CCNE2 and hepatocellular carcinoma: For example, depletion of CBX4 reduces the levels of proliferating cell nuclear antigen (PCNA) and cyclin E2/CCNE2 while increasing the level of cyclin-dependent kinase inhibitor 2A (CDKN2A/p16) to delay the G1/S transition in hepatocellular carcinoma cells 15.