Roles of Src and Epidermal Growth Factor Receptor Transactivation in Transient and Sustained ERK1/2 Responses to Gonadotropin-releasing Hormone Receptor Activation

Abstract

The duration as well as the magnitude of mitogen-activated protein kinase activation has been proposed to regulate gene expression and other specific intracellular responses in individual cell types. Activation of ERK1/2 by the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) is relatively sustained in αT3-1 pituitary gonadotropes and HEK293 cells but is transient in immortalized GT1-7 neurons. Each of these cell types expresses the epidermal growth factor receptor (EGFR) and responds to EGF stimulation with significant but transient ERK1/2 phosphorylation. However, GnRH-induced ERK1/2 phosphorylation caused by EGFR transactivation was confined to GT1-7 cells and was attenuated by EGFR kinase inhibition. Neither EGF nor GnRH receptor activation caused translocation of phospho-ERK1/2 into the nucleus in GT1-7 cells. In contrast, agonist stimulation of GnRH receptors expressed in HEK293 cells caused sustained phosphorylation and nuclear translocation of ERK1/2 by a protein kinase C-dependent but EGFR-independent pathway. GnRH-induced activation of ERK1/2 was attenuated by the selective Src kinase inhibitor PP2 and the negative regulatory C-terminal Src kinase in GT1-7 cells but not in HEK293 cells. In GT1-7 cells, GnRH stimulated phosphorylation and nuclear translocation of the ERK1/2-dependent protein, p90RSK-1 (RSK-1). These results indicate that the duration of ERK1/2 activation depends on the signaling pathways utilized by GnRH in specific target cells. Whereas activation of the Gq/protein kinase C pathway in HEK293 cells causes sustained phosphorylation and translocation of ERK1/2 to the nucleus, transactivation of the EGFR by GnRH in GT1-7 cells elicits transient ERK1/2 signals without nuclear accumulation. These findings suggest that transactivation of the tightly regulated EGFR can account for the transient ERK1/2 responses that are elicited by stimulation of certain G protein-coupled receptors. The duration as well as the magnitude of mitogen-activated protein kinase activation has been proposed to regulate gene expression and other specific intracellular responses in individual cell types. Activation of ERK1/2 by the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) is relatively sustained in αT3-1 pituitary gonadotropes and HEK293 cells but is transient in immortalized GT1-7 neurons. Each of these cell types expresses the epidermal growth factor receptor (EGFR) and responds to EGF stimulation with significant but transient ERK1/2 phosphorylation. However, GnRH-induced ERK1/2 phosphorylation caused by EGFR transactivation was confined to GT1-7 cells and was attenuated by EGFR kinase inhibition. Neither EGF nor GnRH receptor activation caused translocation of phospho-ERK1/2 into the nucleus in GT1-7 cells. In contrast, agonist stimulation of GnRH receptors expressed in HEK293 cells caused sustained phosphorylation and nuclear translocation of ERK1/2 by a protein kinase C-dependent but EGFR-independent pathway. GnRH-induced activation of ERK1/2 was attenuated by the selective Src kinase inhibitor PP2 and the negative regulatory C-terminal Src kinase in GT1-7 cells but not in HEK293 cells. In GT1-7 cells, GnRH stimulated phosphorylation and nuclear translocation of the ERK1/2-dependent protein, p90RSK-1 (RSK-1). These results indicate that the duration of ERK1/2 activation depends on the signaling pathways utilized by GnRH in specific target cells. Whereas activation of the Gq/protein kinase C pathway in HEK293 cells causes sustained phosphorylation and translocation of ERK1/2 to the nucleus, transactivation of the EGFR by GnRH in GT1-7 cells elicits transient ERK1/2 signals without nuclear accumulation. These findings suggest that transactivation of the tightly regulated EGFR can account for the transient ERK1/2 responses that are elicited by stimulation of certain G protein-coupled receptors. G protein-coupled receptors (GPCRs) 1The abbreviations used are: GPCR, G protein-coupled receptor; Csk, C-terminal Src kinase; EGF, epidermal growth factor; EGFR, EGF receptor; HB-EGF, heparin-binding EGF; ERK, extracellular signal-regulated kinase; GnRH, gonadotropin-releasing hormone; GnRHR, GnRH receptor; MAP, mitogen-activated protein; PKC, protein kinase C; PMA, phorbol 12-myristate 13-acetate; RSK, p90 ribosomal S6 kinase; RTK, receptor tyrosine kinase; PBS, phosphate-buffered saline; MEK, MAP kinase/ERK kinase. activate mitogen-activated protein (MAP) kinase signaling cascades by a wide variety of mechanisms. These include the generation of second messengers (Ca2+, PKC, and cAMP), G protein subunit coupling to novel effectors, and activation of receptor tyrosine kinases (RTKs), such as EGFR, platelet-derived growth factor receptor, and insulin-like growth factor receptor (1Gschwind A. Zwick E. Prenzel N. Leserer M. Ullrich A. Oncogene. 