Protein phosphatase 1 isoforms in differentiating C2C12 myocytes.
In muscle protein phosphatase 1 (PP1) is involved in growth factor signal transduction and metabolic regulations. Three isoforms of the catalytic subunit are found in mammalian cells (PP1alpha, PP1gamma1 and PP1delta), with potentially different functions. We investigated the changes in the PP1 isoforms in differentiating C2C12 myoblasts. Few hours after differentiation induction the soluble PP1 activity was reversibly increased, displaying a peak at 6h. This was due to activation mainly of PP1alpha, with no change in the immunodetected protein. A further indication of PP1alpha involvement came from the observation that electroporation of inactive PP1alpha into myoblasts induced a differentiation delay of at least 24h. Subsequently, starting from 9-12 h, the activities and protein levels of all the three soluble PP1 isoforms decreased, reaching a minimum around 48 h. By this time the cells had undergone morphological changes and myosin became immunodetectable. We conclude that PP1 may be involved in myoblast differentiation, based on: 1) its higher activity in myoblasts than in myocytes, 2) the reversible activation of soluble PP1alpha during the first 6h from differentiation induction, 3) the delay in differentiation onset following electroporation of inactive PP1alpha into myoblasts.
Tognarini
M
M
Department of Biomedicine, University of Pisa, Italy.
Villa-Moruzzi
E
E
D000818:Animals; D002454:Cell Differentiation; D002458:Cell Fractionation; D002460:Cell Line; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology* / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D054645:Protein Phosphatase 1; D012995:Solubility; D013997:Time Factors
D007527:Isoenzymes; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1