Phorbol esters inhibit the synthesis of acetylcholine receptors in cultured muscle cells

The acetylcholine receptor (AChR) synthesis, insertion and degradation rates are regulated by numerous intracellular and extracellular agents. Recent studies have shown that Ca2+ and Ca2+ ionophores have a profound regulatory effect on the appearance of AChR clusters and AChR synthesis. These regulatory effects may be mediated through the activation of calcium and phospholipid-dependent protein kinases by agents such as phorbol esters. In this study, we have utilized 4-beta-phorbol-12-myristate-13-acetate (PMA) in order to determine whether the activation of protein kinase C exerts a regulatory effect on the expression of AChRs in cultured chick myotubes. Our results show that 4-beta-phorbol-12-myristate-13-acetate decreased intracellular AChRs and suppressed AChR synthesis without affecting the turnover rate. Control and PMA treated cells labeled with [35S] methionine and immunoprecipitated with a monoclonal antibody to the alpha subunit of AChRs (mAb35) revealed a significant decrease in radioactivity precipitated after exposure to PMA. Polyacrylamide gel electrophoresis revealed no major changes in protein patterns, or in newly synthesized proteins as determined by [35S] methionine incorporation and autoradiography. Other enzymes important in muscle metabolism were not affected by PMA treatment. Our results indicate that activation of protein kinase C results in the suppression of AChRs synthesis and dispersal of AChR clusters.     

Synthesis of FAEEs from glycerol in engineered Saccharomyces cerevisiae using endogenously produced ethanol by heterologous expression of an unspecific bacterial acyltransferase

The high price of petroleum-based diesel fuel has led to the development of alternative fuels, such as ethanol. Saccharomyces cerevisiae was metabolically engineered to utilize glycerol as a substrate for ethanol production. For the synthesis of fatty acid ethyl esters (FAEEs) by engineered S. cerevisiae that utilize glycerol as substrate, heterologous expression of an unspecific acyltransferase from Acinetobacter baylyi with glycerol utilizing genes was established. As a result, the engineered YPH499 (pGcyaDak, pGupWs-DgaTCas) strain produced 0.24 g/L FAEEs using endogenous ethanol produced from glycerol. And this study also demonstrated the possibility of increasing FAEE production by enhancing ethanol production by minimizing the synthesis of glycerol. The overall FAEE production in strain YPH499 fps1Δ gpd2Δ (pGcyaDak, pGupWs-DgaTCas) was 2.1-fold more than in YPH499 (pGcyaDak, pGupWs-DgaTCas), with approximately 0.52 g/L FAEEs produced, while nearly 17 g/L of glycerol was consumed. These results clearly indicated that FAEEs were synthesized in engineered S. cerevisiae by esterifying exogenous fatty acids with endogenously produced ethanol from glycerol. This microbial system acts as a platform in applying metabolic engineering that allows the production of FAEEs from cheap and abundant substrates specifically glycerol through the use of endogenous bioethanol.     

三尖杉培养细胞中抗癌活性成分的研究

从三尖杉（ＣｅｐｈａｌｏｔａｘｕｓｆｏｒｔｕｎｅｉＨｏｏｋ．ｆ．）茎和叶片作外植体在ＭＳ附加ＫＴ ０．１ ｍ ｇ／Ｌ、ＮＡＡ ３ ｍ ｇ／Ｌ培养基上诱导出的愈伤组织,建立了三尖杉悬浮培养细胞系,研究了光、ｐＨ 值、激素、碳源和添加物等因子对悬浮细胞生长的影响。结果表明： ｐＨ ５．８ 及低浓度的糖和ＮＡＡ适于细胞生长,糖含量超过４０ ｇ／Ｌ则不利于细胞生长,ＮＡＡ 大于３ ｍ ｇ／Ｌ抑制细胞生长。蔗糖或葡萄糖作碳源,二者无明显区别。添加水解蛋白或氨基酸不适合细胞生长。白光对细胞生长有明显的抑制作用。建立了灵敏、快速高效液相色谱测定方法,测得离体培养细胞含有三尖杉碱及抗癌酯类生物碱：三尖杉酯碱、异三尖杉酯碱和高三尖杉酯碱。细胞悬浮培养中合成生物碱的能力明显高于固体培养,前者有效生物碱的含量和细胞增长速率均比后者高１ 倍以上。悬浮培养细胞中各生物碱组分比率为：２２％ 三尖杉碱,６％ 氧桥三尖杉碱,８％ 三尖杉酯碱,２３％ 高三尖杉酯碱,４１％ 异三尖杉酯碱。用气相色谱－质谱联用技术,除测得上述生物碱外,还检测到细胞培养物中含有去氧三尖杉酯碱、麦角甾醇、豆甾醇和谷甾醇等化合物     

食管癌细胞NGAL5′侧翼区存在TPA应答元件

在TPA诱导永生化食管上皮细胞癌变中,NGAL(neutrophil gelatinase-associated lipocalin)过表达,提示食管癌细胞NGAL转录调控区可能存在TPA应答元件.为了对食管癌细胞NGAL的这一TPA应答元件进行分段定位鉴定,首先将NGAL5′侧翼区不同长度片段-1 431~ 84-、1 137~ 84、-945~ 84、-657~ 84、-416~ 84和-152~ 84等依次插入质粒pGLP,构建NGAL/pGLP系列报告基因荧光素酶表达载体pGLP-1431、pGLP-1137、pGLP-945、pGLP-657、pGLP-416和pGLP-152;然后将上述质粒分别同pRL-TK共转染食管癌细胞EC109,最后用5 ng/ml的TPA刺激转染的EC109,检测报告基因荧光素酶活力,综合判定报告基因荧光素酶活力变化趋势,并以此对食管癌细胞NGAL5′侧翼区TPA应答元件进行分段定位.实验结果表明,食管癌细胞NGAL5′侧翼-657~-417区段内存在着较强的TPA应答元件.生物信息学分析显示,NGAL5′侧翼-657~-417区段至少存在3个潜在的TPA应答元件,表明有应答TPA刺激的结构基础.这些研究有助于从分子水平揭示TPA诱导永生化食管上皮细胞癌变中NGAL基因过表达机制.     

拟南芥芥子酸酯对UV-B辐射的响应

芥子酸酯(sinapate esters)是拟南芥和其他十字花科植物中大量存在的一类具有紫外吸收作用的羟基肉桂酸衍生物,有研究表明其紫外吸收能力甚至强于类黄酮。以模式植物拟南芥(Arabidopsis thaliana)为实验材料,通过施加低强度(40 μW/cm²)、相对长时间(7 d)的UV-B辐射,考察了拟南芥幼苗和成苗芥子酸酯组分(芥子酰葡萄糖、芥子酰苹果酸)和含量及合成途径关键酶编码基因表达水平对UV-B辐射的响应。经过7 d的UV-B辐射处理,拟南芥幼苗和成苗的芥子酰葡萄糖、芥子酰苹果酸含量均高于对照植株,芥子酸酯表现为响应UV-B辐射而积累。无论是幼苗还是成苗,叶片中芥子酰苹果酸的含量都要比芥子酰葡萄糖高出一个数量级,而且在UV-B处理过程中观察到芥子酰葡萄糖含量减少而芥子酰苹果酸含量增加,催化芥子酰葡萄糖生成芥子酰苹果酸的芥子酰葡萄糖苹果酸转移酶编码基因的表达水平也显著提高,说明芥子酰苹果酸在拟南芥叶片响应UV-B辐射过程中起重要作用并优先合成。另外,拟南芥幼苗中两种芥子酸酯的含量是成苗中的数十倍之多,芥子酸酯合成途径关键酶编码基因fah1和sng1的相对表达量也显著高于成苗。同时,在响应UV-B辐射的过程中,幼苗中芥子酰葡萄糖、芥子酰苹果酸含量的变化幅度(分别是7.01％、6.05％)远远低于成苗叶片中芥子酰葡萄糖、芥子酰苹果酸含量的变化幅度(分别是21.88％、70.63％),这可能意味着拟南芥叶片中芥子酸酯对于UV-B辐射的防护作用,幼苗属于组成型防御(constitutive defense),而到成苗则转变为诱导型防御(inducible defense)。     

Anaerobic degradation of phthalic acid esters during digestion of municipal solid waste under landfilling conditions

Anaerobic microorganisms in municipal solid waste samples from laboratory-scale landfill reactors and a pilot-plant biogas digestor were investigated with the aim of assessing their ability to transform four commercially used phthalic acid esters (PAEs) and phthalic acid (PA). The PAEs studied were diethyl phthalate (DEP), butylbenzyl phthalate (BBP), dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP). No biological transformation of DEHP could be detected in any of the experiments. Together with waste samples from the simulated landfilling conditions, the PAEs (except DEHP) were hydrolytically transformed to their corresponding monoesters. These accumulated as end products, and in most cases they were not further degraded. During incubation with waste from the biogas digestor, the PAEs (except DEHP) were completely degraded to methane and carbon dioxide. The influence of the landfill development phase on the transformations was investigated utilizing PA and DEP as model substances. We found that during both the intense and stable methanogenic (but not the acidogenic) phases, the microoganisms in the samples had the potential to transform PA. A shorter lag phase was observed for the PA transformation in the samples from the stable methanogenic phase as compared with earlier phases. This indicates an increased capacity to degrade PA during the aging phases of the municipal solid waste in landfills. No enhancement of the DEP transformation could be observed as conditions in the methanogenic landfill model changed over a year's time. The results indicate that microorganisms developing in a methanogenic landfill environment have a substantially lower potential to degrade PAEs compared with those developing in a biogas reactor.Abbreviations BBP butylbenzyl phthalate - DEHP bis(2-ethylhexyl) phthalate - CoA coenzyme A - DBP dibutyl phthalate - DEP diethyl phthalate - DS dry solids - MBeP monobenzyl phthalate - MBuP monobutyl phthalate - MEP monoethyl phthalate - MSW municipal solid waste - PA phthalic acid - PAE(s) phthalic acid ester(s) - VFA volatile fatty acids     

