泛素蛋白酶体系统组成及其在疾病中的作用

<正>人体组织细胞中存在多种蛋白降解途径,目前研究最多的是溶酶体降解途径和泛素-蛋白酶体降解途径,其中溶酶体途径主要降解细胞内吞的胞外蛋白质,泛素化降解途径主要降解胞内泛素标记的蛋白质。泛素蛋白降解系统是细胞内一系列生命进程的重要调节方式,与疾病的发生发展关系密切。目前的研究热点主要是针对泛素蛋白酶体系统的治疗疾病的新方法研究。该文就泛素蛋白酶体系统的组成及其在癌症、病毒感染、神经变性性疾病、糖尿病中的作用和治疗进行综述。     

蛋白泛素化降解途径与病毒感染的关系

泛素是具有高度保守性的76个氨基酸蛋白质,通过蛋白酶降解蛋白质。泛素-蛋白酶体途径是真核细胞内重要的蛋白质质控系统,参与调节细胞周期进程、抗原提呈、转录和信号转导等多种细胞生理过程,泛素化底物及其随后的降解过程贯穿于整个细胞的质膜系统,从细胞膜、内质网到核膜等等。病毒也利用泛素-蛋白酶体途径逃避宿主的免疫监测。因此,了解由泛素系统紊乱而引起的病毒感染具有重要意义。     

蛋白泛素化降解途径与病毒感染的关系

泛素是具有高度保守性的76个氨基酸蛋白质，通过蛋白酶降解蛋白质。泛素．蛋白酶体途径是真核细胞内重要的蛋白质质控系统，参与调节细胞周期进程、抗原提呈、转录和信号转导等多种细胞生理过程，泛素化底物及其随后的降解过程贯穿于整个细胞的质膜系统，从细胞膜、内质网到核膜等等。病毒也利用泛素．蛋白酶体途径逃避宿主的免疫监测。因此，了解由泛素系统紊乱而引起的病毒感染具有重要意义。     

PNGase在泛素-蛋白酶体系统和ERAD中的作用和意义

蛋白质代谢的内环境稳定是肿瘤细胞能够存活的关键生物学过程。泛素-蛋白酶体系统(ubiquitin-proteasomesystem,UPS)在细胞蛋白包括细胞周期调控蛋白的降解过程中起着极其重要的作用。因此,这一过程是所有细胞尤其是癌细胞增殖和存活的关键[1]。近年来的研究发现,一种多肽———N-寡糖酶(Peptide:N-glycanase,简称PNGase)与泛素-蛋白酶体途径高度偶联,在蛋白酶体降解细胞蛋白质的过程中发挥着重要的作用,并且已经越来越成为国外学者研究的热点。本文就PNGase参与细胞内蛋白降解机制及PNGase潜在的医学意义进行综述。1蛋白质代谢的泛素…     

蛋白酶体抑制剂MG132对卵巢癌作用机制的研究现状

泛素蛋白酶体途径(UPP)和自噬溶酶体途径(ALP)是真核细胞内蛋白质降解的2种重要途径。MG132是一种可逆性肽醛类蛋白酶体(proteasome)抑制剂,可进入细胞中可逆性抑制蛋白酶体活性,抑制UPP介导的蛋白质降解,从而诱导细胞凋亡。自噬性细胞死亡是一种不同于细胞凋亡的程序性死亡,细胞自噬是细胞利用溶酶体降解自身受损的大分子物质和细胞器的生理性细胞死亡过程。卵巢癌是女性生殖系统三大恶性肿瘤之一。晚期卵巢癌患者的5年生存率约为47%,是妇科恶性肿瘤中导致患者死亡率最高的肿瘤。MG132可通过调节凋亡蛋白表达,促进卵巢癌细胞凋亡,但是否可通过调控凋亡、自噬蛋白表达,促进卵巢癌细胞死亡,则迄今文献报道较少。笔者拟就蛋白酶体抑制剂MG132对卵巢癌的作用机制的最新研究现状进行阐述,旨在为MG132治疗卵巢癌提供理论基础。     

泛素-蛋白酶体途径及其对镉的应答反应

泛素-蛋白酶体途径是真核细胞内一种高效蛋白降解途径。它参与接触镉后细胞抗镉毒性的应答反应，是去除镉接触诱导产生的异常蛋白和修复镉损伤的DNA的重要途径。但接触镉也可使细胞内的泛素蛋白发生积聚，从而影响细胞的存活。这些反应的具体机制还有待进一步深入研究。     

