Role of ceramide in stimulation of the transcription of cytosolic phospholipase A2 and cyclooxygenase 2.

Several lines of evidence have implicated lipid second messengers in the signaling pathways evoked by tumor necrosis factor (TNF). In a previous study, we characterized TNF-resistant sublines derived from murine fibrosarcoma L929 cells. and demonstrated that TNF stimulation of arachidonate metabolism via cytosolic phospholipase A2, (cPLA2) was one of the pathways responsible for the killing of L929 cells. On the other hand, the sphingomyelin cycle, which generates ceramide, is also recognized as a pathway that participates in the apoptosis in certain types of cells. In this study, we evaluated the role of ceramide in TNF-signaling in L929 cells. L929 cells generated ceramide in response to TNF, whereas the TNF-resistant sublines did not. The addition of an exogenous cell-permeable ceramide analogue resulted in the elevated expression of cPLA2 and cyclooxygenase 2 mRNAs in the cells. These results suggest the role of ceramide to amplify the magnitude of signals generated through the PLA2 pathway.