Nuclear translocation of the 1,25-dihydroxycholecalciferol receptor in mouse kidney

We have recently demonstrated that cytosol from mouse kidney contains a receptor-like binding protein for 1,25-dihydroxycholecalciferol (1,25-(OH)2D3). The present studies were undertaken to investigate whether this component undergoes nuclear translocation, thus adding support to the contention that this binding moiety represents a receptor for 1,25-(OH)2D3. Kidney slices from vitamin D-deficient mice were incubated with 1,25-(OH)2[3H]D3 and specific binding was assessed in cytosol and 0.3 M KCl extracts of isolated nuclei. The appearance of specific nuclear-bound 1,25-(OH)2[3H]D3 exhibited a saturation time course and the increase in nuclear binding was accompanied by a concomitant decrease in cytoplasmic binding such that, by 120 min, approximately 80% of specifically bound 1,25-(OH)2[3H]D3 was associated with the nuclear fraction and approximately 20% remained in the cytoplasmic compartment. The nuclear transfer was found to be temperature-dependent and specific for the dihydroxy metabolite. Both the cytoplasmic and nuclear receptors sedimented at 3.2 S in 0.3 M KCl sucrose density gradients. However, under low salt conditions, the cytoplasmic receptor was transformed to yield an approximately 5.4 S peak while the nuclear receptor sedimented unchanged t 3.2 S. In summary, the cytoplasmic 1,25-(OH)2D3 receptor in mammalian kidney undergoes temperature-dependent nuclear translocation and the cytoplasmic and nuclear forms of the receptor can be distinguished by their sedimentation properties.