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Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47907-1264
1To whom correspondence should be addressed. E-mail: teegarden{at}cfs.purdue.edu
ABSTRACT
Ceramide and sphingosine-1-phosphate (S1P) are important dietary lipids involved in cell growth, differentiation, apoptosis and cell survival. Treatment of C3H10T1/2 murine fibroblast cells (10T1/2) with ceramide did not induce apoptosis, a commonly observed effect of ceramide treatment. To determine whether the metabolism of ceramide played a role in this resistance to apoptosis, inhibitors of ceramidase and sphingosine kinase, two important enzymes in sphingolipid metabolism, were used. Treatment of 10T1/2 cells both without or with ceramide plus N-oleoyl-ethanolamine (NOE) and (1S,2R)-D-erythro-s-(N-myristoylamino)-1-phenol-1-propanol (MAPP), two ceramidase inhibitors, resulted in fourfold and eightfold increases, respectively, in apoptosis. Cells treated without or with ceramide plus N,N-dimethylsphingosine (DMS), a potent sphingosine kinase inhibitor, resulted in fourfold and sixfold increases, respectively, in apoptosis. In all treatments the induction of apoptosis was prevented by the addition of S1P. With the addition of S1P with NOE and MAPP as well as with ceramide, treatments reduced the apoptotic response by 30 and 35%, respectively; whereas the addition of S1P with the DMS only and ceramide with DMS treatments reduced the apoptotic response by 60 and 70%, respectively. Studies using labeled ceramide demonstrated ceramide was metabolized to S1P. In addition, a 14-fold increase in apoptosis occurred in cells treated with a nonhydrolyzable analog of ceramide, ceramine, compared with vehicle control. Because inhibiting the conversion of ceramide to S1P resulted in apoptosis, the lack of an apoptotic response to ceramide alone for C3H10T1/2 cells is attributable to the conversion of this pro-apoptotic sphingolipid to the anti-apoptotic metabolite S1P, which is essential for cell survival.
KEY WORDS: • C3H10T1/2 cells • ceramide • sphingosine-1-phosphate • apoptosis
Sphingolipids are significant components of foods that have potentially
powerful anticancer properties (1
, 2
). Recently the
sphingolipids, ceramide and sphingosine-1-phosphate
(S1P)2,have been identified as important signaling molecules involved in cell
growth, differentiation and apoptosis (3
). The
sphingolipid metabolites, ceramide, sphingosine and S1P, may all be
derived from more complex sphingolipids, such as sphingomyelin
(1
). Sphingomyelin is a ubiquitous sphingolipid found in
the plasma membrane of all mammalian cells (4
). Upon
appropriate stimuli, ceramide may be released from sphingomyelin by the
action of distinct sphingomyelinases. There are a variety of agonists
that stimulate sphingomyelin hydrolysis, such as
1-
,25-dihydroxyvitamin D3, tumor necrosis
factor-, interleukin-1ß and ionizing radiation (5
).
Evidence from cell culture studies indicates ceramide activates many
intracellular targets, such as specific kinases, phosphatases, and
transcription factors that mediate a variety of cellular functions
(6
). The most noted cellular effect of ceramide is the
induction of apoptosis, but growth arrest and cell differentiation have
also been observed (7
).
Ceramide is metabolized to sphingosine through the action of
ceramidase, of which three isoforms, including an acidic, neutral and
alkaline form, are currently known (8
). Sphingosine, in
turn, is phosphorylated by sphingosine kinase, producing S1P
(9
). Like ceramide, S1P exerts many actions within cells,
such as cell proliferation and differentiation, as well as cell
survival. Moreover, S1P suppresses ceramide-induced apoptosis
(10
, 11
). Ceramide initiates apoptosis through the
induction of the stress-activated protein kinase (SAPK), a member
of the mitogen-activated protein kinase (MAPK) family
(12
). S1P inhibits ceramide-induced apoptosis through
the activation of the extracellular signal–regulated protein kinase
(ERK), also a MAPK family member (10
). Therefore, ceramide
and S1P have opposing cellular effects mediated through activation of
different MAPK family members producing different cellular outcomes
(13
).
