泛素融合降解蛋白UFD1的结构与功能

泛素-蛋白酶体途径是细胞内蛋白质选择性降解的主要途径,参与多种真核生物细胞生理过程,与细胞的生理功能和病理状态有着密切的关系。该途径中UFD1作为泛素识别因子介导泛素化的靶蛋白至26S蛋白酶体降解。该文在概述泛素-蛋白酶体途径作用机制的基础上,对哺乳动物和酵母UFD1蛋白的结构及其在细胞周期调控、转录调控、内质网相关蛋白降解中的功能进行了综述。     

Development of inhibitors in the ubiquitination cascade

The ubiquitin proteasome system (UPS) is essential in regulating myriad aspects of protein functions. It is therefore a fundamentally important regulatory mechanism that impacts most if not all aspects of cellular processes. Indeed, malfunction of UPS components is implicated in human diseases such as neurodegenerative and immunological disorders and many cancers. The success of proteasome inhibitors in cancer therapy suggests that modulating enzymes in the ubiquitination cascade would be clinically important for therapeutic benefits. In this review, we summarize advances in developing inhibitors of a variety of UPS components. In particular, we highlight recent work done on the protein engineering of ubiquitin as modulators of the UPS, a novel approach that may shed light on innovative drug discovery in the future.     

泛素/26S蛋白酶体系统介导的细胞程序化死亡

在一定的生理或者病理条件下,细胞为了自身发育或者抵御不良刺激,会采取细胞程序化死亡（programmed cell death,PCD）的方式结束生命。泛素/26S蛋白酶体系统（ubiquitin-26S proteasome system,UPS）作为生物体中重要的翻译后蛋白质调节系统,对PCD起着关键的调节作用。该文介绍UPS通过两条细胞凋亡信号转导通路以及天冬氨酸特异性半胱氨酸蛋白酶来调控PCD的研究进展。     

The role of the ubiquitin proteasome system in synapse remodeling and neurodegenerative diseases

The ubiquitin proteasome system is a potent regulatory mechanism used to control protein stability in numerous cellular processes, including neural development. Many neurodegenerative diseases are featured by the accumulation of UPS-associated proteins, suggesting the UPS dysfunction may be crucial for pathogenesis. Recent experiments have highlighted the UPS as a key player during synaptic development. Here we summarize recent discoveries centered on the role of the UPS in synapse remodeling and draw attention to the potential link between the synaptic UPS dysfunction and the pathology of neurodegenerative diseases.     

The ubiquitin-proteasome system in cardiac physiology and pathology

The ubiquitin-proteasome system (UPS) is the major nonlysosomal pathway for intracellular protein degradation, generally requiring a covalent linkage of one or more chains of polyubiquitins to the protein intended for degradation. It has become clear that the UPS plays major roles in regulating many cellular processes, including the cell cycle, immune responses, apoptosis, cell signaling, and protein turnover under normal and pathological conditions, as well as in protein quality control by removal of damaged, oxidized, and/or misfolded proteins. This review will present an overview of the structure, biochemistry, and physiology of the UPS with emphasis on its role in the heart, if known. In addition, evidence will be presented supporting the role of certain muscle-specific ubiquitin protein ligases, key regulatory components of the UPS, in regulation of sarcomere protein turnover and cardiomyocyte size and how this might play a role in induction of the hypertrophic phenotype. Moreover, this review will present the evidence suggesting that proteasomal dysfunction may play a role in cardiac pathologies such as myocardial ischemia, congestive heart failure, and myofilament-related and idiopathic-dilated cardiomyopathies, as well as cardiomyocyte loss in the aging heart. Finally, certain pitfalls of proteasome studies will be described with the intent of providing investigators with enough information to avoid these problems. This review should provide current investigators in the field with an up-to-date analysis of the literature and at the same time provide an impetus for new investigators to enter this important and rapidly changing area of research.     

