PC12细胞的PSI诱导性包含体富集了真核细胞翻译因子

路易小体(Lewy body, LB),位于神经细胞核周(perikaryon)的嗜酸性包含体(eosinophilic inclusion),含有广泛的蛋白质组分,其中一部分是组成型蛋白质(consistent organization),另外一部分则是选择型蛋白质(selective composition).为了在体外获得LB中未知蛋白质的新线索,通过人工合成蛋白酶体抑制剂PSI（proteasomal inhibitor, 10 μmol/L）作用PC 12细胞48 h,使其产生嗜酸性（staining for eosin）和抗α-synuclein阳性（immunostaining for α- synuclein）的PSI诱导性包含体（PSI-induced inclusion）,通过成功的分级分离（fractionation）纯化了完整、纯净的包含体,通过有效的双向电泳（two-dimensional electrophoresis,2-DE）分离了包含体蛋白质,通过无偏差的基质辅助激光解析 离子化飞行时间质谱（matrix- assisted laser desorption/ionization time-of-flight massspectrometry,MALDI-TOF MS）鉴定了真核细胞翻译起始因子-3亚单位5（eukaryotic translation initiation factor 3 subunit 5, eIF-3ε）、真核细胞延伸因子-2（eukaryotic elongation factor 2, eEF-2）和线粒体延伸因子-Tu（mitochondrial elongation factor Tu, EF-Tumt）等真核细胞翻译因子(eukaryotic translation factors).这一结果提示,当蛋白酶体受到抑制时真核细胞翻译因子被富集到PSI诱导性包含体中,并且可能影响其形成过程.     

散发性帕金森病蛋白酶体功能障碍及其所致的路易(小)体形成

散发性帕金森病(sporadic Parkinson's disease, sPD)的主要病理特征之一是中脑黑质致密部(substantia nigra pars compacta, SNpc)残存多巴胺能神经元内核周路易(小)体(Lewy body, LB)形成.LB发生的具体原因和确切过程有待进一步阐释.来自遗传学、尸体解剖和实验科学的报道提示,蛋白酶体功能障碍及其所致的LB形成可能是按照聚集体形成途径(process of aggresomes)进行的.在聚集体形成途径过程中,异常蛋白质聚集基本上经历了非纤维化分子聚集过程(molecular crowding)以及后续的纤维化聚集过程(fibrilation of aggregation).其间,蛋白酶体功能障碍(dysfunction of proteasome)、内质网相关降解丧失(loss of endoplasmic reticulum associated degradation)、非纤维化聚集物(nonfibrilar aggregates)、聚集体(aggresomes)及至纤维化LB (fibrilar LB)等构成了sPD病变过程的主要事件.这提示在sPD病变过程中,蛋白酶体功能障碍及其所致的LB形成过程实质上是细胞信号的转导过程,其间涉及了众多的蛋白质分子.     

帕金森病路易(小)体的蛋白质生物信息学数据分析

原发性帕金森病(idiopathic Parkinson's disease,PD)的主要病理特征之一是出现于中脑特定脑区黑质致密部(substantia nigra pars compacta,SNpc)多巴胺能神经元的路易(小)体(Lewy bodies,LBs),PD病人LBs和/或路易轴突也出现于脑内其他脑区非多巴胺能神经元,比如蓝斑(locus coeruleus,LC)等脑干个别脑区去甲肾上腺素能神经元、额前叶皮层(prefrontal cortex,PFC)、颞叶皮层(temporal cortex,TC)等大脑多个脑区胆碱能神经元．为了明确LBs的蛋白质构成,本文通过蛋白质生物信息学数据分析,就LBs的蛋白质构成归纳了5个方面的要点：a．LBs的组织结构单元是α-突触核蛋白(α-synuclein,α-SYN)表征的2类纤维状聚集物和6类非纤维状聚集物(通常被称为寡聚物);b．病理性α-SYN在LBs内存在5种化学修饰形式;c．19个α-SYN相关蛋白质分别与α-SYN共定位于LBs;d．117个LBs的已知蛋白质被划分为10组不同蛋白质功能群组;e．LBs的蛋白质组学鉴定数据库包含了分别在LC、SNpc和PFC脑区组织水平鉴定的84、124和120个候选蛋白质,在TC脑区细胞水平鉴定的108个候选蛋白质,以及在TC脑区亚细胞水平鉴定的29个候选蛋白质．上述要点广泛、深入地概括了LBs的蛋白质构成．     

