Isolation of Ich-1S (caspase-2S)-binding protein that partially inhibits caspase activity

Members of the caspase family are essential executors of apoptosis. Caspase-2 has two messenger RNAs generated by alternative splicing, which encode caspase-2L and caspase-2S. Although caspase-2L induces apoptosis, caspase-2S also has the ability to antagonize cell death. Experiments in caspase-2-deficient mice showed that caspase-2 functions to delay cell death in some neuronal populations, suggesting that caspase-2S dominantly acts for cell survival in the brain. However, the mechanism of caspase-2S-mediated anti-apoptotic effect is still unclear. Here, we isolated a protein that interacts with caspase-2S, designated as Ich-1S (caspase-2S)-binding protein (ISBP), by yeast two-hybrid screening using full-length caspase-2S cDNA as a bait. ISBP is identical to the recently isolated calcium and integrin-binding protein, and a small molecule calcium-binding protein with two EF-hand motifs of its C-terminus. In vitro transcribed and translated ISBP interacts specifically with glutathione-S-transferase-fused caspase-2S. Moreover, the interaction between ISBP and caspase-2S was observed in cultured cells. Northern blot analysis indicated that ISBP may be a ubiquitous protein. Interestingly, ISBP can partially inhibit the processing of pro-caspase-2L induced by anti-Fas antibody-treated Jurkat cytosolic lysates. These results suggested that ISBP may be the mediator for the survival function of caspase-2S.