Differential activation of mitogen-activated protein kinase in response to basic fibroblast growth factor in skeletal muscle cells.
In the MM14 mouse myoblast cell line, fibroblast growth factor (FGF) stimulates proliferation and represses differentiation. However, the intracellular signaling pathways used by FGF to affect these cellular processes are unknown. The predominant FGF receptor present on MM14 cells, FGFR1, is a receptor tyrosine kinase capable of activating the mitogen-activated protein kinase (MAPK) cascade in fibroblast and neuronal cell lines. To determine whether the FGF signal is mediated via the MAPK cascade in myoblasts, MM14 cells were stimulated with basic FGF (bFGF) and activities of the various kinases were measured. After withdrawal from serum and bFGF for 3 hr, bFGF stimulated MAPK kinase (MAPKK) activity, but MAPK and S6 peptide kinase activities were not detected. In contrast, when serum and bFGF were withdrawn for 10 hr, the activities of MAPKK, MAPK, and S6 peptide kinase were all stimulated by bFGF treatment. The inability of bFGF to stimulate MAPK after 3 hr of withdrawal may be due, in part, to the presence of a MAPK phosphatase activity that was detected in MM14 cell extracts. This dephosphorylating activity diminishes during commitment to terminal differentiation and is inhibited by sodium orthovanadate. Thus, the ability of bFGF to stimulate MAPK in MM14 cells is correlated with the loss of a MAPK phosphatase activity. These results show that although bFGF activates MAPKK in proliferating myoblasts, the mitogenic signal does not progress to the downstream kinases, providing a physiological example of an uncoupling of the MAPK cascade.
Department of Pharmacology, University of Washington, Seattle 98195.
J S
JS
Campbell
M P
MP
Wenderoth
S D
SD
Hauschka
E G
EG
Krebs
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002458:Cell Fractionation; D002460:Cell Line; D004789:Enzyme Activation; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D051379:Mice; D052998:Microcystins; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases; D015398:Signal Transduction; D014638:Vanadates / Q000494:pharmacology
D052998:Microcystins; D010456:Peptides, Cyclic; D011994:Recombinant Proteins; D016222:Fibroblast Growth Factor 2; D014638:Vanadates; C078588:microcystin; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010749:Phosphoprotein Phosphatases