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Cytokine response modifier A (CrmA) inhibits ceramide formation in response to tumor necrosis factor (TNF)-alpha: CrmA and Bcl-2 target distinct components in the apoptotic pathway.

Dbaibo GS, Perry DK, Gamard CJ, Platt R, Poirier GG, Obeid LM, Hannun YA - J. Exp. Med. (1997)

Bottom Line: In contrast, Cytokine response modifier A (CrmA), a potent inhibitor of Interleukin-1 beta converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-alpha-induced death.CrmA, however, did not inhibit the activation of nuclear factor (NF)-kappa B by TNF-alpha, demonstrating that other signaling functions of TNF-alpha remain intact and that ceramide does not play a role in the activation of NF-kappa B.These studies support a distinct role for proteases in the signaling/activation phase of apoptosis acting upstream of ceramide formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
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-alpha (TNF-alpha)-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 beta converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-alpha-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)-kappa B by TNF-alpha, demonstrating that other signaling functions of TNF-alpha remain intact and that ceramide does not play a role in the activation of NF-kappa 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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Schematic presentation of the proposed sites of inhibition of  the ceramide pathway by CrmA and Bcl-2. Activation of sphingomyelinases requires several stages of proteolytic processing (63). The inhibition  of ceramide accumulation by CrmA is hypothesized to be due to its ability to inhibit cysteine or serine proteases probably involved in the processing of sphingomyelinase(s). Bcl-2 functions further downstream by inhibiting effector molecules involved in the execution of the death order  without interfering with the generation of ceramide. The specific target  of Bcl-2 is not yet known. The diagram illustrates the possibility that either proteases or regulatory molecules are targeted by Bcl-2.
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Figure 8: Schematic presentation of the proposed sites of inhibition of the ceramide pathway by CrmA and Bcl-2. Activation of sphingomyelinases requires several stages of proteolytic processing (63). The inhibition of ceramide accumulation by CrmA is hypothesized to be due to its ability to inhibit cysteine or serine proteases probably involved in the processing of sphingomyelinase(s). Bcl-2 functions further downstream by inhibiting effector molecules involved in the execution of the death order without interfering with the generation of ceramide. The specific target of Bcl-2 is not yet known. The diagram illustrates the possibility that either proteases or regulatory molecules are targeted by Bcl-2.

Mentions: The antiapoptotic activity of CrmA has been thought to be due to its ability to inhibit members of the ICE family of cysteine proteases that are homologues of the C. elegans cell death protease CED-3 (2, 4, 25). However, the potency by which CrmA inhibits the various members of this family varies significantly. Whereas picomolar concentrations of CrmA can potently inhibit ICE, concentrations that are over 1,000-fold higher are required to achieve comparable inhibition of Yama/CPP32/apopain, a putative PARP cleaving protease (7). Similarly, CrmA is a poor inhibitor of ICH-1 (23) and CED-3 (3, 55), indicating that it preferentially targets only a subset of ICE family members. This may explain why CrmA is not a universal inhibitor of apoptosis. Based on our findings, the more physiologically relevant target of CrmA appears to be a protease that is activated by TNF-α and is involved in the activation phase, rather than the execution phase, of apoptosis. The recently described Fas– and TNF-α receptor–associated ICE protease FLICE/MACH, is a likely candidate since it was demonstrated that apoptosis induced by its overexpression can be inhibited by CrmA (16). Other apoptotic stimuli such as mitomycin or sodium azide (data not shown) that use a ceramide-independent pathway to activate the death proteases are not inhibited by CrmA (Fig. 8).


Cytokine response modifier A (CrmA) inhibits ceramide formation in response to tumor necrosis factor (TNF)-alpha: CrmA and Bcl-2 target distinct components in the apoptotic pathway.

Dbaibo GS, Perry DK, Gamard CJ, Platt R, Poirier GG, Obeid LM, Hannun YA - J. Exp. Med. (1997)

Schematic presentation of the proposed sites of inhibition of  the ceramide pathway by CrmA and Bcl-2. Activation of sphingomyelinases requires several stages of proteolytic processing (63). The inhibition  of ceramide accumulation by CrmA is hypothesized to be due to its ability to inhibit cysteine or serine proteases probably involved in the processing of sphingomyelinase(s). Bcl-2 functions further downstream by inhibiting effector molecules involved in the execution of the death order  without interfering with the generation of ceramide. The specific target  of Bcl-2 is not yet known. The diagram illustrates the possibility that either proteases or regulatory molecules are targeted by Bcl-2.
© Copyright Policy
Related In: Results  -  Collection

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Figure 8: Schematic presentation of the proposed sites of inhibition of the ceramide pathway by CrmA and Bcl-2. Activation of sphingomyelinases requires several stages of proteolytic processing (63). The inhibition of ceramide accumulation by CrmA is hypothesized to be due to its ability to inhibit cysteine or serine proteases probably involved in the processing of sphingomyelinase(s). Bcl-2 functions further downstream by inhibiting effector molecules involved in the execution of the death order without interfering with the generation of ceramide. The specific target of Bcl-2 is not yet known. The diagram illustrates the possibility that either proteases or regulatory molecules are targeted by Bcl-2.
Mentions: The antiapoptotic activity of CrmA has been thought to be due to its ability to inhibit members of the ICE family of cysteine proteases that are homologues of the C. elegans cell death protease CED-3 (2, 4, 25). However, the potency by which CrmA inhibits the various members of this family varies significantly. Whereas picomolar concentrations of CrmA can potently inhibit ICE, concentrations that are over 1,000-fold higher are required to achieve comparable inhibition of Yama/CPP32/apopain, a putative PARP cleaving protease (7). Similarly, CrmA is a poor inhibitor of ICH-1 (23) and CED-3 (3, 55), indicating that it preferentially targets only a subset of ICE family members. This may explain why CrmA is not a universal inhibitor of apoptosis. Based on our findings, the more physiologically relevant target of CrmA appears to be a protease that is activated by TNF-α and is involved in the activation phase, rather than the execution phase, of apoptosis. The recently described Fas– and TNF-α receptor–associated ICE protease FLICE/MACH, is a likely candidate since it was demonstrated that apoptosis induced by its overexpression can be inhibited by CrmA (16). Other apoptotic stimuli such as mitomycin or sodium azide (data not shown) that use a ceramide-independent pathway to activate the death proteases are not inhibited by CrmA (Fig. 8).

Bottom Line: In contrast, Cytokine response modifier A (CrmA), a potent inhibitor of Interleukin-1 beta converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-alpha-induced death.CrmA, however, did not inhibit the activation of nuclear factor (NF)-kappa B by TNF-alpha, demonstrating that other signaling functions of TNF-alpha remain intact and that ceramide does not play a role in the activation of NF-kappa B.These studies support a distinct role for proteases in the signaling/activation phase of apoptosis acting upstream of ceramide formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
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-alpha (TNF-alpha)-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 beta converting enzyme and related proteases, inhibited ceramide generation and prevented TNF-alpha-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)-kappa B by TNF-alpha, demonstrating that other signaling functions of TNF-alpha remain intact and that ceramide does not play a role in the activation of NF-kappa B. These studies support a distinct role for proteases in the signaling/activation phase of apoptosis acting upstream of ceramide formation.

Show MeSH
Related in: MedlinePlus