The activities of several of the enzymes involved in sphingolipid
metabolism, such as sphingomyelinase, ceramidase and sphingosine
kinase, may be modulated by extracellular stimuli (14
).
For example, both ceramidase and sphingosine kinase may be activated by
platelet-derived growth factor, fibroblast growth factor or
other mitogenic compounds that produce sphingosine and S1P
(15
, 16
). Activation of these enzymes leads to the
elevation of levels of one sphingolipid metabolite more than the other,
and a change in the balance of ceramide to S1P dictates the cellular
response. Therefore, the accumulation of ceramide via sphingomyelinase
activation induces apoptosis, whereas the activation of sphingosine
kinase produces increased levels of S1P and prevents apoptosis. In the
present study we demonstrate that ceramide conversion to S1P is
essential for cell survival in C3H10T1/2 (10T1/2) cells.
MATERIALS AND METHODS
C8-ceramide, C8-ceramine, sphingosine-1-phosphate, N,N-dimethylsphingosine and (1S,2R)-D-erythro-2-(N-myristoylamino)-1-phenol-1-propanol were purchased from Biomol (Plymouth Meeting, PA). N-oleoyl-ethanolamine was purchased from Sigma (St. Louis, MO), and Dulbecco’s modified Eagle medium (DMEM), fetal bovine serum, and trypsin were purchased from Gibco (Rockville, MD). [14C]N-octanoyl-D-erythro-sphingosine (C8-ceramide) was purchased from American Radiolabeled Chemicals (St. Louis, MO). Culture dishes (100 and 60 mm) were obtained from Falcon, and 15-mL polyethylene centrifuge tubes were purchased from Corning Scientific. Reagents used for fluorometric and apoptosis analysis were purchased from Boehringer Mannheim (Indianapolis, IN).
Cell culture.
10T1/2 mouse fibroblast cells (CCL-226) were used in all experiments. Cells were grown in DMEM with 10% fetal bovine serum, 1.0 x 105 units/L penicillin and 100 mg/L streptomycin at 37°C in a humidified atmosphere of 5% CO2 and 95% O2. All experiments were performed with cells in linear growth.
Assessment of apoptosis.
10T1/2 cells were plated at 105,000 cells/dish for 3 days in
100-mm culture dishes. A total of 48 h after plating , cells were
treated with 20 µmol/L C8-ceramide, 20 µmol/L C8-ceramine (a
nonhydrolyzable analog of ceramide) or 2.5 µlmol/L S1P for
24 h. Upon harvesting, both adherent and nonadherent cells were
collected and used for analysis. To harvest nonadherent cells, the
media from each treatment were collected. Adherent cells were rinsed
with calcium magnesium–free phosphate-buffered saline (CMF-PBS)
(137mmol/L sodium chloride, 1.5mmol/L potassium phosphate, 7.2mmol/L
sodium phosphate and 2.7mmol/L potassium chloride, pH 7.4) and rinse
wash was collected. Adherent cells were trypsinized and combined with
nonadherent cells. Cells were pelleted by centrifugation at 2,000 rpm
for 5 min. Flow cytometric analysis was performed as described by
Gorczyca et al. (17
). Briefly, cells were fixed with 1%
formaldehyde PBS (137mmol/L sodium chloride, 1.5mmol/L potassium
phosphate, 7.2mmol/L sodium phosphate, 2.7mmol/L potassium chloride,
0.7mmol/L calcium and 0.5mmol/L magnesium, pH 7.4). DNA strand breaks
were in situ labeled with biotinylated dUTP (b-dUTP) via exogenous
terminal deoxynucleotidyl transferase. DNA content was determined by
cell staining with propidium iodide, and cell cycle position was
determined by b-dUTP incorporation detected by fluoresceinated
avidin, measured at 525 and 620 nm, respectively, by flow cytometry.