淋巴瘤细胞释放的EXO的蛋白质组分分析

目的:分析淋巴瘤细胞释放的胞外体(lymphoma cell-derived exosomes,LCEX)的蛋白质组分.方法:利用Shotgun技术,分析淋巴瘤Raji细胞系和Raji细胞分泌的EXO中所含蛋白种类并进一步进行鉴定.利用网络数据库进行蛋白组分功能分析.结果:Raji细胞共鉴定出了蛋白322种,Raji细胞系分泌的EXO共鉴定出了蛋白197种,其中139种蛋白为二者共有,其余58种为EXO所特有.采用了GO(gene ontology数据库对Raji细胞释放的EXO蛋白功能进行了分析.①LCEX可能主要参与了对细胞内外刺激的应答及对应答的定位(包括与相关细胞之间的粘附、结合等),并参与免疫调节.②利用KEGG数据库分析发现,Raji细胞释放的EXO所负载的蛋白中涉及细胞粘附分子的有8种蛋白分子,主要为ICAM分子及MHC分子;③涉及抗原加工和提呈的有12种蛋白分子,主要是HSP70和HSP90家族的.结论:EXO负载了大部分其来源细胞的蛋白,所负载的蛋白中涉及多种参与免疫调节作用的分子,可能是淋巴瘤细胞参与肿瘤免疫的调节重要机制.     

GST pull-down联合质谱筛选（肌）营养不良短小蛋白结合蛋白1在小鼠睾丸组织中的相互作用蛋白质

（肌）营养不良短小蛋白结合蛋白1（dystrobrevin binding protein 1,dysbindin-1）是溶酶体相关细胞器生物发生复合体-1(biogenesis of lysosome related organelles complex 1, BLOC-1)的1个亚基,在多种组织细胞中广泛表达;然而,其在睾丸组织中的作用至今尚不明确。为寻找（肌）营养不良短小蛋白结合蛋白1在睾丸组织中的相互作用蛋白质,以进一步研究（肌）营养不良短小蛋白结合蛋白1在睾丸中的作用,本研究首先在Rosetta(DE3)菌种中表达可溶性GST-dysbindin-1融合蛋白,经谷胱甘肽 琼脂糖珠亲和纯化后,与小鼠的睾丸组织蛋白质孵育进行GST pull-down实验,并通过液相色谱串联质谱（LC MS/MS）分析筛选（肌）营养不良短小蛋白结合蛋白1在睾丸组织中的相互作用蛋白质。利用BioGPS数据库聚类在睾丸组织中高表达和特异性表达的互作蛋白质,运用DAVID6.8在线分析工具从细胞组分、分子功能、生物学过程和KEGG通路等方面对筛选出的互作蛋白质进行GO（gene ontology）富集分析。本实验共筛选出108个（肌）营养不良短小蛋白结合蛋白1在睾丸组织中的潜在互作蛋白质,其中98个为尚未报道的（肌）营养不良短小蛋白结合蛋白1相互作用蛋白质,7个为睾丸高表达蛋白质,5个为睾丸特异性表达的蛋白质。这些候选蛋白质主要分布在细胞质、细胞核、细胞膜、细胞外泌体等细胞组分中,通过与蛋白质、核酸等分子结合参与蛋白质翻译和转运、囊泡运输及凋亡等生物学过程以及氨基酸生物合成、溶酶体及蛋白酶体等生物学通路。我们推测,在睾丸组织中（肌）营养不良短小蛋白结合蛋白1可能通过与多种蛋白质相互作用参与精子的发生和受精等过程。     

