ABSTRACT
Myogenesis is conducted by transcription factors including MyoD and myogenin. Myogenin is known to be polyubiquitinated by SCF (Skp1/Cullin 1/F-box protein) followed by proteasomal degradation, though the participating F-box protein is remaining unidentified. In this study, we found that myogenin in differentiated myoblasts is destabilized by muscle atrophy-inducing dexamethasone and that MAFbx (muscle atrophy F-box protein) is increased in atrophying myotubes. MAFbx overexpression resulted in MG132-sensitive reduction of myogenin. Myogenin had a MAFbx-recognition motif and interacted with MAFbx. MAFbx activated polyubiquitination of myogenin. The results of this study suggest that MAFbx functions as an F-box protein for ubiquitination of myogenin.
Subject(s)
Muscle Proteins/metabolism , Myogenin/metabolism , SKP Cullin F-Box Protein Ligases/metabolism , Amino Acid Sequence , Animals , Cell Line , Dexamethasone/metabolism , Glucocorticoids/metabolism , Insulin-Like Growth Factor I/metabolism , Mice , Molecular Sequence Data , Muscle Proteins/genetics , Myoblasts/cytology , Myoblasts/physiology , Myogenin/genetics , RNA Interference , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , SKP Cullin F-Box Protein Ligases/geneticsABSTRACT
We found that the levels of all general transcription factors (GTFs) for RNA polymerase II decreased in F9 cells when the cells were subjected to a differentiation procedure. Different from other GTFs, decrease of TFIIB during the differentiation was suppressed by addition of a proteasome inhibitor, MG132. The half-life of TFIIB in the differentiated cells was remarkably reduced compared with that in the undifferentiated cells. Moreover, it was demonstrated that TFIIB is a poly-ubiquitinated protein. Results of this study suggest that components of the transcription machinery decreased in accordance with cell differentiation and that TFIIB is specifically and rapidly degraded by the ubiquitin-proteasome pathway.
