Bcl-2 and caspase inhibition cooperate to inhibit tumor necrosis factor-alpha-induced cell death in a Bcl-2 cleavage-independent fashion.
The ability of proteins of the Bcl-2 family to either induce or inhibit apoptosis is dependent on both cell type and the apoptotic stimulus. We have shown in the murine pro-B cell line FL5.12 that Bcl-2 is incapable of inhibiting tumor necrosis factor alpha (TNFalpha)-induced cell death and is cleaved during this process. One potential explanation for this observation is that caspase activation directly or indirectly inhibits Bcl-2 function. It has been suggested that caspase cleavage of Bcl-2 is responsible for its inability to block certain cell deaths. Consistent with Bcl-2 cleavage being a caspase-mediated event, this cleavage is inhibitable by 50 microM CBZ-Val-Ala-Asp-fluoromethylketone (zVAD-fmk). Furthermore, Bcl-2 can cooperate with the caspase inhibitor zVAD-fmk in a dose-dependent manner to block TNFalpha-induced cell death. Overexpression of Bcl-2 results in a 10-fold decrease in the amount of zVAD-fmk required to inhibit TNFalpha-induced apoptosis. However, cleavage-defective mutants (D31A and D34A) show no enhanced viability relative to wild-type Bcl-2 in response to TNFalpha-induced cell death and also show the same cooperativity with zVAD-fmk. These results suggest that Bcl-2 cleavage is not important for the inhibition of TNFalpha-induced cell death but do not preclude an involvement in a post-commitment phase of apoptosis.
Johnson
B W
BW
Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, Florida 33101, USA.
Boise
L H
LH
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D007377:Interleukin-3 / Q000378:metabolism; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000494:pharmacology*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors*
D000590:Amino Acid Chloromethyl Ketones; D015853:Cysteine Proteinase Inhibitors; D007377:Interleukin-3; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D020169:Caspases