Activation of the 1,25-Dihydroxyvitamin D₃ Receptor in Cultured Rat Osteogenic Sarcoma Cells

Abstract

Activation of the 1,25-dihydroxyvitamin D³, [1,25(OH)₂D₃] receptor-hormone complex was studied in-vitro using cytosolic preparations of rat osteogenic sarcoma cell ROS 17/2-8 and a DNA-cellulose assay. We found that salt was required for extraction of the unoccupied receptor indicating its possible nuclear localization. The 1,25(OH)₂D₃ receptor underwent an activation process similar to other steroid hormones which could be stimulated by heat and salt. At physiological ionic strength 100% of the complexes were, however, activated at 2°C, indicating that the activation process is not absolutely temperature dependent. In contrast to other steroid hormones, 30-50% of the complexes were in an activated state in the absence of heat and salt moreover, alkaline phosphatase and ammonium sulphate had no effect on activation. Activation was also stimulated by ATP and ATP plus 8BrcAMP indicating the possible role of phosphorylation in the activation process; however, further work is required to clarify this point.