Ubiquitin-conjugating enzyme E2T knockdown suppresses hepatocellular tumorigenesis via inducing cell cycle arrest and apoptosis

BACKGROUND Hepatocellular carcinoma(HCC)is now the most common primary liver malignancy worldwide,and multiple risk factors attribute to the occurrence and development of HCC.Recently,increasing studies suggest that ubiquitinconjugating enzyme E2T(UBE2T)serves as a promising prognostic factor in human cancers,although the molecular mechanism of UBE2T in HCC remains unclear.AIM To investigate the clinical relevance and role of UBE2T in HCC development.METHODS UBE2T expression in HCC tissues from the TCGA database and its association with patient survival were analyzed.A lentivirus-mediated strategy was used to knock down UBE2T in HCC cells.qRT-PCR and Western blot assays were performed to check the effect of UBE2T silencing in HCC cells.Cell growth in vitro and in vivo was analyzed by multiparametric high-content screening and the xenograft tumorigenicity assay,respectively.Cell cycle distribution and apoptosis were determined by flow cytometry.The genes regulated by UBE2T were profiled by microarray assay.RESULTS UBE2T was overexpressed in HCC tissues compared with paired and non-paired normal tissues.High expression of UBE2T predicted a poor overall survival in HCC patients.In vitro,lentivirus-mediated UBE2T knockdown significantly reduced the viability of both SMMC-7721 and BEL-7404 cells.In vivo,the xenograft tumorigenesis of SMMC-7721 cells was largely attenuated by UBE2T silencing.The cell cycle was arrested at G1/S phase in SMMC-7721 and BEL-7404 cells with UBE2T knockdown.Furthermore,apoptosis was increased by UBE2T knockdown.At the molecular level,numerous genes were dysregulated after UBE2T silencing,including IL-1B,FOSL1,PTGS2,and BMP6.CONCLUSION UBE2T plays an important role in cell cycle progression,apoptosis,and HCC development.

Functions of three ubiquitin-conjugating enzyme 2 genes in hepatocellular carcinoma diagnosis and prognosis

BACKGROUND Liver cancer ranks the third cause of cancer-related death worldwide.The most common type of liver cancer is hepatocellular carcinoma(HCC).The survival time for HCC patients is very limited by years due to the lack of efficient treatment,failure of early diagnosis,and poor prognosis.Ubiquitination plays an essential role in the biochemical processes of a variety of cellular functions.AIM To investigate three ubiquitination-associated genes in HCC.METHODS Herein,the expression levels of ubiquitin-conjugating enzymes 2(UBE2)including UBE2C,UBE2T,and UBE2S in tumor samples of HCC patients and nontumor controls at the Cancer Genome Atlas(TCGA)database,was comprehensively analyzed.The relationship of UBE2 gene expression level with cancer stage,prognostic outcome,and TP53 mutant status was studied.RESULTS Our results showed that UBE2C,UBE2T,and UBE2S genes were overexpressed in HCC samples compared to non-tumor tissues.Dependent on the cancer progression stage,three UBE2 genes showed higher expression in tumor tissues at all four stages compared to non-tumor control samples.Furthermore,a significantly higher expression of these genes was found in stage 2 and stage 3 cancers compared to stage 1 cancer.Additionally,overexpression of those genes was negatively associated with prognostic outcome and overall survival time.Patients with TP53 mutation showed a higher expression level of three UBE2 genes,indicating an association between UBE2 expression with p53 function.CONCLUSION In summary,this study shed light on the potential roles of UBE2C,UBE2T,UBE2S on diagnostic and prognostic biomarkers for HCC.Moreover,based on our findings,it is appealing to further explore the correlation of those genes with TP53 mutation in HCC and the related mechanisms.

