Vitamin D Hormone: Function and Mechanism of Action

描述（由申请人提供）：本提案的目的是更好地了解维生素D的作用，维生素D是骨骼发育和维持以及钙稳态维持所需的主要因素。该更新申请在具体目标I中提出，使用最近产生的TRPV 6和钙结合蛋白-D9 k缺失小鼠来检查最近鉴定的维生素D响应性肠钙通道TRPV 6的功能意义以及肠钙结合蛋白的功能意义。建议进行研究以检查TRPV 6或钙结合蛋白-D9 k的完全消融对1，25（OH）2D 3调节的肠钙吸收和在低膳食钙条件下对主动钙转运的影响。将检查在TRPV 6敲除（KO）小鼠或钙结合蛋白-D9 k KO小鼠中观察到的钙稳态改变中涉及的补偿和相互作用机制。还提出了研究1，25（OH）2D 3调节肠道TRPV 6基因表达的机制。将产生缺乏TRPV 6和钙结合蛋白-D9 k的小鼠以确定双KO小鼠是否将显示更明显的表型。对这些KO小鼠的研究将使人们对肠钙转运的基本机制有新的认识，这些机制自30多年前发现钙结合蛋白以来一直不完整。在特定目标II中，将继续进行在上一个资助期开始的与24（OH）ase调节相关的研究，24（OH）ase是1，25（OH）2D 3的另一个主要目标。在初步研究中，我们注意到SWI/SNF，它使用ATP水解的能量来重塑染色质，是1，25（OH）2D 3诱导24（OH）ase转录的重要决定因素。本研究拟探讨SWI/SNF在VDR介导的转录中的作用、VDR、CBP、C/EBP B和SWI/SNF之间串扰的分子事件动力学以及与分子事件动力学相关的细胞类型和VDR靶基因特异性。这些拟议的研究补充了在前一个资助期开始的与影响24（OH）ase转录（C/EBP（3，CBP，YY 1和DRIP 205）的因素相关的研究。该提案将与靶蛋白的功能意义相关的研究与1，25（OH）2D 3作用的分子机制相关的研究相结合，将为维生素D介导其生物学效应的机制以及异常调节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.