Action Of The Nuclear Orphan Receptor RTR

核受体超家族是一类依赖配体的转录因子，在包括发育、细胞增殖和分化在内的许多生物过程中调节基因表达。这些受体的活性与疾病有关，因为受体信号通路的改变与各种疾病过程有关。RTR/GCNF是一种核孤儿受体，在早期胚胎发育和配子发生过程中起着重要的基因表达调控作用。在没有配体的情况下，RTR发挥转录抑制因子的作用。在这项研究中，我们进一步表征了这种抑制因子的功能。我们证明RTR抑制基础转录激活，并通过其应答元件（ERRa1- re）抑制雌激素受体相关受体a1 （ERRa1）的转激活。后者至少在一定程度上是由于竞争与相同的RE结合。哺乳动物的两种杂交分析表明，RTR的转录抑制可以通过与协同抑制因子N-CoR的相互作用来介导，而不涉及SMRT或RIP140。GST-RTR的下拉分析表明RTR(:)N-CoR复合物在体外形成。缺失和点突变分析表明，RTR的铰链结构域、螺旋3和螺旋12对其与N-CoR的相互作用至关重要。铰链结构域的S244Y245、螺旋3的K318和螺旋12的K489T490被确定为这种相互作用的关键残基。最近，我们克隆了一个新的基因RAP80，它能够与RTR相互作用，并可能在RTR的抑制功能中发挥作用。RAP80是一个80 kD的核蛋白，在其羧基端含有两个锌指结构域。尽管N-COR和RAP80能够竞争与RTR结合，但RTR的不同区域参与了这些相互作用。我们的研究结果表明，在没有配体的情况下，RTR作为一种活性转录抑制因子发挥作用，并且这种抑制可以通过与协同抑制因子N-CoR的相互作用来介导。RTR通过其阻遏因子功能抑制其他核受体的转录激活。这些抑制因子的活性可能为RTR调节生物过程（如精子发生）提供了重要的机制。

The nuclear receptor superfamily constitutes a class of ligand-dependent transcriptional factors that regulate gene expression during many biological processes, including development, cellular proliferation and differentiation. The activity of these receptors is relevant to disease since alterations in receptor signaling pathways have been linked to various disease processes. RTR/GCNF is a nuclear orphan receptor that plays an important role in the control of gene expression during early embryonic development and gametogenesis. In the absence of ligand, RTR functions as a repressor of transcription. In this study, we further characterized this repressor function. We demonstrated that RTR inhibited basal transcriptional activation and suppressed the transactivation by the estrogen receptor related-receptor a1 (ERRa1) through its response element (ERRa1-RE). The latter was at least in part due to competition for binding to the same RE. Mammalian two hybrid analyses showed that the transcriptional repression by RTR can be mediated through interactions with the co-repressor N-CoR and does not involve SMRT or RIP140. Pull-down analyses with GST-RTR demonstrated the formation of RTR(:)N-CoR complexes in vitro. Deletion and point mutation analyses revealed that the hinge-domain, helix 3 and 12 of RTR are essential for its interaction with N-CoR. The residues S244Y245 in the hinge domain, K318 in helix 3 and K489T490 in helix 12 were identified as being critical for this interaction. Recently we cloned a novel gene referred to as RAP80 that is able to interact with RTR and may play a role in the repressor function of RTR. RAP80 is an 80 kD nuclear protein containing two zinc finger domains at its carboxy terminus. Although N-COR and RAP80 are able to compete for binding to RTR, different regions of RTR are involved in these interactions. Our results demonstrate that, in the absence of ligand, RTR functions as an active transcriptional repressor and that this repression can be mediated through interactions with the co-repressor N-CoR. Through its repressor function, RTR can suppress the transcriptional activation by other nuclear receptors. These repressor activities may provide important mechanisms by which RTR regulate biological processes, such as spermatogenesis.