Positive feedback regulation between Akt2 and MyoD during muscle differentiation. Cloning of Akt2 promoter.
Akt2 is a member of the Akt/PKB family, which is involved in a variety of cellular events including cell survival, proliferation, and differentiation. During skeletal muscle differentiation, the Akt2 but not Akt1 expression was significantly increased. Microinjection of anti-Akt2 but not anti-Akt1 antibody efficiently abrogated myogenesis, indicating that Akt2 plays a specific role in muscle differentiation. It has been well documented that ectopic expression of MyoD is sufficient to induce muscle differentiation in myoblasts. However, the mechanism of induction of Akt2 during muscle differentiation and the significance of Akt2 protein in MyoD-induced myogenesis are largely unknown. In this study, we provide direct evidence that Akt2 is transcriptionally regulated by MyoD and activates MyoD-myocyte enhancer binding factor-2 (MEF2) transactivation activity. The Akt2 promoter was isolated and found to contain nine putative E-boxes (CANNTG), which are putative MyoD binding sites. Electrophoretic mobility shift analyses revealed that MyoD bound to eight of the sites. The expression of MyoD significantly enhanced Akt2 promoter activity and up-regulated Akt2 mRNA and protein levels. Moreover, Akt2 but not Akt1 was activated during differentiation. The expression of Akt2 activated MyoD-MEF2 transcriptional activity and induced myogenin expression. These data indicate that there is a positive feedback regulation loop between Akt2 and MyoD-MEF2 during muscle differentiation, which is essential for MyoD-induced myogenesis.
Kaneko
Satoshi
S
Department of Pathology and Laboratory of Medicine, University of South Florida College of Medicine and H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
Feldman
Richard I
RI
Yu
Lu
L
Wu
Zhenguo
Z
Gritsko
Tatiana
T
Shelley
Sue A
SA
Nicosia
Santo V
SV
Nobori
Tsutomu
T
Cheng
Jin Q
JQ
D001483:Base Sequence; D001665:Binding Sites; D002454:Cell Differentiation; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000502:physiology; D005246:Feedback; D006801:Humans; D064326:MEF2 Transcription Factors; D008969:Molecular Sequence Data; D009132:Muscles / Q000196:embryology*; D017570:MyoD Protein / Q000502:physiology*; D018006:Myogenic Regulatory Factors; D018008:Myogenin / Q000235:genetics; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051057:Proto-Oncogene Proteins c-akt; D014157:Transcription Factors / Q000502:physiology; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; C503799:MYOG protein, human; D017570:MyoD Protein; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C494918:AKT1 protein, human; C494921:AKT2 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt