Phosphatidylinositol 3'-kinase-independent p70 S6 kinase activation by fibroblast growth factor receptor-1 is important for proliferation but not differentiation of endothelial cells.
p70(s6k) has a role in cell cycle progression in response to specific extracellular stimuli. The signal transduction pathway leading to activation of p70(s6k) by fibroblast growth factor receptor-1 (FGFR-1) was examined in FGF-2-treated rat L6 myoblasts. p70(s6k) was activated in a biphasic and rapamycin-sensitive manner. Although phosphatidylinositol 3'-kinase was not activated in the FGF-2 treated cells, as judged from in vitro and in vivo analyses, wortmannin and LY294002 treatment inhibited p70(s6k) activation. Inhibition of protein kinase C (PKC), by bisindolylmaleimide or by chronic phorbol ester treatment of the FGFR-1 cells, suppressed but did not block p70(s6k) activation. In cells expressing a point-mutated FGFR-1, Y766F, unable to mediate PKC activation, p70(s6k) was still activated, in a bisindolylmaleimide- and phorbol ester-resistant manner. The involvement of S6 kinase in FGFR-1-dependent biological responses was examined in murine brain endothelial cells. In response to FGF-2, these cells differentiate to form tube-like structures in collagen gel cultures and proliferate when cultured on fibronectin. p70(s6k) was not activated in endothelial cells on collagen, whereas activation was observed during proliferation on fibronectin. In agreement with this finding, rapamycin inhibited the proliferative but not the differentiation response. Our results indicate that FGFR-1 mediates p70(s6k) activation by a phosphatidylinositol 3'-kinase-independent mechanism that does not require PKC activation and, furthermore, proliferation, but not differentiation of endothelial cells in response to FGF-2, is associated with p70(s6k) activation.
Kanda
S
S
Ludwig Institute for Cancer Research, Biomedical Centre, Box 595, S-751 24 Uppsala, Sweden.
Hodgkin
M N
MN
Woodfield
R J
RJ
Wakelam
M J
MJ
Thomas
G
G
Claesson-Welsh
L
L
D000818:Animals; D001921:Brain / Q000098:blood supply; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000254:growth & development*; D004789:Enzyme Activation; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D009132:Muscles / Q000166:cytology; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases; D051966:Phospholipase C gamma; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011090:Polyenes / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus; D010738:Type C Phospholipases / Q000378:metabolism
D016222:Fibroblast Growth Factor 2; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D051966:Phospholipase C gamma; D017853:Phosphotransferases (Alcohol Group Acceptor); D011090:Polyenes; D017346:Protein Serine-Threonine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D010738:Type C Phospholipases; C496349:Fgfr1 protein, mouse; C496350:Fgfr1 protein, rat