Nucleic acid transfer through cell membranes: towards the underlying mechanisms

Membrane binding of plasmid DNA and endocytic pathways are involved in electrotransfection of mammalian cells

Electric field mediated gene delivery or electrotransfection is a widely used method in various studies ranging from basic cell biology research to clinical gene therapy. Yet, mechanisms of electrotransfection are still controversial. To this end, we investigated the dependence of electrotransfection efficiency (eTE) on binding of plasmid DNA (pDNA) to plasma membrane and how treatment of cells with three endocytic inhibitors (chlorpromazine, genistein, dynasore) or silencing of dynamin expression with specific, small interfering RNA (siRNA) would affect the eTE. Our data demonstrated that the presence of divalent cations (Ca(2+) and Mg(2+)) in electrotransfection buffer enhanced pDNA adsorption to cell membrane and consequently, this enhanced adsorption led to an increase in eTE, up to a certain threshold concentration for each cation. Trypsin treatment of cells at 10 min post electrotransfection stripped off membrane-bound pDNA and resulted in a significant reduction in eTE, indicating that the time period for complete cellular uptake of pDNA (between 10 and 40 min) far exceeded the lifetime of electric field-induced transient pores (∼10 msec) in the cell membrane. Furthermore, treatment of cells with the siRNA and all three pharmacological inhibitors yielded substantial and statistically significant reductions in the eTE. These findings suggest that electrotransfection depends on two mechanisms: (i) binding of pDNA to cell membrane and (ii) endocytosis of membrane-bound pDNA.

Cell de-energization prevents plasmid transformation of yeast Saccharomyces cerevisiae: evidence for the requirement of ATP

The dependence of the yeast Saccharomyces cerevisiae transformation on energy requirement was studied. The inhibitory effect of sodium arsenate, used for the depletion of the intracellular ATP pool, was determined. Incubation of the yeast cells in 5 mM sodium arsenate diminished ATP accumulation by 50% and the transformation efficiency decreased by 65%. To discriminate between ATP produced by substrate level phosphorylation and oxidative phosphorylation, the inhibitory analysis of a mutant with defective mitochondria was performed. Sodium fluoride (10–50 mM), as inhibitor of glycolysis, elicited a concentration-dependent decrease in intracellular ATP levels in both parental and mutant cells. The equal transformation efficiency of the mitochondrial mutant and parental strain, in addition to experiments with oligomycin, demonstrated the independence of plasmid transformation on mitochondrial ATP synthesis. This is consistent with our hypothesis that yeast transformation efficiency is associated with ATP produced by substrate level phosphorylation.

Multiple glycerol shocks increase the calcium phosphate transfection of non-synchronized CHO cells

The exposure of CHO DG44 cells to an osmotic shock, after DNA uptake, results in a cellular volume decrease of approx. 55%. Repetitive osmotic shocks targeted different sub-populations of cells as was demonstrated using two different fluorescent reporter genes. Also the exposure of a calcium phosphate-DNA coprecipitate to high osmolarity in vitro caused the release of the DNA from the precipitate. The results demonstrate the importance of the osmotic shock on the efficient delivery of plasmid DNA to the nucleus of CHO cells following calcium phosphate-mediated transfection.

Primordial proteins and HIV-Part II

Nanobacteria are suspected to be responsible for a number of diseases, i.e., kidney stones, heart disease, ovarian cancer, peripheral neuropathy, and reduced bone mineral density. Being protected by a mineral shell consisting of apatite, the nanovesicles can enter eukaryotic cells. Depending on the host's stress level, nanobacteria may carry a substantial layer of a protein based slime, instrumental in collecting calcium phosphate from the environment. Calcium phosphate is known to mediate the uptake of nucleic acids by eukaryotic cells. Surprisingly, a pathogenic effect of nanobacteria in HIV can be derived primarily from the trafficking of calcium phosphate in HIV infected cells, performed by primordial proteins. The inescapable conclusion is that nanobacteria could promote genetic diversity in HIV.

Primordial proteins and HIV

Primordial proteins regulate the response of nanobacteria to variations in their environment and reinforce existing pathogenic potentials. By analyzing specific response patterns, we predicted the prevalence of nanobacteria in HIV--and in the atmosphere. A current clinical study indicates the identification of a possibly giant nanobacterial reservoir in Africa: a significant fraction of a test group (40 HIV-infected mothers and 13 babies) was infected with nanobacteria. Concurrently, a multitude of 80-300 nm nanovesicles, apparently nanobacteria, were detected in the atmosphere of the Earth. Nanobacterial infections in HIV are possibly comparable to the twin epidemics HIV and tuberculosis. Models inspired by proteomics recommend methods to inactivate nanobacteria (and other slime-producing bacteria) in the body.

Electromobility of plasmid DNA in tumor tissues during electric field-mediated gene delivery

Interstitial transport is a crucial step in plasmid DNA-based gene therapy. However, interstitial diffusion of large nucleic acids is prohibitively slow. Therefore, we proposed to facilitate interstitial transport of DNA via pulsed electric fields. To test the feasibility of this approach to gene delivery, we developed an ex vivo technique to quantify the magnitude of DNA movement due to pulsed electric fields in two tumor tissues: B16.F10 (a mouse melanoma) and 4T1 (a mouse mammary carcinoma). When the pulse duration and strength were 50 ms and 233 V/cm, respectively, we found that the average plasmid DNA movements per 10 pulses were 1.47 microm and 0.35 microm in B16.F10 and 4T1 tumors, respectively. The average plasmid DNA movements could be approximately tripled, ie to reach 3.69 microm and 1.01 microm, respectively, when the pulse strength was increased to 465 V/cm. The plasmid DNA mobility was correlated with the tumor collagen content, which was approximately eight times greater in 4T1 than in B16.F10 tumors. These data suggest that electric field can be a powerful driving force for improving interstitial transport of DNA during gene delivery.

Muscle-specific enhancement of gene expression by incorporation of SV40 enhancer in the expression plasmid

Skeletal muscle is established as an ideal tissue for gene delivery to treat systemic diseases. However, the relatively low levels of gene expression obtained from using naturally occurring promoters, including the strong cytomegalovirus (CMV) enhancer/promoter (E/P), have limited the use of muscle as a target tissue. The relatively weak simian virus 40 (SV40) enhancer is known to have dual functions promoting localization of DNA to the nucleus and activating transcription. An SV40 enhancer incorporated either at the 5' end of CMV E/P or the 3' end of the polyadenylation site gave as much as a 20-fold increase in the level of exogenous gene expression in muscle in vivo, compared with expression observed with CMV E/P alone. The minimum requirement for this enhancement is a single copy of a 72-bp element of the SV40 enhancer, in combination with either the CMV E/P or skeletal actin (SkA) promoter. Enhancement of gene expression in muscle by this SV40 enhancer was also observed by using the powerful electroporation delivery. However, the SV40 enhancer does not increase the level of CMV E/P driven reporter gene expression in dividing tumor cells in vivo and in the dividing myoblast cell C2C12 in vitro. The data suggest that including this enhancer in the plasmid will enhance the level of gene production for muscle-based gene therapy.

Amplifiable DNA from gram-negative and gram-positive bacteria by a low strength pulsed electric field method

An efficient electric field-based procedure for cell disruption and DNA isolation is described. Isoosmotic suspensions of Gram-negative and Gram-positive bacteria were treated with pulsed electric fields of <60 V/cm. Pulses had an exponential decay waveform with a time constant of 3.4 micros. DNA yield was linearly dependent on time or pulse number, with several thousand pulses needed. Electrochemical side-effects and electrophoresis were minimal. The lysates contained non-fragmented DNA which was readily amplifiable by PCR. As the method was not limited to samples of high specific resistance, it should be applicable to physiological fluids and be useful for genomic and DNA diagnostic applications.

Mitochondrial damage as a source of diseases and aging: a strategy of how to fight these

Some aspects of a defense against an oxidative stress are reviewed. All these aspects are focused on the necessity to defend mtDNA against damage. Protecting mechanisms involve the regulation of mitochondrial transport of nucleic acids, and the development of antioxygen defense as preventive measures. In the first case an exclusive role is supposed to play the mitochondrial benzodiazepine receptor and components, regulating the activity of its participants (mitochondrial porin and adenine nucleotide translocator). The possible transport of nucleic acids through Ca(2+)-dependent permeability transition pore, representing one of the functional states of mitochondrial benzodiazepine receptor, is put forth. Such mechanisms can also cover the genomic nuclear-mitochondrial exchange. The second aspect reviews the possible complex of measures to lower the harmful effect of oxygen. Among these measures are mild uncoupling, the opening of a permeability transition pore and cellular apoptosis as was recently suggested by Skulachev. Problems such as cellular aging and mitochondrial diseases, are discussed in light of the relevance to the problem of oxidative stress.