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T31 Cell Line: Differential Roles of Calcium and Protein Kinase C1
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University (N.R., S.S., D.H., Z.N.), Ramat Aviv 69978; and the Department of Membrane Research and Biophysics, The Weizmann Institute of Science (L.N.-L., R.S.), Rehovot 76100, Israel
Address all correspondence and requests for reprints to: Zvi Naor, Ph.D., Department of Biochemistry, Tel Aviv University, Tel-Aviv 69978, Israel. E-mail: NAORZVI{at}CCSG.TAU.AC.IL
| Abstract |
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T31 cell
line. GnRH-a as well as the protein kinase C (PKC) activator
12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulated a
sustained response of MAPK activity, whereas epidermal growth factor
(EGF) stimulated a transient response. MAPK kinase (MEK) is also
activated by GnRH-a, but in a transient manner. GnRH-a and TPA
apparently activated mainly the MAPK isoform ERK1, as revealed by
Mono-Q fast protein liquid chromatography followed by Western blotting
as well as by gel kinase assay. GnRH-a and TPA stimulated the tyrosine
phosphorylation of several proteins, and this effect as well as the
stimulation of MAPK activity were inhibited by the PKC inhibitor GF
109203X. Similarly, down-regulation of TPA-sensitive PKC subspecies
nearly abolished the effect of GnRH-a and TPA on MAPK activity.
Furthermore, the protein tyrosine kinase (PTK) inhibitor genistein
inhibited protein tyrosine phosphorylation and reduced
GnRH-a-stimulated MAPK activity by 50%, suggesting the participation
of genistein-sensitive and insensitive pathways in GnRH-a action.
Although Ca2+ ionophores have only a marginal stimulatory
effect, the removal of Ca2+ markedly reduced MAPK
activation by GnRH-a and TPA, but had no effect on GnRH-a and TPA
stimulation of protein tyrosine phosphorylation. Interestingly, the
removal of Ca2+ also partly inhibited the activation of
MAPK by EGF and vanadate/H2O2. Thus, a
calcium-dependent component(s) downstream of PKC and PTK might also
participate in MAPK activation. Elevation of cAMP by forskolin exerted
partial inhibition on EGF, but not on TPA or GnRH-a action, suggesting
that MEK activators other than Raf-1 might be involved in GnRH action.
We conclude that Ca2+, PTK, and PKC participate in the
activation of MAPK by GnRH-a, with Ca2+ being necessary
downstream to PKC and PTK. | Introduction |
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Signal transduction elicited by hormones and growth factors has been found to involve sequential activation of several cytosolic protein kinases collectively known as the mitogen-activated protein kinase (MAPK) cascade (4, 5, 6, 7, 8, 9, 10). The MAPK gene family converges signals from G protein-coupled receptors (GPCRs) or growth factor receptor tyrosine kinases (RTKs), leading to cellular responses such as differentiation and proliferation. The mechanism of MAPK activation seems to differ among various stimuli. RTKs signal via an adaptor molecule, GRB2, and a guanine nucleotide exchange factor, mSOS, to activate the small GTP-binding protein (G protein), Ras, followed by activation of the MAPK cascade: Raf-1, MAPK kinase (MAPKK; MEK), and MAPK. On the other hand, GPCRs are thought to act via diverse mechanisms, including PKC-dependent and independent pathways, to activate the above cascade (6, 7, 8, 9, 10).
The signals transmitted through the MAPK cascade lead to activation of
a set of regulatory molecules that eventually initiates cellular
responses such as growth and differentiation (4, 5, 6, 7, 8, 9, 10). Recently, it has
been shown that GnRH is capable of activating MAPK in pituitary organ
culture (11) and the
T31 gonadotroph cell line (12, 13) via PKC,
and that MAPK is involved in regulation of gene expression of the
gonadotropin
-subunit (12, 13). We decided to follow the above
reports and study further the mechanism of MAPK (ERK1 and ERK2)
activation by GnRH. We found that GnRHR signaling results in
stimulation of mainly the ERK1 isoform and involves a
Ca2+-dependent pathway that does not include
Gi and Go and seems to require MEK
activators other than Raf1 as well as a protein tyrosine kinase (PTK)
upstream to the MAPK cascade. Furthermore, we show that
Ca2+ is required, but not sufficient, and its site of
action is downstream to PKC and PTK signaling.
