CAR-dependent and CAR-independent pathways of adenovirus vector-mediated gene transfer and expression in human fibroblasts.
Primary fibroblasts are not efficiently transduced by subgroup C adenovirus (Ad) vectors because they express low levels of the high-affinity Coxsackie virus and adenovirus receptor (CAR). In the present study, we have used primary human dermal fibroblasts as a model to explore strategies by which Ad vectors can be designed to enter cells deficient in CAR. Using an Ad vector expressing the human CAR cDNA (AdCAR) at high multiplicity of infection, primary fibroblasts were converted from being CAR deficient to CAR sufficient. Efficiency of subsequent gene transfer by standard Ad5-based vectors and Ad5-based vectors with alterations in penton and fiber was evaluated. Marked enhancement of binding and transgene expression by standard Ad5 vectors was achieved in CAR-sufficient fibroblasts. Expression by AdDeltaRGDbetagal, an Ad5-based vector lacking the arginine-glycine-aspartate (RGD) alphaV integrin recognition site from its penton base, was achieved in CAR-sufficient, but not CAR-deficient, cells. Fiber-altered Ad5-based vectors, including (a) AdF(pK7)betagal (bearing seven lysines on the end of fiber) (b) AdF(RGD)betagal (bearing a high-affinity RGD sequence on the end of fiber), and (c) AdF9sK betagal (bearing a short fiber and Ad9 knob), demonstrated enhanced gene transfer in CAR-deficient fibroblasts, with no further enhancement in CAR-sufficient fibroblasts. Together, these observations demonstrate that CAR deficiency on Ad targets can be circumvented either by supplying CAR or by modifying the Ad fiber to bind to other cell-surface receptors. (+info)
C-myc overexpression and p53 loss cooperate to promote genomic instability.
p53 monitors genomic integrity at the G1 and G2/M cell cycle checkpoints. Cells lacking p53 may show gene amplification as well as the polyploidy or aneuploidy typical of many tumors. The pathways through which this develops, however, are not well defined. We demonstrate here that the combination of p53 inactivation and c-myc overexpression in diploid cells markedly accelerates the spontaneous development of tetraploidy. This is not seen with either N-myc or L-myc. Tetraploidy is accompanied by significantly higher levels of cyclin B and its associated cdc2 kinase activity. Mitotic spindle poisons accelerate the appearance of tetraploidy in cells either lacking functional p53 or overexpressing c-myc whereas the combination is additive. Restoration of p53 function in cells overexpressing c-myc causing rapid apoptosis, indicating that cells yet to become tetraploid have nonetheless suffered irreversible genomic and/or mitotic spindle damage. In the face of normal p53 function, such damage would either be repaired or trigger apoptotis. We propose that loss of p53 and overexpression of c-myc permits the emergence and survival of cells with increasingly severe damage and the eventual development of tetraploidy. (+info)
Telomerase activity is sufficient to allow transformed cells to escape from crisis.
The introduction of simian virus 40 large T antigen (SVLT) into human primary cells enables them to proliferate beyond their normal replicative life span. In most cases, this temporary escape from senescence eventually ends in a second proliferative block known as "crisis," during which the cells cease growing or die. Rare immortalization events in which cells escape crisis are frequently correlated with the presence of telomerase activity. We tested the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in two mortal SVLT-Rasval12-transformed human pancreatic cell lines, TRM-6 and betalox5. The telomerase catalytic subunit, hTRT, was introduced into late-passage cells via retroviral gene transfer. Telomerase activity was successfully induced in infected cells, as demonstrated by a telomerase repeat amplification protocol assay. In each of nine independent infections, telomerase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were then maintained at their new lengths for at least 20 population doublings. These results demonstrate that telomerase activity is sufficient to enable transformed cells to escape crisis and that telomere elongation in these cells occurs in a tightly regulated manner. (+info)
Stabilization of poly-L-lysine/DNA polyplexes for in vivo gene delivery to the liver.
We are developing a self-assembling non-viral in vivo gene delivery vehicle based on poly-l-lysine and plasmid DNA. We have characterized poly-l-lysines of different chain lengths for DNA condensation and strength of DNA binding. Poly-l-lysine chains >20 residues bound DNA efficiently in physiological saline, while shorter chains did not. Attachment of asialoorosomucoid to PLL increased the PLL chain length required for efficient DNA binding in saline and for efficient DNA condensation. By electron microscopy, poly-l-lysine/DNA polyplexes appeared as toroids 25-50 nm in diameter or rods 40-80 nm long; conjugation of asialoorosomucoid to the polylysine component increased the size of resulting polyplexes to 50-90 nm. In water, poly-l-lysine and asialoorosomucoid-PLL polyplexes have effective diameters of 46 and 87.6 nm, respectively. Polyplexes containing only poly-l-lysine and DNA aggregated in physiological saline at all charge ratios and aggregated at neutral charge ratios in water. Attachment of asialoorosomucoid lessened, but did not eliminate, the aggregation of PLL polyplexes, and did not result in efficient delivery of polyplexes to hepatocytes. Conjugation of polyethylene glycol to poly-l-lysine sterically stabilized resulting polyplexes at neutral charge ratios by shielding the surfaces. For efficient in vivo gene delivery, polyplexes will need to be sterically stabilized to prevent aggregation and interaction with serum components. (+info)
Deletion of multiple immediate-early genes from herpes simplex virus reduces cytotoxicity and permits long-term gene expression in neurons.
