PGC-1-一种新的核受体辅助活化因子

PGC-l是一种新发现的核受体转录辅助活化因子。它具有多功能性,诱导线粒体增殖、呼吸、能量代谢及适应性产热,并与糖尿病、肥胖等密切相关。PGC-l具有调节多种核受体和转录因子活性的能力。此外,PGC-l不仅通过与核受体转录因子相互作用调节基因转录,也通过参与RNA后加工过程调节基因表达。     

肿瘤坏死因子受体和配体超家族的新成员

骨原蛋白(OPG)／核因子κB受体激活剂的配体(RANKL)／核因子κB的受体激活剂(RANK)是肿瘤坏死因子受体和配体超家族成员。RANKL由成骨细胞前体／骨髓基质细胞和激活的T淋巴细胞合成,通过结合破骨细胞或树突状细胞表面的RANK受体,促进破骨细胞的形成、融合、激活和存活,并有助于树突状细胞对抗原的提呈作用,OPG作为RANKL的假受体,对此过程具有抑制作用。此外,OPG／RANKL／RANK系统在调节淋巴系统发育、哺乳期动物乳腺腺泡的形成以及大动脉钙化中也起着重要的作用,是一组多功能的细胞因子系统。     

几种核受体核浆穿梭与调控机制

许多核受体属于核转录因子,它们在胞浆合成后快速地转运入核,同时还能够在核浆之间穿梭以行使其特定的生物学功能。核受体的核浆转运主要通过核膜上的核孔复合体,依靠运输载体Importins和Exportins介导以及Ran-GDP提供能量。现对糖皮质激素受体（GR）、雄激素受体（AR）和雌激素受体（ER）等核受体在核浆穿梭转运和调控机制等方面的研究进展进行综述,同时也介绍我们实验室最近发现的视黄素X受体（RXR）核浆穿梭转运的新功能。     

核受体及其转录活化机制研究的新突破

核受体是一类配体依赖的转录因子,它们之间有相似的结构,在进化为来源于同一前体,它们和基础转录因子有直接的联系,与配体结合后,作用于其目标基因的特定应答元件上,从而活化特定基因的转录,核受体介导的转录活化需要有辅活化子和辅阻遏子的参与,这些辅活化子和辅助遏子是有效的转录所必需的,它们能和核受体特异结合,并在核受体和基础转录因子之间发挥中介作用,目前发现普遍存在并在转录过程中具有重要作用的辅活化子有Ｃ     

核受体相关因子1的研究进展

核受体相关因子 1(nuclearreceptor relatedfactor 1,Nurr1)是一种转录因子 ,属于核受体超家族成员 ,主要表达于中脑黑质与腹侧被盖区 ,作为基因转录调控蛋白而参与了中脑多巴胺能神经元的发育与存活、长时记忆、肝再生及炎症等多种生理和病理过程。本文总结和讨论了有关Nurr1的编码基因、分子结构、组织表达及生物学功能等方面研究的新近进展     

核内受体超家族的结构与机能分析

根据受体编码基因建立的系统发育树分析结果,将全部核内受体分为三个亚类。几乎核内受体超家族所有成员都具有相同的结构模式：受体分子由Ａ／Ｂ、Ｃ、Ｄ和Ｅ区构成;这些结构区分别参与配体与受体、受体与ＤＮＡ以及受体与其它核内转录因子的相互作用,调节靶基因的转录激活过程。因此,核内受体超家族是一大类重要的转录调节因子。     

雌激素受体β的研究进展

雌激素受体β（ERβ）属于核受体超家族成员,是一类配体调节的转录因子。ERβ与ERα的结构相似,但在组织学分布、生物学功能等方面不尽相同,具有重要的生理学和病理学意义。本文就ERβ的基因结构、分子生物学特性、组织分布、转录调控的分子机制以及与肿瘤发生、发展的关系作一综述。     

泛素化在TRAF2介导的NF-κB信号通路中的作用

NF-κB（核因子κ增强子结合蛋白）是核转录因子家族成员,具有调节免疫、炎症和细胞存活的功能.它可被TRAF2（tumor necrosis factor receptor associated factor 2,肿瘤坏死因子受体相关因子2）等相关因子活化.TRAF2包含了N-端的环指结构域和C-端的高度保守结构域.它通过与肿瘤坏死因子受体超家族成员相互作用,介导了下游信号通路.而TRAF2的泛素化在过程中是关键的,鞘磷脂作为TRAF2的泛素化连接酶辅助因子,在TRAF2介导的NF-κB信号通路中发挥重要作用.     

