A protein phosphatase 2A (PP2A) inhibition assay using a recombinant enzyme for rapid detection of microcystins

Worldwide blooms of toxic cyanobacteria (blue-green algae) commonly occur in freshwater, often in drinking water sources, necessitating routine monitoring of water quality. Microcystin-LR and related cyanobacterial toxins strongly inhibit protein phosphatase 2A (PP2A) and are therefore assayable by measuring the extent of PP2A inhibition. In this study, we evaluated the suitability of the catalytic subunit of recombinant PP2A (rPP2Ac) expressed with a baculovirus system for use in a microplate microcystin assay. Five microcystin analogs, microcystin-LR, -RR, -YR, -LF, and -LW, and nodularin strongly inhibited rPP2Ac activity with IC(50) values of 0.048, 0.072, 0.147, 0.096, 0.114, and 0.54 nM, respectively. Microcystin-LR in a water sample could be assayed from 0.005 to 5 ng/ml. The assay could detect the toxin at a far lower level than required by the World Health Organization for regulation of microcystin-LR or its equivalent (1 microg/L). Pretreatment or concentration of water samples with low toxin concentrations was not necessary. The microplate assay using rPP2Ac was more sensitive than an enzyme-linked immunosorbent assay (ELISA) method and a cytotoxicity assay. The genetically engineered rPP2Ac was more stable than a commercially available dimeric enzyme, producing accurate and reproducible results. Our results confirm that the rPP2Ac we prepared is an excellent tool for detecting and quantifying microcystins in water.     

Comparison of protein phosphatase inhibition activities and mouse toxicities of microcystins.

Eight naturally purified microcystins (MCs), including MC-LR, -FR, -WR, -RR, [d-Asp(3)]MC-FR, -WR, -RR, and [Dha(7)]MC-RR were utilized to determine the effects of amino acid substitutions and modifications on MC-induced protein phosphatase inhibition activity and mouse toxicity. Catalytic subunits of protein phosphatase 1 (PP-1) and 2A (PP-2A) were purified and subjected to the inhibition assays, and intraperitoneal injection was used to administer MCs into mice for the toxicity assay. It is found that the replacement of the non-polar amino acid l-leucine at the second position of these heptacyclic peptide toxins by a polar l-arginine reduces their mouse toxicities and inhibitory activities against PP-1 and PP-2A to different extends. Demethylation of methyldehydroalanine (Mdha) at the seventh amino acid of MC-RR exhibits the least mouse toxicity and phosphatase inhibition. The loss of a methyl group on the common methylaspartic acid (MeAsp) at the third position of MC-FR, -WR, and -RR does not alter their toxicity levels, but dominantly reduces their activities in PP-1 inhibition compared to other substitutions or modifications. This suggests that the methyl group on MeAsp is also important for MCs inhibition. However, such a tendency is not observed for PP-2A. By comparing the LD(50) values of the mouse toxicity assay and IC(50) values of the PP-1 and PP-2A inhibition assay of eight MCs using linear regression, it is evident that the MC-induced toxicity is much more related to the inhibition of PP-2A than PP-1, which suggests that PP-2A inhibition may play a major role in the MC-induced mouse toxicity.     

PP2A Inhibition Assay Using Recombinant Enzyme for Rapid Detection of Okadaic Acid and Its Analogs in Shellfish

Okadaic acid and its analogs (OAs) responsible for diarrhetic shellfish poisoning (DSP) strongly inhibit protein phosphatase 2A (PP2A) and thus are quantifiable by measuring the extent of the enzyme inhibition. In this study, we evaluated the suitability of the catalytic subunit of recombinant human PP2A (rhPP2Ac) for use in a microplate OA assay. OA, dinophysistoxin-1(DTX1), and hydrolyzate of 7-O-palmitoyl-OA strongly inhibited rhPP2Ac activity with IC(50) values of 0.095, 0.104, and 0.135 nM, respectively. The limits of detection and quantitation for OA in the digestive gland of scallops and mussels were 0.0348 μg/g and 0.0611 μg/g respectively, and, when converted to the whole meat basis, are well below the regulation level proposed by EU (0.16 μg/g whole meat). A good correlation with LC-MS data was demonstrated, the correlation coefficient being 0.996 with the regression slope of 1.097.     

Bacterial degradation of microcystin toxins in drinking water eliminates their toxicity.

Microcystin-LR and -LA were readily biodegraded by a bacterium, Sphingpoyxis sp. LH21, in a treated reservoir water. Detection of the microcystins was conducted using high-performance liquid chromatography (HPLC), protein phosphatase 2A (PP2A) inhibition assay and a cell-based cytotoxicity assay. The HPLC results correlated well with the two assays. The decrease in cytotoxicity, coupled with the associated decrease in microcystin concentrations, indicated that no cytotoxic by-products were being generated, highlighting the applicability of biodegradation as a feasible treatment option for effective microcystin removal.     

Single laboratory validation of a ready-to-use phosphatase inhibition assay for detection of okadaic acid toxins

A phosphatase inhibition assay for detection of okadaic acid (OA) toxins in shellfish, OkaTest, was single laboratory validated according to international recognized guidelines (AOAC, EURACHEM). Special emphasis was placed on the ruggedness of the method and stability of the components. All reagents were stable for more than 6 months and the method was highly robust under normal laboratory conditions. The limit of detection and quantification were 44 and 56 μg/kg, respectively; both below the European legal limit of 160 μg/kg. The repeatability was evaluated with 2 naturally contaminated samples. The relative standard deviation (RSD) calculated was 1.4% at a level of 276 μg/kg and 3.9% at 124 μg/kg. Intermediate precision was estimated by testing 10 different samples (mussel and scallop) on three different days and ranged between 2.4 and 9.5%. The IC(50) values of the phosphatase used in this assay were determined for OA (1.2 nM), DTX-1 (1.6 nM) and DTX-2 (1.2 nM). The accuracy of the method was estimated by recovery testing for OA (mussel, 78-101%; king scallop, 98-114%), DTX-1 (king scallop, 79-102%) and DTX-2 (king scallop, 93%). Finally, the method was qualitatively compared to the mouse bioassay and LC-MS/MS.     

三丁基锡对蛋白磷酸酶2A的抑制机制

目的：研究三丁基锡（TBT）对人羊膜FL细胞蛋白磷酸酶2A（PP2A）活力的抑制机制。方法 FL细胞经不同浓度TBT染毒1 h后,检测PP2A活力及PP2A组成亚基A、C、B55α和B56δ以及C亚基蛋白磷酸化和甲基化水平。结果与对照组比较,3、4、6μmol/L染毒FL细胞内PP2A活力均下降,差异有统计学意义（P＜0.01）;6μmol/L TBT染毒组FL细胞内PP2A组成亚基A蛋白的表达下降,4、6μmol/L TBT染毒组B55α蛋白的表达及C蛋白甲基化水平均降低,差异有统计学意义（P＜0.05）。结论 TBT对FL细胞PP2A活力的抑制作用可能与其抑制B55α和A蛋白亚基表达,降低C亚基Leu309位点的甲基化水平有关。     

Oral administration of cyanobacterial bloom extract induced the altered expression of the PP2A, Bax, and Bcl-2 in mice

The frequent occurrences of the toxic cyanobacterial (specifically Microcystis aeruginosa) bloom are becoming a global environmental issue. Lots of researches have been focused on the pure cyanobacterial toxins, but little on the natural cyanobacterial bloom. This study was undertaken to investigate the effect of the natural cyanobacterial bloom extract on the expression of proteins, which have been shown to be affected by pure microcystins. In current study, the cyanobacterial bloom extract has been administered orally to ICR mice for 7 days with different dosages. The expression level of PP2A, Bcl-2, and Bax was measured via western blotting. The results showed that after 7 days of exposure to cyanobacteria extract, in mice liver tissue, the expression level of PP2A and Bax was increased significantly between the control and treatment groups, but there is no significant change on the Bcl-2 expression. This is the first report to describe the altered expression of PP2A in vivo when mice exposure to natural water blooms extract that means many cellular pathways would be interfered via the change of PP2A activity.     