2001; 20: 1594-1600Crossref PubMed Scopus (414) Google Scholar, 2Pierce K.L. Luttrell L.M. Leftkowitz R.J. Oncogene. 2001; 20: 1532-1539Crossref PubMed Scopus (365) Google Scholar). MAP kinases are a family of serine/threonine protein kinases that are activated by a wide spectrum of stimuli, ranging from mitogens and growth factors to cellular stress and neurotoxic factors. The extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) are closely related members of the MAP kinase family that are predominantly activated by growth factors and GPCRs and play an important role in cell survival, motility, and secretion (3Marinissen M.J. Gutkind J.S. Trends Endocrinol. Metab. 2001; 22: 368-376Scopus (842) Google Scholar). Although the physiological roles of MAP kinase activation are diverse, the convergence of signals emanating from GPCRs and RTKs often leads to the activation of mitogenic pathways associated with cell proliferation. The choice between proliferation and differentiation is primarily determined by the duration and strength of ERK1/2 activation, and transient versus sustained activation of ERK1/2 can elicit different types of responses. Sustained activation of ERK1/2 (e.g. by fibroblast growth factor or nerve growth factor) usually leads to differentiation (4Kao S.-C. Jaiswal R.K. Kolch W. Landreth G.E. J. Biol. Chem. 2001; 276: 18169-18177Abstract Full Text Full Text PDF PubMed Scopus (317) Google Scholar, 5Qui M.S. Green S.H. Neuron. 1992; 9: 705-717Abstract Full Text PDF PubMed Scopus (360) Google Scholar), whereas transient activation (e.g. by EGF) often leads to proliferation (6Marshall C.J. Cell. 1995; 80: 179-185Abstract Full Text PDF PubMed Scopus (4239) Google Scholar, 7Liang C.-C. Chen H.-C. J. Biol. Chem. 2001; 276: 21146-21152Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar). In general, sustained ERK1/2 activation is associated with the translocation of ERK1/2 from the cytoplasm to the nucleus (7Liang C.-C. Chen H.-C. J. Biol. Chem. 2001; 276: 21146-21152Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar, 8Pouyssegur J. Volmat V. Lenormand P. Biochem. Pharmacol. 2002; 64: 755-763Crossref PubMed Scopus (363) Google Scholar, 9Stanciu M. DeFranco D.B. J. Biol. Chem. 2002; 277: 4010-4017Abstract Full Text Full Text PDF PubMed Scopus (131) Google Scholar). Therefore, transient activation has different consequences for gene expression than sustained activation, because nuclear accumulation of active ERK1/2 results in qualitative differences in the activation of transcription factors (6Marshall C.J. Cell. 1995; 80: 179-185Abstract Full Text PDF PubMed Scopus (4239) Google Scholar, 10Liu F. Austin D.A. Mellon P.L. Olefsky J.M. Webster N.J.G. Mol. Endocrinol. 2002; 16: 419-434Crossref PubMed Scopus (171) Google Scholar, 11Tohog A. Pierce K.L. Choy E.W. Lefkowitz R.J. Luttrell L.M. J. Biol. Chem. 2002; 277: 9429-9436Abstract Full Text Full Text PDF PubMed Scopus (329) Google Scholar). We and others have shown that EGFR transactivation by GPCR agonists, such as angiotensin II, lysophosphatidic acid, bradykinin, thrombin, and endothelin-1, has a major role in ERK1/2 activation (12Dikic I. Tokiwa G. Lev S. Courtneidge S.A. Schlessinger J. Nature. 1996; 383: 547-550Crossref PubMed Scopus (880) Google Scholar, 13Prenzel N. Zwick E. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1500) Google Scholar, 14Shah B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar). Depending on the cell type, this process may be inhibited by pertussis toxin, sequestration of free G protein βγ subunits, Ca2+ chelators, and inhibition of PKC, metalloproteinases, and Src (1Gschwind A. Zwick E. Prenzel N. Leserer M. Ullrich A. Oncogene. 2001; 20: 1594-1600Crossref PubMed Scopus (414) Google Scholar, 2Pierce K.L. Luttrell L.M. Leftkowitz R.J. Oncogene. 