In addition to flow cytometeric analysis, apoptosis was assessed using the Cell Death Detection ELISA plus system (Boehringer Mannheim). 10T1/2 cells were plated at 75,000 cells in 60-mm dishes for 2 d. A total of 36 h after plating, while still in linear growth, cells were treated with 10 µmol/L C8-ceramide, 10 µmol/L C8-ceramine or 5 µmol/L S1P in one set of experiments and with 10 µmol/L C8-ceramide, 2.5 µmol/L S1P, 7.5 µmol/L dimethylsphingosine (DMS), 5 µmol/L N-oleoyl-ethanolamine (NOE) and 10 µmol/L (1S,2R)-D-erythro-2-(N-myristoylamino)-1-phenol-1-propanol (MAPP), either alone or in combination in another set of experiments for 12 h. Cells were harvested as described above and apoptosis was assessed as directed by manufacturer’s instructions. This assay is a photometric enzyme-immunoassay based on the detection of in vitro cytoplasmic histone-associated DNA-fragments of mono- and oligonucleosomes. Data are expressed as absorbance at 405 nm of each sample over the vehicle control.
Metabolism of radiolabeled ceramide.
10T1/2 cells were plated at 35,000 cells/dish in 35mm dishes for
2 d. Two mCi/L [14C] C8-ceramide and 20 µmol/L
unlabeled C8-ceramide was added for 2, 4, 6, and 8 h to the media
of the cells. At the end of each short-term time point, media was
removed and the cells were rinsed with CMF-PBS and scraped into 1
mL of 0.1mol/L HCl. Lipids were extracted by a chloroform:methanol:HCl
(100:200:1, v/v) mixture for ceramide and sphingomyelin components and
by a chloroform:methanol:NaCl (2:1:2, v/v) mixture for
sphingosine-1-phosphate. Sphingomyelin, ceramide, and
sphingosine-1-phosphate components were determined by thin layer
chromatography, as described by Olivera et al. (18
) and
Ruis et al. (19
). Briefly, extracted lipids were
sequentially separated using Silica gel coated thin layer
chromatography plates in a chloroform:benzene:ethanol (80:40:75, v/v)
solvent mixture, followed by a chloroform:methanol:28% ammonium
hydroxide (65:25:5, v/v) solvent mixture for ceramide and sphingomyelin
or by a 1-butanol/ethanol/acetic acid/water (8:2:1:2, v/v) mixture for
sphingosine-1-phosphate. Lipids were visualized by iodine and samples
comigrating with standards were scraped and radioactivity determined
via scintillation counting. Data are expressed as CPM/µg protein.
Statistical analysis.
Data were analyzed by one-way ANOVA followed by Duncan’s Multiple
Range test ( = 0.05) with Statistical Analysis Software (SAS)
(Cary, NC).
RESULTS
10T1/2 cells are resistant to ceramide-induced apoptosis.
Treatment of 10T1/2 cells with ceramide, S1P or vehicle control
did not induce apoptosis (Fig. 1
). In addition, 10T1/2 cells were treated with a higher
concentration of ceramide, 50 µm mol/L with no induction of apoptosis
(data not shown).
