Fig. 4

Increased PD-L1 expression is correlated with activation of STAT3 under acidic conditions in MDA-MB-231 cells. A–C Gene set enrichment analysis (GSEA) results according to high and low expression of PD-L1 in breast cancer patients. D The pH of the medium was adjusted with HCl or NaOH, and MDA-MB-231 cells were treated for 18 h. Protein levels were analyzed by western blotting. E MDA-MB-231 cells were incubated under acidic conditions for the indicated periods, and protein levels were analyzed by western blotting. F, G MDA-MB-231 cells were incubated with HCl or lactic acid-treated acidic medium for 18 or 24 h; the acidic culture medium was replaced with new medium or NaHCO₃ was added for 24 h. Protein levels were analyzed by western blotting. H MDA-MB-231 cells were transfected with si-NTC (negative control) or si-STAT3 for 24 h followed by treatment with HCl-treated acidic medium for 18 h. Protein levels were analyzed by western blotting. I MDA-MB-231 cells were transfected with mock-GFP or WT-STAT3-GFP for 48 h. Protein levels were analyzed by western blotting