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 calci diol and calcitriol (1,25-dihydroxyvitamin D3) to initiate degradation of these potent vitamin D metabolites and is tightly regulated. Calci triol 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 eleme nt located upstream of the transcription start site. We now report a v itamin D-response element located between nt -262 and nt -238 of the r at calcidiol 24-hydroxylase gene. This sequence binds the calcitriol r eceptor and confers vitamin D-dependent transactivation of transcripti on to its own, as well as heterologous, promoter.