Vit D and Estrogen Receptor Coactivators in Osteoblasts

描述(申请人提供)：1α，25-二羟基维生素D3(1，25OH2D3)和雌激素(E2)是类固醇激素，对正常骨骼发育和保持骨骼完整性是必不可少的。这些激素通过核受体来调节特定基因或基因网络的转录。这项提议持续的长期目标集中在定义这两个配体激活的受体调节骨骼系统中转录机制的分子机制上。这个继续的建议集中在NR共调节蛋白上，更具体地说，我们发现了一种新的共激活因子NCoA62，它参与了VDR、ER和其他NR介导的反式激活系统。最重要的是，NCoA62与其他NR共调节子无关，如SRC共激活子家族，以及人们对NCoA62的功能知之甚少。在过去4年的资助中，我们在确定NCoA62共激活的意义和潜在的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异二聚体的优先相互作用，VDR-NCoA62-SRCs之间的三元复合体的形成，以及NCoA62和SRCs在VDR激活的转录中的协同作用。这些研究表明，在VDR介导的转录中，NCoA62和不同的辅助激活蛋白之间存在密切的相互作用。根据我们过去4年的研究，我们提出了一个基本假设，即NCoA62是一种新的VDR共激活子，它与VDR-RXR异源二聚体结合在一起，并与其他NR共激活子结合，并且VDR介导的反式激活需要与每一类辅助激活子的相互作用。为了验证这一假设，我们提出了三个具体的目标，这三个目标将：(1)建立NCoA62的功能相关性或生物学意义；(2)表征NCoA62的功能结构域；(3)探索VDR-RXR异源二聚体与多个共激活子组装的分子机制。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。识别骨细胞中VDR和ER的基本转录机制所必需的新成分，最终可能为开发预防骨质疏松性骨丢失或老年人更常见的骨骼异常的新药提供分子靶点。

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.