PELP1/MNAR:一种新的核受体辅助调节因子

脯氨酸-谷氨酸-亮氨酸富集蛋白1/雌激素受体非基因组活性辅助调节因子(proline-,glutamic acid-,leucine-rich protein 1/modulator of nongenomic activity of estrogen receptor,PELP1/MNAR)是一种新近发现的核受体辅助活化因子,具有较为复杂的分子结构,在多种组织中广泛表达。与先前发现的核受体辅助调节因子不同的是:作为一种支架蛋白,PELP1/MNAR既参与核受体调控靶基因转录的基因组作用,又参与了核受体激活激酶信号系统的非基因组作用,并且可能在核受体信号与生长因子信号串话(cross talk)中发挥重要作用。近年的研究表明,PELP1/MNAR在乳腺癌、卵巢癌、子宫内膜癌、前列腺癌等激素依赖性肿瘤中均有异常表达和分布,在激素依赖性肿瘤的发生、发展、转移、耐药形成过程中可能具有重要意义,可望成为内分泌依赖性肿瘤治疗的一个新的靶点。     

脂激活转录因子PPAR的骨生理学效应

脂激活转录因子PPAR属于核受体超家族成员,对细胞生长、分化以及凋亡具有重要影响,与心血管疾病、糖尿病、肥胖及肿瘤细胞的生长有密切关系。本文重点从PPAR对成骨细胞和破骨细胞的作用阐述PPAR的骨生理学效应。     

Acetylation in nuclear receptor signaling and the role of sirtuins

It has been known since the early 1970s that nuclear receptor complexes bind DNA in association with coregulatory proteins. Characterization of these nuclear receptor coregulators has revealed diverse enzymatic activities that temporally and spatially coordinate nuclear receptor activity within the context of local chromatin in response to diverse hormone signals. Chromatin-modifying proteins, which dictate the higher-order chromatin structure in which DNA is packaged, in turn orchestrate orderly recruitment of nuclear receptor complexes. Modifications of histones include acetylation, methylation, phosphorylation, ubiquitylation, sumoylation, ADP ribosylation, deimination, and proline isomerization. At this time, we understand how a subset of these modifications regulates nuclear receptor signaling. However, the effects, particularly of acetylation and demethylation, are profound. The finding that nuclear receptors are directly acetylated and that acetylation in turn directly regulates contact-independent growth has broad therapeutic implications. Studies over the past 7 yr have led to the understanding that nuclear receptor acetylation is a conserved function, regulating diverse nuclear receptor activity. Furthermore, we now know that acetylation of multiple and distinct substrates within nuclear receptor signaling pathways, form an acetylation signaling network from the cell surface to the nucleus. The finding that nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases, the sirtuins, are capable of deacetylating nuclear receptors provides a new level of complexity in the control of nuclear receptor activity in which local intracellular concentrations of NAD may regulate nuclear receptor physiology.     

Glucocorticoid receptors in lung. Comparison between nonactivated and activated forms of the cytoplasmic glucocorticoid binding protein and their relationship to the nuclear binding protein of fetal rabbit lung.

In the absence of salt the cytoplasmic glucocorticoid receptor of fetal rabbit lung sediments at 7 S while the nuclear receptor sediments at 4 S. However, if nuclear extracts are mixed with receptor-depleted cytosol preparations in dilute buffer solutions without added salt, the nuclear 4 S receptor sediments as a 7 S species similar to that observed for the cytoplasmic form under the same conditions suggesting an interaction of the nuclear receptor with other cytosol proteins rather than with itself. In addition, both cytoplasmic and nuclear receptors sediment at 4 S in 0.4 M KCl and a major fraction of the nuclear receptor has an agarose elution profile identical to that of the cytoplasmic receptor. Thus a major fraction of the nuclear receptors is indistinguishable from the cytoplasmic receptors by the methods used. Since the cytoplasmic receptor sediments at 4 S in 0.15 M KCl, it is suggested that in vivo the glucocorticoid receptor may exist as a 4 S species and that the 7 S form described previously may result from an interaction of the 4 S component with other cytosol proteins in hypotonic media. About 25% of the receptor present in nuclear extracts has an agarose elution profile different from that of the cytoplasmic receptor in 0.4 M KCl. This suggests that either the nuclear receptor associates with itself or other nuclear proteins or that more than one form of nuclear receptor exists. Earlier observations suggested that in the absence of hormone the glucocorticoid receptor is localized exclusively in the cytoplasm of lung cells and that the nuclear receptor is formed by a transfer of the cytoplasmic steroid-receptor complex into the nucleus. A prerequisite for this transfer seems to be a modification of the receptor to an active form which can bind to nuclei. This receptor transfomration, referred to in this paper as activation of the receptor, can occur in the absence of nuclei and is highly dependent on temperature and ionic strength. Cytoplasmic receptors activated either by heating or by exposure to high ionic strength are indistinguishable from nonactivated receptors by sucrose density gradient analysis or by agarose gel filtration in solutions containing 0.4 M KCl. Simiarly, no significant difference in the absence of salt is observed after activation by heating. These results suggest that activation of the cytoplasmic glucocorticoid receptor involves conformational changes which favor its transfer and/or binding to nuclear sites rather than conversion of a 4 S species to a faster-sedimenting form by dimerization or by addition of another protein unit as has been proposed for the activation of the estrogen receptor of the rat uterus.     

