Poly-L-ornithine-mediated transformation of mammalian cells

Coating Materials for Neural Stem/Progenitor Cell Culture and Differentiation

Neural stem/progenitor cells (NSPCs) have a potential to treat various neurological diseases, such as Parkinson's Disease, Alzheimer's Disease, and Spinal Cord Injury. However, the limitation of NSPC sources and the difficulty to maintain their stemness or to differentiate them into specific therapeutic cells are the main hurdles for clinical research and application. Thus, for obtaining a therapeutically relevant number of NSPCs in vitro, it is important to understand factors regulating their behaviors and to establish a protocol for stable NSPC proliferation and differentiation. Coating materials for cell culture, such as Matrigel, laminin, collagen, and other coating materials, can significantly affect NSPC characteristics. This article provides a review of coating materials for NSPC culturing in both two dimensions and three dimensions, and their functions in NSPC proliferation and differentiation, and presents a useful guide to select coating materials for researchers.

Study of small-cell lung cancer cell-based sensor and its applications in chemotherapy effects rapid evaluation for anticancer drugs

Small cell lung cancer (SCLC) is a smoking-related cancer disease. Despite improvement in clinical survival, SCLC outcome remains extremely poor. Cisplatin (DDP) is the first-line chemotherapy drug for SCLC, but the choice of second-line chemotherapy drugs is not clear. In this paper, a SCLC cell-based sensor was proposed, and its applications in chemotherapy effects rapid evaluation for anticancer drugs were investigated. SCLC cell lines lung adenocarcinoma cell (LTEP-P) and DDP-resistant lung adenocarcinoma cell (LTEP-P/DDP-1.0) are cultured on carbon screen-printed electrode (CSPE) to fabricate integrated cell-based sensor. Several chemotherapy anticancer drugs, including cisplatin, ifosmamide, gemcitabine, paclitaxel, docetaxel, vinorelbine, etoposide, camptothecin, and topotecan, are selected as experimental chemicals. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests are conducted to evaluate chemotherapy drug effects on LTEP-P and LTEP-P/DDP-1.0 cell lines. Electrical cell-substrate impedance sensing (ECIS) responses to anti-tumor chemicals are measured and processed by double-layered cascaded stochastic resonance (DCSR). Cisplatin solutions in different concentrations measurement results demonstrate that LTEP-P cell-based sensor presents quantitative analysis abilities for cisplatin and topotecan. Cisplatin and its mixtures can also be discriminated. Results demonstrate that LTEP-P cell-based sensor sensitively evaluates chemotherapy drugs' apoptosis function to SCLC cells. LTEP-P/DDP-1.0 cell-based sensor responses demonstrate that gemcitabine, vinorelbine, and camptothecin are ideal second-line drugs for clinical post-cisplatin therapy than other drugs according to MTT test results. This work provides a novel way for SCLC second-line clinical chemotherapy drug screening.

Atomic force microscopy reveals the assembly of potential DNA “nanocarriers” by poly-l-ornithine

Atomic force microscopy (AFM) has been used to visualize the process of condensation of plasmid DNA by poly-L-ornithine on mica surface. AFM images reveal that the transition of negatively charged DNA to condensed nanoparticles on addition of increasing amounts of positively charged poly-L-ornithine (charge ratio (Z+/Z-) varied between 0.1 and 1) at a wide range of DNA concentrations (3-20 ng/microl) occurs through formation of several distinct morphologies. The nature of the complexes is strongly dependent on both the charge ratio and the DNA concentration. Initiation of condensation when the concentration of DNA is low (approximately 3-7 ng/microl) occurs possibly through formation of monomolecular complexes which are thick rod-like in shape. On the contrary, when condensation is carried out at DNA concentrations of 13-20 ng/microl, multimolecular structures are also formed even at low charge ratios. This difference in pathway seems to result in differences in the extent of condensation as well as size and aggregation of the nanoparticles formed at the high charge ratios. To the best of our knowledge, this is the first direct single molecule elucidation of the mechanism of DNA condensation by poly-L-ornithine. Cationic poly-aminoacids like poly-L-ornithine are known to be efficient in delivery of plasmid DNA containing therapeutic genes in a variety of mammalian cell lines by forming condensed "nanocarriers" with DNA. Single molecule insight into the mechanism by which such nanocarriers are packaged during the condensation process could be helpful in predicting efficacy of intracellular delivery and release of DNA from them and also provide important inputs for design of new gene delivery vectors.

