Preferential binding of Grb2 or phosphatidylinositol 3-kinase to the met receptor has opposite effects on HGF-induced myoblast proliferation.
Hepatocyte growth factor (HGF) and its receptor, Met, play a crucial role in regulating adult skeletal myoblast proliferation and differentiation. Met signaling is mediated by phosphorylation of two carboxy-terminal tyrosines, which act as docking sites for a number of intracellular mediators. These include Grb2 and p85, which couple the receptor with the Ras and phosphatidylinositol 3-kinase (PI3K) pathways, respectively. In this study, we define the role of these effectors in response to HGF by utilizing Met mutants, designed to obtain preferential coupling of Met to either Grb2 or PI3K or both. We found that relative to the wild-type receptor, enhanced binding to Grb2 further increases the incorporation of bromodeoxyuridine and the expression of Twist, while decreasing that of p27(Kip1) and myogenin. Conversely, preferential coupling with PI3K induced cell-cycle withdrawal and differentiation. Whereas enhanced Grb2 binding increased the phosphorylation of the mitogen-activated protein kinase/extracellular signal-regulated protein kinases (MAPK/ERK) and abrogated that of p38 MAPK, PI3K had the opposite effect. PD098059 reversed the inhibitory effects of Met on cell proliferation and differentiation, while wortmannin had only a very marginal effect. Taken together, these data suggest that coupling of Met with Grb2 is necessary for HGF-mediated inhibition of muscle differentiation. This inhibition occurs only when PI3K signaling downstream of Met is low. Imposing an efficient coupling of PI3K to Met would lead to upregulation of muscle regulatory factors and subsequent cell differentiation.
Leshem
Yael
Y
Department of Animal Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel.
Gitelman
Inna
I
Ponzetto
Carola
C
Halevy
Orna
O
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D030161:Avian Proteins; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002645:Chickens; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051380:GRB2 Adaptor Protein; D017228:Hepatocyte Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D018008:Myogenin / Q000187:drug effects / Q000378:metabolism; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D019859:Proto-Oncogene Proteins c-met / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000187:drug effects / Q000378:metabolism; D014157:Transcription Factors / Q000187:drug effects / Q000378:metabolism; D051879:Twist-Related Protein 1
D048868:Adaptor Proteins, Signal Transducing; D030161:Avian Proteins; D004791:Enzyme Inhibitors; D051380:GRB2 Adaptor Protein; D018008:Myogenin; D019384:Nucleic Acid Synthesis Inhibitors; D011506:Proteins; D014157:Transcription Factors; C412362:Twist protein, Gallus gallus; D051879:Twist-Related Protein 1; D017228:Hepatocyte Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D019859:Proto-Oncogene Proteins c-met; D020794:Receptor Protein-Tyrosine Kinases