Cardiac type 2 inositol 1,4,5-trisphosphate receptor - Interaction and modulation by calcium/calmodulin-dependent protein kinase II

The type 2 inositol 1,4,5-trisphosphate receptor (InsP(3)R2) was identified previously as the predominant isoform in cardiac ventricular myocytes. Here we reported the subcellular localization of InsP(3)R2 to the cardiomyocyte nuclear envelope (NE). The other major known endo/sarcoplasmic reticulum calcium-release channel ( ryanodine receptor) was not localized to the NE, indicating functional segregation of these channels and possibly a unique role for InsP(3)R2 in regulating nuclear calcium dynamics. Immunoprecipitation experiments revealed that the NE InsP(3)R2 associates with Ca2+/calmodulin-dependent protein kinase II delta (CaMKII delta), the major isoform expressed in cardiac myocytes. Recombinant InsP(3)R2 and CaMKII delta(B) also coimmunoprecipitated after co-expression in COS-1 cells. Additionally, the amino-terminal 1078 amino acids of the InsP(3)R2 were sufficient for interaction with CaMKII delta(B) and associated upon mixing following separate expression. CaMKII can also phosphorylate InsP(3)R2, as demonstrated by P-32 labeling. Incorporation of CaMKII-treated InsP(3)R2 into planar lipid bilayers revealed that InsP(3)-mediated channel open probability is significantly reduced ( similar to 11 times) by phosphorylation via CaMKII. We concluded that the InsP(3)R2 and CaMKII delta likely represent two central components of a multiprotein signaling complex, and this raises the possibility that calcium release via InsP(3)R2 in the myocyte NE may activate local CaMKII signaling, which may feedback on InsP(3)R2 function.