结核分枝杆菌蛋白酶体研究进展

蛋白酶体是一种巨型蛋白质复合物,普遍存在于真核生物和古菌中,也存在于某些原核生物中[1].细胞内除溶酶体之外,蛋白酶体是主要的蛋白降解途径[2],其具有多种催化功能,可以选择性地降解细胞内不需要或受损的蛋白质,对于细胞代谢、基因表达调控、氧化应激等多种生物途径起着非常重要的作用[3].目前对蛋白酶体的认识主要来自于真核生物,其中结核分枝杆菌被认为是唯一具有蛋白酶体的病原性细菌[4].     

泛素-蛋白酶体系统与冠心病

泛素-蛋白酶体系统(UPS)是细胞内除溶酶体外重要的降解系统,也是真核生物细胞内主要的降解系统,UPS不仅是一种清除损伤或陈旧蛋白质的重要机制之一,而且还参与调节炎症、信号转导、转录调控和细胞凋亡等各种细胞生物学功能[1-3]。近年研究表明UPS可调节动脉粥样硬化、缺血后再灌注损伤、心脏衰竭等的发生和发展,且动物试验表明蛋白酶体抑制剂对冠心病可能有效,因而UPS可能成为冠心病诊断、监测和治疗的重要靶点之一。1 UPS的组成和功能UPS系统主要由泛素(Ub)、泛素活化酶(E1)、泛素结合酶(E2 s)、泛素-蛋白连接酶(E3 s)、26S蛋白…     

细胞外泛素作用的研究

泛素最初是从牛胸腺中分离出来的、含有76个氨基酸的多肽,参与T、B淋巴细胞的分化是早期对其功能的定位.随后的研究发现,泛素具有高度的遗传保守性,并普遍存在于所有真核细胞中,这也是其之所以得名"泛素"的原因.后期,因其在细胞内一种ATP依赖的选择性蛋白质降解路径中发挥重要作用,即泛素-蛋白酶体路径(UPP),而受到广泛的关注.在这一路径中,蛋白质首先被泛素标志修饰(即蛋白质的泛素化),然后被蛋白酶体识别,进而被降解.这使得人们对细胞如何控制及分裂蛋白质的研究深入到分子层面.     

胰岛素通过泛素系统对脓毒症病人骨骼肌代谢的调理作用

脓毒症病人中分解代谢增强现象极其普遍,尤以骨骼肌蛋白分解明显。泛素-蛋白酶体途径的激活为脓毒症病人骨骼肌蛋白分解的重要环节。其活性受炎性细胞因子和糖皮质激素等多因素影响。胰岛素在调理泛素-蛋白酶体途径的活性中起着重要的作用。以下就胰岛素通过泛素-蛋白酶体途径对脓毒症病人骨骼肌代谢的调理作用作一综述。     

Role of dendritic cells in recognizing antigens: their binding,transformation and presentation to T lymphocytes

The phenomenon of antigen presentation can be divided into three stages. 1) antigen uptake (recognition and internalization), which first of all concerns exogenous antigens; 2) intracellular enzymatic antigen processing and protein degradation followed by peptide loading of presenting molecules; 3) exocytosis of the antigen presenting molecules complex containing: a) MHC class II/exogenous antigens; b) MHC class I/endogenous antigens; c) MHC class I/exogenous antigens (so-called cross-presentation); d) CD1-lipids. This review presents the main stages of intracellular transport and the traffic of MHC molecules, which are believed to be different in dendritic cells (DC), in comparison with other antigen presenting cells, and enable DC to play the unique role in the initiation of immune response and the induction of tolerance.     