The cytotoxic effect of palytoxin on Caco-2 cells hinders their use for in vitro absorption studies

Palytoxin (PLTX), found in Palythoa zoanthids and Ostreopsis dinoflagellates, has also been detected in crabs and fish, through which it can enter into the food chain. Indeed, PLTX is considered the causative agent of several cases of human seafood poisoning resulting in systemic symptoms. Available epidemiological data on PLTX human toxicity suggest that the intestinal tract may be one of its in vivo targets and its potential site of access into the bloodstream. Hence, the purpose of this study was to investigate the suitability of the human intestinal Caco-2 cell line for evaluating PLTX oral absorption. A detailed analysis of PLTX cytotoxicity revealed a high sensitivity of Caco-2 cells: 4h toxin exposure reduced mitochondrial activity (MTT assay, EC(50) of 8.9±3.7×10(-12)M), cell density (SRB assay, EC(50) of 2.0±0.6×10(-11)M) and membrane integrity (LDH release, EC(50) of 4.5±1.4×10(-9)M and PI uptake, EC(50) of 1.0±0.8×10(-8)M). After low PLTX concentration (1.0×10(-11)M) exposure for 1-8h, followed by 24h recovery time in toxin-free medium, cell density reduction was only partially reversible. These results indicate that, due to the high susceptibility to PLTX cytotoxic effects, Caco-2 cells do not represent an appropriate and reliable model for investigating intestinal barrier permeation by this toxin.     

Detection of okadaic acid and related esters in mussels during diarrhetic shellfish poisoning (DSP) episodes in Greece using the mouse bioassay, the PP2A inhibition assay and HPLC with fluorimetric detection

An approach involving chemical, functional and biological techniques was taken for the detection and quantification of the marine toxin okadaic acid (OA) in mussels from Thermaikos and Saronikos Gulfs, Greece, during DSP episodes that occurred in 2006-2007. Samples were analyzed using the mouse bioassay, high performance liquid chromatography with fluorimetric detection (HPLC-FLD), using l-bromoacetylpyrene (BAP), as a precolumn derivatisation reagent, and the protein phosphatase 2A inhibition assay (PP2AIA) using a commercially available kit. Okadaic acid (OA) and its polar and non-polar esters were detected and quantified by HPLC-FLD, after hydrolysis of the samples during preparation. The detection limit of the HPLC method for OA was 5.86 μg OA/kg, which permits this method to be used for the regulatory control of these toxins in shellfish. Comparison of the results by all three methods revealed excellent consistency.     

Tributyltin induces a G2/M cell cycle arrest in human amniotic cells via PP2A inhibition-mediated inactivation of the ERK1/2 cascades

The molecular mechanisms underlying the cell cycle alterations induced by tributyltin (TBT), a highly toxic environmental contaminant, remain elusive. In this study, cell cycle progression and some key regulators in G2/M phase were investigated in human amniotic cells treated with TBT. Furthermore, protein phosphatase (PP) 2A and the ERK cascades were examined. The results showed that TBT caused a G2/M cell cycle arrest that was accompanied by a decrease in the total cdc25C protein level and an increase in the p-cdc2 level in the nucleus. TBT caused a decrease in PP2A activity and inhibited the ERK cascade by inactivating Raf-1, resulting in the dephosphorylation of MEK1/2, ERK1/2, and c-Myc. Taken together, TBT leads to a G2/M cell cycle arrest in FL cells, an increase in p-cdc2 and a decrease in the levels of total cdc25C protein, which may be caused by the PP2A inhibition-mediated inactivation of the ERK1/2 cascades.     

