克隆、表达及纯化核糖体蛋白S6用于体外激酶活性检测

目的:构建40S核糖体蛋白S6的原核表达载体,表达并纯化S6蛋白,将其作为底物用于S6激酶(S6K)的体外活性测定。方法:采用RT-PCR方法从人胚肾细胞HEK293中获取S6 cDNA,将扩增产物克隆至大肠杆菌表达载体中,进行酶切及测序鉴定;IPTG诱导GST-S6融合蛋白在大肠杆菌中表达,用谷胱甘肽亲和层析纯化GST-S6,免疫沉淀法检测该蛋白是否可作为底物用于S6K的体外激酶活性测定。结果:酶切及测序鉴定表明构建了S6原核表达载体,并表达及纯化出GST-S6融合蛋白,相对分子质量为55×103。该蛋白可用于S6K的体外激酶活性测定,特异性强。结论:S6蛋白的克隆、表达与纯化成功,可用于S6K的体外激酶活性测定,为研究S6K的功能奠定了基础。     

Production and characterization of ZFP36L1 antiserum against recombinant protein from Escherichia coli

Tristetraprolin/zinc finger protein 36 (TTP/ZFP36) family proteins are anti-inflammatory. They bind and destabilize some AU-rich element-containing mRNAs such as tumor necrosis factor mRNA. In this study, recombinant ZFP36L1/TIS11B (a TTP homologue) was overexpressed in E. coli, purified, and used for polyclonal antibody production in rabbits. The antiserum recognized nanograms of the antigen on immunoblots. This antiserum and another antiserum developed against recombinant mouse TTP were used to detect ZFP36L1 and TTP in mouse 3T3-L1 adipocytes and RAW264.7 macrophages. Immunoblotting showed that ZFP36L1 was stably expressed with a size corresponding to the lower mass size of ZFP36L1 expressed in transfected human embryonic kidney 293 cells, but TTP was induced by cinnamon extract and not by lipopolysaccharide (LPS) in adipocytes. In contrast, ZFP36L1 was undetectable, but TTP was strongly induced in LPS-stimulated RAW cells. Quantitative real-time polymerase chain reaction confirmed the higher levels of ZFP36L1 mRNA in adipocytes and TTP mRNA in RAW cells. Low levels of ZFP36L1 expression were also confirmed by Northern blotting in mouse embryonic fibroblasts. These results demonstrate that ZFP36L1 antiserum is useful in the detection of this protein and that TTP and ZFP36L1 are differentially expressed and regulated at the mRNA and protein levels in mouse adipocytes and macrophages.     

Expression and purification of recombinant tristetraprolin that can bind to tumor necrosis factor-alpha mRNA and serve as a substrate for mitogen-activated protein kinases

Tristetraprolin (TTP) is an mRNA-binding protein, but studies of this interaction have been difficult due to problems with the purification of recombinant TTP. In the present study, we expressed human and mouse TTP as glutathione S-transferase and maltose-binding protein (MBP) fusion proteins in Escherichia coli, and purified them by affinity resins and Mono Q chromatography. TTP cleaved from the fusion protein was identified by immunoblotting, MALDI-MS, and protein sequencing, and was further purified to homogeneity by continuous-elution SDS-gel electrophoresis. Purified recombinant TTP bound to the AU-rich element of tumor necrosis factor-alpha (TNFalpha) mRNA and this binding was dependent on Zn(2+). Results from sizing columns suggested that the active species might be in the form of an oligomer of MBP-TTP. Recombinant TTP was phosphorylated by three members of the mitogen-activated protein (MAP) kinase family, p42, p38, and JNK, with half-maximal phosphorylation occurring at approximately 0.5, 0.25, and 0.25 microM protein, respectively. Phosphorylation by these kinases did not appear to affect the ability of TTP to bind to TNFalpha mRNA under the assay conditions. This study describes a procedure for purifying nonfusion protein TTP to homogeneity, demonstrates that TTP's RNA-binding activity is zinc dependent, and that TTP can be phosphorylated by JNK as well as by the other members of the greater MAP kinase family.     