Ii-Key/MHC class II epitope hybrid peptide vaccines for HIV

The Ii-Key/MHC class II epitope hybrid acts on MHC class II molecules to facilitate replacement of antigenic peptides with the epitope tethered to the Ii-Key motif. Hybrid peptides linking an immunoregulatory segment of the Ii protein (Ii-Key peptide) through a polymethylene bridge to MHC class II epitopes of HIV gp160 or gag are potent vaccines to elicit CD4(+) T cell responses. More potent responses to two MHC class II epitopes, HIV gp160(843-852) or HIV gag(279-292), occurred in mice immunized with Ii-Key hybrid peptides than with epitope-only peptides, as measured in IL-4 and IFN-gamma ELISPOT assays of splenic lymphocytes stimulated in vitro by epitope-only peptides. Both the number of responding cells and cytokine output per cell were increased. The Ii-Key/MHC class II epitope hybrid acts on MHC class II molecules to facilitate replacement of antigenic peptides with the epitope tethered to the Ii-Key motif. Such antigenic peptide constructs create opportunities to enhance greatly Th1 or Th2 responses to MHC class II epitopes for therapeutic purposes.     

MHC class I- and class II-restricted processing and presentation of microencapsulated antigens

Macrophages were found of having a strong capacity of phagocytosing small size microcapsules (MS) and presenting microencapsulated antigens to either CD4+ and CD8- T cells. The class I-restricted presentation of microencapsulated tetanus toxoid by macrophages requires an intracellular processing which might follow the phagosome-to-cytosol route to enter the classical MHC class I presentation pathway. In contrast, presentation of microencapsulated cytotoxic peptide PbCS252-260 to specific CD8+ T cells has been observed with different APC and is not blocked by cytochalasin D, suggesting that peptide released from MS may directly bind to MHC class I molecules on the cell surface. In the case of MHC class II-restricted T cells, prefixation or treatment of macrophages with chloroquine, brefeldin A and cycloheximide inhibits the presentation of microencapsulated and soluble tetanus toxoid. These findings illustrate the capacity of microencapsulated antigens to enter different presentation pathways and should facilitate the development of subunit vaccines.     

In vitro processing and presentation of a lipidated cytotoxic T-cell epitope derived from measles virus fusion protein

Lipopeptidic formulations have been described as efficient activators of cytotoxic T lymphocytes (CTL). To better understand the pathway via which lipopeptides reach the MHC class I molecules we studied the intracellular processing and presentation of a measles virus-derived CTL epitope, to which a palmitoyl moiety was added synthetically. The palmitoyl group was conjugated to the N-terminus either directly or via a spacer sequence. The use of single or double fluorescent-labeled lipopeptides allowed the visualization of intracellular processing of these antigens using confocal microscopy. Our data indicate that the spacer composition influences internalization of the conjugate into the cell, proteasomal degradation, translocation into the ER by the transporter associated with antigen processing (TAP), and the intracellular trafficking of lipopeptides.     

Simultaneous cognate epitope recognition by bovine CD4 and CD8 T cells is essential for primary expansion of antigen-specific cytotoxic T-cells following ex vivo stimulation with a candidate Mycobacterium avium subsp. paratuberculosis peptide vaccine

Studies in cattle show CD8 cytotoxic T cells (CTL), with the ability to kill intracellular bacteria, develop following stimulation of monocyte-depleted peripheral blood mononuclear cells (mdPBMC) with antigen presenting cells (APC, i.e. conventional dendritic cells [cDC] and monocyte-derived DC [MoDC]) pulsed with MMP, a membrane protein from Mycobacterium avium subsp. paratuberculosis (Map) encoded by MAP2121c. CTL activity was diminished if CD4 T cells were depleted from mdPBMC before antigen (Ag) presentation by APC, suggesting simultaneous cognate recognition of MMP epitopes presented by MHC I and MHC II molecules to CD4 and CD8 T cells is essential for development of CTL activity. To explore this possibility, studies were conducted with mdPBMC cultures in the presence of monoclonal antibodies (mAbs) specific for MHC class I and MHC class II molecules. The CTL response of mdPBMC to MMP-pulsed APC was completely blocked in the presence of mAbs to both MHC I and II molecules and also blocked in the presence of mAbs to either MHC I or MHC II alone. The results demonstrate simultaneous cognate recognition of Ag by CD4 and CD8 T cells is essential for delivery of CD4 T cell help to CD8 T cells to elicit development of CTL.     