|
To determine if the metabolism of intracellular ceramide played a role
in the resistance to ceramide-induced apoptosis, inhibitors to the
enzyme ceramidase were employed. N-oleoylethanolamine (NOE) is an
inhibitor to the acidic form of ceramidase, and (1S,
2R)-D-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol (MAPP) is an
inhibitor to the alkaline form of ceramidase. Ceramide, S1P, NOE and
MAPP did not stimulate an apoptotic response (Fig. 1)
. However, the
combination of the two ceramidase inhibitors, NOE and MAPP, induced an
apoptotic response fourfold over control treatments (Fig. 1)
. The
addition of ceramide to the inhibitors increased the apoptotic response
eightfold over controls. However, when the ceramide metabolite S1P was
present in the NOE/MAPP inhibitor treatment with or without ceramide,
the apoptotic response was substantially reduced (Fig. 1)
. S1P
reduced the apoptotic response of the NOE and MAPP group by 30% and by
35% in the ceramide plus NOE and MAPP group. Thus, inhibition of
intracellular conversion of ceramide to sphingosine or S1P induced
apoptosis, and this response was increased by exogenously added
ceramide. In addition, exogenous addition of the end product of the
metabolic conversion, S1P, protected the cells from apoptosis. These
results suggest that the conversion of ceramide to S1P is essential for
cell survival.
In addition to the ceramidase inhibitors, DMS, an inhibitor of
sphingosine kinase, the enzyme responsible for phosphorylating
sphingosine to produce S1P, was used. DMS alone induced an apoptotic
response fourfold over ceramide and S1P controls, similar to the
treatment with NOE and MAPP (Fig. 2
). Likewise, the addition of exogenous ceramide with DMS enhanced the
apoptotic response in 10T1/2 cells, with a sixfold increase in
apoptosis over controls. When S1P was added to either the
DMS-treated or DMS- and ceramide-treated cells, the apoptotic
response was markedly reduced (60 and 70%, respectively) (Fig. 2)
.
These results further demonstrate that the conversion of ceramide to
S1P is essential for cell survival.
|
To examine if exogenous ceramide is metabolized to S1P, we used
[14C]-labeled ceramide. Exogenously added
labeled ceramide is metabolized slowly in 10T1/2 cells
(Fig. 3
). Ceramide remains predominantly intact. However, labeled ceramide was
metabolized to sphingosine (Fig. 3)
and, to a lesser extent, converted
to S1P (Fig. 3)
. In addition, <1% of labeled ceramide was
incorporated into the more complex sphingolipids, such as sphingomyelin
and gangliosides (data not shown). Nonetheless, though exogenously
labeled ceramide primarily remains as intact ceramide, it is also
converted to sphingosine and S1P in 10T1/2 cells.
|
To support evidence demonstrating that the metabolism of ceramide is
critical to cell survival, cells were treated with the nonhydrolyzable
ceramide analog, ceramine. As previously shown, treatments with either
ceramide or S1P did not induce apoptosis in 10T1/2 cells
(Fig. 4
). However, treatment with ceramine produced a marked increase in the
number of apoptotic cells, approximately sevenfold that of both
ceramide and S1P treatments (Fig. 4)
. These results suggest that the
metabolism of ceramide, potentially to S1P, in 10T1/2 cells
prevents ceramide-induced apoptosis.
|
). These results also confirm the lack of apoptotic response to ceramide
using flow cytometry to measure apoptosis.
|
DISCUSSION
It has been suggested that a ceramide/S1P rheostat exists within
cells, dictating either an apoptotic fate or a survival response
(10
). The results of the present study demonstrate that
10T1/2 cells are resistant to ceramide-induced apoptosis.
Furthermore, these results demonstrate that the inhibition of ceramide
conversion to its metabolites results in an apoptotic response, which
is prevented through the addition of the metabolite S1P. Thus, these
results demonstrate that the metabolism of ceramide to S1P is crucial
for cell survival.
In support of the ceramide/S1P rheostat hypothesis, we found that when
the enzymes ceramidase and sphingosine kinase are inhibited, an action
which leads to decreased levels of sphingosine and S1P
(21
, 22
), the cells undergo apoptosis. Addition of
exogenous S1P in conjunction with the inhibitors protects the cells
from apoptosis. S1P is a potent inhibitor of ceramide-induced
apoptosis (10
, 11
). Similar to the findings observed in
this study, DMS, a sphingosine kinase inhibitor, stimulates apoptosis
in a number of cell lines (22
). Edsall et al.,
(22
) also demonstrated the prevention of apoptosis by the
addition of S1P when pheochromocytoma PC12 cells were treated with DMS
(23
). Thus, inhibiting the formation of endogenously
produced S1P, and thus shifting the balance from S1P to ceramide, in
unstimulated cells reduces cell survival. These results demonstrate
that regulation of the intracellular levels of ceramide and S1P within
cells leads to either induction or prevention of apoptosis.