Cucurbitacin B induces inhibitory effects via the CIP2A/PP2A/C-KIT signaling axis in t(8;21) acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common subtype of hematological malignancy in humans, and its incidence increases with age. The treatment of AML still faces challenges. Therefore, there is an urgent need to develop more effective targeted therapies. The receptor tyrosine kinase C-KIT confers critical proliferative signals to AML. Cancerous inhibitor of protein phosphatase 2A (CIP2A) is an endogenous inhibitor of protein phosphatase 2A (PP2A), which promotes the growth and transformation of various solid tumors. These actions make CIP2A a promising target for tumor treatment. Here, we reported the effects and underlying mechanisms of a natural compound, cucurbitacin B (CuB), on AML. We reported that CuB suppressed growth and induced apoptosis in AML cells. The inhibition of growth and activation of apoptosis were mediated through CuB-induced downregulation of the CIP2A/PP2A/C-KIT signal pathway. Furthermore, CuB inactivated the JAK2 and STAT3 molecules downstream of C-KIT via the downregulation of CIP2A. These results advance our understanding of CuB-induced growth inhibition and apoptosis and support further investigation of CuB as a CIP2A inhibitor for AML therapies.     

双特异性磷酸酶2对胃癌细胞增殖凋亡的影响及机制研究

目的 探讨双特异性磷酸酶2（DUSP2）基因对胃癌细胞增殖和凋亡的影响及其可能的机制。方法 首先利用在线分析工具KM plotter 分析876例胃癌患者DUSP2表达高低对其总体生存率的影响,并在多种胃癌细胞株（MKN-45、SGC-7901、HGC-27、N-87）中检测DUSP2的表达。进一步构建DUSP2过表达慢病毒载体,包装病毒感染MKN-45细胞,筛选出DUSP2稳定过表达的胃癌细胞株,以空载慢病毒转染并筛选后的胃癌细胞为对照。采用MTS细胞增殖实验检测DUSP2上调表达对胃癌细胞增殖能力的影响;Annexin V-FITC/PI双染流式检测细胞凋亡变化;蛋白质印迹法（Western blot）检测DUSP2、细胞外调节蛋白激酶（ERK）、p-ERK（Thr202/Tyr204）、P38、p-P38等蛋白表达水平。结果 高表达DUSP2的胃癌患者较低表达者有明显的生存优势,并且DUSP2在多株胃癌细胞中呈低表达。Western blot结果显示DUSP2稳定过表达的胃癌细胞（实验组）中DUSP2表达较对照组明显上调,DUSP2稳定过表达的胃癌细胞株构建成功。MTS实验结果表明,实验组细胞活力较对照组明显下降。实验组细胞凋亡率明显高于对照组。Western blot结果表明,实验组细胞中p-ERK（Thr202/Tyr204）及p-P38表达较对照组显著下调。结论 上调DUSP2的表达可显著抑制胃癌细胞的增殖,并促进其凋亡,其机制与DUSP2抑制了ERK、P38的磷酸化水平有关。     

9种中药提取物细胞毒性及其与人结肠腺癌细胞系单层细胞旁通透性的相关性研究

目的了解9种中药提取物对Caco-2细胞毒性与对其细胞单层细胞-细胞间通透性的相关性。方法用MTT法测定9种中药提取物24 h及48 h的细胞毒,并计算IC50值。采用TranswellTM培养板构建Caco-2细胞单层,细胞电阻仪测定受试物对其TEER值的影响,找到影响细胞单层紧密连接的临界剂量,以此剂量与细胞毒参数行相关分析。结果 24、48 h细胞毒参数(IC50)与临界剂量(最大无毒剂量、最小有毒剂量)相关系数均>0.84,相关性检验P值均<0.01。最大无毒剂量与IC50的比值列阵显示,《小品方》甘草饮最小,三七醇提物最大。结论 9种中药提取物对Caco-2细胞毒与该细胞单层细胞旁通透性高度相关,采用细胞毒参数来预估中药提取物在Caco-2单层细胞模型供侧起始最大浓度具可行性。     

