The mechanism of transcriptional repression by the nuclear hormone receptor in the preceuse of hormones by using vitamin D receptor as a model system

通过将PTHrP基因中的负维生素反应元件(NVDRE)导入培养细胞，我们获得了以下结果。1)染色质免疫沉淀(ChIP)分析表明，维生素D将维生素D受体(VDR)和组蛋白脱乙酰基酶2(HDAC2)募集到转基因和内源性PTHrP基因中含有nVDRE的染色质上。2)只有在缺乏维生素D的情况下，HDAC1、乙酰化组蛋白3(AcH3)和乙酰化组蛋白4(AcH4)才被招募到nVDRE区域。这些结果以及我们使用HDAC抑制剂的实验表明，维生素D通过脱乙酰化nVDRE区域周围的染色质来抑制nVDRE基因的表达。3)在随后的免疫沉淀实验中，我们发现VDR与HDAC2以维生素D依赖的方式相互作用。4)此外，我们还通过类似的芯片分析发现，雌激素将雌激素受体和HDAC2募集到含有nVDRE的同一染色质区域。同样，HDAC1、AcH3和AcH4只有在没有雌激素的情况下才被招募。这些结果表明，存在一种共同的机制，通过配基的核激素受体进行负基因调控。

By introducing the negative vitamin response element (nVDRE) in the PTHrP gene into the cultured cells, we obtained the following results. 1) Chromatin immunoprecipitation (ChIP) assay revealed that vitamin D recruited VDR (vitamin D receptor) and HDAC2 (histone deacetylase 2) to the nVDRE-containing chromatin both in the transfected and endogenous PTHrP genes. 2) HDAC1, acetylated histone3 (AcH3) and acetylated histone 4 (AcH4) were recruited to the nVDRE region only in the absence of vitamin D. These results together with our experiments using a HDAC inhibitor suggested vitamin D repressed the expression of the nVDRE-containing gene through deacetylation of the chromatin surrounding the nVDRE region. 3) In the subsequent immunoprecipitation assay, we found that VDR interacted with HDAC2 in a vitamin D-dependent manner. 4) Further, we also found that estrogen recruited estrogen receptor and HDAC2 to the same nVDRE-containing chromatin region by using similar ChIP assay. Likewise, HDAC1, AcH3 and AcH4 were recruited only in the absence of estrogen. These results suggest that there exists a common machinery for negative gene regulation by the liganded nuclear hormone receptors.