Inositol 1,4,5-trisphosphate receptor type 1 is a substrate for caspase-3 and is cleaved during apoptosis in a caspase-3-dependent manner

The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R), an IP3-gated Ca2+ c hannel located on intracellular Ca2+ stores, modulates intracellular Ca2+ s ignaling. During apoptosis of the human T-cell line, Jurkat cells, as induc ed by staurosporine or Fas ligation, IP3R type 1 (LP(3)R1) was found to be cleaved. IP(3)R1 degradation during apoptosis was inhibited by pretreatment of Jurkat cells with the caspase-3 (-like protease) inhibitor, AcDEVD-CHO, and the caspases inhibitor, z-VAD-CH2DCB but not by the caspase-1 (-like p rotease) inhibitor, Ac-YVAD-CHO, suggesting that IP(3)R1 was cleaved by a c aspase-3 (-like) protease. The recombinant caspase-3 cleaved IP(3)R1 in vit ro to produce a fragmentation pattern consistent with that seen in Jurkat c ells undergoing apoptosis. N-terminal amino acid sequencing revealed that t he major cleavage site is (DEVD)-D-1888*R-1892 (mouse IP(3)R1), which invol ves consensus sequence for caspase-3 cleavage (DEVD). To determine whether IP(3)R1 is cleaved by caspase-3 or is proteolyzed in its absence by other c aspases, we examined the cleavage of IP(3)R1 during apoptosis in the MCF-7 breast carcinoma cell line, which has genetically lost caspase-3, Tumor nec rosis factor-alpha- or staurosporine-induced apoptosis in caspase-3-deficie nt MCF-7 cells failed to demonstrate cleavage of IP(3)R1, In contrast, MCF- 7/Casp-3 cells stably expressing caspase-3 showed IP(3)R1 degradation upon apoptotic stimuli. Therefore IP(3)R1 is a newly identified caspase-3 substr ate, and caspase-3 is essential for the cleavage of IP(3)R1 during apoptosi s. This cleavage resulted in a decrease in the channel activity as IP(3)R1 was digested, indicating that caspase-3 inactivates IP(3)R1 channel functio ns.