Phosphatidylinositol 3′-Kinase-independent p70 S6 Kinase Activation by Fibroblast Growth Factor Receptor-1 Is Important for Proliferation but Not Differentiation of Endothelial Cells

Abstract

p70s6k has a role in cell cycle progression in response to specific extracellular stimuli. The signal transduction pathway leading to activation of p70s6k by fibroblast growth factor receptor-1 (FGFR-1) was examined in FGF-2-treated rat L6 myoblasts. p70s6k was activated in a biphasic and rapamycin-sensitive manner. Although phosphatidylinositol 3′-kinase was not activated in the FGF-2 treated cells, as judged fromin vitro and in vivo analyses, wortmannin and LY294002 treatment inhibited p70s6k 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 p70s6k activation. In cells expressing a point-mutated FGFR-1, Y766F, unable to mediate PKC activation, p70s6k 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. p70s6k 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 p70s6k 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 p70s6k activation. p70s6k has a role in cell cycle progression in response to specific extracellular stimuli. The signal transduction pathway leading to activation of p70s6k by fibroblast growth factor receptor-1 (FGFR-1) was examined in FGF-2-treated rat L6 myoblasts. p70s6k was activated in a biphasic and rapamycin-sensitive manner. Although phosphatidylinositol 3′-kinase was not activated in the FGF-2 treated cells, as judged fromin vitro and in vivo analyses, wortmannin and LY294002 treatment inhibited p70s6k 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 p70s6k activation. In cells expressing a point-mutated FGFR-1, Y766F, unable to mediate PKC activation, p70s6k 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. p70s6k 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 p70s6k 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 p70s6k activation. The p70 S6 kinase (p70s6k) 1The abbreviations used are: p70s6k, p70 S6 kinase; DAG, diacylglycerol; DMEM, Dulbecco's modified Eagle's medium; EGF, epidermal growth factor; FBS, fetal bovine serum; FGF, fibroblast growth factor; FKBP-12, FK506 binding protein 12; IBE, immortomouse brain-derived endothelium; MOPS, 4-morpholinepropanesulfonic acid; PI3-kinase, phosphatidylinositol 3-kinase; PIP3, phosphatidylinositol 3,4,5-trisphosphate; PI(4,5)P2, phosphatidylinositol 4,5-bisphosphate; PLC-γ, phospholipase C-γ; PKC, protein kinase C; PMA, phorbol 12-myristate 13-acetate; PMSF, phenylmethylsulfonyl fluoride; PAGE, polyacrylamide gel electrophoresis; TOR, target of rapamycin; BSA, bovine serum albumin; PDGF, platelet-derived growth factor; PIP, phosphatidylinositol phosphate. is a serine/threonine kinase that phosphorylates 40 S ribosomal protein S6, in response to a number of extracellular stimuli (1Jenö P. Ballou L.M. Novak-Hofer I. Thomas G. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 406-410Crossref PubMed Scopus (144) Google Scholar, 2Proud C.G. Trends Biochem. Sci. 1996; 21: 181-185Abstract Full Text PDF PubMed Scopus (199) Google Scholar). The two isoforms of p70s6k, the 70-kDa s6k αII (cytosolic form) and the 85-kDa s6k αI (nuclear form), are derived from alternatively spliced products (3Reinhard C. Thomas G. Kozma S.C. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 4052-4056Crossref PubMed Scopus (98) Google Scholar, 4Grove J.R. Banerjee P. Balasubramanyam A. Coffer P.J. Price D.J. Avruch J. Woodgett J.R. Mol. Cell. Biol. 1991; 11: 5541-5550Crossref PubMed Scopus (151) Google Scholar) from a single gene (3Reinhard C. Thomas G. Kozma S.C. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 4052-4056Crossref PubMed Scopus (98) Google Scholar). Extracellular stimuli induce acute phosphorylation on multiple serine and threonine residues within p70s6k, which are associated with its activation. Four of these residues are located in the carboxyl terminus of p70s6k (5Ferrari S. Bannwarth W. Morley S.J. Totty N.F. Thomas G. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 7282-7286Crossref PubMed Scopus (134) Google Scholar). These sites are potential mitogen-activated protein kinase targets. However, mitogen-activated protein kinase fails to activate p70s6k after phosphorylation of these sitesin vitro (6Mukhopadhyay N.K. Price D.J. Kyriakis J.M. Pelech S. Sanghera J. Avruch J. J. Biol. Chem. 1992; 267: 3325-3335Abstract Full Text PDF PubMed Google Scholar), and p70s6k activation lies on a Ras-independent pathway (7Ballou L.M. Luther H. Thomas G. Nature. 1991; 349: 348-350Crossref PubMed Scopus (153) Google Scholar, 8Ming X.-F. Burgering B.M.T. Wennström S. Claesson-Welsh L. Heldin C.-H. Bos J.L. Kozma S.C. Thomas G. Nature. 1994; 371: 426-429Crossref PubMed Scopus (204) Google Scholar). Protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3-kinase), and protein kinase B have been implicated as upstream signaling molecules of p70s6kactivation in insulin-, platelet-derived growth factor (PDGF)-, epidermal growth factor (EGF)- and interleukin-2-treated cells (9Chou M.M. Blenis J. Curr. Opin. Cell Biol. 1995; 7: 806-814Crossref PubMed Scopus (245) Google Scholar). Recently, p70s6k was moreover shown to complex with and to be activated by the GTP-binding Rho family proteins Rac1 and Cdc42 (10Chou M.M. Blenis J. Cell. 1996; 85: 573-583Abstract Full Text Full Text PDF PubMed Scopus (268) Google Scholar). However, the relative contribution of these pathways to activation of p70S6K is unclear (8Ming X.-F. Burgering B.M.T. Wennström S. Claesson-Welsh L. Heldin C.-H. Bos J.L. Kozma S.C. Thomas G. Nature. 1994; 371: 426-429Crossref PubMed Scopus (204) Google Scholar). Rapamycin is a potent and specific inhibitor of p70s6k, preventing phosphorylation and activation of p70s6k by all known external stimuli (11Kuo C.J. Chung J. Fiorentino D.F. Flanagan W.M. Blenis J. Crabtree G.R. Nature. 1992; 358: 70-73Crossref PubMed Scopus (568) Google Scholar, 12Chung J. Kuo C.J. Crabtree G.R. Blenis J. Cell. 1992; 69: 1227-1236Abstract Full Text PDF PubMed Scopus (1033) Google Scholar, 13Price D.J. Grove J.R. Calvo V. Avruch J. Bierer B.E. Science. 1992; 257: 973-977Crossref PubMed Scopus (591) Google Scholar, 14Jayaraman T. Marks A.R. J. Biol. Chem. 1993; 268: 25385-25388Abstract Full Text PDF PubMed Google Scholar, 15Han J.-W. Pearson R.B. Dennis P.B. Thomas G. J. Biol. Chem. 1995; 270: 21396-21403Abstract Full Text Full Text PDF PubMed Scopus (162) Google Scholar). After binding of rapamycin to its cellular receptor, the FK506-binding protein-12 (FKBP-12), this complex targets TOR kinases in Saccharomyces cerevisiae or the related protein FKBP-12-rapamycin-associated protein/rapamycin-FKBP target 1/mammalian TOR in mammalian cells (16Zheng X.-F. Fiorentino D. Chen J. Crabtree G.R. Schreiber S.L. Cell. 1995; 82: 121-130Abstract Full Text PDF PubMed Scopus (249) Google Scholar, 17Brown E.J. Albers M.W. Shin T.B. Ichikawa K. Keith C.T. Lane W.S. Schreiber S.L. Nature. 1994; 369: 756-758Crossref PubMed Scopus (1684) Google Scholar, 18Brown E.J. Beal P.A. Keith C.T. Chen J. Shin T.B. Schreiber S.L. Nature. 1995; 377: 441-446Crossref PubMed Scopus (621) Google Scholar). Inactivation of p70s6k by rapamycin is associated with selective dephosphorylation of a unique set of serine and threonine sites, flanked by large aromatic residues, in p70s6k (19Pearson R.B. Dennis P.B. Han J.-W. Williamson N.A. Kozma S.C. Wettenhall R.E.H. Thomas G. EMBO J. 1995; 14: 5279-5287Crossref PubMed Scopus (389) Google Scholar). Rapamycin is known to inhibit growth of many types of cells; causing G1 arrest in T lymphocytes and delaying entry into S phase in fibroblasts (11Kuo C.J. Chung J. Fiorentino D.F. Flanagan W.M. Blenis J. Crabtree G.R. Nature. 1992; 358: 70-73Crossref PubMed Scopus (568) Google Scholar, 12Chung J. Kuo C.J. Crabtree G.R. Blenis J. Cell. 1992; 69: 1227-1236Abstract Full Text PDF PubMed Scopus (1033) Google Scholar). Microinjection of a neutralizing antibody against p70s6k or p85s6k has also been shown to block the entry into S phase of injected cells (20Lane H.A. Fernandez A. Lamb N.J.C. Thomas G. Nature. 