Nuclear Receptor Nur77 Facilitates Melanoma Cell Survival under Metabolic Stress by Protecting Fatty Acid Oxidation

1. Download high-res image (276KB)
2. Download full-size image

     

孤儿核受体Nur77对缺/复氧损伤中心肌细胞自噬的调节

目的:研究孤儿核受体Nur77对缺/复氧损伤中心肌细胞自噬的调节作用。方法:差速贴壁法分离乳鼠心肌细胞,经免疫荧光染色鉴定纯度。缺氧(1%O_2、5%CO_2和94%N_2)培养12 h后,常氧培养2 h构建心肌细胞缺/复氧损伤。实时定量PCR和western blot的方法检测Nur77的表达变化。通过siRNA转染抑制心肌细胞nur77表达,通过自噬标志蛋白表达改变作为细胞自噬水平的变化。结果:原代分离的心肌细胞纯度95%以上。缺氧12 h和缺/复氧(12 h/2 h)刺激后,心肌细胞中Nur77表达都明显升高(P0.01)。与缺氧组相比,缺/复氧组细胞质中的水平明显增加(P0.01),细胞核中Nur77水平无明显变化。抑制Nur77后,缺/复氧组自噬水平明显降低,缺氧组心肌细胞自噬水平无明显变化。结论:Nur77参与缺/复氧损伤中心肌细胞自噬水平的调节。     

Regulation of vascular smooth muscle cell proliferation by nuclear orphan receptor Nur77

Endothelium-derived nitric oxide (NO) is a cytoprotective molecule to prevent endothelial cells (ECs) from apoptosis. CREB-binding protein (CBP) is involved in the apoptotic pathway in several tumor cells, however, little is known whether CBP is associated with apoptosis in ECs and the apoptotic effect of CBP on ECs is regulated by NO. Therefore, the purpose of the present study was to investigate whether silencing CBP expression could affect the sensitivity of ECs toward apoptotic stimuli and determined the role of NO. In this study, we found that when CBP expression was silenced by RNA interference, ECs were more prone to apoptosis under serum deprivation, whereas the apoptosis was not significantly induced in the serum-containing condition. The increased apoptosis is paralleled by a reduction of NO, and the apoptosis was reversed by NO donors, suggesting an important role of NO. Furthermore, CBP silencing decreased NO production by downregulating the endothelial NO synthase (eNOS) expression in a dose-dependent manner. These results indicated that CBP silencing is associated with decreased eNOS expression and NO production, and therefore concomitantly increased the sensitivity of ECs toward apoptosis.     

Regulation of the nuclear orphan receptor Nur77 in bone by parathyroid hormone

Osteoblasts function under the control of several hormones and growth factors. Among them, parathyroid hormone (PTH) and steroid hormones have significant effects on bone metabolism. We show that PTH induced the expression of Nur77, a member of the NGFI-B subfamily of nuclear orphan receptors in bone. PTH rapidly and transiently induced Nur77 mRNA in primary mouse osteoblasts that peaked at 1 h and at 10 nM of hormone. Cycloheximide did not affect the induction of Nur77 mRNA, suggesting that protein synthesis is not required for the PTH effect. PTH also induced Nur77 mRNA in calvariae cultures. Finally Nur77 protein expression was induced in nuclear protein extracts of cells treated with PTH. NGFI-B nuclear receptors have been implicated in retinoic acid, vitamin D, and thyroid hormone signaling. We propose that induction of NGFI-B nuclear orphan receptors represents a potential cross-talk mechanism between PTH and steroid hormone signaling to regulate bone metabolism.     

Ionomycin-induced apoptosis of thymocytes is independent of Nur77 NBRE or NurRE binding, but is accompanied by Nur77 mitochondrial targeting

The induction of thymocyte apoptosis through the Nur77-mediated intrinsic pathway can be of physiological importance in the clonal deletion of autoreactive thymocytes during negative selection in the thymus and/or in thymocytes undergoing oncogenic transformation. Ionomycin treatment induces endogenous Nur77 expression as well as apoptosis and cytochrome c release in thymocytes. Here it is shown for the first time that in normal thymocytes undergoing apoptosis, ionomycin induces translocation of endogenous Nur77 not only to the nucleus, but also to mitochondria. Immunosuppressant FK506 inhibits Nur77 NBRE and NurRE binding activity but has no effect on thymocytes apoptosis, the subcellular localization of Nur77, or cytochrome c release. This indicates that thymocytes can undergo apoptosis through the intrinsic Nur77-mediated mitochondrial pathway and that the transactivation activity of Nur77 monomers or dimers is not necessary for thymocyte apoptosis.     