Lignans from the fruits of cornus kousa burg. and their cytotoxic effects on human cancer cell lines

The fruits of Cornus kousa Burg. were extracted with 80% aqueous MeOH, and the concentrated extract partitioned with EtOAc, n-BuOH and H2O. Six lignans were isolated from the EtOAc fraction through repeated silica gel, ODS and Sephadex LH-20 column chromatographies. From the physico-chemical data, including NMR, MS and IR, the chemical structures of the compounds were determined to be (+)-pinoresinol (1), (-)-balanophonin (2), (+)-laricresinol (3), erythro-guaiacylglycerol-beta-coniferyl aldehyde ether (4), threo-guaiacylglycerol-beta-coniferyl aldehyde ether (5) and dihydrodehydrodiconiferyl alcohol (6), which were isolated for the first time from this plant. Most of these compounds showed cytotoxicity against human colon carcinoma (HCT-116) and human hepatocellular carcinoma (HepG2) cell lines in vitro, with IC50 values ranging from 19.1 to 71.3 microg/mL.     

黄芪颗粒和黄芪注射液对CYP1A2、CYP2D、CYP2C亚酶活性影响的实验研究

目的通过体内和体外实验研究黄芪颗粒和黄芪注射液对CYP1A2、CYP2D、CYP2C亚酶的活性影响。方法建立体外"cocktail"反应体系,利用LC/MS/MS法测定酶代谢产物,计算黄芪颗粒和黄芪注射液对CYP1A2、CYP2D6、CYP2C9和CYP2C19亚酶活性的影响;大鼠随机分为对照组和实验组,不同浓度黄芪颗粒和黄芪注射液连续灌胃10 d,制备肝微粒体并进行"cocktail"反应,评价两种药物体内对大鼠CYP1A2、CYP2D1、CYP2C6和CYP2C11亚酶活性影响。结果在体外"cocktail"实验中,黄芪颗粒和黄芪注射液明显地抑制了CYP2D6、CYP2C19和CYP1A2亚酶活性,而二者对于CYP2C9亚酶活性无影响。在大鼠灌胃给药实验中,黄芪颗粒在剂量32、160和800 mg.kg-1.d-1提高CYP1A2亚酶活性2.13、3.23和2.20倍,黄芪注射液在剂量0.16、0.8、4 g.kg-1.d-1提高CYP1A2亚酶活性1.65、2.26和2.89倍,而二者均未诱导CYP2D1、CYP2C6和CYP2C11亚酶活性增加。结论黄芪颗粒和黄芪注射液对CYP2D6、CYP2C19活性有抑制作用,对大鼠CYP1A2活性有诱导作用。     

PTH2 receptor-mediated inhibitory effect of parathyroid hormone and TIP39 on cell proliferation

The parathyroid hormone (PTH) has dual mitogenic and inhibitory effects on cell proliferation, depending on the cell type and experimental conditions. PTH can signal via two different receptors, both positively coupled to the adenylyl cyclase/cyclic AMP pathway which can mimic some of the proliferative effects of PTH. We evaluated the role of the type-2 PTH (PTH2) receptor on cell proliferation in clonal human embryonic kidney HEK293 cells stably expressing the human PTH2 receptor. Using a cyclic AMP-responsive gene-reporter, we confirmed that the tuberoinfundibular peptide (TIP39) and various human (h) PTH fragments including hPTH-(1-34) were potent agonists (EC(50) in the range of 0.01-0.3 nM) whereas the bovine (b) PTH peptides b(Tyr(34))PTH-(7-34) and its tryptophan derivative b[D-Trp(12),Tyr(34)]PTH-(7-34) behaved as antagonists (IC(50)=117 and 249 nM, respectively). hPTH-(1-34) produced a dose-dependent inhibition of cell proliferation (EC(50)=8.5+/-0.4 nM) after 3 days and this effect was fully reversed by the tryptophan derivative antagonist. The same effect was observed with TIP39 which caused a 30% maximal inhibition. These findings reveal that PTH2 receptor activation can inhibit cell proliferation and might explain the dual functionality of PTH on cell proliferation.     

