Oxytocin stimulation of RGS2 mRNA expression in cultured
human myometrial cells
Eun Sung
Park1,
Clement O.
Echetebu1,
Solweig
Soloff1, and
Melvyn S.
Soloff1,2
1 Department of Obstetrics and Gynecology, 2 Sealy
Center for Molecular Science, University of Texas Medical Branch,
Galveston, Texas 77555-1062
 |
ABSTRACT |
Regulators of G protein signaling (RGS
proteins) interact with G
q and G
i and
accelerate GTPase activity. These proteins have been characterized only
within the past few years, so our understanding of their importance is
still preliminary. We examined the effect of oxytocin on RGS2 mRNA
expression to help determine the role of RGS proteins in oxytocin
signaling in human myometrial cells in primary culture. Oxytocin
increased RGS2 mRNA concentration maximally by 1 or 2 h in a
dose-dependent and agonist-specific manner. RGS2 mRNA levels were also
elevated by treatment with Ca2+ ionophore, phorbol ester,
or forskolin. Oxytocin's effects were completely inhibited by an
intracellular Ca2+ chelator and partially blocked by a
protein kinase C inhibitor, indicating that intracellular
Ca2+ concentration is the primary signal for oxytocin
elevation of RGS2 mRNA levels. Use of pharmacological inhibitors
indicated that part of oxytocin-stimulated RGS2 mRNA expression is
mediated by Gi/tyrosine kinase activities. Although
oxytocin does not stimulate increases in intracellular cAMP
concentration, agents that elevate intracellular cAMP concentrations
and cause myometrial relaxation may possibly cause heterologous
desensitization to oxytocin via RGS2 expression. These results suggest
that RGS2 may be important in regulating the myometrial response to oxytocin.
intracellular calcium; protein kinase C; G proteins; forskolin; adenosine 3',5'-cyclic monophosphate; regulator of G protein
 |
INTRODUCTION |
PROTEINS TERMED
REGULATORS of G protein signaling (RGS proteins) are a diverse
multiprotein family that interacts with activated G
subunits to
block signaling by Gi and/or Gq classes of G
proteins (12). The RGS protein binding results in
accelerated hydrolysis of G
-bound GTP. As part of the general class
of GTPase-activating proteins, RGS proteins may be important for
turning off many G protein-mediated physiological responses, accounting
for attenuated responses or, in the extreme, what appears to be
uncoupling of G protein activity from liganded receptors.
GTPase-activating proteins have been characterized only within the past
few years, so our understanding of their importance is still
rudimentary. Several RGS mRNAs are constitutively expressed at high
levels (8, 22), suggesting that the corresponding proteins
might be readily available for the acute desensitization of signaling. In contrast, RGS2 mRNA levels are typically low in resting cells but
are upregulated for several hours after stimulation by various agents
in different cell types (11, 13, 14, 19, 22, 26). RGS2
mRNA is presumably synthesized in response to an initial stimulus and
then blocks subsequent hormone-signaling events.
Oxytocin (OT) is a G protein-coupled receptor agonist that stimulates
uterine smooth muscle contraction. Human myometrial cells in culture
express OT receptors, and, although these cells are not in an
appropriate environment to contract, they possess signal pathways
involved in the stimulation of contraction. Thus myosin light chain
kinase activity can be activated in myometrial smooth muscle cells by
elevation of intracellular Ca2+ concentrations
(2). OT also stimulates an increase in prostacyclin synthesis by a G protein-sensitive (pertussis toxin-inhibitable) pathway in cultured human myometrial cells (20). RGS2
presumably is expressed in all cell types, but nothing is known of its
function in uterine smooth muscle cells. We have shown in the present
studies that OT stimulates increased expression of RGS2 mRNA in human myometrial cells in primary culture and elucidated the major signal pathways involved.
 |
MATERIALS AND METHODS |
Reagents.
Reagents were obtained from the following sources: OT and OT antagonist
[d(CH2)5,Tyr(Me)2,Thr4,Tyr-NH29]ornithine
vasotocin from Peninsula Laboratories (Belmont, CA); pertussis
toxin, GF-109203X,
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), genestein, wortmannin, and phorbol 12-myristate 13-acetate (PMA) from Biomol Research Laboratories (Plymouth Meeting, PA); FBS from Atlanta Biological (Atlanta, GA); MEM and cell culture reagents from GIBCO-BRL (Grand Island, NY). All other chemicals were
obtained from Sigma (St. Louis, MO).
Myometrial cell culture.
The University of Texas Medical Branch Committee on Research Involving
Human Subjects approved the use of human tissue. Myometrial samples
were taken from women by caesarean section near the end of gestation,
and cells were prepared as described previously (5). The
cells were maintained in MEM containing 10% (vol/vol) FBS, 1 mM sodium
pyruvate, 2 mM L-glutamine, 100 IU/ml penicillin G, 100 µg/ml streptomycin sulfate, and 15 µg/ml amphotericin B at 37°C
(95% humidity) in the presence of 5% CO2. The cells,
which were used at confluence between passages 3 and 10, were serum starved overnight (about 16 h) before treatment with OT or other agents.
Northern blot analysis.
Total RNA was isolated from cultured human myometrium cells using
TRIzol reagent (GIBCO-BRL Life Technologies, Rockville, MD). Samples of
20 µg of RNA were subjected to electrophoresis in 1%
agarose-formaldehyde gels and transferred to nylon membranes for
Northern blotting. The RGS2 probe was obtained by RT-PCR and cloned
into pGEM-T Easy (Promega, Madison, WI). We identified selected clones
by restriction enzyme digestion and DNA sequencing. Hybridizations were
performed using random primed cDNA fragments of the entire coding
regions of RGS2 gene labeled with [
-32P]dCTP (3,000 Ci/mmol; Amersham Pharmacia Biotech, Piscataway, NJ) in ExpressHyb
hybrization solution (Clontech Laboratories, Palo Alto, CA) overnight
at 68°C. The blots were rinsed for 10 min at room temperature with
1× saline-sodium citrate (SSC) and 0.1% SDS solution and then 45 min
at 65°C with 0.2× SSC and 0.1% SDS solution. The blots were exposed
to a Cyclone phosphor screen (Packard Instrument, Meriden, CT) for
image analysis and to X-ray film at
80°C for 1-3 days. After
the films were developed, the nylon membranes were stripped and
reprobed with the human
-tubulin cDNA, which was synthesized by
RT-PCR, cloned, and labeled by random priming as described for the RGS2 probe.
Analysis of data.
Experiments were repeated on myometrial cells derived from three
separate women. The results of the Northern blots were analyzed densitometrically and quantified using ImageQuant software (Packard Instrument). In cases where a percent change is reported, the values
were obtained by expressing the RGS2 mRNA concentration relative to
that of
-tubulin mRNA. Because of variability in the results between
cells in primary culture from different patients, the data are
presented as a representative Northern blot from a triplicate set. The
changes in RGS2 expression within each treatment group were comparable
in all cases.
 |
RESULTS |
OT specifically increases RGS2 mRNA expression.
Treatment of human myometrial cells with 100 nM OT resulted in an
increase in the amount of RGS2 mRNA by 30 min (Fig.
1). Maximal stimulation was apparent by
1-2 h (Fig. 1). An effect of OT at 2 h was seen with as
little as 0.1 nM OT, and 1 nM OT gave a near-maximal response (Fig.
2A). The effects of OT were blocked by the OT antagonist (Fig. 2B).

View larger version (30K):
[in this window]
[in a new window]
|
Fig. 1.
Northern blot analysis of the effects of oxytocin (100 nM) on regulator of G protein (RGS2) mRNA levels in cultured human
myometrial cells. After analysis, the blots were reprobed to determine
-tubulin mRNA concentration, which was used to normalize RGS2 mRNA
levels. -TUB, -tubulin.
|
|

View larger version (54K):
[in this window]
[in a new window]
|
Fig. 2.
Specificity of the RGS2 mRNA response to oxytocin (OT).
A: dose-response relationship between OT concentration and
RGS2 mRNA levels. Cells were treated with OT for 2 h.
B: inhibition of the OT-stimulated RGS2 mRNA response by OT
antagonist (OTA). Cells were treated either with 10 nM OT, 100 nM OT
antagonist, or both for 2 h.
|
|
Mediators in OT-stimulated RGS2 mRNA expression.
OT signaling in the myometrium has been shown to occur via
Gq/phospholipase C (PLC) and activation of protein kinase C
(PKC; see Refs. 9, 21, 24).
Treatment of myometrial cells with the Ca2+ ionophore
A-23187 (50 µM) to elevate intracellular Ca2+
concentrations resulted in an increase in RGS2 mRNA levels, with a
maximal increase at ~2 h (Fig.
3A). A-23187 treatment,
however, caused the degradation of mRNA at later time points, as was
apparent by
-tubulin analysis (Fig. 3A). Increases in
intracellular Ca2+ concentrations generated by OT treatment
appear to be responsible for OT-stimulated expression of RGS2 mRNA, as
pretreatment of cells with the Ca2+ chelator BAPTA-AM (10 and 30 µM) blocked the effects of OT (Fig. 3B). The
effects of A-23187 treatment were also blocked by the two
concentrations of BAPTA-AM (Fig. 3B).

View larger version (53K):
[in this window]
[in a new window]
|
Fig. 3.
Involvement of intracellular Ca2+
concentration on OT-stimulated RGS2 mRNA expression. A:
effect of Ca2+ ionophore A-23187 after 2 h of
treatment. B: effect of
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM
(BAPTA-AM) pretreatment on A-23187- and OT-stimulated RGS2 mRNA
expression.
|
|
OT signaling through stimulation of PLC activity results in activation
of PKC. Activation of PKC by PMA also stimulated an increase in RGS2
mRNA 2 h after treatment (Fig. 4).
This effect was blocked by pretreatment with the PKC inhibitor
GF-109203X, at 1 and 10 µM. The effects of OT on RGS2 mRNA levels,
however, were only partially blocked by the same doses of GF-109203X.

View larger version (21K):
[in this window]
[in a new window]
|
Fig. 4.
Effect of protein kinase C (PKC) activation by phorbol
12-myristate 13-acetate (PMA; 100 nM) and inhibition of PKC activity by
GF-109203X (1 and 10 µM) on RGS2 mRNA expression. Cells were
pretreated with inhibitor for 30 min, followed by treatment with either
PMA or OT (100 nM) for 2 h.
|
|
Increases in intracellular cAMP have been shown to induce increases in
RGS2 mRNA levels in certain cell types but not others. Elevation of
intracellular cAMP concentration by forskolin treatment caused a marked
increase in RGS2 mRNA levels (Fig. 5).
Thus human myometrial cells are in the category of cell type that
responds to cAMP with an increase in RGS2 mRNA expression.
Synergy between signal pathway activators on RGS2 expression.
The effects of A-23187 and PMA were potentiated by cotreatment with
forskolin (Fig. 6). Likewise, A-23187
synergized with PMA to enhance RGS2 mRNA expression. The effects of PMA
in conjunction with either A-23187 or forskolin were notable in that
PMA alone was not stimulatory at the time point taken. The findings
indicate that RGS2 mRNA levels are regulated along separate and
complementary pathways with respect to increased intracellular
Ca2+ concentrations, activation of PKC, and elevation of
intracellular cAMP levels.

View larger version (31K):
[in this window]
[in a new window]
|
Fig. 6.
Synergistic effects of A-23187 (50 µM), forskolin (25 µM), and PMA (100 nM) on RGS2 mRNA expression. Cells were treated for
2 h.
|
|
Other potential pathways mediating OT stimulation of RGS2 mRNA
expression.
The effects of OT on stimulation of inositol trisphosphate and
increased intracellular Ca2+ concentrations are mediated by
both pertussis toxin-sensitive and -insensitive pathways
(25). Pretreatment of human myometrial cells with
pertussis toxin (either 200 or 400 ng/ml) for 18 h blunted the
increase in RGS2 expression stimulated by 2 h of treatment with OT
(Fig. 7). There was a 32-51%
reduction in OT-stimulated RGS2 expression with pertussis toxin
treatment. These findings indicate that a portion of the effects of OT
on RGS2 mRNA are mediated by Gi/o. Agonists for receptors
coupled to Gi/o have been shown to cross-talk through
G
to nonreceptor and receptor tyrosine kinase pathways
(17). In keeping with the pertussis toxin effect,
pretreatment of human myometrial cells with the tyrosine kinase
inhibitor genestein (25 and 50 µM) for 2 h also partially
inhibited (28-40%) the stimulation of RGS2 mRNA expression by 100 nM OT (Fig. 7).

View larger version (18K):
[in this window]
[in a new window]
|
Fig. 7.
Inhibition of OT-stimulated RGS2 mRNA expression by
pertussis toxin (PTx) and genestein (Gen), a tyrosine kinase inhibitor.
The myometrial cells were pretreated with either pertussis toxin for
18 h or with genestein for 30 min before treatment with OT for
2 h.
|
|
 |
DISCUSSION |
The RGS2 mRNA expression in human myometrial cells in primary
culture was elevated in the presence of 10% FBS, but it was substantially diminished after 18 h of serum deprivation.
Subsequent treatment of cells with OT caused a marked increase in RGS2
mRNA levels after 1 or 2 h, with a rise that was obvious after 30 min. Near-maximal effects were obtained with 1 nM OT, which is near the
EC50 value for OT stimulation of intracellular
Ca2+ and inositol phosphate elevation in human myometrial
cells in primary culture (25). These findings indicate
that the effects of OT on RGS2 mRNA are physiologically relevant. The
effects of OT were ligand specific, since the OT antagonist blocked the
rise in RGS2 mRNA levels.
There is still relatively little known about what regulates different
RGS proteins. Based on the limited data available, the signal pathways
involved in RGS2 mRNA expression appear to depend on cellular context.
In human neuroblastoma SH-SY5Y cells, RGS2 mRNA levels are increased by
activation of muscarinic receptors and a PKC-dependent mechanism
(26). The RGS2 expression was not affected by increases in
either intracellular Ca2+ or cAMP concentrations. PKC also
appears to mediate RGS2 mRNA increases by ANG II in vascular smooth
muscle cells (11). Tyrosine kinase inhibition and
Ca2+ deprivation did not affect this increase in RGS2 mRNA
concentration. A greater increase was seen in levels of RGS1 mRNA in
human B lymphocytes in response to a PKC activator than to a
Ca2+ ionophore (ionomycin), whereas the opposite was true
for RGS2 mRNA synthesis in blood mononuclear cells (13).
Elevation of intracellular cAMP induces RGS2 expression in cultured rat
osteoblasts (19) and PC-12 cells (22). Thus,
depending on the cell type, RGS2 expression can be induced exclusively
by PKC, intracellular Ca2+, or cAMP. Each one of these
pathways mediates the actions of G protein-coupled receptors and likely
contributes to feedback regulation of the G proteins involved.
As we have shown in our present studies, there are multiple pathways
that lead to increased RGS2 mRNA levels in human myometrial cells (Fig.
8). The primary signal that mediates the
effects of OT appears to be linked to PLC-mediated stimulation of
intracellular Ca2+ concentrations. OT also activates PKC
via PLC-stimulated increases in diacylglycerol concentration. PKC
likely catalyzes the phosphorylation of specific proteins that are
involved in increased RGS2 mRNA levels. Partial inhibition of the
effects of OT on RGS2 mRNA expression by pertussis toxin indicates that
Gi/o plays a role in signaling increases in RGS2 mRNA
levels. In view of the similar degree of inhibition caused by pertussis
toxin and genestein, we speculate that G
linked to tyrosine
kinase activation mediates a portion of the OT effect on RGS2 mRNA
expression. This type of transactivation by G
has been described
in other G protein-coupled receptor systems (16, 17).
Increases in intracellular cAMP concentrations also caused a rise in
RGS2 mRNA levels, presumably independent of the OT receptor, which is
not coupled to Gs. cAMP produces relaxation of smooth
muscle by activation of cAMP-dependent protein kinase A, which
interferes with several processes involved in smooth muscle contraction
(3, 30). We speculate that there is the potential for
heterologous regulation of OT action by agents that generate
intracellular cAMP. The resulting increase in RGS2 expression might
attenuate the responses to OT or other uterotonins acting via G
proteins. Agents that increase myometrial cell cAMP levels include
-adrenergic drugs (15), relaxin (18),
corticotropin-releasing hormone (10), calcitonin
gene-related peptide (1), adrenomedullin (1),
and parathyroid hormone-related peptide (29), among others.

View larger version (22K):
[in this window]
[in a new window]
|
Fig. 8.
Summary of multiple pathways involved in upregulating
RGS2 mRNA expression in human myometrial cells in primary culture. The
primary signal mediating the effects of OT was an elevation in
intracellular Ca2+ concentration. PKC activation appeared
to be secondary. Independent of the effects of OT, forskolin (which
elevates intracellular cAMP concentrations) also increased RGS2 mRNA
expression. About one-half of the OT effect is mediated by
Gi/o and tyrosine kinase activity, as reflected by
inhibition by pertussis toxin and genestein, respectively. Tyrosine
kinase activation has been shown in other systems to be coupled to
Gi activation, presumably through G interactions.
OTR, OT receptor; PLC, phospholipase C; DAG, diacylglycerol; PKA,
protein kinase A; InsP3, inositol trisphosphate.
|
|
The role of RGS2 in myometrial cell function remains to be established.
It has been tacitly assumed that RGS2 functions as a GTPase. Thus an
increase in RGS2 protein levels after an initial stimulation might be
expected to attenuate subsequent signaling. In support of this
possibility, Phaneuf and coworkers (23) found that
exposing cultured human myometrial cells to OT for a prolonged period
caused desensitization of the response to OT. There was a concomitant
90% reduction in the number of high-affinity receptor binding sites.
Immunoblot and flow cytometry data indicated, however, that the total
amount of OT receptor protein on the cell membrane surface was
unaffected by OT treatment. These findings suggest that desensitization
could occur at the G protein level (possibly involving RGS2) rather
than at the receptor level.
Recent studies have indicated that RGS2 phosphorylation, along with
RGS2 protein synthesis, may also be an important means of regulating
GTPase activity. Phosphorylation of RGS2 by PKC in vitro diminished
RGS2 activity stoichiometrically (28). There is evidence
that RGS2 also has functions that are not associated with GTPase
activity. RGS2 inhibits cAMP production by directly inhibiting the
activity of adenylyl cyclase type III, the predominant adenylyl cyclase
isoform in olfactory neurons (4). Although a clear
understanding of the role in RGS2 mRNA in human myometrial cells
remains to be established, the profound changes in RGS2 mRNA
concentration elicited by OT suggest that RGS2 serves an important
regulatory function with respect to OT action in these cells.
Upregulation of RGS2 mRNA has also been demonstrated in vivo, in
ovarian granulosa cells after human chorionic gonadotropin treatment
(27). Because the myometrium undergoes marked changes in
sensitivity to OT during pregnancy (6, 7), future studies are needed to elucidate the importance of RGS2 in the responsiveness of
the myometrium to OT in vivo.
 |
ACKNOWLEDGEMENTS |
We thank Dr. Garland D. Anderson and the Department of Obstetrics
and Gynecology for supporting these studies.
 |
FOOTNOTES |
Current address for C. O. Echetebu: Dept. of Physiology and
Biophysics, University of Texas Medical Branch, Galveston, TX 77555-0641.
Address for reprint requests and other correspondence: M. S. Soloff, Dept. of Obstetrics & Gynecology, The Univ. of Texas Medical
Branch, 301 Univ. Blvd., Galveston, TX 77555-1062 (E-mail: msoloff{at}utmb.edu).
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
10.1152/ajpendo.00437.2001
Received 22 September 2001; accepted in final form 2 November 2001.
 |
REFERENCES |
1.
Casey, ML,
Smith J,
Alsabrook G,
and
MacDonald PC.
Activation of adenylyl cyclase in human myometrial smooth muscle cells by neuropeptides.
J Clin Endocrinol Metab
82:
3087-3092,
1997[Abstract/Free Full Text].
2.
Chen, C,
Zheng B,
Han J,
and
Lin SC.
Characterization of a novel mammalian RGS protein that binds to G
proteins and inhibits pheromone signaling in yeast.
J Biol Chem
272:
8679-8685,
1997[Abstract/Free Full Text].
3.
De Lanerolle, P,
Nishikawa M,
Yost DA,
and
Adelstein RS.
Increased phosphorylation of myosin light chain kinase after an increase in cyclic AMP in intact smooth muscle.
Science
223:
1415-1417,
1984[ISI][Medline].
4.
Dessauer, CW,
Srikumar D,
Chen J,
Yuen J,
Yilma S,
Dennis JC,
Morrison EE,
Vodyanoy V,
and
Kehrl JH.
RGS2 regulates signal transduction in olfactory neurons by attenuating activation of adenylyl cyclase III.
Nature
409:
1051-1055,
2001[ISI][Medline].
5.
Echetebu, CO,
Ali M,
Izban MG,
Mackay L,
and
Garfield RE.
Localization of regulatory protein binding sites in the proximal region of human myometrial connexin 43 gene.
Mol Hum Reprod
5:
757-766,
1999[Abstract/Free Full Text].
6.
Fuchs, AR,
Fuchs F,
Husslein P,
Soloff MS,
and
Fernstrom MJ.
Oxytocin receptors and human parturition: a dual role for oxytocin in the initiation of labor.
Science
215:
1396-1398,
1982[ISI][Medline].
7.
Fuchs, AR,
Periyasamy S,
Alexandrova M,
and
Soloff MS.
Correlation between oxytocin receptor concentration and responsiveness to oxytocin in pregnant rat myometrium: effects of ovarian steroids.
Endocrinology
113:
742-749,
1983[Abstract].
8.
Gold, SJ,
Ni YG,
Dohlman HG,
and
Nestler EJ.
Regulators of G-protein signaling (RGS) proteins: region-specific expression of nine subtypes in rat brain.
J Neurosci
17:
8024-8037,
1997[Abstract/Free Full Text].
9.
Grammatopoulos, DK,
and
Hillhouse EW.
Activation of protein kinase C by oxytocin inhibits the biological activity of the human myometrial corticotropin-releasing hormone receptor at term.
Endocrinology
140:
585-594,
1999[Abstract/Free Full Text].
10.
Grammatopoulos, DK,
and
Hillhouse EW.
Role of corticotropin-releasing hormone in onset of labour.
Lancet
354:
1546-1549,
1999[ISI][Medline].
11.
Grant, SL,
Lassegue B,
Griendling KK,
Ushio-Fukai M,
Lyons PR,
and
Alexander RW.
Specific regulation of RGS2 messenger RNA by angiotensin II in cultured vascular smooth muscle cells.
Mol Pharmacol
57:
460-467,
2000[Abstract/Free Full Text].
12.
Hepler, JR.
Emerging roles for RGS proteins in cell signalling.
Trends Pharmacol Sci
20:
376-382,
1999[ISI][Medline].
13.
Heximer, SP,
Cristillo AD,
and
Forsdyke DR.
Comparison of mRNA expression of two regulators of G-protein signaling, RGS1/BL34/1R20 and RGS2/G0S8, in cultured human blood mononuclear cells.
DNA Cell Biol
16:
589-598,
1997[ISI][Medline].
14.
Ingi, T,
Krumins AM,
Chidiac P,
Brothers GM,
Chung S,
Snow BE,
Barnes CA,
Lanahan AA,
Siderovski DP,
Ross EM,
Gilman AG,
and
Worley PF.
Dynamic regulation of RGS2 suggests a novel mechanism in G-protein signaling and neuronal plasticity.
J Neurosci
18:
7178-7188,
1998[Abstract].
15.
Lecrivain, JL,
Cohen-Tannoudji J,
Robin MT,
Coudouel N,
Legrand C,
and
Maltier JP.
Molecular mechanisms of adenylyl cyclase desensitization in pregnant rat myometrium following in vivo administration of the
-adrenergic agonist, isoproterenol.
Biol Reprod
59:
45-52,
1998[Abstract/Free Full Text].
16.
Leopoldt, D,
Hanck T,
Exner T,
Maier U,
Wetzker R,
and
Nürnberg B.
G
stimulates phosphoinositide 3-kinase-
by direct interaction with two domains of the catalytic p110 subunit.
J Biol Chem
273:
7024-7029,
1998[Abstract/Free Full Text].
17.
Luttrell, LM,
Della Rocca GJ,
van Biesen T,
Luttrell DK,
and
Lefkowitz RJ.
G
subunits mediate Src-dependent phosphorylation of the epidermal growth factor receptor. A scaffold for G protein-coupled receptor-mediated Ras activation.
J Biol Chem
272:
4637-4644,
1997[Abstract/Free Full Text].
18.
Meera, P,
Anwer K,
Monga M,
Oberti C,
Stefani E,
Toro L,
and
Sanborn BM.
Relaxin stimulates myometrial calcium-activated potassium channel activity via protein kinase A.
Am J Physiol Cell Physiol
269:
C312-C317,
1995[Abstract/Free Full Text].
19.
Miles, RR,
Sluka JP,
Santerre RF,
Hale LV,
Bloem L,
Boguslawski G,
Thirunavukkarasu K,
Hock JM,
and
Onyia JE.
Dynamic regulation of RGS2 in bone: potential new insights into parathyroid hormone signaling mechanisms.
Endocrinology
141:
28-36,
2000[Abstract/Free Full Text].
20.
Molnar, M,
Rigo J, Jr,
Romero R,
and
Hertelendy F.
Oxytocin activates mitogen-activated protein kinase and up-regulates cyclooxygenase-2 and prostaglandin production in human myometrial cells.
Am J Obstet Gynecol
181:
42-49,
1999[ISI][Medline].
21.
Morrison, JJ,
Dearn SR,
Smith SK,
and
Ahmed A.
Activation of protein kinase C is required for oxytocin-induced contractility in human pregnant myometrium.
Hum Reprod
11:
2285-2290,
1996[Abstract].
22.
Pepperl, DJ,
Shah-Basu S,
VanLeeuwen D,
Granneman JG,
and
MacKenzie RG.
Regulation of RGS mRNAs by cAMP in PC12 cells.
Biochem Biophys Res Commun
243:
52-55,
1998[ISI][Medline].
23.
Phaneuf, S,
Asboth G,
Carrasco MP,
Linares BR,
Kimura T,
Harris A,
and
Lopez Bernal A.
Desensitization of oxytocin receptors in human myometrium.
Hum Reprod
4:
625-633,
1998[Abstract].
24.
Phaneuf, S,
Carrasco MP,
Europe-Finner GN,
Hamilton CH,
and
Lopez Bernal A.
Multiple G proteins and phospholipase C isoforms in human myometrial cells: implication for oxytocin action.
J Clin Endocrinol Metab
81:
2098-2103,
1996[Abstract].
25.
Phaneuf, S,
Europe-Finner GN,
Varney M,
MacKenzie IZ,
Watson SP,
and
Lopez Bernal A.
Oxytocin-stimulated phosphoinositide hydrolysis in human myometrial cells: involvement of pertussis toxin-sensitive and -insensitive G-proteins.
J Endocrinol
136:
497-509,
1993[Abstract].
26.
Song, L,
De Sarno P,
and
Jope RS.
Muscarinic receptor stimulation increases regulators of G-protein signaling 2 mRNA levels through a protein kinase C-dependent mechanism.
J Biol Chem
274:
29689-29693,
1999[Abstract/Free Full Text].
27.
Ujioka, T,
Russell DL,
Okamura H,
Richards JS,
and
Espey LL.
Expression of regulator of G-protein signaling protein-2 gene in the rat ovary at the time of ovulation.
Biol Reprod
63:
1513-1517,
2000[Abstract/Free Full Text].
28.
Waldo, GL,
Hollinger S,
Hepler JR,
and
Harden TK.
Protein kinase C phosphorylates RGS2 and modulates its capacity for negative regulation of G
11 signaling.
J Biol Chem
276:
5438-5444,
2001[Abstract/Free Full Text].
29.
Williams, ED,
Leaver DD,
Danks JA,
Moseley JM,
and
Martin TJ.
Effect of parathyroid hormone-related protein (PTHrP) on the contractility of the myometrium and localization of PTHrP in the uterus of pregnant rats.
J Reprod Fertil
102:
209-214,
1994[Abstract].
30.
Yue, C,
Dodge KL,
Weber G,
and
Sanborn BM.
Phosphorylation of serine 1105 by protein kinase A inhibits phospholipase C
3 stimulation by G
q.
J Biol Chem
273:
18023-18027,
1998[Abstract/Free Full Text].
Am J Physiol Endocrinol Metab 282(3):E580-E584
0193-1849/02 $5.00
Copyright © 2002 the American Physiological Society