Immunohistochemical localization of type 2 inositol 1,4,5-trisphosphate receptor to the nucleus of different mammalian cells

The inositol 1,4,5-trisphosphate receptor (InsP(3)R) is a ligand-gated Ca2+ channel responsible for the release of Ca2+ from intracellular stores in the response of a wide variety of cells to external stimuli. Molecular cloning studies have revealed the existence of three types of InsP(3)R encoded by distinct genes. In the study presented here, we used selective anti-InsP(3)R antibodies to determine the intracellular location of each InsP3R subtype in bovine aortic endothelial cells, bovine adrenal glomerulosa cells, and COS-7 cells. InsP(3)R1 was found to be widely distributed throughout the cytosol and most abundantly in the perinuclear region identified as the endoplasmic reticulum (co-localization with protein disulfide isomerase). The intracellular location of InsP(3)R3 was similar to that of InsP(3)R1. Surprisingly, InsP(3)R2 was found mostly associated to the cell nucleus. This observation was made with two antibodies recognizing different epitopes on InsP(3)R2. Binding studies revealed the presence of a high affinity-binding site for [H-3] InsP(3) on purified nuclei from bovine adrenal cortex. Confocal images showed that InsP(3)R2 was not confined to the nuclear envelope but was distributed relatively uniformly within the nucleus. Our results demonstrate that the three types of InsP(3)R are not similarly distributed within a specific cell type. Our results also suggest the existence of an intranuclear membrane network on which InsP(3)R2 is abundantly expressed. (C) 2002 Wiley-Liss, Inc.