Vitamin D Hormone: Function and Mechanism of Action

描述(由申请人提供)：本建议的目的是为了更好地了解维生素D的作用，维生素D是骨骼发育和维持以及维持钙稳态所必需的主要因素。这一新的申请提出了专门的目的I，利用最近产生的TRPV6和Calbindin-D9k缺失小鼠，检查最近发现的维生素D反应的肠道钙通道TRPV6的功能意义，以及肠道钙结合素的功能意义。本研究旨在研究完全阻断TRPV6或Calbindin-D9k对1，25(OH)2D3调节的肠道钙吸收的影响，以及在低钙饮食条件下对主动钙转运的影响。在TRPV6基因敲除(KO)小鼠或Calbindin-D9k KO小鼠中观察到的钙稳态改变所涉及的代偿和相互作用机制将被研究。还建议研究1，25(OH)2D3调节肠道TRPV6基因表达的机制。将产生同时缺乏TRPV6和Calbindin-D9k的小鼠，以确定双KO小鼠是否会表现出更明显的表型。对这些KO小鼠的研究将导致对涉及肠道钙转运的基本机制的新见解，自30多年前发现钙结合蛋白以来，这些机制一直不完整。在具体目标II中，将继续开展在上一批赠款期间开始的与调节24(OH)酶有关的研究，这是1，25(OH)2D3的另一个主要目标。在初步研究中，我们注意到SWI/SNF是1，25(OH)2D3诱导24(OH)酶转录的重要决定因素，它利用ATP水解的能量来重塑染色质。研究包括SWI/SNF在VDR介导的转录中的作用，VDR、CBP、C/EBPB和SWI/SNF之间相互作用的分子事件的动力学，以及与分子事件动力学相关的细胞类型和VDR靶基因的特异性。这些拟议的研究补充了前一批赠款期间开始的有关影响24(OH)酶转录的因素的研究(C/EBP(3，CBP，YY1和DRIP205))。这一建议结合了与靶蛋白功能意义相关的研究和与1，25(OH)2D3作用的分子机制相关的研究，将为维生素D介导其生物学效应的机制以及异常调控如何参与骨质疏松症等疾病提供新的见解。

DESCRIPTION (provided by applicant): The object of this proposal is to obtain a better understanding of the actions of vitamin D, a principal factor required for the development and maintenance of bone as well as for maintenance of calcium homeostasis. This renewal application proposes in specific aim I to examine the functional significance of the recently identified vitamin D responsive intestinal calcium channel TRPV6, as well as the functional significance of intestinal calbindin, using recently generated TRPV6 and calbindin-D9k null mice. Studies are proposed to examine the effect of complete ablation of TRPV6 or calbindin-D9k on 1,25(OH)2D3 regulated intestinal calcium absorption and on active calcium transport under low dietary calcium conditions. Compensatory and reciprocal mechanisms involved in the alterations in calcium homeostasis observed in the TRPV6 knockout (KO) mouse or the calbindin-D9k KO mouse will be examined. Studies are also proposed to examine the mechanisms by which 1,25(OH)2D3 regulates intestinal TRPV6 gene expression. Mice lacking both TRPV6 and calbindin-D9k will be generated to determine whether double KO mice will display a more pronounced phenotype. Studies with these KO mice will result in new insight into basic mechanisms involved in intestinal calcium transport that have remained incomplete since the discovery of calbindin over 30 years ago. In specific aim II studies begun in the last grant period related to the regulation of 24(OH)ase, the other major target of 1,25(OH)2D3, will be continued. In preliminary studies we noted that SWI/SNF, which uses the energy of ATP hydrolysis to remodel chromatin, is an important determinant of 1,25(OH)2D3 induced 24(OH)ase transcription. Studies are proposed to examine the role of SWI/SNF in VDR mediated transcription, the kinetics of the molecular events in the cross talk between VDR, CBP, C/EBP B and SWI/SNF as well as cell type and VDR target gene specificity related to the kinetics of the molecular events. These proposed studies complement studies begun in the previous grant period related to the factors that affect 24(OH)ase transcription (C/EBP (3, CBP, YY1 and DRIP205). This proposal, which combines studies related to the functional significance of target proteins with studies related to the molecular mechanism of 1,25(OH)2D3 action, will provide new insight into the mechanisms by which vitamin D mediates its biological effects and how aberrant regulation may be involved in diseases such as osteoporosis.