Comparative study and identification of potent eukaryotic transcriptional repressors in gene switch systems

Regulable Transgene Expression in Dorsal Root Ganglia of a Replication-Defective Herpes Simplex Virus Type 1 Vector by Means of Sciatic Nerve Injection

BACKGROUND

Targeted and controllable gene delivery to neurons is essential to efforts to facilitate peripheral nerve regeneration. The authors investigated both the in vitro and in vivo expression profiles of a tetracycline-controlled, replication-defective, herpes simplex virus type 1-based vector.

METHODS

Mouse primary dorsal root ganglia cells were infected with QR9TO-LacZ in the absence or presence of tetracycline. LacZ gene expression was examined. It was also injected into sciatic nerves in CD-1 mice fed with and without tetracycline. LacZ expression in the upstream dorsal root ganglia was examined.

RESULTS

Following inoculation with QR9TO-LacZ, approximately 40 percent of the cultured primary dorsal root ganglia cells exhibited strong LacZ activity in the presence of tetracycline at 48 and 72 hours, whereas little was detected in those in the absence of tetracycline. Quantitative analysis revealed that the β-galactosidase activity within cells exposed to tetracycline increased 181-fold at 48 hours (p < 0.001) and 47-fold at 72 hours after infection (p < 0.05) compared with those without tetracycline. However, this LacZ transgene activity in the presence of tetracycline tapered off to less than sevenfold over baseline 168 hours after infection (p < 0.05). Furthermore, successful uptake of this replication-defective viral vector was evident in upstream dorsal root ganglia after sciatic nerve injection in mice. In addition, its expression profile was similar to that in vitro, as strong β-galactosidase activity was evident only in mice fed with a doxycycline-containing diet, and it tapered off by 168 hours.

CONCLUSION

The replication-defective herpes simplex virus type 1-based vector, which provides tightly regulated transgene expression in dorsal root ganglia by means of peripheral nerve injection, represents an appealing approach to improve peripheral nerve regeneration.

MAR-mediated integration of plasmid vectors for in vivo gene transfer and regulation

BACKGROUND

The in vivo transfer of naked plasmid DNA into organs such as muscles is commonly used to assess the expression of prophylactic or therapeutic genes in animal disease models.

RESULTS

In this study, we devised vectors allowing a tight regulation of transgene expression in mice from such non-viral vectors using a doxycycline-controlled network of activator and repressor proteins. Using these vectors, we demonstrate proper physiological response as consequence of the induced expression of two therapeutically relevant proteins, namely erythropoietin and utrophin. Kinetic studies showed that the induction of transgene expression was only transient, unless epigenetic regulatory elements termed Matrix Attachment Regions, or MAR, were inserted upstream of the regulated promoters. Using episomal plasmid rescue and quantitative PCR assays, we observed that similar amounts of plasmids remained in muscles after electrotransfer with or without MAR elements, but that a significant portion had integrated into the muscle fiber chromosomes. Interestingly, the MAR elements were found to promote plasmid genomic integration but to oppose silencing effects in vivo, thereby mediating long-term expression.

CONCLUSIONS

This study thus elucidates some of the determinants of transient or sustained expression from the use of non-viral regulated vectors in vivo.

Recent advances in mammalian synthetic biology-design of synthetic transgene control networks

Capitalizing on an era of functional genomic research, systems biology offers a systematic quantitative analysis of existing biological systems thereby providing the molecular inventory of biological parts that are currently being used for rational synthesis and engineering of complex biological systems with novel and potentially useful functions-an emerging discipline known as synthetic biology. During the past decade synthetic biology has rapidly developed from simple control devices fine-tuning the activity of single genes and proteins to multi-gene/protein-based transcription and signaling networks providing new insight into global control and molecular reaction dynamics, thereby enabling the design of novel drug-synthesis pathways as well as genetic devices with unmatched biological functions. While pioneering synthetic devices have first been designed as test, toy, and teaser systems for use in prokaryotes and lower eukaryotes, first examples of a systematic assembly of synthetic gene networks in mammalian cells has sketched the full potential of synthetic biology: foster novel therapeutic opportunities in gene and cell-based therapies. Here we provide a concise overview on the latest advances in mammalian synthetic biology.

Random screening for dominant-negative mutants of the cytomegalovirus nuclear egress protein M50

Inactivation of gene products by dominant-negative (DN) mutants is a powerful tool to assign functions to proteins. Here, we present a two-step procedure to establish a random screen for DN alleles, using the essential murine cytomegalovirus gene M50 as an example. First, loss-of-function mutants from a linker-scanning library were tested for inhibition of virus reconstitution with the help of FLP-mediated ectopic insertion of the mutants into the viral genome. Second, DN candidates were confirmed by conditional expression of the inhibitory proteins in the virus context. This allowed the quantification of the inhibitory effect, the identification of the morphogenesis block, and the construction of DN mutants with improved activity. Based on these observations a DN mutant of the homologous gene (UL50) in human cytomegalovirus was predicted and constructed. Our data suggest that a proline-rich sequence motif in the variable region of M50/UL50 represents a new functional site which is essential for nuclear egress of cytomegalovirus capsids.

A new inducible adenoviral expression system that responds to inflammatory stimuli in vivo

BACKGROUND

Gene transfer using inducible promoters, which control expression of transgenic proteins in response to physiological conditions, may have significant advantages. In this study, we tried to achieve an inducible adenoviral expression system for physiologically responsive gene therapy of autoimmune or inflammatory diseases.

