New insight into the structure and functions of the vitamin D receptor.

The past 5 years has witnessed marked progress toward a higher understanding of the vitamin D endocrine system. Presently, we have a more complete picture of the VDR itself, the DNA sequences to which it binds, and the other coreceptors with which it interacts. This last feature is perhaps the most startling recent development in the vitamin D endocrine system. It clearly suggests a potential role for retinoids and their vitamin A-derived ligands in the mechanism of vitamin D action. These two fat-soluble vitamins not only have quite discrete functionalities, but they may also play requisite roles in the pathway of each other. This is particularly intriguing because the actions of vitamin D were attributed originally to vitamin A. Only later were these two vitamins functionally dissected. Now, approximately 75 years later, the emerging data suggest that selected actions of these two fat-soluble vitamins may indeed be linked.