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Title: Distinct sites of action of Bcl-2 and Bcl-xL in the ceramide pathway of apoptosis. Author: El-Assaad W, El-Sabban M, Awaraji C, Abboushi N, Dbaibo GS. Journal: Biochem J; 1998 Dec 15; 336 ( Pt 3)(Pt 3):735-41. PubMed ID: 9841888. Abstract: We studied the inhibition of tumour necrosis factor alpha (TNFalpha)- and camptothecin-induced apoptosis by Bcl-2 and Bcl-xL as they relate to the ceramide pathway. Expression of either Bcl-2 or Bcl-xL provided significant protection from the apoptotic effects of TNFalpha or camptothecin. In contrast to Bcl-2, Bcl-xL overexpression did not protect cells from ceramide-induced apoptosis. On the other hand, Bcl-xL prevented the accumulation of endogenous ceramide in response to TNFalpha or camptothecin, whereas Bcl-2 showed little effect on ceramide formation. Moreover, Bcl-xL, but not Bcl-2, totally inhibited a caspase-8-like activity in cell lysates stimulated with TNFalpha. These results identify a different mechanism of action for Bcl-xL compared with Bcl-2 and they demonstrate that Bcl-xL targets a point upstream of ceramide generation, whereas Bcl-2 functions downstream of ceramide in the TNFalpha- and camptothecin-activated pathways of apoptosis.[Abstract] [Full Text] [Related] [New Search]