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      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

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          Insulin-like growth factor-I (IGF-I) activates not only the AKT pathway responsible for skeletal myogenesis but also the extracellular signal–regulated kinase (ERK) 1/2 cascade that inhibits myogenesis. The ephrinA/EphA signal facilitates IGF-I–induced myogenesis by inhibiting the Ras-ERK1/2 pathway via p120 Ras GTPase-activating protein.


          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.

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          Most cited references 44

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          Mice carrying null mutations of the genes encoding insulin-like growth factor I (Igf-1) and type 1 IGF receptor (Igf1r).

          Newborn mice homozygous for a targeted disruption of insulin-like growth factor gene (Igf-1) exhibit a growth deficiency similar in severity to that previously observed in viable Igf-2 null mutants (60% of normal birthweight). Depending on genetic background, some of the Igf-1(-/-) dwarfs die shortly after birth, while others survive and reach adulthood. In contrast, null mutants for the Igf1r gene die invariably at birth of respiratory failure and exhibit a more severe growth deficiency (45% normal size). In addition to generalized organ hypoplasia in Igf1r(-/-) embryos, including the muscles, and developmental delays in ossification, deviations from normalcy were observed in the central nervous system and epidermis. Igf-1(-/-)/Igf1r(-/-) double mutants did not differ in phenotype from Igf1r(-/-) single mutants, while in Igf-2(-)/Igf1r(-/-) and Igf-1(-/-)/Igf-2(-) double mutants, which are phenotypically identical, the dwarfism was further exacerbated (30% normal size). The roles of the IGFs in mouse embryonic development, as revealed from the phenotypic differences between these mutants, are discussed.
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            Eph receptor signalling casts a wide net on cell behaviour.

            Eph receptor tyrosine kinases mould the behaviour of many cell types by binding membrane-anchored ligands, ephrins, at sites of cell-cell contact. Eph signals affect both of the contacting cells and can produce diverse biological responses. New models explain how quantitative variations in the densities and signalling abilities of Eph receptors and ephrins could account for the different effects that are elicited on axon guidance, cell adhesion and cell migration during development, homeostasis and disease.
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              Myogenin expression, cell cycle withdrawal, and phenotypic differentiation are temporally separable events that precede cell fusion upon myogenesis

               K. Walsh,  V Andres (1996)
              During terminal differentiation of skeletal myoblasts, cells fuse to form postmitotic multinucleated myotubes that cannot reinitiate DNA synthesis. Here we investigated the temporal relationships among these events during in vitro differentiation of C2C12 myoblasts. Cells expressing myogenin, a marker for the entry of myoblasts into the differentiation pathway, were detected first during myogenesis, followed by the appearance of mononucleated cells expressing both myogenin and the cell cycle inhibitor p21. Although expression of both proteins was sustained in mitogen-restimulated myocytes, 5- bromodeoxyuridine incorporation experiments in serum-starved cultures revealed that myogenin-positive cells remained capable of replicating DNA. In contrast, subsequent expression of p21 in differentiating myoblasts correlated with the establishment of the postmitotic state. Later during myogenesis, postmitotic (p21-positive) mononucleated myoblasts activated the expression of the muscle structural protein myosin heavy chain, and then fused to form multinucleated myotubes. Thus, despite the asynchrony in the commitment to differentiation, skeletal myogenesis is a highly ordered process of temporally separable events that begins with myogenin expression, followed by p21 induction and cell cycle arrest, then phenotypic differentiation, and finally, cell fusion.

                Author and article information

                Role: Monitoring Editor
                Mol Biol Cell
                Mol. Bio. Cell
                Molecular Biology of the Cell
                The American Society for Cell Biology
                15 September 2011
                : 22
                : 18
                : 3508-3519
                aDepartment of Cell Biology, National Cerebral and Cardiovascular Center Research Institute, Osaka 565-8565, Japan
                bDivision of Cardiology, Department of Internal Medicine, Jikei University School of Medicine, Tokyo 105-8461, Japan
                University of Pennsylvania
                Author notes
                *Address correspondence to: Shigetomo Fukuhara ( fuku@ 123456ri.ncvc.go.jp ).
                © 2011 Minami et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License ( http://creativecommons.org/licenses/by-nc-sa/3.0).

                “ASCB®,” “The American Society for Cell Biology®,” and “Molecular Biology of the Cell®” are registered trademarks of The American Society of Cell Biology.


                Molecular biology


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