RNF20 and neoplasm: Furthermore, some of Smurfs’ special substrates [e.g., Skp1-cullin-1-F-box protein (SCF) ubiquitin ligase complex, ring finger protein 20 (RNF20)] have a wholly opposite role in tumor progression in different cell types and cellular contexts, which further broadens the complexity of Smurfs’ regulation of biological functions (33, 35–37).