Expression and purification of full-length mouse CARM1 from transiently transfected HEK293T cells using HaloTag technology

Coactivator-associated arginine methyl transferase 1 (CARM1) is a protein arginine methyltransferase (PRMT) family member that functions as a coactivator in androgen and estrogen signaling pathways and plays a role in the progression of prostate and breast cancer. CARM1 catalyzes methylation of diverse protein substrates. Prior attempts to purify the full-length mouse CARM1 protein have proven unsatisfactory. The full-length protein expressed in Escherichia coli forms insoluble inclusion bodies that are difficult to denature and refold. The presented results demonstrate the use of a novel HaloTag? technology to purify full-length CARM1 from both E. coli and mammalian HEK293T cells. A small amount of CARM1 was purified from E. coli; however, the protein was truncated on the N-terminus by 10-50 amino acids, most likely due to endogenous proteolytic activity. In contrast, substantial quantities of soluble full-length CARM1 were purified from transiently transfected HEK293T cells. The CARM1 from HEK293T cells was isolated alongside a number of co-purifying interacting proteins. The covalent bond formed between the HaloTag and the HaloLink resin allowed the use of stringent wash conditions without risk of eluting the CARM1 protein. The results also illustrate a highly effective approach for purifying and enriching both CARM1-associated proteins as well as substrates for CARM1's methyltransferase activity.     

Role of PRL-3, a human muscle-specific tyrosine phosphatase, in angiotensin-II signaling

Action of protein kinases and phosphatases contributes to myocardial hypertrophy. PRL-3, a protein tyrosine phosphatase, was identified in a cDNA library from an explanted human heart obtained from a patient with idiopathic cardiomyopathy. PRL-3 is expressed in heart and skeletal muscle, exhibiting approximately 76% identity to the ubiquitous tyrosine phosphatase PRL-1, which was reported to increase cell proliferation. PRL-3 was cloned into E. coli and purified using affinity chromatography. PRL-3 activity was determined using the substrate 6,8-difluoro-4-methylumbelliferyl phosphate, and was inhibited by vanadate and analogs. HEK293 cells expressing PRL-3 demonstrated increased growth rates versus nontransfected cells or cells transfected with the catalytically inactive C104S PRL-3 mutant. The tyrosine phosphatase inhibitor, potassium bisperoxo (bipyridine) oxovanadate V, normalizes the growth rate of PRL-3 expressing cells to that of parental HEK293 cells in a concentration-dependent manner. Using FLIPR analysis, parental HEK293 cells mobilize calcium when stimulated with angiotensin-II (AngII). However, calcium mobilization is inhibited in cells expressing wild-type PRL-3 when stimulated with AngII, while cells expressing the inactive mutant of PRL-3 mobilize calcium to the same extent as parental HEK293 cells. Western blots comparing PRL-3 transfected cells to parental HEK293 cells showed dephosphorylation of p130(cas) in response to AngII. These data suggest a role for PRL-3 in the modulation of intracellular calcium transients induced by AngII.     

Conserved high affinity ligand binding and membrane association in the native and refolded extracellular domain of the human glycine receptor alpha1-subunit

The strychnine-sensitive glycine receptor (GlyR) is a ligand-gated chloride channel composed of ligand binding alpha- and gephyrin anchoring beta-subunits. To identify the secondary and quaternary structures of extramembraneous receptor domains, the N-terminal extracellular domain (alpha1-(1-219)) and the large intracellular TM3-4 loop (alpha1-(309-392)) of the human GlyR alpha1-subunit were individually expressed in HEK293 cells and in Escherichia coli. The extracellular domain obtained from E. coli expression was purified in its denatured form and refolding conditions were established. Circular dichroism and Fourier-transform-infrared spectroscopy suggested approximately 25% alpha-helix and approximately 48% beta-sheet for the extracellular domain, while no alpha-helices were detectable for the TM3-4 loop. Size exclusion chromatography and sucrose density centrifugation indicated that isolated glycine receptor domains assembled into multimers of distinct molecular weight. For the extracellular domain from E. coli, we found an apparent molecular weight compatible with a 15mer by gel filtration. The N-terminal domain from HEK293 cells, analyzed by sucrose gradient centrifugation, showed a bimodal distribution, suggesting oligomerization of approximately 5 and 15 subunits. Likewise, for the intracellular domain from E. coli, a single molecular mass peak of approximately 49 kDa indicated oligomerization in a defined native structure. As shown by [(3)H]strychnine binding, expression in HEK293 cells and refolding of the isolated extracellular domain reconstituted high affinity antagonist binding. Cell fractionation, alkaline extraction experiments, and immunocytochemistry showed a tight plasma membrane association of the isolated GlyR N-terminal protein. These findings indicate that distinct functional characteristics of the full-length GlyR are retained in the isolated N-terminal domain.     

