Department of Pharmacology, Pharmacy College, Nantong University, Nantong 226001, China.
Int J Mol Sci. 2022 May 21;23(10):5766. doi: 10.3390/ijms23105766.
A novel function of retinoid X receptor beta (RXRβ) in endothelial cells has been reported by us during the formation of atherosclerosis. Here, we extended the study to explore the cellular mechanisms of RXRβ protein stability regulation. In this study, we discovered that murine double minute-2 (MDM2) acts as an E3 ubiquitin ligase to target RXRβ for degradation. The result showed that MDM2 directly interacted with and regulated RXRβ protein stability. MDM2 promoted RXRβ poly-ubiquitination and degradation by proteasomes. Moreover, mutated MDM2 RING domain (C464A) or treatment with an MDM2 inhibitor targeting the RING domain of MDM2 lost the ability of MDM2 to regulate RXRβ protein expression and ubiquitination. Furthermore, treatment with MDM2 inhibitor alleviated oxidized low-density lipoprotein-induced mitochondrial damage, activation of TLR9/NF-κB and NLRP3/caspase-1 pathway and production of pro-inflammatory cytokines in endothelial cells. However, all these beneficial effects were reduced by the transfection of RXRβ siRNA. Moreover, pharmacological inhibition of MDM2 attenuated the development of atherosclerosis and reversed mitochondrial damage and related inflammation in the atherosclerotic process in LDLr mice, along with the increased RXRβ protein expression in the aorta. Therefore, our study uncovers a previously unknown ubiquitination pathway and suggests MDM2-mediated RXRβ ubiquitination as a new therapeutic target in atherosclerosis.
我们曾报道过视黄酸 X 受体 β（RXRβ）在血管内皮细胞形成动脉粥样硬化过程中的新功能。在此基础上，我们进一步研究了 RXRβ 蛋白稳定性调节的细胞机制。在这项研究中，我们发现鼠双微体 2（MDM2）作为一种 E3 泛素连接酶，可将 RXRβ 作为靶标进行降解。结果表明，MDM2 可直接与 RXRβ 相互作用并调节其蛋白稳定性。MDM2 通过蛋白酶体促进 RXRβ 的多泛素化和降解。此外，突变的 MDM2 RING 结构域（C464A）或用靶向 MDM2 RING 结构域的 MDM2 抑制剂处理，会丧失 MDM2 调节 RXRβ 蛋白表达和泛素化的能力。此外，用 MDM2 抑制剂处理可减轻氧化型低密度脂蛋白诱导的内皮细胞线粒体损伤、TLR9/NF-κB 和 NLRP3/caspase-1 途径的激活以及促炎细胞因子的产生。然而，用 RXRβ siRNA 转染后，所有这些有益作用都减少了。此外，MDM2 的药理学抑制可减轻 LDLr 小鼠动脉粥样硬化的发展，并逆转动脉粥样硬化过程中的线粒体损伤和相关炎症，同时增加主动脉中 RXRβ 蛋白的表达。因此，我们的研究揭示了一条以前未知的泛素化途径，并提出了 MDM2 介导的 RXRβ 泛素化作为动脉粥样硬化的一个新的治疗靶点。