METHODS

A luciferase reporter vector with a hybrid promoter containing the human IL-1beta enhancer region (-3690 to - 2720) and the human CIITA promoter IV (-399 to + 2) was constructed. A replication-deficient adenovirus was engineered with luciferase controlled by the IL1beta/CIITApIV promoter (Ad-IL1beta/CIITApIV-Luc). The reporter vector or adenovirus was transfected to C57Bl/6 myeloid dendritic cells (DCs), RAW264.7, and Hep G2 to study the in vitro characteristics of this hybrid promoter. An inflammation model was prepared by injecting lipopolysaccharide (LPS) into Balb/c mice intraperitoneally (i.p.), and infected with Ad-IL1beta/CIITApIV-Luc or Ad-CMV-Luc to study the in vivo characteristics of the IL1beta/CIITApIV promoter.

RESULTS

The IL1beta/CIITApIV hybrid promoter has pronounced promoter activity, broad-range responsiveness to cytokines or LPS, and can be rechallenged after first induction. In the inflammation model, IL1beta/CIITApIV could drive hepatic luciferase expression increasedly rapidly after LPS challenge and in a LPS dose-dependent manner.

CONCLUSIONS

Using the IL1beta/CIITApIV hybrid promoter in gene transfer vectors may make it possible to produce transgenic proteins in vivo in direct relationship with the intensity and duration of an individual's status. By providing endogenously controlled production of transgenic proteins, this approach might limit the severity of autoimmune or inflammatory response without interfering with the beneficial components of host defense and immunity.

Conditional cytomegalovirus replication in vitro and in vivo

We have established a conditional gene expression system for cytomegalovirus which allows regulation of genes independently from the viral replication program. Due to the combination of all elements required for regulated expression in the same viral genome, conditional viruses can be studied in different cell lines in vitro and in the natural host in vivo. The combination of a self-sufficient tetracycline-regulated expression cassette and Flp recombinase-mediated insertion into the viral genome allowed fast construction of recombinant murine cytomegaloviruses carrying different conditional genes. The regulation of two reporter genes, the essential viral M50 gene and a dominant-negative mutant gene (m48.2) encoding the small capsid protein, was analyzed in more detail. In vitro, viral growth was regulated by the conditional expression of M50 by 3 orders of magnitude and up to a millionfold when the dominant-negative small capsid protein mutant was used. In vivo, viral growth of the dominant-negative mutant was reduced to detection limits in response to the presence of doxycycline in the organs of mice. We believe that this conditional expression system is applicable to genetic studies of large DNA viruses in general.

An inflammation-inducible adenoviral expression system for local treatment of the arthritic joint

To achieve a disease-regulated transgene expression for physiologically responsive gene therapy of arthritis, a hybrid promoter was constructed. The human IL-1 beta enhancer region (-3690 to -2720) upstream of the human IL-6 promoter region (-163 to +12) was essential in mounting a robust response in HIG-82 synovial fibroblasts and in RAW 264,7 macrophages. A replication-deficient adenovirus was engineered with luciferase (Luc) controlled by the IL-1/IL-6 promoter (Ad5.IL-1/IL-6-Luc). LPS caused a 23- and 4.6-fold induction of Luc. activity in RAW cells infected with Ad5.IL-1/IL-6-Luc or the conventional Ad5.CMV-Luc construct, respectively. Next, adenoviruses (10(6) ffu) were injected into the knees of C57Bl/6 mice. An intra-articular injection of zymosan, 3 days after Ad5.IL-1/IL-6-Luc, increased Luc. activity by 39-fold but had no effect in the Ad5.CMV-Luc joints. The constitutive CMV promoter was rapidly silenced and could not be reactivated in vivo. In contrast, the IL-1/IL-6 promoter could be reactivated by Streptococcal cell wall (SCW)-induced arthritis up to 21 days after infection. Next the IL-1/IL-6 promoter was compared to the C3-Tat/HIV-LTR two-component system in wild-type, IL-6(-/-) and IL-1(-/-) gene knockout mice. Both systems responded well to LPS-, zymosan- and SCW-induced arthritis. However, the basal activity of the IL-1/IL-6 promoter was lower and IL-6 independent. This study showed that the IL-1/IL-6 promoter is feasible to achieve disease-regulated transgene expression for treatment of arthritis.

Identification and characterization of NIF3L1 BP1, a novel cytoplasmic interaction partner of the NIF3L1 protein

The NIF3L1 protein is strongly conserved during evolution from bacteria to mammals and recently its function in neuronal differentiation has been demonstrated. In the present study we identified novel binding partners of human NIF3L1 by screening a HeLa cDNA-library using the yeast two-hybrid system. We could show that the NIF3L1 protein is interacting with itself and with the NIF3L1 binding protein 1 (NIF3L1 BP1), a novel protein of 23.67kDa bearing a putative leucine zipper domain. Furthermore, both interactions were confirmed using the mammalian two-hybrid system. Deletion analyses clearly demonstrated that a C-terminal region of 100 amino acids of the NIF3L1 BP1 is sufficient for the interaction with NIF3L1. The NIF3L1 BP1 is ubiquitously expressed and cotransfection experiments revealed that NIF3L1 and NIF3L1 BP1 interact in the cytoplasm of human LNCaP cells. This study provides novel insights into the cellular function of the NIF3L1 protein.