CD274 and cancer: In multiple human cancer cell lines, Zhang et al. revealed that the fluctuation in the expression level of PD-L1 during different cell cycles was the highest in phase M and early phase G1, followed by a sharp decline in late-phase G1 and phase S, which was mainly because PD-L1 protein expression is regulated by ubiquitination-mediated degradation through cyclin D-CDK4 and the cullin 3-SPOP E3 ligase [32].