Molecular identification of the gene encoding porcine tristetraprolin (TTP)

Tristetraprolin (TTP) is a CCCH tandem zinc finger protein that can bind to and destabilize certain mRNAs containing AU-rich element (ARE) binding sites. In this study, a novel porcine cDNA has been isolated by expressed sequence tag assembly and subsequently confirmed by RT-PCR analysis, and designated porcine TTP (poTTP). The open reading frame of the poTTP cDNA is 981 bp, encoding 326 amino acids. The poTTP gene is approximately 2.5 kb in size and contains a single intron. Southern blotting analysis demonstrated that it is a single copy gene. Real-time quantitative PCR analysis revealed that the poTTP gene is constitutively expressed in all detected tissues, and with the highest mRNA level in lymphoid tissues spleen and thymus. Recombinant His₆-tagged poTTP protein and its two zinc finger mutants (C146G and H127I) were efficiently expressed and purified from Escherichia coli BL21 (DE3), respectively. In vitro, RNA-electrophoretic mobility shift assay confirmed a direct interaction between poTTP protein and porcine TNF-α (poTNF-α) mRNA ARE probe; this interaction was eliminated when using either two zinc finger mutants of poTTP. Consistently, mutations within the ARE region prevented the binding interaction between recombinant poTTP protein and poTNF-α mRNA ARE probe. These results indicate that poTTP is an ARE-binding protein that might regulate the turnover of certain mRNAs in vivo.     

DEK蛋白的真核表达纯化及其活性检测

利用Bac-to-Bac杆状病毒表达系统表达DEK蛋白并进行纯化。首先以pFastBacI质粒构建重组质粒pFastBacI-DEK,转化DH10Bac大肠杆菌后获得重组穿梭载体Bacmid-DEK,通过脂质体介导转染Sf9细胞产生具有强感染力的重组杆状病毒AcNPV-DEK。用此重组杆状病毒AcNPV-DEK感染Sf9细胞表达His-DEK融合蛋白。在非变性条件下,利用Ni-NTA agarose对表达的His-DEK融合蛋白进行纯化,经SDS-PAGE和Western blotting分析,在50 kDa处出现特异性蛋白条带并证实其为His-DEK融合蛋白。凝胶迁移阻滞实验表明,融合蛋白His-DEK与DNA 的结合具有结构特异性,其与超螺旋型DNA结合活性强于与线性化DNA的结合活性。真核表达并纯化的融合蛋白His-DEK与DNA的结合活性要明显强于原核表达的融合蛋白His-CDB。DEK 蛋白的磷酸化修饰会阻碍其与DNA的结合,而Sf9细胞中表达的融合蛋白His-DEK存在磷酸化修饰,将His-DEK去磷酸化后,其与DNA的结合活性有所提高。     

Stable expression of human melanocortin 3 receptor fused to EGFP in the HEK293 cells

Among the melanocortins alpha-MSH is known to be involved in feeding behavior. These hormones mediate their effects through G protein-coupled receptors by stimulating adenylate cyclase. In this study, we have developed an in vitro expression model for human melanocortin 3 receptor (hMC3R) tagged at its C terminus with EGFP. The corresponding chimeric cDNA was stably expressed in HEK293 cells. The selected clones expressing the hMC3R-EGFP exhibited cell surface fluorescence and responded to NDP-MSH stimulation by producing cAMP in a dose-dependent manner (EC(50): 0.3 nM). Binding studies revealed a single class of binding sites with a K(D) of 2.24 nM. Moreover, Agouti-related protein was also demonstrated to be an antagonist of the hMC3R-EGFP. Thus, the hMC3R tagged with EGFP stably expressed in HEK293 cells, exhibiting the same characteristics than the wild-type hMC3R, is the only model of expression of this receptor allowing its direct localization inside living cells.     

