Retinoic acid-binding protein in a human cell (MCF-7) from breast carcinoma

A specific retinoic acid-binding protein was demonstrated by sucrose density gradient centrifugation and saturation binding analysis in MCF-7 human breast cancer cells. In contrast, retinol-binding protein could not be detected in this cell line. By Scatchard analysis, this retinoic acid-binding protein was found to have a dissociation constant (Kd) of 154 nM and to bind a maximum of 14 pmoles of [3H] retinoic acid per milligram of cytoplasmic protein. Experiments with intact attached cells revealed the Kd to be 125 nM, which is very close to the value obtained for cytoplasmic extract. The binding of [3H] retinoic acid was abolished by unlabeled retinoic acid. Retinal and alpha-retinoic acid competed for binding sites but were less potent than unlabeled retinoic acid. Retinol, retinyl acetate, and the analog Ro 10-9359 showed little of no competition for the retinoic acid-binding site. A specific retinoic acid-binding protein was also demonstrated by gel electrophoresis. The presence of retinoic acid binding protein in MCF-7 cells suggests that the biologic effects of retinoic acid may be mediated by this specific protein.