High Level of Ubiquitin Conjugate Enzyme E2O Indicates Poor Prognosis of Patients with Hepatocellular Carcinoma

Objective Ubiquitin conjugate enzyme E2O(UBE2O)is a ubiquitin-conjugating enzyme that has been reported to be involved in tumorigenesis.This study investigated the role of UBE2O in hepatocellular carcinoma(HCC).Methods The expression of UBE2O was detected using qRT-PCR,Western blotting,and immunohistochemical staining.Cell proliferation and Transwell assays were used to detect proliferation,migration,and invasion of HCC cells,respectively.Bioinformatic analysis was performed to analyze the relationship between UBE2O and the clinical features,prognosis,and immune cell infiltration of HCC.Results UBE2O was significantly over-expressed in HCC tissues.High expression of UBE2O was associated with poor tumor grade and poor prognosis.Functional experiments showed that down-regulation of UBE2O inhibited HCC cell proliferation,migration,and invasion.Co-expression gene analysis and gene set enrichment analysis showed that UBE2O was associated with protein hydrolysis,cell cycle,and cancer-related pathways in HCC.The results of immune analysis revealed that the expression of UBE2O was positively correlated with the immune infiltration and expression of immune-related chemokines of HCC.Conclusions UBE2O is significantly correlated with the prognosis of HCC and may be a valuable prognostic biomarker for HCC.

Functionalized selenium nanoparticles ameliorated acetaminophen-induced hepatotoxicity through synergistically triggering PKCδ/Nrf2 signaling pathway and inhibiting CYP 2E1

Selenium nanoparticles(SeNPs)have been demonstrated potential for use in diseases associated with oxidative stress.Functionalized SeNPs with lower toxicity and higher biocompatibility could bring better therapeutic activity and clinical application value.Herein,this work was conducted to investigate the protective effect of Pleurotus tuber-regium polysaccharide-protein complex funtionnalized SeNPs(PTR-SeNPs)against acetaminophen(APAP)-induced oxidative injure in HepG2 cells and C57BL/6J mouse liver.Further elucidation of the underlying molecular mechanism,in particular their modulation of Nrf2 signaling pathway was also performed.The results showed that PTR-SeNPs could significantly ameliorate APAP-induced oxidative injury as evidenced by a range of biochemical analysis,histopathological examination and immunoblotting study.PTR-SeNPs could hosphorylate and activate PKCδ,depress Keap1,and increase nuclear accumulation of Nrf2,resulting in upregulation of GCLC,GCLM,HO-1 and NQO-1 expression.Besides,PTR-SeNPs suppressed the biotransformation of APAP to generate intracellular ROS through CYP 2E1 inhibition,restoring the mitochondrial morphology.Furthermore,the protective effect of PTR-SeNPs against APAP induced hepatotoxicity was weakened as Nrf2 was depleted in vivo,indicating the pivotal role of Nrf2 signaling pathway in PTR-SeNPs mediated hepatoprotective efficacy.Being a potential hepatic protectant,PTR-SeNPs could serve as a new source of selenium supplement for health-promoting and biomedical applications.

Cloning and identification of an Ubiquitinconjugating enzyme E2 D2 gene from Japanese lamprey Lampetra japonica

The modification of proteins with ubiquitin is an important cellular mechanism for targeting abnormal or short-lived proteins for degradation.Ubiquitin-conjugating enzyme E2 D2 is a protein that is encoded by the UBE2D2 gene.Here,we report a lamprey(La UBE2D2)gene which contained 441-bp open reading frame(ORF)encoding 147 amino acids with a typical UBC domain.Real-time PCR assay showed that the highest expression of the protein in adult lamprey was in the leukocytes,the lowest expression was in the skin,kidney and liver.The high conservation in amino acid sequence of the La UBE2D2protein with the UBE2D2s from Homo sapiens,Danio rerio,Oreochromis niloticus and Takifugu rubripes,implied that it had similar function with UBE2D2proteins from other species.