The ubiquitin‐proteasome system in plant responses to environments

The ubiquitin‐proteasome system (UPS) is a rapid regulatory mechanism for selective protein degradation in plants and plays crucial roles in growth and development. There is increasing evidence that the UPS is also an integral part of plant adaptation to environmental stress, such as drought, salinity, cold, nutrient deprivation and pathogens. This review focuses on recent studies illustrating the important functions of the UPS components E2s, E3s and subunits of the proteasome and describes the regulation of proteasome activity during plant responses to environment stimuli. The future research hotspots and the potential for utilization of the UPS to improve plant tolerance to stress are discussed.     

In situ dynamically monitoring the proteolytic function of the ubiquitin-proteasome system in cultured cardiac myocytes

The ubiquitin-proteasome system (UPS) is responsible for turnover of most cellular proteins in eukaryotes. Protein degradation by the UPS serves quality control and regulatory functions. Proteasome inhibition showed great promise in effectively treating cancer and restenosis. UPS dysfunction in cardiac hypertrophy and failure has recently been suspected but remains to be investigated. A system capable of monitoring dynamic changes in proteolytic function of the UPS in cardiac myocytes in situ would no doubt benefit significantly efforts to decipher the pathogenic significance of UPS dysfunction in the heart and to evaluate the effect of proteasome inhibition on cardiac myocytes. We successfully established such a system in cultured cardiac myocytes by delivering and expressing a modified green fluorescence protein (GFPu) gene using recombinant adenoviruses. GFPu contains a ubiquitination signal sequence fused to the COOH terminus. Fluorescence microscopy and Western blots revealed that protein abundance of modified green fluorescent protein (GFPu), but not wild-type green fluorescent protein, in cultured cardiac myocytes was incrementally increased when function of the proteasomes was inhibited in various degrees by specific inhibitors. The increase in GFPu protein levels and fluorescence intensity is paralleled by a decrease in the in vitro peptidase activity of the proteasomes. Our results demonstrate that GFPu can be used as a surrogate marker to monitor dynamic changes in proteolytic function of the UPS in cardiac myocytes in situ. Application of this novel system reveals that moderate levels of H2O2, a reactive oxygen species generator, impair proteolytic function of the UPS in cultured cardiac myocytes.     

细菌转录起始调控机制*

原核生物同一种群的每个细胞都是和外界环境直接接触的,它们主要通过开启或关闭某些基因的表达来适应环境条件。所以,环境因子往往是调控的效应因子,必须严格调控转录来确保细胞对环境改变做出有效且充分的反应。原核生物基因的表达受多种因素的调控,而对于大多数细菌来说,调控基因表达的关键步骤是启动子识别和RNA聚合酶启动转录。在细菌的细胞中,可以通过调节RNA聚合酶的活性以及改变RNA聚合酶对启动子的结合来优化基因的转录过程以适应不同环境变化。总结了目前已发现的参与细菌细胞转录调节的各类因子,从这些因子对启动子的作用、RNA聚合酶的作用以及两者的相互作用等方面阐述它们调控基因表达的分子机制。总结多种基因调控的作用,加深对转录起始过程的认识,希望能对未来调控转录起始过程来实现目标基因的高效表达和不利基因的抑制表达提供思路,为以后的工业菌株改造提供依据。     

Ubiquitin-proteasome system components are upregulated during intestinal regeneration

The ubiquitin proteasome system (UPS) is the main proteolytic system of cells. Recent evidence suggests that the UPS plays a regulatory role in regeneration processes. Here, we explore the possibility that the UPS is involved during intestinal regeneration of the sea cucumber Holothuria glaberrima. These organisms can regenerate most of their digestive tract following a process of evisceration. Initially, we identified components of H. glaberrima UPS, including sequences for Rpn10, β3, and ubiquitin-RPL40. Predicted proteins from the mRNA sequences showed high degree of conservation that ranged from 60% (Rpn10) to 98% (Ub-RPL40). Microarrays and RT-PCR experiments showed that these genes were upregulated during intestinal regeneration. In addition, we demonstrated expression of alpha 20S proteasome subunits and ubiquitinated proteins during intestinal regeneration and detected them in the epithelium and connective tissue of the regenerating intestine. Finally, the intestinal regeneration was altered in animals treated with MG132, a proteasome inhibitor. These findings support our contention that proteasomes are playing an important role during intestinal regeneration.     