普萘洛尔对映异构体诱导HUVEC细胞的蛋白质表达谱差异

手性药物只能通过严格的手性识别才能选择性地与特定生物大分子相互作用,在药动学、药效学等方面上表现出手性特征.以非选择性β肾上腺素能受体阻滞剂普萘洛尔（PRO）的对映异构体R(+)/S(-)-PRO为模型药物,分别作用于人脐静脉内皮细胞（HUVEC）,提取全细胞蛋白质,经双向电泳、MALDI-TOF-MS、SWISSPROT数据库分析鉴定差异表达蛋白质;共筛选出22个差异表达蛋白质点,鉴定了HSP86、HSP84、GRP75、KLC18、KBTB2、TGM2、GBLP、GCNT2、RAB36、KLH34等10种蛋白质.研究表明,PRO对映异构体可引起广泛的基因表达改变,涉及信号分子、代谢酶、骨架蛋白、伴侣蛋白等,且具有显著的手性特征,这可能与PRO显著的手性生物学特征有紧密联系,但仍需开展进一步深入研究,以明确产生PRO手性生物学特征的多种途径和机制.蛋白质组学技术为深入了解药物的手性生物学特征及其作用机制提供了新的思路和策略,对手性药物开发和临床合理用药有着重要的意义.     

应用蛋白质组学技术筛选胃癌SGC-7901细胞中的let-7a功能相关蛋白

为探讨let-7a表达下调在胃癌发病中的机制,高通量地检测了与let-7a功能相关的蛋白质.首先采用基因克隆技术稳定过表达SGC-7901细胞系的let-7a基因,然后用蛋白质组学技术研究稳定过表达该基因对SGC-7901细胞蛋白质表达谱的影响.通过对SGC-7901/let-7a细胞的蛋白质表达谱改变的研究,并用基质辅助激光解吸电离飞行时间质谱(MALDI-TOF-MS)分析鉴定了10个差异表达蛋白质.这些差异表达蛋白质可能是let-7a功能相关蛋白质,其中抗氧化蛋白2、胰岛素样生长因子结合蛋白2、二硫化蛋白异构酶A2、四氢叶酸合成酶、细胞周期素依赖性激酶抑制蛋白1、Rho-GTPsae激活蛋白4表达上调,Skp2蛋白、血小板黏附蛋白CD41、纤维连接蛋白、Cks1蛋白表达下调.部分差异表达蛋白质如细胞周期素依赖性激酶抑制蛋白1、Skp2蛋白和纤维连接蛋白经蛋白质印迹分析进行了验证.在SGC-7901/let-7a中鉴定的10个差异表达蛋白质涉及到细胞周期的调控、分子基因表达调控、细胞黏附、细胞代谢等众多事件,它们可能作为let-7a功能相关蛋白质,为阐明let-7a表达下调在胃癌发病中的机制提供了重要线索.     

藤黄新酸抑制肝癌细胞生长的机制研究

在肿瘤细胞中蛋白酶体活性的抑制可以导致细胞凋亡和周期阻滞.藤黄新酸(TH2)是从中药藤黄中提取的一个新的(口山)酮类衍生物.研究结果显示,TH2可以抑制人肝癌Bel-7402细胞的增殖,诱导细胞产生凋亡,且呈浓度和时间依赖性.同时,10μmol/L的TH2与细胞作用24h后,可以导致早期凋亡标志性蛋白PARP发生裂解.在体外采用特异性荧光底物检测TH2对蛋白酶体活性的影响,发现该化合物能够抑制蛋白酶体的糜乳蛋白酶样、胰蛋白酶样活性和谷氨酰后水解活性.抑癌基因p53是细胞内的蛋白酶体降解底物,TH2可使p53蛋白的降解受到阻滞,表达增加.由此可见,TH2具有抑制人肝癌Bel-7402细胞增殖、诱导细胞凋亡的作用,可能的分子机制与其抑制细胞内蛋白酶体活性、导致p53蛋白降解受阻有关.     

