Raf-1 activation stimulates proliferation and inhibits IGF-stimulated differentiation in L6A1 myoblasts
| Autor: | D. Z. Ewton, S. A. Coolican, Derina S. Samuel, F. J. Mcwade, T. D. Petley, J. R. Florini |
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| Rok vydání: | 1999 |
| Předmět: |
MAPK/ERK pathway
medicine.medical_specialty Myoblast proliferation Endocrinology Diabetes and Metabolism Morpholines Clinical Biochemistry Muscle Fibers Skeletal Transfection Biochemistry Gene Expression Regulation Enzymologic MAP2K7 Endocrinology Internal medicine medicine c-Raf Enzyme Inhibitors Insulin-Like Growth Factor I Muscle Skeletal Cells Cultured MAPK14 Flavonoids Mitogen-Activated Protein Kinase 3 biology Estradiol Chemistry Myogenesis Akt/PKB signaling pathway Biochemistry (medical) Cell Differentiation General Medicine Cell biology Proto-Oncogene Proteins c-raf Chromones Mitogen-activated protein kinase Calcium-Calmodulin-Dependent Protein Kinases biology.protein Mitogen-Activated Protein Kinases Cell Division Signal Transduction |
| Zdroj: | Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme. 31(2-3) |
| ISSN: | 0018-5043 |
| Popis: | Our previous work has demonstrated that the insulin-like growth factors (IGFs), acting through a single receptor, stimulate both proliferation and differentiation of L6A1 myoblasts. This unique model system has enabled us to closely examine the switch that regulates these two opposing responses. We have previously shown, using specific inhibitors of the IGF-I signal transduction pathway, that the mitogenic response is mediated by the Ras/Raf/MAP kinase pathway and the myogenic response by the PI 3-kinase/p70s6k pathway (Coolican SA, Samuel DS, Ewton DZ, McWade FJ, Florini JR, J Biol Chem 1997; 272: 6653-62). In that study we found that PD098059, an inhibitor of MEK activation, inhibited the proliferative response, but dramatically enhanced IGF-stimulated differentiation which was associated with elevation of p70s6k activity. Since there have been reports of elevation of Raf-1 activity in PD098059-treated L6 myoblasts, and stimulation of p70s6k activity in cells expressing an activated Raf-1, it was important to determine whether or not Raf-1 elevation plays a role in the myogenic response. To test this, we have transfected L6A1 myoblasts with delta Raf-1:ER, an estradiol-regulated form of oncogenic Raf-1. We found that activation of Raf-1 by estradiol resulted in increased phosphorylation of p42 and p44 MAP kinases and stimulation of proliferation. In contrast, Raf-1 activation inhibited all measured aspects of the myogenic response: myogenin expression, creatine kinase elevation, and fusion of myoblasts to form myotubes. In addition, we found no elevation of p70s6k activity upon Raf-1 activation. These results indicate the following: (1) stimulation of myogenic differentiation by PD098059 treatment is not simply due to the elevation of Raf-1, (2) Raf-1 has a positive role in the MAP kinase pathway and myoblast proliferation, and (3) Raf-1 activation inhibits myogenesis, possibly by forcing cells to remain in the proliferative state. |
| Databáze: | OpenAIRE |
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