Hypoxia upregulates the expression of PD-L1 via NPM1 in breast cancer.

Background: A hypoxic microenvironment is the most frequent characteristic in tumor microenvironment. Programmed death-ligand 1 (PD-L1) is an important molecule and therapeutic target that mediates the immune response of tumor cells. Previous studies have shown that hypoxia can lead to increased expression of Nucleophosmin 1 (NPM1) and PD-L1. However, the exact regulatory mechanisms of NPM1 and PD-L1 expression under hypoxic conditions are still poorly understood.

Methods: The relationships among hypoxia, NPM1 and PD-L1 were explored by western blotting, immunofluorescence staining, flow cytometry and chromatin immunoprecipitation-quantitativePCR(ChIP-qPCR). Animal tumor models were established to explore the effect of NPM1 expression on tumor growth. The relationships between NPM1 and breast cancer (BC) clinical features and immune infiltration were revealed by bioinformatics analysis.

Results: NPM1 mediates increased PD-L1 expression in the hypoxic microenvironment of BC. HIF-1α can increase the expression of NPM1 by activating the p-AKT pathway and binding to the NPM1 promoter. Increased expression of NPM1 can promote tumor growth and inhibit T cell infiltration. Bioinformatics analysis showed that the high expression of NPM1 was associated with poorer survival and immunosuppression in patients with BC.

Conclusions: The hypoxic microenvironment promotes PD-L1 expression via NPM1 in BC, which may be further associated with the inhibition of tumor immunity. NPM1 may serve as a potential target for modulating PD-L1 immunotherapy.