CD274 and breast cancer: In non-small cell lung cancer, hepatocellular carcinoma, and breast cancer, the reduction of COP1 (E3 ligase constitutive photomorphogenesis protein 1) increases c-Jun accumulation and subsequently inhibits the expression of histone deacetylase 3 (HDAC3), thereby enhancing histone H3 acetylation and promoting PD-L1 transcription [199].