Identification of a caspase-2 isoform that behaves as an endogenous inhibitor of the caspase cascade.

Abstract	Procaspase-2 is one of the aspartate-specific cysteine proteases that are activated in response to various apoptotic stimuli. Two isoforms of human procaspase-2 have been described initially. Overexpression of the long isoform (caspase-2L) promotes cell death whereas the short isoform (caspase-2S) antagonizes some apoptotic pathways. In the present study, we identified two additional CASP-2 mRNAs, designated CASP-2L-Pro and CASP-2s-Pro. The proteins encoded by these isoforms corresponded to the prodomain of procaspase-2L and -2S, in which the last alpha-helix of their caspase recruitment domains was deleted. Caspase-2L-Pro mRNA and protein were detected in a series of human tissues and cell lines. Yeast 2-hybrid assays and immunoprecipitation studies indicated that caspase-2L-Pro can interact with procaspase-2L and the adaptor protein RAIDD/CRADD, but not with FADD/MORT1 or APAF-1 adaptor proteins. The addition of recombinant caspase-2L-Pro negatively interfered with cytochrome c/dATP-mediated activation of the caspase cascade in a cell-free system. In transient expression studies of human B lymphoma Namalwa cells, overexpression of caspase-2L-Pro weakly induced apoptosis, which was prevented by a D83A/E87A double mutation. In stable selected CASP-2L-Pro-transfected Namalwa cells, overexpression of caspase-2L-Pro delayed apoptotic DNA fragmentation induced by death receptor agonists (anti-Fas antibodies, tumor necrosis factor-alpha) and DNA topoisomerase I- (camptothecin) and II- (etoposide) inhibitors, and prevented etoposide-induced activation of the caspase cascade. These inhibitory effects were not observed in stable transfected cells expressing the D83A/E87A double mutant. Altogether, these data indicated that the caspase-2L-Pro isoform functions as an endogenous apoptosis inhibitory protein that antagonizes caspase activation and cell death.
Authors	N Droin, M Beauchemin, E Solary, R Bertrand
Journal	Cancer research (Cancer Res) Vol. 60 Issue 24 Pg. 7039-47 (Dec 15 2000) ISSN: 0008-5472 [Print] United States
PMID	11156409 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	Antineoplastic Agents, Phytogenic Caspase Inhibitors Cytochrome c Group Nucleic Acid Synthesis Inhibitors Protein Isoforms RNA, Messenger Recombinant Proteins Tumor Necrosis Factor-alpha Etoposide Caspase 2 Caspases
Topics	Amino Acid Sequence Antineoplastic Agents, Phytogenic (pharmacology) Apoptosis Base Sequence Blotting, Southern Blotting, Western Caspase 2 Caspase Inhibitors Caspases (biosynthesis, chemistry, genetics) Cell Death Cell Line Cell-Free System Cloning, Molecular Cytochrome c Group (metabolism) DNA Fragmentation Dose-Response Relationship, Drug Enzyme Activation Etoposide (pharmacology) Humans Kinetics Lymphoma (metabolism) Molecular Sequence Data Mutagenesis, Site-Directed Mutation Nucleic Acid Synthesis Inhibitors (pharmacology) Precipitin Tests Protein Binding Protein Isoforms Protein Structure, Tertiary RNA, Messenger (metabolism) Recombinant Proteins (metabolism) Sequence Homology, Amino Acid Time Factors Tissue Distribution Transfection Tumor Cells, Cultured Tumor Necrosis Factor-alpha (metabolism) Two-Hybrid System Techniques

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