Akt2 is implicated in skeletal muscle differentiation and specifically binds Prohibitin2/REA.
Akt1 and Akt2 are the major isoforms of Akt expressed in muscle cells and muscle tissue. We have performed siRNA silencing of Akt1 and Akt2 in C2 myoblasts to characterize their specific implication in muscle differentiation. Whereas silencing Akt2, and not Akt1, inhibited cell cycle exit and myoblast differentiation, Akt2 overexpression led to an increased proportion of differentiated myoblasts. In addition, we demonstrate that Akt2 is required for myogenic conversion induced by MyoD overexpression in fibroblasts. We show Akt2, but not Akt1, binds Prohibitin2/Repressor of Estrogen Activator, PHB2/REA, a protein recently implicated in transcriptionnal repression of myogenesis. Co-immunoprecipitation experiments on endogenous proteins showed the Akt2-REA complex does not contain Prohibitin1. We have analyzed expression and localization of PHB2/REA during proliferation and differentiation of mouse and human myoblasts. PHB2/REA shows punctated nuclear staining which partially co-localizes with Akt2 in differentiated myotubes and PHB2 levels decrease at the onset of myogenic differentiation concomitant with an increase in Akt2. There appears to be an inverse correlation between Akt2 and PHB2 protein levels where cells silenced for Akt2 expression show increased level of PHB2/REA and overexpression of Akt2 resulted in decreased Prohibitin2/REA. Taken together, these results, along with our previous observations, clearly show that Akt2 and not Akt1 plays a major and early role in cell cycle exit and myogenic differentiation and this function involves its specific interaction with PHB2/REA.
Héron-Milhavet
Lisa
L
Cell Biology Unit, Institut de Génétique Humaine, Montpellier, France.
Mamaeva
Daria
D
Rochat
Anne
A
Lamb
Ned J C
NJ
Fernandez
Anne
A
D000818:Animals; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003470:Culture Media; D003593:Cytoplasm / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D019085:Fluorescent Antibody Technique, Direct; D020869:Gene Expression Profiling; D051379:Mice; D008845:Microinjections; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000201:enzymology; D018008:Myogenin / Q000378:metabolism; D011233:Precipitin Tests; D000091402:Prohibitins; D011485:Protein Binding; D020033:Protein Isoforms / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D003470:Culture Media; D018008:Myogenin; C000717331:PHB2 protein, human; C000717333:Phb2 protein, mouse; D000091402:Prohibitins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C494922:Akt2 protein, mouse; D051057:Proto-Oncogene Proteins c-akt