DIFFERENTIAL-EFFECTS OF SPHINGOMYELINASE AND CELL-PERMEABLE CERAMIDE ANALOGS ON PROLIFERATION OF SWISS 3T3 FIBROBLASTS

Metabolites of sphingomyelin, ceramide and sphingosine, have previousl y been implicated in cell growth regulation. Here we show that cell-pe rmeable ceramide analogs and treatment with sphingomyelinase, which hy drolyzes sphingomyelin located on the outer leaflet of the bilayer, in crease the progression of quiescent Swiss 3T3 fibroblasts through the S phase of the cell cycle leading to an increase in cell division. Alt hough both potentiate the mitogenic effects of several growth factors [14], sphingomyelinase treatment antagonized the mitogenic effect pf t he tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), while c eramide analogs had no effect, and sphingosine, a further metabolite o f ceramide, potentiated the mitogenic effect of TPA. Concomitantly, sp hingomyelinase, but not ceramide analogs, blunted the rapid increase i n membrane-associated protein kinase C (PKC) activity induced by TPA w ithout affecting the translocation of PKC alpha, delta, epsilon or zet a isoforms. Moreover, in contrast to sphingosine which activates phosp holipase D (PLD) leading to an increase in phosphatidic acid levels, s phingomyelinase, 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 o f 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. (C) 1997 Elsevier Science B.V.