Lipkin S M, Nelson C A, Glass C K, Rosenfeld M G
Eukaryotic Regulatory Biology Program, School of Medicine, University of California, San Diego, La Jolla 92093-0648.
Proc Natl Acad Sci U S A. 1992 Feb 15;89(4):1209-13. doi: 10.1073/pnas.89.4.1209.
Retinoic acid receptors are ligand-dependent transcription factors that stimulate gene transcription from promoters containing retinoic acid or thyroid hormone response elements. We describe a high-affinity binding site from the rat oxytocin promoter that mediates negative transcriptional regulation by the retinoic acid receptor. To examine whether strong, constitutive transactivation domains would be capable of stimulating gene transcription when bound to this DNA binding site that normally mediates transcriptional repression, we fused the transactivation domain of the herpes simplex viral protein VP16 to the amino terminus of the retinoic acid receptor and tested the activity of the chimeric protein on the negative retinoic acid response element. This chimeric retinoic acid receptor acted as a strong, constitutive transactivator when bound to promoters containing palindromic thyroid hormone/retinoic acid response elements but surprisingly it still repressed gene transcription when bound to promoters containing the oxytocin-negative retinoic acid response element. These results suggest that a negative DNA binding site itself can inhibit the function of even potent constitutive transactivation domains, and provide evidence that tethering of a constitutive transactivation domain to DNA is insufficient to activate gene transcription.
维甲酸受体是依赖配体的转录因子，可刺激含有维甲酸或甲状腺激素反应元件的启动子进行基因转录。我们描述了大鼠催产素启动子上的一个高亲和力结合位点，它介导维甲酸受体的负转录调控。为了研究强组成型反式激活结构域与这个通常介导转录抑制的DNA结合位点结合时是否能够刺激基因转录，我们将单纯疱疹病毒蛋白VP16的反式激活结构域融合到维甲酸受体的氨基末端，并测试了嵌合蛋白对负维甲酸反应元件的活性。当与含有回文甲状腺激素/维甲酸反应元件的启动子结合时，这种嵌合维甲酸受体作为一种强组成型反式激活剂起作用，但令人惊讶的是，当与含有催产素负维甲酸反应元件的启动子结合时，它仍然抑制基因转录。这些结果表明，负DNA结合位点本身可以抑制即使是强大的组成型反式激活结构域的功能，并提供证据表明将组成型反式激活结构域与DNA连接不足以激活基因转录。
