Nurr1/NR4A2 is an orphan nuclear receptor transcription factor implicated as a potential drug target for neurological disorders including Alzheimer's and Parkinson's diseases. Previous studies identified small molecule modulators of NR4A nuclear receptors including Nurr1 and Nur77/NR4A1; it remains unclear whether these ligands affect Nurr1 through direct binding or indirect non-binding mechanisms. We assessed a panel of twelve ligands reported to affect NR4A activity for Nurr1-dependent and Nurr1-independent transcriptional effects and binding to the Nurr1 ligand-binding domain (LBD). Most of the NR4A ligands show Nurr1-independent effects on transcription in a cell type-specific manner, suggesting they may function through binding to effector proteins whose downstream activities influence Nurr1 function. Protein NMR spectroscopy structural footprinting data show that 4-amino-7-chloroquinoline derivatives (amodiaquine and chloroquine) and cytosporone B directly bind the Nurr1 LBD. In contrast, other NR4A ligands including commercially available compounds such as C-DIM12, celastrol, camptothecin, IP7e, isoalantolactone, and TMPA do not bind the Nurr1 LBD. Interestingly, previous crystal structures indicate that cytosporone B analogs bind to surface pockets in the Nur77 LBD, but protein NMR data indicate cytosporone B likely binds to the Nurr1 orthosteric pocket. These findings should influence medicinal chemistry efforts that desire to optimize Nurr1-binding ligands as opposed to ligands that function through binding to Nurr1 effector proteins.

中文翻译：

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直接结合和调节孤儿核受体Nurr1的NR4A配体的评估。

Nurr1 / NR4A2是一种孤儿核受体转录因子，被认为是包括阿尔茨海默氏症和帕金森氏症在内的神经系统疾病的潜在药物靶标。先前的研究确定了NR4A核受体的小分子调节剂，包括Nurr1和Nur77 / NR4A1。尚不清楚这些配体是否通过直接结合或间接非结合机制影响Nurr1。我们评估了一组十二种配体，据报道它们会影响NR4A的Nurr1依赖性和Nurr1非依赖性转录作用以及与Nurr1配体结合域（LBD）的结合。大多数NR4A配体以细胞类型特异性方式对转录显示出Nurr1独立的影响，表明它们可能通过与下游活动影响Nurr1功能的效应蛋白结合而发挥作用。蛋白质NMR光谱的结构足迹数据显示4-氨基-7-氯喹啉衍生物（阿马二醌和氯喹）和细胞孢子B直接结合Nurr1 LBD。相反，其他NR4A配体（包括可商购的化合物，例如C-DIM12，celastrol，喜树碱，IP7e，异戊内酯和TMPA）不结合Nurr1 LBD。有趣的是，先前的晶体结构表明，胞孢菌素B类似物与Nur77 LBD中的表面囊结合，但蛋白质NMR数据表明，胞孢菌素B可能与Nurr1正构囊结合。这些发现将影响药物化学工作，这些工作需要优化与Nurr1结合的配体，而不是通过与Nurr1效应子蛋白结合而起作用的配体。