Involvement of growth factor receptor-bound protein-2 in rat hepatocyte growth.
Growth factor receptor-bound protein-2 (GRB-2) is a protein linking receptor tyrosine kinase and Sos (Son of Sevenless gene; Ras GDP/GTP exchange protein), leading to activation of the Ras-mitogen-activated protein kinase (MAPK) cascade. So far, it remains unclear how GRB-2 plays a role in signal transduction pathways evoked by hepatotrophic factors. This study was attempted to evaluate the involvement of GRB-2 in signalling in rat hepatocyte growth. Using rat cultured hepatocytes stimulated by hepatotrophic factors and regenerating livers after partial hepatectomy (PH) we examined GRB-2-mediated linkage of hepatotrophic factor receptors to signal transducing molecules such as Sos or dynamin-II by immunoprecipitation and western blot analysis. In primary cultured hepatocytes stimulated with hepatocyte growth factor (HGF) or epidermal growth factor (EGF), GRB-2 linked HGF receptor or EGF receptor, respectively, to Sos which activated the mitogen-activated protein kinase (MAPK) cascade. In contrast, in primary cultured hepatocytes stimulated with insulin, GRB-2 linked insulin receptor substrate-1 (IRS-1) to dynamin-II as well as Sos. In the early phase after PH, GRB-2 activated the Ras-MAPK cascade by linking HGF receptor, IRS-1, or EGF receptor to Sos. In the late phase after PH, a complex of IRS-1-GRB-2 associated with dynamin-II, indicating that GRB-2 may transduce signals from IRS-1 to dynamin-II. We conclude that GRB-2 may play a role in transmitting signals from hepatotrophic factors to not only MAPK but also to other signalling pathways in hepatocyte growth.
First Department of Medicine, Osaka University School of Medicine, Japan.
S
S
Wada
Y
Y
Sasaki
M
M
Horimoto
T
T
Ito
Y
Y
Ito
Y
Y
Tanaka
T
T
Toyama
A
A
Kasahara
N
N
Hayashi
M
M
Hori
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002455:Cell Division / Q000502:physiology*; D002478:Cells, Cultured; D051380:GRB2 Adaptor Protein; D008099:Liver / Q000166:cytology*; D008115:Liver Regeneration / Q000502:physiology; D008297:Male; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases; D011506:Proteins / Q000502:physiology*; D019859:Proto-Oncogene Proteins c-met; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495950:Grb2 protein, rat; D011506:Proteins; D011505:Protein-Tyrosine Kinases; D019859:Proto-Oncogene Proteins c-met