1993; 363: 170-172Crossref PubMed Scopus (318) Google Scholar, 21Reinhard C. Fernandez A. Lamb N.J.C. Thomas G. EMBO J. 1994; 13: 1557-1565Crossref PubMed Scopus (180) Google Scholar). These results indicate that p70s6k activation is important for cell cycle progression. Fibroblast growth factors (FGF) are heparin-binding polypeptide growth factors, which form a family of nine members (22Friesel R.E. Maciag T. FASEB J. 1995; 9: 919-925Crossref PubMed Scopus (406) Google Scholar). Extracellular signaling by FGFs is transduced via specific receptor tyrosine kinases, denoted FGF receptor-1 to -4 (23Partanen J. Vainikka S. Korhonen J. Armstrong E. Alitalo K. Prog. Growth Factor Res. 1992; 4: 69-83Abstract Full Text PDF PubMed Scopus (102) Google Scholar, 24Givol D. Yayon A. FASEB J. 1992; 6: 3362-3369Crossref PubMed Scopus (400) Google Scholar). Heparin and heparan sulfate proteoglycans are known to modulate ligand binding to the receptor tyrosine kinase. Binding of FGFs to the receptor tyrosine kinase leads to receptor dimerization and activation of the kinase domain, followed by autophosphorylation of the receptor and association with downstream signaling components. Thus far, only one Src homology 2 (SH2) domain-containing protein, phospholipase C-γ (PLC-γ), has been shown to bind to FGF via a autophosphorylation in the receptor D. W. J. Mol. Cell. Biol. 1991; 11: PubMed Google Scholar). The FGF are known to mediate a of cellular as cell proliferation, and differentiation (23Partanen J. Vainikka S. Korhonen J. Armstrong E. Alitalo K. Prog. Growth Factor Res. 1992; 4: 69-83Abstract Full Text PDF PubMed Scopus (102) Google Scholar, 24Givol D. Yayon A. FASEB J. 1992; 6: 3362-3369Crossref PubMed Scopus (400) Google Scholar). have shown that murine brain endothelial cells to and FGF-2 treatment by proliferation or by the in vitro as of cells cultured in collagen S. E. Claesson-Welsh L. Cell Growth 1996; 7: Google Scholar). is that signal transduction or to the receptor, to these p70s6k has been shown to be activated in cells C. K. S. J. J. Biol. Chem. 1992; 267: Full Text PDF PubMed Google Scholar). In this have used of signal transduction known to to as as a FGF receptor unable to bind PLC-γ, to p70s6k activation and to its in cellular responses to L6 expressing FGF receptor-1 and point-mutated FGF receptor-1 P. S. Claesson-Welsh L. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar) cultured in Dulbecco's modified Eagle's with fetal bovine The cell is a endothelial cell from large T brain S. E. Claesson-Welsh L. Cell Growth 1996; 7: Google Scholar). The cells cultured in epidermal growth factor endothelial growth and fetal bovine on the as cells cultured on with on with collagen in the of two of collagen of collagen of of and of and the was into which Rapamycin was in a of as a and was and to the cells FGF-2 was in a of After in was to the cells FGF-2 was in a of and to this was in and was to the cells FGF-2 12-myristate was in a of and of PKC, was to the cells and the was for which FGF-2 was tyrosine kinase was as autophosphorylation of receptor protein in vitro as S. E. Claesson-Welsh L. Cell Growth 1996; 7: Google Scholar). cells cultured in and the was by and cultured or by FGF-2 for and cell was in phenylmethylsulfonyl and After of with receptor-1 S. C. Claesson-Welsh L. Growth 1991; 4: PubMed Scopus Google Scholar), receptor protein was followed by with Protein After with on for and proteins by gel The gel was and treated with for and and on The was as (3Reinhard C. Thomas G. Kozma S.C. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 4052-4056Crossref PubMed Scopus (98) Google Scholar) with L6 cells cultured on or with ligand for or cells on or with BSA, cultured for and with FGF-2, for with which is of After cells in on cell was in and After the was for and of protein was with the (3Reinhard C. Thomas G. Kozma S.C. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 4052-4056Crossref PubMed Scopus (98) Google Scholar) for 2 followed by with Protein with with MOPS, and in of The kinase was by of of of 40 S ribosomal protein, and of to the The for and was by of followed by in After the gel was and and on in FBS, or with FGF-2 or platelet-derived growth for and in and cell with Protein with with with with and with The in of and of phosphatidylinositol for and for of and and for The was by of with and the phase was with products in in on with and by in for products by and on L6 cells expressing FGFR-1 with BSA, and and for in of cells with FGF-2 for and the into and as A. D.J. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). The to the by on a with a of and by with which in by the as A. S.J. Scholar). cells as the was and by the of The into and in The kinase and the was by and a and the of was by to a in brain endothelial cells into with a of in and cultured The was to FBS, or FBS, with or FGF-2 was as and the was for from the by and the cell number was by a as S. E. Claesson-Welsh L. Cell Growth 1996; 7: Google Scholar). In cells on the of collagen in of a of in with or FGF-2 was to cells. was for which the was and the of collagen was the cells. After of the of collagen, and rapamycin or with or FGF-2 was and cells cultured p70s6k is known to be activated in response to PDGF, EGF, and serum (9Chou M.M. Blenis J. Curr. Opin. Cell Biol. 1995; 7: 806-814Crossref PubMed Scopus (245) Google Scholar). activation of p70s6k is with a followed by a C. K. S. J. J. Biol. Chem. 1992; 267: Full Text PDF PubMed Google Scholar, A.R. D. Thomas G. Cell. Full Text PDF PubMed Scopus Google Scholar). The of the is not but the phase is to biological A.R. D. Thomas G. Cell. Full Text PDF PubMed Scopus Google Scholar). signal transduction pathways have been implicated in used L6 expressing the FGF or a point-mutated FGF Y766F, to signal transduction pathways leading to p70s6kactivation in response to that and FGF L6 cells of and that the to ligand with of tyrosine kinase In the cells of FGF and FGF-2 of the cells to induce p70s6k activation not p70s6kactivation was examined by of p70s6k, from and cells, followed by in kinase and in the of 40 S as a for the After of the 40 S ribosomal protein was a p70s6k activation was after and of FGF-2 to and B that activated in a in L6 cells expressing the FGF In the receptor expressing cells the of was However, of p70s6k was in the and FGF receptor-1 expressing cells. These results indicate that for p70s6k activation be transduced via FGF receptor-1 and that the autophosphorylation which is for binding and activation of PLC-γ, is not for FGF signal transduction pathways have been implicated in p70s6k activation, and of the of and PKC have been used to for pathways these the of wortmannin and bisindolylmaleimide in In chronic treatment of cells with was used to 2 that treatment of the FGFR-1 expressing L6 cells with of these and Rapamycin to the of p70 to the of of cells with p70s6k to the when used a of not have shown that activation of FGF in endothelial cells, does not to activation of in vitro S. A. K. Heldin C.-H. S. Claesson-Welsh L. 1994; 9: Google Scholar). In to activation in vitro of in L6 expressing FGF receptor-1 The was L6 expressing FGF which for or with a was used to in the L6 cells. and with followed by for phosphorylation of phosphatidylinositol by the cells PI3-kinase, by the in relative to In the FGF-2-treated cells, the of did not as with the of results against the of for not of in vivo L6 cells expressing FGFR-1 that FGF-2 also did not as by in The that FGF-2 of with a in the into within and in associated with was a in associated with the of is and the is to in the the associated with with These that by wortmannin of p70s6kactivation in the cells did not the of FGF-2 on in receptor-1 expressing L6 in in a The FGF receptor-1 the to mediate phosphorylation and activation of to and leading to and activation of PKC, In the FGF receptor-1 expressing cells, PKC still be activated in response to FGF-2, via of DAG, by of a on or FGFR-1 expressing L6 cells In the receptor expressing L6 cells was in response to FGF-2, and of of was by treatment not In the receptor expressing L6 cells, did not in response to FGF-2 of FGF-2 on in L6 cells expressing the FGF receptor-1 or the of of cells. in a shown in the of the phase was in FGF receptor-1 and receptor expressing cells. that the of p70s6k in the receptor expressing cells was not by treatment with to inhibit PKC, or chronic to PMA, to cellular PKC In these cells, rapamycin and wortmannin not still on p70s6k activation. These indicate that in the of PKC activation, and pathways to for the of the pathway for has been that p70s6k is in in the cell cycle (11Kuo C.J. Chung J. Fiorentino D.F. Flanagan W.M. Blenis J. Crabtree G.R. Nature. 