Electric field-mediated gene transfer (electroporation) into mouse Friend and human K562 erythroleukemic cells

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

Transfection of Human Breast Epithelial Cells with Foreign Dna Using Different Transfecting Techniques

The introduction of DNA into eukaryotic cells is a powerful technique for the study of gene regulation. This requires both a technique by which genes can efficiently be introduced into cells and a recipient cell representative of the tissue under study. We have utilized a spontaneously immortalized human breast epithelial cell line, CMF-10, which is phenotypically normal for introducing a neomycin-resistant gene contained in the plasmid Homer 6 (pHo6). Three different transfection methods were tested: calcium phosphate, with and without glycerol shock, using as control NIH/3T3 cells, and strontium phosphate and electroporation. In MCF-10 cells the efficiency of calcium phosphate mediated DNA transfection, which was measured as the number of colonies growing in neomycin-containing medium, was 21 and 140 fold higher than in MCF-10 cells transfected by electroporation and strontium phosphate methods, respectively. Glycerol shock enhanced three fold transfection efficiencies. NIH/3T3 transfected cells by calcium phosphate method showed a transfection efficiency similar to that of MCF-10 cells, however, glycerol shock did not improve the efficiency. These studies revealed that calcium phosphate combined with glycerol shock is the most efficient technique for transfection of genomic DNA into human breast epithelial cells.

Permeabilization of adhered cells using an inert gas jet

Various cell transfection techniques exist and these can be broken down to three broad categories: viral, chemical and mechanical. This protocol describes a mechanical method to temporally permeabilize adherent cells using an inert gas jet that can facilitate the transfer of normally non-permeable macromolecules into cells. We believe this technique works by imparting shear forces on the plasma membrane of adherent cells, resulting in the temporary formation of micropores. Once these pores are created, the cells are then permeable to genetic material and other biomolecules. The mechanical forces involved do run the risk of permanently damaging or detaching cells from their substrate. There is, therefore, a narrow range of inert gas dynamics where the technique is effective. An inert gas jet has proven efficient at permeabilizing various adherent cell lines including HeLa, HEK293 and human abdominal aortic endothelial cells. This protocol is appropriate for the permeabilization of adherent cells both in vitro and, as we have demonstrated, in vivo, showing it may be used for research and potentially in future clinical applications. It also has the advantage of permeabilizing cells in a spatially restrictive manner, which could prove to be a valuable research tool.

Attachment, replication and thrombogenicity of genetically modified endothelial cells

Endothelial cell seeding of prosthetic surfaces has been proposed as a technique to improve the patency of vascular grafts following arterial reconstruction. The introduction of specific recombinant DNA into seeded endothelial cells may enhance the anti-thrombogenic nature of the endothelial-blood interface with a consequent reduction in graft thrombosis. However, the successful use of genetically modified endothelial cells in the seeding process relies on the cells retaining normal function in terms of cellular replication, attachment and secretion of anti-thrombotic mediators. Successful genetic manipulation of human endothelial cells has been accomplished by viral and chemical methods.

AIM

To study the functional characteristics of electrontransfected endothelial cells.

METHODS AND RESULTS

Endothelial cells were electro-transfected with the test plasmid pTCF at a transfection efficiency of 10% utilising a single electric pulse with an electric field of 1000 volts/cm and a time constant of 12.8ms. The functional status of transfected endothelial cells was then compared with a control endothelial cell population. There were no significant differences in replication (p = 0.76), attachment (p = 0.43), basal (p = 0.89) or stimulated (p = 0.11) prostacyclin release between transfected cells as compared with control endothelial cells.

CONCLUSIONS

Genetically modified cells are functionally normal, and may be used in endothelial cell seeding of prosthetic vascular surfaces.

Optimisation of gene transfer into vascular endothelial cells using electroporation

OBJECTIVES

We have examined the conditions required to obtain optimum transfection efficiencies for human umbilical vein endothelial cells by transduction with a plasmid conferring neomycin resistance.

MATERIALS AND METHODS

Preliminary studies examined the effects of electric discharges using the Biorad Gene Pulser on endothelial cells. Post-electroporation, there was a significant decrease in cell survival with increasing voltages (100-400 volts; p = 0.03), capacitances [125-960 microFarads (microF); p = 0.02], number of electric pulses (1-2; p = 0.03) and decreasing cell concentrations (p = 0.01). The optimal cell concentration was 3 x 10(6) cells/ml. Transfection studies utilised the neomycin resistance expressing plasmid, pTCF; transfectants were selected with the neomycin analogue G-148.

RESULTS

Electro-transfection was optimised with increasing voltages (p = 0.02) and capacitances (p = 0.01) using a single pulse. Optimal transfection was obtained using 400 volts with a capacitance of 960 microF using a single pulse; the median transfection efficiency was 10%. Transduced endothelial cells stably expressed the plasmid for 12 days and at least two cell passages.

CONCLUSIONS

The results indicate that endothelial cells can be efficiently transduced by electroporation to stably express an introduced gene. This may have important implications in vascular surgery.

Functional analysis of the 4 bp deletion identified in the 5' untranslated region of one of the beta-globin genes from a Chinese beta-thalassaemic heterozygote

Two plasmids have been constructed in which a beta-galactosidase/phleomycin-resistance fusion gene reporter is placed under the control of the human beta-globin gene promoter and 5' untranslated region including or not including nucleotides 40-43 previously found deleted in one Chinese beta-thalassaemic allele. Transient expression assays of these two plasmids failed to reveal any significative effect of this 4 bp deletion either on the level of the beta-galactosidase activity produced in HeLa cells transfected in standard conditions, or on the rate of synthesis of the beta-galactosidase protein in transfected HeLa cells submitted to increasing osmotic shocks. These results suggest that this 4 bp deletion is not responsible for the beta-thalassaemic phenotype in vivo.

Gene transfer into human leukemia cell lines by electroporation: experience with exponentially decaying and square wave pulse

The efficiency of gene transfer into human leukemia cell lines by electroporation was investigated. For both transient expression (beta-galactosidase gene) and stable transformation (neomycin resistance gene), the transfer efficiency into leukemia cell lines using a square wave pulse was superior to that using an exponentially decaying wave. The transfer rate of pMoZtk (containing beta-galactosidase gene) into K562 by electroporation using a square wave was approximately 5%, compared with 1% by an exponentially decaying pulse. Whereas the transfer rate of pMAM-neo into K562 by electroporation using an exponentially decaying pulse was less than 10(-5), a square wave generated much more efficient introduction rate of nearly 10(-3). In the other leukemia cell lines also, some square wave yields were better than exponential yields and all square wave yields were at least as good as the exponential yields.

Production of human tissue-type plasminogen activator in different mammalian cell lines using an Epstein-Barr virus vector

Human tissue-type plasminogen activator (t-PA) cDNA inserted into an Epstein-Barr virus (EBV) derived expression vector was transfected into human HeLa, 293, K-562 and hamster CHO-K1 cells and the expression of t-PA was studied. The best t-PA producing cell clones were found among CHO-K1 cells (up to 11 micrograms d-1 per 10(6) cells). However, HeLa and 293 cells were most efficiently transfected, e.g. about 70% of the selected cell clones were t-PA positive. The vector DNA copy numbers correlated with the mRNA levels and the protein levels for all cell lines analysed, with the exception for the K-562 cell line, where the production of t-PA was very low. The results obtained indicated that the highest expression levels were achieved in low density cultures.

High Efficiency Transformation of Intact Yeast Cells by Electric Field Pulses

We have developed an efficient method that electrically introduces DNA into intact yeast cells. Saccharomyces cerevisiae was used as a model in order to optimize the transformation protocol. Transformation efficiencies of 10(7) transformants/micrograms of plasmid DNA were obtained with a square wave electric pulse of 2.7 kV/cm during 15 milliseconds. The technique is simple and rapid. Even small quantities of DNA (100 pg) can be used to transform 10(8) cells. Important parameters are the pulse field strength and duration. Pretreatment of the yeast cells in the early phase of exponential growth with dithiothreitol increases transformation efficiency. The method has been successfully applied to various strains of S. cerevisiae as well as to other types of yeast.

Epstein-Barr virus episome-based promoter function in human myeloid cells

Epstein-Barr virus (EBV) episomal replicons offer an expeditious means for amplifying transfected genes in human cells. A panel of EBV episomes was constructed to assess the relative utility of five distinct eukaryotic promoter elements for high level and inducible gene expression in stably transfected human myeloid leukemia cells. The Rous sarcoma virus 3' long terminal repeat (LTR) was most highly suited for EBV episome-based gene expression, whereas the lymphopapilloma virus and the SV40 early regulatory elements exhibited substantially lower activities. Chemically responsive promoter elements, such as the SV40 early, human metallothionein IIA and rat GRP78 gene promoters, retained their inducibility when EBV episome-based. Differences in gene expression obtained with the episomes reflected differential promoter activity rather than significant variations in episome copy numbers per cell. These observations provide guidelines for the optimal design of EBV episomal expression vectors for human expression work.

The effect of exogenous human ras and myc oncogenes in morphological differentiation of the rat pheochromocytoma PC12 cells

An electroporation technique was employed to study the effect of oncogenes H-ras and c-myc after their short-term expression in the rat pheochromocytoma PC12 cells. It was found that within 6 days after electroporation the mutant T24 H-ras 1 gene induced differentiation of PC12 cells whereas the c-myc blocked NGF-induced differentiation. The induction of differentiation by the T24 H-ras gene may suggest a physiological role of the ras gene in cell differentiation as well as in cell proliferation.

Electric shock-mediated transfection of cells. Characterization and optimization of electrical parameters

The effect of various parameters on the electric shock-mediated permeabilization and transfection of CHO cells has been investigated. Up to 70% of the cells can be maintained transiently permeable to erythrosin B for periods of at least 1 h at 20 degrees C. Electrical conditions optimal for transient permeabilization were also optimal for efficient DNA transfection by pSV2neo. However, the DNA must be present during exposure to the electric field for efficient transformation. The same requirement existed for voltage-induced DNA toxicity. The results suggest that DNA moves into the cells by electrophoresis, not by simple diffusion. Based on these observations a simple, rapid procedure for optimizing the conditions for electric shock-mediated DNA transfer into cells has been developed.