Regulation and Methylation of Tumor Suppressor MiR-124 by Androgen Receptor in Prostate Cancer Cells

Prostate cancer (PCa) is the most frequently diagnosed cancer for men in the developed world. Androgen receptor signaling pathway plays an important role in prostate cancer progression. Recent studies show that microRNA miR-124 exerts a tumor suppressive function in prostate cancer. However, the relationship between AR and miR-124 is unclear. In the present study, we found a negative feedback loop between AR and miR-124 expression. On one hand, miR-124 was a positively regulated target gene of the AR, on the other hand, overexpression of miR-124 inhibited the expression of AR. In addition, we found that miR-124-2 and miR-124-3 promoters were hypermethylated in AR-negative PCa cells. Furthermore, overexpression of miR-124 inhibited proliferation rates and invasiveness capacity of PCa cells in vitro, and suppressed xenograft tumor growth in vivo. Taken together, our results support a negative feedback loop between AR and miR-124 expression. Methylation of miR-124-2 and miR-124-3 may serve as a biomarker for AR-negative PCa cells, and overexpression of miR-124 might be of potential therapeutic value for the treatment of PCa.     

前列腺素核受体系统信号转导及基因表达调控

脂肪酸和前列腺素等脂代谢的产物不仅通过膜受体起作用,也可以通过与核受体结合来调节基因表达.前列腺素I₂(PGI₂)既可以与G蛋白偶联的细胞表面IP受体起作用,也可以通过核受体过氧化物酶体增殖因子活化受体（PPARs）发挥生物学功能.前列腺素E₂(PGE₂)的受体（EPs）不仅仅在质膜上有,最近在核膜上也发现了EPs受体.前列腺素核受体介导的信号转导途径与膜受体介导的信号途径不同,对于基因转录的调控机制也不同.     

核孤儿受体在胆固醇分解代谢过程中的调控作用

由胆固醇合成胆汁酸有两条途径。一条是经典途径或中性途径[1] ,也是合成胆汁酸最主要的途径 ,其限速反应为胆固醇 7α 羟化酶 (由Ｃｙｐ7ａ编码 )催化胆固醇羟化为 7α 羟胆固醇的反应。近几年发现另一条胆汁酸合成的酸性途径[2 ] ,这一途径开始于胆固醇转变为氧固醇 (ｏｘｙｓｔｅｒｏｌ) ,然后经氧固醇 7α 羟化酶 (由Ｃｙｐ7ｂ编码 )催化产生 7α 羟氧固醇化合物 ,再融入胆汁酸合成经典途径的下游步骤。由于胆固醇在体内有重要作用 ,有效调节胆固醇分解代谢以维持胆固醇水平的动态平衡十分重要。研究发现 ,胆汁酸以及合成过程中的中间产…     

辅调节因子在核受体基因表达调控中的作用

核受体 ( nuclear receptor)在增强或抑制基因转录时 ,需借助于诸多辅调节因子的协同作用 ,使调节更为精细、有效及特异 .辅调节因子 ( coregulator)可区分为辅激活因子 ( coactivator)和辅抑制因子 ( corepressor)两大类 ,均具有多种功能各异的蛋白质因子 ,分别汇聚于核受体上构成不同复合体 .它们的主要作用机理是 :( 1 )促使核小体中的组蛋白乙酰基化 ,导致与 DNA的结合松散 ;或脱乙酰基 ,而使组蛋白与 DNA的结合回复紧密状态 ,从而创造一个有利于转录或封闭转录的局部环境 ;( 2 )作用于通用转录因子及 RNA聚合酶 ,以激活转录或抑制转录 .