Vitamin D receptor interaction with specific DNA requires a nuclear protein and 1,25-dihydroxyvitamin D3

The regulation of osteocalcin gene expression by 1,25-dihydroxyvitamin D3 is mediated by the vitamin D receptor and a cis-acting DNA response element that has been identified within the 5' region of the osteocalcin promoter. In this report, we show that vitamin D receptors derived from nuclear extracts of mammalian cells bind directly to this cis-acting element in vitro and do so in a manner requiring hormone. Vitamin D receptors derived from reticulocyte lysate translations in vitro or from extracts of a Saccharomyces cerevisiae strain that expresses the recombinant protein also bind the osteocalcin responsive element, but only when nuclear extracts of mammalian cells are provided. The vitamin-D-receptor-DNA-binding accessory factor is isolated by salt extraction, labile to temperature, and sensitive to tryptic digestion. These studies suggest that the high-affinity interaction of the vitamin D receptor with the osteocalcin vitamin D response element in vitro requires both 1,25-dihydroxyvitamin D3 and an accessory protein derived from the mammalian cell nucleus.