Aarnisalo Piia, Kim Chae-Hee, Lee Jae Woon, Perlmann Thomas
Ludwig Institute for Cancer Research, Karolinska Institute, Stockholm, Sweden SE 171 77.
J Biol Chem. 2002 Sep 20;277(38):35118-23. doi: 10.1074/jbc.M201707200. Epub 2002 Jul 18.
Nurr1, an orphan nuclear receptor mainly expressed in the central nervous system, is essential for the development of the midbrain dopaminergic neurons. Nurr1 binds DNA as a monomer and exhibits constitutive transcriptional activity. Nurr1 can also regulate transcription as a heterodimer with the retinoid X receptor (RXR) and activate transcription in response to RXR ligands. However, the specific physiological roles of Nurr1 monomers and RXR-Nurr1 heterodimers remain to be elucidated. The aim of this study was to define structural requirements for RXR-Nurr1 heterodimerization. Several amino acid substitutions were introduced in both Nurr1 and RXR in the I-box, a region previously shown to be important for nuclear receptor dimerization. Single amino acid substitutions introduced in either Nurr1 or RXR abolished heterodimerization. Importantly, heterodimerization-deficient Nurr1 mutants exhibited normal activities as monomers. Thus, by introducing specific amino acid substitutions in Nurr1, monomeric and heterodimeric properties of Nurr1 can be distinguished. Interestingly, substitutions in the RXR I-box differentially affected heterodimerization with Nurr1, retinoic acid receptor, thyroid hormone receptor, and constitutive androstane receptor demonstrating that the dimerization interfaces in these different heterodimers are functionally unique. Furthermore, heterodimerization between RXR and Nurr1 had a profound influence on the constitutive activity of Nurr1, which was diminished as a result of RXR interaction. In conclusion, our data show unique structural and functional properties of RXR-Nurr1 heterodimers and also demonstrate that specific mutations in Nurr1 can abolish heterodimerization without affecting other essential functions.
Nurr1是一种主要在中枢神经系统表达的孤儿核受体，对中脑多巴胺能神经元的发育至关重要。Nurr1作为单体与DNA结合并表现出组成型转录活性。Nurr1还可以与视黄酸X受体（RXR）形成异二聚体来调节转录，并响应RXR配体激活转录。然而，Nurr1单体和RXR-Nurr1异二聚体的具体生理作用仍有待阐明。本研究的目的是确定RXR-Nurr1异二聚化的结构要求。在I-box区域的Nurr1和RXR中都引入了几个氨基酸替换，该区域先前已被证明对核受体二聚化很重要。在Nurr1或RXR中引入的单个氨基酸替换消除了异二聚化。重要的是，缺乏异二聚化能力的Nurr1突变体作为单体表现出正常活性。因此，通过在Nurr1中引入特定的氨基酸替换，可以区分Nurr1的单体和异二聚体特性。有趣的是，RXR I-box中的替换对与Nurr1、视黄酸受体、甲状腺激素受体和组成型雄烷受体的异二聚化有不同的影响,表明这些不同异二聚体中的二聚化界面在功能上是独特的。此外，RXR和Nurr1之间的异二聚化对Nurr1的组成型活性有深远影响，由于RXR相互作用，该活性降低。总之，我们的数据显示了RXR-Nurr1异二聚体独特的结构和功能特性，也证明了Nurr1中的特定突变可以消除异二聚化而不影响其他基本功能。