The unoccupied nuclear oestradiol receptor in the rat uterus and hypothalamus during the oestrous cycle.

The nuclear oestrogen receptor population in the rat uterus contained an unoccupied receptor component that bound oestradiol with the high affinity (Kd congruent to 0.5 nM) characteristic of oestrogen receptors. This unoccupied receptor was present at all phases of the oestrous cycle. Its content changed in parallel with that of the total nuclear receptor during the cycle. Oestradiol administration to the immature rat resulted in increases in the uterine content of long-term nuclear receptors (i.e., those still present 8 h after administration); these increases were due to occupied oestrogen receptors, since the content of unoccupied receptor was unchanged. Our previous experiments [White & Lim (1980) Biochem. J. 190, 833-837] have shown in contrast, that oestradiol administration results in an increase in the content of unoccupied nuclear receptor in the hypothalamus. However, as in the uterus, similar cyclic changes in the content of unoccupied nuclear receptor occurred in parallel with those of the total nuclear receptor population in the hypothalamus. Differences and similarities between the unoccupied nuclear receptor of the uterus and hypothalamus are briefly discussed.     

A rapid immunological procedure for the isolation of hormonally sensitive rat fat-cell plasma membrane.

1. The administration of dihydrotestosterone to rats orchidectomized 7 days previously stimulated the synthesis of nuclear receptor in prostatic cells several hours in advance of DNA synthesis and mitosis. 2. The synthesis of nuclear receptor is tightly coupled to cell proliferation; consequently, in resting cells, there is no further net synthesis of nuclear receptor above the maximum of approx. 8000 molecules/cell. 3. After orchidectomy a rapid decline in the concentration of free androgen in the nuceus and a slower decline in the concentration of nuclear receptor are observed. 4. Owing to the apparent scarcity of receptor-inactivating factors in the nucleus, and the inverse relationship between amounts of nuclear and cytoplasmic receptors, it is concluded that the nuclear receptor is discharged into the cytoplasm after orchidectomy. 5. The formation of the cytoplasmic receptor is an early event preceding the onset of cellular autolysis. 6. Regressing prostate develops the capacity to eliminate cytoplasmic receptor, and this capacity is retained by the regenerating prostate for at least 14 days. 7. The synthesis of nuclear receptor in early G1 phase may control the entry of cells into the cell cycle and the prolonged retention of receptor in the nucleus may prevent the activation of autophagic processes.     

From the structure of steroid receptors to their assessment by immunocytochemistry in target cells

Immunohistochemical studies with antibodies to steroid hormone receptors provide new insight in the mechanism of action of steroid hormones. Immunologically reactive estrogen and progesterone receptors are found exclusively in cell nuclei of target cells even in the absence of the hormonal ligand. A hormonal treatment inducing receptor transformation and "translocation" to the nucleus does not modify the intracellular distribution of the receptor. This result is in contradiction with most biochemical studies which show a displacement of receptor from the cytosolic fraction to the nuclear fraction after hormone-receptor complex formation. We propose that different affinity levels of the non-transformed and hormone-complexed receptor molecules for nuclear structure produce unequal losses of nuclear receptor during homogenization. A lesser loss appears as an increase in nuclear binding sites or immunologically reactive receptor. The glucocorticosteroid receptor differs from the others in that it shows an increase of nuclear immunoreactive receptor after hormone administration. This result was accepted as evidence for a nuclear translocation in the sense initially proposed for all steroid hormones. Alternatively, one may propose another explanation based on the same experimental artefact as invoked for the estrogen and progesterone cytosol receptors. A higher affinity of the hormone-complexed receptor entails a lesser loss from the nucleus during tissue processing, and consequently an apparent increase in nuclear staining. Such a possibility is currently tested in parallel with the progesterone receptor.     

