Vit D and Estrogen Receptor Coactivators in Osteoblasts

描述（由申请人提供）：α，25 -二羟基维生素D3 （1,25 oh2d3）和雌激素（E2）是类固醇激素，对正常骨骼发育和维持骨骼完整性至关重要。这些激素通过核受体发挥作用，调节特定基因或基因网络的转录。本研究的长期目标是确定这两种配体激活受体调节骨骼系统转录机制的分子机制。这篇续篇的建议侧重于NR调节蛋白，更具体地说，我们发现了一种新的共激活剂NCoA62，它参与了VDR-， ER-和其他NR介导的转激活系统。最重要的是，NCoA62与SRC家族共激活剂等其他NR调节性物质无关，而且人们对NCoA62发挥作用的机制知之甚少。在过去4年的资助中，我们在确定NCoA62共激活的意义和潜在分子机制方面取得了相当大的进展。最重要的发现包括NCoA62与VDR-RXR异源二聚体的优先相互作用，vdr -NCoA62- src之间形成三元配合物，以及NCoA62和src在vdr激活转录中的协同作用。这些研究表明，在vdr介导的转录中，NCoA62与不同的辅激活蛋白之间存在密切的相互作用。基于我们过去4年的项目研究，我们提出了一个一般假设，即NCoA62是一种新型的VDR共激活剂，它与VDR- rxr异源二聚体结合，并与其他NR共激活剂结合，并且与每个共激活剂类的相互作用是VDR介导的交易激活所必需的。为了验证这一假设，我们提出了三个具体目标：(1)建立NCoA62的功能相关性或生物学意义；(2)表征NCoA62的功能域；(3)利用VDR-RXR异源二聚体探讨多共激活剂组装的分子机制。这些研究旨在提高我们对骨骼中维生素D和雌激素依赖性转录的基本机制的理解，并将确定参与这一复杂过程的重要转录因子。鉴定对骨细胞中VDR和ER的基本转录机制至关重要的新成分可能最终为开发新型药物提供分子靶标，以防止骨质疏松性骨质流失，或在老年人中观察到的更普遍的骨骼异常。

DESCRIPTION (provided by applicant): 1alpha, 25-dihydroxyvitamin D3 (1,25OH2D3) and estrogen (E2) are steroid hormones that are essential for normal skeletal development, and for maintaining bone integrity. These hormones function through nuclear receptors to regulate the transcription of specific genes or gene networks. The continuing long-term goal of this proposal centers on defining the molecular mechanisms through which these two ligand-activated receptors regulate the transcription machinery in the skeletal system. This continuation proposal focuses on NR comodulatory proteins and, more specifically, on our discovery of a novel coactivator, NCoA62, that is involved in VDR-, ER-, and other NR-mediated transactivation systems. Most importantly, NCoA62 is unrelated to other NR comodulators, such as the SRC family of coactivators, and the mechanisms through which NCoA62 functions are poorly understood. In the past 4 years of funding, we have made considerable progress in defining the significance and potential molecular mechanisms involved in NCoA62 coactivation. The most significant findings include the preferential interaction of NCoA62 with the VDR-RXR heterodimer, ternary complex formation between VDR-NCoA62-SRCs, and the cooperative effects of NCoA62 and SRCs in VDR-activated transcription. These studies imply an intimate interplay between NCoA62 and distinct coactivator proteins in VDR-mediated transcription. On the basis of our past 4 years on this project, we propose the general hypothesis that NCoA62 is a novel VDR coactivator that associates with the VDR-RXR heterodimer in association with other NR coactivators, and the interaction with each coactivator class is required for VDR-mediated transactivation. To test this hypothesis, we propose three Specific Aims that will: (1) establish the functional relevance or biological significance of NCoA62; (2) characterize functional domains of NCoA62; and (3) probe the molecular mechanisms of multi-coactivator assemblies with the VDR-RXR heterodimer. These studies are designed to improve our understanding of the fundamental mechanisms involved in vitamin D- and estrogen-dependent transcription in bone, and they will define important transcriptional factors involved in this complex process. Identifying novel components that are essential to the basic transcriptional mechanisms of VDR and ER in bone cells may eventually provide molecular targets to develop novel drugs that protect against osteoporotic bone loss, or the more general skeletal abnormalities observed in the elderly.