The tetracycline-responsive promoter contains functional interferon-inducible response elements

Development of a new recombineering system for Agrobacterium species

Discovery of new and efficient genetic engineering technologies for Agrobacterium will broaden the capacity for fundamental research on this genus and for its utilization as a transgenic vehicle. In this study, we aim to develop an efficient recombineering system for Agrobacterium species. We examined isolates of Agrobacterium and the closely related genus Rhizobium to identify pairs of ET-like recombinases that would aid in the recombineering of Agrobacterium species. Four pairs of ET-like recombinases, named RecETh1h2h3h4_AGROB6, RecETh1h2P3_RHI597, RecET_RHI145, and RecETh_RHI483, were identified in Agrobacterium tumefaciens str. B6, Rhizobium leguminosarum bv. trifolii WSM597, Rhizobium sp. LC145, and Rhizobium sp. Root483D2, respectively. Eight more candidate recombineering systems were generated by combining the new ET-like recombinases with Redγ or Pluγ. The PluγET_RHI145 system, RecETh1h2h3h4_AGROB6 system, and PluγETh_RHI483 system were determined to be the most efficient recombineering system for the type strains A. tumefaciens C58, A. tumefaciens EHA105, and R. rhizogenes NBCR13257, respectively. The utility of these systems was demonstrated by knocking out the istB and istA fusion gene in C58, the celI gene in EHA105, and the 3'-5' exonuclease gene and endoglucanase gene in NBCR13257. Our work provides an effective genetic manipulation strategy for Agrobacterium species. IMPORTANCE Agrobacterium is a powerful transgenic vehicle for the genetic manipulation of numerous plant and fungal species and even animal cells. In addition to improving the utility of Agrobacterium as a transgenic vehicle, genetic engineering tools are important for revealing crucial components that are functionally involved in T-DNA translocation events. This work developed an efficient and versatile recombineering system for Agrobacterium. Successful genome modification of Agrobacterium strains revealed that this new recombineering system could be used for the genetic engineering of Agrobacterium.

Methylation profile of hepatitis B virus is not influenced by interferon α in human liver cancer cells

Interferon (IFN) α is used for the treatment of chronic hepatitis B virus (HBV) infection, but the molecular mechanisms underlying its antiviral effect have not been fully elucidated. Epigenetic modifications regulate the transcriptional activity of covalently closed circular DNA (cccDNA) in cells with chronic HBV infection. IFN‑α has been shown to modify cccDNA‑bound histones, but it is not known whether the anti‑HBV effect of IFN‑α involves methylation of cccDNA. The present study aimed to determine whether IFN‑α induced methylation of HBV cccDNA in a cell‑based model in which HepG2 cells were directly infected with wild‑type HBV virions. Methylation status of HBV cccDNA was assessed using global DNA methylation ELISA assay, methylation‑specific PCR and bisulfite sequencing. IFN‑α suppressed HBV DNA and RNA transcripts, but methylation profiles were similar between the control and IFN‑α treated groups. Chromatin immunoprecipitation results revealed binding of DNA methyltransferases (DNMT) 3A and DNMT3B to HBV cccDNA and treatment with IFN‑α suppressed the recruitment of DNMT3B to cccDNA. Taken together, these results suggest that IFN‑α does not induce methylation of HBV cccDNA. Therefore, it was concluded that methylation is unlikely to contribute to the anti‑HBV effect of IFN‑α in HepG2 cells, and that alternative mechanisms need to be sought to enhance cccDNA methylation as a novel therapy against HBV.

A Green-Light-Responsive System for the Control of Transgene Expression in Mammalian and Plant Cells

The ever-increasing complexity of synthetic gene networks and applications of synthetic biology requires precise and orthogonal gene expression systems. Of particular interest are systems responsive to light as they enable the control of gene expression dynamics with unprecedented resolution in space and time. While broadly used in mammalian backgrounds, however, optogenetic approaches in plant cells are still limited due to interference of the activating light with endogenous photoreceptors. Here, we describe the development of the first synthetic light-responsive system for the targeted control of gene expression in mammalian and plant cells that responds to the green range of the light spectrum in which plant photoreceptors have minimal activity. We first engineered a system based on the light-sensitive bacterial transcription factor CarH and its cognate DNA operator sequence CarO from Thermus thermophilus to control gene expression in mammalian cells. The system was functional in various mammalian cell lines, showing high induction (up to 350-fold) along with low leakiness, as well as high reversibility. We quantitatively described the systems characteristics by the development and experimental validation of a mathematical model. Finally, we transferred the system into A. thaliana protoplasts and demonstrated gene repression in response to green light. We expect that this system will provide new opportunities in applications based on synthetic gene networks and will open up perspectives for optogenetic studies in mammalian and plant cells.

Discovery of recombinases enables genome mining of cryptic biosynthetic gene clusters in Burkholderiales species

Natural products biosynthesized by cryptic gene clusters represent a largely untapped source for drug discovery. However, mining of these products by promoter engineering is restricted by the lack of streamlined genetic tools, especially in nonmodel biosynthetic gene cluster (BGC)-rich bacteria. Here, we describe the discovery of a pair of bacteriophage recombinases and application of recombinase-assisted promoter engineering to rapidly identify and activate several cryptic biosynthetic gene clusters in two Burkholderiales strains that currently lack effective genetic tools. Construction of an efficient genome engineering platform in a natural product producer expedites mining of cryptic BGCs in their native backgrounds, and host melioration for yield or structure optimization. This strategy enables potentially scalable discovery of novel metabolites with intriguing bioactivities from many other bacteria.

Bacterial genomes encode numerous cryptic biosynthetic gene clusters (BGCs) that represent a largely untapped source of drugs or pesticides. Mining of the cryptic products is limited by the unavailability of streamlined genetic tools in native producers. Precise genome engineering using bacteriophage recombinases is particularly useful for genome mining. However, recombinases are usually host-specific. The genome-guided discovery of novel recombinases and their transient expression could boost cryptic BGC mining. Herein, we reported a genetic system employing Red recombinases from Burkholderiales strain DSM 7029 for efficient genome engineering in several Burkholderiales species that currently lack effective genetic tools. Using specialized recombinases-assisted in situ insertion of functional promoters, we successfully mined five cryptic nonribosomal peptide synthetase/polyketide synthase BGCs, two of which were silent. Two classes of lipopeptides, glidopeptins and rhizomides, were identified through extensive spectroscopic characterization. This recombinase expression strategy offers utility within other bacteria species, allowing bioprospecting for potentially scalable discovery of novel metabolites with attractive bioactivities.

GM-CSF overexpression after influenza a virus infection prevents mortality and moderates M1-like airway monocyte/macrophage polarization

BACKGROUND

Influenza A viruses cause life-threatening pneumonia and lung injury in the lower respiratory tract. Application of high GM-CSF levels prior to infection has been shown to reduce morbidity and mortality from pathogenic influenza infection in mice, but the mechanisms of protection and treatment efficacy have not been established.

METHODS

Mice were infected intranasally with influenza A virus (PR8 strain). Supra-physiologic levels of GM-CSF were induced in the airways using the double transgenic GM-CSF (DTGM) or littermate control mice starting on 3 days post-infection (dpi). Assessment of respiratory mechanical parameters was performed using the flexiVent rodent ventilator. RNA sequence analysis was performed on FACS-sorted airway macrophage subsets at 8 dpi.

RESULTS

Supra-physiologic levels of GM-CSF conferred a survival benefit, arrested the deterioration of lung mechanics, and reduced the abundance of protein exudates in bronchoalveolar (BAL) fluid to near baseline levels. Transcriptome analysis, and subsequent validation ELISA assays, revealed that excess GM-CSF re-directs macrophages from an "M1-like" to a more "M2-like" activation state as revealed by alterations in the ratios of CXCL9 and CCL17 in BAL fluid, respectively. Ingenuity pathway analysis predicted that GM-CSF surplus during IAV infection elicits expression of anti-inflammatory mediators and moderates M1 macrophage pro-inflammatory signaling by Type II interferon (IFN-γ).

CONCLUSIONS

Our data indicate that application of high levels of GM-CSF in the lung after influenza A virus infection alters pathogenic "M1-like" macrophage inflammation. These results indicate a possible therapeutic strategy for respiratory virus-associated pneumonia and acute lung injury.

The Tetracycline Responsive System

Constitutive gene expression is not always the appropriate expression system because the unphysiological levels of expressed protein could be detrimental in studies examining biological roles of proteins, or continued expression may be unnecessary after therapeutic effects have been achieved in gene therapy . We have utilized pharmacologically regulated gene expression systems to achieve fine control of gene expression levels which facilitate research in basic biology and translates to use in experimental gene therapy studies. In this chapter, we outline the application of a tightly controlled tetracycline responsive gene expression system.

Single vector non-leaky gene expression system for Drosophila melanogaster

An ideal transgenic gene expression system is inducible, non-leaky, and well tolerated by the target organism. While the former has been satisfactorily realized, leakiness and heavy physiological burden imposed by the existing systems are still prominent hurdles in their successful implementation. Here we describe a new system for non-leaky expression of transgenes in Drosophila. PRExpress is based on a single transgenic construct built from endogenous components, the inducible hsp70 promoter and a multimerized copy of a Polycomb response element (PRE) controlled by epigenetic chromatin regulators of the Polycomb group. We show that this system is non-leaky, rapidly and strongly inducible, and reversible. To make the application of PRExpress user-friendly, we deliver the construct via site-specific integration.

Applying an Inducible Expression System to Study Interference of Bacterial Virulence Factors with Intracellular Signaling

The technique presented here allows one to analyze at which step a target protein, or alternatively a small molecule, interacts with the components of a signaling pathway. The method is based, on the one hand, on the inducible expression of a specific protein to initiate a signaling event at a defined and predetermined step in the selected signaling cascade. Concomitant expression, on the other hand, of the gene of interest then allows the investigator to evaluate if the activity of the expressed target protein is located upstream or downstream of the initiated signaling event, depending on the readout of the signaling pathway that is obtained. Here, the apoptotic cascade was selected as a defined signaling pathway to demonstrate protocol functionality. Pathogenic bacteria, such as Coxiella burnetii, translocate effector proteins that interfere with host cell death induction in the host cell to ensure bacterial survival in the cell and to promote their dissemination in the organism. The C. burnetii effector protein CaeB effectively inhibits host cell death after induction of apoptosis with UV-light or with staurosporine. To narrow down at which step CaeB interferes with the propagation of the apoptotic signal, selected proteins with well-characterized pro-apoptotic activity were expressed transiently in a doxycycline-inducible manner. If CaeB acts upstream of these proteins, apoptosis will proceed unhindered. If CaeB acts downstream, cell death will be inhibited. The test proteins selected were Bax, which acts at the level of the mitochondria, and caspase 3, which is the major executioner protease. CaeB interferes with cell death induced by Bax expression, but not by caspase 3 expression. CaeB, thus, interacts with the apoptotic cascade between these two proteins.

MxA inhibits hepatitis B virus replication by interaction with hepatitis B core antigen

Human MxA, an interferon-inducible cytoplasmic dynamin-like GTPase, possesses antiviral activity against multiple RNA viruses. Recently, MxA has also been demonstrated to have activity against the hepatitis B virus (HBV), a well-known DNA virus responsible for acute and chronic liver disease in humans. We investigated the molecular mechanism for the anti-HBV activity of MxA. Our results demonstrated that in HepG2.2.15 cells, MxA GTPase independently suppressed the production of hepatitis B surface antigen and HBV DNA without changing the level of hepatitis B core antigen (HBcAg) and the distribution of HBV mRNA. MxA significantly reduced the level of the encapsidated pregenomic RNA. Through its central interactive domain, MxA interacted with HBcAg, causing accumulation of the proteins in perinuclear compartments. MxA-HBcAg interaction significantly affected the dynamics of HBcAg by immobilizing HBcAg in the perinuclear structures.

CONCLUSION

MxA displays antiviral activity against HBV involving a mechanism of MxA-HBcAg interaction that may interfere with core particle formation.

Stem cell-based therapies for bone repair

This article provides an overview of the cellular and molecular events involved in bone repair and the current approaches to using stem cells as an adjunct to this process. The article emphasizes the key role of osteoprogenitor cells in the formation of bone and where the clinical applications of current research may lend themselves to large animal orthopaedics. The processes involved in osteogenic differentiation are presented and strategies for bone formation, including induction by osteogenic factors, bioscaffolds, and gene therapy, are reviewed.

