胰岛素对生长激素的分泌和细胞内信号传导的影响（英文）

生长激素(growth hormone,GH)在行使其功能时需要经历一系列的过程,包括从垂体分泌和进入血液循环到达靶器官或细胞(受体前过程)以及和生长激素受体(GH receptor,GHR)结合并引发细胞内信号转导(受体后过程)。胰岛素可以直接或间接地影响这些过程。GH从垂体的生长激素分泌细胞中分泌需要依赖于下丘脑释放的生长激素释放激素(GH-releasing hor-mone,GHRH)和生长激素抑制素(somatostatin,SS),在生理或病理条件下,胰岛素可以对这两种激素以及GH分泌细胞施加不同影响,从而干预GH的分泌及循环水平。血糖、血脂以及饮食习惯都可以改变胰岛素对GH的影响。胰岛素还能通过影响GHR的敏感性,以及影响胰岛素样生长因子-1(insulin-like growth factor 1,IGF-1),进而影响GH。受体后过程也是GH行使功能的重要一环,细胞内信号转导依赖于信号通路完成。GH信号转导通路和胰岛素的信号通路有部分交叉,这使得两者的信号可以相互作用,胰岛素通过这种作用对GH的信号转导产生影响。还有很多因素可以改变胰岛素对GH的影响,包括细胞因子信号抑制物、GHR敏感性以及JAK2蛋白和胰岛素受体底物间的相互作用,且随着胰岛素浓度升高和作用时间延长,胰岛素对GH的影响趋向于增强。但胰岛素的浓度和时间对GH分泌和细胞内信号转导的具体影响还未完全阐明。胰岛素和SS的关系也有待进一步研究。     

酰化型和去酰化型ghrelin可促进人内脏脂肪细胞的脂质积聚

Ghrelin是主要由胃分泌的含28个氨基酸残基的多肽,是生长激素促分泌受体(growth hormone secretagogue receptor,GHS-R)的内源性配体.     

吉富罗非鱼两种生长激素受体基因的分离及与增重相关的SNPs位点

实验分离了吉富罗非鱼(Oreochromis niloticus)两种生长激素受体基因GHR1和GHR2的全长cDNA以及GHR1阅读框中外显子2～9、GHR2阅读框外显子2～8的DNA序列.在GHR1和GHR2分别找到6个和16个SNPs位点,其中只有2个位点在外显子部分.使用PCR-RFLP方法检测了5个家系共12...     

川金丝猴垂体生长激素基因的克隆与初步分析

本研究通过PCR克隆测序,初步确定了川金丝猴(Rhinopithecus roxellanae)的垂体生长激素基因的全部外显子核苷酸序列及推断出相应的氨基酸序列（包括26个氨基酸的信号肽序列以及191个氨基酸的成熟蛋白序列）。我们构建了灵长类7个物种垂体生长激素基因进化关系的基因树。垂体生长激素氨基酸序列的比较和垂体生长激素重要功能位点分析的结果显示：猴科的猕猴与疣猴科的川金丝猴垂体生长激素基因差异非常小。我们推测在猴超科动物中,垂体生长激素无明显功能上的差异。 Abstract:Putative pituitary growth hormone gene of Rhinopithecus roxellanae was cloned and sequenced.All exons sequences and deduced amino acid sequence (containing 26 residues signal peptide and 191 residues mature protein) were obtained.We constructed a phylogenetic tree,which well reflected the true evolutionary relationship of pituitary growth hormone genes from 7 primates species.From the results of amino acids sequence comparison and analysis of functionally important sites of growth hormone,pituitary growth hormone of macaque from Cercopithecidae and snub-nosed golden monkey from Colobidae show little difference.We indicated that pituitary growth hormone from Cercopithecoidea species have no apparently functional difference.     

