The adenovirus E4orf6 E3 ubiquitin ligase complex assembles in a novel fashion

The human adenovirus E4orf6 and E1B55K proteins are part of an E3 ubiquitin ligase complex that degrades p53, Mre11 and probably other cellular polypeptides. Our group has demonstrated previously that this complex contains Cul5, Rbx1 and Elongin B and C and is formed through interactions of these cellular proteins with E4orf6. Although this E4orf6 complex is similar in many ways to the cellular SCF and VBC E3 ligase complexes, our previous work indicated that unlike all known Cullin-containing complexes, E4orf6 contains two functional BC-box motifs that permit interactions with Elongin B and C. Here we show that a third BC-box exists that also appears to be fully functional. In addition, we attempted to identify a region in E4orf6 responsible for the specific selection of Cul5, which we show herein by knocking down Cul5 protein levels, is essential for p53 degradation. One sequence within E4orf6 shares limited homology with the 'Cul5 box motif', a recently identified sequence found to be responsible for selection of Cul5 in some cellular Cullin-containing E3 ligase complexes; however, genetic analysis indicated that this motif is not involved in Cullin binding or p53 degradation. Thus E4orf6 appears to utilize a different mechanism for Cul5 selection, and, both in terms of interactions with Elongin B and C and with Cul5, assembles the E3 ligase complex in a highly novel fashion.     

Multiple functions of the E3 ubiquitin ligase CHIP in immunity

The carboxyl terminal of Hsp70-interacting protein (CHIP) is an E3 ubiquitin ligase that plays a pivotal role in the protein quality control system by shifting the balance of the folding-refolding machinery toward the degradative pathway. However, the precise mechanisms by which nonnative proteins are selected for degradation by CHIP either directly or indirectly via chaperone Hsp70 or Hsp90 are still not clear. In this review, we aim to provide a comprehensive model of the mechanism by which CHIP degrades its substrate in a chaperone-dependent or direct manner. In addition, through tight regulation of the protein level of its substrates, CHIP plays important roles in many physiological and pathological conditions, including cancers, neurological disorders, cardiac diseases, bone metabolism, immunity, and so on. Nonetheless, the precise mechanisms underlying the regulation of the immune system by CHIP are still poorly understood despite accumulating developments in our understanding of the regulatory roles of CHIP in both innate and adaptive immune responses. In this review, we also aim to provide a view of CHIP-mediated regulation of immune responses and the signaling pathways involved in the model described. Finally, we discuss the roles of CHIP in immune-related diseases.     

Mechanism of CRL4(Cdt2), a PCNA-dependent E3 ubiquitin ligase

Eukaryotic cell cycle transitions are driven by E3 ubiquitin ligases that catalyze the ubiquitylation and destruction of specific protein targets. For example, the anaphase-promoting complex/cyclosome (APC/C) promotes the exit from mitosis via destruction of securin and mitotic cyclins, whereas CRL1(Skp2) allows entry into S phase by targeting the destruction of the cyclin-dependent kinase (CDK) inhibitor p27. Recently, an E3 ubiquitin ligase called CRL4(Cdt2) has been characterized, which couples proteolysis to DNA synthesis via an unusual mechanism that involves display of substrate degrons on the DNA polymerase processivity factor PCNA. Through its destruction of Cdt1, p21, and Set8, CRL4(Cdt2) has emerged as a master regulator that prevents rereplication in S phase. In addition, it also targets other factors such as E2F and DNA polymerase η. In this review, we discuss our current understanding of the molecular mechanism of substrate recognition by CRL4(Cdt2) and how this E3 ligase helps to maintain genome integrity.     