Inhibition of tristetraprolin deadenylation by poly(A) binding protein

Tristetraprolin (TTP) is the prototype for a family of RNA binding proteins that bind the tumor necrosis factor (TNF) messenger RNA AU-rich element (ARE), causing deadenylation of the TNF poly(A) tail, RNA decay, and silencing of TNF protein production. Using mass spectrometry sequencing we identified poly(A) binding proteins-1 and -4 (PABP1 and PABP4) in high abundance and good protein coverage from TTP immunoprecipitates. PABP1 significantly enhanced TNF ARE binding by RNA EMSA and prevented TTP-initiated deadenylation in an in vitro macrophage assay of TNF poly(A) stability. Neomycin inhibited TTP-promoted deadenylation at concentrations shown to inhibit the deadenylases poly(A) ribonuclease and CCR4. Stably transfected RAW264.7 macrophages overexpressing PABP1 do not oversecrete TNF; instead they upregulate TTP protein without increasing TNF protein production. The PABP1 inhibition of deadenylation initiated by TTP does not require the poly(A) binding regions in RRM1 and RRM2, suggesting a more complicated interaction than simple masking of the poly(A) tail from a 3'-exonuclease. Like TTP, PABP1 is a substrate for p38 MAP kinase. Finally, PABP1 stabilizes cotransfected TTP in 293T cells and prevents the decrease in TTP levels seen with p38 MAP kinase inhibition. These findings suggest several levels of functional antagonism between TTP and PABP1 that have implications for regulation of unstable mRNAs like TNF.     

The glycosyl phosphatidylinositol anchor of human T-cadherin binds lipoproteins

T-cadherin (T-cad) is a Ca(2+)-dependent cell adhesion glycoprotein bound to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. T-cad expressed on vascular smooth muscle cells (SMC) binds lipoproteins on blot. To analyze the molecular basis for the interaction of T-cad with lipoproteins we expressed recombinant human T-cad in HEK293 cells. Whereas membrane-bound T-cad from SMC and T-cad transfected HEK293 cells bind lipoproteins, T-cadherin proteins cleaved from the cell surface by phosphatidylinositol-specific phospholipase C (PI-PLC) do not. The lipoprotein-binding function is also lacking both for a recombinant human T-cad expressed in HEK293 cells without the GPI signal sequence, and for a human T-cad form expressed in Escherichia coli that contains the signal sequence for GPI attachment but is not modified with a GPI. We conclude that the GPI moiety of T-cadherin is necessary and sufficient to mediate lipoprotein binding.     

大熊猫FOXL2基因的克隆、序列分析及表达

从大熊猫基因组中克隆了FOXL2基因,并对其进行序列分析及原核表达和真核表达.将FOXL2编码区序列克隆到原核表达载体pET-32a(+)中,转化大肠杆菌BL21,经IPTG诱导表达出FOXL2重组蛋白.成功构建了真核表达载体FOXL2-pcDNA3.1/V5-His C,并通过脂质体介导转染HEK293细胞,Western blot检测FOXL2蛋白表达.SDS-PAGE分析表明,FOXL2重组蛋白在诱导4h后表达量达到峰值,其大小约为58.9 kDa,Western blot分析结果显示重组蛋白能够被抗His单克隆抗体特异性识别.FOXL2基因的克隆及其表达为进一步进行FOXL2的活性检测以及应用研究奠定了基础.     

