Skp2与恶性肿瘤的关系

细胞内泛素-蛋白酶体途径通过泛素化许多周期相关蛋白对其进行降解,在细胞周期发展、基因转录及信号转导等过程巾发挥重要作用。此途径主要包括两步,即蛋白的泛素化,由泛素激活酶（E1）、泛素结合酶（E2）及泛素连接酶（E3）等共同完成;经泛素化的蛋白随后被26S蛋白酶体复合物降解。     

USP22在恶性肿瘤中的研究进展

去泛素化酶从不同底物上移除泛素,起到调控蛋白质活性和维持细胞内环境稳态的作用。去泛素化酶在细胞的转录后修饰过程中发挥重要作用,当去泛素化酶调控机制出现异常则会引起不同类型疾病的发生。而异常表达特异性去泛素化酶22（ USP22）常与癌症预后不良有关。本文就USP22在肿瘤中的研究现状进行综述。     

PSMD7基因在人食管鳞癌组织中的表达及影响癌细胞增殖、凋亡的机制研究

背景与目的：26S蛋白酶体非ATP酶调节亚基7（26S proteasome non-ATPase regulatory subunit 7,PSMD7）作为组成19S蛋白酶体盖子结构的核心成员是否参与肿瘤的发生、发展,以及具体的分子机制尚不清楚。本实验将研究PSMD7基因在人食管鳞癌组织中的表达,以及对癌细胞增殖及凋亡的影响。方法：采用实时荧光定量聚合酶链反应（real-time fluorescent quantitative polymerase chain reaction,RTFQ-PCR）和蛋白质印迹法（Western blot）检测食管鳞癌及其癌旁正常组织标本中PSMD7的mRNA及蛋白表达情况。在人食管鳞癌细胞系TE-1中,用慢病毒介导的RNA干扰技术下调PSMD7的表达,观察细胞增殖及凋亡的变化,检测线粒体膜电位的变化、细胞质中Cyt C的表达以及凋亡相关因子的表达。结果：PSMD7基因的mRNA和蛋白在食管鳞癌组织中的表达显著高于癌旁正常组织（P<0.05）,PSMD7蛋白的高表达与淋巴结转移阳性呈正相关（P<0.05）。抑制PSMD7蛋白的表达可使细胞的增殖能力降低（P<0.05）,并促进细胞的凋亡（P<0.05）,同时线粒体膜电位降低,促进Cyt C释放进入细胞质,激活caspase级联反应,说明抑制PSMD7的表达诱导细胞凋亡是通过线粒体信号通路进行的。结论：PSMD7在食管鳞癌中呈高表达,并通过线粒体依赖的方式促进TE-1细胞凋亡。     

Cullin3在肿瘤中的研究进展

泛素一蛋白酶体系统（ubiquitin—proteasome system,UPS）是蛋白质翻译后调控的重要途径,能够维持机体内蛋白质水平的平衡。Cullin3（Cul3）作为支架蛋白参与构成泛素连接酶复合物,通过与具有BTB（bric—abrac,tramtrack,and broad complex）结构域的接头蛋白结合,特异性识别底物并介导底物泛素化,参与胚胎发育、细胞周期调控和血压调节等生理过程。研究发现,Cul3功能失调后导致原癌蛋白积累或过度降解肿瘤抑制蛋白,与肿瘤密切相关。因此,本文将就泛素-蛋白酶体系统、E3泛素连接酶复合物,以及Cul3介导底物蛋白降解从而促进或抑制肿瘤的发生、发展作综述。     

去泛素化酶USP22在恶性肿瘤中多样性的作用机制

泛素特异性酶22（USP22）是哺乳动物中一种高度保守的泛素水解酶，通过对底物蛋白的去泛素化修饰阻止蛋白降解，参与调节基因转录、DNA损伤修复及胚胎发育等生命过程，已被证实调控多种途径介导肿瘤的发生发展。本文着重讨论USP22通过去泛素化修饰功能调节肿瘤发生发展的相关作用机制。     