水稻叶片对镉胁迫响应的蛋白质差异表达

为揭示水稻镉抗性的分子机理,以抗镉水稻品种P1312777和镉敏感水稻品种IR24为材料,在镉离子浓度为0(对照)、50和100 μmol·L-1条件下水培处理7 d,应用蛋白质组学方法分析了2种水稻叶片对镉胁迫响应的蛋白质差异表达.结果表明:镉胁迫下水稻PI312777叶片中共检测到差异表达蛋白质点31个,通过MALDI-TOF/MS分析,鉴定了其中的24个蛋白质(包括20个不同蛋白质,4个重复检出蛋白质);IR24叶片中共检测到差异表达蛋白质点19个,其中15个蛋白质得到鉴定.PI312777叶片鉴定出的20个蛋白质覆盖了IR24叶片鉴定的15个蛋白质,前者有4个与光合作用相关,11个与细胞防御代谢相关,3个与其他代谢相关,2个为功能未知蛋白.与对照相比,不同浓度镉胁迫下,抗镉水稻PI312777叶片中热激蛋白、谷胱甘肽还原酶、蛋白酶体α亚基6型、果糖1,6-二磷酸醛缩酶、硫氧还蛋白和DNA重组修复蛋白均上调表达;镉敏感水稻IR24叶片中热激蛋白、谷胱甘肽还原酶、蛋白酶体α亚基6型的表达无显著差异,果糖1,6-二磷酸醛缩酶和硫氧还蛋白则下调表达.此外,DNA重组修复蛋白仅在镉胁迫的PI312777叶片中表达.水稻PI312777比IR24具有更强的镉抗性与这些差异表达的蛋白质密切相关.     

胃癌细胞高尔基体的蛋白质组学技术平台的建立

采用蔗糖密度梯度超速离心法分离纯化高尔基体,双向凝胶电泳（2-DE）分离高尔基体蛋白质,用ImageMaster 2D软件分析所得图谱,基质辅助激光解吸离子化飞行时间质谱(MALDI—TOF MS)鉴定蛋白质点等一系列亚细胞器蛋白质组学方法建立胃癌细胞内高尔基体的蛋白图谱。结果显示分离出的纯度较高的高尔基体建立了分辨率和重复性均较好的双向电泳图谱,运用质谱技术鉴定出12个蛋白质,包括蛋白合成相关蛋白、膜融合蛋白、调节蛋白、凋亡相关蛋白、运输蛋白、细胞增殖分化相关蛋白。通过亚细胞器分离纯化,双向电泳的蛋白分离及MALDI-TOF MS蛋白鉴定分析,首次成功建立了胃癌细胞SGC7901中高尔基体的蛋白质组学技术路线,为胃癌细胞内高尔基体功能的深入研究奠定了基础。     

Chaperone proteins identified from synthetic proteasome inhibitor-induced inclusions in PC12 cells by proteomic analysis

Chaperone proteins are significant in Lewy bodies, but the profile of chaperone proteins is incompletely unraveled. Proteomic analysis is used to determine protein candidates for further study. Here, to identify potential chaperone proteins from agent-induced inclusions, we carried out proteomic analysis of artificially synthetic proteasome inhibitor (PSI)-induced inclusions formed in PC12 cells exposed to 10 μM PSI for 48 h. Using biochemical fractionation, 2-D electrophoresis, and identification through peptide mass fingerprints searched against multiple protein databases, we repeatedly identified eight reproducible chaperone proteins from the PSI-induced inclusions. Of these, 58 kDa glucose regulated protein, 75 kDa glucose regulated protein, and calcium-binding protein 1 were newly identified. The other five had been reported to be consistent components of Lewy bodies. These findings suggested that the three potential chaperone proteins might be recruited to PSI-induced inclusions in PC12 cells under proteasome inhibition.     

