title: EphrinA/EphA signal facilitates insulin-like growth factor-I-induced myogenic differentiation through suppression of the Ras/extracellular signal-regulated kinase 1/2 cascade in myoblast cell lines.
abstract: Insulin-like growth factor-I (IGF-I) activates not only the phosphatidylinositol 3-kinase (PI3K)-AKT cascade that is essential for myogenic differentiation but also the extracellular signal-regulated kinase (ERK) 1/2 cascade that inhibits myogenesis. We hypothesized that there must be a signal that inhibits ERK1/2 upon cell-cell contact required for skeletal myogenesis. Cell-cell contact-induced engagement of ephrin ligands and Eph receptors leads to downregulation of the Ras-ERK1/2 pathway through p120 Ras GTPase-activating protein (p120RasGAP). We therefore investigated the significance of the ephrin/Eph signal in IGF-I-induced myogenesis. EphrinA1-Fc suppressed IGF-I-induced activation of Ras and ERK1/2, but not that of AKT, in C2C12 myoblasts, whereas ephrinB1-Fc affected neither ERK1/2 nor AKT activated by IGF-I. IGF-I-dependent myogenic differentiation of C2C12 myoblasts was potentiated by ephrinA1-Fc. In p120RasGAP-depleted cells, ephrinA1-Fc failed to suppress the Ras-ERK1/2 cascade by IGF-I and to promote IGF-I-mediated myogenesis. EphrinA1-Fc did not promote IGF-I-dependent myogenesis when the ERK1/2 was constitutively activated. Furthermore, a dominant-negative EphA receptor blunted IGF-I-induced myogenesis in C2C12 and L6 myoblasts. However, the inhibition of IGF-I-mediated myogenesis by down-regulation of ephrinA/EphA signal was canceled by inactivation of the ERK1/2 pathway. Collectively, these findings demonstrate that the ephrinA/EphA signal facilitates IGF-I-induced myogenesis by suppressing the Ras-ERK1/2 cascade through p120RasGAP in myoblast cell lines.
authors.affiliation: Department of Cell Biology, National Cerebral and Cardiovascular Center Research Institute, Osaka 565-8565, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Minami
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Koyama
authors.forename: Yuki
authors.initials: Y
authors.lastname: Wakayama
authors.forename: Shigetomo
authors.initials: S
authors.lastname: Fukuhara
authors.forename: Naoki
authors.initials: N
authors.lastname: Mochizuki
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002459:Cell Fusion; D002460:Cell Line; D036342:Ephrins / Q000378:metabolism; D055785:Gene Knockdown Techniques; D007141:Immunoglobulin Fc Fragments / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D036082:Receptor, EphA1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D036104:Receptor, EphA2 / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D020729:p120 GTPase Activating Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D036342:Ephrins; D007141:Immunoglobulin Fc Fragments; D020729:p120 GTPase Activating Protein; D007334:Insulin-Like Growth Factor I; D036082:Receptor, EphA1; D036104:Receptor, EphA2; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D018995:Myosin Heavy Chains; D016283:Proto-Oncogene Proteins p21(ras)