Anti-arthritic effects of FasL gene transferred intra-articularly by an inducible lentiviral vector containing improved tet-on system

The objective of this study is to construct and identify an inducible lentiviral vector containing improved tet-on system and FasL gene and observe its effects on pristane-induced arthritis (PIA). FasL gene was amplified from the spleen of Lewis rats by RT-PCR. The tet-on system was improved with insertion of a chicken chromatin insulator (cHS4) element and an rtTA-dependent, tet-responsive element containing modifications of the tetO sequence (TRE-tight1). Pro-apoptosis effect of the vector pTREFasLcHS4V16 on synovial cells was evaluated by flow cytometer in vitro. Anti-arthritis effects of the vector on PIA after intra-articular injection were observed by clinical evaluation and joint histology. Cytokines in synovial tissue were measured by ELISA. The recombinant inducible lentiviral vector pTREFasLcHS4V16 was successfully constructed. The expression response and the pro-apoptosis effects of the vector were doxycycline dose-dependent. The vector injected intra-articularly attenuated the severity of PIA and decreased the level of cytokines in inflamed joints. pTREFasLcHS4V16 with an improved tet-on system can precisely regulate the expression of FasL gene and apoptosis. Anti-arthritis effects were observed after intra-articular injection of the inducible vector.

Adjusting transgene expression levels in lymphocytes with a set of inducible promoters

BACKGROUND

Inducible gene expression systems are powerful research tools and could be of clinical value in the future, with lymphocytes being likely prime application targets. However, currently available regulatable promoters exhibit variation in their efficiency in a cell line-dependent-manner and are notorious for basal leakiness or poor inducibility. Data concerning the regulatory properties of different inducible promoters are scarce for lymphocytes. In the present study, we report a comprehensive analysis of how various inducible promoters perform and how their combination with a transsilencer and a reverse transactivator can result in optimally controlled gene expression in T-cells.

METHODS

The performance of the tetracycline-regulated (Tet)-inducible promoters Tet-responsive element (TRE), mouse mammary tumor virus (MMTV)/TRE, TREtight and second generation TRE (SG/TRE) was compared in several B-cell lines and in Jurkat T-cells using transient transfections in combination with Tet-On. To monitor transgene expression in a Jurkat cell line containing a transsilencer and a reverse transactivator, expression cassettes encoding enhanced green fluorescent protein, CD123 or a constitutively active, cytotoxic caspase-3 were flanked with insulators and stably integrated. The performance of TREtight and SG/TRE was furthermore analysed in transiently transfected primary CD4(+) human T-cells.

RESULTS

The promoters exhibit greatly diverging characteristics. MMTV/TRE permits moderate, TRE and TREtight permits intermediate and SG/TRE permits very high expression levels. TRE and SG/TRE are leaky, whereas MMTV/TRE and TREtight provide stringent expression control. Tetracycline derivatives add flexibility to transgene expression by introducing intermediate expression levels.

CONCLUSIONS

The different expression profiles of the promoters increase the flexibility to adjust transgene expression levels. The promoters provide an additional option to optimize system performance for many applications.

Inhibition of hepatitis B virus replication by MyD88 involves accelerated degradation of pregenomic RNA and nuclear retention of pre-S/S RNAs

Myeloid differentiation primary response protein 88 (MyD88), which can be induced by alpha interferon (IFN-alpha), has an antiviral activity against the hepatitis B virus (HBV). The mechanism of this antiviral activity remains poorly understood. Here, we report that MyD88 inhibited HBV replication in HepG2.2.15 cells and in a mouse model. The knockdown of MyD88 expression weakened the IFN-alpha-induced inhibition of HBV replication. Furthermore, MyD88 posttranscriptionally reduced the levels of viral RNA. Remarkably, MyD88 accelerated the decay of viral pregenomic RNA in the cytoplasm. Mapping analysis showed that the RNA sequence located in the 5'-proximal region of the pregenomic RNA was critical for the decay. In addition, MyD88 inhibited the nuclear export of pre-S/S RNAs via the posttranscriptional regulatory element (PRE). The retained pre-S/S RNAs were shown to degrade in the nucleus. Finally, we found that MyD88 inhibited the expression of polypyrimidine tract-binding protein (PTB), a key nuclear export factor for PRE-containing RNA. Taken together, our results define a novel antiviral mechanism against HBV mediated by MyD88.

Hepatitis B and C virus coinfection: a novel model system reveals the absence of direct viral interference

Coinfection with hepatitis B virus (HBV) and hepatitis C virus (HCV) has been associated with severe liver disease and frequent progression to cirrhosis and hepatocellular carcinoma. Clinical evidence suggests reciprocal replicative suppression of the two viruses, or viral interference. However, interactions between HBV and HCV have been difficult to study due to the lack of appropriate model systems. We have established a novel model system to investigate interactions between HBV and HCV. Stable Huh-7 cell lines inducibly replicating HBV were transfected with selectable HCV replicons or infected with cell culture-derived HCV. In this system, both viruses were found to replicate in the same cell without overt interference. Specific inhibition of one virus did not affect the replication and gene expression of the other. Furthermore, cells harboring replicating HBV could be infected with cell culture-derived HCV, arguing against superinfection exclusion. Finally, cells harboring replicating HBV supported efficient production of infectious HCV.

CONCLUSION

HBV and HCV can replicate in the same cell without evidence for direct interference in vitro. Therefore, the viral interference observed in coinfected patients is probably due to indirect mechanisms mediated by innate and/or adaptive host immune responses. These findings provide new insights into the pathogenesis of HBV-HCV coinfection and may contribute to its clinical management in the future.

Unexpected expression pattern of tetracycline-regulated transgenes in mice

In generating a conditional transgenic murine model based on a tetracycline-regulated system, we obtained unexpected patterns of expression due to the transcriptional inactivity of the tet-responder promoter. Here we show strong cell-type-restricted expression that was variegated to an extent determined by the number of responder transgene copies integrated into the host genome.

Rac1 GTPase is activated by hepatitis B virus replication--involvement of HBX

Hepatitis B virus (HBV) is a causative agent for liver diseases including hepatocellular carcinoma. Understanding its interactions with cellular proteins is critical in the elucidation of the mechanisms of disease progression. Using a cell-based HBV replication system, we showed that HBV replication in HepG2 cells resulted in a cellular morphological changes displaying membrane rufflings and lamellipodia like structures reminiscent of cells expressing constitutively activated Rac1. We also showed that activated Rac1 resulted in increased viral replication. HBV replication specifically activated wild type Rac1, but not Cdc42. The Rac1 activation by HBV replication also resulted in the phosphorylation of ERK1/2 and AKT, the downstream targets of Rac1 signaling cascade. The smallest HBV viral protein, HBX, was able to activate the endogenous Rac1 and induce membrane ruffling when transfected into cells. Significantly, HBX was found to directly interact with a Rac1 nucleotide exchange factor (betaPIX) through a SH3 binding motif. Taken together, we have shown the interaction of HBV with the Rho GTPase, affecting cell morphology through the Rac1 activation pathway. HBV may possibly make use of an activated Rac1 signaling pathway for increased replication and resultant metastatic effects.

