HSV-1 infected cell proteins influence tetracycline-regulated transgene expression

Herpes Simplex Virus: A Versatile Tool for Insights Into Evolution, Gene Delivery, and Tumor Immunotherapy

Herpesviruses are prevalent throughout the animal kingdom, and they have coexisted and coevolved along with their host species for millions of years. Herpesviruses carry a large (120-230 kb) double-stranded DNA genome surrounded by a protein capsid, a tegument layer consisting of viral and host proteins, and a lipid bilayer envelope with surface glycoproteins. A key characteristic of these viruses is their ability to enter a latent state following primary infection, allowing them to evade the host's immune system and persist permanently. Herpesviruses can reactivate from their dormant state, usually during times of stress or when the host's immune responses are impaired. While herpesviruses can cause complications with severe disease in immune-compromised people, most of the population experiences few ill effects from herpesvirus infections. Indeed, herpes simplex virus 1 (HSV-1) in particular has several features that make it an attractive tool for therapeutic gene delivery. Herpes simplex virus 1 targets and infects specific cell types, such as epithelial cells and neurons. The HSV-1 genome can also accommodate large insertions of up to 14 kb. The HSV-1-based vectors have already achieved success for the oncolytic treatment of melanoma. In addition to serving as a vehicle for therapeutic gene delivery and targeted cell lysis, comparative genomics of herpesviruses HSV-1 and 2 has revealed valuable information about the evolutionary history of both viruses and their hosts. This review focuses on the adaptability of HSV-1 as an instrument for gene delivery and an evolutionary marker. Overall, HSV-1 shows great promise as a tool for treating human disease and studying human migration patterns, disease outbreaks, and evolution.

A haploid HSV-1 genome platform for vector development: testing of the tetracycline-responsive switch shows interference by infected cell protein 0

BACKGROUND

Although herpes simplex virus type 1 (HSV-1) has outstanding properties for gene delivery vectors and its genome is available in bacterial artificial chromosomes (BACs) for mutagenesis studies, one impediment is the presence of approximately 15.4 kb of DNA sequences that are duplicated in the HSV-1 genome, complicating vector construction and stability.

METHODS

As a useful platform for building HSV-1 vectors, we have constructed a fully haploid HSV-1 genome BAC by deletion of one of these repeats, confirming that viral propagation in culture is not impaired. We used this ΔIR mutant to subsequently investigate whether the insertion of tetracycline-responsive tetO elements into the ICP34.5-ICP0 gene region can be used to control HSV-1 lytic replication.

RESULTS

The results of the present study show that ΔIR mutants deleted for ICP34.5 are viable for replication but not when the ICP0 promoter is also disrupted, thus indicating that regulation of infected cell protein 0 (ICP0) levels in the absence of ICP34.5 could be a viable means for controlling growth of HSV-1 vectors. Surprisingly, however, the tetO elements inserted into the ICP0 promoter did not confer ligand responsiveness to growth or ICP0 expression. Further analysis by transfection experiments revealed that ICP0 itself interferes with the tetracycline switch and reduces the the inducibility of this system.

CONCLUSIONS

Our new haploid HSV-1 BAC is a useful platform for building multiply deleted HSV-1 vectors. Deletion of the gene for ICP34.5 in this backbone renders viral growth dependent on ICP0, although ICP0 expression could not be regulated by tet-responsive transcriptional regulators.

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.

HSV-1 as a Model for Emerging Gene Delivery Vehicles

The majority of viral vectors currently used possess modest cargo capability (up to 40 kb) being based on retroviruses, lentiviruses, adenoviruses, and adenoassociated viruses. These vectors have made the most rapid transition from laboratory to clinic because their small genomes have simplified their characterization and modification. However, there is now an increasing need both in research and therapy to complement this repertoire with larger capacity vectors able to deliver multiple transgenes or to encode complex regulatory regions, constructs which can easily span more than 100 kb. Herpes Simplex Virus Type I (HSV-1) is a well-characterized human virus which is able to package about 150 kb of DNA, and several vector systems are currently in development for gene transfer applications, particularly in neurons where other systems have low efficiency. However, to reach the same level of versatility and ease of use as that of smaller genome viral vectors, simple systems for high-titer production must be developed. This paper reviews the major HSV-1 vector systems and analyses the common elements which may be most important to manipulate to achieve this goal.

