NEDD8 and hepatocellular carcinoma: However, in HCC cells transfected with HA-PCNA K164R plasmid, HA-PCNA K164R could not bind to NEDD8 in controls, NEDD8 overexpression and NEDD8 knockdown groups, and the level of HA-PCNA K164R K48-linked polyubiquitination and PCNA protein levels were not altered between the above groups (Fig. 5F and Supplementary Fig. 3E).