去泛素化酶在肿瘤发生中的作用

泛素-蛋白酶体系统是细胞内非常重要的蛋白质降解调节系统。蛋白质泛素化和去泛素化调节的动态平衡,影响或者调节细胞的生长发育、信号转导、神经病变或者肿瘤等许多细胞生理病理过程。目前研究证实,细胞内广泛存在多种去泛素化酶,通过选择性地降解或稳定癌基因、抑癌基因以及其他与细胞生物学相关的底物蛋白,与肿瘤的发生、发展密切相关。本文对去泛素化酶的分类、结构、作用机制、活性调节及其在肿瘤发生中的作用作一综述,拟为研究肿瘤的发生、发展提供新的理论依据,并有助于我们开发以及应用针对去泛素化酶的分子靶向药物。     

Skp2 的研究进展

  细胞内泛素-蛋白酶体途径通过对泛素化蛋白进行降解，在细胞周期发展、基因转录及信号转导等过程中发挥重要作用。此途径主要包括两步，即蛋白的泛素化，由泛素激活酶(E1)，泛素结合酶(E2)及泛素连接酶(E3)等共同完成；经泛素化的蛋白随后被26S蛋白酶体复合物降解。E3家族成员SCFSkp2泛素连接酶由Skp2与Skp1，Cul1／cdc53及Rbxl结合形成。Skp2属F-盒蛋白家族成员,在泛素化过程中负责对底物蛋白的识别而决定SCF^Skp2复合物作用的特异性。Skp2 通过对多种靶蛋白的泛素化降解而与细胞周期调控及肿瘤的发生、发展和预后密切相关。     

E3泛素连接酶FBXL5与恶性肿瘤关系的研究进展

泛素化修饰是蛋白质降解的信号,调节体内蛋白质翻译后修饰的重要途径之一[1] ,密切参与细胞周期、信号转导、DNA修复、免疫反应、转录调控等. 泛素化修饰中的泛素连接酶与肿瘤的发生、发展密切相关[2]. 泛素化修饰被3种关键酶共同介导,其中E3泛素连接酶介导活泛素分子从结合酶E2转移到底物,不同的泛素连接酶靶向不同的底物蛋白,决定泛素化修饰的特异性,故E3连接酶于泛素化修饰中具有至关重要作用,已成为当前研究、探讨的热点问题之一.     

薯蓣皂苷靶向泛素-蛋白酶体的抗肿瘤活性研究

目的基于中药活性分子开发靶向泛素-蛋白酶体系统(UPS)的抗肿瘤小分子。方法建立稳定表达UbG76V-GFP融合蛋白的细胞系来筛选靶向UPS的新型小分子抑制剂。通过Suc-LLVY-AMC、Z-LLE-AMC和Boc-LRR-AMC底物检测薯蓣皂苷对20S蛋白酶体水解酶活性的影响,使用Ub-AMC底物评价其对细胞内去泛素化酶活性的作用。采用Western blot检测薯蓣皂苷对细胞内泛素化水平的影响。CCK-8和克隆形成实验检测薯蓣皂苷对肿瘤细胞增殖的抑制作用。结果通过UbG76V-GFP报告系统筛选发现薯蓣皂苷是新型的UPS抑制剂,可以抑制细胞内去泛素化酶活性,增强细胞内泛素化水平,抑制肿瘤细胞增殖,减少克隆形成。结论薯蓣皂苷靶向泛素-蛋白酶体可显著抑制肿瘤细胞增殖。     

去泛素化酶在肝癌发生发展中的研究进展

泛素-蛋白酶体途径(ubiquitin-proteasome pathway,UPP)是细胞内蛋白降解的重要调节系统。近年来的研究发现,去泛素化酶在肝癌中发挥重要作用。去泛素化酶可以逆转蛋白质泛素化降解过程,进而影响肿瘤的发生发展过程,包括凋亡和自噬、肿瘤的信号通路、细胞周期的调节和DNA损伤等。小分子抑制剂可以通过抑制去泛素化酶的功能起到抗肿瘤作用。本文对去泛素化酶在肝癌发生发展中的作用及特异性去泛素化酶小分子抑制剂进行综述,为寻找肝癌新的药物治疗靶点提供理论依据。     

Over-expression of genes and proteins of ubiquitin specific peptidases (USPs) and proteasome subunits (PSs) in breast cancer tissue observed by the methods of RFDD-PCR and proteomics

