Abstract
Background:
Nasopharyngeal carcinoma (NPC) is a malignant tumor characterized by a large number of tumor-infiltrating lymphocytes and high expression of programmed death ligand-1 (PD-L1). Interferon-gamma (IFN-γ) has proven to be the strongest inducers of PD-L1. This study aims at investigating the effect of IFN-γ on the expression of natural killer group 2, member D ligands (NKG2DLs), a series of immune-activating proteins, and their further effect on immune killing in NPC.
Methods:
RNA-seq data from the Gene Expression Omnibus database was downloaded and analyzed for the correlation between IFN-γ and NKG2DLs. IHC staining of clinical biopsy samples was performed to support the correlation between IFN-γ and ULBP3. Different NPC cell lines were treated with IFN-γ (100 U/ml) and the expression of PD-L1 and ULBP3 were detected at different time points. The 5-8F cell lines with PD-L1 over-expression and ULBP3 knockout were established and the T-cell cytotoxicity assay was performed to investigate the effect of ULPB3 on cytotoxicity.
Results:
Correlation analysis and IHC staining showed that the expression of ULBP3 had a significant negative correlation with IFN-γ in NPC patients. The vitro assays revealed that ULBP3 can be time-dependently down-regulated by IFN-γ. The cytotoxicity of CD8+ T-cells that were co-cultured with ULBP3 knockout 5-8F cells was significantly impaired compared to wild type 5-8F cells.
Conclusions:
IFN-γ can significantly down-regulate the expression of ULBP3 in NPC. And the down-regulation of ULBP3 and the up-regulation of PD-L1 are both mediated by IFN-γ and may collectively play a role in the inhibition of immune killing in NPC.