HPV16/18和HPV16E6/E7DNA在宫颈癌组织中的表达

目的检测HPV16/18和HPV16E6/E7 DNA在宫颈癌组织中的表达,探讨其在宫颈癌发病中的作用.方法应用PCR和琼脂糖凝胶电泳方法检测46例宫颈癌组织中HPV16/18和HPV16E6/E7DNA.结果 46例宫颈癌中56.5%(26/46)扩增HPV16/18 DNA,其中宫颈鳞癌25例,宫颈腺癌1例.正常对照组20例HPV16/18DNA均为阴性,与宫颈癌组相比差异有显著性(P<0.01).HPV16/18 DNA阳性拷贝对数值为4.32±2.45.HPV16E6,E7DNA分别有53.8%(14/26)、46.2%(12/26)扩增.结论 HPV16/18和HPV16E6/E7 DNA与宫颈癌的发生密切相关,是宫颈癌恶性转化的关键之一,预示着宫颈癌有较强的增殖能力和转移能力.     

HPV16 E6 augments Wnt signaling in an E6AP-dependent manner

In this study we investigated the effect of HPV16 E6 on the Wnt/β-catenin oncogenic signaling pathway. Luciferase reporter assays indicated that ectopically expressed E6 significantly augmented the Wnt/β-catenin/TCF-dependent signaling response in a dose-dependent manner. This activity was independent of the ability of E6 to target p53 for degradation or bind to the PDZ-containing E6 targets. Epistasis experiments suggested that the stimulatory effect is independent of GSK3β or APC. Coexpression, half-life determination, cell fractionation and immunofluorescence analyses indicated that E6 did not alter the expression levels, stability or cellular distribution of β-catenin. Further experiments using E6 mutants defective for E6AP binding and E6AP knockdown cells indicated the absolute requirement of the ubiquitin ligase E6AP for enhancement of the Wnt signal by E6. Thus, this study suggests a role for the E6/E6AP complex in augmentation of the Wnt signaling pathway which may contribute to HPV induced carcinogenesis.     

泛素E3连接酶TRIM10在心肌细胞肥大中的作用

目的:探讨泛素E3连接酶TRIM10在心肌细胞肥大中的作用及分子机制。方法:培养原代的大鼠乳鼠心肌细胞,siRNA-TRIM10与siRNA对照(siRNA-control)或过表达腺病毒Ad-TRIM10与空载对照Ad-GFP转染细胞24 h,然后用苯肾上腺素(phenylephrine,PE)处理细胞24 h。Western blot检测TRIM10、AKT和ERK1/2的蛋白水平;免疫荧光染色观察心肌细胞的大小;实时荧光定量PCR检测心房钠尿肽(ANP)和脑钠尿肽(BNP)的mRNA的表达水平。结果:与对照组相比,PE处理明显上调心肌细胞中TRIM10蛋白的表达水平。siRNA-TRIM10敲低内源性TRIM10表达后明显减小PE诱导的心肌细胞体积,抑制ANP和BNP的mRNA的表达以及降低AKT和ERK1/2的磷酸化水平;而过表达TRIM10则呈现出与siRNA-TRIM10完全相反的结果。结论:TRIM10可调节心肌细胞肥大,其作用可能与AKT和ERK信号相关。     

The RAG1 N-terminal domain is an E3 ubiquitin ligase

RAG1 and RAG2 initiate V(D)J recombination, which is the assembly of immunoglobulin and T cell receptor genes. The N-terminal region of RAG1 can be deleted, leaving an enzymatic "core" able to catalyze the complete reaction. Here we report that the N-terminal portion of RAG1 has a distinct enzymatic role separate from the rest of the protein. It acts as an E3 ligase in the ubiquitylation of a test substrate and formation of polyubiquitin chains in vitro. This finding suggests a new way in which V(D)J recombination can be regulated and coupled to other aspects of cell physiology.     

Essential role of the E3 ubiquitin ligase Cbl-b in T cell anergy induction

Antigen-specific immunotolerance limits the expansion of self-reactive T cells involved in autoimmune diseases. Here, we show that the E3 ubiquitin ligase Cbl-b is upregulated in T cells after tolerizing signals. Loss of Cbl-b in mice results in impaired induction of T cell tolerance both in vitro and in vivo. Importantly, rechallenge of Cbl-b mutant mice with the tolerizing antigen results in massive lethality. Moreover, ablation of Cbl-b resulted in exacerbated autoimmunity. Mechanistically, loss of Cbl-b rescues reduced calcium mobilization of anergic T cells, which was attributed to Cbl-b-mediated regulation of PLCgamma-1 phosphorylation. Our results show a critical role for Cbl-b in the regulation of peripheral tolerance and anergy of T cells.     

