Tissue-Specific Regulatory Effects of Vitamin D and Its Receptor on Calbindin-D28K and Calbindin-D9K

The balance between calcium and vitamin D is essential in mammalian development. Calbindin-D28K (CaBP-28K) and calbindin-D9K (CaBP-9K) are cytosolic vitamin D– dependent calcium-binding proteins that mediate the dynamic equilibrium of vitamin D and calcium, particularly in the absorption of intestinal calcium, in urinary calcium excretion, and in bone formation. However, the precise roles of CaBP-28K and CaBP-9K are not well understood. CaBP-9K/CaBP-28K double-knockout (KO) mice have a normal phenotype under conditions of normal dietary intake of calcium. Conversely, when given a calciumdeficient diet, these double-KO mice have greater reductions in serum calcium levels and bone length than do wild-type mice. In this review, we summarize and interpret the body of literature regarding the relationship of vitamin D and its receptor with CaBP-28K and CaBP-9K in mammals.