2001; 20: 1532-1539Crossref PubMed Scopus (365) Google Scholar, 12Dikic I. Tokiwa G. Lev S. Courtneidge S.A. Schlessinger J. Nature. 1996; 383: 547-550Crossref PubMed Scopus (880) Google Scholar, 13Prenzel N. Zwick E. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1500) Google Scholar, 14Shah B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar, 15Eguchi S. Dempsey J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). Whereas ERK1/2 activation can be transient or responses are usually of duration (4Kao S.-C. Jaiswal R.K. Kolch W. Landreth G.E. J. Biol. Chem. 2001; 276: 18169-18177Abstract Full Text Full Text PDF PubMed Scopus (317) Google Scholar, 5Qui M.S. Green S.H. Neuron. 1992; 9: 705-717Abstract Full Text PDF PubMed Scopus (360) Google Scholar, C.J. Cell. 1995; 80: 179-185Abstract Full Text PDF PubMed Scopus (4239) Google Scholar, 14Shah B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar). that GPCRs that ERK1/2 phosphorylation EGFR transactivation to the signaling of receptor activation Wallasch C. A. A. Ullrich A. J. 16: PubMed Scopus Google Scholar, E. Prenzel N. Ullrich A. Trends Pharmacol. 1999; 20: Full Text Full Text PDF PubMed Scopus Google Scholar, B.H. Catt K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The expression or of RTKs can a variety of and J. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, E. J. Ullrich A. Trends Mol. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar), and are tightly regulated in the of physiological responses. for the and of and ERK1/2 activation J. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, D.A. PubMed Scopus Google Scholar), and the between and responses the strength and duration of the signals that the cell in to GPCR or The a C-terminal and is and A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar, A. M. R. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). this signaling to be relatively sustained in pituitary gonadotropes and other cell types as well as in HEK293 cells F. Austin D.A. Mellon P.L. Olefsky J.M. Webster N.J.G. Mol. Endocrinol. 2002; 16: 419-434Crossref PubMed Scopus (171) Google Scholar, A. M. J. A. R. P.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Green J. Endocrinol. 2002; PubMed Scopus Google Scholar). However, that GnRH-induced ERK1/2 activation in the GT1-7 hypothalamic cell is transient B.H. Catt K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The for such signaling by GnRH and on cellular of activated ERK1/2 are not of the of GnRH on the duration of ERK1/2 activation that GnRH in GT1-7 cells Src and EGFR transactivation that results in transient phosphorylation of not nuclear In contrast, ERK1/2 responses to activation of expressed in HEK293 cells are of Src and EGFR but are on and to sustained activation and accumulation of ERK1/2 in the was from EGF was from and pertussis was from from ERK1/2 and from and to from and EGFR, and from and was from and from and was from The Src negative regulatory kinase was by of and from or by of in of of and with of and with to the of in HEK293 was with an and into the between and HEK293 cells in and with of in of for 2 the cells and in a the was in for 2 and the on a HEK293 cells. or HEK293 cells with in the cells to for by with The cells with agonist and in for cells for in as B.H. Catt K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and with and stimulated in the of The with acid, and was by cells on for and in for The cells with GnRH or EGF for the cells in and in for The cells by in for and in and for in in with and with or or the cells with and in and the with a with and the cells on with PBS, in and 1 and The by for with and with specific and protein or The with and in for the and the by on cells in and for with The and the cells with and in of The for and for The was on and to The with and with with for 1 The with or and with a In the and with other stimulation of GT1-7 cells, receptors for GnRH and EGF, caused but transient ERK1/2 activation, with a and In the cells, EGF caused but transient ERK1/2 activation EGF and GnRH caused phosphorylation of the EGFR as by of the EGFR and with ERK1/2 activation by GnRH and EGF was by the selective EGFR kinase with the for EGFR transactivation GnRH-induced ERK1/2 signaling in GT1-7 cells transactivation GnRH-induced ERK1/2 phosphorylation in GT1-7 of GnRH and EGF on tyrosine phosphorylation of the EGFR in GT1-7 cells. The cells stimulated with for 2 and in The cell with as and with cells. and of the selective EGFR tyrosine kinase on ERK1/2 phosphorylation by GnRH and GT1-7 with for stimulation with GnRH or EGF for The cells with PBS, in and by of by and C have shown that the HB-EGF, is by of the by in to a variety of K.L. Luttrell L.M. Leftkowitz R.J. Oncogene. 