Vitamin D Hormone: Function and Mechanism of Action

描述(由申请人提供)：本建议的目的是获得 更好地了解维生素D的作用，这是需要的一个主要因素 用于骨骼的发育和维护，以及用于维护 钙稳态。本续展申请书针对具体目标提出 继续研究Calbindin的功能意义，第一个 已知的维生素D作用靶标。在上一个资助期内提供的研究 Calbindin-D28k保护肿瘤坏死因子诱导的细胞死亡的首个证据 在成骨细胞中，钙结合蛋白通过结合和 抑制caspase 3。这些发现具有重要的治疗作用 影响，将继续下去。我们将确定Calbindin-D28k是否可以 防止糖皮质激素和肿瘤坏死因子诱导的骨骼细胞死亡 细胞。我们将确定Calbindin的哪个区域与caspase 3结合，以及 钙结合蛋白是否能抑制细胞远端的其他半胱氨酸酶 死亡之路。此外，我们将确定Calbindin是否也可以通过 影响其他钙调节蛋白，包括最近发现的 顶端钙通道，ECAC，与 钙结合蛋白。除了钙结合蛋白，1，25(OH)2D3的另一个已知的显著作用 在肠和肾脏中，24(OH)酶的合成增加。在具体目标2中， 为了进一步了解1，25(OH)2D3的分子机理 行动，在上一次赠款期间开始的与管制 24(OH)ASE将继续进行。在初步研究中，我们注意到CCAATT 1，25(OH)2D3诱导肾脏增强子结合蛋白β(C/EBPbeta)的表达 和成骨细胞，并可以增强转录反应 24(OH)酶为1，25(OH)2D3。有人建议进行研究来检验这种机制。 C/EBPβ、AS参与VDR介导的24(OH)酶转录调控 以及C/EBPbeta在我们观察到的 PKA信号通路和1，25(OH)2D3。这些研究将建立C/EBPbeta 作为一个新的1，25(OH)2D3靶基因，将首次表明一个角色 对于24(OH)酶转录中的C/EBPβ。建议的研究是对 在前一个资助期开始的研究与影响因素有关 24(OH)酶转录(YY1、TFIIB、DRIP205、CBP)及其信号转导效应 24(OH)酶转录和辅因子募集途径。这项提议， 它结合了与理解功能相关的研究 靶蛋白的意义以及与分子相关的研究 1，25(OH)2D3的作用机理，将为深入了解其作用机理提供新的思路 维生素D通过哪些途径介导其生物学效应以及如何异常调节 可能与骨质疏松症等疾病有关。

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 continue studies related to the functional significance of calbindin, the first known target of vitamin D action. Studies in the previous grant period provided the first evidence that calbindin-D28k protects against TNF-induced cell death in osteoblasts and that calbindin protects against cell death by binding to and inhibiting caspase 3. These findings, which have important therapeutic implications, will be continued. We will determine whether calbindin-D28k can protect against glucocorticoid, as well as TNF-induced cell death in bone cells. We will determine which region of calbindin binds to caspase 3, and whether calbindin can inhibit other caspases in the distal portion of the cell death pathway. In addition, we will determine whether calbindin can also act by affecting other calcium regulatory proteins, including the recently identified apical calcium channel, ECaC, which is colocalized in the same cells as calbindin. Besides calbindin, the other known pronounced effect of 1,25(OH)2D3 in intestine and kidney is increased synthesis of 24(OH)ase. In Specific Aim 2, in order to obtain further insight into the molecular mechanism of 1,25(OH)2D3 action, studies begun in the last grant period related to the regulation of 24(OH)ase will be continued. In preliminary studies, we have noted that CCAATT enhancer binding protein beta (C/EBPbeta) is induced by 1,25(OH)2D3 in kidney and osteoblastic cells and can enhance the transcriptional response of 24(OH)ase to 1,25(OH)2D3. Studies are proposed to examine the mechanisms involved in modulation of VDR-mediated 24(OH)ase transcription by C/EBPbeta, as well as the role of C/EBPbeta in the cross-talk we have observed between the PKA signaling pathway and 1,25(OH)2D3. These studies would establish C/EBPbeta as a novel 1,25(OH)2D3 target gene and would indicate for the first time a role for C/EBPbeta in 24(OH)ase transcription. The proposed studies complement the studies begun in the previous grant period related to the factors that affect 24(OH)ase transcription (YY1, TFIIB, DRIP205, CBP) and the effect of signaling pathways on 24(OH)ase transcription and cofactor recruitment. This proposal, which combines studies related to an understanding of 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.