title: A calcineurin- and NFAT-dependent pathway regulates Myf5 gene expression in skeletal muscle reserve cells.
abstract: Myf5 is a member of the muscle regulatory factor family of transcription factors and plays an important role in the determination, development, and differentiation of skeletal muscle. However, factors that regulate the expression and activity of Myf5 itself are not well understood. Recently, a role for the calcium-dependent phosphatase calcineurin was suggested in three distinct pathways in skeletal muscle: differentiation, hypertrophy, and fiber-type determination. We propose that one downstream target of calcineurin and the calcineurin substrate NFAT in skeletal muscle is regulation of Myf5 gene expression. For these studies, we used myotube cultures that contain both multinucleated myotubes and quiescent, mononucleated cells termed 'reserve' cells, which share many characteristics with satellite cells. Treatment of such myotube cultures with the calcium ionophore ionomycin results in an approximately 4-fold increase in Myf5 mRNA levels, but similar effects are not observed in proliferating myoblast cultures indicating that Myf5 is regulated by different pathways in different cell populations. The increase in Myf5 mRNA levels in myotube cultures requires the activity of calcineurin and NFAT, and can be specifically enhanced by overexpressing the NFATc isoform. We used immunohistochemical analyses and fractionation of the cell populations to demonstrate that the calcium regulated expression of Myf5 occurs in the mononucleated reserve cells. We conclude that Myf5 gene expression is regulated by a calcineurin- and NFAT-dependent pathway in the reserve cell population of myotube cultures. These results may provide important insights into the molecular mechanisms responsible for satellite cell activation and/or the renewal of the satellite cell pool following activation and proliferation.
authors.affiliation: Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: B B
authors.initials: BB
authors.lastname: Friday
authors.forename: G K
authors.initials: GK
authors.lastname: Pavlath
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D015759:Ionomycin / Q000494:pharmacology; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008815:Mice, Inbred Strains; D009124:Muscle Proteins / Q000235:genetics*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D051787:Myogenic Regulatory Factor 5; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D014176:Protein Biosynthesis / Q000187:drug effects; D012190:Retroviridae; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D008164:Luminescent Proteins; D009124:Muscle Proteins; C497418:Myf5 protein, mouse; D051787:Myogenic Regulatory Factor 5; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D015759:Ionomycin; D019703:Calcineurin