STEREOSPECIFICITY OF SPHINGOSINE-INDUCED INTRACELLULAR CALCIUM MOBILIZATION AND CELLULAR PROLIFERATION

Sphingosine is a positive regulator of cell growth in Swiss 3T3 fibrob lasts (Zhang, H., Buckley, N. E., Gibson, K., and Spiegel, S. (1990) J . Biol. Chem. 265, 76-81). The present study investigated the stereosp ecificity of sphingosine-induced cell proliferation and its mitogenic signal transduction mechanisms. D-(+)-erythro Stereoisomers (cis and t rans) stimulated DNA synthesis, whereas neither L-(-)-threo-sphingosin e (cis or trans) nor DL-threo-dihydrosphingosine had any effect. Previ ously, we have shown that sphingosine-1-phosphate may mediate the mito genic effect of sphingosine (Zhang, H., Desai, N. N., Olivera, A., Sek i, T., Brooker, G., and Spiegel, S. (1991) J. Cell Biol. 114, 155-167) . However, no major differences were found in the formation of D-(+)-e rythro and L-(-)-threo- sphingosine-1-phosphate derived from the respe ctive sphingosine isomers in intact cells. Thus, the stereospecificity of the response to sphingosine may reside at the level of specific in tracellular targets for sphingosine-1-phosphate. Sphingosine-1-phospha te triggers dual signal transduction pathways of activation of phospho lipase D leading to increases in the levels of phosphatidic acid and m obilization of calcium from internal stores. Both D-(+)-erythro- and L -(-)-threo-sphingosine isomers induced similar increases in phosphatid ic acid concomitant with identical decreases in phosphatidylcholinelev els. In contrast, only the D-(+)-erythro-stereoisomers (cis and trans) were effective in releasing calcium from intracellular stores. Our re sults suggest that the formation of phosphatidic acid is not sufficien t to mediate sphingosine-stimulated DNA synthesis. However, the stereo specificity of the sphingosine-induced mobilization of calcium from in ternal stores seems to correlate with the induction of DNA synthesis b y sphingosine stereoisomers.