Lipolytic activity from Halobacteria: screening and hydrolase production

Strains of Halobacteria from an Algerian culture collection were screened for their lipolytic activity against p-nitrophenyl butyrate (PNPB) and p-nitrophenyl palmitate (PNPP). Most strains were active on both esters and 12% hydrolyzed olive oil. A strain identified as Natronococcus sp. was further studied. It grew optimally at 3.5 M NaCl, pH 8 and 40 degrees C. An increase in temperature shifted the optimum salt concentration range for growth from a wider range of 2-4 M, obtained at 25-30 degrees C, to a narrower range of 3.5-4 M, obtained at 35-40 degrees C. At 45 degrees C the optimum salt concentration was 2 M. These results show a clear correlation between salt and temperature requirement. The optimum conditions for the production of hydrolytic activity during growth were: 3.5 M NaCl and pH 8 for PNPB hydrolytic activity and 4 M NaCl and pH 7.5 for PNPP hydrolytic activity; both at 40 degrees C. The clear supernatant of cells grown at 4 M NaCl showed olive oil hydrolysis activity (in presence of 4 M NaCl) demonstrating the occurrence of a lipase activity in this strain. To our knowledge, this is the first report of a lipase activity at such high salt concentration.     

黄芫花提取物对V_(79)细胞和WB肝细胞的生物学效应 1.细胞连接通讯与增殖活性的相关性变化

用SLDT技术、细胞生长曲线、~3H-TdR掺入、细胞分裂指数和流式细胞光度术等方法在V_(79)细胞和WB肝细胞中观察到中药促癌物黄芫花提取物刺激细胞增殖的作用与对细胞GJIC抑制的作用有平行相关性。黄芫花提取物抑制V_(79)细胞的GJIC,同时刺激DNA合成,使细胞周期M期时相百分比升高,与TPA的效应相似,对黄芫花提取物促癌作用机理、GJIC抑制与细胞增殖周期的相关性进行分析讨论。     

Inhibition of Bradykinin-Induced Phosphoinositide Hydrolysis and Ca Mobilisation by Phorbol Ester in Rat Cultured Vascular Smooth Muscle Cells

Regulation of the increase in inositol phosphate (IP) production and intracellular Ca²⁺ concentration ([Ca²⁺]_i by protein kinase C (PKC) was investigated in cultured rat vascular smooth muscle cells (VSMCs). Pretreatment of VSMCs with phorbol 12-myristate 14-acetate (PMA, 1 μM) for 30 min almost abolished the BK-induced IP formation and Ca²⁺ mobilisation. This inhibition was reduced after incubating the cells with PMA for 4 h, and within 24 h the BK-induced responses were greater than those of control cells. The concentrations of PMA giving a half-maximal (pEC₅₀) and maximal inhibition of BK induced an increase in [Ca²⁺]_i, were 7.8 ± 0.3 M and 1 μM, n = 8, respectively. Prior treatment of VSMCs with staurosporine (1 μM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. Paralleling the effect of PMA on the BK-induced IP formation and Ca²⁺ mobilisation, the translocation and downregulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of the cells with PMA for various times, translocation of PKC-, βI, βII, δ, ε, and ζ isozymes from the cytosol to the membrane were seen after 5 min, 30 min, 2 h, and 4 h of treatment. However, 24-h treatment caused a partial downregulation of these PKC isozymes in both fractions. Treatment of VSMCs with 1 μM PMA for either 1 or 24 h did not significantly change the K_D and B_max of the BK receptor for binding (control: K_D = 1.7 ± 0.2 nM; B_max = 47.3 ± 4.4 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. In conclusion, these resuts demonstrate that translocation of PKC-, βI, βII, δ, ε, and ζ induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca²⁺ mobilisation in VSMCs.     

Full model for reversible kinetics of lipase-catalyzed sugar-ester synthesis in 2-methyl 2-butanol

A kinetic model derived from the ping-pong bi-bi reversible mechanism is proposed to described the acylation of glucose by lauric acid in 2-methyl 2-butanol mediated by Candida antarctica lipase at 60 degrees C. The model accounts for the effect of all four compounds in the reaction mixture, namely lauric acid, glucose, water, and lauroyl glucose ester. A supersaturated glucose solution was used to avoid limitations by glucose dissolution rate. Experiments with varied initial water content were performed to determine the effect of water on the initial reaction rate. The full time course of ester formation is described by five parameters: (a) three parameters evaluated from initial rate measurements; (b) the equilibrium constant, independently evaluated; and (c) one extra parameter fitted to the progress curve of ester formation. This reduced form of a full reversible kinetic model based on the ping-pong bi-bi mechanism is able to describe the complete course of lauroyl glucose ester synthesis. The proposed model provides a good fit for the experimental results.