Ceramide treatment alone did not result in an apoptotic response;
however, treatment with ceramine did induce apoptosis. Ceramine differs
from ceramide in that the amide-linked fatty acyl group of ceramide
is replaced with an amine-linked fatty alkyl group
(20
). The presence of this amine bond in the ceramide
structure does not allow it to be metabolized by the enzyme ceramidase,
which hydrolyzes the fatty acyl group off of ceramide-producing
sphingosine. Hence the ceramide analog ceramine cannot be metabolized
to either sphingosine or S1P. Therefore, in the cells treated with
ceramine, the balance of ceramide to S1P is shifted to ceramide and the
cells undergo apoptosis.
The intracellular levels of ceramide and S1P can be altered because of
extracellular agents. Extracellular stimuli such as cytokines and
growth factors can influence the enzymatic activity of several of the
enzymes involved in sphingolipid metabolism, such as sphingomyelinase,
ceramidase and sphingosine kinase (14
). The increase in
activity of one enzyme over another can lead to the accumulation of
ceramide or the production of S1P, thus changing the cellular rheostat.
Our data suggest that the activities of ceramidase and sphingosine
kinase in 10T 1/2 cells are maintained at levels that produce
S1P. Muller et al. (24
) observed the metabolism of
[14C]palmitoylceramide in U937 cells over a
2.5-h time period, and, similar to our results, most of the labeled
ceramide remained intact. But in their study, a small amount of label
also was incorporated into diacylglycerol and phosphatidylcholine
(24
). In our studies, we were able to detect a proportion
of the exogenously added radiolabel from ceramide incorporated into S1P
(Fig. 3)
. S1P cellular levels are normally quite low but can become
markedly increased after various stimuli (25
, 26
). Thus, it
was not surprising to find such a low level of radiolabeled S1P. Though
small, the results of the current study demonstrate that the metabolism
of ceramide to S1P is important for cellular survival.
Ceramide and S1P can function as lipid second messengers upon
appropriate stimuli (27
, 28
). However, in the absence of
such stimuli, the intracellular levels of ceramide and S1P must be
maintained at low levels to prevent the induction of apoptosis or
cellular proliferation when such a response is not required. Therefore,
in 10T1/2 cells, although ceramide treatment alone did not
induce apoptosis, preventing the metabolism of ceramide to S1P markedly
stimulated apoptosis. Furthermore, even though a small amount of
labeled ceramide was metabolized to S1P, this amount was sufficient to
prevent apoptosis. Therefore, treatment of 10T1/2 cells with
ceramide does not result in apoptosis attributable to the conversion of
ceramide to S1P, and S1P is required for cell survival in 10T1/2
cells.
ACKNOWLEDGMENTS
We would like to thank Jerry Brower for his help in the preparation of this article.
FOOTNOTES
2 Abbreviations: b-dUTP, biotinylated dUTP;
CMF-PBS, calcium magnesium–free phosphate-buffered saline;
DMEM, Dulbecco’s modified Eagle medium; DMS, dimethylsphingosine; ERK,
the extracellular signal–regulated protein kinase; MAPK,
mitogen-activated protein kinase; MAPP,
(1S,2R)-D-erythro-2-(N-myristoylamino)-1-phenol-1-propanol;
NOE, N-oleoyl-ethanolamine; SAPK, stress-activated
protein kinase; S1P, sphingosine-1-phosphate; 10T1/2,
C3H10T1/2. 
Manuscript received 5 April 2001. Initial review completed 4 June 2001. Revision accepted 10 August 2001.