Nrf-2 expression in ulcerative colitis lesions and its correlation with antioxidant enzyme levels and tissue injury

Objective:To study the Nrf-2 expression in ulcerative colitis lesions and its correlation with antioxidant enzyme levels and tissue injury.Methods: Patients who were diagnosed with ulcerative colitis and colon polyp by colonoscopy and pathology biopsy in the Yan'an People's Hospital between May 2013 and April 2016 were selected and enrolled in UC group and control group respectively. Lesion tissue was collected to determine the mRNA expression of Nrf-2, antioxidant enzymes, intestinal mucosa function molecules and intestinal mucosa apoptosis molecules as well as the levels of antioxidant enzymes.Results: Nrf-2, SOD, GSH-Px, CAT, Fas, FasL, NF-kB, TNF-α and Bak mRNA expression in lesions of UC group were significantly higher than those of control group while SOD, GSH-Px and CAT levels as well as cingulin, claudin-2, galectin-1, galectin-3 and galectin-9 mRNA expression were significantly lower than those of control group;Nrf-2 mRNA expression in lesion of UC group was positively correlated with SOD, GSH-Px, CAT, Fas, FasL, NF-kB, TNF-α and Bak mRNA expression, and negatively correlated with SOD, GSH-Px and CAT levels as well as cingulin, claudin-2, galectin-1, galectin-3 and galectin-9 mRNA expression.Conclusions:Compensatory high Nrf-2 expression in ulcerative colitis is closely related to oxidative stress and intestinal mucosa tissue injury.

重组血管紧张素转换酶2对ApoE基因缺陷小鼠肾脏caspase信号及细胞凋亡的影响

目的·探讨载脂蛋白E（ApoE）基因敲除（KO）小鼠肾脏caspase信号和凋亡水平的改变以及重组血管紧张素转换酶2（ACE2）干预治疗对其的影响。方法·采用11～12周龄的ApoEKO小鼠，每日经微泵输入1.5 mg/kg血管紧张素Ⅱ（Ang Ⅱ）和/或2 mg/kg重组人ACE2（rhACE2）治疗，为期2周。分别采用蛋白质印迹法和TUNEL法检测小鼠肾脏组织中细胞凋亡及相关信号改变。结果·与野生型对照组相比，ApoEKO小鼠肾脏细胞凋亡水平升高。Ang Ⅱ输入后促使ApoEKO小鼠收缩压水平升高，肾脏细胞凋亡水平、活化型caspase-3和caspase-8表达以及血浆尿素氮与肌酐水平均明显升高，上述作用可被重组ACE2干预所逆转。结论·重组ACE2治疗在降低Ang Ⅱ输入的ApoEKO小鼠血压水平的同时，可明显改善肾脏细胞凋亡和肾功能，提示ACE2对动脉粥样硬化性肾脏损伤具有一定的功效。

血管紧张素转化酶和载脂蛋白E基因多态性对新诊2型糖尿病患者亚临床动脉粥样硬化的预测

目的为探讨血管紧张素转化酶和载脂蛋白E基因多态性与新诊2型糖尿病多因素强化干预条件下亚临床动脉粥样硬化发生的关系。方法采用聚合酶链反应—限制性片段长度多态性方法检测湖南地区汉族新诊2型糖尿病患者及93例无糖尿病对照者血管紧张素转化酶及载脂蛋白E的基因多态性,分别比较血管紧张素转化酶和载脂蛋白E基因型间以及两基因型协同作用下体重、血糖、血压、血脂和胰岛素抵抗等代谢指标水平的差异,比较分析无动脉粥样硬化与亚临床动脉粥样硬化患者血管紧张素转化酶及载脂蛋白E基因型分布特点。采用Logistic回归模型分析血管紧张素转化酶、载脂蛋白E基因型及二者协同作用下与多因素干预条件下亚临床动脉粥样硬化发生的关系。结果157例新诊2型糖尿病患者中,载脂蛋白E基因型及等位基因频率分布与对照组比较差异无显著性(P>0.05);血管紧张素转化酶Ⅰ等位基因频率显著高于对照组(0.707比0.581,P<0.05),血管紧张素转化酶DD携带者收缩压水平与II及ID携带者比较差异无显著性(P>0.05)。载脂蛋白E4/X基因型携带者低密度脂蛋白胆固醇水平显著高于2/X携带者(P<0.01);血管紧张素转化酶及载脂蛋白E基因型对收缩压及低密度脂蛋白胆固醇水平无交互作用。两基因多态性与各代谢指标干预1年达标情况和动脉内中膜厚度无相关关系(P>0.05)。血管紧张素转化酶DD携带者无一例发生亚临床动脉粥样硬化,与非DD携带者比较差异接近显著性(P=0.059),未发现载脂蛋白E基因多态性与亚临床动脉粥样硬化发生的相关性。结论以上提示,载脂蛋白E基因多态性对新诊2型糖尿病患者多因素干预条件下亚临床动脉粥样硬化的发生无预测作用;血管紧张素转化酶DD基因型可能是新诊2型糖尿病患者多因素干预条件下亚临床动脉粥样硬化发生的负性预测因子。