Isolation and characterization of a novel 530-kDa protein complex (PC530) capable of associating with the 20S proteasome from starfish oocytes

A novel protein complex called PC530 was purified concomitantly with proteasomes from oocytes of the starfish, Asterina pectinifera, by chromatography with DEAE-cellulose, phosphocellulose, Mono Q, and Superose 6 columns. The molecular mass of this complex was estimated to be 530 kDa by Ferguson plot analysis and about 500 kDa by Superose 6 gel filtration. Since the 1500-kDa proteasome fractions contain the PC530 subunits as well as the 20S proteasomal subunits, and also since the purified PC530 and the 20S proteasome were cross-linked with a bifunctional cross-linking reagent, it is thought that PC530 is able to associate with the 20S proteasome. The PC530 comprises six main subunits with molecular masses of 105, 70, 50, 34, 30, and 23 kDa. The 70-kDa subunit showed a sequence similarity to the S3/p58/Sun2/Rpn3p subunit of the 26S proteasome, whereas the other subunits showed little or no appreciable similarity to the mammalian and yeast regulatory subunits. These results indicate that starfish oocytes contain a novel 530-kDa protein complex capable of associating with the 20S proteasome, which is distinctly different from PA700 or the 19S regulatory complex in molecular size and subunit composition.     

Endogenous dopamine (DA) renders dopaminergic cells vulnerable to challenge of proteasome inhibitor MG132

This study demonstrated that dopaminergic MN9D and PC12 cells were more vulnerable than non-dopaminergic N2A cells to the challenge by proteasome inhibitor MG132, which could be alleviated by reductants and alpha-methyl tyrosine (alpha-MT), a specific tyrosine hydroxylase inhibitor. Furthermore, challenging non-dopaminergic N2A cells with exogenous DA could aggravate MG132-induced cell viability decrease, which could be abrogated by reductants but not by alpha-MT. It was observed that alpha-MT could decrease endogenous DA content in dopaminergic MN9D and PC12 cells while N2A cells could take in exogenous DA into cytosol. The endogenous DA in dopaminergic cells was demonstrated to inhibit proteasome activity in the cells and further sensitize the proteasome to MG132 inhibition. In addition, the endogenous DA was also implicated for the increased level of lipid peroxidation and ubiquitinated proteins as well as inclusion bodies formation when non-dopaminergic cells were challenged with exogenous DA. Taken together it is proposed that endogenous DA in dopaminergic neurons could promote selective dopaminergic neurodegeneration, especially under the conditions of exopathic or idiopathic defects of ubiquitin–proteasome system (UPS), which may be abolished by reductant remedy.     

Synphilin-1 degradation by the ubiquitin-proteasome pathway and effects on cell survival

Parkinson's disease is characterized by loss of nigral dopaminergic neurons and the presence of cytoplasmic inclusions known as Lewy bodies. alpha-Synuclein and its interacting partner synphilin-1 are among constituent proteins in these aggregates. The presence of ubiquitin and proteasome subunits in these inclusions supports a role for this protein degradation pathway in the processing of proteins involved in this disease. To begin elucidating the kinetics of synphilin-1 in cells, we studied its degradation pathway in HEK293 cells that had been engineered to stably express FLAG-tagged synphilin-1. Pulse-chase experiments revealed that this protein is relatively stable with a half-life of about 16 h. Treatment with proteasome inhibitors resulted in attenuation of degradation and the accumulation of high molecular weight ubiquitinated synphilin-1 in immunoprecipitation/immunoblot experiments. Additionally, proteasome inhibitors stimulated the formation of peri-nuclear inclusions which were immunoreactive for synphilin-1, ubiquitin and alpha-synuclein. Cell viability studies revealed increased susceptibility of synphilin-1 over-expressing cells to proteasomal dysfunction. These observations indicate that synphilin-1 is ubiquitinated and degraded by the proteasome. Accumulation of ubiquitinated synphilin-1 due to impaired clearance results in its aggregation as peri-nuclear inclusions and in poor cell survival.     

Analysis of Drosophila 26 S proteasome using RNA interference.