| Materials and Methods |
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-32P]ATP was purchased from Rotem Industries
(Beersheba, Israel). Genistein, phenylmethylsulfonylfluoride, EGTA,
12-O-tetradecanoyl phorbol-13-acetate (TPA), EGF
(recombinant), forskolin, and other chemicals were purchased from Sigma
Chemical Co. (St. Louis, MO). Recombinant ERK2 used in the MAPKK assay
was prepared as previously described (15). Anti-P-tyrosine antibodies
were obtained from Zymed (San Francisco, CA). Anti-MAPK serum was
generously donated by Dr. Y. Granot, Ben-Gurion University (Beer-Sheva,
Israel). The selective PKC inhibitor bisindolylmaleimide (GF 109203X)
(16) was purchased from Calbiochem (Laufelfingen, Switzerland).
Buffers
Detergent lysis buffer consisted of 50 mM Tris-HCl
(pH 6.8), 2 mM EGTA, 1 mM sodium orthovanadate,
20 mM NaCl, 10 mM ß-glycerophosphate, 28
mM ß-mercaptoethanol, 1 mM
phenylmethylsulfonylfluoride, 20% glycerol, 50 nM each of
okadaic acid and calyculin A, and 0.5% Nonidet P-40.
Buffer A consisted of 50 mM ß-glycerophosphate (pH 7.3), 1.5 mM EGTA, 1 mM EDTA, 1 mM dithiothreitol, and 0.1 mM sodium orthovanadate.
Buffer H consisted of 50 mM ß-glycerophosphate (pH 7.3), 1.5 mM EGTA, 1 mM EDTA, 1 mM dithiothreitol, 0.1 mM sodium orthovanadate, 1 mM benzamidine, 10 mg/ml aprotinin, 10 mg/ml leupeptin, and 2 mg/ml pepstatin A.
Cell culture
T31 cells were grown in DMEM supplemented with 5% FCS, 5%
horse serum, penicillin (100 U/ml), and streptomycin (0.1 mg/ml). At
7080% confluence, the cells were serum-starved for 18 h in
DMEM, and 0.25% each of FCS and horse serum and stimulants were added
in DMEM at the indicated concentration for the given length of
time.
Fractionation and assay of MAPK and MAPKK
For determination of MAPK activity in cell extracts, the cells
were rinsed twice with ice-cold PBS and lysed for 10 min in detergent
lysis buffer. Samples of 5 µl (
2 µg protein) were subjected to
MAPK assay at 22 C for 20 min. The reaction mixture (25 µl) contained
50 mM HEPES (pH 7.8), 50 µM
[
-32P]ATP (12 cpm/fmol), 2 mM EGTA, 28
mM ß-mercaptoethanol, 2 mM MnCl2,
10 mM MgCl2, 0.8 mM sodium
orthovanadate, and EGF receptor peptide (1 mg/ml). Reactions were
quenched by spotting 10 µl of the reaction mixture on
phosphocellulose paper squares (P81, Whatman, Clifton, NJ), which were
washed in 150 mM phosphoric acid. Phosphate incorporation
was measured by the Cerenkov method.
An in-gel kinase assay was performed as previously described (17), using myelin basic protein (MBP; 0.5 mg/ml gel) as a substrate.
For determination of fractionated MAPK and MAPKK activities (15), cells were harvested in buffer H and disrupted by two 7-sec sonication (50 watts) on ice, followed by centrifugation at 20,000 x g for 15 min at 4 C.
For DE-52 cellulose fractionation, the cytosolic extracts (0.5 ml) were applied to minicolumns (0.35 ml). The flow-through and wash in 0.02 M NaCl in buffer A were collected and measured as previously described (18) for MAPKK activity in a double couple assay in the presence or absence of recombinant ERK2. The eluate of 0.22 M NaCl in buffer A (0.75 ml) contained more than 85% MAPK activity, measured toward MBP as recently described (15).
For fast protein liquid chromatography fractionation, the cytosolic extracts (6 mg protein from 2 x 108 cells) were loaded on a 1 ml Mono-Q column and fractionated using a 00.4 M linear NaCl gradient in buffer A (1 ml/min; 1-ml fractions) as described by Ahn et al. (19). Even fractions were assayed for MAPKK and MAPK activities as described below.
Immunoblotting
Proteins in the cell extracts were separated on 7.518%
PAGE-SDS gels (ratio of acrylamide to bisacrylamide, 30:0.5) and
electrotransferred to nitrocellulose papers at 4 C and 100 V in 50
mM glycine and 50 mM Tris-HCl, pH 8.8. For
detection of phosphotyrosine-containing proteins, the papers were
blocked for 60 min in 1% BSA and 0.5% Tween-20 in TBS (20
mM Tris, pH 8.3, and 150 mM NaCl) and treated
overnight with 0.1 µg/ml affinity-purified rabbit anti-P-tyrosine
antibodies (Zymed). After intensive washing, the signals were
visualized using horseradish peroxidase-conjugated goat antirabbit IgG
and the enhanced chemiluminescence method.
Experiments, in duplicate or triplicate, were repeated two or three times, and the results shown are from a representative experiment.
| Results |
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T31 cells with GnRH-a or TPA resulted in a rapid
activation of MAPK (within 1 min), as revealed by phosphorylation of
EGF receptor peptide or MBP (Fig. 1
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T31 cell lysate also
revealed the enhanced activation of ERK1 by GnRH-a (not shown). Similar
to GnRH-a, TPA caused preferential activation of ERK1 (not shown). As
the ratio of ERK2 to ERK1 in
T31 cells is about 3:1 (Fig. 4B
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T31 cells with PTX (100 ng/ml; 18 h) had no
significant effect on stimulation of MAPK activity by GnRH-a, TPA, and
EGF (Fig. 5
T31 cells do not involve PTX-sensitive G
proteins such as Gi or Go. On the
other hand, PTX inhibited (by 47%) serum (10% FCS) stimulation of
MAPK activity (Fig. 5
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T31 cells with GnRH-a resulted in the elevation
of tyrosine phosphorylation of several proteins of 42, 46, 85, 95, 100,
125, and 170 kDa (Fig. 6
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T31 cell lysate (not
shown).
We also examined the activation of MAPK in PKC down-regulated cells.
Prolonged pretreatment of the cells with TPA (100 ng/ml; 16 h)
reduced endogenous PKC activity by about 90% (26, 27). GnRH-a and TPA
stimulation of MAPK activity was abolished in the PKC down-regulated
cells (Fig. 9
). Further examination of GnRH-a
stimulation of MAPK in control and PKC down-regulated cells at
different time points revealed loss of responsiveness at all time
points examined (Fig. 9
, inset). The data rules out a
possible PKC-independent transient response elicited by GnRH-a.
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| Discussion |
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Transient activation of MAPK is thought to be associated with cellular
growth and proliferation, whereas prolonged activation is involved in
differentiation (31, 32). GnRH-a, which triggers differentiated
cellular functions such as gonadotropin secretion and synthesis, is
also found capable of inducing a sustained MAPK signal in the
gonadotroph
T31 cell line. Thus, prolonged activation of MAPK
might be associated with alternative cellular functions. Furthermore,
GnRH-a is shown here to apparently activate mainly the ERK1 isoform,
whereas other ligands were reported to activate mainly ERK2 (4, 5, 6, 7, 8, 9, 10).
The significance of the differential activation of ERK1 vs.
ERK2 is under investigation. Interestingly, unlike the prolonged MAPK
activation, stimulation of MAPKK (MEK) by GnRH-a was transient,
suggesting that distinct termination signals and protein phosphatases
operate on these two members of the signaling cascade during GnRH-a
action.
Different mechanisms were proposed for MAPK activation by ligands
operating via GPCRs. Thrombin and lysophosphatidic acid stimulate MAPK
via Gi in a PTX-sensitive, PKC-independent
pathway (20, 21), whereas endothelin-1 acts in a PTX-sensitive and
PKC-dependent mechanism (22). The agents acting via muscarinic
receptors m1 and m2 stimulate MAPK apparently via the ß
-subunits
of G proteins (Gi and Gq) in a
Ras-dependent, PKC-independent process (33). Other
Gq-linked receptors, such as that for bombesin, are thought
to mediate activation of MAPK almost entirely via PKC (34), or in the
case of TRH, activation is mediated partly by PKC and also by a
Ras-dependent pathway (35). The results presented here for GnRH-a
represent another aspect of signaling, emphasizing the differential
role of PKC and Ca2+ in MAPK activation. In contrast to a
previous report (23), our results indicate that
Gi and Go are not involved in GnRH-a
activation of MAPK by demonstrating the lack of inhibition of the
GnRH-a response by pertussis toxin. The reason for the discrepancy is
not known. Thus, GnRH-a stimulation of MAPK activity is most likely
mediated by Gq via activation of phospholipase C (36, 37).
Activation of MAPK by RTKs, GPCRs, and phorbol esters was inhibited by
elevation of cAMP (17, 28, 29; see Ref. 30 for review). However, in the
PC12 cell line, forskolin seems to slightly elevate basal MAPK activity
without affecting its maximal stimulated activity (17). The reason for
this discrepancy is probably due to the pattern of MEK activator
expression in PC12 cells (17). Indeed, the stimulation of basal MAPK
activity by forskolin and the lack of inhibition of the GnRH-a and TPA
responses observed here resemble the effect of forskolin in PC12 cells.
However, the partial inhibition of EGF-stimulated activity suggests
that more than one signaling mechanism leads to MAPK activation in
T31 cells. Thus, EGF stimulates MAPK activity by both
cAMP-sensitive and insensitive pathways, whereas GnRH-a and TPA act by
a cAMP-insensitive mechanism. One possible explanation for these
distinct pathways is that GnRH-a and TPA signals might be transmitted
by MEK activators that are distinct from the cAMP-sensitive Raf-1 (30, 38), whereas EGF signals use both Raf-1 and the other MEK
activators.
Elevation of Ca2+ by ionomycin had marginal effect on MAPK
activity in
T31 cells. The results differ from those reported in
other cell systems, where elevated Ca2+ activated MAPK (39, 40). Furthermore, raising the levels of extracellular Ca2+
inhibited EGF-induced ERK2 activity in human primary keratinocytes
(41). On the contrary, in our system, removal of Ca2+
markedly reduced the GnRH-a and EGF responses. Thus, Ca2+
is necessary, but not sufficient, for mediating GnRH-a elevation of
MAPK activity. On the other hand, TPA elevates MAPK activity, whereas
PKC inhibition or its depletion resulted in inhibition of the GnRH-a
response. Thus, PKC is necessary and sufficient for mediating the
GnRH-a effect. As activation of phosphoinositide turnover by GnRH is
Ca2+ independent (36), it is possible that the
Ca2+-requiring step involves the activation of a
Ca2+-dependent PKC subtype, consistent with the report that
PKC
activates Raf-1 by direct phosphorylation (42). However, the
inhibitory effect of Ca2+ removal on the action of GnRH-a
as well as that of EGF or vanadate/H2O2 on MAPK
activity, but not on protein tyrosine phosphorylation or PTK activity,
suggests that another Ca2+-binding protein might
participate in the activation process downstream from PKC and PTK.
One of the targets of MAPK is the cytosolic phospholipase A2, which is phosphorylated and activated by MAPK (43). As the release of arachidonic acid and formation of its lipoxygenase products play a role in GnRH-induced gonadotropin release and gonadotropin subunit gene expression (44, 45, 46, 47, 48, 49), it is likely that activation of MAPK by GnRH is required to enable stimulation of the arachidonate cascade. In addition, some potential MAPK substrates, such as c-fos, Elk1, Ets2, and TAL-1 (6, 7, 8, 9, 10), might be required for GnRH actions as regulators of nuclear transcriptional activity.
Consistent with the reported effect of a general PKC activator such as
TPA on protein tyrosine phosphorylation (50, 51), GnRH-a, stimulated
the tyrosine phosphorylation of proteins of 42, 46, 85, 95, 100, 125,
and 170 kDa, which might represent p42/p44 MAPKs, focal adhesion kinase
(p125FAK) (21), and others. Interestingly, the phosphotyrosyl proteins
induced by GnRH-a were inhibited by the selective PKC inhibitor GF
109203X, with an IC50 of about 1 µM, with the
exception of pp125, which required higher doses of the drug
(IC50, 30 µM). As inhibition of GnRH-a- and
TPA-induced MAPK activation by GF 109203X was observed at an
IC50 of 1.8 µM, some of the
tyrosine-phosphorylated proteins, but not pp125, might be linked to
MAPK in a manner yet to be determined. This is further supported by the
inhibitory effect of the PTK inhibitor genistein on GnRH-a stimulation
of MAPK activity. Furthermore, as the GnRH effect on protein tyrosine
phosphorylation and MAPK activation is fully dependent on PKC, whereas
genistein only partly inhibits (50%) the activation of MAPK by GnRH,
it seems likely that at least two PKC subspecies that specialize in
PTK-dependent and -independent signaling participate in the action of
GnRH on MAPK. Nevertheless, PKC-sensitive mechanisms are involved in
GnRH-a-induced protein tyrosine phosphorylation, which apparently are
manifested upstream of MAPK activation. Based on the data presented
here, we propose a model for GnRH-induced MAPK activation (Fig. 12
). The present study opens a new vista in elucidating
the mechanism of action of the neurohormone GnRH, which is the first
key hormone of reproduction, and sheds further light on the pathways
involved in RTKs vs. GPCRs leading to activation of
MAPK.
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| Acknowledgments |
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T31 cells, and Ms. T. Fuchs
and Drs. U. Zor, Y. Granot, and M. Liscovitch for their interest and
help during the studies. We also thank Mrs. Angela Cohen for editorial
assistance. | Footnotes |
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2 Incumbent of the Samuel and Isabela Friedman Career Development
Chair. ![]()
Received October 3, 1996.
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T31 cell line: role in
gonadotropin releasing hormone. Biochemistry 33:1279512799[CrossRef][Medline]
T31 cell line: role in
gonadotropin-releasing hormone action. Biochem J 316:667670
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A. Chamson-Reig, E. M. Sorianello, P. N. Catalano, M. O. Fernandez, O. P. Pignataro, C. Libertun, and V. A. R. Lux-Lantos Gonadotropin-Releasing Hormone Signaling Pathways in an Experimental Ovarian Tumor Endocrinology, July 1, 2003; 144(7): 2957 - 2966. [Abstract] [Full Text] [PDF] |
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D. J. Haisenleder, H. A. Ferris, and M. A. Shupnik The Calcium Component of Gonadotropin-Releasing Hormone-Stimulated Luteinizing Hormone Subunit Gene Transcription Is Mediated by Calcium/Calmodulin-Dependent Protein Kinase Type II Endocrinology, June 1, 2003; 144(6): 2409 - 2416. [Abstract] [Full Text] [PDF] |
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G. Y. Bedecarrats, K. D. Linher, and U. B. Kaiser Two Common Naturally Occurring Mutations in the Human Gonadotropin-Releasing Hormone (GnRH) Receptor Have Differential Effects on Gonadotropin Gene Expression and on GnRH-Mediated Signal Transduction J. Clin. Endocrinol. Metab., February 1, 2003; 88(2): 834 - 843. [Abstract] [Full Text] [PDF] |
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D. Harris, D. Chuderland, D. Bonfil, S. Kraus, R. Seger, and Z. Naor Extracellular Signal-Regulated Kinase and c-Src, But Not Jun N-Terminal Kinase, Are Involved in Basal and Gonadotropin-Releasing Hormone-Stimulated Activity of the Glycoprotein Hormone {alpha}-Subunit Promoter Endocrinology, February 1, 2003; 144(2): 612 - 622. [Abstract] [Full Text] [PDF] |
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B. H. Shah, J.-W. Soh, and K. J. Catt Dependence of Gonadotropin-releasing Hormone-induced Neuronal MAPK Signaling on Epidermal Growth Factor Receptor Transactivation J. Biol. Chem., January 24, 2003; 278(5): 2866 - 2875. [Abstract] [Full Text] [PDF] |
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M. Desclozeaux, I. N. Krylova, F. Horn, R. J. Fletterick, and H. A. Ingraham Phosphorylation and Intramolecular Stabilization of the Ligand Binding Domain in the Nuclear Receptor Steroidogenic Factor 1 Mol. Cell. Biol., October 15, 2002; 22(20): 7193 - 7203. [Abstract] [Full Text] [PDF] |
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V. V. Vasilyev, M. A. Lawson, D. Dipaolo, N. J. G. Webster, and P. L. Mellon Different Signaling Pathways Control Acute Induction versus Long-Term Repression of LH{beta} Transcription by GnRH Endocrinology, September 1, 2002; 143(9): 3414 - 3426. [Abstract] [Full Text] [PDF] |
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V. V. Vasilyev, F. Pernasetti, S. B. Rosenberg, M. J. Barsoum, D. A. Austin, N. J. G. Webster, and P. L. Mellon Transcriptional Activation of the Ovine Follicle-Stimulating Hormone-{beta} Gene by Gonadotropin- Releasing Hormone Involves Multiple Signal Transduction Pathways Endocrinology, May 1, 2002; 143(5): 1651 - 1659. [Abstract] [Full Text] [PDF] |
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F. Liu, D. A. Austin, P. L. Mellon, J. M. Olefsky, and N. J. G. Webster GnRH Activates ERK1/2 Leading to the Induction of c-fos and LH{beta} Protein Expression in L{beta}T2 Cells Mol. Endocrinol., March 1, 2002; 16(3): 419 - 434. [Abstract] [Full Text] [PDF] |
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D. Harris, D. Bonfil, D. CHuderland, S. Kraus, R. Seger, and Z. Naor Activation of MAPK Cascades by GnRH: ERK and Jun N-Terminal Kinase Are Involved in Basal and GnRH-Stimulated Activity of the Glycoprotein Hormone LH{beta}-Subunit Promoter Endocrinology, March 1, 2002; 143(3): 1018 - 1025. [Abstract] [Full Text] [PDF] |
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W. R. Duan, M. Ito, Y. Park, E. T. Maizels, M. Hunzicker-Dunn, and J. L. Jameson GnRH Regulates Early Growth Response Protein 1 Transcription Through Multiple Promoter Elements Mol. Endocrinol., February 1, 2002; 16(2): 221 - 233. [Abstract] [Full Text] [PDF] |
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D.J. Haisenleder, L.J. Workman, L.L. Burger, K.W. Aylor, A.C. Dalkin, and J.C. Marshall Gonadotropin Subunit Transcriptional Responses to Calcium Signals in the Rat: Evidence for Regulation by Pulse Frequency Biol Reprod, December 1, 2001; 65(6): 1789 - 1793. [Abstract] [Full Text] [PDF] |
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T. Zhang, M. W. Wolfe, and M. S. Roberson An Early Growth Response Protein (Egr) 1 cis-Element Is Required for Gonadotropin-releasing Hormone-induced Mitogen-activated Protein Kinase Phosphatase 2 Gene Expression J. Biol. Chem., November 30, 2001; 276(49): 45604 - 45613. [Abstract] [Full Text] [PDF] |
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H. M. Everest, J. N. Hislop, T. Harding, J. B. Uney, A. Flynn, R. P. Millar, and C. A. McArdle Signaling and Antiproliferative Effects Mediated by GnRH Receptors After Expression in Breast Cancer Cells Using Recombinant Adenovirus Endocrinology, November 1, 2001; 142(11): 4663 - 4672. [Abstract] [Full Text] [PDF] |
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T. A. Jackson, R. E. Schweppe, D. M. Koterwas, and A. P. Bradford Fibroblast Growth Factor Activation of the Rat PRL Promoter is Mediated by PKC{delta} Mol. Endocrinol., September 1, 2001; 15(9): 1517 - 1528. [Abstract] [Full Text] [PDF] |
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G. Maya-Nunez and P. Michael Conn Cyclic Adenosine 3',5'-Monophosphate (cAMP) and cAMP Responsive Element-Binding Protein Are Involved in the Transcriptional Regulation of Gonadotropin-Releasing Hormone (GnRH) Receptor by GnRH and Mitogen-Activated Protein Kinase Signal Transduction Pathway in GGH3 Cells Biol Reprod, August 1, 2001; 65(2): 561 - 567. [Abstract] [Full Text] [PDF] |
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S. K. Kang, C.-J. Tai, P. S. Nathwani, K.-C. Choi, and P. C. K. Leung Stimulation of Mitogen-Activated Protein Kinase by Gonadotropin-Releasing Hormone in Human Granulosa-Luteal Cells Endocrinology, February 1, 2001; 142(2): 671 - 679. [Abstract] [Full Text] [PDF] |
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R. Sosnowski, P. L. Mellon, and M. A. Lawson Activation of Translation in Pituitary Gonadotrope Cells by Gonadotropin-Releasing Hormone Mol. Endocrinol., November 1, 2000; 14(11): 1811 - 1819. [Abstract] [Full Text] |
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M. S. Johnson, E. M. Lutz, C. J. MacKenzie, W. B. Wolbers, D. N. Robertson, P. J. Holland, and R. Mitchell Gonadotropin-Releasing Hormone Receptor Activation of Extracellular Signal-Regulated Kinase and Tyrosine Kinases in Transfected GH3 Cells and in {alpha}T3-1 Cells Endocrinology, September 1, 2000; 141(9): 3087 - 3097. [Abstract] [Full Text] [PDF] |
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P. G. Andreis, A. Markowska, H. C. Champion, G. Mazzocchi, L. K. Malendowicz, and G. G. Nussdorfer Adrenomedullin Enhances Cell Proliferation and Deoxyribonucleic Acid Synthesis in Rat Adrenal Zona Glomerulosa: Receptor Subtype Involved and Signaling Mechanism Endocrinology, June 1, 2000; 141(6): 2098 - 2104. [Abstract] [Full Text] [PDF] |
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J. M. Mulvaney and M. S. Roberson Divergent Signaling Pathways Requiring Discrete Calcium Signals Mediate Concurrent Activation of Two Mitogen-activated Protein Kinases by Gonadotropin-releasing Hormone J. Biol. Chem., May 5, 2000; 275(19): 14182 - 14189. [Abstract] [Full Text] [PDF] |
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R. Grosse, S. Roelle, A. Herrlich, J. Hohn, and T. Gudermann Epidermal Growth Factor Receptor Tyrosine Kinase Mediates Ras Activation by Gonadotropin-releasing Hormone J. Biol. Chem., April 14, 2000; 275(16): 12251 - 12260. [Abstract] [Full Text] [PDF] |
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R. Grosse, A. Schmid, T. Schoneberg, A. Herrlich, P. Muhn, G. Schultz, and T. Gudermann Gonadotropin-releasing Hormone Receptor Initiates Multiple Signaling Pathways by Exclusively Coupling to Gq/11 Proteins J. Biol. Chem., March 24, 2000; 275(13): 9193 - 9200. [Abstract] [Full Text] [PDF] |
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A. Kimura, M. Ohmichi, K. Tasaka, Y. Kanda, H. Ikegami, J. Hayakawa, K. Hisamoto, K.-i. Morishige, S. Hinuma, H. Kurachi, et al. Prolactin-releasing Peptide Activation of the Prolactin Promoter Is Differentially Mediated by Extracellular Signal-regulated Protein Kinase and c-Jun N-terminal Protein Kinase J. Biol. Chem., February 4, 2000; 275(5): 3667 - 3674. [Abstract] [Full Text] [PDF] |
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J. M. Mulvaney, T. Zhang, C. Fewtrell, and M. S. Roberson Calcium Influx through L-type Channels Is Required for Selective Activation of Extracellular Signal-regulated Kinase by Gonadotropin-releasing Hormone J. Biol. Chem., October 15, 1999; 274(42): 29796 - 29804. [Abstract] [Full Text] [PDF] |
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A. Kimura, M. Ohmichi, H. Kurachi, H. Ikegami, J. Hayakawa, K. Tasaka, Y. Kanda, Y. Nishio, H. Jikihara, N. Matsuura, et al. Role of Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Cascade in Gonadotropin-releasing Hormone-induced Growth Inhibition of a Human Ovarian Cancer Cell Line Cancer Res., October 1, 1999; 59(20): 5133 - 5142. [Abstract] [Full Text] [PDF] |
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G. B. Call and M. W. Wolfe Gonadotropin-Releasing Hormone Activates the Equine Luteinizing Hormone {beta} Promoter Through a Protein Kinase C/Mitogen-Activated Protein Kinase Pathway Biol Reprod, September 1, 1999; 61(3): 715 - 723. [Abstract] [Full Text] |
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W. R. Duan, J. L. Shin, and J. L. Jameson Estradiol Suppresses Phosphorylation of Cyclic Adenosine 3',5'-Monophosphate Response Element Binding Protein (CREB) in the Pituitary: Evidence for Indirect Action via Gonadotropin-Releasing Hormone Mol. Endocrinol., August 1, 1999; 13(8): 1338 - 1352. [Abstract] [Full Text] |
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M. W. Wolfe and G. B. Call Early Growth Response Protein 1 Binds to the Luteinizing Hormone-{beta} Promoter and Mediates Gonadotropin-Releasing Hormone-Stimulated Gene Expression Mol. Endocrinol., May 1, 1999; 13(5): 752 - 763. [Abstract] [Full Text] |
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X.-b. Han and P. M. Conn The Role of Protein Kinases A and C Pathways in the Regulation of Mitogen-Activated Protein Kinase Activation in Response to Gonadotropin-Releasing Hormone Receptor Activation Endocrinology, May 1, 1999; 140(5): 2241 - 2251. [Abstract] [Full Text] |
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B. R. White, D. L. Duval, J. M. Mulvaney, M. S. Roberson, and C. M. Clay Homologous Regulation of the Gonadotropin-Releasing Hormone Receptor Gene Is Partially Mediated by Protein Kinase C Activation of an Activator Protein-1 Element Mol. Endocrinol., April 1, 1999; 13(4): 566 - 577. [Abstract] [Full Text] |
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M. S. Roberson, T. Zhang, H. L. Li, and J. M. Mulvaney Activation of the p38 Mitogen-Activated Protein Kinase Pathway by Gonadotropin-Releasing Hormone Endocrinology, March 1, 1999; 140(3): 1310 - 1318. [Abstract] [Full Text] |
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J. J. Evans Modulation of Gonadotropin Levels by Peptides Acting at the Anterior Pituitary Gland Endocr. Rev., February 1, 1999; 20(1): 46 - 67. [Abstract] [Full Text] |
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X. Lin and P. M. Conn Transcriptional Activation of Gonadotropin-Releasing Hormone (GnRH) Receptor Gene by GnRH: Involvement of Multiple Signal Transduction Pathways Endocrinology, January 1, 1999; 140(1): 358 - 364. [Abstract] [Full Text] |
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I. M. Colin and J. L. Jameson Estradiol Sensitization of Rat Pituitary Cells to Gonadotropin-Releasing Hormone: Involvement of Protein Kinase C- and Calcium-Dependent Signaling Pathways Endocrinology, September 1, 1998; 139(9): 3796 - 3802. [Abstract] [Full Text] [PDF] |
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D. J. Haisenleder, M. E. Cox, S. J. Parsons, and J. C. Marshall Gonadotropin-Releasing Hormone Pulses Are Required to Maintain Activation of Mitogen-Activated Protein Kinase: Role in Stimulation of Gonadotrope Gene Expression Endocrinology, July 1, 1998; 139(7): 3104 - 3111. [Abstract] [Full Text] [PDF] |
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N. L. Levi, T. Hanoch, O. Benard, M. Rozenblat, D. Harris, N. Reiss, Z. Naor, and R. Seger Stimulation of Jun N-Terminal Kinase (JNK) by Gonadotropin-Releasing Hormone in Pituitary {alpha}T3-1 Cell Line Is Mediated by Protein Kinase C, c-Src, and CDC42 Mol. Endocrinol., June 1, 1998; 12(6): 815 - 824. [Abstract] [Full Text] |
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R. E. Schweppe, A. A. Frazer-Abel, A. Gutierrez-Hartmann, and A. P. Bradford Functional Components of Fibroblast Growth Factor (FGF) Signal Transduction in Pituitary Cells. IDENTIFICATION OF FGF RESPONSE ELEMENTS IN THE PROLACTIN GENE J. Biol. Chem., December 5, 1997; 272(49): 30852 - 30859. [Abstract] [Full Text] [PDF] |
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O. Benard, Z. Naor, and R. Seger Role of Dynamin, Src, and Ras in the Protein Kinase C-mediated Activation of ERK by Gonadotropin-releasing Hormone J. Biol. Chem., February 9, 2001; 276(7): 4554 - 4563. [Abstract] [Full Text] [PDF] |
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T. Yokoi, M. Ohmichi, K. Tasaka, A. Kimura, Y. Kanda, J. Hayakawa, M. Tahara, K. Hisamoto, H. Kurachi, and Y. Murata Activation of the Luteinizing Hormone beta Promoter by Gonadotropin-releasing Hormone Requires c-Jun NH2-terminal Protein Kinase J. Biol. Chem., July 7, 2000; 275(28): 21639 - 21647. [Abstract] [Full Text] [PDF] |
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