Taft J L, Larkins R G
Biochem Biophys Res Commun. 1986 Jan 14;134(1):218-26. doi: 10.1016/0006-291x(86)90550-4.
Conversion of circulating 25-hydroxyvitamin D3 (25(OH)D3) to its active metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) occurs in the renal tubule mitochondrion. Recent reports have implicated the cytoskeleton in certain other steroid metabolizing cells as a mediator of a rate-limiting mitochondrial transport step. Whilst the activity of the renal converting enzyme, a typical steroid hydroxylase, is known to be regulated closely by a number of well studied factors, no information is available to indicate whether an analogous transport step is relevant to the regulation of vitamin D metabolism. Cytochalasin B and vinblastine were used as chemical antagonists of the microfilamentous and microtubular elements of the cytoskeleton. Both agents inhibited the conversion of 25(OH)D3 to 1,25(OH)2D3 by isolated vitamin D-deficient chick renal tubules in a dose-dependent manner. At the concentrations required to inhibit 25(OH)D3-1 alpha-hydroxylase activity in whole cells, these agents inhibited neither isolated mitochondrial 1,25(OH)2D3 production, nor 24,25(OH)2D3 synthesis by vitamin D-replete tubules. The cytoskeletal antagonists were found to increase the content of labelled 1,25(OH)2D3 and 25(OH)D3 in a mitochondrial fraction prepared by Percoll fractionation of tubule cells pre-exposed to the antagonists and labelled 25(OH)D3 substrate. The data suggest that disruption of the cytoskeleton may result in inhibition of transport of newly synthesised 1,25(OH)2D3 out of the mitochondrion and through the cell, and accumulating 1,25(OH)2D3 may oppose its further synthesis. This is consistent with a transport process mediated by the cytoskeleton being involved in the regulation of renal vitamin D metabolism.
循环中的25-羟基维生素D3（25(OH)D3）转化为其活性代谢产物1,25-二羟基维生素D3（1,25(OH)2D3）的过程发生在肾小管线粒体中。最近的报道表明，在某些其他类固醇代谢细胞中，细胞骨架作为限速线粒体转运步骤的介质发挥作用。虽然已知肾转化酶（一种典型的类固醇羟化酶）的活性受到许多深入研究的因素的密切调节，但尚无信息表明类似的转运步骤是否与维生素D代谢的调节有关。细胞松弛素B和长春碱被用作细胞骨架微丝和微管成分的化学拮抗剂。这两种药物均以剂量依赖的方式抑制了分离的维生素D缺乏雏鸡肾小管将25(OH)D3转化为1,25(OH)2D3的过程。在抑制全细胞中25(OH)D3-1α-羟化酶活性所需的浓度下，这些药物既不抑制分离的线粒体产生1,25(OH)2D3，也不抑制维生素D充足的肾小管合成24,25(OH)2D3。发现细胞骨架拮抗剂会增加通过对预先暴露于拮抗剂和标记的25(OH)D3底物的肾小管细胞进行Percoll分级分离制备的线粒体部分中标记的1,25(OH)2D3和25(OH)D3的含量。数据表明，细胞骨架的破坏可能导致新合成的1,25(OH)2D3从线粒体中转运出来并穿过细胞的过程受到抑制，而积累的1,25(OH)2D3可能会抑制其进一步合成。这与由细胞骨架介导的转运过程参与肾维生素D代谢的调节是一致的。
