Identification of a vitamin D-response element in the rat calcidiol (25-hydroxyvitamin D3) 24-hydroxylase gene.

The calcidiol (25-hydroxyvitamin D3) 24-hydroxylase is one of the key enzymes in the metabolism of vitamin D. This enzyme acts on both calcidiol and calcitriol (1,25-dihydroxyvitamin D3) to initiate degradation of these potent vitamin D metabolites and is tightly regulated. Calcitriol itself induces this enzyme and acts at the transcriptional level. Transcriptional regulation of genes by calcitriol has been shown to occur via the vitamin D-receptor binding to a vitamin D-response element located upstream of the transcription start site. We now report a vitamin D-response element located between nt -262 and nt -238 of the rat calcidiol 24-hydroxylase gene. This sequence binds the calcitriol receptor and confers vitamin D-dependent transactivation of transcription to its own, as well as heterologous, promoter.