Herpes simplex virus type 1 ICP27 induces p38 mitogen-activated protein kinase signaling and apoptosis in HeLa cells

The herpes simplex virus type 1 (HSV-1) protein ICP27 has been implicated in a variety of functions important for viral replication including host shutoff, viral gene expression, activation of mitogen-activated protein kinases p38 and Jun N-terminal protein kinase (JNK), and apoptosis inhibition. In the present study we sought to examine the functions of ICP27 in the absence of viral infection by creating stable HeLa cell lines that inducibly express ICP27. Here, we characterize two such cell lines and show that ICP27 expression is associated with a cellular growth defect. The observed defect is caused at least in part by the induction of apoptosis as indicated by caspase-3 activation, annexin V staining, and characteristic changes in cellular morphology. In an effort to identify the function of ICP27 responsible for inducing apoptosis, we show that ICP27 expression is sufficient to activate p38 signaling to a level that is similar to that observed during wild-type HSV-1 infection. However, ICP27 expression alone is unable to lead to a strong activation of JNK signaling. Using chemical inhibitors, we show that the ICP27-mediated activation of p38 signaling is responsible for the observed induction of apoptosis in the induced cell lines. Our findings suggest that during viral infection, ICP27 activates p38 and JNK signaling pathways via two distinct mechanisms. ICP27 directly activates p38 signaling, leading to stimulation of the host cell apoptotic pathways. In contrast, robust activation of JNK signaling by ICP27 requires one or more delayed early or late viral gene products and may be associated with the inhibition of apoptosis.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

Highly efficient regulation of gene expression by tetracycline in a replication-defective herpes simplex viral vector

Employing the tetracycline repressor tetR and the wild-type hCMV major immediate-early promoter, we have developed a highly sensitive tetracycline-inducible transcription switch in mammalian cells (T-REx; Invitrogen, Carlsbad, CA, USA). In view of the previous difficulty in achieving regulatable gene expression in recombinant HSV vector systems, we constructed a T-REx-encoding replication-defective HSV-1 recombinant, QR9TO-lacZ, that encodes two copies of the tetR gene controlled by the HSV-1 immediate-early ICP0 promoter and a reporter, the LacZ gene, under the control of the tetO-bearing hCMV major immediate-early promoter. Infection of cells, such as Vero, PC12, and NGF-differentiated PC12 cells, with QR9TO-lacZ led to 300- to 1000-fold tetracycline-regulated gene expression. Moreover, the expression of the LacZ gene by QR9TO-lacZ can be finely controlled by tetracycline in a dose-dependent fashion. Efficiently regulated gene expression can also be achieved in vivo following intracerebral and footpad inoculations in mice. The demonstrated capability of T-REx for achieving high levels of sensitively regulated gene expression in the context of the HSV-1 genome will significantly expand the utility of HSV-based vector systems for studying gene function in the nervous system and delivering regulated gene expression in therapeutic applications, particularly in the treatment of CNS diseases.

Long-term inducible expression in striatal neurons from helper virus-free HSV-1 vectors that contain the tetracycline-inducible promoter system

Direct gene transfer into neurons in the brain via a virus vector system has potential for both examining neuronal physiology and for developing gene therapy treatments for neurological diseases. Many of these applications require precise control of the levels of recombinant gene expression. The preferred method for controlling the levels of expression is by use of an inducible promoter system, and the tetracycline (tet)-inducible promoter system is the preferred system. Helper virus-free Herpes Simplex Virus (HSV-1) vectors have a number of the advantages, including their large size and efficient gene transfer. Also, we have reported long-term (14 months) expression from HSV-1 vectors that contain a modified neurofilament heavy gene promoter. A number of studies have reported short-term, inducible expression from helper virus-containing HSV-1 vector systems. However, long-term, inducible expression has not been reported using HSV-1 vectors. The goal of this study was to obtain long-term, inducible expression from helper virus-free HSV-1 vectors. We examined two different vector designs for adapting the tet promoter system to HSV-1 vectors. One design was an autoregulatory design; one transcription unit used a tet-regulated promoter to express the tet-regulated transcription factor tet-off, and another transcription unit used a tet-regulated promoter to express the Lac Z gene. In the other vector design, one transcription unit used the modified neurofilament heavy gene promoter to express tet-off, and another transcription unit used a tet-regulated promoter to express the Lac Z gene. The results showed that both vector designs supported inducible expression in cultured fibroblast or neuronal cell lines and for a short time (4 days) in the rat striatum. Of note, only the vector design that used the modified neurofilament promoter to express tet-off supported long-term (2 months) inducible expression in striatal neurons.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Glioma-specific and cell cycle-regulated herpes simplex virus type 1 amplicon viral vector

We have engineered a novel herpes simplex virus type 1 (HSV-1)-based amplicon viral vector, whereby gene expression is controlled by cell cycle events. In nondividing cells, trans-activation of the cyclin A promoter via interaction of the Gal4/NF-YA fusion protein with the Gal4-binding sites is prevented by the presence of a repressor protein, cell cycle-dependent factor 1 (CDF-1). CDF-1 is specifically expressed during the G(0)/G(1) phase of the cell cycle and its binding site is located within the cyclin A promoter. In actively proliferating cells, trans-activation could take place because of the absence of CDF-1. Our results showed that when all these cell cycle-specific regulatory elements are incorporated in cis into a single HSV-1 amplicon plasmid vector backbone (pC8-36), reporter luciferase activity is greatly enhanced. Transgene expression mediated by this series of HSV-1 amplicon plasmid vectors and amplicon viral vectors could be regulated in a cell cycle-dependent manner in a variety of cell lines. In a further attempt to target transgene expression to a selected group of actively proliferating cells such as glial cells, we have replaced the cytomegalovirus promoter of the pC8-36 amplicon plasmid with the glial cell-specific GFAP enhancer element. With this latter viral construct, cell type-specific and cell cycle-dependent transgene expression could subsequently be demonstrated specifically in glioma-bearing animals. Taken together, our results suggest that this series of cell cycle-regulatable HSV-1 amplicon viral vectors could potentially be adapted as useful tools for the treatment of human cancers.

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.

Prostate-tumor targeting of gene expression by lentiviral vectors containing elements of the probasin promoter

BACKGROUND

Lentiviruses are retroviruses that can infect and stably integrate into the chromatin of non-dividing cells. The purpose of this study was to determine whether lentiviral vectors containing the probasin (PB) promoter displayed prostate-specific, androgen-regulated, and persistent gene expression.

METHODS

Three lentiviral-PB promoter/enhanced green fluorescent protein (EGFP)-reporter vectors together with a control lentiviral-CMV-EGFP, were tested by microscopy and flowcytometry for expression of EGFP after infection of human prostate cancer cells (LNCaP, PC-3, PC-3(hAR), and Du145 cells) and non-prostate cells (COS-1, HeLa, HeLa(hAR), and MCF-7 cells).

RESULTS

All cells infected in vitro with lentiviral-CMV vectors expressed EGFP, whereas with lentiviral-PB vectors (the most potent being Lv-ARR(2)PB), reporter expression was only observed in LNCaP cells with a small amount seen in androgen-independent PC-3 cells. Stable or transient transfection of androgen receptor only raised EGFP expression in prostate-derived cell lines, but did not change tumor specificity. With Lv-ARR(2)PB infected LNCaP cells, androgens regulated EGFP both in vitro and in vivo. After intra-tumor injection of this vector, EGFP expression was observed in LNCaP tumors, but not in A-549 lung or CaKi-2 kidney tumors.