Role of MHC class Ib molecule,H2-M3 in host immunity against tuberculosis

The MHC class I family comprises both classical (class Ia) and non-classical (class Ib) members. While the prime function of classical MHC class I molecules (MHC class Ia) is to present peptide antigens to pathogen-specific cytotoxic T cells, non-classical MHC-I (MHC class Ib) antigens perform diverse array of functions in both innate and adaptive immunity. Vaccines against intracellular pathogens such as Mycobacterium tuberculosis need to induce strong cellular immune responses. Recent studies have shown that MHC class I molecules play an important role in the protective immune response to M. tuberculosis infection. Both MHC Ia-restricted and MHC class Ib-restricted M. tuberculosis -reactive CD8⁺ T cells have been identified in humans and mice, but their relative contributions to immunity is still uncertain. Unlike MHC class Ia-restricted CD8⁺ T cells, MHC class Ib-restricted CD8⁺ T cells are constitutively activated in naive animals and respond rapidly to infection challenge, hence filling the temporal gap between innate and adaptive immunity. The present review article summarizes the general host immunity against M. tuberculosis infection highlighting the possible role of MHC class Ib molecule, H2-M3 and their ligands (N-formylated peptides) in protection against tuberculosis.     

Naked DNA in cells: An inducer of major histocompatibility complex molecules to evoke autoimmune responses?

The major histocompatibility complex (MHC) is the exclusive chaperone that presents intracellular antigens, either self or foreign to T cells. Interestingly, aberrant expression of MHC molecules has been reported in various autoimmune target tissues such as thyroid follicular cells in Grave’s disease. Herein, we review the discovery of an unexpected effect of cytosolic double-stranded DNA (dsDNA), despite its origins, to induce antigen processing and presenting genes, including MHC molecules, in non-immune cells. Moreover, we highlight several recent studies that suggest cell injury endows thyroid epithelial cells with a phenotype of mature antigen presenting cells by inducing multiple antigen processing and presenting genes via releasing genomic DNA fragments into the cytosol. We discuss the possibility that such cytosolic dsDNA, in naked form without binding to histone proteins, might be involved in the development of cell damage-triggered autoimmune responses. We also discuss the possible molecular mechanism by which cytosolic dsDNA can induce MHC molecules. It is reasonable to speculate that cytosolic dsDNA-induced MHC class I is partially due to an autocrine/paracrine effect of type I interferon (IFN). While the mechanism of cytosolic dsDNA-induced MHC class II expression appears, at least partially, distinct from that mediated by IFN-γ. Further in-depth are required to clarify this picture.     

Peptide-binding assays and HLA II transgenic Abeta degrees mice are consistent and complementary tools for identifying HLA II-restricted peptides

The identification of MHC class II-restricted peptides has become a priority for the development of peptide-based prophylactic and therapeutic vaccines. The aim of this study was to assess the correlations between peptide-binding assays on purified HLA II molecules and immunization of human HLA II transgenic mice deficient in murine class II molecules (Abeta degrees ). We used as models two MHC class II-restricted peptides, one derived from the HIV Nef regulatory protein (Nef (56-68)) and the other from the Schistosoma mansoni 28-kDa glutathione-S-transferase (Sm28GST (190-211)). High correlations were found between the two approaches, which showed that the Nef (56-68) and Sm28GST (190-211) peptides may represent promiscuous ligands for HLA-DQ and for HLA-DR molecules, respectively. We suggest a rational method based on the combination of peptide-binding assays and HLA II transgenic mice experiments as consistent and complementary tools for selecting T helper epitopes.     

Modulation of immunoproteasome subunits by liposomal lipid A

Liposomes are phospholipid vesicles that have been used as carriers of antigens and adjuvants. Lipid A, the endotoxic moiety of Gram-negative bacterial lipopolysaccharide is a potent adjuvant and incorporation into liposomes essentially reduces the endotoxic activity of lipid A. In this study, we analyzed the effect of liposomal lipid A [L(LA)] on the MHC class I antigen processing machinery in murine antigen presenting cells (APCs). L(LA) enhanced the surface expression of MHC class I, class II, CD80, and CD86 molecules, induced the secretion of IFN-gamma, IL-12p40, TNF-alpha and IL-10, and caused a shift in the proteasome profile from constitutive to immunoproteasomes as observed by the induction of beta2i, beta5i, PA28alpha, and PA28beta subunits. L(LA) acts through the production of IFN-gamma as demonstrated with APCs generated from IFN-gamma knockout mice. L(LA) therefore appears to act as an intracellular adjuvant by upregulating the antigen processing machinery, which could result in efficient antigen presentation.