膀胱移行细胞癌组织中沉默信息调节因子2相关酶1和E钙黏附素的表达及其相关性

目的探讨膀胱移行细胞癌组织中沉默信息调节因子2相关酶1(SIRT-1)及E钙黏附素(E-cadherin)的定性表达情况及其相关性。方法选取2015年1月至2019年8月于西安交通大学第二附属医院行手术治疗的膀胱移行细胞癌患者81例,取手术切除的膀胱移行细胞癌组织和癌旁正常组织,免疫组织化学法检测SIRT-1及E-cadherin蛋白的表达,比较癌组织与癌旁正常组织中SIRT-1和E-cadherin阳性表达率,以及不同临床病理特征膀胱移行细胞癌患者癌组织中SIRT-1和E-cadherin的阳性表达率,分析SIRT-1与E-cadherin表达的相关性。结果SIRT-1阳性染色主要位于细胞核及细胞质,E-cadherin阳性染色主要位于细胞膜及细胞质。膀胱移行细胞癌组织中SIRT-1阳性表达率明显高于癌旁正常组织[92.6%(75/81)比13.6%(11/81)],而E-cadherin阳性表达率明显低于癌旁正常组织[25.9%(21/81)比93.8%(76/81)],差异均有统计学意义(χ^2=101.523、77.724,均P<0.001)。肿瘤分期Ⅲ~Ⅳ期和伴淋巴结转移患者的癌组织中SIRT-1阳性表达率分别高于肿瘤分期Ⅰ~Ⅱ期和无淋巴结转移患者,E-cadherin表达水平分别低于肿瘤分期Ⅰ~Ⅱ期和无淋巴结转移患者(均P<0.05)。经Spearman秩相关分析,膀胱移行细胞癌组织中SIRT-1与E-cadherin的表达呈负相关(ρ=-0.371,P=0.001)。结论膀胱移行细胞癌组织中SIRT-1阳性表达率增高,而E-cadherin阳性表达率降低,二者表达均与肿瘤分期、淋巴结转移有关且二者表达呈负相关。

哮喘患儿血清COX-2、IL-8、IgE的动态变化及其临床意义

目的:探讨哮喘儿童血清环氧化酶-2(COX-2)、白细胞介素8(IL-8)、IgE的动态变化及其临床意义。方法:应用双抗体夹心ELISA法检测121例哮喘患儿血清COX-2、IL-8、Ig-E水平,其中发作期62例,缓解期59例,设正常对照60名。结果:哮喘组血清COX-2、IL-8、IgE水平均明显高于对照组(P<0.01);哮喘急性发作期血清COX-2、IL-8、IgE水平亦均明显高于缓解期(P<0.01)。结论:COX-2与IL-8可能参与了哮喘急性发作患儿的发病过程,COX-2与IL-8可能发挥正反馈调节作用,促进哮喘患儿IgE分泌;哮喘缓解期仍存在炎症反应。细胞因子网络失衡可能是哮喘发病的分子生物学基础,拮抗COX-2或其细胞因子网络可能有助于缓解哮喘患儿的病情。