1992; 358: 70-73Crossref PubMed Scopus (568) Google Scholar, H.A. Fernandez A. Lamb N.J.C. Thomas G. Nature. 1993; 363: 170-172Crossref PubMed Scopus (318) Google Scholar) and for cell examined the of p70s6k in a murine brain endothelial cell proliferation or The cell was from large T S. E. Claesson-Welsh L. Cell Growth 1996; 7: Google Scholar). have shown on the growth the cells differentiate form tube-like structures when on a or in collagen or proliferate on in response to cultured on a the cells on a to in response to FGF-2 treatment as judged from of in P. K. and L. for the and receptor expressing endothelial cells for of activated p70s6k in response to FGF-2 in activation of p70s6k was in cells on fibronectin. activation of p70s6k was in cells on collagen cells for the of p70 activation was of that in cells cultured on treated the endothelial cells, on or in collagen with rapamycin to block p70s6k activation in response to The of rapamycin on proliferation was by the in cell number of cells in in rapamycin treatment inhibited proliferation of cells treated with FGF-2 in serum not or serum in a manner. However, of endothelial cells in collagen in response to FGF-2 was not by a of rapamycin in agreement with the p70s6k activation, in these has on differentiation of murine brain endothelial cells cultured in collagen cultured two of collagen in the or of FGF-2 rapamycin treatment for that FGF receptor-1 mediates activation of p70s6k in cell types and that treatment of the cells with and p70s6k activation. These are known to signal transduction pathways in of the serine/threonine kinase. However, the these pathways The rapamycin a complex with FKBP-12, a that be in protein and the complex and the of and mammalian TOR (9Chou M.M. Blenis J. Curr. Opin. Cell Biol. 1995; 7: 806-814Crossref PubMed Scopus (245) Google Scholar). The TOR which have been all have a to and that the TOR proteins a family of kinases (16Zheng X.-F. Fiorentino D. Chen J. Crabtree G.R. Schreiber S.L. Cell. 1995; 82: 121-130Abstract Full Text PDF PubMed Scopus (249) Google Scholar). to mammalian TOR, derived from rat J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, J. EMBO J. 1995; 14: PubMed Scopus Google Scholar). this is to TOR has been on the that TOR of kinase as with TOR E.J. Beal P.A. Keith C.T. Chen J. Shin T.B. Schreiber S.L. Nature. 1995; 377: 441-446Crossref PubMed Scopus (621) Google Scholar). In the kinase was not by rapamycin T. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar). In TOR to be for S6 kinase activation, rapamycin S6 kinase activation of cell and (11Kuo C.J. Chung J. Fiorentino D.F. Flanagan W.M. Blenis J. Crabtree G.R. Nature. 1992; 358: 70-73Crossref PubMed Scopus (568) Google Scholar, 12Chung J. Kuo C.J. Crabtree G.R. Blenis J. Cell. 1992; 69: 1227-1236Abstract Full Text PDF PubMed Scopus (1033) Google Scholar). The complex does not to inhibit the kinase of TOR in be on the of TOR protein binding to or phosphorylation of G1 (16Zheng X.-F. Fiorentino D. Chen J. Crabtree G.R. Schreiber S.L. Cell. 1995; 82: 121-130Abstract Full Text PDF PubMed Scopus (249) Google Scholar). TOR to upstream as receptor tyrosine kinases, has not been also to be shown TOR S6 kinase that of S6 which is inhibited by still the in response to that TOR is not in this phosphorylation P.B. Kozma S.C. Thomas G. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar). The of activation of p70s6k by FGF was as with in cell this is the of activation of p70s6k in cells not in and p70s6k activation be to multiple pathways leading to p70s6k activation. the to the of p70s6k activation in cells, has implicated as upstream of p70s6k J. A. Blenis J. Nature. 