生长激素受体的研究进展

生长激素（GH）在促进动物生长、发育等代谢过程中起着重要作用,GH发挥生理作用的第一步是与靶细胞膜表面的生长激素受体（CHR）结合。现已基本阐明了CHR的结构及由CHR介导的信号转导途径,对GHR基因表达调节的机制也有了一定的了解。GHR是由约620个氨基酸组成的单链跨膜糖蛋白,其胞外区、跨膜区及胞区内分别由约245、25及350个氨基酸组成。由GHR介导的信号转导途径主要有：①酪氨酸激酶系统;②蛋白激酶C途径;③胰岛素受体底物途径。营养状况及GH等内分泌因子对GHR的表达也有调节作用。     

小鼠生长激素受体基因环状转录本的克隆及其表达规律

根据文献报道并通过circBase数据库查找,发现小鼠生长激素受体基因(growth hormone receptor, GHR)存在8个环状转录本。为确定GHR基因环状转录本(circGHR)的真实存在,探究其表达规律,本研究以昆明小鼠(Mus musculus)为研究对象,通过PCR扩增和测序检测circGHR的真实存在,并筛选出一个circGHR作为目标分子,通过RNase R处理和反转录证实了circGHR的环形结构,利用qRT-PCR分析circGHR和GHR mRNA的时空表达规律。结果表明:小鼠circGHR全长为820nt,由GHR基因外显子2～8环化形成。RNaseR耐受性分析表明,小鼠circGHR具备环形分子的一般特征,不易被RNase R降解。与oligo-d(T)18引物相比,随机引物对circGHR具有较高的反转录效率,进一步说明circGHR是一个不含poly(A)的环状结构分子。组织表达谱结果表明,circGHR在1周龄和7周龄小鼠肝脏和肾脏高表达,在胸肌和腿肌中低表达;circGHR在肝脏和胸肌组织的时序表达谱结果表明circGHR表达无显著差异;circGHR在腿肌组织的时序表达谱结果表明,circGHR在小鼠5周龄之前为低表达,在7周龄以后表现为高表达。本研究结果证实了小鼠GHR基因存在一个环状转录本circGHR,并初步揭示了circGHR的表达规律,为后期深入开展小鼠circGHR的生物学功能及其在小鼠生长发育过程中的作用机制奠定基础。     

兔GHR基因单核苷酸多态性及其与屠宰性状的相关性

摘要: 采用PCR-SSCP技术和DNA测序的方法, 对比利时兔、天府黑兔、齐卡巨型兔、哈尔滨白兔以及加利福尼亚兔5个肉兔品种的生长激素受体(Growth hormone receptor, GHR)基因进行单核苷酸多态性分析。结果发现了2个单核苷酸多态位点, 分别位于外显子10的705(T→C)和810 (C→T)。通过最小二乘分析SNPs及其与屠宰性状的关系发现, 基因型AA和MM所对应的活重、全净膛、屠宰率最小二乘均值都显著低于基因型BB和NN(P<0.05)。但各基因型饲料转化率最小二乘均值差异不显著(P>0.05)。由此可以初步推断, GHR基因是影响兔体重和屠宰率等屠宰性状的主要候选基因。     

生长激素信号通路的重要调控因子-SOCS-2

生长激素(growth hormone,GH)由垂体前叶分泌,经循环系统运输到靶组织,调控机体发育及多种物质代谢.细胞因子信号传送阻抑物-2(suppressor of cytokine signaling-2,SOCS-2)是SOCS家族中一员,在调控GH信号通路中发挥着极其重要作用.GH能诱导SOCS-2表达,而诱导产生的SOCS-2又能反馈调节GH信号通路,但其调节机理还不清楚.     

Ghrelin 发现和结构的研究现状

Ghrelin是生长激素促分泌素受体(growth hormone secretagogue receptor,GHSR)的内源性配体,是1999年由Kojima等[]人从大鼠胃组织中发现的含28个氨基酸的多肽,主要由胃黏膜泌酸腺X/A样细胞分泌并通过与其特异性受体结合而产生多种生物学效应。本文总结了近几年的文章,旨在通过对Ghrelin的发现和结构的介绍,为以后的相关研究奠定基础。     

Growth hormone receptor ubiquitination, endocytosis, and degradation are independent of signal transduction via Janus kinase 2.

