REGULATION OF VITAMIN D RECEPTOR GENE EXPRESSION

活性激素1，25-二羟基维生素D3[1，25(OH)2D3]，作用于靶点 通过与特定的维生素D受体(VDR)结合。规模的大小 1，25(OH)2D3引起的反应直接依赖于 VDR的浓度又受多种因素的调节。 这笔赠款的前提是VDR基因表达的调节是 一种关键机制，调节目标细胞对 1，25(OH)3D3以细胞特有的方式。VDR表达的调节可能是 在转录或转录后水平上。这种细胞特有的 适应机制使不同器官的反应 差动调制到1，25(OH)2D#的一般循环水平。 这项拨款建议探索维生素D受体基因的几类调控因素。 主要在人体组织中表达，主要在肠道和骨骼中表达 作为关键的目标细胞。大多数研究将在培养细胞中进行 但使用手术中取出的大鼠和人体组织进行的实验也是 有计划的。初步数据显示，所有监管机构都将 研究实质上调制了各种目标中VDR的数量 细胞。有待研究的调节剂包括：1)糖皮质激素，通过 肠道和骨骼中VDR和抗维生素D作用的下调可能 导致糖皮质激素引起的骨质疏松症。2)雌激素，通过 肠道和骨骼中VDR的上调可能有助于维持 正常骨骼，一种在绝经期丢失时可能有助于 骨质疏松。3)血清和生长因子(EGF、IGF-1、胰岛素) 促进细胞增殖，上调VDR水平。4) 蛋白激酶C的激活剂，包括佛波酯，可增加细胞 增殖，但将VDR降至基础水平，并抑制血清和生长 因子上调调节。5)包括cAMP在内的蛋白激酶A激活剂 它们比血清和生长因子更能上调VDR。6) 促降钙激素PTH和PTH-RP通过刺激作用于细胞 蛋白激酶A和C具有重要的VDR调节活性。 VDR的调节机制将从多个层面进行研究 包括VDR的丰度、亲和力和半衰期的变化 蛋白质、VDR mRNA的积聚和转录速率。的研究 VDR基因5‘上游区域将使用VDR启动子-CAT 报告质粒转染多个靶细胞进行检测 在分子水平上调节VDR基因表达的调控元件 水平。 该研究计划的长期目标包括开发一种 对VDR基因表达调控因素的认识及其意义 这种调控发生的分子机制。由于VDR是 受多种激素和因素的调节，对此的调节 关键基因是研究生物大分子相互作用的理想模型系统 这些因素调控着VDR的表达。除了……之外 理解1，25(OH)2D3在经典领域的作用机制 钙稳态，这笔赠款还将探索扩大的范围 维生素D的作用，因为它与调节细胞生长和 受VDR调制影响的分化。

The active hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], acts in target cells by binding to specific vitamin D receptors (VDR). The magnitude of the response elicited by 1,25(OH)2D3 is directly dependent on the concentration of VDR which, in turn, is regulated by a variety of factors. The premise of this grant is that the regulation of VDR gene expression is a critical mechanism that modulates the responsiveness of target cells to 1,25(OH)3D3 in a cell-specific manner. Regulation of VDR expression may be at the transcriptional or post-transcriptional level. This cell-specific mechanism of adaptation allows the response of the various organs to be differentially modulated to a general circulating level of 1,25(OH)2D#. This grant proposes to explore several categories of regulators of VDR gene expression, predominantly in human tissues, focusing on intestine and bone as critical target cells. Most studies will be performed in cultured cells but experiments using rat and human tissue removed at surgery are also planned. Preliminary data indicate that all of the regulators to be investigated substantially modulate the number of VDR in various target cells. The regulators to be studied include: 1) Glucocorticoids, which by down-regulation of VDR and anti-vitamin D action sin intestine and bone may contribute to glucocorticoid-induced osteoporosis. 2) Estrogens, which by up-regulation of intestinal and bone VDR may contribute to maintaining normal bone, a mechanism which when lost at the menopause may contribute to osteoporosis. 3) Serum and growth factors (EGF, IGF-1, Insulin) which increase cell proliferation as well as up-regulating VDR levels. 4) Activators of protein kinase C including phorbol esters which increase cell proliferation but decrease VDR to basal levels and inhibit serum and growth factor-up regulation. 5) Activators of protein kinase A including cAMP which up-regulate VDR even more than serum and growth factors. 6) Calcitropic hormones PTH and PTH-RP, which act on cells by stimulating protein kinase A and C and have important VDR regulatory activity. The mechanism of VDR regulation will be investigated at multiple levels including changes in the abundance, affinity and half-life of the VDR protein, accumulation of VDR mRNA and rate of transcription. Studies of the 5' upstream region of the VDR gene will employ a VDR promoter-CAT reporter plasmid transfected into various target cells to allow examination of the regulatory elements that modulate VDR gene expression at a molecular level. The long range goals of this research program included developing an understanding of the factors that regulate VDR gene expression and the molecular mechanisms by which that regulation takes place. Since VDR is regulated by a variety of hormones and factors, the regulation of this critical gene is an ideal model system for the study of the interactions of these factors as they regulate the expression of VDR. In addition to understanding the mechanism of 1,25(OH)2D3 action in the classic sphere of calcium homeostasis, this grant will also explore the expanded scope of vitamin D action as it relates to regulation of cell growth and differentiation as influenced by VDR modulation.