Gene expression following direct injection of DNA into liver

RNA polymerase III transcription repressed by Rb through its interactions with TFIIIB and TFIIIC2

The retinoblastoma susceptibility gene product (Rb) generally represses RNA polymerase III (Pol III)-directed transcription. This implies that Rb interacts with essential transcription factors. Mutations in either the A or B subdomains in the Rb pocket interfere with Rb-mediated repression of Pol III-directed transcription, which indicates that both subdomains are directly involved in this activity. Addition of either purified TFIIIB or purified TFIIIC2 partially relieves Rb-mediated repression and restores activity to nuclear extracts that had been depleted of essential factors by binding to Rb. Pull down and coimmunoprecipitation experiments as well as functional assays indicate that Rb interacts with both TFIIIB and TFIIIC2 and that the A subdomain is primarily required for binding TFIIIB and the B subdomain for binding TFIIIC2. While Rb interacts with both factors, the A subdomain is more important than the B subdomain in directing Rb-mediated repression, and TFIIIB is the principal target of that activity.

Palindromic sequences preceding the terminator increase polymerase III template activity

Four consecutive T residues in the sense strand are sufficient to terminate transcription by RNA polymerase III (pol III). Previously we observed that compared with this minimally sufficient terminator, five T residues immediately preceded by a palindromic sequence increases transcriptional expression both in vitro and in vivo, raising the question of whether a palindromic sequence has a role in pol III termination. Here we observe that site-directed mutations which eliminate the dyad symmetry of the palindromic sequence decrease transcriptional expression. Similar effects are observed whether dyad symmetry is eliminated in regions of the palindrome which are proximal or distal with respect to the terminator. Compensatory mutations at either site to restore dyad symmetry rescue transcriptional activity. These observations suggest that a higher order structure, such as a RNA hairpin, immediately preceding the terminator increases pol III transcriptional activity.

Transgene expression of plasmid DNAs directed by viral or neural promoters in the rat brain

The use of circular plasmid DNA may be an alternative method for the transfer of genes into the brain and is presumably easier to use than other vectors, such as viruses or genetically engineered cells. The effectiveness and time course of the expression of a reporter gene (LacZ), directed by appropriate promoters, was studied after stereotaxic injection of naked plasmid DNAs into the rat thalamus, cortex or cerebellum. The efficiencies of three different promoters, the human cytomegalovirus (HCMV) promoter and the glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) promoters (specific for astrocytes and neurons, respectively) to drive reporter gene expression were compared. Efficient expression of beta-gal, detected by X-gal histochemistry or immunochemistry, required the use of 50 microg of DNA and was detectable as early as 48 h after injection. Expression increased until day 8, remained stable until day 15, then decreased over 2 months, probably as a result of non-specific degradation of the plasmids within the transfected cells rather than from specific down-regulation of promoters, as the same time course was seen with all three promoters tested. Depending on the promoter used (GFAP or NSE), LacZ was preferentially expressed within astrocytes or neurons, respectively. The GFAP promoter was found to be as efficient as the HCMV promoter, possibly due to the reactive gliosis induced by plasmid injection which is known to up-regulate GFAP expression.

Surfactant inhibits cationic liposome-mediated gene transfer

We have demonstrated that tracheal insufflation of recombinant plasmid DNA results in transfection of rat lungs to the same extent as insufflation of plasmid-cationic liposome complex. To understand this observation better, we investigated the in vitro gene transfer of plasmid DNA in the presence and absence of cationic liposome and the effect of surfactant on gene transfer. The chloramphenicol acetyltransferase (CAT) expression plasmids pBL-CAT and pSV-CAT were studied in three cell types: rat fetal lung fibroblast (RFL-6), calf pulmonary artery endothelial cell (CPAE), and rat type II alveolar epithelial cell (type II AE). Three cationic liposomes were tested: DDAB (dimethyl-dioctadecyl ammonium bromide)-liposome, DOTAP (dioleoyltrimethyl ammonium propane)-liposome, and lipofectin. The results revealed that (i) plasmid DNA alone caused a dose-dependent, low-level transfection, most efficiently in RFL-6 followed by CPAE and type II AE, (ii) DDAB-liposome markedly enhanced gene transfer, most efficiently in RFL-6 followed by CPAE and type II AE, (iii) Survanta, a naturally derived surfactant preparation, and Exosurf, a synthetic surfactant, while having no effect on in vitro gene transfer by plasmid DNA alone, markedly inhibited cationic liposome-mediated gene transfer, (iv) dipalmitoyl phosphatidylcholine was responsible for the inhibitory effect of Exosurf, and (v) inhibition of cationic liposome-mediated gene transfer by Exosurf was not due to inhibition of plasmid DNA-cationic liposome complex uptake or interference with the promoter and enhancer. The observed inhibition of cationic liposome-mediated gene transfer by surfactant may in part explain our previous observation that tracheal insufflation of plasmid DNA and plasmid-cationic liposome complex results in equal lung gene transfer.