The ubiquitin-proteasome system is required in growth hormone receptor (GHR) endocytosis. For cytokine receptors, which lack intrinsic tyrosine kinase activity, signal transduction is initiated by the activation of a member of the Janus kinase (JAK) family. Previously, we have shown that GHR and JAK2 tyrosine (de) phosphorylation are regulated via the ubiquitin system. In this study, we examined the role of JAK2-mediated signal transduction in GHR internalization and down-regulation. Mutation of the attachment site for JAK2, box-1, in the GHR cytoplasmic tail resulted in the complete absence of GHR and JAK2 phosphorylation. This modification did not alter the rate and extent of receptor-bound growth hormone internalization as compared with a functional GHR, nor did it change its turnover and transport to the plasma membrane. In addition, the receptor was still normally ubiquitinated and remained dependent on both an intact ubiquitin system and proteasomal action for its internalization. Thus, GHR ubiquitination, endocytosis, and degradation occur independently of GHR signal transduction via JAK2. We conclude that whereas endocytosis and degradation require the ubiquitin system, they are independent of GHR signal transduction.     

The signal transduction of the growth hormone receptor is regulated by the ubiquitin/proteasome system and continues after endocytosis

The growth hormone receptor (GHR) intracellular domain contains all of the information required for signal transduction as well as for endocytosis. Previously, we showed that the proteasome mediates the clathrin-mediated endocytosis of the GHR. Here, we present evidence that the proteasomal inhibitor MG132 prolongs the GH-induced activity of both GHR and JAK2, presumably through stabilization of GHR and JAK2 tyrosine phosphorylation. If proteasomal inhibitor was combined with ligand in an endocytosis-deficient GHR mutant, the same phenomenon occurred indicating that proteasomal action on tyrosine dephosphorylation is independent of endocytosis. Experiments with a GHR-truncated tail mutant (GHR-(1-369)) led to a prolonged JAK2 phosphorylation caused by the loss of a phosphatase-binding site. This raised the question of what happens to the signal transduction of the GHR after its internalization. Co-immunoprecipitation of GH.GHR complexes before and after endocytosis showed that JAK2 as well as other activated proteins are bound to the GHR not only at the cell surface but also intracellularly, suggesting that the GHR signal transduction continues in endosomes. Additionally, these results provide evidence that GHR is present in endosomes both in its full-length and truncated form, indicating that the receptor is down-regulated by the proteasome.     

Development of a novel ligand that activates JAK2/STAT5 signaling through a heterodimer of prolactin receptor and growth hormone receptor

The objective of this study was to determine if a functional heterodimer of prolactin receptor (PRLR) and growth hormone receptor (GHR) can be formed in humans. A novel ligand was designed that is composed of a GHR antagonist (B2036) and a PRLR antagonist (G129R) fused in tandem (B2036-G129R). Because both B2036 and G129R are binding site 2 inactive antagonists, the B2036-G129R fusion protein, in theory contains only two functional binding site 1s: one for GHR and one for PRLR. We examined the behavior of this chimeric ligand in cell lines known to express GHR, PRLR, or both receptors. The data presented show that B2036-G129R is inactive in IM-9 cells that express only GHR or Nb2 cells that express PRLR. In T-47D cells that coexpress PRLR and GHR, B2036-G129R activates JAK2/STAT5 signaling. These findings provide evidence that B2036-G129R is able to activate signal transduction through a heterodimer of PRLR and GHR in humans.     

The ubiquitin conjugation system is required for ligand-induced endocytosis and degradation of the growth hormone receptor.

The ubiquitin-dependent protein degradation system has recently been implicated in downregulation of signal transducing receptors. Growth hormone receptor (GHR) cDNA was transfected into Chinese hamster ovary cells, which exhibit a temperature-sensitive defect in ubiquitin conjugation (CHO-ts20), as well as into wild-type cells (CHO-E36). Upon binding of growth hormone (GH), two GHR polypeptides dimerize and initiate signal transduction. In CHO-E36 and in CHO-ts20 at the permissive temperature the GHR was ubiquitinated and degraded in a GH-dependent fashion. However, at the non-permissive temperature in CHO-ts20 cells, neither GH-dependent uptake nor degradation of the GHR was observed, while in CHO-E36 cells both GHR uptake and degradation were accelerated. Incubation of CHO-E36 cells with inhibitors of endosomal/lysosomal function (NH4Cl, bafilomycin A1) markedly reduced ligand-induced GHR degradation. Our results indicate that a functional ubiquitin conjugating system is required for GH-induced endocytosis and that degradation of both the exoplasmic and cytoplasmic portions of the GHR occurs within the endosomal/lysosomal compartment.     