Vinyl Polymers as Non-Viral Gene Delivery Carriers: Current Status and Prospects

Since the first application of polymers as non-viral gene delivery systems in 1965 by Vaheri and Pagano using functionalised dextran (A. Vaheri and J. S. Pagano, "Infectious poliovirus RNA: a sensitive method of assay", Virology 1965, 27, 434-6), a large number of different polymers have been developed, studied and compared for application as DNA carriers. Vinyl-based polymers are one type of polymers that have gained considerable interest. The interest in developing this particular type of polymer is partly related to the straightforward way in which large amounts of these polymers can be prepared by radical (co)polymerisation. This opens up a path for establishing a wide range of structure-property relations using polymer libraries. The present review aims to give an overview of past and ongoing research using vinyl-based gene delivery systems. The application of cationic, neutral and zwitterionic polymers as DNA carriers is summarised and discussed. [structure: see text] Chemical structure of DEAE-functionalised dextran.

Coexpression after electroporation of plasmid mixtures into muscle in vivo

AIM

Muscle is perhaps the most frequently considered tissue for non-viral gene therapy, in particular after gene transfer by electroporation. Expression in muscle is stable, but since the cell turnover is so slow incorporation in the host genome is not required. This raises interesting practical and theoretical questions related to the behaviour of the transgenic DNA under such conditions.

METHODS

We have investigated expression of reporter genes from plasmid mixtures electroporated into the extensor digitorum longus (EDL) muscle in mice in order to assess the degree of coexpression.

RESULTS

Under conditions where the reporter is easily identified the coexpression rate was 100%, as none of 287 fibres from five different muscles expressing blue fluorescent protein (BFP) failed to express green fluorescent protein (GFP). With other reporter combinations the rate was lower, but this we attribute to marginal sensitivity for fluorescent proteins, or from reporter protein degradation for beta-galactosidase.

CONCLUSIONS

The high degree of coexpression suggests that a large copy number takes part in the final transcription with this system. The finding also enhances the usefulness of muscle and electroporation for gene therapy and experimental biology.

Investigation on light-addressable potentiometric sensor as a possible cell-semiconductor hybrid

This article reports an investigation on light-addressable potentiometric sensor (LAPS) to be used as a possible biological cell-semiconductor hybrid that will enable us to make an interface between the physical and biological system. To increase the surface potential sensitivity, we used a LAPS structure with single insulator (SiO2) coated with poly-L-ornithine and laminin (PLOL) on Si. Efficient culturing of PC-12 and nerve cells of Lymnaea stagnalis on PLOL-coated Si3N4 and SiO2 was achieved. The thickness of the PLOL layer was found to be about 4 nm by the atomic force microscope (AFM) measurement. Using the advantage of this thin layer of PLOL, we compared the performance of a novel structure to the previously reported "PLOL-coated Si3N4/SiO2/Si" structure. Due to high insulating capacitance, the photocurrent response of the novel LAPS was found to be very steep. As a result, higher sensitivity was achieved. This steepness did not degrade during 10 days when the sensor surface was kept in contact with the cell culture medium and environment. The thickness of PLOL layer, its ability to improve the biological cell adhesion, enhanced sensitivity, and experiment with simulated neural action potential (AP) applied to the novel LAPS show a good promise for LAPS to be a biological cell-semiconductor hybrid.

Pharmaceutical and biological properties of poly(amino acid)/DNA polyplexes

Physicochemical properties of polyplexes formed between pRSVlacZ and poly(amino acid)s were investigated as a paradigm of more complex, synthetic virus-like, DNA delivery systems, that are of interest to many gene delivery laboratories. We observed the interaction between polymer and DNA using ethidium exclusion, and determined the size distributions and the zeta potentials of polyplexes. We correlated these properties with their fundamental interactions with cultured B16 murine melanoma cells, and the resulting efficiency of transfection. A variety of poly(amino acid)s each condensed DNA to produce particles with mean hydrodynamic diameters of approximately 100 nm (a typical span of a population was 80-120nm). Poly(amino acid) polyplexes were unstable in electrolyte solutions such as cell culture media. The apparent particle size increased in electrolyte, depending on the charge ratio, to diameters up to 700 nm. This was thought to be due to aggregation, since neutral particles were most sensitive. When the charge ratio (+/-) exceeded unity polyplexes had positive zeta potentials (which peaked at approximately +30 mV), bound non-specifically to cells, were internalised and in the presence of an endosomolytic agent were able to transfect cells. Though all cationic poly(amino acid)s investigated formed polyplexes with similar physical properties, their biological properties were significantly different. Polyplexes prepared with poly-L-ornithine were the most effective transfection agents, but poly(lys-co-ala, 1: 1) systems appeared to be inactive. This may reflect the differences in uncoupling of DNA and polymer, which is expected to be necessary for passage through the nuclear pore. Uncoupling of polycation and DNA was investigated by exposing the complexes to dextran sulphate. Release of DNA was detected by increased fluorescence at 600 nm in the presence of ethidium. Release of DNA was incomplete from polyplexes formed with high molecular weight polylysine. This may explain the lower levels of transfection observed with high molecular weight polylysine. The significance of these observations for design of advanced non-viral gene delivery systems is discussed.

In vitro cytotoxicity of poly(amidoamine)s: relevance to DNA delivery

We have examined the cytotoxicity of a number of poly(amidoamine) polymers which have been proposed for use as DNA delivery systems and compared them to the charged polyamino acid polylysine. Most of the poly(amidoamine)s tested were shown to be remarkably non-toxic to both HepG2 and HL60 cell lines. However, one of the structures (NG30, co-monomers methylene bisacrylamide, dimethylethylene diamine) did show cytotoxicity similar to that of polylysine. A second PAA structure (NG37, NG38, NG39, co-monomers bisacryloyl piperazine, 2-methyl piperazine) showed mild cytotoxicity towards both cell lines, related to the degree of polymerisation. The results support the idea that the cytotoxicity of polycations has a strong structural basis rather than being an effect due only to charge. As a consequence of their general reduced level of cytotoxicity, poly(amidoamine)s appear to have possible advantages for complexation with DNA over some other cationic polymers as a key component of DNA delivery systems.

N-Ras induces alterations in Golgi complex architecture and in constitutive protein transport

Aberrant glycosylation of proteins and lipids is a common feature of many tumor cell types, and is often accompanied by alterations in membrane traffic and an anomalous localization of Golgi-resident proteins and glycans. These observations suggest that the Golgi complex is a key organelle for at least some of the functional changes associated with malignant transformation. To gain insight into this possibility, we have analyzed changes in the structure and function of the Golgi complex induced by the conditional expression of the transforming N-Ras(K61) mutant in the NRK cell line. A remarkable and specific effect associated with this N-Ras-induced transformation was a conspicuous rearrangement of the Golgi complex into a collapsed morphology. Ultrastructural and stereological analyses demonstrated that the Golgi complex was extensively fragmented. The collapse of the Golgi complex was also accompanied by a disruption of the actin cytoskeleton. Functionally, N-Ras-transformed KT8 cells showed an increase in the constitutive protein transport from the trans-Golgi network to the cell surface, and did not induce the appearance of aberrant cell surface glycans. The Golgi complex collapse, the actin disassembly, and the increased constitutive secretion were all partially inhibited by the phospholipase A2 inhibitor 4-bromophenylacyl bromide. The results thus suggest the involvement of the actin cytoskeleton in the shape of the Golgi complex, and intracellular phospholipase A2 in its architecture and secretory function.

Positive autoregulation of ras genes expression in fibroblasts

We have studied the effect of ectopic overexpression of a ras gene on the expression of the other two members of the ras gene family. We obtained NIH3T3 cell lines stably transfected with inducible H-ras and N-ras oncogenes. The expression of these genes is driven by a glucocorticoid-responsive promoter and the addition of dexamethasone resulted in a dramatic induction (10-20-fold) of H- or N-ras mRNA, peaking 4 h after hormone addition. The induction of the expression of ras oncogenes resulted in a transformed phenotype. In quiescent NIH3T3 cells transfected with inducible H-ras oncogenes, the induction of H-Ras was followed 12 h later by a 3-fold increase in the mRNA expression of endogenous K-ras and N-ras. Similarly, in NIH3T3 transfected with inducible N-ras oncogene, the induction of N-ras was followed by an increase in the expression of endogenous K- and H-ras genes. Interestingly, the effect was not limited to the mutated N-ras, as a similar result was obtained in cells transfected with N-ras proto-oncogene. The induction of ras genes expression was not linked to cell cycle progression as it was reproduced in cells arrested in S-phase by pretreatment with hydroxyurea. These results suggest the presence of a positive cross-regulation in the expression among the members of the Ras family. This effect could play a role in Ras-mediated carcinogenesis.