Expression of the Rho-GEF Pbl/ECT2 is regulated by the UBE3A E3 ubiquitin ligase

We applied genetic tools available in Drosophila to identify candidate substrates of the UBE3A ubiquitin ligase, the gene responsible for Angelman syndrome (AS). Human UBE3A was expressed in Drosophila heads to identify proteins differentially regulated in UBE3A-expressing versus wild-type extracts. Using two-dimensional gel and MALDI-TOF analysis, we detected 20 proteins that were differentially regulated by over-expression of human UBE3A in Drosophila heads. One protein responsive to UBE3A was the Rho-GEF pebble (pbl). Here, we present three lines of evidence suggesting that UBE3A regulates Pbl. First, we show genetic evidence that UBE3A and the Drosophila de-ubiquitinase fat facets (faf) exert opposing effects on Pbl function. Secondly, we find that both Pbl and ECT2, the mammalian orthologue of Pbl called epithelial cell transforming sequence 2 oncogene, physically interact with their respective ubiquitin E3 ligases. Finally, we show that Ect2 expression is regulated by Ube3a in mouse neurons as the pattern of Ect2 expression is dramatically altered in the hippocampus and cerebellum of Ube3a null mice. These results suggest that an orthologous UBE3A post-translational regulatory pathway regulates neuronal outgrowth in the mammalian brain and that dysregulation of this pathway may result in neurological phenotypes including AS and possibly other autism spectrum disorders.     

Regulation of peripheral T cell tolerance by the E3 ubiquitin ligase Cbl-b

The family of the Casitas B-lineage Lymphoma (Cbl) proteins, c-Cbl, Cbl-b, and Cbl-3, function as E3 ubiquitin ligases and molecular adaptors. In particular, Cbl-b acts as a gatekeeper in T cell activation that controls activation thresholds and the requirement for co-stimulation. Loss of Cbl-b expression renders animals susceptible to antigen-triggered autoimmunity suggesting that Cbl-b is a key autoimmunity gene. In addition, Cbl-b plays a critical role in T cell anergy and escape from regulatory T cells (Treg) suppression. Modulation of Cbl-b might provide us with a unique opportunity for future immune treatment of human disorders such as autoimmunity, immunodeficiency, or cancer.     

Itch相关免疫调控的研究进展

Itch, one of the main E3 ligases, plays an important role in immune responses as a negative regulator in the ubiquitination of PLC-γ, PKC-θ, JunB,and notch. Itch deficiency leads to sever inflammatory disorders and immunological abnormality. Many efforts have been made in disclosing the Itch-promoted protein ubiquitination, modulation of its ligase, transdution of downstream signals in T cell anergy and differentiation in the past years.     

Itch相关免疫调控的研究进展

Itch是新近发现的泛素连接酶E3之一,其参与细胞内多种信号蛋白如PLC．1、PKC-0、JunB、notch等的泛素化修饰过程,调控细胞表型及功能。Itch缺陷可引起小鼠严重的免疫紊乱和炎症反应,其负向免疫调节作用已在基因敲除动物模型上得以证实。近年来的研究对Itch结构、调控和被调控途径、参与的信号通路等有了更进一步的认识,逐步揭示出Itch在T细胞增殖、分化和诱导免疫耐受中的作用机制。     

Itch相关免疫调控的研究进展

Itch, one of the main E3 ligases, plays an important role in immune responses as a negative regulator in the ubiquitination of PLC-γ, PKC-θ, JunB,and notch. Itch deficiency leads to sever inflammatory disorders and immunological abnormality. Many efforts have been made in disclosing the Itch-promoted protein ubiquitination, modulation of its ligase, transdution of downstream signals in T cell anergy and differentiation in the past years.     

