Association of Type 1 Inositol 1,4,5-Trisphosphate Receptor with AKAP9 (Yotiao) and Protein Kinase A

Inositol 1,4,5-trisphosphate receptors (InsP₃R) play a key role in intracellular calcium (Ca²⁺) signaling. Three InsP₃R isoforms are expressed in mammals. Type 1 InsP₃R (InsP₃R1) is a predominant neuronal isoform. Neuronal InSP₃R1 is one of the major substrates of protein kinase A (PKA) phosphorylation. In our previous study (Tang, T. S., Tu, H., Wang, Z., and Bezprozvanny, I. (2003) J. Neurosci. 23, 403-415) we discovered a direct association between InSP₃R1 and protein phosphatase 1α (PP1α). In functional experiments we demonstrated that phosphorylation by PKA activates InsP₃R1 and that dephosphorylation by PP1α inhibits InSP₃R1. To extend these findings, here we investigated the possibility of InsP₃R1-PKA association. In a series of biochemical experiments we demonstrate the following findings. 1) InsP₃R1 and PKA associate in the brain. 2) InsP₃R1-PKA association is mediated by the AKAP9 (Yotiao) multifunctional PKA anchoring protein. 3) InsP₃R1-AKAP9 association is mediated via the leucine/isoleucine zipper (LIZ) motif in the InSP ₃R1 coupling domain and the fourth LIZ motif in AKAP9. 4) The InSP₃R association with AKAP9 is specific for type 1 InsP ₃R. 5) Both the SII(+) and the SII(-) coupling domain splice variants of InsP₃R1 bind to AKAP9. 6) Binding to AKAP9 promotes association of neuronal InSP₃R1 with the NR1 NMDA receptor; and 7) neuronal InSP₃R1 associate with PP1 directly via carboxy-terminus and indirectly via AKAP9. The obtained results advance our understanding of cross-talk between cAMP and InsP₃/Ca²⁺ signaling pathways in the brain.