Controlled expression of the transcriptional activator gene virG in Agrobacterium tumefaciens by using the Escherichia coli lac promoter

The Agrobacterium VirG protein is normally expressed from two promoters in response to multiple stimuli, including plant-released phenolics (at promoter P1) and acidic growth media (at promoter P2). To simplify the analysis of vir gene induction, we sought to create Agrobacterium strains in which virG could be expressed in a controllable fashion. To study the possibility of using the lac promoter and repressor, we constructed a plasmid containing the lac promoter fused to the lacZ structural gene. A derivative of this plasmid containing the lacIq gene was also constructed. The plasmid not containing lacIq expressed high levels of beta-galactosidase. The plasmid containing lacIq expressed beta-galactosidase at very low levels in the absence of o-nitrophenyl-beta-D-galactoside (IPTG) and at moderate levels in the presence of IPTG. We also fused the lac promoter to a virG::lacZ translational fusion and found that IPTG elevated expression of this translational fusion to moderate levels, though not to levels as high as from the stronger of the two native virG promoters. Finally, the lac promoter was used to express the native virG gene in strains containing a virB::lacZ translational fusion. virB expression in this strain depended on addition of IPTG as well as the vir gene inducer acetosyringone. In a similar strain lacking lacIq, virB expression was greater than in a strain in which virG was expressed from its native promoters. Expression of virG from the lac promoter did not alter the acidic pH optimum for vir gene induction, indicating that the previously observed requirement for acidic media was not due solely to the need to induce P2.     

Transient promoter activity in primary rat mammary epithelial cells evaluated using particle bombardment gene transfer

Summary The relative strengths of several commonly used viral promoters in primary cultures of rat mammary epithelial cells were studied using a particle bombardment gene transfer method. NIH 3T3 cells were also examined as a representative cell line. Initially, the conditions necessary for efficient gene transfer using particle bombardment were determined. Discharge voltage for particle bombardment was evaluated to maximize the levels of gene expression and cell viability. After transfection, transgene expression decreased over a 5-day period in both mammary cells and NIH 3T3 cells. Particle bombardment gene transfer was at least fivefold more efficient than lipofection, calcium phosphate co-precipitation, or electroporation. The activity of five viral enhancer/promoters was compared using a luciferase gene assay system. The relative promoter strengths in mammary cells were determined to be: RSV ≈ CMV ≈ SV40 > MLV > MMTV. Tissue-specific activity of the MMTV-LTR was demonstrated, although this promoter conferred the lowest expression level among the promoters tested.     

Differential expression of mammalian or viral promoter-driven gene in adherent versus suspension cells

Although expression vectors using viral and mammalian promoters constitutively express genes of interest in adherent cells, few studies have examined whether the function of these vectors in suspended cells, such as in over-agar or soft agar assay (an in vitro cell transformation assay), is as robust as when they are in adherent cells. The selection of appropriate expression vector to optimally express genes in suspended cells would be useful in determining whether these genes play a critical role in maintaining colony formation or cell transformation. To compare promoter-driven expression vector function in adherent versus suspension cells, we performed transient transfection assays using viral (simian virus 40 [SV40] and cytomegalovirus [CMV]) and mammalian (beta-actin) promoters fused to luciferase or beta-galactosidase reporter gene. Over-agar assay was used to suspend cells on top of agar, which allowed cell retrieval and analysis. We found that beta-actin and SV40 promoters exhibited suppressed gene expression of 70 and 56%, respectively, in cells suspended on agar compared with those attached on plates. The suppressed response by the exogenous beta-actin promoter in suspension was consistent with the response of the endogenous beta-actin promoter activity because the steady-state level of beta-actin messenger ribonucleic acid in suspended cells was significantly reduced by 50% relative to that expressed in attached cells. In contrast to SV40 promoter, CMV promoter activity was not decreased in cells suspended in over-agar when compared with adherent cells. These studies show that regardless of mammalian or viral vectors, one cannot assume that all expression vectors behave similarly in both suspension and adherent state.     