Gene transfer by biolistic process

Gene transfer into somatic tissues is a tool for both the study of gene function in the basic science laboratory and for gene therapy and genetic immunization in the clinic. Biolistic processes can be used to deliver both viral and nonviral vectors into somatic tissues. This review discusses the advantages and disadvantages of three biolistic processes: jet injection, microparticle bombardment, and needle and syringe injection. Jet injection and needle and syringe injection can be used to deliver both viral and nonviral vectors. Both jet injection and microparticle bombardment can be used to target a broad range of tissues. Needle and syringe injection has been most widely used in muscle tissue. The choice of which biolistic process to use is dependent on the specific application.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Studies of in vivo Gene Transfer by Electropulsation at the Low Skin Resistance Points (LSRPs)

Electropulsation has been proved to be a powerful technique for DNA transfection in vitro. This study was undertaken to assess the feasibility and evaluate the potential of applying this approach for facilitating gene transfer in vivo. The pCMVβ plasmid, containing the Escherichia coli lacZ open reading frame under the cytomegalovirus early promoter, was complexed with poly-L-lysine (PLL) and injected directly into the livers of Wistar rats; electropulsation was then applied either at the low skin resistance points (LSRPs) of the skin, the non-LSRP, or directly at the liver by either a portable electrostimulator or an electropulsation unit. The locations of the LSRPs were detected by the unijunction transistor (UJT) relaxation oscillator. Seventy-two hours after gene transfer, the animals were sacrificed and the livers were excised, followed by examination of the transgene expression. The results obtained from X-gal staining, in situ hybridization, and Western blot analysis indicated that lacZ gene was expressed in the livers. Variations of the electropulsation parameters, including site of electropulsation, wave type, amplitude of the pulses, repetition rate, duty cycle, and duration of electropulsation treatment, do not reveal any statistically significant effects of differences of these variables on the transgene expression. Comparison of the results obtained from direct injection of PLL/pCMVβ (1:1) followed by electropulsation at the LSRPs with that of direct PLL/pCMVβ (1:1) injection, however, suggests that gene transfer by electropulsation achieved a higher transfection efficiency in vivo (p >. 05).

Pharmaceutical approach to somatic gene therapy

The pharmaceutical approach to somatic gene therapy is based on consideration of a gene as a chemical entity with specific physical, chemical and colloidal properties. The genes that are required for gene therapy are large molecules (> 1 x 10(6) Daltons, > 100 nm diameter) with a net negative charge that prevents diffusion through biological barriers such as an intact endothelium, the plasma membrane or the nuclear membrane. New methods for gene therapy are based on increasing knowledge of the pathways by which DNA may be internalized into cells and traffic to the nucleus, pharmaceutical experience with particulate drug delivery systems, and the ability to control gene expression with recombined genetic elements. This article reviews two themes in the development of gene therapies: first, the current approaches involving the administration of cells, viruses and plasmid DNA; second, the emerging pharmaceutical approach to gene therapy based on the pharmaceutical characteristics of DNA itself and methods for advanced drug delivery.

A novel cationic lipid greatly enhances plasmid DNA delivery and expression in mouse lung

Effective gene therapy for lung tissue requires the use of efficient vehicles to deliver the gene of interest into lung cells. When plasmid DNA encoding chloramphenicol acetyltransferase (CAT) was administered intranasally to BALB/c mice without carrier lipids, CAT activity was detected in mouse lung extracts. Plasmid DNA delivered with optimally formulated commercially available transfection reagents expressed up to 10-fold more CAT activity in lung than observed with naked DNA alone. Liposome formulations consisting of (+/-)-N-(3-aminopropyl)-N,N-dimethyl-2,3-bis (dodecyloxy)-1-propanaminium bromide (GAP-DLRIE) plus the neutral colipid dioleoylphosphatidylethanolamine (DOPE) enhanced CAT expression by more than 100-fold relative to plasmid DNA alone. A single administration of GAP-DLRIE liposome-CAT DNA complexes to mouse lung elicited peak expression at days 1-4 posttransfection, followed by a gradual return to baseline by day 21 postadministration. Readministration of GAP-DLRIE liposome CAT complexes at day 21 led to another transient peak of reporter gene expression. Histological examination of lungs treated with GAP-DLRIE complexed beta-galactosidase DNA revealed that alveolar epithelial cells were the primary locus of expression and that up to 1% of all alveoli contained epithelial cells expressing the transgene.

An improved plasmid DNA expression vector for direct injection into skeletal muscle

In previous work, the direct injection of 50 micrograms of a plasmid DNA vector encoding firefly luciferase (VR1205) into murine quadriceps muscle produced an average of 6.5 ng of luciferase per muscle at 7 days postinjection. In this report, various elements of the VR1205 vector were modified to increase gene expression levels or to eliminate undesired viral sequences. Expression of the modified vectors was then compared to VR1205 using the intramuscular injection assay. In general, modifications to promoter, enhancer, and intronic sequences either decreased luciferase expression levels or had no effect. However, modifications to the polyadenylation and transcriptional termination sequences, plasmid backbone elements, and the luciferase gene itself each increased luciferase expression levels. The best-expressing vector, designated VR1255, contained a combination of these incrementally beneficial changes. A single intramuscular injection of 50 micrograms of VR1255 produced 300 ng of luciferase at 7 days postinjection, an expression level 46-fold higher than the VR1205 vector (or 22-fold higher, excluding modifications to the luciferase gene) and 154-fold higher than a commercially available luciferase expression vector. Thus, VR1255 represents an improved plasmid DNA vector that may be useful for gene therapy applications.

