Mouse vitamin D-24-hydroxylase: Molecular cloning, tissue distribution, and transcriptional regulation by 1 alpha,25-dihydroxyvitamin D-3

Vitamin D-24-hydroxylase (24-OHase) is a cytochrome P-450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D-3 (25OHD(3)) and 1 alpha,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] to 24,25-dihydroxyvitamin D-3 and 1,24,25-trihydroxyvitamin D-3, respectively. A full-length complementary DNA for mouse 24-OHase has now been characterized. The complementary DNA consists of 3309 bp and encodes a protein of 514 amino acids that shows 82% and 95% sequence identity with the human and rat enzymes, respectively. Northern blot analysis of tissues from mice injected with 1,25-(OH)(2)D-3 (24 pmol/g) revealed that the 3.4-kb 24-OHase messenger RNA (mRNA) is most abundant in kidney and intestine, with smaller amounts present in skin, thymus, and bone. RT-PCR and Southern blot analysis detected 24-OHase mRNA in several other tissues including lung, testis, spleen, pancreas, and heart. Intraperitoneal injection of 1,25-(OH)(2)D-3 induced dose- and time-dependent increases in both 24-OHase mRNA abundance and enzyme activity in mouse kidney. Similarly, 1,25-(OH)(2)D-3-induced increases in both 24-OHase mRNA and activity were apparent in the duodenum. Although 1,25-(OH)(2)D-3 increased the amount of 24-OHase mRNA in skin, enzyme activity was not detected in this tissue. Pretreatment of mice with cycloheximide (400 mu g/g), an inhibitor of protein synthesis, potentiated the increase in 24-OHase mRNA abundance, but blocked the increase in 24-OHase activity, induced by 1,25-(OH)(2)D-3 in kidney and duodenum, suggesting that 24-OHase gene expression may be regulated not only by the vitamin D receptor but also by a short-lived repressor protein.