Ceramides induce apoptosis in HeLa cells and enhance cytochrome c-induced apoptosis in Xenopus egg extracts

Ceramide has been reported to induce typical apoptotic changes in nuclei in cubated in a cell-free system, and that the addition of ceramide bypasses t he requirement for mitochondria. Here, we explore the possible pathways by which ceramide induces apoptosis either in intact cells or in a cell-free s ystem which we have developed. We found that in the cell-free system, C2-ce ramide is not able to induce apoptosis in nuclei whereas cytochrome c does, but it is able to induce HeLa cells to undergo apoptosis. Ceramide is also not able to induce apoptosis when added into the cell-free system together with purified mitochondria. Further investigation showed that C2-ceramide at certain concentrations greatly increases nuclear apoptosis caused by cyt ochrome c in the cell-free system. From these results we conclude that the induction of apoptosis by ceramide may require intact cells in which some u nknown signal transduction pathways are involved.