Construction of a lentiviral T/A vector for direct analysis of PCR-amplified promoters

The promoter plays an important role in the regulation of gene expression. To analyze a promoter’s activity, we developed a novel lentiviral T/A vector that contains two reporter genes, a luciferase (Luc2) gene and a green fluorescent protein (Venus) gene, that are linked via an internal ribosome entry site (IRES2). To test the performance of this vector, phosphoglycerate kinase-1 (PGK) and elongation factor-1α (EF1α) promoters were amplified by PCR and inserted into this lentiviral T/A vector using T4 DNA ligase, yielding two promoter–reporter vectors: pLent-T-PGK and pLent-T-EF1α. When these vectors were transfected into 293T cells, we observed a higher level of Venus expression under a fluorescence microscopy in the case of pLent-T-EF1α as compared to pLent-T-PGK. The results of the luciferase reporter assay showed that the ratio of the promoter activities of EF1α and PGK was approximately 9:1. The two promoter–reporter vectors were also packaged as lentiviral particles to conduct promoter activity assay in cultured cells. The ratio of the promoter activities of EF1α and PGK was 4.23:1 when they were infected into 293T cells at a multiplicity of infection of 1. This value is comparable to that of a parallel experiment using the commercial luciferase reporter vector pGL4.10 with an activity ratio of 5.99:1 for EF1α and PGK. These results indicate that lentiviral T/A vector will be a useful tool for analysis of promoter activity and specificity.     

Pitfall of an internal control plasmid: response of Renilla luciferase (pRL-TK) plasmid to dihydrotestosterone and dexamethasone

The thymidine kinase promoter-Renilla luciferase reporter plasmid (pRL-TK) is commonly used as a control for transfection efficiency in the Dual-Luciferase Reporter Assay System. While investigating hormone response elements in the promoters of the androgen-dependent, epididymis-specific EP2 gene, we found that hormone treatment affected the luciferase activity of pRL-TK-transfected cells. In African Green Monkey Kidney (CV-1) cells, cotransfected transiently with a hormone-responsive promoter-firefly luciferase reporter plasmid and with pRL-TK, Renilla luciferase activity increased in response to dihydrotestosterone (DHT) and decreased in response to dexamethasone (DEX). When a thromboxane synthase promoter Renilla luciferase plasmid (pRL-TS) was used in place of pRL-TK, Renilla luciferase activity remained constant in CV-1 cells treated with DHT but decreased in CV-1 cells treated with DEX. In transfection studies, internal control plasmid expression in response to treatment must be carefully monitored to ensure proper interpretation of normalized results.     

Gene Expression in Bacteria Directed by Plant-specific Regulatory Sequences

The regulation of gene expression represents a specific process which has different structural and functional requirements in different groups of organisms. It is thus assumed that regulatory sequences of eucaryotes cannot be recognized in procaryotes. This assumption is of interest for risk assessments of the environmental impact of deliberate release experiments with genetically modified organisms. In order to analyse the extent of heterologous gene expression caused by the transfer of plant-specific regulatory sequences into bacteria, we constructed fusions between plant-specific regulatory sequences and the coding regions of the luxAB genes for the luciferase of the bioluminescent bacterium Vibrio harveyi, transferred the fusions into different bacterial species and measured the luminescence to quantify the expression of the luciferase genes. The regulatory sequences investigated included (a) the 35S promoter of the Cauliflower mosaic virus, (b) the B33 promoter of a class I patatin gene of potatoes, (c) the promoter of the ST-LS1 gene of potatoes and (d) the promoter of the rolC gene of Agrobacterium rhizogenes. We could show that in addition to the 35S promoter, which has already been described as being recognized in Escherichia coli, the sequences containing the B33 and the ST-LS1 promoters are recognized in bacteria. Luciferase gene expression promoted by the sequence with the ST-LS1 promoter could be observed in E. coli, Yersinia enterocolitica and Agrobacterium tumefaciens. Comparison of the luminescence caused by fusions between luxAB and different promoters on the chromosome and on an endogenous plasmid of Y. enterocolitica demonstrated that the level of the heterologous gene expression caused by the fragment with the ST-LS1 promoter was within the range of gene expression levels caused by endogenous promoters of Y. enterocolitica.     

Firefly luciferase gene transmission and expression in transgenic medaka (Oryzias latipes).

Plasmids containing the luciferase gene from the firefly (Photinus pyralis) fused to the Chinese hamster metallothioneine I promoter (ChMTI) were microinjected into the pronuclei of medaka (Oryzias latipes) eggs, which were then artificially inseminated. Evidence of integration into the genome was gained from observation of germ-line transmission in a mendelian fashion from the F1 to the F2 generation. However, gene expression (light emission) could not be demonstrated in the established transgenic line. In a separate program, transient expression of gene constructs containing the luciferase gene fused to various promoters was compared in medaka embryos. Plasmids were microinjected into pronuclei, and homogenates from 3-day-old embryos were measured for light emission using a luminometer. Among the various promoters tested (SV40, RSV-LTR, ChMTI, HSP70, and mouse albumin), the highest levels of luciferase gene expression were observed in gene constructs containing ChMTI and HSP70 gene promoters. Expression in these two constructs was significantly increased following administration of ZnSO4 or heat treatment, respectively. Plasmids were also introduced into goldfish fibroblast-like cells in vitro, in which enzymatically active luciferase was transiently expressed. Assaying for expression of luciferase provided a rapid and sensitive method for monitoring promoter activity. The potential usefulness of this fish species for cancer research is discussed based on accumulated information from carcinogenesis studies.     

不同异源启动子与MDVgB启动子及其复合启动子的活性比较

为了选择适宜的启动子调控外源基因的表达,以改善马立克氏病病毒为载体的重组病毒的免疫保护力。将hCMV立即早期启动子及增强子、SV40早晚期启动子及增强子或hCMV立即早期增强子的部分序列分别与马立克氏病病毒(MDV)自身的囊膜糖蛋白B基因(gB)启动子核心部分在体外杂合,分别构建复合启动子PhCMV-gB、PSV-gB或Pen-gB;将这些启动子与虫荧光素酶报告基因相连,构建表达载体。利用脂质体将以上质粒与内标质粒(pSV-β-LacZ)共转染鸡胚成纤维次代细胞,于转染后48h,将细胞刮下来,利用荧光素酶测定试剂盒和β-半乳糖苷酶测定试剂盒分别测定转染细胞的荧光素酶和β-半乳糖苷酶的活性,通过荧光素酶和β-半乳糖苷酶活性的比值获得虫荧光素酶的相对活性,利用虫荧光素酶的相对活性进行启动子的活性比较。结果表明,复合启动子相对马立克氏病病毒自身的gB启动子,活性有不同程度的提高,其中复合启动子PhCMV-gB的活性最高,而复合启动子PSV-gB和Pen-gB的活性相当;但与商业强启动子相比,复合启动子活性要弱一些或相当。因此,从某种意义上讲,这些复合启动子既具有gB启动子的一些特性,又有商业强启动子的一些特性,为以马立克氏病毒为载体的新兴疫苗的开发奠定了基础。     

携带不同数量增强子的嵌合型肝脏特异性启动子的构建及其体外实验研究

通过PCR手段成功获得肝细胞特异性启动子人α1-抗胰蛋白酶启动子hAATp(human α1-antitrypsin promoter,hAATp)及具有增强子功能的肝脏特异的肝调控区HCR (hepatic control region,HCR)。在此基础上,通过分子克隆手段构建获得携带有不同数量的HCR增强子的嵌合型肝脏特异性hAAT启动子,并在下游连入报告基因Luciferase,然后将重组质粒转染人肝癌细胞系HepG2、小鼠肝癌细胞系Hepa1-6、人胚肾细胞系HEK293和人脑星形胶质母细胞瘤细胞系U87-MG,通过检测Luciferase表达活性分析携带不同数量增强子的肝脏特异性启动子的启动活性及其组织特异性。结果表明,携带有3个增强子的嵌合型肝脏特异性启动子活性及特异性最好,为肝脏类疾病的靶向性治疗研究奠定了基础。     

Expanding the genetic toolbox for Leptospira species by generation of fluorescent bacteria

Our knowledge of the genetics and molecular basis of the pathogenesis associated with Leptospira, in comparison to those of other bacterial species, is very limited. An improved understanding of pathogenic mechanisms requires reliable genetic tools for functional genetic analysis. Here, we report the expression of gfp and mRFP1 genes under the control of constitutive spirochetal promoters in both saprophytic and pathogenic Leptospira strains. We were able to reliably measure the fluorescence of Leptospira by fluorescence microscopy and a fluorometric microplate reader-based assay. We showed that the expression of the gfp gene had no significant effects on growth in vivo and pathogenicity in L. interrogans. We constructed an expression vector for L. biflexa that contains the lacI repressor, an inducible lac promoter, and gfp as the reporter, demonstrating that the lac system is functional in Leptospira. Green fluorescent protein (GFP) expression was induced by the addition of isopropyl-β-d-thiogalactopyranoside (IPTG) in L. biflexa transformants harboring the expression vector. Finally, we showed that GFP can be used as a reporter to assess promoter activity in different environmental conditions. These results may facilitate further advances for studying the genetics of Leptospira spp.     