UBE2C regulates proliferation and invasion of neuroblastoma: An experimental study

Objective:To study the regulatory effect of ubiquitin-conjugating enzyme 2C (UBE2C) on the proliferation and invasion of neuroblastoma.Methods: SH-SY5Y neuroblastoma cell lines were cultured and randomly divided into UBE2C-siRNA group and NC-siRNA group that were transfected with UBE2C siRNA and NC siRNA respectively. 24 h after siRNA transfection, the RNA in the cells was extracted, and fluorescence quantitative PCR reaction was used to detect the mRNA expression of pro-proliferation genes YB-1, CyclinD1, CDK4, Aurora-A and Ki-67, anti-proliferation genes LC3, Beclin1, GRP78, IRE1α, PERK and ATF6 as well as invasion genes KLF4, RIPK3, HIF-1α, Integrinβ1 and MMP9.Results: YB-1, CyclinD1, CDK4, Aurora-A, Ki-67, KLF4, RIPK3, HIF-1α, Integrinβ1 and MMP9 mRNA expression in UBE2C-siRNA group of cells were significantly lower than those in NC-siRNA group whereas LC3, Beclin1, GRP78, IRE1α, PERK and ATF6 mRNA expression were significantly higher than those in NC-siRNA group.Conclusions: Inhibition of the UBE2C gene can regulate the expression of proliferation and invasion genes in neuroblastoma to hinder cell proliferation and invasion.

Correlation of KLF4 and UBE2C expression levels in neuroblastoma with cell adhesion and migration

Objective: To study the correlation of KLF4 and UBE2C expression levels in neuroblastoma with cell adhesion and migration. Methods: A total of 56 children who were diagnosed with neuroblastoma in the Central Hospital of Enshi Autonomous Prefecture between May 2014 and February 2017 were selected as the NB group of the study, and the lesion tissue was collected;38 children who were treated in the Central Hospital of Enshi Autonomous Prefecture due to serious hydronephrosis during the same period were selected as the control group of the study, and the normal adrenal gland tissue was collected. The mRNA expression and protein expression of KLF4 and UBE2C as well as the protein expression of cell adhesion molecules and migration molecules in clinical tissue samples were determined. Results: The mRNA expression and protein expression of KLF4 in neuroblastoma tissue of NB group were greatly lower than those of control group whereas the mRNA expression and protein expression of UBE2C were greatly higher than those of control group;PDLIM1, AMF, GPx1, L1CAM, Nrg1, RANK, RANKL, Inβ1, MTA1 and MMP9 protein expression in neuroblastoma tissue of NB group were greatly higher than those of control group, negatively correlated with the protein expression KLF4, and positively correlated with the protein expression of UBE2C. Conclusion: The low expression of KLF4 and the high expression of UBE2C in neuroblastoma can promote the adhesion and migration of tumor cells.

戊型肝炎病人和实验感染戊型肝炎病毒的猕猴血清抗－HEV ORF2和ORF3的动态变化

应用人工合成的戊型肝炎病毒（ＨＥＶ）基因组开放读码框架２（ＯＲＦ２）和３（ＯＲＦ３）两段多肽，分别建立了酶联免疫试验（ＥＩＡ），检测８５份实验感染ＨＥＶ的猕猴和１４３份戊型肝炎（简称戊肝）病人血清，结果两组抗－ＨＥＶＯＲＦ２阳性率分别为７０．８９％和６８．５３％，均显著高于抗－ＨＥＶＯＲＦ３（分别为４０．０３％和５７．３４％），且前者阳转时间较早，持续阳性时间也较长。虽然多数（９７．３％）抗－ＨＥＶＯＲＦ３阳性血清，抗－ＨＥＶＯＲＦ２也为阳性，但有少数血清（２．７％）抗－ＨＥＶＯＲＦ２为阴性。上述结果提示，ＨＥＶ基因组ＯＲＦ２和ＯＲＦ３编码的蛋白含有不同的抗原表位，可引起宿主不同的免疫反应。因此，在制备抗－ＨＥＶＥＩＡ试剂时，应联合应用ＯＲＦ２和ＯＲＦ３多肽，以提高其灵敏度和特异性。