LITERATURE CITED
1. Merrill, A. H., Jr, Schmelz, E. M., Dillehay, D. L., Spiegel, S., Shayman, J. A., Schroeder, J. J., Riley, R. T., Voss, K. A. & Wang, E. (1997) Sphingolipids–the enigmatic lipid class: biochemistry, physiology, and pathophysiology. Toxicol. Appl. Pharmacol. 142:208-225.[Medline]
2. Vesper, H., Schmelz, E. M., Nikolova-Karakashian, M. N., Dillehay, D. L., Lynch, D. V. & and Merrill, A. H., Jr (1999) Sphingolipids in food and the emerging importance of sphingolipids to nutrition. J. Nutr. 129:239-250.
3. Hannun, Y. A. (1994) The sphingomyelin cycle and the second messenger function of ceramide. J. Biol. Chem. 269:3125-3128.
4. Kolesnick, R. (1994) Signal transduction through the sphingomyelin pathway. Mol. Chem. Neuropathol. 21:287-297.[Medline]
5. Hannun, Y. A. (1996) Functions of ceramide in coordinating cellular responses to stress. Science 274:1855-1859.
6. Pena, L. A., Fuks, Z. & Kolesnick, R. (1997) Stress-induced apoptosis and the sphingomyelin pathway. Biochem. Pharmacol. 53:615-621.[Medline]
7. Hannun, Y. A. & Luberto, C. (2000) Ceramide in the eukaryotic stress response. Trends Cell. Biol. 10:73-80.[Medline]
8. Mao, C., Xu, R., Bielawska, A. & Obeid, L. M. (2000) Cloning of an alkaline ceramidase from Saccharomyces cerevisiae: an enzyme with reverse (CoA-independent) ceramide synthase activity. J. Biol. Chem. 275:6876-6884.
9. Olivera, A., Rosenthal, J. & Spiegel, S. (1994) Sphingosine kinase from Swiss 3T3 fibroblasts: a convenient assay for the measurement of intracellular levels of free sphingoid bases. Anal. Biochem. 223:306-312.[Medline]
10. Cuvillier, O., Pirianov, G., Kleuser, B., Vanek, P. G., Coso, O. A., Gutkind, S. & Spiegel, S. (1996) Suppression of ceramide-mediated programmed cell death by sphingosine-1-phosphate. Nature 381:800-803.[Medline]
11. Cuvillier, O., Rosenthal, D. S., Smulson, M. E. & Spiegel, S. (1998) Sphingosine 1-phosphate inhibits activation of caspases that cleave poly(ADP-ribose) polymerase and lamins during Fas- and ceramide-mediated apoptosis in Jurkat T lymphocytes. J. Biol. Chem. 273:2910-2916.
12. Verheij, M., Bose, R., Lin, X. H., Yao, B., Jarvis, W. D., Grant, S., Birrer, M. J., Szabo, E., Zon, L. I., Kyriakis, J. M., Haimovitz-Friedman, A., Fuks, Z. & Kolesnick, R. N. (1996) Requirement for ceramide-initiated SAPK/JNK signalling in stress-induced apoptosis. Nature 380:75-79.[Medline]
13. Jarvis, W. D., Fornari, F. A., Jr, Auer, K. L., Freemerman, A. J., Szabo, E., Birrer, M. J., Johnson, C. R., Barbour, S. E., Dent, P. & Grant, S. (1997) Coordinate regulation of stress- and mitogen-activated protein kinases in the apoptotic actions of ceramide and sphingosine. Mol. Pharmacol. 52:935-947.
14. Luberto, C. & Hannun, Y. A. (1999) Sphingolipid metabolism in the regulation of bioactive molecules. Lipids 34:S5-S11.
15. Coroneos, E., Martinez, M., McKenna, S. & Kester, M. (1995) Differential regulation of sphingomyelinase and ceramidase activities by growth factors and cytokines: implications for cellular proliferation and differentiation. J. Biol. Chem. 270:23305-23309.