Novel baculovirus DNA elements strongly stimulate activities of exogenous and endogenous promoters.

A DNA sequence upstream from the polyhedrin gene of baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) was found to activate strongly the expression of full or minimal promoters derived from AcMNPV and other sources. Promoters tested included the minimal CMV (CMVm) promoter from human cytomegalovirus, the full heat shock 70 promoter from Drosophila, and the minimal p35 promoter from baculovirus. Deletion and mutagenesis analyses showed that this functional polyhedrin upstream (pu) activator sequence contains three open reading frames (ORFs), ORF4, ORF5, and lef2. In plasmid transfection assays, the pu sequence was able to confer high level luciferase expression driven by all of these full or minimal promoters in insect Sf21 cells. A known baculovirus enhancer, the homologous region (hr) of AcMNPV, further enhanced the expression of these promoters. Experiments showed that although multiple hr sequences function in an additive manner, pu and hr together function synergistically, resulting in as much as 18,000-fold promoter activation. Furthermore, a modified CMVm promoter containing pu and/or hr was inserted into the baculovirus genome to drive the luciferase coding region. The CMVm promoter expressed luciferase much earlier, and although it expressed a bit less than did the p10 promoter, the CMVm promoter gave rise to greater luciferase activity. Therefore, we have uncovered a cryptic viral sequence capable of activating a diverse group of promoters. Finally, these experiments demonstrate that synthetic sequences containing pu, hr, and different full or minimal promoters can generate a set of essentially unlimited novel promoters for weak to very strong expression of foreign proteins using baculovirus.     

Correlation between the levels of survivin and survivin promoter-driven gene expression in cancer and non-cancer cells

Survivin, a member of the inhibitor of apoptosis (IAP) protein family, is associated with malignant transformation and is over-expressed in most human tumors. Using lipoplex-mediated transfection, we evaluated the activity of the reporter enzyme, luciferase, expressed from plasmids encoding the enzyme under the control of either the cytomegalovirus (CMV) or survivin promoters, in tumor- and non-tumor-derived human and murine cells. We also examined whether there is a correlation between the survivin promoter-driven expression of luciferase and the level of endogenous survivin. Human cancer cells (HeLa, KB, HSC-3, H357, H376, H413), oral keratinocytes, GMSM-K, and chemically immortalized human mammary cells, 184A-1, were transfected with Metafectene at 2 μl/1 μg DNA. Murine squamous cell carcinoma cells, SCCVII, mouse embryonic fibroblasts, NIH-3T3, and murine immortalized mammary cells, NMuMG, were transfected with Metafectene PRO at 2 μl/1 μg DNA. The expression of luciferase was driven by the CMV promoter (pCMV.Luc), the human survivin promoter (pSRVN.Luc-1430), or the murine survivin promoters (pSRVN.Luc-1342 and pSRVN.Luc-194). Luciferase activity was measured, using the Luciferase Assay System and expressed as relative light units (RLU) per ml of cell lysate or per mg of protein. The level of survivin in the lysates of human cells was determined by ELISA and expressed as ng survivin/mg protein. In all cell lines, significantly higher luciferase activity was driven by the CMV promoter than by survivin promoters. The expression of luciferase driven by the CMV and survivin promoters in murine cells was much higher than that in human cells. The cells displayed very different susceptibilities to transfection; nevertheless, high CMV-driven luciferase activity appeared to correlate with high survivin-promoter driven luciferase expression. The survivin concentration in lysates of cancer cells ranged from 5.8 ± 2.3 to 24.3 ± 2.9 ng/mg protein (mean, 13.7 ng/mg). Surprisingly, elevated survivin protein was determined in lysates of non-tumor-derived cells. Survivin levels for GMSM-K and 184A-1 cells, were 16.7 ± 8.7 and 13.5 ± 6.2 ng/mg protein, respectively. The expression of endogenous survivin did not correlate with the level of survivin promoter-driven transgene activity in the same cells. The expression of survivin by non-tumorigenic, transformed cell lines may be necessary for their proliferative activity. The level of survivin promoter-driven gene expression achieved via liposomal vectors in OSCC cells was too low to be useful in cancer-cell specific gene therapy.