Specific cytosol binding proteins for 25(OH)D3 and 1.25(OH)2D3 in human breast cancers

Binding proteins for 1.25 (OH) 2D3 were investigated in thirty breast cancers. Human breast cancer was shown to contain specific, high affinity cytosol binding proteins for 1.25 (OH) 2D3 and 25 (OH) D3. The binding protein for 1.25 (OH) 2D3 sedimented at 3.7 S and the binding protein for 25 (OH) D3 at about 6.0 S on sucrose density gradient analysis containing 0.3 M KCl and 1 mM dithiothreitol in buffer. Kd for 1.25 (OH) 2D3 were from 0.1 x 10(-11) M to 7.1 x 10(-11) M measured by Scatchard plots. Competition binding studies indicated that the relative specificity of the binding protein for 1.25 (OH) 2D3 much greater than 25 (OH) D3 greater than 1 alpha (OH) D3, 24,25 (OH)2D3 greater than D3 much greater than Estradiol-17 beta. 1.25 (OH) 2D3 receptor-positive was detected in twenty-eight out of thirty breast cancers.