Anticancer activity of oncolytic adenovirus vector armed with IFN-alpha and ADP is enhanced by pharmacologically controlled expression of TRAIL

We have previously described oncolytic adenovirus (Ad) vectors KD3 and KD3-interferon (IFN) that were rendered cancer-specific by mutations in the E1A region of Ad; these mutations abolish binding of E1A proteins to p300/CBP and pRB. The antitumor activity of the vectors was enhanced by overexpression of the Adenovirus Death Protein (ADP, E3-11.6K) and by replication-linked expression of IFN-alpha. We hypothesized that the anticancer efficacy of the KD3-IFN vector could be further improved by expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). E1-deleted Ad vectors were constructed carrying reporter genes for enhanced green fluorescent protein or secreted placental alkaline phosphatase (SEAP) and a therapeutic gene for TRAIL under control of the TetON system. Expression of the genes was increased in the presence of a helper virus and the inducer doxycycline such that up to 231-fold activation of expression for the TetON-SEAP vector was obtained. Coinfection with TetON-TRAIL augmented oncolytic activity of KD3 and KD3-IFN in vitro. Induction of TRAIL expression did not reduce the yield of progeny virus. Combination of TetON-TRAIL and KD3-IFN produced superior antitumor activity in vivo as compared with either vector alone demonstrating the efficacy of a four-pronged cancer gene therapy approach, which includes Ad oncolysis, ADP overexpression, IFN-alpha-mediated immunotherapy, and pharmacologically controlled TRAIL activity.

Vitamin H-regulated transgene expression in mammalian cells

Although adjustable transgene expression systems are considered essential for future therapeutic and biopharmaceutical manufacturing applications, the currently available transcription control modalities all require side-effect-prone inducers such as immunosupressants, hormones and antibiotics for fine-tuning. We have designed a novel mammalian transcription-control system, which is reversibly fine-tuned by non-toxic vitamin H (also referred to as biotin). Ligation of vitamin H, by engineered Escherichia coli biotin ligase (BirA), to a synthetic biotinylation signal fused to the tetracycline-dependent transactivator (tTA), enables heterodimerization of tTA to a streptavidin-linked transrepressor domain (KRAB), thereby abolishing tTA-mediated transactivation of specific target promoters. As heterodimerization of tTA to KRAB is ultimately conditional upon the presence of vitamin H, the system is vitamin H responsive. Transgenic Chinese hamster ovary cells, engineered for vitamin H-responsive gene expression, showed high-level, adjustable and reversible production of a human model glycoprotein in bench-scale culture systems, bioreactor-based biopharmaceutical manufacturing scenarios, and after implantation into mice. The vitamin H-responsive expression systems showed unique band pass filter-like regulation features characterized by high-level expression at low (0–2 nM biotin), maximum repression at intermediate (100–1000 nM biotin), and high-level expression at increased (>100 000 nM biotin) biotin concentrations. Sequential ON-to-OFF-to-ON, ON-to-OFF and OFF-to-ON expression profiles with graded expression transitions can all be achieved by simply increasing the level of a single inducer molecule without exchanging the culture medium. These novel expression characteristics mediated by an FDA-licensed inducer may foster advances in therapeutic cell engineering and manufacturing of difficult-to-produce protein therapeutics.

Review: gene- and stem cell-based therapeutics for bone regeneration and repair

Many clinical conditions require regeneration or implantation of bone. This is one focus shared by neurosurgery and orthopedics. Current therapeutic options (bone grafting and protein-based therapy) do not provide satisfying solutions to the problem of massive bone defects. In the past few years, gene- and stem cell-based therapy has been extensively studied to achieve a viable alternative to current solutions offered by modern medicine for bone-loss repair. The use of adult stem cells for bone regeneration has gained much focus. This unique population of multipotential cells has been isolated from various sources, including bone marrow, adipose, and muscle tissues. Genetic engineering of adult stem cells with potent osteogenic genes has led to fracture repair and rapid bone formation in vivo. It is hypothesized that these genetically modified cells exert both an autocrine and a paracrine effects on host stem cells, leading to an enhanced osteogenic effect. The use of direct gene delivery has also shown much promise for in vivo bone repair. Several viral and nonviral methods have been used to achieve substantial bone tissue formation in various sites in animal models. To advance these platforms to the clinical setting, it will be mandatory to overcome specific hurdles, such as control over transgene expression, viral vector toxicity, and prolonged culture periods of therapeutic stem cells. This review covers a prospect of cell and gene therapy for bone repair as well as some very recent advancements in stem cell isolation, genetic engineering, and exogenous control of transgene expression.

Inducibility of doxycycline-regulated gene in neural and neuroendocrine cells strongly depends on the appropriate choice of a tetracycline-responsive promoter

Elucidation of the mechanisms underlying specific receptor activation of neural and neuroendocrine cells will require the establishment of cellular systems that permit the regulation of the expression of the protein of interest. In a tetracycline (Tet)-regulated system, the gene encoding the protein of interest is under the control of a Tet promoter and its transcription is activated in the presence of doxycycline (Dox) by the Tet transactivator rtTA. Acceptable inducibility of the gene's expression requires a high level of its expression in the presence of Dox and a minimal basal expression in the absence of Dox. Two Tet promoters are compared here, the original PhCMV*-1 and the second-generation Ptight, with respect to the inducibility of the gene of interest in neuroendocrine and neural cells genetically engineered to express rtTA, namely PC12-Tet-On cells and MB-G-18 cells (mouse brain-derived cells with the phenotype of neuron-restricted precursors). This study demonstrates that the use of Ptight provided a much higher Dox-induced maximal expression in both cell lines, while the basal activities of the two Tet promoters were at similar levels. The additional use of the Tet-controlled silencer (tTS) caused almost complete abrogation of the leakiness of the Ptight promoter and an increase in the inducibility of the regulated gene, but the maximal levels of gene expression driven in the presence of Dox were also markedly reduced.

Stringent and reproducible tetracycline-regulated transgene expression by site-specific insertion at chromosomal loci with pre-characterised induction characteristics

Background

The ability to regulate transgene expression has many applications, mostly concerning the analysis of gene function. Desirable induction characteristics, such as low un-induced expression, high induced expression and limited cellular heterogeneity, can be seriously impaired by chromosomal position effects at the site of transgene integration. Many clones may therefore need to be screened before one with optimal induction characteristics is identified. Furthermore, such screens must be repeated for each new transgene investigated, and comparisons between clones with different transgenes is complicated by their different integration sites.