We have utilized double-stranded RNA interference (RNAi) to examine the effects of reduced expression of individual subunits of the 26 S proteasome in Drosophila S2 cells. RNAi significantly decreased mRNA and protein levels of targeted subunits of both the core 20 S proteasome and the PA700 regulatory complex. Cells deficient in any of several 26 S proteasome subunits (e.g. d beta 5, dRpt1, dRpt2, dRpt5, dRpn2, and dRpn12) displayed decreased proteasome activity (as judged by hydrolysis of succinyl-Leu-Leu-Val-Tyr-aminomethylcoumarin), increased apoptosis, decreased cell proliferation without a specific block of the cell cycle, and accumulation of ubiquitinated cellular proteins. RNAi of many individual 26 S proteasome subunits promoted increased expression of many non-targeted subunits. This effect was not mimicked by chemical proteasome inhibitors such as lactacystin. Reduced expression of most targeted subunits disrupted the assembly of the 26 S proteasome. RNAi of six of eight targeted PA700 subunits disrupted that structure and caused accumulation of increased levels of uncapped 20 S proteasome. Notable exceptions included RNAi of dRpn10, a polyubiquitin binding subunit, and dUCH37, a ubiquitin isopeptidase. dRpn10-deficient cells showed a significant increase in succinyl-Leu-Leu-Val-Tyr-aminomethylcoumarin hydrolyzing activity of the 26 S proteasomes but accumulated polyubiquitinated proteins. d beta 5-Deficient cells had a phenotype similar to that of most PA700-deficient cells but also accumulated low molecular mass complexes containing subunits of the 20 S proteasome, probably representing unassembled precursors of the 20 S proteasomes. Cells deficient in several of the 26 S proteasome subunits were more resistant to otherwise toxic concentrations of various proteasome inhibitors. Our data suggest that those cells adapted to grow in conditions of impaired ubiquitin and proteasome-dependent protein degradation.     

Endogenous dopamine (DA) renders dopaminergic cells vulnerable to challenge of proteasome inhibitor MG132

This study demonstrated that dopaminergic MN9D and PC12 cells were more vulnerable than non-dopaminergic N2A cells to the challenge by proteasome inhibitor MG132, which could be alleviated by reductants and alpha-methyl tyrosine (alpha-MT), a specific tyrosine hydroxylase inhibitor. Furthermore, challenging non-dopaminergic N2A cells with exogenous DA could aggravate MG132-induced cell viability decrease, which could be abrogated by reductants but not by alpha-MT. It was observed that alpha-MT could decrease endogenous DA content in dopaminergic MN9D and PC12 cells while N2A cells could take in exogenous DA into cytosol. The endogenous DA in dopaminergic cells was demonstrated to inhibit proteasome activity in the cells and further sensitize the proteasome to MG132 inhibition. In addition, the endogenous DA was also implicated for the increased level of lipid peroxidation and ubiquitinated proteins as well as inclusion bodies formation when non-dopaminergic cells were challenged with exogenous DA. Taken together it is proposed that endogenous DA in dopaminergic neurons could promote selective dopaminergic neurodegeneration, especially under the conditions of exopathic or idiopathic defects of ubiquitin-proteasome system (UPS), which may be abolished by reductant remedy.     

Regulation of PSMB5 Protein and β Subunits of Mammalian Proteasome by Constitutively Activated Signal Transducer and Activator of Transcription 3 (STAT3): POTENTIAL ROLE IN BORTEZOMIB-MEDIATED ANTICANCER THERAPY*

