Demonstration of a 1,25-Dihydroxycholecalciferol Cytoplasmic Receptor-Like Binder in Mouse Kidney

Isolated mouse renal tubule cells have been employed to demonstrate the presence of a specific high affinity cytoplasmic binding protein for 1,25-dihydroxycholecalciferol (1,25(OH)2D3) in kidney. This receptor-like macromolecule sedimented at 3.2 S in hypertonic sucrose density gradients. Scatchard analysis of [3H]1,25-(OH)2D3 binding at O C revealed an apparent Kd of 0.2 nM and a concentration of binding sites of 50 fmol/mg cytosol protein. In competition experiments, the binder exhibited a low affinity for other vitamin D3 metabolites; the order of potency was 1,25(OH)2D3 greater than 250HD3 greater than u alpha OHD3 greater than 24R,25(OH)2D3. The sedimentation properties, binding affinity, and specificity of this 1,25(OH)2D3 binding protein are strikingly similar to the receptors in rat intestine, mouse bone, and human intestine. The demonstration of a renal receptor-like binder adds further support to the concept that the kidney is a 1,25(OH)2D3 target organ.