Insulin-like growth factor-I rapidly activates multiple signal transduction pathways in cultured rat cardiac myocytes.
In response to insulin-like growth factor-I (IGF-I), neonatal rat cardiac myocytes exhibit a hypertrophic response. The elucidation of the IGF-I signal transduction system in these cells remains unknown. We show here that cardiac myocytes present a single class of high affinity receptors (12,446 +/- 3,669 binding sites/cell) with a dissociation constant of 0.36 +/- 0.10 nM. Two different beta-subunits of IGF-I receptor were detected, and their autophosphorylation was followed by increases in the phosphotyrosine content of extracellular signal-regulated kinases (ERKs), insulin receptor substrate 1, phospholipase C-gamma1, and phosphatidylinositol 3-kinase. IGF-I transiently activates c-Raf in cultured neonatal cardiac myocytes, whereas A-raf is activated much less than c-Raf. Two peaks of ERK activity (ERK1 and ERK2) were resolved in cardiac myocytes treated with IGF-I by fast protein liquid chromatography, both being stimulated by IGF-I (with EC50 values for the stimulation of ERK1 and ERK2 by IGF-I of 0.10 and 0. 12 nM, respectively). Maximal activation of ERK2 (12-fold) and ERK1 (8.3-fold) activities was attained after a 5-min exposure to IGF-I. Maximal activation of p90 S6 kinase by IGF-I was achieved after 10 min, and then the activity decreased slowly. Interestingly, IGF-I stimulates incorporation of [3H]phenylalanine (1.6-fold) without any effect on [3H]thymidine incorporation. These data suggest that IGF-I activates multiple signal transduction pathways in cardiac myocytes some of which may be relevant to the hypertrophic response of the heart.
Foncea
R
R
Departamento de Bioquímica y Biología Molecular, Facultad Ciencias Químicas y Farmacéuticas, Universidad de Chile, Olivos 1007, Santiago, Chile.
Andersson
M
M
Ketterman
A
A
Blakesley
V
V
Sapag-Hagar
M
M
Sugden
P H
PH
LeRoith
D
D
Lavandero
S
S
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009206:Myocardium / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D007334:Insulin-Like Growth Factor I; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf; D010738:Type C Phospholipases; D014443:Tyrosine