NAE1 and liver cancer: The expression levels of NEDD8, E1 NEDD8-activating enzymes (NAE1/UBA3) and the NEDD8 conjugation enzyme E2 (UBE2M/UBE2F) have been shown to be up-regulated in various solid tumors, such as lung adenocarcinoma and lung squamous cell carcinoma, intrahepatic cholangiocarcinoma, liver cancer, colorectal cancer, glioblastoma, head and neck tumor, esophageal squamous cell carcinoma and renal cell carcinoma relative to adjacent normal tissues [15–22].