Modulation of Type 1 Inositol (1,4,5)-Trisphosphate Receptor Function by Protein Kinase A and Protein Phosphatase 1α

Type 1 inositol (1,4,5)-trisphosphate receptors (InsP3R1s) play a major role in neuronal calcium (Ca2+) signaling. The InsP3R1s are phosphorylated by protein kinase A (PKA), but the functional consequences of InsP3R1 phosphorylation and the mechanisms that control the phosphorylated state of neuronal InsP3R1s are poorly understood. In a yeast two-hybrid screen of rat brain cDNA library with the InsP3R1-specific bait, we isolated the protein phosphatase 1α (PP1α). In biochemical experiments, we confirmed the specificity of the InsP3R1–PP1α association and immunoprecipitated the InsP3R1–PP1 complex from rat brain synaptosomes and from the neostriatal lysate. We also established that the association with PP1 facilitates dephosphorylation of PKA-phosphorylated InsP3R1 by the endogenous neostriatal PP1 and by the recombinant PP1α. We demonstrated that exposure of neostriatal slices to 8-bromo-cAMP, dopamine, calyculin A, or cyclosporine A, but not to 10 nm okadaic acid, promotes the phosphorylation of neostriatal InsP3R1 by PKA in vivo. We discovered that PKA activates and PP1α inhibits the activity of recombinant InsP3R1 reconstituted into planar lipid bilayers. We found that phosphorylation of InsP3R1 by PKA induces at least a fourfold increase in the sensitivity of InsP3R1 to activation by InsP3 without shifting the peak of InsP3R1 bell-shaped Ca2+dependence. Based on these data, we suggest that InsP3R1 may participate in cross talk between cAMP and Ca2+signaling in the neostriatum and possibly in other regions of the brain.