Identification of a novel ubiquitin conjugation motif, required for ligand-induced internalization of the growth hormone receptor.

In addition to its role in selective protein degradation, the conjugation of ubiquitin to proteins has also been implicated in the internalization of plasma membrane proteins, including the alpha-factor receptor Ste2p, uracil permease Fur4p, epithelial sodium channel ENaC and the growth hormone receptor (GHR). Binding of GH to its receptor induces receptor dimerization, resulting in the activation of signal transduction pathways and an increase of GHR ubiquitination. Previously, we have shown that the ubiquitin conjugation system mediates GH-induced GHR internalization. Here, we present evidence that a specific domain of the GHR regulates receptor endocytosis via the ubiquitin conjugation system. This ubiquitin-dependent endocytosis (UbE) motif consists of the amino acid sequence DSWVEFIELD and is homologous to sequences in other proteins, several of which are known to be ubiquitinated. In addition, we show that GH internalization by a truncated GHR is independent of the presence of lysine residues in the cytosolic domain of this receptor, while internalization still depends on an intact ubiquitin conjugation system. Thus, GHR internalization requires the recruitment of the ubiquitin conjugation system to the GHR UbE motif rather than the conjugation of ubiquitin to the GHR itself.     

Growth hormone activity in mitochondria depends on GH receptor Box 1 and involves caveolar pathway targeting

Growth hormone (GH) binding to its receptor (GHR) initiates GH-dependent signal transduction and internalization pathways to generate the biological effects. The precise role and way of action of GH on mitochondrial function are not yet fully understood. We show here that GH can stimulate cellular oxygen consumption in CHO cells transfected with cDNA coding for the full-length GHR. By using different GHR cDNA constructs, we succeeded in determining the different parts of the GHR implicated in the mitochondrial response to GH. Polarography and two-photon excitation fluorescence microscopy analysis showed that the Box 1 of the GHR intracellular domain was required for an activation of the mitochondrial respiration in response to a GH exposure. However, confocal laser scanning microscopy demonstrated that cells lacking the GHR Box 1 could efficiently internalize the hormone. We demonstrated that internalization mediated either by clathrin-coated pits or by caveolae was able to regulate GH mitochondrial effect: these two pathways are both essential to obtain the GH stimulatory action on mitochondrial function. Moreover, electron microscopic and biochemical approaches allowed us to identify the caveolar pathway as essential for targeting GH and GHR to mitochondria.     

An agonist-induced conformational change in the growth hormone receptor determines the choice of signalling pathway

The growth and metabolic actions of growth hormone (GH) are believed to be mediated through the GH receptor (GHR) by JAK2 activation. The GHR exists as a constitutive homodimer, with signal transduction by ligand-induced realignment of receptor subunits. Based on the crystal structures, we identify a conformational change in the F'G' loop of the lower cytokine module, which results from binding of hGH but not G120R hGH antagonist. Mutations disabling this conformational change cause impairment of ERK but not JAK2 and STAT5 activation by the GHR in FDC-P1 cells. This results from the use of two associated tyrosine kinases by the GHR, with JAK2 activating STAT5, and Lyn activating ERK1/2. We provide evidence that Lyn signals through phospholipase C gamma, leading to activation of Ras. Accordingly, mice with mutations in the JAK2 association motif respond to GH with activation of hepatic Src and ERK1/2, but not JAK2/STAT5. We suggest that F'G' loop movement alters the signalling choice between JAK2 and a Src family kinase by regulating TMD realignment. Our findings could explain debilitated ERK but not STAT5 signalling in some GH-resistant dwarfs and suggest pathway-specific cytokine agonists.