2001; 20: 1532-1539Crossref PubMed Scopus (365) Google Scholar, 13Prenzel N. Zwick E. Leserer M. Abraham R. Wallasch C. Ullrich A. Nature. 1999; 402: 884-888Crossref PubMed Scopus (1500) Google Scholar, 15Eguchi S. Dempsey J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). the of in transactivation of the EGFR by GnRH, GT1-7 cells with the selective and stimulated with shown in GnRH-induced activation of However, on ERK1/2 activation by EGF or These findings indicate the of and the of GnRH signaling on of the We the of GnRH on ERK1/2 signaling in HEK293 cells with the These cells and have been used in to the signaling of the A. M. R. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, A. M. J. A. R. P.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in GT1-7 cells, ERK1/2 activation by EGF was a between 2 and and EGF stimulation caused phosphorylation of the EGFR that was attenuated by in a and In to GT1-7 cells, GnRH stimulation of HEK293 cells caused and sustained ERK1/2 activation EGF, but not GnRH or PMA, caused phosphorylation of the EGFR ERK1/2 activation was not by the selective EGFR kinase the of EGF on ERK1/2 phosphorylation These findings that GnRH-induced ERK1/2 activation in HEK293 cells is of EGFR of EGFR transactivation by GnRH in HEK293 and of EGFR tyrosine kinase inhibition by on ERK1/2 phosphorylation by GnRH and EGF in HEK293 cells. The cells with of for stimulation with GnRH and EGF for The of the of on ERK1/2 activation by GnRH and EGF is shown in the phosphorylation in cells without was as and the are as a of the of transient and sustained activation of ERK1/2 on translocation to the nucleus, the cellular of ERK1/2 in GT1-7 and HEK293 cells was by shown in and nuclear translocation of ERK1/2 the sustained ERK1/2 activation by GnRH in HEK293 cells and was not in GT1-7 cells. In EGF to nuclear translocation of ERK1/2 in GT1-7 cells EGF These that the transient GnRH-induced ERK1/2 phosphorylation in GT1-7 cells that transactivation of the EGFR not translocation of activated ERK1/2 into the However, in HEK293 cells, GnRH causes sustained phosphorylation responses that are of EGFR transactivation and are by nuclear translocation of the activated the of the signaling of GnRH in these cell the of GnRH-induced ERK1/2 of by with for ERK1/2 phosphorylation by GnRH in GT1-7 and HEK293 cells with the major role of in GnRH However, on the phosphorylation of EGFR and ERK1/2 in these cell types. These suggest that is a of GnRH-induced ERK1/2 activation in cell types. that activation in GT1-7 cells causes phosphorylation of ERK1/2 EGFR the cells with and ERK1/2 phosphorylation by that ERK1/2 activation by for was attenuated by in GT1-7 cells but not in HEK293 cells These suggest that activation signals the EGFR in GT1-7 cells. Src kinase has been in EGFR the of Src inhibition on ERK1/2 of Src by the selective Src kinase or of attenuated ERK1/2 activation in GT1-7 cells However, ERK1/2 activation was not by PP2 or not In to in GT1-7 cells, Src inhibition on ERK1/2 activation in HEK293 cells These results that Src kinase is for ERK1/2 activation in GT1-7 cells and of the In contrast, GnRH not Src and EGFR transactivation in HEK293 cells and not the signaling of ERK1/2 ERK1/2 is often to the nucleus and elicits a variety of responses (3Marinissen M.J. Gutkind J.S. Trends Endocrinol. Metab. 2001; 22: 368-376Scopus (842) Google Scholar). However, GnRH nor EGF caused nuclear translocation of ERK1/2 in GT1-7 cells, as shown in GnRH is to expression in these cells, of activation M. Catt K.J. PubMed Scopus Google Scholar). other signaling are in the of mitogenic signals from activated ERK1/2 to the nucleus, the of ERK1/2 with p90 ribosomal S6 or translocation to the nucleus phosphorylation by ERK1/2 M. S. Mol. Cell. Endocrinol. 