Results

To circumvent these problems we have developed a "screen and insert" strategy in which clones carrying a transgene for a fluorescent reporter are first screened for those with optimal induction characteristics. Site-specific recombination (SSR) is then be used repeatedly to insert any new transgene at the reporter transgene locus of such clones so that optimal induction characteristics are conferred upon it. Here we have tested in a human fibrosarcoma cell line (HT1080) two of many possible implementations of this approach. Clones (e.g. Rht14-10) in which a GFP reporter gene is very stringently regulated by the tetracycline (tet) transactivator (tTA) protein were first identified flow-cytometrically. Transgenes encoding luciferase, I-SceI endonuclease or Rad52 were then inserted by SSR at a LoxP site adjacent to the GFP gene resulting stringent tet-regulated transgene expression. In clone Rht14-10, increases in expression from essentially background levels (+tet) to more than 10⁴-fold above background (-tet) were reproducibly detected after Cre-mediated insertion of either the luciferase or the I-SceI transgenes.

Conclusion

Although previous methods have made use of SSR to integrate transgenes at defined sites, none has effectively combined this with a pre-selection step to identify integration sites that support optimal regulatory characteristics. Rht14-10 and similar HT1080-derived clones can now be used in conjunction with a convenient delivery vector (pIN2-neoMCS), in a simple 3-step protocol leading to stringent and reproducible transgene regulation. This approach will be particularly useful for transgenes whose products are very active at low concentrations and/or for comparisons of multiple related transgenes.

Tetracycline regulated systems in functional oncogenomics

The increasing number of proteomic and DNA-microarray studies is continually providing a steady acquisition of data on the molecular abnormalities associated with human tumors. Rapid translation of this accumulating biological information into better diagnostics and more effective cancer therapeutics in the clinic depends on the use of robust function-testing strategies. Such strategies should allow identification of molecular lesions that are essential for the maintenance of the transformed phenotype and enable validation of potential drug-targets. The tetracycline regulated gene expression/ suppression systems (Tet-systems) developed and optimized by bioengineers over recent years seem to be very well suited for the function-testing purposes in cancer research. We review the history and latest improvements in Tet-technology in the context of functional oncogenomics.

Conditional expression of interferon-γ to enhance host responses to pulmonary bacterial infection

Strategies to augment host defense against pulmonary infection run the risk of inducing excess pulmonary inflammation and tissue injury. To address this problem, we investigated conditional expression in lung tissue of the murine interferon-gamma (IFN-gamma) transgene. A recombinant adenoviral vector (AdTetIFN) was constructed by placing a murine IFN-gamma cDNA downstream of a tetracycline (Tet)-responsive promoter, inserted into a replication-defective adenoviral vector. Co-infection of target cells with AdTetIFN and a second vector encoding a reverse tetracycline controlled transactivator allowed doxycycline (Dox)-regulated IFN-gamma production. We then administered 10(8) plaque-forming units (PFU) of AdTetIFN to mice by intratracheal injection. When the mice were provided with Dox in drinking water (0.5mg/ml in 5% sucrose), there was significant release of IFN-gamma in lavage fluid by ELISA in comparison to mice on water/sucrose alone (399+/-74 pg/ml vs undetectable, p<0.01). IFN-gamma in lavage fluid was associated with upregulation of Class II Major histocompatibility complex markers on alveolar macrophages by flow cytometry, suggesting macrophage activation. We then injected AdTetIFN into mice three days prior to challenge with 10(4) CFU Klebsiella pneumoniae. Test mice were maintained on water+Dox and control mice on water+sucrose. Bacterial burden was assayed in lung tissue at serial intervals. At 24h after challenge, mice on doxycycline had significantly lower infection burden in comparison to mice on water/sucrose (0.77+/-0.05 colony forming units/lung for 10(8) PFU AdTetIFN plus Dox compared to 1.4+/-0.11 colony-forming units/lung for AdTetIFN without Dox, p<0.05). Survival of the vector treated mice given doxycycline in drinking water was also enhanced. Microscopic examination of lavaged cells showed a significant increase in pulmonary neutrophils in the AdTetIFN+Dox mice in comparison to AdTetIFN+sucrose mice (16+/-1.0 x 10(5) vs 10+0.8 cells/lung, p<0.05). We conclude that local release of IFN-gamma can be selectively activated to enhance neutrophil recruitment and host resistance to bacterial pneumonia.

Pharmacologic transgene control systems for gene therapy

Pharmacologic transgene-expression dosing is considered essential for future gene therapy scenarios. Genetic interventions require precise transcription or translation fine-tuning of therapeutic transgenes to enable their titration into the therapeutic window, to adapt them to daily changing dosing regimes of the patient, to integrate them seamlessly into the patient's transcriptome orchestra, and to terminate their expression after successful therapy. In recent years, decisive progress has been achieved in designing high-precision trigger-inducible mammalian transgene control modalities responsive to clinically licensed and inert heterologous molecules or to endogenous physiologic signals. Availability of a portfolio of compatible transcription control systems has enabled assembly of higher-order control circuitries providing simultaneous or independent control of several transgenes and the design of (semi-)synthetic gene networks, which emulate digital expression switches, regulatory transcription cascades, epigenetic expression imprinting, and cellular transcription memories. This review provides an overview of cutting-edge developments in transgene control systems, of the design of synthetic gene networks, and of the delivery of such systems for the prototype treatment of prominent human disease phenotypes.

An improved Tet-On regulatable FasL-adenovirus vector system for lung cancer therapy

Gene therapy is a new therapeutic approach for the treatment of human cancers. Gene expression systems that can be regulated by drugs have been developed to improve the safety and efficacy of therapeutic transgene delivery. One of the most promising systems is the tetracycline (Tet)-responsive system in the Tet-On configuration. A major problem of the Tet-On system if used in viral vectors is the high basal activity of the Tet response element (TRE) promoter leading to leaky expression of transgenes under uninduced conditions. We therefore evaluated novel TRE promoters for controlling gene expression in an adenovirus vector (AdV) Tet-On system and further investigated them for expression of the pro-apoptotic CD95/Fas ligand (FasL) in human epithelial carcinoma cell line (HeLa) and lung cancer cells. Plasmid-based reporter gene assays showed that modifications within the tetO (7) and minimal immediate early cytomegalovirus promoter (CMV)(min) sequence of the TRE promoter reduced its leakiness and led to a markedly improved regulatability by doxycycline. Among several TRE promoters tested, a new construct (TRE-Tight1) containing modifications of both the tetO (7) sequence and the CMV(min) showed 11-fold reduced leakiness and 1.5-fold increased absolute transgene expression levels after induction, as compared to the original TRE. Under induced conditions, a TRE-Tight1 promoter-dependent AdV expressing the pro-apoptotic CD95L/FasL induced apoptosis and cell lysis in HeLa cells as efficiently as an AdV containing the original TRE promoter. In contrast to the latter, however, the vector with the modified TRE promoter left cells totally unaffected in the absence of the inducer. Stringently regulated induction of apoptosis and cell death by TRE-Tight1-AdV was also demonstrated in three human lung cancer cell lines. These data show that the novel TRE-Tight1 promoter has a high potential for closely controlled and efficient expression of cytotoxic genes in AdV-based anti-cancer approaches.

