ENDOTHELIAL-CELL DEATH INDUCED BY TUMOR-NECROSIS-FACTOR-ALPHA IS INHIBITED BY THE BCL-2 FAMILY MEMBER, A1

Endothelial cells play a central role in the inflammatory process, Tum or necrosis factor-cy (TNF) is a multifunctional cytokine which elicit s many of the inflammatory responses of endothelial cells, While TNF d irectly causes apoptosis of tumor cells and virally infected cells, no rmal cells are generally resistant. However, most resistant cells, inc luding human endothelial cells, can be rendered susceptible to TNF by inhibiting RNA or protein synthesis. This finding suggests that TNF pr ovides a cell survival signal in addition to a death signal. We have p reviously cloned a human Bcl-2 homologue, Al, and shown that it is spe cifically induced by proinflammatory cytokines but not by endothelial growth factors. In this study, we show that retroviral-mediated transf er of the Al cDNA to a human microvascular endothelial cell line provi des protection against cell death initiated by TNF in the presence of actinomycin D. The induction of Al by TNF in this system is mediated v ia a protein kinase C pathway, Since TNF signaling has also been shown to proceed via ceramides, we tested whether exogenous ceramides could induce Al, Our findings indicate that ceramides do not induce Al but do up-regulate c-jun and induce endothelial death. Ceramide-activated endothelial death is also inhibited by Al, suggesting that TNF may ini tiate divergent survival and death pathways via separate lipid second messengers.