Murayama A, Takeyama K, Kitanaka S, Kodera Y, Hosoya T, Kato S
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Biochem Biophys Res Commun. 1998 Aug 10;249(1):11-6. doi: 10.1006/bbrc.1998.9098.
25-Hydroxyvitamin D3 1 alpha-hydroxylase (1 alpha-hydroxylase) catalyzes hydroxylation, mainly in the kidney, of 25-hydroxyvitamin D3 [25(OH)D3] into 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], a hormonal form of vitamin D, acting as a key enzyme of vitamin D biosynthesis. Reflecting its biological significance, this enzymatic activity is differentially regulated by several factors involving calcium homeostasis, though the molecular mechanism is poorly understood. In our recent study (K. Takeyama, et al., 1997), we cloned the cDNA of mouse 1 alpha-hydroxylase, and this led us to investigate the regulation of gene expression and the function of the promoter of this gene. Here we report the isolation of the 5' flanking region of the human 1 alpha-hydroxylase gene and the identification of the human 1 alpha-hydroxylase promoter by a primer extension assay. We found that in the identified promoter, a positively regulatory region to parathyroid hormone (PTH) and calcitonin and a negatively regulatory region to 1 alpha,25(OH)2D3 are located around -4 and -0.5 kb, respectively. Thus, we provide direct evidence that the positive and negative regulation of 1 alpha-hydroxylase gene expression by hormones takes place at transcriptional levels through two distinct promoter regions.
25-羟基维生素D3 1α-羟化酶（1α-羟化酶）主要在肾脏中催化25-羟基维生素D3[25(OH)D3]羟基化为1α,25-二羟基维生素D3[1α,25(OH)2D3]，后者是维生素D的一种激素形式，该酶是维生素D生物合成的关键酶。尽管其分子机制尚不清楚，但鉴于其生物学意义，这种酶活性受到涉及钙稳态的多种因素的差异调节。在我们最近的研究（K. Takeyama等人，1997年）中，我们克隆了小鼠1α-羟化酶的cDNA，这促使我们研究该基因的表达调控及其启动子的功能。在此，我们报告了人类1α-羟化酶基因5'侧翼区域的分离以及通过引物延伸试验对人类1α-羟化酶启动子的鉴定。我们发现，在所鉴定的启动子中，甲状旁腺激素（PTH）和降钙素的正调控区域以及1α,25(OH)2D3的负调控区域分别位于约-4 kb和-0.5 kb处。因此，我们提供了直接证据，表明激素对1α-羟化酶基因表达的正负调控是通过两个不同的启动子区域在转录水平上发生的。