The E3 ubiquitin ligase Itch deficiency promotes antigen-driven B-cell responses in mice

Deficiency of Itch, an E3 ubiquitin ligase, usually induced severe systemic and progressive autoimmune disease. The Itch function is well studied in T cells but not in B cells. We hypothesize that B-cell-specific Itch deficiency promoted antigen-induced B-cell activation and antibody-expressing plasma cell (PC) production. We found that unlike Itch KO, Itch cKO (CD19^creItch^f/f) mice did not demonstrated a significant increase in the sizes of spleens and LNs, antibody level, and base mutation of antibody gene. However, in line with the fact that Itch expression decreased in GC B cells, PCs, and plasmablast (PB)-like SP 2/0 cells, Itch deficiency promoted B-cell activation and antibody production induced by antigens including lipopolysaccharide (LPS) and sheep red blood cells (SRBCs). Mechanistically, we found that Itch deficiency promotes antigen-induced cytokine production because Itch controls the proteins (e.g., eIF3a, eIF3c, eIF3h) with translation initiation factor activity. Altogether, our data suggest that Itch deficiency promotes antigen-driven B-cell response. This may provide hints for Itch-targeted treatment of patients with autoimmune disease.     

HPV16 E6E7抗原表达模型的建立

目的 用基因重组技术构建pcDNA-E6E7真核表达载体.方法 经限制性内切酶和序列分析,用脂质体转染技术将其转入B16细胞,G418稳定筛选后IFA法检测其表达,RT-PCK法检测HPV16E6E7mRNA的生成,并将转染细胞接种小鼠皮下,观察成瘤情况.结果 酶切鉴定证实重组质粒中插入的目的基因片段及载体大小、方向和插入住点均正确,在转染的B16细胞中可见绿色荧光并检测到HPV16E6E7mRNA的生成,接种的转染细胞在小鼠皮下100%成瘤.结论 提示B16细胞转染E6E7后其致瘤性与转染空载体组和野生型B16细胞组无明显差异.     

TAM receptors attenuate murine NK-cell responses via E3 ubiquitin ligase Cbl-b

TAM receptors (Tyro3, Axl, and Mer) are receptor tyrosine kinases (RTKs) that are expressed by multiple immune cells including NK cells. Although RTKs typically enhance cellular functions, TAM receptor ligation blocks NK-cell activation. The mechanisms by which RTKs block NK-cell signaling downstream of activating receptors are unknown. In this report, we demonstrate that TAM receptors attenuate NK cell responses via the activity of E3 ubiquitin ligase Casitas B lineage lymphoma b (Cbl-b). Specifically, we show that Tyro3, Axl, and Mer phosphorylate Cbl-b, and Tyro3 ligation activates Cbl-b by phosphorylating tyrosine residues 133 and 363. Ligation of TAM receptors by their ligand Gas6 suppresses activating receptor-stimulated NK-cell functions such as IFN-γ production and degranulation, in a TAM receptor kinase- and Cbl-b-dependent manner. Moreover, Gas6 ligation induces the degradation of LAT1, a transmembrane adaptor protein required for NK cell activating receptor signaling, in WT but not in Cbl-b knock-out NK cells. Together, these results suggest that TAM receptors may attenuate NK-cell function by phosphorylating Cbl-b, which in turn dampens NK-cell activation signaling by promoting the degradation of LAT1. Our data therefore support a mechanism by which RTKs attenuate, rather than stimulate, signaling pathways via the activation of ubiquitin ligases.     

pcDNA3/HPV16 E6真核表达质粒的构建及裸DNA注射动物实验观察

目的探讨ＨＰＶ１６Ｅ６基因ＤＮＡ诱发体液和细胞免疫反应的能力。方法利用基因工程技术构建了ＨＰＶ１６Ｅ６真核表达质粒ｐｃＤＮＡ３／Ｅ６，脂质体法转染Ｃｏｓ７细胞，肌肉注射免疫ＢＡＬＢ／ｃ小鼠，免疫组化技术检测抗体产生及抗原表达。结果被转染的Ｃｏｓ７细胞表达ＨＰＶ１６Ｅ６蛋白免疫小鼠产生抗ＨＰＶ１６Ｅ６抗体。结论这一结果为ＨＰＶ１６相关宫颈癌治疗性ＤＮＡ疫苗的研制提供了资料。