16. Rani, C. S., Wang, F., Fuior, E., Berger, A., Wu, J., Sturgill, T. W., Beitner-Johnson, D., LeRoith, D., Varticovski, L. & Spiegel, S. (1997) Divergence in signal transduction pathways of platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptors: involvement of sphingosine 1-phosphate in PDGF but not EGF signaling. J. Biol. Chem. 272:10777-10783.
17. Gorczyca, W., Bigman, K., Mittelman, A., Ahmed, T., Gong, J., Melamed, M. R. & Darzynkiewicz, Z. (1993) Induction of DNA strand breaks associated with apoptosis during treatment of leukemias. Leukemia 7:659-670.[Medline]
18. Olivera, A., Romanowski, A., Rani, C. S. & Spiegel, S. (1997) Differential effects of sphingomyelinase and cell-permeable ceramide analogs on proliferation of Swiss 3T3 fibroblasts. Biochim. Biophys. Acta. 1348:311-323.[Medline]
19. Rius, R. A., Edsall, L. C. & Spiegel, S. (1997) Activation of sphingosine kinase in pheochromocytoma PC12 neuronal cells in response to trophic factors. FEBS Lett 417:173-176.[Medline]
20. Karasavvas, N., Erukulla, R. K., Bittman, R., Lockshin, R. & Zakeri, Z. (1996) Stereospecific induction of apoptosis in U937 cells by N-octanoyl-sphingosine stereoisomers and N-octyl-sphingosine: the ceramide amide group is not required for apoptosis. Eur. J. Biochem. 236:729-737.[Medline]
21. Strelow, A., Bernardo, K., Adams-Klages, S., Linke, T., Sandhoff, K., Kronke, M. & Adam, D. (2000) Overexpression of acid ceramidase protects from tumor necrosis factor-induced cell death. J. Exp. Med. 192:601-612.
22. Edsall, L. C., Van Brocklyn, J. R., Cuvillier, O., Kleuser, B. & Spiegel, S. (1998) N,N-Dimethylsphingosine is a potent competitive inhibitor of sphingosine kinase but not of protein kinase C: modulation of cellular levels of sphingosine 1-phosphate and ceramide. Biochemistry 37:12892-12898.[Medline]
23. Edsall, L. C., Pirianov, G. G. & Spiegel, S. (1997) Involvement of sphingosine 1-phosphate in nerve growth factor-mediated neuronal survival and differentiation. J. Neurosci. 17:6952-6960.
24. Muller, G., Ayoub, M., Storz, P., Rennecke, J., Fabbro, D. & Pfizenmaier, K. (1995) PKC zeta is a molecular switch in signal transduction of TNF-alpha, bifunctionally regulated by ceramide and arachidonic acid. EMBO J 14:1961-1969.[Medline]
25. Olivera, A. & Spiegel, S. (1993) Sphingosine-1-phosphate as second messenger in cell proliferation induced by PDGF and FCS mitogens. Nature 365:557-560.[Medline]
26. Bornfeldt, K. E., Graves, L. M., Raines, E. W., Igarashi, Y., Wayman, G., Yamamura, S., Yatomi, Y., Sidhu, J. S., Krebs, E. G. & Hakomori, S. (1995) Sphingosine-1-phosphate inhibits PDGF-induced chemotaxis of human arterial smooth muscle cells: spatial and temporal modulation of PDGF chemotactic signal transduction. J. Cell. Biol. 130:193-206.
27. Mathias, S. & Kolesnick, R. (1993) Ceramide: a novel second messenger. Adv. Lipid Res. 25:65-90.[Medline]
28. Mattie, M., Brooker, G. & Spiegel, S. (1994) Sphingosine-1-phosphate, a putative second messenger, mobilizes calcium from internal stores via an inositol trisphosphate-independent pathway. J. Biol. Chem. 269:3181-3188.
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