Insulin signaling leading to proliferation, survival, and membrane ruffling in C2C12 myoblasts.
We have recently shown that insulin induced myogenesis in the mouse C2C12 skeletal muscle cell line by activation of phosphatidylinositol (PI) 3-kinase/p70S6-kinase and p38-mitogen-activated protein kinase (MAPK) and downregulation of p42/p44-MAPK. This study investigated the insulin-signaling pathways involved in mitogenesis, survival, and membrane ruffling in C2C12 myoblasts, a cellular system that besides IGF-I receptors, expressed a high number of functional insulin receptors. Insulin (10 nM) rapidly stimulated beta-chain insulin receptor and IRS-1 tyrosine phosphorylation, IRS-2 being poorly and SHC not phosphorylated at all. However, an association of SHC with IRS-1 was found under insulin stimulation. Insulin stimulated IRS-1 association with p85alpha leading to the activation of PI3-kinase, and, subsequently AKT and p70S6-kinases. Moreover, both p42/p44- and p38-MAPKs resulted in phosphorylation after insulin stimulation. Insulin treatment for 24 h produced mitogenesis, as demonstrated by the increase in ((3)H)-thymidine incorporation, DNA content, the expression of PCNA and cyclin D1 proteins, and the proportion of cells in S + G2/M phases of the cell cycle. This mitogenic effect of insulin was precluded by inhibition of p70S6-kinase (either by rapamycin or by the PI3-kinase inhibitor LY294002) as well as by inhibition of p44/p42-MAPK with PD098059, but was not affected by inhibition of p38-MAPK. Serum deprivation of C2C12 myoblasts resulted in growth arrest at the GO/G1 phases of the cell cycle and apoptosis, as detected either by DNA laddering or by increase in the percentage of hypodiploid cells. Insulin rescued serum-deprived cells from apoptosis in an AKT-dependent manner, as demonstrated by the inhibition of AKT-activity by the use of LY294002 and ML-9, meanwhile neither inhibition of p70S6-kinase, nor MAPK affected insulin-induced survival. Finally, we evaluated the capacity of insulin to modulate actin cytoskeleton rearrangement. Insulin stimulation of myoblasts produced membrane ruffling and decreased actin stress fibers; this biological response being dependent of p38-MAPK, as demonstrated by the use of the p38-MAPK inhibitors SB203580 or PD169316, but independent of PI3-kinase and p42/p44-MAPK.
Conejo
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Departmento de Bioquimica y Biologia Molecular, Facultad de Farmacia, Universidad Complutense, 28040-Madrid, Spain.
Lorenzo
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D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000648:ultrastructure; D002470:Cell Survival / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000502:physiology; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D048051:p38 Mitogen-Activated Protein Kinases
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D019000:Phosphotyrosine; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D019893:Ribosomal Protein S6 Kinases; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D048051:p38 Mitogen-Activated Protein Kinases; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; C528034:Shc1 protein, mouse