Downregulation of Ski and SnoN co-repressors by anisomycin.

Abstract Proteasome pathway regulates TGF-β signaling; degradation of activated Smad2/3 and receptors turns TGF-β signal off, while degradation of negative modulators such as Ski and SnoN maintains the signal. We have found that anisomycin is able to downregulate Ski and SnoN via proteasome as TGF-β does, but through a mechanism independent of Smad activation. The mechanism used by anisomycin to downregulate Ski and SnoN is also independent of MAPK activation and protein synthesis inhibition. TGF-β signal was the only pathway described causing Ski and SnoN degradation, thus this new effect of anisomycin on endogenous Ski and SnoN proteins suggests alternative processes to downregulate these negative modulators of TGF-β signaling.