CDKN1B and neoplasm: Jab1/CSN5 plays an essential role in positively regulating cellular proliferation by functionally inactivating several key negative regulatory proteins and tumor suppressors through their subcellular localization, degradation, and deneddylation, including p53, Smad 4/7, and the cyclin-dependent kinase inhibitor p27Kip1 (p27) [5-8].