title: Endothelin-1 activates extracellular signal-regulated kinases 1/2 via transactivation of platelet-derived growth factor receptor in rat L6 myoblasts.
abstract: OBJECTIVE
  Endothelin (ET) system plays a critical role in the development of insulin resistance and type 2 diabetes. In skeletal muscle, differentiation of myoblasts to myotubes is accompanied by the development of insulin sensitivity. Activation of extracellular signal-regulated kinase (ERK) 1/2 inhibits the differentiation of myoblasts, leading to insulin resistance. Although ET receptor (ETR) stimulation generally activates ERK1/2, the mechanism for ETR-mediated ERK1/2 activation in skeletal muscle is unknown. The purpose of this study was to determine the signal transduction pathway involved in ET-1-stimulated ERK1/2 phosphorylation in L6 myoblasts derived from rat skeletal muscle.
  
  
  METHODS
  Changes in phosphorylation levels of ERK1/2 following stimulation with ET-1 were analyzed by Western blot in L6 myoblasts. To inhibit receptor internalization, dominant-negative dynamin (K44A) was overexpressed in L6 myoblasts using adenovirus-mediated gene transfer.
  
  
  RESULTS
  ET-1 induced phosphorylation of ERK1/2 in L6 myoblasts. The ERK1/2 phosphorylation was abolished by BQ123 (a selective ET type A receptor (ETAR) antagonist), YM-254890 (a Gαq/11 protein inhibitor), and AG370 (a platelet-derived growth factor receptor (PDGFR) kinase inhibitor), while U-73122 (a phospholipase C (PLC) inhibitor) was less potent. The ERK1/2 phosphorylation was inhibited by overexpression of dominant-negative dynamin (K44A). These results suggest that ETAR stimulation induces ERK1/2 phosphorylation in L6 myoblasts through Gq/11 protein-dependent, PLC-independent PDGFR transactivation which requires dynamin-dependent ETAR internalization.
  
  
  CONCLUSIONS
  Because activation of ERK1/2 is considered to inhibit differentiation of myoblasts with the development of insulin sensitivity, the ETAR-mediated PDGFR transactivation and subsequent ERK1/2 activation play an important role in ET-1-induced insulin resistance.
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Harada
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan. Electronic address: horinouc@med.hokudai.ac.jp.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Horinouchi
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Tsunaki
authors.initials: T
authors.lastname: Higa
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Akimasa
authors.initials: A
authors.lastname: Hoshi
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Tsunehito
authors.initials: T
authors.lastname: Higashi
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Terada
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Mai
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Prabha
authors.initials: P
authors.lastname: Nepal
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Mika
authors.initials: M
authors.lastname: Horiguchi
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Chizuru
authors.initials: C
authors.lastname: Hatate
authors.affiliation: Department of Cellular Pharmacology, Hokkaido University Graduate School of Medicine, Hokkaido 060-8638, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Miwa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D034281:Dynamins / Q000235:genetics; D019332:Endothelin-1 / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018014:Gene Transfer Techniques; D005799:Genes, Dominant; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance; D018482:Muscle, Skeletal / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D044022:Receptor, Endothelin A / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D019332:Endothelin-1; D007328:Insulin; D044022:Receptor, Endothelin A; D017479:Receptors, Platelet-Derived Growth Factor; D048049:Extracellular Signal-Regulated MAP Kinases; D034281:Dynamins; D002118:Calcium
keywords: endothelin receptor; endothelin-1; extracellular signal-regulated kinases 1/2; phosphorylation; platelet-derived growth factor receptor; skeletal muscle; transactivation