Department of Biochemistry & Molecular Biology, College of Medicine, Yeungnam University, Daegu, South Korea.
College of Pharmacy, Yeungnam University, Gyeongsan, South Korea.
Sci Rep. 2018 Sep 17;8(1):13895. doi: 10.1038/s41598-018-32391-5.
Nur77 is a member of the NR4A subfamily of nuclear receptors and has been shown to regulate various biological processes such as apoptosis and inflammation. Here, we show that Nur77 ubiquitination is mediated by the tripartite motif 13 (Trim13), a RING-type E3 ubiquitin ligase. The interaction between Nur77 and Trim13 was confirmed by co-immunoprecipitation. Moreover, we found that Lys539 in Nur77 ubiquitination is targeted for Trim13, which leads to Nur77 degradation. The Trim13-mediated ubiquitination of Nur77 was optimal in the presence of the E2 enzyme UbcH5. Importantly, in addition to Trim13-mediated ubiquitination, the stability of Nur77 was also regulated by casein kinase 2α (CK2α). Pharmacological inhibition of CK2 markedly increased Nur77 levels, whereas overexpression of CK2α, but not its inactive mutant, dramatically decreased Nur77 levels by promoting Nur77 ubiquitination. CK2α phosphorylated Ser154 in Nur77 and thereby regulated Nur77 protein levels by promoting its ubiquitin-mediated degradation. Importantly, we also show that degradation of Nur77 is involved in TNFα-mediated IL-6 production via CK2α and Trim13. Taken together, these results suggest that the sequential phosphorylation and ubiquitination of Nur77 controls its degradation, and provide a therapeutic approach for regulating Nur77 activity through the CK2α-Trim13 axis as a mechanism to control the inflammatory response.
Nur77 是核受体 NR4A 亚家族的成员，已被证明能调节多种生物学过程，如细胞凋亡和炎症。在这里，我们发现 Nur77 的泛素化是由三基序蛋白 13（Trim13）介导的，Trim13 是一种 RING 型 E3 泛素连接酶。通过共免疫沉淀证实了 Nur77 和 Trim13 之间的相互作用。此外，我们发现 Nur77 泛素化的 Lys539 是 Trim13 的作用靶点，导致 Nur77 降解。Trim13 介导的 Nur77 泛素化在 E2 酶 UbcH5 存在的情况下效果最佳。重要的是，除了 Trim13 介导的泛素化外，Nur77 的稳定性还受到酪蛋白激酶 2α（CK2α）的调节。CK2α 的药理学抑制显著增加了 Nur77 水平，而 CK2α 的过表达（而不是其无活性突变体）通过促进 Nur77 泛素化显著降低了 Nur77 水平。CK2α 在 Nur77 上磷酸化 Ser154，从而通过促进其泛素介导的降解来调节 Nur77 蛋白水平。重要的是，我们还表明，Nur77 的降解参与了 TNFα 介导的 IL-6 产生，这是通过 CK2α 和 Trim13 实现的。总之，这些结果表明，Nur77 的顺序磷酸化和泛素化控制其降解，并提供了一种通过 CK2α-Trim13 轴调节 Nur77 活性的治疗方法，作为控制炎症反应的一种机制。
