title: Type 1 inositol-1,4,5-trisphosphate receptor is a late substrate of caspases during apoptosis.
abstract: Apoptosis is characterized by the proteolytic cleavage of hundreds of proteins. One of them, the type 1 inositol-1,4,5-trisphosphate receptor (IP(3) R-1), a multimeric receptor located on the endoplasmic reticulum (ER) membrane that is critical to calcium homeostasis, was reported to be cleaved during staurosporine (STS) induced-apoptosis in Jurkat cells. Because the reported cleavage site separates the IP(3) binding site from the channel moiety, its cleavage would shut down a critical signaling pathway that is common to several cellular processes. Here we show that IP(3) R-1 is not cleaved in 293 cells treated with STS, TNFα, Trail, or ultra-violet (UV) irradiation. Further, it is not cleaved in Hela or Jurkat cells induced to undergo apoptosis with Trail, TNFα, or UV. In accordance with previous reports, we demonstrate that it is cleaved in a Jurkat cell line treated with STS. However its cleavage occurs only after poly(ADP-ribose) polymerase (PARP), which cleavage is a hallmark of apoptosis, and p23, a poor caspase-7 substrate, are completely cleaved, suggesting that IP(3) R-1 is a relatively late substrate of caspases. Nevertheless, the receptor is fully accessible to proteolysis in cellulo by ectopically overexpressed caspase-7 or by the tobacco etch virus (TEV) protease. Finally, using recombinant caspase-3 and microsomal fractions enriched in IP(3) R-1, we show that the receptor is a poor caspase-3 substrate. Consequently, we conclude that IP(3) R-1 is not a key death substrate.
authors.affiliation: Faculty of Medicine and Health Sciences, Department of Pharmacology, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke QC J1H 5N4, Canada.
authors.forename: Ghadi
authors.initials: G
authors.lastname: Elkoreh
authors.forename: Véronique
authors.initials: V
authors.lastname: Blais
authors.forename: Eric
authors.initials: E
authors.lastname: Béliveau
authors.forename: Gaétan
authors.initials: G
authors.lastname: Guillemette
authors.forename: Jean-Bernard
authors.initials: JB
authors.lastname: Denault
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D010450:Endopeptidases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D051381:Rats
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; D010450:Endopeptidases; C099488:TEV protease; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D002118:Calcium