Proteasome functional insufficiency in cardiac pathogenesis

The ubiquitin-proteasome system (UPS) is responsible for the degradation of most cellular proteins. Alterations in cardiac UPS, including changes in the degradation of regulatory proteins and proteasome functional insufficiency, are observed in many forms of heart disease and have been shown to play an important role in cardiac pathogenesis. In the past several years, remarkable progress in understanding the mechanisms that regulate UPS-mediated protein degradation has been achieved. A transgenic mouse model of benign enhancement of cardiac proteasome proteolytic function has been created. This has led to the first demonstration of the necessity of proteasome functional insufficiency in the genesis of important pathological processes. Cardiomyocyte-restricted enhancement of proteasome proteolytic function by overexpression of proteasome activator 28α protects against cardiac proteinopathy and myocardial ischemia-reperfusion injury. Additionally, exciting advances have recently been achieved in the search for a pharmacological agent to activate the proteasome. These breakthroughs are expected to serve as an impetus to further investigation into the involvement of UPS dysfunction in molecular pathogenesis and to the development of new therapeutic strategies for combating heart disease. An interplay between the UPS and macroautophagy is increasingly suggested in noncardiac systems but is not well understood in the cardiac system. Further investigations into the interplay are expected to provide a more comprehensive picture of cardiac protein quality control and degradation.     

Proteasome deubiquitinases as novel targets for cancer therapy

The ubiquitin-proteasome system (UPS) is a conserved pathway regulating numerous biological processes including protein turnover, DNA repair, and intracellular trafficking. Tumor cells are dependent on a functioning UPS, making it an ideal target for the development of novel anti-cancer therapies. The development of bortezomib (Velcade^®) as a treatment for multiple myeloma and mantle cell lymphoma has verified this and suggests that targeting other components of the UPS may be a viable strategy for the treatment for cancer. We recently described a novel class of proteasome inhibitors that function by an alternative mechanism of action (D’Arcy et al., 2011). The small molecule b-AP15 blocks the deubiquitinase (DUB) activity of the 19S regulatory particle (19S RP) without inhibiting the proteolytic activities of the 20S core particle (20S CP). b-AP15 inhibits two proteasome-associated DUBs, USP14 and UCHL5, resulting in a rapid accumulation of high molecular weight ubiquitin conjugates and a functional proteasome shutdown. Interestingly, b-AP15 displays several differences to bortezomib including insensitivity to over-expression of the anti-apoptotic mediator Bcl-2 and anti-tumor activity in solid tumor models. In this review we will discuss the potential of proteasome deubiquitinase inhibitors as additions to the therapeutic arsenal against cancer.     

An insight into the ubiquitin-proteasomal axis and related therapeutic approaches towards central nervous system malignancies

The Ubiquitin-Protease system (UPS) is a major destruction system responsible for eliminating dysfunctional/misfolded proteins, thus acting as a pivotal regulator of protein homeostasis in eukaryotic cells. In this review, the UPS system and its various functions in the cell and their detailed impact such as cell cycle control, DNA damage response, apoptosis, and cellular stress regulations have been elucidated with a focus on the central nervous system. Since the Ubiquitin-Protease pathway(UPP) plays a prominent role in the sculpting of the CNS cells and their maintenance, it is naturally deeply involved in many malignancies that develop due to dysregulation of the UPS. Understanding the major disruptive players of the UPS in the development of these malignancies, for example, insoluble protein aggregates or inclusion bodies deposits due to malfunctioning of the UPS has paved the pathway for the development of new therapeutics. Here, the de-regulation of the UPS at various checkpoints in CNS malignancies has been detailed, thus facilitating an easy comprehension of the different targets that remain to be explored yet. The present therapeutic advancements in the field of CNS malignancies management through UPS targeting have also been included thus broadening the scope of drug development. Thus, this review while shedding sufficient light on the details of the UPS system and its connection to CNS malignancies, also opens new avenues for therapeutic advancements in the form of novel targetable UPP proteins and their interactions.