title: GH regulation of IGF-I and suppressor of cytokine signaling gene expression in C2C12 skeletal muscle cells.
abstract: GH is required for normal postnatal growth and metabolism. GH stimulates postnatal growth through induction of IGF-I gene expression. Although the liver is the major site of GH-regulated IGF-I, recent evidence indicates that GH-regulated IGF-I expression in nonhepatic tissues is sufficient for normal postnatal growth. One potentially important nonhepatic site of GH-stimulated IGF-I expression is skeletal muscle, as injection of GH into animals leads to increased IGF-I mRNA in this tissue. Nevertheless, direct effects of GH in skeletal muscle cells in culture have not been reported. We therefore tested the C2C12 myogenic cell line for its response to GH and demonstrate that C2C12 skeletal muscle cells rapidly respond to physiological levels of GH with increased tyrosine phosphorylation of the GH receptor, Janus kinase 2, signal transducer and activator of transcription-5a and -5b, insulin receptor substrate-1, and activation of MAPKs/ERKs and protein kinase B/Akt. In these cells, GH stimulates the expression of IGF-I and two members of the suppressors of cytokine signaling family, cytokine-inducible SH2-containing protein and suppressor of cytokine signaling-2. Treatment of C2C12 myoblasts with either the MAPK kinase inhibitor PD98059 or the PI3K inhibitor wortmannin results in higher levels of GH-induced IGF-I and suppressor of cytokine signaling-2 mRNA expression, suggesting that activation of MAPK and PI3K pathways has an inhibitory role in IGF-I and suppressor of cytokine signaling-2 gene regulation. Therefore, C2C12 cells provide the first in vitro model system to study various aspects of GH action in skeletal muscle.
authors.affiliation: Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Sadowski
authors.forename: T T
authors.initials: TT
authors.lastname: Wheeler
authors.forename: L H
authors.initials: LH
authors.lastname: Wang
authors.forename: H B
authors.initials: HB
authors.lastname: Sadowski
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter / Q000502:physiology; D019382:Human Growth Hormone / Q000494:pharmacology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D053614:Janus Kinase 2; D051379:Mice; D008894:Milk Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000235:genetics*; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism
chemical_list: D004247:DNA; D004268:DNA-Binding Proteins; D019382:Human Growth Hormone; D017874:Immediate-Early Proteins; D007334:Insulin-Like Growth Factor I; D053614:Janus Kinase 2; D008894:Milk Proteins; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; C106643:SOCS2 protein, human; C491409:Socs2 protein, mouse; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse