1 Molecular Cardiology Program, Divisions of Cardiology and Circulatory Physiology, Departments of Medicine and Pharmacology, Columbia University College of Physicians and Surgeons, New York 10032; and 2 New York University College of Dentistry, Basic Science Division, New York, New York 10010
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ABSTRACT |
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Ceramide, a product of sphingomyelin turnover, is a lipid second
messenger that mediates diverse signaling pathways, including those
leading to cell cycle arrest and differentiation. The mechanism(s) by
which ceramide signals downstream events have not been fully elucidated. Here we show that, in Xenopus
laevis oocytes, ceramide-induced maturation is
associated with the release of intracellular calcium stores. Ceramide
caused a dose-dependent elevation in the second messenger inositol
1,4,5-trisphosphate (IP3) via
activation of Gq/11 and
phospholipase C-
X. Elevation of
IP3, in turn, activated the
IP3 receptor calcium release
channel on the endoplasmic reticulum, resulting in a rise in
cytoplasmic calcium. Thus our study demonstrates that cross talk
between the ceramide and phosphoinositide signaling pathways modulates
intracellular calcium homeostasis.
meiotic maturation; calcium signaling; phospholipase C
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INTRODUCTION |
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SPHINGOLIPID METABOLITES are important second
messengers involved in cellular signaling pathways (44). Second
messenger metabolites of sphingolipids are generated in response to
diverse stimuli, including progesterone (50), tumor necrosis
factor-, and interleukin-1 (25). These stimuli trigger intracellular hydrolysis of sphingomyelin via sphingomyelinases, resulting in the
generation of ceramide, which can be further metabolized to sphingosine
and subsequently phosphorylated to form sphingosine 1-phosphate by
ceramidase and sphingosine kinase, respectively (25).
Ceramide mediates signaling leading to apoptosis and the regulation of cell cycle progression (17, 41, 55). Direct targets for ceramide have been identified, including a ceramide-activated protein kinase (29, 56), a ceramide-activated phosphatase (9), the guanine nucleotide exchange factor vav (18), and protein kinase C (30).
The steroid hormone progesterone, the physiological trigger of Xenopus laevis oocyte meiotic maturation, stimulates sphingomyelin hydrolysis in oocytes, resulting in a time- and concentration-dependent increase in ceramide mass and a decrease in sphingomyelin mass (50). Moreover, direct application of C2- and C6-ceramide analogs triggers meiotic cell cycle progression in Xenopus oocytes (8, 50).
Previous studies identified an important role for intracellular calcium release via the inositol 1,4,5-trisphosphate receptor (IP3R) on the endoplasmic reticulum in determining the rate of progesterone-induced maturation in Xenopus oocytes (24). However, the signaling events linking progesterone and 1,4,5-trisphosphate (IP3)-induced intracellular calcium release have not been fully elucidated.
The present study was designed to gain a better understanding of
calcium-dependent signaling during meiotic maturation and the possible
role of ceramide therein. Toward this end, we examined ceramide-induced
maturation in Xenopus laevis oocytes.
We showed that ceramide causes a rise in
IP3, resulting in the release of intracellular calcium stores that are mediated by
Gq/11 and phospholipase C
(PLC)-
X.
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MATERIALS AND METHODS |
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Reagents. Ceramides,
1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphorylcholine
(ET-18-OCH3),
U-73122, and pertussis toxin (PTX) were purchased from Calbiochem (Palo
Alto, CA). Ceramides were dissolved in 98% ethanol and 2% dodecane
(Sigma Chemical, St. Louis, MO). Stock solutions of ceramides were
stored at 80°C. Ceramide was sonicated in the cell culture
medium for 40 min immediately before use. Sphingomyelinases from
Staphylococcus auerus and from Streptomyces species were purchased
from Sigma. Cells were incubated with PTX as previously described (48).
PTX (stock 100 µg/ml) was activated by incubation in 100 mM
dithiothreitol (2:1 volume PTX to dithiothreitol) at 37°C for 30 min. Cells injected with PTX mRNA (30 µg/ml) were also stored in
PTX-containing medium (2 µg/ml) for 18-24 h before voltage
clamp. PTX mRNA and QEHA peptide were kind gifts of
Drs. E. Reuveny and D. Logothetis, respectively. Oligonucleotide
injection was performed as previously described (24). The
sequences of the IP3R and PLC-
X oligonucleotides were as
follows: IP3R antisense,
5'-AACTAGACATCTTGTCTGACATTGCTGCAG-3'; IP3R
sense, 5'-CTGCAGCAATGTCAGACAAGATGTCTAGTT-3'; PLC-
X
antisense, 5'-TCATATCATCACTTAGATCAAGGATCTCCGG-3';
PLC-
X sense, 5'-CCGGAGATCCTTGATCTAAGTGATGATATGA-3'.
Oocytes. Ovarian fragments were surgically removed from adult female Xenopus laevis frogs previously anesthetized by hypothermia. The fragments were washed in NDE solution (5 mM HEPES-NaOH, pH 7.6, 96 mM NaCl, 2 mM KCl, 1.8 mM CaCl2, 1 mM MgCl2, 2.5 mM sodium pyruvate, 100 U/ml penicillin, and 100 µg/ml streptomycin). Fully grown stage 6 oocytes (11) were treated with collagenase (2 mg/ml type I collagenase; Sigma). Oocytes were maintained in NDE solution at 18°C until further use. Meiotically mature eggs were induced by incubation in ND-96 solution (96 mM NaCl, 2 mM KCl, 2 mM MgCl2, and 5 mM HEPES, pH 7.5) containing 10 µg/ml progesterone (Sigma). Oocytes were judged to be meiotically mature by the appearance of a white spot on the animal pole, indicating the release of the first polar body (24). For quantitative comparison, the time required for the maturation of 50% of oocytes marked by the appearance of germinal vesicle breakdown was determined (16).
Electrophysiological measurements.
Electrophysiological measurements were performed in ND-96 solution
(24). Currents were recorded using a double-microelectrode voltage
clamp and a TEV 200 amplifier (Dagan). Data are presented as mean
values ± SE, where n is the number
of oocytes examined. Statistical analysis was performed using
Student's t-test, and significance
was accepted at P < 0.05. In all
cases, similar data were obtained from oocytes derived from two or more
animals. The calcium-activated chloride current
[ICl(Ca)]
had a reversal potential of 21.0 ± 3.0 mV
(n = 4) corresponding to the reversal
potential of the chloride current (1) and was blocked by 300 µM of
niflumic acid (51), a specific inhibitor of
ICl(Ca)
(n = 3). Experiments were performed in
nominally calcium-free media to exclude the possibility that the rise
in cytosolic calcium resulted from calcium influx.
C16-ceramide injections were
performed using a stock solution of 250 µM
C16-ceramide such that 20 nl
yielded an estimated intracellular concentration of 10 µM, assuming
cytoplasmic oocyte volume of 0.5 µl. External application of
sphingomyelinase (0.1-8.0 U/ml) induced nonspecific plasma
membrane leaks that prevented recording of
ICl(Ca) or
measurement of IP3 levels in
Xenopus oocytes. Oocytes were
incubated with the indicated tyrosine kinase inhibitors (Calbiochem)
for 3 h. Inhibitors were dissolved in 0.1% DMSO, and controls were
treated with 0.1% DMSO alone. The rabbit
anti-Gq/11 antibody (52) was from NEN Life Sciences (Boston, MA). Oocytes were injected with 50 nl
of the undiluted antibody and incubated for 3 h, and controls were
injected with 50 nl of boiled antibody.
IP3 measurements.
Freshly isolated Xenopus laevis
oocytes (150/tube) were stimulated with 150 µl of ceramide at the
indicated concentration in ND-96 buffer at 23°C. After 0, 30, or
120 s, 150 µl of ice-cold 9% perchloric acid (PCA) were added to the
mixture to quench IP3 formation.
Oocytes were immediately homogenized with a glass pestle, and samples
were placed on ice. For time 0,
oocytes were first quenched with 150 µl of 9% PCA. All subsequent
steps were performed at 4°C unless otherwise specified using
siliconized tubes, pipettes, and syringes. After quenching with 9% PCA
and homogenization, each sample was centrifuged at 17,000 g for 30 min, the volume of the
supernatant in each tube was measured, and 330 µl were separated into
aliquots and kept at 20°C until use.
IP3 was extracted from each tube
by precipitation with potassium perchlorate in the presence of KOH and
HEPES (38). The supernatant (400 µl) was assayed for
IP3 (39, 46) by binding to a
radiolabeled, purified IP3-binding
protein isolated from bovine adrenal gland (39). Bovine adrenal cortex
was dissected from 6 to 10 glands, homogenized in 200 mM
NaHCO3 and 1 mM dithiothreitol at
4°C. The homogenate was centrifuged two times at 5,000 g for 20 min. The final pellet was
resuspended in 12 ml of homogenization buffer at a protein
concentration of 20-40 mg/ml. The binding protein was separated
into aliquots at 30 mg/tube and kept at
80°C until use; each
tube was thawed only one time. Protein determination was performed
using the Bio-Rad (Hercules, CA) protein assay with bovine gamma
globulin as the standard.
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RESULTS |
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Ceramide-induced maturation. In the
present study, we found that sphingomyelinase and
C2- and
C16-ceramide induced maturation in
Xenopus laevis oocytes (Fig.
1). Progesterone-induced oocyte maturation
required 7.2 ± 0.9 h (n = 5).
C16-ceramide also induced maturation but with a slower time course requiring 9.8 ± 1.1 h (n = 5, P < 0.01; Fig. 1). Added together,
C16-ceramide and progesterone acted synergistically, reducing the time required to achieve maturation to 5.5 ± 0.8 h (n = 5, P < 0.01). Injection of heparin (20 nl, 10 mg/ml) to inhibit IP3R
slowed the time courses of progesterone-induced maturation (11.3 ± 0.3 h, n = 5, P < 0.01) and
C16-ceramide-induced maturation
(12.3 ± 1.3 h, n = 5, P < 0.01). Sphingomyelinase injected into the oocytes to achieve a final concentration of 1 U/ml also induced Xenopus oocyte maturation (6.0 ± 0.7 h, n = 5), and
injection of heparin (20 nl, 10 mg/ml) slowed the time course of
sphingomyelinase-induced maturation (11.7 ± 0.3 h,
n = 5, P < 0.01; Fig. 1).
C2-ceramide (final concentration
7.5 µM) induced Xenopus oocyte
maturation (8.5 ± 0.3 h, n = 5;
Fig. 1), which is consistent with recent findings (33): injection of
heparin slowed the time of
C2-ceramide-induced maturation
(12.5 ± 0.2 h, n = 5, P < 0.01). Injection of solvent had
no effect on oocyte maturation. Taken together, our data indicate that
both ceramide and the IP3R can
modulate the time course of progesterone-induced maturation. Our data
further suggest that IP3-mediated
intracellular calcium release plays a role in modulating progesterone-induced maturation in agreement with data from earlier studies (20, 24). A possible explanation for the slower time course of
ceramide-induced maturation, compared with progesterone-induced maturation, may be that ceramide must diffuse to a specific location within the cell to activate downstream signaling.
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Ceramide-induced calcium release.
Application of a cell-permeable analog of
C2-ceramide (Fig.
2A)
induced the release of intracellular calcium in a dose-dependent manner
in Xenopus laevis oocytes. Cytosolic
calcium levels were monitored by recording
ICl(Ca) in Xenopus oocytes as previously
described (24). Maximal release of intracellular calcium was seen with
50 µM C2-ceramide
[ICl(Ca) = 959 ± 190 nA, n = 20; Fig.
2A]. A biologically inactive
form of ceramide, dihydroceramide (10 µM; see Ref. 2), induced
only negligible release of calcium
[ICl(Ca) = 12.5 ± 14.0 nA, n = 10; Fig.
2A].
C8-ceramide (100 µM) also
induced calcium release in oocytes
[ICl(Ca) = 402 ± 95 nA, n = 5].
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Injection of a nonpermeable analog of natural
C16-ceramide to achieve an
intracellular concentration of 10 µM also induced the release of
intracellular calcium
[ICl(Ca) = 110.0 ± 19.5 nA, n = 42; Fig.
2B]. The response to
C16-ceramide was dose dependent [0.5 µM
C16-ceramide-induced
ICl(Ca) = 40.5 ± 18.5 nA, n = 9; 2 µM
C16-ceramide-induced
ICl(Ca) = 71.0 ± 20.0 nA, n = 10; Fig. 2B]. Ethanol, the major
component of the vehicle for ceramide, is known to induce calcium
release in Xenopus laevis oocytes
(21). However, injection of the vehicle alone induced an
ICl(Ca) = 21.0 ± 7.0 nA (n = 8, P < 0.01; Fig.
2B), which was significantly smaller than the response to C16-ceramide.
The amount of vehicle was equivalent to that required to yield a 10 µM intracellular concentration of
C16-ceramide. The cell-permeable
ceramide analog C2-ceramide was
applied externally in the perfusion bath, whereas the nonpermeable C16-ceramide was injected locally.
Therefore, C2-ceramide was acting
on the entire oocyte membrane, whereas
C16-ceramide acted locally on the
plasma membrane near the injection site. This explains why we
consistently observed a greater effect in response to
C2-ceramide. Sphingomyelinase
injected in Xenopus oocytes (estimated
final concentration 1 U/ml) induced an
ICl(Ca) =179.7 ± 35.0 nA (n = 30; Fig.
3B).
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The ceramide-induced increase in cytosolic calcium was due to intracellular calcium release, since the experiments were performed with negligible extracellular calcium. Xenopus laevis oocytes have IP3R but do not express the other major form of intracellular calcium release channel, the ryanodine receptor (24, 26). On this basis, we hypothesized that the ceramide-induced elevation of cytosolic calcium was mediated through the phosphoinositide pathway, resulting in activation of IP3-induced intracellular calcium release. Therefore, we examined the effects of ceramide on the known components of the phosphoinositide/calcium release pathway: heterotrimeric GTP-binding proteins, nonreceptor protein tyrosine kinases, PLC, IP3, and intracellular calcium stores.
Activaton of IP3R by ceramide.
Previous studies have shown that progesterone induces a transient
increase in IP3 levels in
Xenopus oocytes (49).
C2-ceramide (5 µM) induced an
approximately threefold increase in
IP3 level (from 0.258 ± 0.047 to 0.785 ± 0.090 nmol/oocyte, n = 7, P < 0.001), with the peak
occurring within 30 s (Fig.
4A and
Table 1).
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Involvement of PLC-X via
Gq/11
in ceramide-mediated
calcium release.
Previous reports (3, 54) have shown that PLC-
plays a role in oocyte
maturation and egg activation. It was also reported (43) that
C2- and
C6-ceramides were able to increase
tyrosine phosphorylation of the focal adhesion kinase
p125FAK.
C16-ceramide-induced
ICl(Ca) was not
inhibited by the tyrosine kinase inhibitors genistein (50 µM) or
herbimycin A (10 µM). In control oocytes (incubated with 0.1% DMSO),
injection of C16-ceramide (2 µM)
induced
ICl(Ca) = 76 ± 5.4 nA (n = 20)
compared with 67 ± 5.2 nA [n = 10, P = statistically not
significant (NS)] for oocytes incubated with 10 µM herbimycin A
and 106.5 ± 32.7 (n = 10, P = NS) for oocytes incubated with 50 µM genistein. Similar results were obtained when both genistein and
herbimycin A were used in combination (data not shown). These data
indicate that activation of PLC-
through tyrosine phosphorylation is
not involved in the calcium-mobilizing action of ceramide in
Xenopus oocytes.
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DISCUSSION |
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The results of the present study demonstrate that ceramide causes a
dose-dependent elevation in the second messenger
IP3 via activation of
Gq/11 and PLC-
X. Elevation
of IP3, in turn, activates the
IP3R/calcium release channel on
the endoplasmic reticulum, resulting in a rise in cytoplasmic calcium.
Intracellular calcium release is important for controlling the rate of
progesterone (24)- and ceramide-induced maturation in
Xenopus laevis oocytes.
Previous reports have demonstrated that C6-ceramide can potentiate calcium release in human platelets (53). In contrast, C2-ceramide did not mobilize calcium in either human T lymphocytes (Jurkat; see Ref. 42) or in a pancreatic duct adenocarcinoma cell line (37). Thus the calcium-mobilizing effects of ceramide appear to be cell-type specific.
The concentrations of ceramide used in the present study (from 2 to 50 µM) are consistent with those used in many previous studies (7, 22, 36). Moreover, because only ~10% of externally applied C2-ceramide is taken up by the cell, the concentration of C2-ceramide inside the cell should be ~10 times less than the concentration of ceramide in our external solution (2).
The effects reported in our studies were observed using both a truncated form of ceramide, C2-ceramide, as well as naturally occurring C16-ceramide and sphingomyelinase. Extensive studies by others (2) have demonstrated that, during the first 30 min after C2-ceramide application, ~1% of C2-ceramide is metabolized and, even after 4 h, ~90% of the C2-ceramide remains intact in cells, demonstrating that C2-ceramide is poorly metabolized. In our own experiments, concentration-dependent effects on calcium signaling were observed within 5 min. Thus it is likely that the effects we report were due to ceramide and not to its metabolites. Interestingly, it has been reported that, in Xenopus oocytes, sphingosine is rapidly converted to ceramide, and short-chain ceramides are converted to long-chain ceramides without accumulation of sphingosine (50).
Inhibition of the ceramide-induced calcium release by heparin and IP3R antisense oligonucleotides suggests that calcium release occurs via the IP3R. It has been reported that sphingosine-induced calcium release occurs via an IP3-independent mechanism (6, 23, 32, 45). In Xenopus oocytes, injection of sphingosine 1-phosphate does not induce calcium release (12). This suggests that ceramide-induced mobilization of intracellular calcium stores is unlikely to be due to the conversion of ceramide to sphingosine 1-phosphate.
The effects of ceramide versus those of sphingosine appear to be somewhat cell specific. For example, in dermal fibroblasts, sphingosine (5 and 30 µM) induced hydrolysis of phosphoinositides within 5 s, resulting in elevated IP3 levels, followed 30-40 s later by increased levels of intracellular calcium (4). Moreover, in these same cells, sphingosine 1-phosphate induced a more rapid intracellular calcium release than sphingosine but did not raise IP3 levels, and C2-ceramide did not affect phosphoinositide turnover or calcium mobilization. PTX partially inhibited the sphingosine-mediated rise in IP3 levels consistent with an effect involving G proteins and PLC.
In considering the effects of sphingosine 1-phosphate on calcium mobilization, it is important to note that sphingosine 1-phosphate acts extracellularly as well as intracellularly. Extracellular sphingosine 1-phosphate binds to a specific receptor, endothelial differentiation gene 1 (EDG1), that activates PLC to mobilize calcium (36, 57). This extracellular effect of sphingosine 1-phosphate does not explain the observed effects of ceramide in our experiments, since the same calcium-mobilizing effects were seen when ceramide was injected intracellularly; therefore, ceramide could not be acting on the sphingosine 1-phosphate receptor.
The delay in the time course of Xenopus oocyte maturation due to heparin injection was reproducible and consistent with our previously published data (24) that showed blocking the expression of the IP3R delays progesterone-induced maturation. Indeed, the magnitude of the heparin-induced delay is similar to that seen when IP3R expression is blocked with antisense oligonucleotides, as we reported previously (24). Nevertheless, the signals governing maturation are complex, and one cannot exclude the possibility that certain metabolites of ceramide play an active role. However, the fact that both C16-ceramide and C2-ceramide had similar effects on calcium signaling argues that ceramide itself is involved in the IP3-dependent calcium signal during maturation, since the metabolism of C2-ceramide is negligible.
A growing list of molecules with diverse structural properties (e.g.,
neuropeptides, peptide hormones, polyamines, venom peptides, local
anesthetics, taste substances) have been shown to directly activate G
proteins (34, 35). Ceramide could act in a similar manner, by direct
activation of Gq/11 protein.
Alternatively, G protein-coupled receptors may attain an active
conformation in the absence of agonist by spontaneous isomerization and
may yield constitutive, agonist-independent activity (27, 40 ).
Although we do not know the mechanism by which ceramide may activate
Gq/11
, it is possible that
ceramide can indirectly induce agonist-independent activity of
Gq/11
-coupled receptors and
thus activate the downstream cascade, resulting in the production of
IP3.
In summary, we have demonstrated, for the first time, cross talk between the ceramide and phosphoinositide signaling pathways. The link between these two lipid second messenger pathways provides a mechanism for the mobilization of intracellular calcium observed in response to elevated levels of ceramide. Calcium oscillations triggered by ceramide-mediated activation of IP3R may be involved in the regulation of gene expression (10, 28) during meiotic maturation in Xenopus laevis oocytes.
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ACKNOWLEDGEMENTS |
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We thank I. Tabas and R. Iyengar for helpful comments on the manuscript, D. Logothetis for the PTX mRNA, and E. Reuveny for the QEHA peptide.
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FOOTNOTES |
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This study was supported by National Institutes of Health (NIH) Grants AI-39794, HL-61503, and HL-56180 to A. R. Marks and NIH Grant DE-10745 and a grant from the Binational Agricultural Research and Development Fund foundation to A. I. Spielman. E. Kobrinsky is on leave from the Institute of Theoretical and Experimental Biophysics, Pushchino, Moscow Region, Russia.
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. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: A. R. Marks, Molecular Cardiology Program, Box 65, Columbia Univ. College of Physicians & Surgeons, Rm. 9-401, 630 West 168th St., New York, NY 10032 (E-mail: arm42{at}columbia.edu).
Received 13 April 1999; accepted in final form 14 June 1999.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Barish, M. E.
A transient calcium-dependent chloride current in the immature Xenopus oocyte.
J. Physiol. (Lond.)
342:
309-325,
1983[Abstract].
2.
Bielawska, A.,
H. M. Crane,
D. Liotta,
L. M. Obeid,
and
Y. A. Hannun.
Selectivity of ceramide-mediated biology.
J. Biol. Chem.
268:
26226-26232,
1993
3.
Carol, D. J.,
C. S. Ramarao,
L. M. Mehlmann,
S. Roche,
M. Terasaki,
and
L. A. Jaffe.
Calcium release at fertilization in starfish eggs is mediated by phospholipase C.
J. Cell Biol.
138:
1303-1311,
1997
4.
Chao, C. P.,
S. J. Laulederkind,
and
L. R. Ballou.
Sphingosine-mediated phosphatidylinositol metabolism and calcium mobilization.
J. Biol. Chem.
269:
5849-5856,
1994
5.
Chen, J.,
M. DeVivo,
J. Dingus,
A. Harry,
J. Li,
J. Sui,
D. J. Carty,
J. L. Blank,
J. H. Exton,
R. H. Stoffel,
J. Iglese,
R. J. Lefkowitz,
D. E. Logothetis,
J. D. Hildelrandt,
and
R. A. Iyengar.
A region of adenylyl cyclase 2 critical for regulation by G protein subunits.
Science
268:
1166-1169,
1995[Medline].
6.
Choi, O. H.,
J.-H. Kim,
and
J.-P. Kinet.
Calcium mobilization via sphyngosine kinase in signalling by the FcRI antigen receptor.
Nature
380:
634-636,
1996[Medline].
7.
Cuvillier, O.,
G. Pirianov,
B. Kleuser,
P. G. Vanek,
O. A. Coso,
J. S. Gutkind,
and
S. Spiegel.
Suppression of ceramide-medited programmed cell death by sphingosine-1-phosphate.
Nature
381:
800-803,
1996[Medline].
8.
De Smedt, V.,
H. Rime,
C. Jessus,
and
R. Ozon.
Inhibition of glycosphingolipid synthesis induces p34cdc2 activation in Xenopus oocyte.
FEBS Lett.
375:
249-253,
1995[Medline].
9.
Dobrovsky, R. T.,
and
Y. A. Hannun.
Ceramide stimulates a cytosolic protein phosphatase.
J. Biol. Chem.
267:
5048-5051,
1992
10.
Dolmetsch, R. E.,
K. Xu,
and
R. S. Lewis.
Calcium oscillations increase the efficiency and specificity of gene expression.
Nature
392:
933-936,
1998[Medline].
11.
Dumont, J. N.
Oogenesis in Xenopus laevis (Daudin) I. Stages of oocyte development in laboratory maintained animals.
J. Morphol.
136:
153-180,
1972[Medline].
12.
Durieux, M. E.,
S. J. Carlisle,
M. N. Salafranca,
and
K. R. Lynch.
Endogenous responses to sphyngosine-1-phosphate in Xenopus laevis oocytes: similarities with lysophosphatidic acid signaling.
Am. J. Physiol.
264 (Cell Physiol. 33):
C1360-C1364,
1993
13.
Ehrlich, B. E.,
E. Kaftan,
S. Bezprozvannaya,
and
I. Bezprozvanny.
The pharmacology of intracellular Ca(2+)-release channels.
Trends Pharmacol. Sci.
15:
145-149,
1994[Medline].
14.
Filtz, T. M.,
A. Paterson,
and
T. K. Harden.
Purification and G protein subunit regulation of a phospholipase C-beta from Xenopus laevis oocytes.
J. Biol. Chem.
271:
31121-31126,
1996
15.
Gallo, C. J.,
T. L. Z. Jones,
A. M. Aragay,
and
L. A. Jaffe.
Increased expression of alphaq family G-proteins during oocyte maturation and early development of Xenopus laevis.
Dev. Biol.
177:
300-308,
1996[Medline].
16.
Gelerstein, S.,
H. Shapira,
N. Dascal,
R. Yekuel,
and
Y. Oron.
Is a decrease in cyclic AMP a necessary and sufficient signal for maturation of amphibian oocytes?
Dev. Biol.
127:
25-32,
1988[Medline].
17.
Ghosh, S.,
J. C. Strum,
and
R. M. Bell.
Lipid biochemistry: functions of glycerolipids and sphyngolipids in cellular signaling.
FASEB J.
11:
45-50,
1997
18.
Gulbins, E.,
K. M. Coggeshal,
B. Baier,
D. Telford,
C. Langlet,
G. Baier-Bitterlich,
N. Bonnefoy- Berard,
P. Burn,
A. Wittinghofer,
and
A. Altman.
Direct stimulation of Vav guanine nucleotide exchange activity for ras by phorbol esters and diglycerides.
Mol. Cell. Biol.
14:
4749-4758,
1994[Abstract].
19.
Guttridge, K. L.,
L. D. Smith,
and
R. Miledi.
Xenopus Gq subunit activates the phosphatidylinositol pathway in Xenopus oocytes but does not consistently induce oocyte maturation.
Proc. Natl. Acad. Sci. USA
92:
1297-1301,
1995[Abstract].
20.
Han, J.-K.,
and
S.-K. Lee.
Reducing PIP2 hydrolysis, Ins (1,4,5)P3 receptor availability or calcium gradients inhibits progesterone-stimulated Xenopus oocyte maturation.
Biochem. Biophys. Res. Commun.
217:
931-939,
1995[Medline].
21.
Ilyin, V.,
and
I. Parker.
Effects of alcohols on responses evoked by inositol trisphosphate in Xenopus oocytes.
J. Physiol. (Lond.)
448:
339-354,
1992[Abstract].
22.
Kanety, H.,
R. Hemy,
M. Z. Papa,
and
A. Karasik.
Sphingomyelinase and ceramide suppress insulin-induced tyrosine phosphorylation of the insulin receptor substrate-1.
J. Biol. Chem.
271:
9895-9897,
1996
23.
Kindman, L. A.,
S. Kim,
T. V. McDonald,
and
P. Gardner.
Characterization of a novel intracellular sphingolipid-gated Ca 2+-permeable channel from rat basophilic leukemia cells.
J. Biol. Chem.
269:
13088-13091,
1994
24.
Kobrinsky, E.,
K. Ondrias,
and
A. R. Marks.
Expressed ryanodine receptor can substitute for the inositol 1,4,5-trisphophosphate receptor in Xenopus laevis oocytes during progesterone induced maturation.
Dev. Biol.
172:
531-540,
1995[Medline].
25.
Kolesnick, R.,
and
D. W. Golde.
The sphingomyelin pathway in tumor necrosis factor and interleukin-1 signaling.
Cell
77:
325-328,
1994[Medline].
26.
Kume, S.,
A. Muto,
J. Aruga,
T. Nakagawa,
T. Michikawa,
T. Furuichi,
S. Nakade,
H. Okano,
and
K. Mikoshiba.
The Xenopus oocyte IP3 receptor: structure, function and localization in oocytes.
Cell
73:
555-570,
1993[Medline].
27.
Leurs, R.,
M. J. Smit,
A. E. Alewijnse,
and
H. Timmerman.
Agonist-independent regulation of constitutively active G-protein-coupled receptors.
Trends Biochem. Sci.
23:
418-422,
1998[Medline].
28.
Li, W.,
J. Llopis,
M. Whitney,
G. Zlokarnik,
and
R. Y. Tsien.
Cell-permeant InsP3 ester shows that Ca2+ spike frequency can optimize gene expression.
Nature
392:
936-941,
1998[Medline].
29.
Liu, J.,
S. Mathias,
Z. Yang,
and
R. H. Kolesnik.
Renaturation and TNF stimulation of a 97 kDA ceramide-activated protein kinase.
J. Biol. Chem.
269:
3047-3052,
1994
30.
Lozano, J.,
E. Berra,
M. M. Municio,
M. T. Diaz-Meco,
I. Dominiquez,
L. Sanz,
and
J. Moscat.
Protein kinase C isoform is critical for kappa -dependent promotor activation by sphyngomyelinase.
J. Biol. Chem.
269:
19200-19202,
1994
31.
Ma, H.-W.,
R. D. Blitzer,
E. C. Healy,
R. T. Premont,
E. M. Landau,
and
R. Iyengar.
Receptor-evoked Cl current in Xenopus oocytes is mediated through a
-type phospholipase C.
J. Biol. Chem.
268:
19915-19918,
1993
32.
Mattie, M.,
G. Brooker,
and
S. Spiegel.
Sphyngosine-1-phosphate, a putative second messenger, mobilizes calcium from internal stores via an inositol trisphosphate-independent pathway.
J. Biol. Chem.
269:
3181-3188,
1994
33.
Morril, G. A.,
and
A. B. Kostelow.
Progesterone release of lipid second messengers at the amphibian oocyte plasma membrane: role of ceramide in initiating the G2/M transition.
Biochem. Biophys. Res. Commun.
246:
359-363,
1998[Medline].
34.
Naim, M.,
R. Seifert,
B. Nurnberg,
L. Grunbaum,
and
G. Schultz.
Some taste substances are direct activators of G-proteins.
Biochem. J.
297:
451-454,
1994[Medline].
35.
Odagaki, Y.,
N. Nishi,
and
T. Koyama.
Receptor-mediated and receptor-independent activation of G-proteins in rat brain membranes.
Life Sci.
62:
1537-1541,
1998[Medline].
36.
Okamoto, H.,
N. Takuwa,
K. Gonda,
H. Okazaki,
K. Chang,
Y. Yatomi,
H. Shigematsu,
and
Y. Takuwa.
EDG1 is a functional sphingosine-1-phosphate receptor that is linked via a Gi/o to multiple signaling pathways, including phospholipase C activation, Ca 2+ mobilization, Ras-mitogen-activated protein kinase activation, and adenylate cyclase inhibition.
J. Biol. Chem.
273:
27104-27110,
1998
37.
Orlati, S.,
M. Cavazzoni,
and
M. Rgolo.
Sphingosine-induced inhibition of capacitative calcium influx in CFPAC-1 cells.
Cell Calcium
20:
399-407,
1996[Medline].
38.
Palmer, S.,
P. T. Hawkins,
R. H. Michell,
and
C. J. T. Kirk.
The labelling of polyphosphoinositides with [32]Pi and the accumulation of inositol phosphates in vasopressin-stimulated hepatocytes.
Biochem. J.
238:
491-499,
1986[Medline].
39.
Palmer, S.,
and
M. J. O. Wakelam.
Mass measurement of the inositol 1,4,5-trisphosphate using a specific binding assay.
In: Methods in Inositide Research, edited by R. F. Irvine. New York: Raven, 1990, p. 127-134.
40.
Pauwels, P. J.,
and
T. Wurch.
Review: amino acid domains involved in constitutive activation of G-protein-coupled receptors.
Mol. Neurobiol.
17:
109-135,
1998[Medline].
41.
Saba, J. D.,
L. M. Obeid,
and
Y. A. Hannun.
Ceramide: an intracellular mediator of apoptosis and growth supression.
Philos. Trans. R. Soc. Lond. B Biol. Sci.
351:
233-244,
1996[Medline].
42.
Sakano, S.,
H. Takemura,
K. Yamada,
K. Imoto,
M. Kaneko,
and
H. Ohshika.
Ca2+ mobilizing action of sphingosine in Jurkat human leukemia T cells.
J. Biol. Chem.
271:
11148-11155,
1996
43.
Seufferlein, T.,
and
E. Rosengurt.
Sphingosine induces p125FAK and paxillin tyrosine phosphorylation, actin stress fiber formation, and focal contact assembly in Swiss 3T3 cells.
J. Biol. Chem.
269:
27610-27617,
1994
44.
Spiegel, S.,
D. Foster,
and
R. Kolesnik.
Signal transduction through lipid second messengers.
Curr. Opin. Cell Biol.
8:
159-167,
1996[Medline].
45.
Spiegel, S.,
and
A. H. Merril.
Sphingolipid metabolism and cell growth regulation.
FASEB J.
10:
1388-1397,
1996
46.
Spielman, A. I.,
H. Nagai,
G. Sunavala,
M. Dasso,
T. Huque,
and
J. G. Brand.
Second messenger assays.
In: Experimental Cell Biology of Taste and Olfaction, edited by A. I. Spielman,
and J. G. Brand. Boca Raton, FL: CRC, 1995, p. 203-210.
47.
Stachecki, J. J.,
and
D. R. Armant.
Regulation of blastocele formation by intracellular calcium release is mediated trough a phospholipase C-dependent pathway in mice.
Biol. Reprod.
55:
1292-1298,
1996[Abstract].
48.
Stehno-Bittel, L.,
G. Krapivinsky,
L. Krapivinsky,
C. Perez-Terzic,
and
D. E. Clapham.
The G protein beta gamma subunit transduces the muscarinic receptor signal for Ca2+ release in Xenopus oocytes.
J. Biol. Chem.
270:
30068-30074,
1995
49.
Stith, B. J.,
C. Jaynes,
M. Goalstone,
and
S. Silva.
Insulin and progesterone increase 32PO4-labeling of phospholipids and inositol 1,4,5,-trisphosphate mass in Xenopus oocytes.
Cell Calcium
13:
341-352,
1992[Medline].
50.
Strum, J. C.,
K. I. Swenson,
J. E. Turner,
and
R. M. Bell.
Ceramide triggers meiotic cell cycle progression in Xenopus oocytes.
J. Biol. Chem.
270:
13541-13547,
1995
51.
White, M. M.,
and
M. Aylwin.
Niflumic and flufenamic acids are potent reversible blockers of Ca2+-activated Cl channels in Xenopus oocytes.
Mol. Pharmacol.
37:
720-724,
1990[Abstract].
52.
Wilson, B. A.,
X. Zhu,
M. Ho,
and
L. Lu.
Pasteurella multocida toxin activates the inositol trisphosphate signaling pathway in Xenopus oocytes via Gq-coupled phospholipase C-
1.
J. Biol. Chem.
272:
1268-1275,
1997
53.
Wong, K.,
and
X. B. Li.
C6-ceramide maintains elevated cytosolic calcium levels in activated platelets.
Thromb. Res.
81:
219-229,
1996[Medline].
54.
Yim, D. L.,
L. K. Opresko,
H. S. Wiley,
and
R. Nuccitelli.
Highly polarized EGF receptor tyrosine kinase activity initiates egg activation in Xenopus.
Dev. Biol.
162:
41-55,
1994[Medline].
55.
Zhang, J.,
N. Alter,
J. C. Reed,
C. Borner,
L. M. Obeid,
and
Y. A. Hannun.
Bcl-2 interrupts the ceramide-mediated pathway of cell death.
Proc. Natl. Acad. Sci. USA
93:
5325-5328,
1996
56.
Zhang, Y.,
B. Yao,
S. Delikat,
S. Bayoumy,
X. H. Lin,
S. Basu,
M. McGinley,
P. Y. Chan-Hui,
H. Lichenstein,
and
R. Kolesnick.
Kinase suppressor of Ras is ceramide-activated protein kinase.
Cell
89:
63-72,
1997[Medline].
57.
Zondag, G. C.,
F. R. Postma,
I. V. Etten,
I. Verlaan,
and
W. H. Moolenaar.
Sphingosine 1-phosphate signalling through the G-protein-coupled receptor EDG-1.
Biochem. J.
330:
605-609,
1998[Medline].
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