Department of Biophysics and Cell Biology, Faculty of Medicine, Doctoral School of Molecular Medicine, University of Debrecen, Debrecen, Hungary.
Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary; Princess Maxima Centre for Pediatric Oncology, Utrecht, the Netherlands.
J Biol Chem. 2023 Feb;299(2):102896. doi: 10.1016/j.jbc.2023.102896. Epub 2023 Jan 11.
We found previously that nuclear receptors (NRs) compete for heterodimerization with their common partner, retinoid X receptor (RXR), in a ligand-dependent manner. To investigate potential competition in their DNA binding, we monitored the mobility of retinoic acid receptor (RAR) and vitamin D receptor (VDR) in live cells by fluorescence correlation spectroscopy. First, specific agonist treatment and RXR coexpression additively increased RAR DNA binding, while both agonist and RXR were required for increased VDR DNA binding, indicating weaker DNA binding of the VDR/RXR dimer. Second, coexpression of RAR, VDR, and RXR resulted in competition for DNA binding. Without ligand, VDR reduced the DNA-bound fraction of RAR and vice versa, i.e., a fraction of RXR molecules was occupied by the competing partner. The DNA-bound fraction of either RAR or VDR was enhanced by its own and diminished by the competing NR's agonist. When treated with both ligands, the DNA-bound fraction of RAR increased as much as due to its own agonist, whereas that of VDR increased less. RXR agonist also increased DNA binding of RAR at the expense of VDR. In summary, competition between RAR and VDR for RXR is also manifested in their DNA binding in an agonist-dependent manner: RAR dominates over VDR in the absence of agonist or with both agonists present. Thus, side effects of NR-ligand-based (retinoids, thiazolidinediones) therapies may be ameliorated by other NR ligands and be at least partly explained by reduced DNA binding due to competition. Our results also complement the model of NR action by involving competition both for RXR and for DNA sites.
我们之前发现，核受体（NRs）以配体依赖的方式与它们共同的伴侣视黄酸 X 受体（RXR）竞争形成异二聚体。为了研究它们在 DNA 结合上的潜在竞争，我们通过荧光相关光谱法监测活细胞中视黄酸受体（RAR）和维生素 D 受体（VDR）的迁移。首先，特定激动剂处理和 RXR 共表达可附加性地增加 RAR 的 DNA 结合，而 RAR 和 RXR 均需要增加 VDR 的 DNA 结合，表明 VDR/RXR 二聚体的 DNA 结合较弱。其次，RAR、VDR 和 RXR 的共表达导致 DNA 结合竞争。没有配体时，VDR 减少 RAR 的 DNA 结合部分，反之亦然，即 RXR 分子的一部分被竞争伙伴占据。RAR 或 VDR 的 DNA 结合部分被自身激动剂增强，而被竞争 NR 的激动剂减弱。当用两种配体处理时，RAR 的 DNA 结合部分增加的程度与自身激动剂相同，而 VDR 的增加程度较小。RXR 激动剂也以牺牲 VDR 为代价增加 RAR 的 DNA 结合。总之，RAR 和 VDR 对 RXR 的竞争也表现在它们的激动剂依赖性 DNA 结合中：在没有激动剂或两种激动剂都存在的情况下，RAR 占主导地位。因此，NR-配体（视黄醇、噻唑烷二酮）治疗的副作用可能会被其他 NR 配体改善，并且至少部分解释为由于竞争导致 DNA 结合减少。我们的结果还通过涉及 RXR 和 DNA 结合的竞争，补充了 NR 作用的模型。
