Zinc modulates the structure and binding of the DNA binding domain of the 1 alpha,25-dihydroxyvitamin D-3 receptor to specific vitamin D response element DNA (Nature Biotechnology 16, 262-266, 1998). To determine whether zinc alters 1 alpha,25-dihydroxyvitamin D-3-regulated genes in cells, we permanently transfected rat osteoblasts with two vitamin D-dependent promoter-reporter systems and examined their responses to 1 alpha,25-dihydroxyvitamin D-3 in the presence of increasing amounts of extracellular zinc. When extracellular zinc concentrations were increased in the presence of 1 alpha,25-dihydroxyvitamin D-3, there was an increase in the activity of 1 alpha,25-dihydroxyvitamin D-3-dependent promoters with increasing concentrations of zinc. The effect was specific for zinc since metals such as copper failed to increase the activity of 1 alpha,25-dihydroxyvitamin D-3-dependent promoters. The concentration of the vitamin D receptor within the cell and the affinity of 1 alpha,25-dihydroxyvitamin D-3 for its receptor remained unchanged with added zinc. Our results show that zinc increases the activity of 1 alpha,25-dihydroxyvitamin D-3-dependent promoters in osteoblasts.