1999; PubMed Scopus Google Scholar). EGF and GnRH stimulated phosphorylation of in GT1-7 cells in a phosphorylation was attenuated by inhibition of and Src phosphorylation was inhibited by and the but not by the Src phosphorylation by GnRH was by the EGFR kinase These indicate that GnRH-induced phosphorylation in GT1-7 cells is by PKC, and EGFR transactivation and that Src of the is to the nucleus GnRH in GT1-7 cells. was predominantly in the However, GnRH stimulation caused accumulation of in the nucleus These results suggest that the in gene expression in GT1-7 cells M. Catt K.J. PubMed Scopus Google be by ERK1/2-dependent phosphorylation of results on cell type, GnRH-induced ERK1/2 activation can the pathway and activation, with on the duration and cellular of the activated Although in GT1-7 cells and EGFR transactivation that results in transient ERK1/2 activation, expressed in HEK293 cells are not to Src and EGFR activation and elicit sustained ERK1/2 responses. The that EGF stimulation of in GT1-7 and HEK293 cells causes transient ERK1/2 activation without nuclear translocation that GnRH-induced signaling such as the of ERK1/2 activation, are determined by the to this is on EGFR the in and ERK1/2 activation are (1Gschwind A. Zwick E. Prenzel N. Leserer M. Ullrich A. Oncogene. 2001; 20: 1594-1600Crossref PubMed Scopus (414) Google Scholar, 2Pierce K.L. Luttrell L.M. Leftkowitz R.J. Oncogene. 2001; 20: 1532-1539Crossref PubMed Scopus (365) Google Scholar, 14Shah B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar, Wallasch C. A. A. Ullrich A. J. 16: PubMed Scopus Google Scholar). the signaling pathways by transactivation of the EGFR, or by EGF are B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar, Wallasch C. A. A. Ullrich A. J. 16: PubMed Scopus Google Scholar, B.H. Catt K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). 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Austin D.A. Mellon P.L. Olefsky J.M. Webster N.J.G. Mol. Endocrinol. 2002; 16: 419-434Crossref PubMed Scopus (171) Google and HEK293 cells A. M. R. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, A. M. J. A. R. P.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In HEK293 cells, GnRH causes sustained ERK1/2 activation that is of Src and EGFR activation and In contrast, ERK1/2 activation in GT1-7 cells is is generation of by activation, and the transient signaling of the EGFR 1 and of the EGFR by GnRH is not a of GnRH target cells and not in HEK293 cells A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google and αT3-1 pituitary gonadotropes R. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). the duration of GnRH-induced signaling to ERK1/2 with the transient phosphorylation of the EGFR GnRH sustained GnRH receptor EGF causes transient ERK1/2 activation in GT1-7 and HEK293 cells 1 and ERK1/2 activation, in that by is closely regulated of negative mechanisms. The duration of signaling be to and of the (4Kao S.-C. Jaiswal R.K. Kolch W. Landreth G.E. J. Biol. Chem. 2001; 276: 18169-18177Abstract Full Text Full Text PDF PubMed Scopus (317) Google Scholar, J. Cell. Full Text Full Text PDF PubMed Scopus Google and to negative phosphorylation of by a kinase of that results in of the (4Kao S.-C. Jaiswal R.K. Kolch W. Landreth G.E. J. Biol. Chem. 2001; 276: 18169-18177Abstract Full Text Full Text PDF PubMed Scopus (317) Google Scholar, D.A. PubMed Scopus Google Scholar). the of the of ERK1/2 activation by GnRH in the cell signaling such as the of with the between sustained ERK1/2 signaling and nuclear nuclear of the ERK1/2 was in HEK293 cells a to that in pituitary gonadotropes F. Austin D.A. Mellon P.L. Olefsky J.M. Webster N.J.G. Mol. Endocrinol. 2002; 16: 419-434Crossref PubMed Scopus (171) Google Scholar). In contrast, GnRH stimulation of GT1-7 cells caused transient ERK1/2 phosphorylation without nuclear translocation of activated ERK1/2 1 and on the of ERK1/2 are with M. J. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus (131) Google in ERK1/2 activated by angiotensin the pathway (e.g. in HEK293 was to the nucleus, whereas ERK1/2 activated the pathway was as in GT1-7 cells. that the of Src and is an important factor in the of GPCR In G. P. J. J. Biol. PubMed Scopus Google that of negative in cells caused sustained signaling by nuclear translocation of whereas expression of negative in transient signaling without accumulation of ERK1/2 into the The of translocation of ERK1/2 in is not A. Pierce K.L. Choy E.W. Lefkowitz R.J. Luttrell L.M. J. Biol. Chem. 2002; 277: 9429-9436Abstract Full Text Full Text PDF PubMed Scopus (329) Google that angiotensin activation of pathway in cells caused translocation of activated ERK1/2 into the nucleus, of caused of ERK1/2 in the However, this not account for the of activated ERK1/2 in GT1-7 cells, because GnRH signaling are not by or of J. Green J. Endocrinol. 2002; PubMed Scopus Google Scholar, M. A. G. P.L. Mol. Endocrinol. PubMed Google Scholar). Although cells with GPCRs or signaling have into the of receptor the of cells receptors and signaling may from of cells GPCRs M.J. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, J. J. Biol. 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A. 1999; PubMed Scopus Google Scholar). and growth factors such as nerve growth factor and fibroblast growth are to translocation of activated ERK1/2 into the nucleus and in target gene transcription and However, EGF stimulation elicits responses in of nuclear translocation of cell and cell A. C. C. G. J. PubMed Scopus Google Scholar, S. M. M. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar, S. M. J. Cell. 2002; PubMed Scopus Google Scholar, I. S. R. Oncogene. 2001; 20: PubMed Scopus Google Scholar). EGF is well to and PubMed Scopus Google Scholar, M. PubMed Scopus Google Scholar). that GnRH and EGF activation of cell signaling such as protein kinase in GT1-7 cells. and J. is that the of EGF in GnRH in GT1-7 cells is related to the generation of cell F. Austin D.A. Mellon P.L. Olefsky J.M. Webster N.J.G. Mol. Endocrinol. 2002; 16: 419-434Crossref PubMed Scopus (171) Google that GnRH causes nuclear accumulation of ERK1/2 and activation of the and in Although GnRH to nuclear translocation of ERK1/2 in GT1-7 cells, caused of nuclear transcription factors such as M. Catt K.J. PubMed Scopus Google Scholar). The of such activation in the of nuclear accumulation of activated ERK1/2 is not other signaling are in the of mitogenic signals from ERK1/2 in the to the nucleus, the of ERK1/2 with translocation to the nucleus phosphorylation by The are serine/threonine kinases that are by activated ERK1/2 and to the nucleus, transcription factors protein, and factor M. S. Mol. Cell. Endocrinol. 1999; PubMed Scopus Google Scholar). that EGF and GnRH stimulated phosphorylation of in GT1-7 cells EGFR transactivation in a GnRH translocation of into the is that the nuclear of GnRH and EGF in GT1-7 cells are the protein, of has the of ERK1/2 activation on EGFR transactivation in cell types by specific agonists, angiotensin in cells S. F. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar), in cells E. Prenzel N. Ullrich A. Trends Pharmacol. 1999; 20: Full Text Full Text PDF PubMed Scopus Google Scholar), and lysophosphatidic acid, and in cells Wallasch C. A. A. Ullrich A. J. 16: PubMed Scopus Google Scholar). of the EGFR transactivation is Src kinase (1Gschwind A. Zwick E. Prenzel N. Leserer M. Ullrich A. Oncogene. 2001; 20: 1594-1600Crossref PubMed Scopus (414) Google Scholar, 12Dikic I. Tokiwa G. Lev S. Courtneidge S.A. Schlessinger J. Nature. 1996; 383: 547-550Crossref PubMed Scopus (880) Google Scholar, 14Shah B.H. Catt K.J. Mol. Pharmacol. 2002; 61: 343-351Crossref PubMed Scopus (81) Google Scholar, B.H. Catt K.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). with results that ERK1/2 activation is on Src kinase as well as EGFR activation in GT1-7 cells but not in HEK293 cells 2 and not have a major role in HEK293 cells with other GPCRs such as angiotensin 2001; PubMed Scopus Google Scholar), lysophosphatidic acid, and receptors S. Lefkowitz R.J. Luttrell L.M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The ERK1/2 activation is of EGFR transactivation in these cells is not indicate that of active causes phosphorylation of the EGFR in HEK293 Therefore, is that the of EGFR transactivation by GnRH in HEK293 cells is to activation of Src or is by that ERK1/2 activation by is of Src activation in HEK293 cells Luttrell Luttrell L.M. Lefkowitz R.J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In results that GnRH-induced ERK1/2 activation in GT1-7 cells Src and EGFR transient responses to elicited by However, expressed in HEK293 cells not Src and EGFR transactivation and sustained ERK1/2 phosphorylation. the of signals EGFR transactivation to of EGF stimulation in the individual cell types in this These pathways are in the shown in is that such signaling for the of phosphorylation elicited by agonist activation of GPCRs expressed in cell types.