ATP modulation of Ca2+ release by type-2 and type-3 InsP3R: Differing ATP sensitivities and molecular determinants of action

Authors:
Betzenhauser MJ, Wagner LE 2nd, Iwai M, Michikawa T, Mikoshiba K, Yule DI
In:
Source: J Biol Chem
Publication Date: (2008)
Issue: 283(31): 21579-87
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
DT40
Species: chicken
Tissue Origin: blood
Platform:
Nucleofectorâ„¢ I/II/2b
Abstract
ATP enhances Ca2+ release from inositol (1,4,5)-trisphosphate receptors (InsP3R). However, the three isoforms of InsP3R are reported to respond to ATP with differing sensitivities. Ca2+ release through InsP3R1 is positively regulated at lower ATP concentrations than InsP3R3, and InsP3R2 has been reported to be insensitive to ATP modulation. We have re-examined these differences by studying the effects of ATP on InsP3R2 and InsP3R3 expressed in isolation on a null background in DT40 InsP3R-knockout cells. We report that the Ca2+ releasing activity, as well as the single channel open probability of InsP3R2 was enhanced by ATP, but only at sub-maximal InsP3 levels. Further, InsP3R2 was more sensitive to ATP modulation than InsP3R3 under similar experimental conditions. Mutations in the ATPB sites of InsP3R2 and InsP3R3 were generated and the functional consequences of these mutations were tested. Surprisingly, mutation of the ATPB site in InsP3R3 had no effect on ATP modulation suggesting an additional locus for the effects of ATP on this isoform. In contrast, ablation of the ATPB site of InsP3R2 eliminated the enhancing effects of ATP. Furthermore, this mutation had profound effects on the patterns of intracellular calcium signals, providing evidence for the physiological significance of ATP binding to InsP3R2.