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.