A novel recombinant hyperaffinity inositol 1,4,5-trisphosphate (IP3) absorbent traps IP3, resulting in specific inhibition of IP3-mediated calcium signaling

We have developed a novel recombinant hyperaffinity inositol 1,4,5-trisphosphate (IP3) absorbent, called the "IP3 sponge," which we constructed on the basis of the ligand-binding site of the mouse type 1 IP3 receptor (IP3R1). The IP3 sponge exhibited similar to1000-fold higher affinity for IP3 than the parental IP3R1 and specifically competed with the endogenous IP3R for binding to IP3-Trapping IP3 with the IP3 sponge inhibited IP3-induced Ca2+ release (IICR) from cerebellar microsomes in a dose-dependent manner. The IP3 sponge expressed in HEK293 cells also inhibited HCR in response to stimulation with carbachol or ATP. Its inhibitory effects were dependent upon the level of its expression over the increased IP3 contents. Moreover, the IP3 sponge significantly reduced the carbachol-induced phosphorylation of cAMP-response element-binding protein in HEK293 cells, indicating that the activation of cAMP-response element-binding protein by Ca2+-dependent phosphorylation may be partly attributable to IICR.