Engineered Streptomyces quorum-sensing components enable inducible siRNA-mediated translation control in mammalian cells and adjustable transcription control in mice

BACKGROUND

Recent advances in functional genomics, gene therapy, tissue engineering, drug discovery and biopharmaceuticals production have been fostered by precise small-molecule-mediated fine-tuning of desired transgenes.

METHODS

Capitalizing on well-evolved quorum-sensing regulatory networks in Streptomyces coelicolor we have designed a mammalian regulation system inducible by the non-toxic butyrolactone SCB1. Fusion of the S. coelicolor SCB1 quorum-sensing receptor ScbR to the human Kox-1-derived transsilencing domain reconstituted a mammalian transsilencer (SCS) able to repress transcription from SCS-specific operator-containing promoters in a reverse SCB1-adjustable manner.

RESULTS

This quorum-sensing-derived mammalian transgene control system (Q-ON) enabled precise SCB1-specific fine-tuning of (i) desired transgene transcription in a variety of mammalian/human cell lines and human primary cells, (ii) small interfering RNA-mediated posttranscriptional knockdown (siRNA) in mammalian cells, and (iii) dosing of a human glycoprotein in mice.

CONCLUSIONS

As exemplified by Q-ON technology, bacterial quorum-sensing regulons may represent a near-infinite source for the design of mammalian gene control systems compatible with molecular interventions relevant to future gene therapy and tissue engineering scenarios.

Liver-specific expression of interferon gamma following adenoviral gene transfer controls hepatitis B virus replication in mice

Interferons control viral replication and the growth of some malignant tumors. Since systemic application may cause severe adverse effects, tissue-specific expression is an attractive alternative. Liver-directed interferon gene therapy offers promising applications such as chronic viral hepatitis B or C or hepatocellular carcinoma and thus needs testing in vivo in suitable animal models. We therefore used the Tet-On system to regulate gene expression in adenoviral vectors, and studied the effect of liver-specific and regulated interferon gamma expression in a mouse model of chronic hepatitis B virus (HBV) infection. In a first generation adenoviral vector, genes encoding for firefly luciferase and interferons alpha, beta or gamma, respectively, were coexpressed under control of the bidirectional tetracycline-regulated promoter P(tet)bi. Liver-specific promoters driving expression of the reverse tetracycline controlled transactivator ensured local expression in the livers of HBV transgenic mice. Following gene transfer, we demonstrated low background, tight regulation and a 1000-fold induction of gene expression by doxycycline. Both genes within the bidirectional transcription unit were expressed simultaneously, and in a liver-specific fashion in cell culture and in living mice. Doxycycline-dependent interferon gamma expression effectively controlled HBV replication in mice, but did not eliminate HBV transcripts. This system will help to study the effects of local cytokine expression in mouse disease models in detail.

Mutagenesis by reversible promoter insertion to study the activation of NF-kappaB

Genetic dissection of signaling pathways in mammalian cells involves screening or selecting phenotypic mutants obtained by a variety of techniques. Limitations in current methods include inadequate genome coverage and difficulty in validating the link between mutation and phenotype. We describe an improved method for insertional mutagenesis with retroviral vectors and show that the ability to induce mutations increases greatly if a randomly inserted promoter directs transcription into the host DNA. The mutant phenotype is due to the expression of a hybrid transcript derived from the vector and the insertion site. Because other alleles of the affected gene remain intact, the phenotype is dominant, but is reversible by inactivating the promoter, for example, by site-specific recombination. Importantly, in mutant clones with multiple inserts, limited excision yields progeny with different patterns of inserts remaining. Characterizing these progeny allows the mutant phenotype to be associated with a specific target gene. Relative simplicity and robust target validation make the method suitable for a broad range of applications. We have used this technique to search for proteins that regulate NF-kappaB-dependent signaling in human cells. Two validated targets are the relA gene, which codes for the NF-kappaB p65 subunit, and the NF-kappaB regulator act1. Overexpression of the corresponding proteins, caused by insertion of a promoter into the first intron of each gene, leads to NF-kappaB-dependent secretion of factors that activate NF-kappaB through cell-surface receptors, establishing an autocrine loop.

Tight control of transgene expression by lentivirus vectors containing second-generation tetracycline-responsive promoters

BACKGROUND

The goal of this study was to design improved regulatable lentivirus vector systems. The aim was to design tetracycline (tet)-regulatable lentivirus vectors based on the Tet-on system displaying low background expression in the absence of the doxycycline (DOX) inducer and high transgene expression levels in the presence of DOX.

METHODS

We constructed a binary lentivirus vector system that is composed of a self-inactivating (SIN) lentivirus vector bearing inducible first- or second-generation tet-responsive promoter elements (TREs) driving expression of a transgene and a second lentivirus vector encoding a reverse tetracycline-controlled transactivator (rtTA) that activates transgene expression from the TRE in the presence of DOX.

RESULTS

We evaluated a number of different rtTAs and found rtTA2S-M2 to induce the highest levels of transgene expression. Regulated transgene expression was stable in human breast carcinoma cells implanted into nude mice for up to 11 weeks. In an attempt to minimize background expression levels, the chicken beta-globin cHS4 insulator element was cloned into the 3' long terminal repeat (LTR) of the transgene transfer vector. The cHS4 insulator element reduced background expression but expression levels following DOX addition were lower than those observed with vectors lacking an insulator sequence. In a second strategy, vectors bearing second-generation TREs harboring repositioned tetracycline operator elements were used. Such vectors displayed greatly reduced leakiness in the absence of DOX and induced transgene expression levels were up to 522-fold above those seen in the absence of DOX.

CONCLUSIONS

Inducible lentivirus vectors bearing insulators or second-generation TREs will likely prove useful for applications demanding the lowest levels of background expression.