High-efficiency stable DNA transfection using cationic detergent and glycerol

We show that a brief exposure to a simple cationic detergent, in combination with a glycerol 'shock', can result in high frequencies of stable DNA transfection into mammalian cells. Using both Chinese hamster and human cell lines, frequencies of 1 per 1000, or even 1 per 100, viable cells can be achieved readily after optimizing the transfection conditions in a simple buffer. The mechanism of DNA transfer is proposed to differ from that for polycationic liposomes: as well as supplying a hydrophobic counterion, CDAB may promote a conformational change in DNA, allowing the DNA to be readily taken up after the glycerol shock to the cell.

Enhancement of HSV-DNA infectivity, in Vero and RS cells, by a modified calcium-phosphate transfection technique

Infectivity of herpes simplex virus (HSV) DNA was assessed by employing the calcium-phosphate transfection technique described by Chen and Okayama, originally applied to increase the efficiency of plasmid transfection by N, N-bis (2-hydroxyethyl)-2-aminoethane sulfonic acid (BES). The experimental conditions and efficiency of this transfection procedure were evaluated comparing the viral progeny titers obtained by the Chen and Okayama transfection method using DNA from wild-type strains of HSV-1 and HSV-2, as well as from mutant strains, with the viral progeny obtained by the most widely used transfection technique introduced by Graham and van der Eb. Furthermore, recombinant virus production was evaluated in marker transfer and marker rescue experiments, comparing both transfection techniques, using DNA fragments cotransfected with whole viral DNA into African green monkey (Vero) or rabbit skin (RS) cells. The viral production obtained from HSV-DNA transfected cells was enhanced approximately 1000-fold when the Chen and Okayama procedure was applied.

Poly-L-ornithine-mediated transfection of human keratinocytes

Human keratinocytes are notoriously difficult to transfect. We have optimized a method for introducing plasmid DNA into keratinocytes that pairs the polycation poly-L-ornithine with a dimethylsulfoxide (DMSO) shock. The optimum poly-L-ornithine conditions for keratinocyte transfection entailed incubating the cells with 12 micrograms/ml poly-L-ornithine and 10 micrograms DNA for 6 h, followed by a 4-min 25% DMSO shock. Based on kinetic studies, 1 h is enough time to produce 10% positive cells in transient transfections, which increases up to an average of 20% after 6 h. Transfected cells survive passaging, and marker plasmids and selection can be used to yield stable transfectants at a rate twofold higher than in cells transfected with polybrene and DMSO. Transient transfection rates were significantly higher using poly-L-ornithine/DMSO than with the polybrene/DMSO or polybrene/glycerol methods previously reported. Overall, transfection mediated by poly-L-ornithine provides an efficient and inexpensive means of transiently or stably introducing DNA into keratinocytes.

Immortalization and characterization of bovine peritoneal macrophages transfected with SV40 plasmid DNA

A transformed bovine peritoneal macrophage cell line was developed and characterized. Primary peritoneal macrophages were transformed by calcium-phosphate transfection with SV40 plasmid DNA. The transformed cell line retained the morphology of resident peritoneal macrophages as determined by light microscopy and histochemical analysis showed non-specific esterase activity. In addition, immunohistochemical staining of transformed peritoneal macrophages for lysozyme activity was positive. Transformed cells phagocytized Staphylococcus aureus, lysed chicken red blood cell (RBC) targets with and without opsonization and produced hydrogen peroxide radicals and interleukin-6 upon stimulation with opsonized zymosan and lipopolysaccharide, respectively. Transformed cells were also able to ingest and kill Mycobacterium paratuberculosis, an acid-fast bacillus. These results suggest that this cell line should be useful to study interactions between the bovine and intracellular pathogens.