UBE2C affects breast cancer proliferation through the AKT/mTOR signaling pathway

Background:Ubiquitin-conjugating enzyme E2C(UBE2C)has been shown to be associated with the occurrence of various cancers and involved in many tumorigenic processes.This study aimed to investigate the specific molecular mechanism through which UBE2C affects breast cancer(BC)proliferation.Methods:BC-related datasets were screened according to filter criteria in the Gene Expression Omnibus(GEO)database and The Cancer Genome Atlas(TCGA)database.Then differentially expressed genes(DEGs)were identified using Venn diagram analysis.By using DEGs,we conducted the following analyses including Gene ontology(GO),Kyoto Encyclopedia of Genes and Genomes(KEGG),protein-protein interaction(PPI),and survival analysis,and then validated the function of the hub geneUBE2C using quantitative reverse transcription-polymerase chain reaction(RT-qPCR),cell counting kit-8(CCK-8)assay,transwell assay,and Western blot assay.Results:In total,151 DEGs were identified from the GEO and TCGA databases.The results of GO analysis demonstrated that the DEGs were significantly enriched with mitotic nuclear division,lipid droplet,and organic acid-binding.KEGG analysis showed that the peroxisome proliferators-activated receptor(PPAR)signaling pathway,regulation of lipolysis in adipocytes,and proximal tubule bicarbonate reclamation were significantly enriched in the signal transduction pathway category.The top three hub genes that resulted from the PPI network wereFOXM1,UBE2C,andCDKN3.The results of survival analysis showed a close relationship between UBE2C and BC.The results of CCK-8 and transwell assays suggested that the proliferation and invasion ofUBE2C knockdown cells were significantly inhibited(P<0.050).The results of Western blot assay showed that the level of phosphorylated phosphatase and tensin homology deleted on chromosome 10(p-PTEN)was obviously increased(P<0.050),whereas the levels of phosphorylated protein kinase B(p-AKT),phosphorylated mammalian target of rapamycin(p-mTOR),and hypoxia-inducible factor-1 alpha(HIF-1α)were dramatically decreased(P<0.050)in theUBE2C knockdown cell.Conclusion:UBE2C can promote BC proliferation by activating the AKT/mTOR signaling pathway.

Crosstalk between CYP2E1 and PPARα substrates and agonists modulate adipose browning and obesity

Although the functions of metabolic enzymes and nuclear receptors in controlling physiological homeostasis have been established, their crosstalk in modulating metabolic disease has not been explored.Genetic ablation of the xenobiotic-metabolizing cytochrome P450 enzyme CYP2 E1 in mice markedly induced adipose browning and increased energy expenditure to improve obesity. CYP2 E1 deficiency activated the expression of hepatic peroxisome proliferator-activated receptor alpha(PPARa) target genes,including fibroblast growth factor(FGF) 21, that upon release from the liver, enhanced adipose browning and energy expenditure to decrease obesity. Nineteen metabolites were increased in Cyp2 e1-null mice as revealed by global untargeted metabolomics, among which four compounds, lysophosphatidylcholine and three polyunsaturated fatty acids were found to be directly metabolized by CYP2 E1 and to serve as PPARa agonists, thus explaining how CYP2 E1 deficiency causes hepatic PPARa activation through increasing cellular levels of endogenous PPARa agonists. Translationally, a CYP2 E1 inhibitor was found to activate the PPARa-FGF21-beige adipose axis and decrease obesity in wild-type mice, but not in liver-specific Pparanull mice. The present results establish a metabolic crosstalk between PPARa and CYP2 E1 that supports the potential for a novel anti-obesity strategy of activating adipose tissue browning by targeting the CYP2 E1 to modulate endogenous metabolites beyond its canonical role in xenobiotic-metabolism.