Functional characterization of the interaction between human La and hepatitis B virus RNA

The La protein is a multifunctional RNA-binding protein and has also been suggested to be involved in the stabilization of hepatitis B virus (HBV) RNA. Here we demonstrate that antibodies against the human La protein specifically precipitate HBV RNA from HBV ribonucleoprotein-containing mammalian cell extracts, providing evidence for the association between human La and HBV RNA. Moreover, we report that the turnover of HBV RNA depends on structural features and less on the primary sequence of the La-binding site on the viral RNA. In addition we show that the interaction between human La and HBV RNA in vitro is modulated by accessory factor(s) in a phosphorylation-dependent manner. Taken together these data indicate that both structural features, the composition of La/HBV ribonucleoprotein particles as well as interacting cellular factors, are critical determinants in the regulation of the stability of the HBV RNA.

Endogenous GATA Factors Bind the Core Sequence of the tetO and Influence Gene Regulation with the Tetracycline System

The tetracycline-regulated eukaryotic gene expression systems have been applied in numerous areas of bioscience. The systems utilize a tetracycline-responsive promoter (P(tet)) and synthetic transactivators (tTA or rtTA) that bind to the promoter in the presence or absence of doxycycline, regulating gene expression. Both the basal activity of the P(tet) and the magnitude of regulation by the system vary between cell types. In this investigation we have mapped the positions of endogenous transcription factor binding sites within the P(tet) and through deletion studies determined the portion of the promoter that contributes to basal activity. The tetracycline operator (tetO) repeats appear to be the source of basal activity and they were shown to harbor motifs for GATA transcription factors. The GATA motif is located within the central core of the tetO and so has the potential to compete with tTA and rtTA binding. The molecular interactions of endogenous and overexpressed GATA factors with the GATA motif in the tetO were demonstrated and effects on function of the tetracycline-regulated gene expression system investigated. GATA factors are widespread in embryonic tissues, are expressed within several adult cell types, and display altered expression in disease states. We suggest that endogenous GATA factor expression may influence the degree of gene regulation by the tetracycline system between different cell types. The findings of this study may have implications for the application of the tetracycline system in gene therapy.

Gene regulation by tetracyclines. Constraints of resistance regulation in bacteria shape TetR for application in eukaryotes

The Tet repressor protein (TetR) regulates transcription of a family of tetracycline (tc) resistance determinants in Gram-negative bacteria. The resistance protein TetA, a membrane-spanning H+-[tc.M]+ antiporter, must be sensitively regulated because its expression is harmful in the absence of tc, yet it has to be expressed before the drugs' concentration reaches cytoplasmic levels inhibitory for protein synthesis. Consequently, TetR shows highly specific tetO binding to reduce basal expression and high affinity to tc to ensure sensitive induction. Tc can cross biological membranes by diffusion enabling this inducer to penetrate the majority of cells. These regulatory and pharmacological properties are the basis for application of TetR to selectively control the expression of single genes in lower and higher eukaryotes. TetR can be used for that purpose in some organisms without further modifications. In mammals and in a large variety of other organisms, however, eukaryotic transcriptional activator or repressor domains are fused to TetR to turn it into an efficient regulator. Mechanistic understanding and the ability to engineer and screen for mutants with specific properties allow tailoring of the DNA recognition specificity, the response to inducer tc and the dimerization specificity of TetR-based eukaryotic regulators. This review provides an overview of the TetR properties as they evolved in bacteria, the functional modifications necessary to transform it into a convenient, specific and efficient regulator for use in eukaryotes and how the interplay between structure--function studies in bacteria and specific requirements of particular applications in eukaryotes have made it a versatile and highly adaptable regulatory system.

Using yeast to place human genes in functional categories

The availability of the draft sequence of the human genome has created a pressing need to assign functions to each of the 35,000 or so genes that it defines. One useful approach for this purpose is to use model organisms for both bioinformatic and functional comparisons. We have developed a complementation system, based on the model eukaryote Saccharomyces cerevisiae, to clone human cDNAs that can functionally complement yeast essential genes. The system employs two regulatable promoters. One promoter, tetO (determining doxycycline-repressible expression), is used to control essential S. cerevisiae genes. The other, pMET3 (which is switched off in the presence of methionine), is employed to regulate the expression of mammalian cDNAs in yeast. We have demonstrated that this system is effective for both individual cDNA clones and for cDNA libraries, permitting the direct selection of functionally complementing clones. Three human cDNA libraries have been constructed and screened for clones that can complement specific essential yeast genes whose expression is switched off by the addition of doxycycline to the culture medium. The validity of each complementation was checked by showing that the yeast cells stop their growth in the presence of doxycycline and methionine, which represses the expression of the yeast and mammalian coding sequence, respectively. Using this system, we have screened 25 tetO replacement strains and succeeded in isolating human cDNAs complementing six essential yeast genes. In this way, we have uncovered a novel human ubiquitin-conjugating enzyme, have isolated a human cDNA clone that may function as a signal peptidase and have demonstrated that the functional segment of the human Psmd12 proteosome sub-unit contains a PINT domain.

A predictable ligand regulated expression strategy for stably integrated transgenes in mammalian cells in culture

Several strategies for regulated stable transgene expression in mammalian cells have been described. These strategies have different strengths and weaknesses, however they all share a common problem, namely predictability in application. Here we address this problem using the leading strategy for ligand inducible transgene expression, the tetracycline repressor system. Initially, we found the best stable clone out of 48 examined showed only 6-fold inducibility. Hence we looked for additions and modifications that improve the chances of a successful outcome. We document three important aspects; first, use of a mammalian codon-optimized tetracycline repressor gene; second, addition of a steroid hormone receptor ligand binding domain to the tetracycline repressor-virion protein 16 fusion protein activator; third, flanking the tet-operator/transgene cassette with insulator elements from the chicken beta-globin locus. By inclusion of these three design features, 18/18 clones showed low basal and highly inducible (>50 x) expression.

Artificial mammalian gene regulation networks-novel approaches for gene therapy and bioengineering

Recently developed strategies for targeted molecular interventions in mammalian cells have created novel opportunities in biotechnological and biomedical research with huge economic and therapeutic impact: the design of mammalian cells with desired phenotypes for biopharmaceutical manufacturing, tissue engineering and gene therapy. These advances have been enabled by constructing artificial gene regulation systems with control modalities similar to those evolved in key regulatory networks of mammalian cells. This review highlights recurring cellular regulation strategies and artificial gene regulation technology currently in use for rational reprogramming of cellular key events including metabolism, growth, differentiation and cell death to achieve sophisticated bioprocess and therapeutic goals.