Polybrene/DMSO-assisted gene transfer. Generating stable transfectants with nanogram amounts of DNA

Polybrene/DMSO-assisted gene transfer is a simple and versatile transfection strategy capable of producing high numbers of stable transfectants from adherent monolayer cultures with low (nanogram) quantities of exogenous DNA. The procedure involves two stages: adsorption and internalization. The former is mediated by polybrene (a polycation polymer) and favors the uniform coating of target cells with polybrene-DNA complexes. Following adsorption, the cells are permeabilized by a brief exposure to dimethyl sulfoxide (DMSO) to facilitate the uptake of DNA complexes. Diverse cell types can be exposed to a wide range of polybrene concentrations without adverse effects. By contrast, the key determinant of success is the DMSO permeabilization regime, which must be configured independently for each cell line. Protocols optimized for gene transfer in murine and human fibroblasts are presented along with a guide for the rapid optimization of the method. The advantages and limitations of the method are also discussed.

Human immunodeficiency virus type 1 Tat does not transactivate mature trans-acting responsive region RNA species in the nucleus or cytoplasm of primate cells

Human immunodeficiency virus (HIV)-encoded transactivator Tat is essential for viral gene expression and replication. By interacting with a nascent RNA stem-loop called the trans-acting responsive region (TAR). Tat increases rates of initiation and/or elongation of HIV transcription. Several reports have also suggested that Tat has additional effects on mature HIV RNA species including modification of primary transcripts in the nucleus and their increased translation in the cytoplasm. These posttranscriptional effects are most pronounced in the Xenopus oocyte. To investigate directly whether Tat has similar effects on viral transcripts in cells that are permissive for HIV replication, we cotransfected and microinjected human and monkey cells with Tat and TAR in the form of DNA or RNA. Whereas Tat transactivated TAR DNA targets, it did not transactivate TAR RNA targets in the nucleus of microinjected cells or in the cytoplasm of transfected cells. We conclude that in cells permissive for viral replication, Tat exerts its effect primarily at the level of HIV transcription.

Effect of myogenic determination on tumorigenicity of chemically transformed 10T1/2 cells

Transforming agents have been postulated to interfere with cellular differentiation programs, thus causing uncontrolled growth. Inducing transformed cells to differentiate can result in loss of the transformed phenotype since many end-stage differentiated cells are unable to divide. We attempted to bypass or suppress the tumorigenic phenotype of 3-methylcholanthrene (MCA)-transformed 10T1/2 cells (MCA Cl 15C1) by induction of myogenic determination. MCA Cl 15C1 cells were either treated with the hypomethylating drug 5-azacytidine (5-aza-CR) or were transfected with the muscle determination gene MyoD1, both of which induce a myogenic phenotype in 10T1/2 cells. Colonies containing myoblast-like cells were isolated and examined. Muscle markers were detected both in 5-aza-CR-treated and in MyoD1-transfected myogenic clones by immunofluorescence and northern analyses. The myogenic clones did not show decreased tumorigenicities relative to that of the parental cells upon subcutaneous injection in nude mice. Some of the resulting tumors, however, were classified as rhabdomyosarcomas rather than fibrosarcomas. Although induction of myogenic determination was not sufficient to abolish the tumorigenic phenotype of MCA Cl 15C1 cells, several tumors showed decreased levels of MyoD1 mRNA, suggesting that growth in vivo either selected for or caused decreased determination gene expression.

Efficient transfection and expression of heterologous genes in PC12 cells

The PC12 pheochromocytoma cell line has been a favorite model system for cell and neurobiologists, but has proven relatively refractory to standard DNA transfection methods. We have found that the cationic lipid "lipofectin" provides a simple, gentle, and nontoxic procedure that vastly improves transfection efficiencies in PC12 cells. Transient expression of chloramphenicol acetyl transferase (CAT) driven by a Rous sarcoma virus long terminal repeat (LTR) is much more efficient using lipofectin when compared with calcium phosphate as a transfection procedure. Additionally, transient transfection of nerve growth factor (NGF)-differentiated PC12 cells proceeds with equal efficiency relative to naive, uninduced cells. Using the lipofectin procedure, the frequency of stable transfection is 100-fold higher than that reported with standard calcium phosphate precipitation protocols. To examine the effectiveness of different promoters for efficient expression of heterologous DNA in PC12 cells, three different promoter-bearing constructs were utilized. Each construct contains a different promoter sequence upstream from a chicken calsequestrin cDNA. A human cytomegalovirus (CMV) immediate early promoter construct produced the highest level of expression, followed by a human beta-actin promoter construct. Expression from a mouse Moloney sarcoma virus LTR construct could not be detected. These results overcome the previous transfection problems of low efficiency and low viability that have plagued many PC12 cell investigations.