The ubiquitin-proteasome system facilitates the degradation of ubiquitin-tagged proteins and performs a regulatory role in cells. Elevated proteasome activity and subunit expression are found in several cancers. However, the inherent molecular mechanisms responsible for increased proteasome function in cancers remain unclear despite the well investigated and defined role of the mammalian proteasome. This study was initiated to elucidate the mechanisms involved in the regulation of β subunits of the mammalian proteasome. Suppression of STAT3 tyrosine phosphorylation coordinately decreased the mRNA and protein levels of the β subunits of the 20 S core complex in DU145 cells. Notably, PSMB5, a molecular target of bortezomib, was shown to be a target of STAT3. Knockdown of STAT3 decreased PSMB5 protein. Inhibition of phospho-STAT3 substantially reduced PSMB5 protein levels in cells expressing constitutively active-STAT3. Accumulation of activated STAT3 resulted in the induction of PSMB5 promoter and protein levels. In addition, a direct correlation was observed between the endogenous levels of PSMB5 and constitutively active STAT3. PSMB5 and STAT3 protein levels remained unaltered following the inhibition of proteasome activity. The EGF-induced concerted increase of β subunits was blocked by inhibition of the EGF receptor or STAT3 but not by the PI3K/AKT or MEK/ERK pathways. Decreased proteasome activities were due to reduced protein levels of catalytic subunits of the proteasome in STAT3-inhibited cells. Combined treatments with bortezomib and inhibitor of STAT3 abrogated proteasome activity and enhanced cellular apoptosis. Overall, we demonstrate that aberrant activation of STAT3 regulates the expression of β subunits, in particular PSMB5, and the catalytic activity of the proteasome.     

Identification of the Immunoproteasome as a Novel Regulator of Skeletal Muscle Differentiation

While many of the molecular details of myogenesis have been investigated extensively, the function of immunoproteasomes (i-proteasomes) in myogenic differentiation remains unknown. We show here that the mRNA of i-proteasome subunits, the protein levels of constitutive and inducible proteasome subunits, and the proteolytic activities of the 20S and 26S proteasomes were significantly upregulated during differentiation of skeletal muscle C2C12 cells. Knockdown of the i-proteasome catalytic subunit PSMB9 by short hairpin RNA (shRNA) decreased the expression of both PSMB9 and PSMB8 without affecting other catalytic subunits of the proteasome. PSMB9 knockdown and the use of i-proteasome-specific inhibitors both decreased 26S proteasome activities and prevented C2C12 differentiation. Inhibition of the i-proteasome also impaired human skeletal myoblast differentiation. Suppression of the i-proteasome increased protein oxidation, and these oxidized proteins were found to be more susceptible to degradation by exogenous i-proteasomes. Downregulation of the i-proteasome also increased proapoptotic proteins, including Bax, as well as cleaved caspase 3, cleaved caspase 9, and cleaved poly(ADP-ribose) polymerase (PARP), suggesting that impaired differentiation is likely to occur because of significantly increased apoptosis. These results demonstrate for the first time that i-proteasomes, independent of constitutive proteasomes, are critical for skeletal muscle differentiation of mouse C2C12 cells.     

Proteome analysis of rice blast fungus (Magnaporthe grisea) proteome during appressorium formation

We used two-dimensional gel electrophoresis (2-DE) to identify the proteins that are induced in the rice blast fungus Magnaporthe grisea during appressorium formation. Proteins were extracted from conidia that had germinated on hydrophilic glass plates or from germinated and appressoria-forming conidia on leaf wax-coated hydrophobic glass plates after 4, 8, and 12 h of incubation. Differentially expressed protein spots during appressorium formation were confirmed from gels after 2-DE analysis where proteins had been labeled with (35)S methionine and stained with silver. Internal amino acid sequencing identified five proteins among several proteins induced during appressorium formation. Two denoted as M. grisea proteasome homolgues (MgP1 and MgP5) were 20S proteasome alpha subunits. The remaining three were scytalone dehydratase (SCD), and serine carboxypeptidase Y (CPY). None of the five have been reported previously in the rice blast fungus apart from SCD. We further investigated the role the alpha subunit of 20S proteasome plays in appressorium formation. We confirmed by Western blot analysis that MgP5 is highly expressed during appressorium formation and found that it is also markedly induced by nitrogen- and carbon-starvation, in particular by the former. These observations suggest that the 20S proteasome may be involved in remobilizing storage proteins, which then help to build the appressorium. Thus, fungal proteome analysis may provide important clues about developmental changes such as the generation of the appressorium.