Regulation of Lipid Signaling Pathways for Cell Survival and Apoptosis by bcl-2 in Prostate Carcinoma Cells

Compelling evidence indicates that activation of the JNK/SAPK signaling pathway is obligatory for apoptosis induction by multiple cell stresses that activate the sphingomyelin cycle. Moreover, ectopic expression of bcl-2 can impair apoptosis signaling by most of the cell stresses that activate the ceramide/JNK pathway. Here we show that enforced expression of bcl-2 protects prostate carcinoma cells against the induction of apoptosis by exogenous C₂-ceramide. Moreover, enforced bcl-2 expression blocked the capacity of C₂-ceramide to activate JNK1, indicating bcl-2 functions at the level of JNK1 or upstream of JNK1 in the ceramide/JNK pathway. The contribution of bcl-2 to the regulation of the arachidonate pathway for prostate carcinoma cell survival was also investigated using highly selective inhibitors of arachidonate metabolism. Our results indicate bcl-2 can protect cells against diminished availability of arachidonic acid, 12-HETE, and 15-HETE. Finally, arachidonic acid substantially suppresses the induction of apoptosis by C₂-ceramide, providing evidence for the opposing influences of these lipid signaling pathways in the mediation of prostate carcinoma cell survival. These results provide evidence for opposing influences of the ceramide and arachidonate signaling pathways in the mediation of cell death and cell survival, respectively, in prostate carcinoma cells and suggest a dual role for bcl-2 in this context.