Regulation of chicken alpha and beta actin genes and their hybrids inserted into myogenic mouse cells

We have investigated the regulation of intact non-muscle (beta) and muscle-specific (skeletal alpha) chicken actin genes and of hybrids of these two genes (alpha 5'-beta 3' and beta 5'-alpha 3') transferred into the mouse myogenic non-fusing cell line BC3H1. BC3H1 cells express members of the actin multigene family in a differentiation-dependent manner. When proliferating, the cells accumulate large amounts of non-muscle actin mRNA; when the cells are induced to differentiate, the amount of non-muscle actin mRNA decreases and the amount of muscle-specific actin mRNA increases. The transferred beta-actin gene is efficiently expressed in undifferentiated cells and appropriately down-regulated upon differentiation. In contrast, the transferred alpha-actin gene is inefficiently expressed and not consistently up-regulated. Results with the intact and hybrid genes, taken together, are consistent with the hypothesis that both 5' and 3' halves of these genes contain sequences important in regulating the efficiency and/or developmental timing of their expression in BC3H1 cells. By nuclear run-on experiments we found no evidence for gene-specific changes in the rate of transcription of the transferred actin genes during myogenesis. We conclude that the differentiation-dependent changes in expression of the intact beta-actin gene in BC3H1 cells must be regulated at the post-transcriptional level.

Biosynthesis of the reverse transcriptase of hepatitis B viruses involves de novo translational initiation not ribosomal frameshifting

Retroviruses and many other types of genetic elements replicate by reverse transcription of RNA. Although structurally and biologically very diverse, such elements carry conserved polymerase genes (pol) that encode proteins required for reverse transcription. In most cases, the pol gene is preceded by an overlapping gene encoding one or more nucleocapsid proteins, in a different reading frame. Because both coding regions are represented in a single mRNA, the question arises of how the reverse transcriptase in the alternative reading frame is expressed. In retroviruses and retrotransposons it is expressed as a nucleocapsid-polymerase fusion protein by ribosomal frameshifting during translation of the overlapping region. We have examined the mechanism of polymerase biosynthesis in another family of animal viruses that use reverse transcription, the hepatitis B viruses. Genetic and biochemical studies reveal that these viruses do not use ribosomal frameshifting to generate this enzyme, but instead direct translation initiation at an internal initiation (AUG) codon in the polymerase gene.

Factors influencing efficiency and reproducibility of polybrene-assisted gene transfer

A systematic investigation of factors influencing the efficiency of polybrene-assisted gene transfer for both transient and stable foreign gene expression was carried out utilizing NIH 3T3 fibroblasts as prototypic recipients for the plasmid expression vectors pSV2cat and pSV2neo. While transfection cocktail composition and cell density, in addition to polybrene exposure conditions and exogenous DNA concentration, each played an important role, the key determinant to achieving excellent transfection efficiency proved to be the DMSO treatment regimen. Under optimal conditions, the yield of colonies resistant to the neomycin analog, G418, increased linearly at the rate of 10 clones/ng of input (native form I pSV2neo) DNA up to a plasmid concentration of 50 ng, whereupon the dose-response for colony recovery became semilogarithmic. The incidence of stable transformants was doubled by linearization of the vector DNA, whereas the addition of carrier DNA to the transfection cocktail was without effect until present at concentrations above 10-fold molar excess, at which point the efficacy of gene transfer declined rapidly. Combined Southern and dot-blot analyses of transformed cell DNA demonstrated that the polybrene-DMSO procedure led to the stable integration of relatively few copies of the marker gene in each transformant; the actual number varied from 1-3 to 10-15 per host genome, depending on the concentration of pSV2neo DNA added. The potential for the adaptation of this DNA transfection procedure for general use with other mammalian cell types, as well as its technical strengths and weaknesses, is discussed.