Interferon regulatory factor-1 mediates interferon-gamma-induced apoptosis in ovarian carcinoma cells

Interferon-gamma (IFN-gamma), as one of interferon family that regulates antiviral, antiproliferative, and immunomodulatory responses, has been implicated for the growth regulation of ovarian cancer cells. However, the molecular mechanisms are not yet fully defined. To analyze detailed mechanisms, the ovarian cancer cell lines (2774, PA-1, OVCAR-3, and SKOV-3) were treated with IFN-gamma. The growth of 2774 was most effectively suppressed than that of other cells in both time-course and dose-dependent experiments. The order of sensitivity in other cells was PA-1 >> OVCAR-3 > SKOV-3 (not responded at all). The DNA fragmentation and DAPI staining assays suggested that the IFN-gamma-mediated cytotoxicity could be triggered by apoptosis. The treatment induced IFN regulatory factor-1 (IRF-1) in two IFN-gamma-sensitive cells (2774, PA-1), whereas IRF-1 was not induced in two IFN-gamma-resistant cells (OVCAR-3, SKOV-3). The levels of p53 and p21WAF1 were not strikingly changed in all four cells. Interestingly, the expression of interleukin-converting enzyme (ICE, or caspase-1) was increased by the treatment in a kinetically consistent manner to the induction of IRF-1. However, CD95 (Fas/APO-1) was not changed. Apoptosis was greatly induced, when IRF-1 was transiently expressed in PA-1 without the treatment of IFN-gamma. However, it was repressed when IRF-1 together with IRF-2, an antagonist of IRF-1, were coexpressed. In addition, the effect of IFN-gamma was reduced in the 2774 and PA-1 cells stably expressing either IRF-1 antisense or IRF-2 sense, as shown by the cytotoxicity and FACS analysis. Furthermore, the IFN-gamma-induced apoptosis was greatly reduced, when inhibitors of ICE were treated into PA-1 cells. Taken together, these results suggest that IRF-1 directly mediates the IFN-gamma-induced apoptosis via the activation of caspase-1 gene expression in IFN-gamma-sensitive ovarian cancer cells.

Efficient human immunodeficiency virus replication requires a fine-tuned level of transcription

Transcription represents a crucial step in the life cycle of human immunodeficiency virus (HIV) and is highly regulated. Here we show that the strength of the viral long terminal repeat (LTR) promoter is optimized for efficient replication. Artificially increasing the rate of LTR-driven transcription was strongly detrimental for viral fitness, and HIV was able to regain replication capacity by selecting for variants with a weaker LTR. Strikingly, the strength of the evolved promoter was equivalent to that of the wild-type LTR.

Regulated gene expression in gene therapy

The original model of gene therapy, that of efficient delivery, durable transfer, and stable expression of transgenes to correct a gene defect underlying an inherited disease, is limited in light of improved understanding of the processes involved. Techniques that enable regulated expression of transgenes may enhance safety and allow us to regulate the timing and level of expression with a goal of precisely targeting a therapeutic level between the extremes of suboptimal and supraoptimal thresholds. Using regulated systems to control protein expression has practical and possibly essential roles for the success of safe and effective gene therapy in a number of clinical situations. Pharmacologically regulated gene expression is an evolving tool, and no individual system may be effective in all clinical applications.

Evaluation of the tetracycline- and ecdysone-inducible systems for expression of neurotransmitter receptors in mammalian cells

Establishing a stable cell line that expresses a particular protein of interest is often a laborious and time-consuming experience. With constitutive expression systems, a gradual loss of the highly expressing clones over a given time span and/or a severe counter-selection due to toxicity of the expressed protein for the host cell line are major drawbacks. In both cases, inducible expression systems offer a valuable alternative. Over the years, many regulated expression systems have been developed and evaluated. In the present study, we compare the efficiency, the advantages and the drawbacks of a tetracycline- and an ecdysone-inducible system for expression of the reporter protein chloramphenicol acetyltransferase and of different G-protein-coupled serotonin (5-HT) receptors. A high level of expression of different 5-HT receptors was obtained with the tetracycline-inducible system. In the cell line L929, which stably expresses the tetracycline-responsive transactivator, a maximum ligand binding of 20,000 and 9500 fmol/mg protein was measured for the h5-HT(1B) and h5-ht(1F) receptors, respectively. In the HEK293rtTA cell line, levels of 15,700, 3000, and 9100 fmol bound ligand/mg protein were obtained for the h5-HT(1B), h5-ht(1F) and h5-HT(4b) receptors, respectively. These high expression levels remained stable for several months of continuous culture. Although the ecdysone-inducible expression system was useful for tightly regulated expression, the levels were far lower than those obtained with the tetracycline system (e.g. 640 fmol bound ligand/mg protein for the h5-ht(1F) receptor in HEK293EcR).

Lack of a role of the interferon-stimulated response element-like region in interferon alpha -induced suppression of Hepatitis B virus in vitro

The antiviral effect of interferon-alpha (IFNalpha) on hepatitis B virus (HBV) is well documented in vitro and in vivo, but the mechanisms involved are elusive. Recently, an interferon-stimulated response like element (ISRE) competent for binding of interferon-stimulated gene factor-3gamma (p48) has been identified in the HBV enhancer I region. Mutation of this element was shown to abrogate IFNalpha-mediated reduction of HBV X-gene promoter-driven reporter gene expression. This suggested a role of the ISRE and of p48 in IFNalpha-induced antiviral activity against productive HBV infection. Here, we analyzed the antiviral effect of both IFNalpha and enhanced p48 expression on complete HBV genomes containing the wild-type or mutated ISRE. In human hepatoma cells transfected with both genomes, viral RNA and replicative intermediates were reduced by IFNalpha treatment to a similar degree. Enhanced p48 expression increased IFNalpha-induced suppression of HBV RNA significantly from 75 +/- 22.5% to 46 +/- 9.8%, but this was independent of the integrity of the ISRE-like region. These data imply that p48 neither mediates the antiviral activity of IFNalpha against HBV nor down-regulates enhancer I activity by binding directly to the HBV ISRE-like region, but rather argue for an indirect role of p48.

Gene therapy for spine fusion

Gene therapy is a novel therapeutic modality for repair and regeneration of musculoskeletal tissues, including the spine. Various methods for therapeutic gene transfer are presented in this article. Several studies in which gene transfer has been used specifically to enhance spine fusion in animal models are reviewed.