CDK4 and hepatocellular carcinoma: This is consistent with our findings that the USP1 inhibitor ML-323 and siUSP1 treatments lead to G0/G1 arrest in HCC cells and the downregulation of the protein expression of cyclin D1, cyclin E1, CDK2, CDK4 in the initial stage of the G1 phase, in which cyclin D binds and activates CDK4 [37].