The ubiquitin–proteasome system facilitates the degradation of damaged proteins and regulators of growth and stress response. Alterations in this proteolytic system are associated with a variety of human pathologies. By restriction fragment differential display polymerase chain reaction (RFDD-PCR) and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF-TOF MS) based on two-dimensional polyacrylamide gel electrophoresis (2-DE), differentially expressed genes and proteins of ubiquitin specific proteases (USPs), proteasome subuinits (PSs) and ubiquitin protein ligase E3A (UBE3A) were analyzed between breast cancer and adjacent normal tissues. Some of them were further verified as over-expression by immunohistochemical stain. Five genes of proteasome subunits (PSs), including PSMB5, PSMD1, PSMD2, PSMD8 and PSMD11, four genes of USPs, including USP9X, USP9Y, USP10 and USP25, and ubiquitin protein ligase E3A (UBE3A) were over-expressed (>3-fold) in breast cancer tissue compared to adjacent normal tissue, and over-expression (>4-fold) of proteins of PSMA1 and SMT3A were observed in breast cancer tissue. PSMD8, PSMD11 and UBE3A were further verified as over-expression by immunohistochemical stain. The action of ubiquitin–proteasome system were obviously enhanced in breast cancer, and selectively intervention in action of ubiquitin–proteasome system may be a useful method of treating human breast cancer.     

Proteasomal non-catalytic subunit PSMD2 as a potential therapeutic target in association with various clinicopathologic features in lung adenocarcinomas

We previously identified PSMD2, a subunit of the 19S regulatory complex of proteasomes, as a constituent of a signature associated with the acquisition of metastatic phenotype and poor prognosis in lung cancers. In the present study, we found that knockdown of PSMD2 decreased proteasome activity, and induced growth inhibition and apoptosis in lung cancer cell lines. These effects of siRNA-mediated PSMD2 inhibition were associated with changes in the balance between phosphorylated AKT and p38, as well as with induction of p21. In addition, patients with higher PSMD2 expression had poorer prognosis and a small fraction of lung cancer specimens carried increased copies of PSMD2. Notably, our findings clearly illustrate that lung adenocarcinomas can be divided into two groups; those with and without general upregulation of proteasome pathway genes including PSMD2. This general upregulation was significantly more prevalent in the non-terminal respiratory unit (non-TRU)-type, a recently proposed genetically and clinicopathologically relevant expression profile-defined classification of adenocarcinomas (P?相似文献   

Proteasome function is required for DNA damage response and fanconi anemia pathway activation

Proteasome inhibitors sensitize tumor cells to DNA-damaging agents, including ionizing radiation (IR), and DNA cross-linking agents (melphalan and cisplatin) through unknown mechanisms. The Fanconi anemia pathway is a DNA damage-activated signaling pathway, which regulates cellular resistance to DNA cross-linking agents. Monoubiquitination and nuclear foci formation of FANCD2 are critical steps of the Fanconi anemia pathway. Here, we show that proteasome function is required for the activation of the Fanconi anemia pathway and for DNA damage signaling. Proteasome inhibitors (bortezomib and MG132) and depletion of 19S and 20S proteasome subunits (PSMD4, PSMD14, and PSMB3) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, whereas depletion of DSS1/SHFM1, a subunit of the 19S proteasome that also directly binds to BRCA2, did not inhibit FANCD2 monoubiquitination or foci formation. On the other hand, DNA damage-signaling processes, such as IR-induced foci formation of phosphorylated ATM (phospho-ATM), 53BP1, NBS1, BRCA1, FANCD2, and RAD51, were delayed in the presence of proteasome inhibitors, whereas ATM autophosphorylation and nuclear foci formation of gammaH2AX, MDC1, and RPA were not inhibited. Furthermore, persistence of DNA damage and abrogation of the IR-induced G(1)-S checkpoint resulted from proteasome inhibition. In summary, we showed that the proteasome function is required for monoubiquitination of FANCD2, foci formation of 53BP1, phospho-ATM, NBS1, BRCA1, FANCD2, and RAD51. The dependence of specific DNA damage-signaling steps on the proteasome may explain the sensitization of tumor cells to DNA-damaging chemotherapeutic agents by proteasome inhibitors.     

A new mechanism of ubiquitin-dependent proteolytic pathway--polyubiquitin chain recognition and proteasomal targeting

The RPN10 subunit of 26S proteasome and several UBA domain proteins can bind to the polyubiquitin chain and play a role as ubiquitin receptors of the 26S proteasome. Although it was thought that substrate recognition is an essential step in the proteasome-mediated protein degradation, deletion of rpn10 genes in yeast does not influence the viability of cells but instead causes only a mild phenotype, suggesting that the above ubiquitin receptors are redundantly involved in substrate delivery to the proteasome. However, their functional difference is still enigmatic. In this review, we summarize recent advances in polyubiquitin chain recognition/delivery system and provide potential applications to modulate this system as a probable target for drug development.     

