title: Neuregulin-dependent protein synthesis in C2C12 myotubes and rat diaphragm muscle.
abstract: The nerve-derived trophic factor neuregulin (NRG) is a prime candidate molecule for modulating muscle fiber growth. NRG regulates signal transduction in skeletal muscle through activation of ErbB receptors present at the neuromuscular junction. In this study, we hypothesize that NRG increases protein synthesis in maturing muscle via a phosphatidylinositol 3-kinase (PI3K)-dependent mechanism. NRG signal transduction and its ability to stimulate protein synthesis (measured by incorporation of [(3)H]phenylalanine into the protein pool) were investigated in differentiated C(2)C(12) myotubes and rat diaphragm muscle (DIAm). In C(2)C(12) myotubes, NRG dose dependently increased phosphorylation of ErbB3 and recruitment of the p85 subunit of PI3K. NRG also increased phosphorylation of Akt, a downstream effector of PI3K. NRG treatment increased total protein synthesis by 35% compared with untreated control myotubes. This NRG-induced increase in Akt phosphorylation and protein synthesis was completely blocked by wortmannin, an inhibitor of PI3K but was unaffected by PD-98059, an inhibitor of MEK. In DIAm obtained from 3-day-old rat pups, Akt phosphorylation increased approximately 30-fold with NRG treatment (vs. untreated DIAm). NRG treatment also significantly increased protein synthesis in the DIAm by 29% after 3 h of incubation with [(3)H]phenylalanine (vs. untreated DIAm). Pretreatment with wortmannin abolished the NRG-induced increase in protein synthesis, suggesting a critical role for PI3K in this response. The results of the present study support the hypothesis that nerve-derived NRG contributes to the regulation of skeletal muscle mass by increasing protein synthesis via activation of PI3K.
authors.affiliation: Department of Physiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Hellyer
authors.forename: Carlos B
authors.initials: CB
authors.lastname: Mantilla
authors.forename: Eunice W
authors.initials: EW
authors.lastname: Park
authors.forename: Wen-Zhi
authors.initials: WZ
authors.lastname: Zhan
authors.forename: Gary C
authors.initials: GC
authors.lastname: Sieck
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003964:Diaphragm / Q000187:drug effects* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006133:Growth Substances / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D020880:Neuregulins / Q000494:pharmacology*; D018739:Oncogene Proteins v-erbB / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D006133:Growth Substances; D020880:Neuregulins; D018739:Oncogene Proteins v-erbB; D051057:Proto-Oncogene Proteins c-akt; D000077191:Wortmannin