电针益肾调督法对Aβ_(1-42)诱导的阿尔兹海默病模型大鼠海马Aβ相关清除酶的影响（英文）

目的:探讨电针益肾调督法对阿尔茨海默病模型大鼠β-淀粉样蛋白(Aβ)相关清除酶的影响。方法:将40只Wistar雄性大鼠随机分为正常组、假手术组、模型组和电针组,每组10只。正常组常规饲养。假手术组双侧海马注射5μL生理盐水,造模后常规饲养。模型组与电针组双侧海马各注射5μL Aβ_(1-42),电针组造模后于"百会""肾俞"行电针干预,5 Hz,连续波,每次15min,每日1次,连续15d。干预结束后用Western-blot法检测各组大鼠海马组织中脂蛋白酯酶(LPL)、胰岛素降解酶(IDE)、转甲状腺素蛋白(TTR)、载脂蛋白E (APoE)、α_2巨球蛋白(α_2M)及β淀粉样蛋白1-42(Aβ_(1-42))的表达。结果:与假手术组相比,模型组LPL、IDE、TTR、APoE及α_2M在海马组织中的表达较弱(P<0.05, P<0.01), Aβ_(1-42)在海马中的表达较强(P<0.01);与模型组相比,电针组LPL、IDE、TTR、APoE及α2M在海马组织中的表达较强(P<0.05, P<0.01), Aβ_(1-42)在海马中的表达较弱(P<0.01)。结论:电针益肾调督法可上调Aβ_(1-42)诱导的阿尔兹海默病模型大鼠海马组织中LPL、IDE、TTR、APoE及α_2M的表达,促进Aβ的降解,有助于改善阿尔兹海默病的病理变化,延缓其病程进展。

Ubiquitination in Abscisic Acid-Related Pathway

Ubiquitination is emerging as a tight regulatory mechanism that is necessary for all aspects of development and survival of all eukaryotes. Recent genomic and genetic analysis in Arabidopsis suggests that ubiquitination may also play important roles in plant response to the phytohormone abscisic acid （ABA）. Many components of the ubiquitination pathway, such as ubiquitin-conjugating enzyme E2, ubiquitin ligase E3 and components of the proteasome, have been identified or predicted to be essential in ABA biosynthesis, catabolism and signaling. In addition, the ubiquitination-related pathway, sumoylation, is also involved in ABA signaling. We summarize in this report recent developments to elucidate their roles in the ABA-related pathway.

Mapping the Binding Site of P53 on UBC9 by NMR Spectroscopy

Human UBC9 is a member of the E2 family of proteins. However, instead of conjugating to ubiquitin, it conjugates to a ubiquitin homologue SUMO-1 (also known as UBL1, GMP1, SMTP3, PICT-1 and sentrin). The SUMO-1 conjugation pathway is very similar to that of ubiquitin with regard to the primary sequences of the ubiquitin activating enzymes (E1), the three-dimensional structures of the ubiquitin conjugating enzymes (E2), and the chemistry of the overall conjugation pathway. The interaction of p53 and UBC9, the E2 of the SUMO-1 pathway, has been studied by nuclear magnetic resonance spectroscopy. A peptide corresponding to the nuclear localization domain of p53 specifically interacts with UBC9 and this interaction is likely to be important for conjugation of p53 with SUMO-1. The largest chemical shift changes on UBC9 occur at residues 94 and 129-135. This region is adjacent to the active site and has significant dynamic behavior on the μs-ms and ps-ns timescales. Correlation of chemical shift changes and mobility of these residues further suggest the importance of these residues in substrate recognition.