Activation of ATP-ubiquitin-dependent proteolysis in skeletal muscle in vivo and murine myoblasts in vitro by a proteolysis-inducing factor (PIF).

Loss of skeletal muscle is a major factor in the poor survival of patients with cancer cachexia. This study examines the mechanism of catabolism of skeletal muscle by a tumour product, proteolysis-inducing factor (PIF). Intravenous administration of PIF to normal mice produced a rapid decrease in body weight (1.55 +/- 0.12 g in 24 h) that was accompanied by increased mRNA levels for ubiquitin, the Mr 14 000 ubiquitin carrier-protein, E2, and the C9 proteasome subunit in gastrocnemius muscle. There was also increased protein levels of the 20S proteasome core and 19S regulatory subunit, detectable by immunoblotting, suggesting activation of the ATP-ubiquitin-dependent proteolytic pathway. An increased protein catabolism was also seen in C(2)C(12)myoblasts within 24 h of PIF addition with a bell-shaped dose-response curve and a maximal effect at 2-4 nM. The enhanced protein degradation was attenuated by anti-PIF antibody and by the proteasome inhibitors MG115 and lactacystin. Glycerol gradient analysis of proteasomes from PIF-treated cells showed an elevation in chymotrypsin-like activity, while Western analysis showed a dose-related increase in expression of MSSI, an ATPase that is a regulatory subunit of the proteasome, with a dose-response curve similar to that for protein degradation. These results confirm that PIF acts directly to stimulate the proteasome pathway in muscle cells and may play a pivotal role in protein catabolism in cancer cachexia.     

Deubiquitinase inhibition by small-molecule WP1130 triggers aggresome formation and tumor cell apoptosis

Recent evidence suggests that several deubiquitinases (DUB) are overexpressed or activated in tumor cells and many contribute to the transformed phenotype. Agents with DUB inhibitory activity may therefore have therapeutic value. In this study, we describe the mechanism of action of WP1130, a small molecule derived from a compound with Janus-activated kinase 2 (JAK2) kinase inhibitory activity. WP1130 induces rapid accumulation of polyubiquitinated (K48/K63-linked) proteins into juxtanuclear aggresomes, without affecting 20S proteasome activity. WP1130 acts as a partly selective DUB inhibitor, directly inhibiting DUB activity of USP9x, USP5, USP14, and UCH37, which are known to regulate survival protein stability and 26S proteasome function. WP1130-mediated inhibition of tumor-activated DUBs results in downregulation of antiapoptotic and upregulation of proapoptotic proteins, such as MCL-1 and p53. Our results show that chemical modification of a previously described JAK2 inhibitor results in the unexpected discovery of a novel DUB inhibitor with a unique antitumor mechanism.     

A portrayal of E3 ubiquitin ligases and deubiquitylases in cancer

E3 ubiquitin ligases and deubiquitylating enzymes (DUBs) are the key components of ubiquitin proteasome system which plays a critical role in cellular protein homeostasis. Any shortcoming in their biological roles can lead to various diseases including cancer. The dynamic interplay between ubiquitylation and deubiquitylation determines the level and activity of several proteins including p53, which is crucial for cellular stress response and tumor suppression pathways. In this review, we describe the different types of E3 ubiquitin ligases including those targeting tumor suppressor p53, SCF ligases and RING type ligases and accentuate on biological functions of few important E3 ligases in the cellular regulatory networks. Tumor suppressor p53 level is tightly regulated by multiple E3 ligases including Mdm2, COP1, Pirh2, etc. SCF ubiquitin ligase complexes are key regulators of cell cycle and signal transduction. BRCA1 and VHL RING type ligases function as tumor suppressors and play an important role in DNA repair and hypoxia response respectively. Further, we discuss the biological consequences of deregulation of the E3 ligases and the implications for cancer development. We also describe deubiquitylases which reverse the process of ubiquitylation and regulate diverse cellular pathways including metabolism, cell cycle control and chromatin remodelling. As the E3 ubiquitin ligases and DUBs work in a substrate specific manner, an improved understanding of them can lead to better therapeutics for cancer.