1994; PubMed Scopus Google Scholar). In of in activation of p70 K. A. Avruch J. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar). Rapamycin and wortmannin inhibit phosphorylation the set of serine sites in p70s6k, that these target the pathway J.-W. Pearson R.B. Dennis P.B. Thomas G. J. Biol. Chem. 1995; 270: 21396-21403Abstract Full Text Full Text PDF PubMed Scopus (162) Google Scholar). However, to wortmannin and rapamycin has been to of K. Grove J.R. Avruch J. Mol. Cell. Biol. 1995; PubMed Scopus Google Scholar) the that these modulate to be The serine/threonine kinase kinase B has been to and p70s6k, with B.M.T. Coffer P.J. Nature. 1995; PubMed Scopus Google Scholar, K. A. Cell. 1995; Full Text PDF PubMed Scopus Google Scholar). In this wortmannin was used to inhibit FGF receptor-1 in the of activation, in vitro or in of the to activate PI3-kinase, FGFR-1 in L6 cells activation of kinase B in response to FGF-2 not The of wortmannin to inhibit S6 kinase of was also shown by K. K. H. K. K. A. Biochem. Res. 1995; PubMed Scopus Google Scholar). In cells expressing a form of the of PI3-kinase, S6 kinase was still activated in response to In wortmannin treatment S6 kinase p70s6k not to inhibited by wortmannin J. EMBO J. 1995; 14: PubMed Scopus Google of on protein E.J. Beal P.A. Keith C.T. Chen J. Shin T.B. Schreiber S.L. Nature. 1995; 377: 441-446Crossref PubMed Scopus (621) Google Scholar) or of TOR J. C. G. EMBO J. 1996; PubMed Scopus Google Scholar) by H. S. K. J. Biol. Chem. 1993; 268: Full Text PDF PubMed Google Scholar) but also as phospholipase A. D.J. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). The inhibitor also S6 kinase activation in L6 cells expressing FGFR-1 not Although LY294002 has been to be a specific the of targets for this as as wortmannin is still not V. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, B.E. L.M. T. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). is that the target of wortmannin in the S6 kinase pathway is not but a or of upstream of S6 kinase. PKC is activated in response to FGF receptor-1 of to and phosphatidylinositol Nature. 1993; PubMed Scopus Google Scholar). is also as a of of the of are with a and for of the for of is phospholipase which is activated by In cells expressing FGF receptor-1 the autophosphorylation J. E. J. D. Nature. 1992; 358: PubMed Scopus Google Scholar, W. T. J. Nature. 1992; 358: PubMed Scopus Google Scholar) phospholipase and in is activated in response to In and PKC activation are S6 kinase p70 activation in L6 cells expressing the was only of cells expressing the or with bisindolylmaleimide or inhibited in the receptor cells but in cells expressing the from these that as the and for p70s6k activation in response to FGF-2 of the as with the has been shown that p70s6k is in response to PKC is not activated by this of PKC but not p70s6k activation D. Lane H.A. Thomas G. J. Biol. Chem. 1992; 267: Full Text PDF PubMed Google Scholar). PKC to a role in p70s6k activation but is not The phosphorylation of the 40 S ribosomal S6 has been implicated in the selective of a family of gene Inhibition of S6 neutralizing or treatment with leads to a block in cell cycle progression C.G. Trends Biochem. Sci. 1996; 21: 181-185Abstract Full Text PDF PubMed Scopus (199) Google Scholar, M.M. Blenis J. Curr. Opin. Cell Biol. 1995; 7: 806-814Crossref PubMed Scopus (245) Google Scholar). However, rapamycin p70s6k activation in cell cell cycle progression in cells (11Kuo C.J. Chung J. Fiorentino D.F. Flanagan W.M. Blenis J. Crabtree G.R. Nature. 1992; 358: 70-73Crossref PubMed Scopus (568) Google Scholar). has been to be to the of signal transduction pathways in the proliferative response. proliferation of endothelial cell was by on the these cells form in response to FGF-2 response was not by which is in agreement that is of for the is to the in which is by S6 kinase. Wennström for on and for