Armbrecht H J, Chen M L, Hodam T L, Boltz M A
Geriatric Research, Education, and Clinical Center, Veterans' Affairs Medical Center, St Louis, Missouri 63125, USA.
J Endocrinol. 1997 May;153(2):199-205. doi: 10.1677/joe.0.1530199.
The biologically active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)2D), acts on intestinal, renal, and bone cells to regulate skeletal and mineral metabolism. 1,25(OH)2D also induces 24-hydroxylase activity in these target cells. The 24-hydroxylase hydroxylates 1,25(OH)2D to 1,24,25-trihydroxyvitamin D and 25(OH)D to 24,25-dihydroxyvitamin D. The production of 1,24,25-trihydroxyvitamin D is thought to be the first step in the inactivation of 1,25(OH)2D by its target tissues. Previous studies have characterized the induction of the 24-hydroxylase by 1,25(OH)2D in clonal cell lines from intestine and bone. The purpose of these studies was to characterize the induction of the 24-hydroxylase by 1,25(OH)2D in the kidney, using the clonal rat renal cell line NRK-52E. 1,25(OH)2D (10(-7)M) increased the mRNA levels for the cytochrome P450 component of the 24-hydroxylase (P450cc24) by sevenfold after 36 h in NRK-52E cells. 1,25(OH)2D increased P450cc24 mRNA levels in a dose-dependent manner with an EC50 of 10(-8) M. In parallel experiments, 1,25(OH)2D significantly increased 24-hydroxylase enzyme activity after 48-72 h. The increase in P450cc24 mRNA induced by 1,25(OH)2D required ongoing transcription and translation and was inhibited by H-7, a protein kinase C inhibitor. Tetradecanoyl phorbol acetate markedly increased the magnitude of the tissue responsiveness to 1,25(OH)2D by a protein kinase C-dependent pathway. These studies demonstrate that 1,25(OH)2D increases P450cc24 mRNA levels in NRK-52E cells by a mechanism requiring new protein synthesis and involving protein kinase C. This is in contrast to the action of 1,25(OH)2D in intestinal cells, which does not require new protein synthesis, and in osteoblastic cells, which does not involve protein kinase C.
维生素D的生物活性形式，1,25 - 二羟维生素D（1,25(OH)2D），作用于肠道、肾脏和骨细胞以调节骨骼和矿物质代谢。1,25(OH)2D还可诱导这些靶细胞中的24 - 羟化酶活性。24 - 羟化酶将1,25(OH)2D羟化为1,24,25 - 三羟维生素D，并将25(OH)D羟化为24,25 - 二羟维生素D。1,24,25 - 三羟维生素D的产生被认为是其靶组织使1,25(OH)2D失活的第一步。先前的研究已对1,25(OH)2D在来自肠道和骨骼的克隆细胞系中诱导24 - 羟化酶的过程进行了表征。这些研究的目的是利用克隆大鼠肾细胞系NRK - 52E来表征1,25(OH)2D在肾脏中诱导24 - 羟化酶的过程。在NRK - 52E细胞中，1,25(OH)2D（10^(-7)M）在36小时后使24 - 羟化酶的细胞色素P450成分（P450cc24）的mRNA水平增加了7倍。1,25(OH)2D以剂量依赖的方式增加P450cc24 mRNA水平，EC50为10^(-8) M。在平行实验中，1,25(OH)2D在48 - 72小时后显著增加了24 - 羟化酶的酶活性。1,25(OH)2D诱导的P450cc24 mRNA增加需要持续的转录和翻译，并受到蛋白激酶C抑制剂H - 7的抑制。十四酰佛波醇乙酸酯通过蛋白激酶C依赖的途径显著增加了组织对1,25(OH)2D的反应程度。这些研究表明，1,25(OH)2D通过一种需要新蛋白质合成并涉及蛋白激酶C的机制增加NRK - 52E细胞中P450cc24 mRNA的水平。这与1,25(OH)2D在肠道细胞中的作用相反，后者不需要新蛋白质合成，也与在成骨细胞中的作用相反，后者不涉及蛋白激酶C。