小鼠FANCL抗体制备及组织表达谱分析

FANCL是一个范可尼氏贫血新蛋白,它作为泛素E3连接酶催化FANCD2的单一泛素化,在修复DNA损伤、维持染色体稳定的FA途径中起着关键作用。胚胎期FANCL与小鼠原始生殖细胞增殖密切相关,成年睾丸中FANCL与几个生殖细胞特异性蛋白形成一个睾丸特异网络,可能参与影响精子的生成。采用RT-PCR方法从小鼠总RNA中扩增克隆FancL全长cDNA片段,构建表达质粒,在大肠杆菌中表达了6His-FANCL蛋白,用表达蛋白作为抗原免疫新西兰白兔制备了抗FANCL多抗血清。采用镍离子金属螯合柱纯化6His-FANCL蛋白后,通过与活性基团-NHS交联制备了FANCL抗原柱,亲和纯化了FANCL多抗。为了验证抗体活性和特异性,在HEK293T细胞中瞬时表达了HA-FANCL融合蛋白,分别用HA单抗和纯化多抗进行Western印迹分析,结果表明获得了特异性的FANCL抗体。为了观察FANCL在组织中的表达谱,制备了多种小鼠组织匀浆蛋白,使用纯化的FANCL多抗进行Western印迹分析,在脑、心、肺、肝、脾、肾、睾丸、卵巢、子宫和肌肉组织中都检测到FANCL蛋白的表达,说明FANCL在小鼠组织中是广泛表达的,这与其是DNA修复复合物中的重要成员相一致。     

Production of lentiviral vectors in suspension cells using low proportion of supercoiled circular plasmid DNA

The supercoiled circular (SC) topology form of plasmid DNA has been regarded to be advantageous over open circular or linearized analogue in transfection and expression efficiency, and therefore are largely demanded in the biopharmaceutical manufacturing. However, production of high-purity SC plasmid DNA would result in high manufacturing cost. The effect of SC proportion in plasmid DNA on the quality of packaged lentiviral vectors has never been reported. In this study, we established an efficient system for production of high-titer lentiviral vectors using suspension HEK293SF cells in serum-free media, and the lentiviral titer was not associated with the proportion of SC plasmid DNA. Plasmids DNA with different proportion of SC, open-circular, and linearized forms were prepared using the thermal denaturation method, and were transfected to adherent HEK293T or suspension HEK293SF cells for packaging of lentiviral vectors. The titer of lentiviral vectors from HEK293T cells, but not from HEK293SF cells, was significantly impaired when the proportion of SC plasmid DNA decreased from 60–80% to 30–40%. Further decrease of SC plasmid proportion to 3% led to a dramatic reduction of lentiviral titer no matter the packaging cell line was. However, lentiviral vectors from HEK293SF cells still showed a high titer even when the proportion of SC plasmid DNA was 3%. This study demonstrated that extremely high proportion of SC plasmid DNA was not required for packaging of high-titer lentiviral vector in HEK293SF cells, at least under our manufacturing process.     

人免疫缺陷病毒早期蛋白Nef的表达、纯化及免疫原性研究

目的：通过原核细胞表达人免疫缺陷病毒（HIV）Nef抗原,制备特异抗血清,为Nef抗原检测提供技术方法。方法：以HIVBotswana毒株基因组为模板,用PCR法获得Nef蛋白编码基因,将其克隆到pET30a载体中,在大肠杆菌中表达Nef融合蛋白;用纯化的融合蛋白免疫BALB／c小鼠获得抗血清,用真核表达的Nef抗原对其特异性进行分析。结果：构建的Nef融合基因在大肠杆菌中获得表达,相对分子质量约为36x103,免疫BALB／c小鼠获得针对融合蛋白的高效价抗血清,ELISA抗体滴度为1：6400;免疫荧光和Westemblot检测表明,该抗血清能特异地与重组痘苗病毒表达的Nef抗原反应。结论：在大肠杆菌中表达了HIVNef融合蛋白,制备了Nef融合蛋白的高效价小鼠免疫血清,该血清能特异性识别HIVNef抗原,为HlVNef抗原检测提供了技术方法。