Transrepression of AP-1 by nuclear receptors in Drosophila

Mammalian cell culture studies have shown that several members of the nuclear receptor super family such as glucocorticoid receptor, retinoic acid receptor and thyroid hormone receptor can repress the activity of AP-1 proteins by a mechanism that does not require the nuclear receptor to bind to DNA directly, but that is otherwise poorly understood. Several aspects of nuclear receptor function are believed to rely on this inhibitory mechanism, which is referred to as transrepression. This study presents evidence that nuclear receptor-mediated transrepression of AP-1 occurs in Drosophila melanogaster. In two different developmental situations, embryonic dorsal closure and wing development, several nuclear receptors, including Seven up, Tailless, and Eagle antagonize AP-1. The inhibitory interactions with nuclear receptors are integrated with other modes of AP-1 regulation, such as mitogen-activated protein kinase signaling. A potential role of nuclear receptors in setting a threshold of AP-1 activity required for the manifestation of a cellular response is discussed.     

Agonist-independent nuclear localization of the Apelin, angiotensin AT1, and bradykinin B2 receptors

Signaling of the apelin, angiotensin, and bradykinin peptides is mediated by G protein-coupled receptors related through structure and similarities of physiological function. We report nuclear expression as a characteristic of these receptors, including a nuclear localization for the apelin receptor in brain and cerebellum-derived D283 Med cells and the AT(1) and bradykinin B(2) receptors in HEK-293T cells. Immunocytochemical analyses revealed the apelin receptor with localization in neuronal nuclei in cerebellum and hypothalamus, exhibiting expression in neuronal cytoplasm or in both nuclei and cytoplasm. Confocal microscopy of HEK-293T cells revealed the majority of transfected cells displayed constitutive nuclear localization of AT(1) and B(2) receptors, whereas apelin receptors did not show nuclear localization in these cells. The majority of apelin receptor-transfected cerebellum D283 Med cells showed receptor nuclear expression. Immunoblot analyses of subcellular-fractionated D283 Med cells demonstrated endogenous apelin receptor species in nuclear fractions. In addition, an identified nuclear localization signal motif in the third intracellular loop of the apelin receptor was disrupted by a substituted glutamine in place of lysine. This apelin receptor (K242Q) did not exhibit nuclear localization in D283 Med cells. These results demonstrate the following: (i) the apelin receptor exhibits nuclear localization in human brain; (ii) distinct cell-dependent mechanisms for the nuclear transport of apelin, AT(1), and B(2) receptors; and (iii) the disruption of a nuclear localization signal sequence disrupts the nuclear translocation of the apelin receptor. This discovery of apelin, AT(1), and B(2) receptors with agonist-independent nuclear translocation suggests major unanticipated roles for these receptors in cell signaling and function.     

Molecular size of the nuclear thyroid hormone receptor

Among the previously reported putative nuclear thyroid hormone receptor forms having molecular masses of 56-59 kDa and 45-49 kDa, respectively, only the former can be the endogenous receptor. The latter must be a degradation product because it is virtually absent in rat liver nuclear extracts prepared in the presence of 20% glycerol and 5 mM Mg2+, which inhibit degradation. In the absence of glycerol, the receptor form of lower mass was present in large amounts in nuclear extracts. Sucrose could not replace glycerol as a protective agent, even in the presence of Mg2+. Thus, the endogenous nuclear thyroid hormone receptor appears to be labile under the experimental conditions used in preparing nuclear extracts. The molecular mass of the nuclear receptor was determined to be 57 kDa on the basis of SDS-polyacrylamide gel electrophoresis after photoaffinity labeling of nuclear proteins with (3,5-125I)-labeled thyroxine.     

Ligand-selective targeting of the glucocorticoid receptor to nuclear subdomains is associated with decreased receptor mobility

The association between nuclear distribution and mobility of the human glucocorticoid receptor was examined in living COS-1 cells using yellow fluorescent protein- and cyan fluorescent protein-tagged receptors. Quantitation of the nuclear distribution induced by an array of glucocorticoid ligands revealed a continuum from a random (cortisone) to a nonrandom (triamcinolone acetonide) receptor distribution. Structure-function analysis revealed that the 9-fluoro and 17-hydroxy groups on the steroid significantly impact nuclear receptor distribution. Using time-lapse microscopy, the triamcinolone acetonide-induced receptor distribution did not change significantly over a period of 15 sec. However, using fluorescence recovery after photobleaching, the individual receptors moved at a much faster rate, indicating rapid exchange of receptors on immobile nuclear subdomains. Receptor mobilities for 13 different steroids, measured by fluorescence recovery after photobleaching, appeared to correlate with receptor distribution. Ligands that induced a nonrandom distribution induced slower receptor mobility and vice versa. Finally, application of 2-photon confocal microscopy revealed differences in receptor mobility between nuclear subdomains. Areas of high receptor concentration showed slower mobility than areas of low receptor concentration. Thus, glucocorticoid receptors can be targeted (depending on the ligand) to relatively immobile nuclear subdomains. The transient association of receptor with these domains decreases the mobility of the receptor.