Differential effects of sphingomyelinase and cell-permeable ceramide analogs on proliferation of Swiss 3T3 fibroblasts.
Metabolites of sphingomyelin, ceramide and sphingosine, have previously been implicated in cell growth regulation. Here we show that cell-permeable ceramide analogs and treatment with sphingomyelinase, which hydrolyzes sphingomyelin located on the outer leaflet of the bilayer, increase the progression of quiescent Swiss 3T3 fibroblasts through the S phase of the cell cycle leading to an increase in cell division. Although both potentiate the mitogenic effects of several growth factors [14], sphingomyelinase treatment antagonized the mitogenic effect of the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), while ceramide analogs had no effect, and sphingosine, a further metabolite of ceramide, potentiated the mitogenic effect of TPA. Concomitantly, sphingomyelinase, but not ceramide analogs, blunted the rapid increase in membrane-associated protein kinase C (PKC) activity induced by TPA without affecting the translocation of PKC alpha, delta, epsilon or zeta isoforms. Moreover, in contrast to sphingosine which activates phospholipase D (PLD) leading to an increase in phosphatidic acid levels, sphingomyelinase, but not ceramide analogs, reduced TPA-stimulated PLD activity. Our results suggest that the signaling pathways utilized by sphingomyelinase differ from those of cell-permeable ceramide analogs, and both act differently than sphingosine. The differential effects of exogenous short-chain ceramide analogs and sphingomyelinase call for caution in using these analogs as tools to study the role of ceramide in diverse cellular functions.
Olivera
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Department of Biochemistry and Molecular Biology, Georgetown University, Medical Center, Washington, DC 20007, USA.
Romanowski
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Rani
C S
CS
Spiegel
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S
D016475:3T3 Cells / Q000166:cytology*; D000818:Animals; D002453:Cell Cycle; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D002463:Cell Membrane Permeability; D002518:Ceramides / Q000494:pharmacology*; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D010739:Phospholipase D / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology*; D013109:Sphingomyelins / Q000494:pharmacology; D013110:Sphingosine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002518:Ceramides; D010743:Phospholipids; D013109:Sphingomyelins; D011493:Protein Kinase C; D013108:Sphingomyelin Phosphodiesterase; D010739:Phospholipase D; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate