SHORT-CHAIN CERAMIDE-1-PHOSPHATES ARE NOVEL STIMULATORS OF DNA-SYNTHESIS AND CELL-DIVISION - ANTAGONISM BY CELL-PERMEABLE CERAMIDES

Ceramide and ceramide-1-phosphate are sphingolipid analogues of diacyl glycerol and phosphatidate, respectively, and they are putative second messengers of agonist-stimulated sphingomyelin metabolism. The intera ctions of exogenous cell-permeable ceramides and ceramide-1-phosphates in modifying DNA synthesis and signal transduction were investigated in Rat-1 fibroblasts. C-2- and C-8-Ceramide-1-phosphates (N-acetylsphi ngosine-1-phosphate and N-octanoylsphingosine-1-phosphate, respectivel y) at 1-10 mu M stimulated DNA synthesis and cell division. This effec t was blocked by cell-permeable ceramides. C-2-Ceramide stimulated the conversion of exogenous C-8-ceramide-1-phosphate to C-8-ceramide, wit h very little production of sphingosine or sphingosine-1-phosphate. Th is mechanism may be partly responsible for preventing the stimulation of DNA synthesis. Unlike phosphatidate or lyso-phosphatidate, concentr ations of C-8-ceramide-1-phosphate that stimulated DNA synthesis did n ot inhibit adenylate cyclase activity, nor did they increase the activ ities of phospholipase D or mitogen-activated protein kinases (42- and 44 kDa isoforms). Although ceramide-1-phosphate can be considered as an analogue of phosphatidate, the effects of this compound on signal t ransduction differ considerably from those of phosphatidate. This work demonstrates that short-chain ceramide-1-phosphates can be used as no vel external agonists that can stimulate DNA synthesis. This effect ca n be counteracted by short-chain ceramides.