Intracellular Localization and Translocation of 1α, 25-Dihydroxyvitamin D₃ Receptor in Osteoblasts

抄録

The intracellular localization and translocation of the 1α, 25-dihydroxyvitamin D₃ receptor (1α, 25(OH)₂D₃ receptor) in osteoblasts of mouse parietal bone and MC3T3-E1 cells were examined immunocytochemically using a rat monoclonal antibody to 1α, 25(OH)₂D₃ receptor. In osteoblasts of parietal bones in vivo, immunoreactivity for 1α, 25(OH)₂D₃ receptor was detected not only in the nuclei but also in lysosomal structures, and also sparsely in the cytoplasmic matrix. The transport of 1α, 25(OH)₂D₃ receptor was investigated immunocytochemically after incubation with 1α, 25(OH)₂ D₃. In osteoblasts of parietal bones, after 1min incubation with 10^-8M 1α, 25(OH)2D₃, the perinuclear cytoplasm showed intense immunoreactivity for 1α, 25(OH)₂ D₃ receptor. After 10min incubation, immunoreactivity was intense in the nuclei, especially in the heterochromatin. In MC3T3-E1 cells, after 1min incubation with 1α, 25(OH)₂D₃, immunoreactivity for 1α, 25(OH)₂ D₃ receptor was found in the form of a fibrillar structure extending radially to the periphery of the cells. The immunostaining pattern of anti-1α, 25(OH)₂D₃ receptor was similar to the distribution of microtubules stained with anti-β-tubulin antibody. After 10min incubation, the nuclei showed intense immunoreactivity for 1α, 25(OH)₂D₃ receptor. Incubation with colchicine dissociated the fibrillar structures and inhibited the intranuclear localization of the 1α, 25(OH)₂D₃ receptor. These findings suggest that the 1α, 25(OH)₂D₃ receptor is located in the nuclei, in lysosomal structures and also sparsely in the cytoplasmic matrix of osteoblasts in vivo, and that the receptor is transported to the perinuclear cytoplasm via microtubules to be then translocated into the nucleus, especially into the heterochromatin.