E盒结合锌指蛋白 2促进肺腺癌细胞 A549迁移的作用研究

目的 研究转录因子E盒结合锌指蛋白2(zinc finger E-box-bindingprotein,ZEB2)在肺癌组织中的表达及促进结肺癌细胞A549迁移的作用.方法 研究起止时间为2018年3月至2019年5月.采用免疫组化法检测肺癌组织及癌旁组织中ZEB2蛋白的表达情况;Transwell法检测干扰或过表达ZEB2对A549细胞迁移作用的影响;RT-PCR和蛋白质印迹法(Western blotting)检测ZEB1对A549细胞中转移相关分子-E钙黏素(E-cadherin)表达的影响.结果 与对照组相比,干扰ZEB2表达可抑制A549细胞的迁移能力,对照组穿过Transwell小室的细胞数量为(37.6±8.1)个,干扰ZEB2组为(12.3±3.2)个;相反,过表达ZEB2可促进A549细胞的迁移能力,对照组为(48.3±4.2)个,过表达ZEB2组为(129.6±12.1)个;干扰ZEB2可促进E-cadherin基因和蛋白的表达,过表达ZEB2则可抑制E-cadherin基因和蛋白的表达;ZEB2在肺癌组织中的表达明显高于在癌旁组织中的表达.结论 ZEB2在肺癌组织中高表达并可促进肺腺癌细胞迁移能力.     

A new morphospecies of Microcystis sp. forming bloom in the Cheffia dam (Algeria): seasonal variation of microcystin concentrations in raw water and their removal in a full-scale treatment plant

Toxic cyanobacterial blooms are an increasing problem in Algeria. The production of cyanotoxins (microcystins) and their presence in drinking water represent growing hazards to human health. In this study, seasonal variations in the concentrations of total microcystins and physicochemical parameters (pH, temperature, dissolved oxygen, nitrate, orthophosphate, and chlorophyll-a) were analyzed in the Cheffia dam (Algeria), mainly used to supply drinking water. The removal of cyanobacterial cells and microcystins was also evaluated in full-scale plant associated with the Cheffia reservoir. The levels of microcystins (MCYSTs) in both raw and drinking water were evaluated using the protein phosphatase type 2A (PP2A) inhibition test as MCYST-LR equivalents. Identification of microcystin variants was achieved by LC/MS/MS. During the period of study (March-December 2004), microscopic observation showed the dominance in the autumn months (September-November) of a new morphospecies of Microcystis sp. The MCYST-LR equivalent concentrations in raw water varied between 50.8 and 28,886 ng L(-1). The highest level of toxins was observed in October 2004 and was significantly correlated with the chlorophyll-a. Three variants of microcystins assigned as microcystin-YR (MCYST-YR), microcystin-LR (MCYST-LR), and 6Z-Adda stereoisomer of MCYST-LR were observed in the crude extract of the Microcystis sp. bloom sample. During the bloom period, total elimination of Microcystis sp. and toxins were achieved through a classical treatment plant comprised of coagulation and flocculation, powdered activated carbon at 15 mg L(-1), slow sand filtration and chlorination before storage.     

Exploring the Requirements for the Hydrophobic Scaffold and Polar Amine in inhibitors of M2 from Influenza A Virus

Inhibitors targeting the influenza A virus M2 (A/M2) proton channel, have lost their effectiveness due to widespread resistance. As a first step in the development of new inhibitors that address this problem, we have screened several focused collections of small molecules using two electrode voltage patch clamp assays (TEVC) on Xenopus laevis Oocyte. Diverse head groups and scaffolds of A/M2 inhibitors have been explored. It has been found that not only amine, but also hydroxyl, aminooxyl, guanidine and amidine compounds are active against the A/M2 proton channel. Moreover, the channel is able to accommodate a wide range of structural variation in the apolar scaffold. This study offers information to guide the next generation of A/M2 proton channel inhibitor design.