targets for future immunotherapy. METHODS: RNA-seq was performed on breast cancer cells with silenced PD-L1 to screen for differentially expressed genes, followed by bioinformatics analysis. Clinical specimens from breast cancer patients undergoing primary surgery without preoperative treatment were collected, along with in vitro analysis to validate the potential mechanism. RESULTS: RNA-seq data revealed a significant positive correlation between Ecto-5'-nucleotidase (NT5E) expression and PD-L1. Bioinformatics analysis corroborated this positive correlation. Immunohistochemistry staining demonstrated higher NT5E expression associated with increased lymph node metastasis. High expression of the NT5E gene was associated with poor overall survival (OS) in breast cancer patients, as determined by KM plotter analysis. Following PD-L1 gene silencing by siRNA in breast cancer cells, NT5E mRNA and protein expression significantly decreased. Conversely, no significant changes were observed in PD-L1 expression after NT5E gene silencing. In vitro experiments confirmed that cancer cell proliferation and metastasis abilities were significantly reduced by either PD-L1 or NT5E gene down-regulation. Western blotting demonstrated that PD-L1 expressed by cancer cells regulates NT5E expression through the MAPK/ERK signaling pathway. CONCLUSION: This study proposes a potential mechanism wherein tumor-expressing PD-L1 regulates NT5E through the MAPK/ERK pathway. Down-regulation of PD-L1 or NT5E can significantly inhibit the proliferation and metastatic ability of cancer cells, potentially providing practical therapeutic targets and prognostic markers for combined PD-L1 immunotherapy in breast cancer.