Herpes simplex virus type 1 (HSV-1) has many attractive features that suggest its utility for gene transfer to neurons. However, viral cytotoxicity and transient transgene expression limit practical applications even in the absence of viral replication. Mutant viruses deleted for the immediate early (IE) gene, ICP4, an essential transcriptional transactivator, are toxic to many cell types in culture in which only the remaining IE genes are expressed. In order to test directly the toxicity of other IE gene products in neurons and develop a mutant background capable of longterm transgene expression, we generated mutants deleted for multiple IE genes in various combinations and tested their relative cytotoxicity in 9L rat gliosarcoma cells, Vero monkey kidney cells, and primary rat cortical and dorsal root neurons in culture. Viral mutants deleted simultaneously for the IE genes encoding ICP4, ICP22 and ICP27 showed substantially reduced cytotoxicity compared with viruses deleted for ICP4 alone or ICP4 in combination with either ICP22, ICP27 or ICP47. Infection of neurons in culture with these triple IE deletion mutants substantially enhanced cell survival and permitted transgene expression for over 21 days. Such mutants may prove useful for efficient gene transfer and extended transgene expression in neurons in vitro and in vivo. (+info)
Inducible long-term gene expression in brain with adeno-associated virus gene transfer.
Recombinant adeno-associated virus (rAAV) vectors hold promise for treating a number of neurological disorders due to the ability to deliver long-term gene expression without toxicity or immune response. Critical to these endeavors will be controlled expression of the therapeutic gene in target cells. We have constructed and tested a dual cassette rAAV vector carrying a reporter gene under the control of the tetracycline-responsive system and the tetracycline transactivator. Transduction in vitro resulted in stable expression from the vector that can be suppressed 20-fold by tetracycline treatment. In vivo experiments, carried out to 6 weeks, demonstrated that vector-transduced expression is sustained until doxycycline administration upon which reporter gene expression is reduced. Moreover, the suppression of vector-driven expression can be reversed by removal of the drug. These studies demonstrate long-term regulated gene expression from rAAV vectors. This system will provide a valuable approach for controlling vector gene expression both in vitro and in vivo. (+info)
Adenoviral gene transfer into the normal and injured spinal cord: enhanced transgene stability by combined administration of temperature-sensitive virus and transient immune blockade.
This study characterized gene transfer into both normal and injured adult rat dorsal spinal cord using first (E1-/E3-) or second (E1-/E2A125/E3-, temperature-sensitive; ts) generation of replication-defective adenoviral (Ad) vectors. A novel immunosuppressive regimen aimed at blocking CD4/CD45 lymphocytic receptors was tested for improving transgene persistence. In addition, the effect of gene transfer on nociception was also evaluated. Seven days after treatment, numerous LacZ-positive cells were observed after transfection with either viral vector. By 21 days after transfection, beta-galactosidase staining was reduced and suggestive of ongoing cytopathology in both Ad-treated groups, despite the fact that the immunogenicity of LacZ/Adts appeared less when compared with that elicited by the LacZ/Ad vector. In contrast, immunosuppressed animals showed a significant (P < or = 0.05) increase in the number of LacZ-positive cells not displaying cytopathology. In these animals, a concomitant reduction in numbers of macrophages/microglia and CD4 and CD8 lymphocytes was observed. Only animals that received LacZ/Adts and immunosuppression showed transgene expression after 60 days. Similar results were observed in animals in which the L4-L5 dorsal roots were lesioned before transfection. Gene transfer into the dorsal spinal cord did not affect nociception, independent of the adenovirus vector. These results indicate that immune blockade of the CD4/CD45 lymphocytic receptors enhanced transgene stability in adult animals with normal or injured spinal cords and that persistent transgene expression in the spinal cord does not interfere with normal neural function. (+info)
Antitumor effect of allogenic fibroblasts engineered to express Fas ligand (FasL).
Fas ligand is a type II transmembrane protein which can induce apoptosis in Fas-expressing cells. Recent reports indicate that expression of FasL in transplanted cells may cause graft rejection and, on the other hand, tumor cells may lose their tumorigenicity when they are engineered to express FasL. These effects could be related to recruitment of neutrophils by FasL with activation of their cytotoxic machinery. In this study we investigated the antitumor effect of allogenic fibroblasts engineered to express FasL. Fibroblasts engineered to express FasL (PA317/FasL) did not exert toxic effects on transformed liver cell line (BNL) or colon cancer cell line (CT26) in vitro, but they could abrogate their tumorigenicity in vivo. Histological examination of the site of implantation of BNL cells mixed with PA317/FasL revealed massive infiltration of polymorphonuclear neutrophils and mononuclear cells. A specific immune protective effect was observed in animals primed with a mixture of BNL or CT26 and PA317/FasL cells. Rechallenge with tumor cells 14 or 100 days after priming resulted in protection of 100 or 50% of animals, respectively. This protective effect was due to CD8+ cells since depletion of CD8+ led to tumor formation. In addition, treatment of pre-established BNL tumors with a subcutaneous injection of BNL and PA317/FasL cell mixture at a distant site caused significant inhibition of tumor growth. These data demonstrate that allogenic cells engineered with FasL are able to abolish tumor growth and induce specific protective immunity when they are mixed with neoplastic cells. (+info)