Expression of naked DNA in human, pig, and mouse skin

The insertion and expression of genes in the epidermis may have a variety of therapeutic uses, including the treatment of skin diseases. Here we show that when both human skin organ cultures and human skin grafts on immunocompromised mice are injected with naked DNA, the DNA is taken-up and genes are expressed in the epidermis in a manner similar to both pig skin injected in vivo and injected pig skin organ cultures. In contrast, DNA injected into mouse skin is expressed not just in the epidermis, but also in the dermis and underlying fat and muscle tissue, and is expressed at lower levels. These findings suggest that genes can be expressed in human skin, after injection of naked DNA, and indicate that pig skin is an appropriate model for the study of DNA uptake and gene expression in human skin. The organ cultures of human and pig skin may be useful in understanding how naked DNA is internalized and expressed after in vivo injections. Additionally, skin obtained from patients with skin disease may be studied as skin grafts and organ cultures to help optimize genetic approaches for the treatment of skin diseases prior to clinical trials, by determining if the injected gene can provide a therapeutic benefit.

Intraluminal water increases expression of plasmid DNA in rat lung

Effective gene delivery to specific organs is a major goal for human gene therapy. The lung's structure allows instillation of agents into the airspaces, directly adjacent to the lung epithelium. We hypothesized that the airspace instillation of hypotonic solutions would increase the permeability of the lung epithelium and increase DNA uptake. This hypothesis was tested by instilling plasmid DNA (p4241) encoding the luciferase gene in isotonic and hypotonic solutions. The highest luciferase expression in the lung was achieved after the instillation of this plasmid DNA in distilled water. Aerosolization of water just before the instillation of the plasmid DNA also enhanced the expression level of luciferase in the lung. In addition, an intralobar instillation of the plasmid DNA in water significantly increased the luciferase expression, suggesting that the instillation of the plasmid over a smaller surface area increased expression. Levels of expression could be measured for 3 days. Water increases the permeability of lung epithelial cells transiently and/or enhances gene expression and can be used to achieve gene expression in the lung airspaces for short intervals without toxicity.

Liver-directed gene transfer and application to therapy

The liver is an important and attractive target for the development of gene therapy strategies. Many genetic diseases are manifested in the liver, and both infectious and malignant diseases affect this organ. Retroviral and adenoviral vectors have been shown to infect hepatocytes with varying efficiently in vitro and in vivo. The presence of unique receptors at the cellular membrane of hepatocytes has stimulated the development of transfer strategies based on receptor targeting of vectors. The results of a first clinical trial for gene therapy in the liver based on ex vivo gene delivery has shown both the feasibility and the limits of current technology. This review discusses both existing vectors and strategies and prospective developments towards liver-directed gene therapy of genetic and malignant diseases.

Direct gene transfer of a plasmid carrying the herpes simplex virus-thymidine kinase gene (HSV-TK) in transplanted murine melanoma: in vivo study

The aim of the study was to use a virus-free system to transfer the Herpes Simplex Virus-thymidine kinase (HSV-TK) gene in mice bearing melanoma tumours. B16 F1 murine melanoma cells were injected subcutaneously. On days 11 and 14, an intratumoral injection of either naked plasmid containing the HSV-TK gene (pAG0) or pAG0-lipofectamine complexes was given. Ganciclovir (120 mg/kg/day) was given for 5 days starting on day 14. Tumour weight reduction (40-50%) was observed in treated animals versus different control groups. Moreover, histopathological analysis on tumours showed large areas of cavitary necrosis (85%) in treated groups compared to controls (10%). Using a simple and safe method, the results presented here demonstrated that virus-free mediated delivery of the HSV-TK gene is efficient in vivo in murine malignant melanoma.

RNA polymerase III promoter and terminator elements affect Alu RNA expression

Promoter elements derived from the 7SL RNA gene stimulate RNA polymerase III (Pol III) directed Alu transcription in vitro. These elements also stimulate expression of Alus transfected into 293 cells, but transcripts from these same constructs are undetectable in HeLa cells. A terminator resembling the terminator for the 7SL RNA gene has no effect on in vitro Alu template activity, but increases expression in vivo in a position independent manner. Alu transcripts generated from templates with and without this terminator have identical half-lives, indicating that this terminator stimulates expression by increasing template activity. Together, these results show that Alu expression may be regulated at multiple levels and can respond to cis-acting elements. This new found ability to express Alu transcripts by transient transfection provides an opportunity to monitor their post-transcriptional fate. Primary Alu transcripts are not extensively adenylated or deadenylated following transcription, but are short-lived compared to 118 nt scAlu RNA. In addition to Alu RNA, transfected templates encode scAlu RNA, but very high levels of Alu RNA expression does not increase the abundance of scAluRNA. ScAluRNA is not merely a transient RNA degradation product, but is instead tightly regulated by factors other than the abundance of primary transcripts.