Basic Fibroblast Growth Factor-induced Activation of Novel CREB Kinase during the Differentiation of Immortalized Hippocampal Cells

Abstract

Growth factors bind to their specific receptors on the responsive cell surface and thereby initiate dramatic changes in the proliferation, differentiation, and survival of their target cells. In the present study we have examined the mechanism by which growth factor-induced signals are propagated to the nucleus, leading to the activation of transcription factor, cis-acting cAMP response element (CRE)-binding protein (CREB), in immortalized hippocampal progenitor cells (H19-7). During the differentiation of H19-7 cells by basic fibroblast growth factor (bFGF) a critical regulatory Ser133 residue of CREB was phosphorylated followed by an increase of CRE-mediated gene transcription. Expression of S133A CREB mutants blocked the differentiation of H19-7 cells by bFGF. Although the kinetics of CREB phosphorylation by EGF was transient, bFGF induced a prolonged pattern of CREB phosphorylation. Interestingly, bFGF-induced CREB phosphorylation and subsequent CRE-mediated gene transcription is not likely to be mediated by any of previously known signaling pathways that lead to phosphorylation of CREB, such as mitogen-activated protein kinases, protein kinase A, protein kinase C, phosphatidylinositol 3-kinase-p70S6K, calcium/calmodulindependent protein kinase, and casein kinase 2. By using in vitro in gel kinase assay the presence of a novel 120-kDa bFGF-inducible CREB kinase was identified. These findings identify a new growth factor-activated signaling pathway that regulates gene expression at the CRE. Growth factors bind to their specific receptors on the responsive cell surface and thereby initiate dramatic changes in the proliferation, differentiation, and survival of their target cells. In the present study we have examined the mechanism by which growth factor-induced signals are propagated to the nucleus, leading to the activation of transcription factor, cis-acting cAMP response element (CRE)-binding protein (CREB), in immortalized hippocampal progenitor cells (H19-7). During the differentiation of H19-7 cells by basic fibroblast growth factor (bFGF) a critical regulatory Ser133 residue of CREB was phosphorylated followed by an increase of CRE-mediated gene transcription. Expression of S133A CREB mutants blocked the differentiation of H19-7 cells by bFGF. Although the kinetics of CREB phosphorylation by EGF was transient, bFGF induced a prolonged pattern of CREB phosphorylation. Interestingly, bFGF-induced CREB phosphorylation and subsequent CRE-mediated gene transcription is not likely to be mediated by any of previously known signaling pathways that lead to phosphorylation of CREB, such as mitogen-activated protein kinases, protein kinase A, protein kinase C, phosphatidylinositol 3-kinase-p70S6K, calcium/calmodulindependent protein kinase, and casein kinase 2. By using in vitro in gel kinase assay the presence of a novel 120-kDa bFGF-inducible CREB kinase was identified. These findings identify a new growth factor-activated signaling pathway that regulates gene expression at the CRE. Growth factors act by binding to cell surface receptors to elicit the regulation of cell growth and differentiation. This, in turn, triggers a variety of intracellular signaling pathways that ultimately control cell physiology. Activation of signaling cascades results in the pattern of gene expression through the functional modulation of various transcription factors. Basic fibroblast growth factor (bFGF) 1The abbreviations used are: FGFfibroblast growth factorbFGFbasic FGFCaM kinasecalcium/calmodulin-dependent kinaseCK2casein kinase 2CREcAMP response elementCREBCRE binding proteinDRB5,6-dichloro-1-β-d-ribofuranosylbenzimidazoleEGFepidermal growth factorERKextracellular signal-regulated protein kinaseGFPgreen fluorescent proteinJNKc-Jun N-terminal kinaseMAPKmitogen-activated protein kinaseMAPKAP kinase 2MAPK activated protein kinase 2MEKMAPK kinaseNGFnerve growth factorPI-3Kphosphatidylinositol 3′-kinaseSEKstress-activated protein kinase kinaseTKthymidine kinasePKAprotein kinase APKCprotein kinase CPAGEpolyacrylamide gel electrophoresisGSTglutathioneS-transferase is a potent mitogenic factor that is also known to initiate changes important for neural differentiation, survival, and plasticity (1Lo D.C. Neuron. 