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CrmA and Bcl-2 Target Distinct Components in the
Apoptotic Pathway
By



From the * Department of Pediatrics, Proteases are now firmly established as major regulators of the "execution" phase of apoptosis.
Here, we examine the role of proteases and their relationship to ceramide, a proposed mediator of apoptosis, in the tumor necrosis factor-
Department of Medicine, and ¶ Department of Cell Biology,
Duke University Medical Center, Durham, North Carolina 27710; and the
Laboratory of Molecular
Endocrinology, Laval University, Sainte-Foy, Quebec, G1V-4G2, Canada
(TNF-
)-induced pathway of cell death. Ceramide
induced activation of prICE, the protease that cleaves the death substrate poly(ADP-ribose)
polymerase. Bcl-2 inhibited ceramide-induced death, but not ceramide generation. In contrast,
Cytokine response modifier A (CrmA), a potent inhibitor of Interleukin-1
converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-
-induced death.
Exogenous ceramide could overcome the CrmA block to cell death, but not the Bcl-2 block.
CrmA, however, did not inhibit the activation of nuclear factor (NF)-
B by TNF-
, demonstrating that other signaling functions of TNF-
remain intact and that ceramide does not play a role in the activation of NF-
B. These studies support a distinct role for proteases in the signaling/activation phase of apoptosis acting upstream of ceramide formation.
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