4.7 Article

Characterization of caspase-8L: a novel isoform of caspase-8 that behaves as an inhibitor of the caspase cascade

Journal

BLOOD
Volume 99, Issue 11, Pages 4070-4078

Publisher

AMER SOC HEMATOLOGY
DOI: 10.1182/blood.V99.11.4070

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Caspase-8 (Fas-associating protein with death domain-like interleukin-1beta-converting enzyme [FLICE]/MACH/Mch5) belongs to a family of cysteine proteases presumed to be the apex of the apoptotic signaling pathways. We recently reported the presence of a novel isoform of caspase-8, named caspase-8L, generated by the alternative splicing of human caspase-8 gene, from human peripheral blood lymphocytes by reverse transcriptase-polymerase chain reaction. We herein report a functional analysis of caspase-8L in the Fas-mediated apoptotic pathway. Caspase-8L is missing the catalytic site of caspase-8 but retains 2 N-terminal repeats of the death-effector domain. The caspase-8L messenger RNA was detected in various tissues but not in any cell lines examined. In human peripheral blood lymphocytes, caspase-8L was strongly suggested to be expressed at the protein level. In MCF-7 cells, caspase-8L transfection itself did not affect cell viability but instead inhibited the apotosis induced by the cotransfection of caspase-8 in a dominant negative manner. Moreover, Fas-mediated apoptosis was inhibited in caspase-8L-transfected Jurkat cells, which were associated with a reduction In the caspase-8 catalytic activity. In vitro binding assays demonstrated that caspase-8L bound to FADD (Fas-associating protein with death domain) and caspase-8a and blocked the binding of caspase-8 to FADD. In in vivo binding assays, transfected caspase-8L bound to endogeneous FADD. Thus, caspase-8L acts as an Inhibitor of caspase-8 by interfering with the binding of caspase-8 to FADD and Is Involved In the regulation of Fas-mediated apoptosis. (C) 2002 by The American Society of Hematology.

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