1995; 15: 979-981Abstract Full Text PDF PubMed Scopus (244) Google Scholar). Mechanisms underlying these diverse actions of bFGF are not well understood but may result, at least in part, from distinct signaling pathways controlling gene expression. The bFGF receptor belongs to the tyrosine kinase class of membrane receptors. The binding of bFGF to its receptor results in the activation of Ras-dependent mitogen-activated protein kinase (MAPK) cascade (2Wood K.W. Sarnecki C. Roberts T.M. Blenis J. Cell. 1992; 68: 1041-1050Abstract Full Text PDF PubMed Scopus (661) Google Scholar). Coupled phosphorylation events induce the sequential activation of Raf-1 kinase, MAPK kinase (MEK), and MAPK (or extracellular signal-regulated protein kinase (ERK)) (3Schaeffer H. Weber M.J. Mol. Cell. Biol. 1999; 19: 2435-2444Crossref PubMed Scopus (1407) Google Scholar). fibroblast growth factor basic FGF calcium/calmodulin-dependent kinase casein kinase 2 cAMP response element CRE binding protein 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole epidermal growth factor extracellular signal-regulated protein kinase green fluorescent protein c-Jun N-terminal kinase mitogen-activated protein kinase MAPK activated protein kinase 2 MAPK kinase nerve growth factor phosphatidylinositol 3′-kinase stress-activated protein kinase kinase thymidine kinase protein kinase A protein kinase C polyacrylamide gel electrophoresis glutathioneS-transferase Multiple signaling pathways converge at the level of the cyclic AMP response element (CRE)-binding protein (CREB), a transcriptional factor that regulates expression of CRE-containing genes (4Montminy M. Annu. Rev. Biochem. 1997; 66: 807-822Crossref PubMed Scopus (860) Google Scholar). CREB mediates cellular responses to a variety of physiological signals, including neurotransmitters, depolarization, synaptic activity, mitogenic and differentiating factors, and stressors (5Bonni A. Ginty D.D. Dudek H. Greenberg M.E. Mol. Cell. Neurosci. 1995; 6: 168-183Crossref PubMed Scopus (264) Google Scholar, 6Deisseroth K. Bito H. Tsien R.W. Neuron. 1996; 16: 89-101Abstract Full Text Full Text PDF PubMed Scopus (607) Google Scholar, 7Tan Y. Rouse J. Zhang A. Cariati S. Cohen P. Comb M.J. EMBO J. 1996; 15: 4629-4642Crossref PubMed Scopus (568) Google Scholar, 8Iordanov M. Bender K. Ade T. Schmid W. Sachsenmaier S. Engel K. Gaestel M. Rahmsdorf H. Herrlich P. EMBO J. 1997; 16: 1009-1022Crossref PubMed Scopus (198) Google Scholar, 9Pende M. Fisher T.L. Simpson P.B. Russell J.T. Blenis J. Gallo V. J. Neurosci. 1997; 17: 1291-1301Crossref PubMed Google Scholar). Upon phosphorylation at Ser133, CREB can facilitate transcriptional activation of the genes containing the CRE motif (10Gonzalez G.A. Montminy M.R. Cell. 1989; 59: 675-680Abstract Full Text PDF PubMed Scopus (2064) Google Scholar). The activity of CREB is regulated after various kinds of stimulation by multiple kinases, including protein kinase A (PKA), protein kinase C (PKC), isozymes of calcium/calmodulin-dependent kinase (CaM kinase) (11Sheng M. Thompson M.A. Greenberg M.E. Science. 1991; 252: 1427-1430Crossref PubMed Scopus (1289) Google Scholar, 12Matthews R.P. Guthrie C.R. Wailes L.M. Zhao X. Means A.R. McKnight G.S. Mol. Cell. Biol. 1994; 14: 6107-6116Crossref PubMed Scopus (498) Google Scholar, 13Tokumitsu H. Brickey D.A. Glod J. Hidaka H. Sikela J. Soderling T.R. J. Biol. Chem. 1994; 269: 28640-28647Abstract Full Text PDF PubMed Google Scholar), p90RSK (14Xing J. Ginty D.D. Greenberg M.E. Science. 1996; 273: 959-963Crossref PubMed Scopus (1086) Google Scholar), p70S6K (15de Groot R.P. Ballou L.M. Sassone-Corsi P. Cell. 1994; 79: 81-91Abstract Full Text PDF PubMed Scopus (209) Google Scholar), and MAPK-activated protein (MAPKAP) kinase-2 (7Tan Y. Rouse J. Zhang A. Cariati S. Cohen P. Comb M.J. EMBO J. 1996; 15: 4629-4642Crossref PubMed Scopus (568) Google Scholar). Moreover, phosphorylation of CREB at Ser133 regulates expression of the c-fos, somatostatin, and tyrosine hydroxylase genes in PC12 cells (10Gonzalez G.A. Montminy M.R. Cell. 1989; 59: 675-680Abstract Full Text PDF PubMed Scopus (2064) Google Scholar,16Nagamoto-Combs K. Piech K.M. Best J.A. Sun B. Tank A.W. J. Biol. Chem. 1997; 272: 6051-6058Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). To identify signaling pathways transmitting extracellular FGF signal to nucleus, the induction mechanism of immediate early genepip92 by bFGF was previously studied in rat hippocampal progenitor H19-7 cells. Although signaling through Raf-1 occurs exclusively through the SRE, bFGF can also activate a region of thepip92 promoter that contains a CREB binding site near the site of transcription initiation (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google Scholar). Given the role for CREB in regulating genes that mediate a multitude of cellular responses and to investigate the signaling mechanisms by which bFGF regulates gene expression, we examined the effect of bFGF-induced neuronal differentiation on the activation of CREB and subsequent CRE-mediated gene transcription in neuronal H19-7 cells. The present study suggests that CRE-mediated gene transcription appears to be important during the differentiation of neuronal H19-7 cells induced by bFGF and the activation of novel protein kinase signaling pathway is required for the bFGF responsiveness. Fetal bovine serum, Dulbecco's modified Eagle's medium, hygromycin, and geneticin were purchased from Life and were purchased from A, and were purchased from EGF and bFGF were purchased from The assay of and kinase 2 were purchased from and a assay was purchased from and CREB were purchased from and was from were purchased from and were by M. and CREB expression and and were by K. A CREB Ser133 phosphorylation site to was by J. and were by D. and was by C. The rat neuronal hippocampal progenitor cell was by the containing that is at and at as M. Rosner M.R. S. A. 1992; PubMed Scopus Google Scholar). cells were by of H19-7 cells Raf-1 by a of Raf-1 to the of receptor as K.C. Rosner M.R. Mol. Cell. Biol. 1997; 17: PubMed Scopus Google Scholar). The cells were at in containing bovine and of geneticin to on the cells were also in to differentiation, cells were to in for 2 The H19-7 cells were bFGF. cells were a of neuronal differentiation, changes were by the of in and the expression of neuronal were by and cells are as cells containing at least the of cell cells were of kinase to bFGF stimulation to the activation of the cells were for to the activation of kinase A was by using a as which contains green fluorescent protein gene by the was used as an control to In the thymidine kinase promoter was used as a activity was by using a assay and the cells were as a control for CRE-mediated gene transcription. were A containing and cell were by and to a the were a to the The membrane was a and the were by activity was using the assay The cells were in and were as of cell was used to The of and kinase 2 were by using and kinase 2 assay as in the The of was and was by of The to the was after The assay for activity of was in a containing and in the presence of in a of The was by the of cell including and at for The was by of the on to The was in and the was by A gel for was by using of as the for phosphorylation. The cell bFGF in the presence of various protein kinase were to the gel and phosphorylation were as M. Gomes I. Rosner M.R. 1997; Google Scholar). To bFGF its effect on the activation of transcription factor CREB and subsequent CRE-mediated gene we the gene expression of CRE-containing of H19-7 cells bFGF in the increase of CRE-mediated gene transcription in a and a after 2 To the role of CREB phosphorylation on CRE-mediated gene cells were CREB expression such as in which of CREB are by in which of CREB are and a target of protein kinase A that to Ser133 of CREB is to Expression of CREB the of regulatory Ser133 residue the activation of activity by bFGF These results that the stimulation of H19-7 cells bFGF CREB through the phosphorylation of its Ser133 residue followed by the activation of CRE-mediated gene transcription. The functional role of CREB activation during differentiation of H19-7 cells was of H19-7 cells bFGF differentiation at at which is J. M. Rosner M.R. 1994; PubMed Scopus Google Scholar). cells are to mitogenic stimulation by and neuronal such as and A CREB protein Ser133 phosphorylation site to was used to the activation of CREB, and a green fluorescent protein gene was used as a for the CREB expression was and the of in cells was in H19-7 cells. was that the for in the cell is in H19-7 cells M. J. M. D. M. Rosner M.R. Mol. Cell. Biol. 1996; 16: PubMed Scopus Google Scholar). in control cells not a of cells in cells that in the in to cells in the these results that a CREB phosphorylation by bFGF is likely to a role in the differentiation of neuronal H19-7 cells. To the that bFGF its effect on the activation of CREB during CRE-mediated gene was by using an specific for the of During the differentiation of H19-7 cells by Ser133 residue in the CREB protein was phosphorylated and for after growth factor stimulation in CREB phosphorylation are known to be critical in the and regulation of and differentiation of neuronal PC12 cells (5Bonni A. Ginty D.D. Dudek H. Greenberg M.E. Mol. Cell. Neurosci. 1995; 6: 168-183Crossref PubMed Scopus (264) Google Scholar). H19-7 cells to EGF and bFGF. Although EGF a at the the of but not differentiation at the J. M. Rosner M.R. 1994; PubMed Scopus Google Scholar). on was examined CREB phosphorylation by EGF and bFGF in H19-7 cells. In to prolonged CREB phosphorylation by EGF leading to but not differentiation, induced CREB and was to these results that CREB activation by bFGF is important to a on the of hippocampal progenitor cell to to neuronal cells. Upon binding to its receptor and an tyrosine kinase activity leading to the increase in intracellular phosphorylation of intracellular and activation of immediate early such as and M.A. J. Biochem. Biol. PubMed Scopus Google Scholar). To the signaling pathways of the effect of receptor tyrosine kinase on bFGF-induced CREB phosphorylation was in A, A, a which and receptor tyrosine by blocked the CREB phosphorylation by bFGF in H19-7 cells. of the cells of receptor tyrosine kinases, also CREB phosphorylation to the that of bFGF of bFGF receptors is known to activate and a subsequent kinase cascade in the activation of and (2Wood K.W. Sarnecki C. Roberts T.M. Blenis J. Cell. 1992; 68: 1041-1050Abstract Full Text PDF PubMed Scopus (661) Google Scholar). To identify early events in the signaling pathway leading to CREB the role of activation was of the activation of but not CREB phosphorylation by bFGF that CREB is phosphorylated signaling pathway during the differentiation of H19-7 cells by bFGF. In neuronal PC12 the which in activate kinase of of which were to CREB Ser133 phosphorylation (14Xing J. Ginty D.D. Greenberg M.E. Science. 1996; 273: 959-963Crossref PubMed Scopus (1086) Google Scholar). A pathway by which p90RSK is activated by growth factor receptors sequential activation of and was previously that the stimulation of H19-7 cells bFGF induced the activation of the in the differentiation M. J. M. D. M. Rosner M.R. Mol. Cell. Biol. 1996; 16: PubMed Scopus Google Scholar). To the signals by H19-7 cells were a Weber M.J. M. Mol. Cell. Biol. PubMed Scopus Google Scholar). Upon to is activated to signaling events after Raf-1 in A, stimulation of cells bFGF a and prolonged CREB which was to that in H19-7 cells. To CREB was phosphorylated by the cells were for bFGF Although blocked the activation of by bFGF in cell K.C. Rosner M.R. Mol. Cell. Biol. 1997; 17: PubMed Scopus Google Scholar), was of CREB phosphorylation a of CREB phosphorylation by cells were leading to the activation of Raf-1 kinase followed by the sequential activation of pathway and the differentiation of the cells K.C. Rosner M.R. Mol. Cell. Biol. 1997; 17: PubMed Scopus Google Scholar), CREB was not phosphorylated at The induction by is to Raf-1 induction of by was in the H19-7 cells the protein (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google Scholar). these that bFGF-induced signals leading to the CREB phosphorylation are not through pathway in H19-7 cells. In MAPK-activated protein kinase-2 an that of kinase, was to mediate CREB Ser133 phosphorylation in cells to bFGF (7Tan Y. Rouse J. Zhang A. Cariati S. Cohen P. Comb M.J. EMBO J. 1996; 15: 4629-4642Crossref PubMed Scopus (568) Google Scholar). To investigate the effect of stress-activated protein kinases, such as and kinase, on bFGF-induced CREB H19-7 cells were kinase and CREB phosphorylation and subsequent induction of activity by kinase promoter were in effect on the of bFGF to induce CREB phosphorylation and to CRE-mediated activity that CREB phosphorylation is not mediated by the activation of stress-activated kinase-2 a we previously that of of results in a of induced by K.C. S. Lau L.F. Gomes I. J. Biochem. PubMed Scopus Google activity by in H19-7 cells K.C. M. J. PubMed Scopus Google Scholar). In was to be activated by activated Raf-1 (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google bFGF C. the of stimulation in and H19-7 cells. the in of the cells for not the activation of by bFGF a the of the activity that of these results that bFGF-induced CREB phosphorylation is not mediated the activation of stress-activated signaling The binding of bFGF to its receptor is known to induce receptor at and activation of C, which in Ser133 residue of CREB is a of phosphorylation and is phosphorylated by G.A. Montminy M.R. PubMed Scopus Google Scholar), we examined of the of CREB phosphorylation during the differentiation