PMID:21859719

Citation	Kopil, CM, Vais, H, Cheung, KH, Siebert, AP, Mak, DO, Foskett, JK and Neumar, RW (2011) Calpain-cleaved type 1 inositol 1,4,5-trisphosphate receptor (InsP(3)R1) has InsP(3)-independent gating and disrupts intracellular Ca(2+) homeostasis. J. Biol. Chem. 286:35998-6010
Abstract	The type 1 inositol 1,4,5-trisphosphate receptor (InsP(3)R1) is a ubiquitous intracellular Ca(2+) release channel that is vital to intracellular Ca(2+) signaling. InsP(3)R1 is a proteolytic target of calpain, which cleaves the channel to form a 95-kDa carboxyl-terminal fragment that includes the transmembrane domains, which contain the ion pore. However, the functional consequences of calpain proteolysis on channel behavior and Ca(2+) homeostasis are unknown. In the present study we have identified a unique calpain cleavage site in InsP(3)R1 and utilized a recombinant truncated form of the channel (capn-InsP(3)R1) corresponding to the stable, carboxyl-terminal fragment to examine the functional consequences of channel proteolysis. Single-channel recordings of capn-InsP(3)R1 revealed InsP(3)-independent gating and high open probability (P(o)) under optimal cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) conditions. However, some [Ca(2+)](i) regulation of the cleaved channel remained, with a lower P(o) in suboptimal and inhibitory [Ca(2+)](i). Expression of capn-InsP(3)R1 in N2a cells reduced the Ca(2+) content of ionomycin-releasable intracellular stores and decreased endoplasmic reticulum Ca(2+) loading compared with control cells expressing full-length InsP(3)R1. Using a cleavage-specific antibody, we identified calpain-cleaved InsP(3)R1 in selectively vulnerable cerebellar Purkinje neurons after in vivo cardiac arrest. These findings indicate that calpain proteolysis of InsP(3)R1 generates a dysregulated channel that disrupts cellular Ca(2+) homeostasis. Furthermore, our results demonstrate that calpain cleaves InsP(3)R1 in a clinically relevant injury model, suggesting that Ca(2+) leak through the proteolyzed channel may act as a feed-forward mechanism to enhance cell death.
Links	PubMed PMC3195633 Online version:10.1074/jbc.M111.254177
Keywords	Animals; Calcium/metabolism; Calcium Channels/metabolism; Calcium Ionophores/pharmacology; Calcium Signaling/drug effects; Calpain/metabolism; Calpain/pharmacology; Cell Death/drug effects; Cell Line; Endoplasmic Reticulum/metabolism; Homeostasis/drug effects; Inositol 1,4,5-Trisphosphate Receptors/metabolism; Ion Channel Gating/drug effects; Ionomycin/pharmacology; Male; Proteolysis/drug effects; Purkinje Cells/metabolism; Rats; Rats, Long-Evans
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RAT:ITPR1	part_of	GO:0043231: intracellular membrane-bounded organelle	ECO:0000314: direct assay evidence used in manual assertion		C		Seeded From UniProt	complete

References

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