of H19-7 cells. of the cells to bFGF-induced phosphorylation of CREB that bFGF CREB phosphorylation a pathway distinct from that activated by In bFGF-induced CREB phosphorylation was not such as C and not a the activation by was to the level by and at a growth factors activate a protein kinase that is activated by a pathway T. S. 1994; PubMed Scopus Google and that appears to be by the activation of J. A. Blenis J. 1994; PubMed Scopus Google Scholar, J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). CREB and CRE of the CREB were phosphorylated in vitro by p70S6K (15de Groot R.P. Ballou L.M. Sassone-Corsi P. Cell. 1994; 79: 81-91Abstract Full Text PDF PubMed Scopus (209) Google Scholar). The is an and specific of the activation of p70S6K J. Blenis J. Cell. 1992; Full Text PDF PubMed Scopus Google Scholar). a and activation of p70S6K J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, B. Wang Blenis J. C.R. Mol. Cell. Biol. 1994; 14: PubMed Scopus Google Scholar). the H19-7 cells were the of CREB phosphorylation induced by bFGF were not a of at the blocked the activation of p70S6K by in H19-7 cells Ser133 residue of CREB is phosphorylated in response to an increase in intracellular cAMP and by (10Gonzalez G.A. Montminy M.R. Cell. 1989; 59: 675-680Abstract Full Text PDF PubMed Scopus (2064) Google Scholar, M. Thompson M.A. Greenberg M.E. Science. 1991; 252: 1427-1430Crossref PubMed Scopus (1289) Google by kinase R.P. Guthrie C.R. Wailes L.M. Zhao X. Means A.R. McKnight G.S. Mol. Cell. Biol. 1994; 14: 6107-6116Crossref PubMed Scopus (498) Google Scholar, 13Tokumitsu H. Brickey D.A. Glod J. Hidaka H. Sikela J. Soderling T.R. J. Biol. Chem. 1994; 269: 28640-28647Abstract Full Text PDF PubMed Google Scholar, P. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). H19-7 cells were specific kinase H. T. M. A. M. Hidaka H. J. Biol. Chem. Full Text PDF PubMed Google Scholar, H. Sun P. Brickey D. Soderling Soderling T.R. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar), activation and the activation of kinase 2 by were of the cells not the of CREB phosphorylation that of bFGF In of the cells specific for and kinase such as and not a of CREB phosphorylation by bFGF not CREB is known to be a of S. S. of Google Scholar). CREB was to be phosphorylated in a cell and the of CREB is phosphorylated by K. A. Biochem. J. 1999; PubMed Scopus Google Scholar). Although the of specific 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole blocked the induction of activity by not bFGF-induced CREB the cells were for to bFGF the of CREB phosphorylation were not not these results that CREB phosphorylation not the activation of previously known CREB kinase such as kinase, To identify bFGF-inducible CREB in vitro in gel kinase were by using as the containing protein from H19-7 cells that bFGF in the presence of various protein kinase were by and for CREB phosphorylation in the in a and kinase of was In the results previously CREB of and are activated by bFGF Although of the cells the of and kinase not the activity of kinase, a activity bFGF. In the 120-kDa kinase is by bFGF the protein kinase for and were during the kinase assay as well as the of H19-7 the activation pattern of novel was not not that the novel CREB are not regulated by protein kinase activity was the in which of CREB to protein not was used as a These results that a novel bFGF-inducible CREB kinase of the Ser133 residue and is likely to an important role in the differentiation of immortalized hippocampal neuronal cells. The present study that bFGF the phosphorylation of CREB at Ser133, which an important role during the differentiation of neuronal H19-7 cells. to an increase in the transcriptional activity of CREB, as by using a CREB was to an important role in neuronal differentiation. CREB phosphorylation D.D. A. Greenberg M.E. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar), and a in a of PC12 A. Y. Y. M. K. K. T. M. J. 1998; PubMed Scopus Google Scholar). In cAMP induced and activated CREB H. J. PubMed Scopus Google Scholar). A of may be of CREB phosphorylation the of in cells have not kinase, and p90RSK have to By using specific we that CREB activation appears not to any of the signaling pathways leading to the phosphorylation of CREB in H19-7 cells. not the that a of known pathways is for CREB and the of are not and to the of the a such as is not to In cAMP activated the transcription factor and induced neuronal differentiation of PC12 cells its activation of the MAPK cascade M.R. H. Cell. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). These cell actions of cAMP the expression of the kinase, and activation of the activated by by is a of and an of is that the differentiating signal of bFGF is through the activation of but not by which also be important for the differentiation of H19-7 cells. on the that of the cells various protein kinase not the of phosphorylated CREB by FGF and and the of novel CREB kinase from an in gel kinase assay not to the of protein kinases, study the presence of a new growth factor-activated signaling pathway that regulates gene expression at the CRE. The of CREB phosphorylation in the presence of that bFGF signals are through which was in induction a for that the of EGF and the for novel kinase (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google Scholar). A in the signal during is be the results in and and from the (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google that the activation of pathway is not required for the CREB phosphorylation by bFGF. these CREB phosphorylation by EGF is not in the presence of was to phosphorylation of CREB and activate cellular gene expression a mechanism K. Montminy M. J. Biol. Chem. 1999; 273: Full Text Full Text PDF Scopus Google Scholar). is and activated by diverse such as growth factor, and and cell survival J. Biol. 1998; PubMed Scopus Google Scholar). of the that activation of is mediated through signaling and that may novel on the was the activation of is in the activation of CREB by bFGF in H19-7 cells. The that was not bFGF-induced CREB phosphorylation by and the of novel CREB kinase not to that of suggests that the activation of is not for CRE-mediated gene induction by bFGF. to of PC12 cells to physiological of induced a phosphorylation of CREB, and effect was not mediated by any of the previously known CREB activation pathways D. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). Although EGF and bFGF induce intracellular signaling these growth factors ultimately elicit cellular responses in H19-7 cells. PC12 to the cell and cells that in Cell. Google Scholar). In to EGF is a for PC12 cells. By controlling the phosphorylation of transcription factors such as and CREB and thereby regulating the expression of immediate early gene and response MAPK pathway was to the signals of cell including and differentiation. EGF the MAPK pathway and the in kinetics for the response of PC12 and H19-7 cells to these (17Chung K.C. Gomes I. Wang D. Lau L.F. Rosner M.R. Mol. Cell. Biol. 1998; 18: 2272-2281Crossref PubMed Scopus (63) Google M. J. M. D. M. Rosner M.R. Mol. Cell. Biol. 1996; 16: PubMed Scopus Google Scholar, Cell. 1995; Full Text PDF PubMed Scopus Google Scholar). In cells to bFGF activation of the MAPK for In the mitogenic EGF to activation of the MAPK signaling after the EGF Neuron. 1992; Full Text PDF PubMed Scopus Google Scholar, S. H. C. Cohen P. Biochem. J. 1992; Scopus Google Scholar). In of EGF receptors are in PC12 the of activation is and the PC12 cells a neuronal pathway in response to EGF S. K. H. Cohen P. A. Biol. 1994; Full Text Full Text PDF PubMed Scopus Google Scholar). and Greenberg Greenberg M.E. Annu. Rev. Neurosci. 1996; 19: PubMed Scopus Google that activation of the signaling pathway in PC12 cells can in the phosphorylation of transcription factors such as may CREB to activate response genes that have their regulatory response genes be activated in response to but not and that to the of a neuronal (5Bonni A. Ginty D.D. Dudek H. Greenberg M.E. Mol. Cell. Neurosci. 1995; 6: 168-183Crossref PubMed Scopus (264) Google Scholar). have the of genes that to such as tyrosine hydroxylase J. J. Biol. Chem. Full Text PDF PubMed Google Scholar), L.M. P. C. Mol. Cell. Biol. 6: PubMed Scopus Google Scholar), and neuronal J. J. Neurosci. 1992; PubMed Google Scholar). The for neuronal differentiation on PC12 cells is that prolonged activation of is and for differentiation. have that is not in neuronal cells. prolonged MAPK is not for the differentiation of H19-7 prolonged activation of Raf-1 is M. J. M. D. M. Rosner M.R. Mol. Cell. Biol. 1996; 16: PubMed Scopus Google Scholar), that physiological MAPK is that pathways are not required for CREB phosphorylation by bFGF in H19-7 cells suggests that mitogenic and differentiating signals through distinct pathways PC12 and H19-7 are to Rosner for and for the J. J. M. and D. for B. for the and H. S. J. H. and Y. for also M. Comb for the K. and J. for and various CREB expression D. for and and C. for