CONCLUSIONS

Lv-ARR(2)PB may be an ideal vector for prostate-tumor targeting and for persistent, hormone-enhanced expression of a therapeutic gene to treat slow growing prostate tumors.

Herpes simplex virus type-1 infection upregulates cellular promoters and telomerase activity in both tumor and nontumor human cells

Targeted gene expression through viral vectors has been a promising approach for gene therapy. However, the effects of viral gene products expressed from virus vectors on the expression of the host gene are not well known. In the present study, we examined the activities of cellular promoters, including the promoter for genes of human telomerase reverse transcriptase (hTERT), tyrosinase and probasin, in both tumor and normal cells after infection with herpes simplex virus type 1 (HSV-1) vectors. Our results showed that infection with replication-defective HSV-1 vectors significantly upregulated the activity of all three cellular promoters in a nonsequence specific fashion in all cell types tested. Furthermore, viral infection upregulated activities of the hTERT promoter and endogenous telomerase in nontumoral cells. Additional experiments suggested that the viral immediate-early gene product, infected cell protein 0, might be responsible for the deregulation of cellular promoter activity and activation of telomerase. Our study alerts to the potential risk of oncogenesis through deregulation of host gene expression, such as the telomerase by viral vectors in normal cells.

A strict-late viral promoter is a strong tumor-specific promoter in the context of an oncolytic herpes simplex virus

Confinement of transgene expression to target cells is highly desirable in gene therapy. Current strategies of transcriptional targeting to tumors usually rely on tissue-specific promoters to control gene expression. However, such promoters generally have much lower activity than the constitutive viral promoters. We have explored an alternative approach, using a strict-late viral promoter (UL38p) in the context of an oncolytic herpes simplex virus (HSV) for tumor-selective gene expression. As with many DNA viruses, the genomic transcription of HSV is a tightly regulated molecular cascade in which early and late phases of gene expression are separated by viral DNA replication. In particular, some of the late transcripts are categorized as strict-late, whose expression depends rigorously on the initiation of viral DNA replication. Our in vitro and in vivo characterization showed that in normal nondividing cells, where the oncolytic HSV has limited ability to replicate, the UL38p has minimal activity. However, in tumor or cycling cells where the virus can fully replicate, transgene expression from UL38p was almost as high as from the cytomegalovirus immediate-early promoter. These results suggest that delivery of therapeutic genes driven by UL38p through an oncolytic HSV may be an effective approach to gene therapy for malignant diseases.

Single HSV-amplicon vector mediates drug-induced gene expression via dimerizer system

A variety of viral vectors have been used to deliver genes into various tissues. Most have typically relied on either viral or cell-specific mammalian promoters to express transgenes. More recently, regulated promoter systems have been developed to fine-tune gene expression. Due to limited transgene capacity in most viral vectors, regulatory elements are typically subcloned into two separate vectors, which must be delivered simultaneously to a target cell. Here, we have cloned all the components of the rapamycin-based "dimerizer" system into the pantropic HSV-amplicon vector and used it to deliver and regulate red fluorescent protein (RFP) expression in cultured cells in a drug-dose-dependent manner. 293T/17 cells infected at an m.o.i. of 1 transducing unit/cell and induced with 20 nM rapamycin resulted in a 25-fold increase in RFP mRNA levels after 24 h as assessed by quantitative RT-PCR. However, due to a reduced ability to detect RFP optically, only a 5-fold induction in the number of RFP-expressing cells was noted by FACS analysis 48 h after infection. Further, there was at least 100-fold variation in the levels of RFP in individual, infected cells in the induced state. Gene induction in several neuronal models, including primary cell culture and organotypic cultures, as well as in rodent brain, was observed.

Antitumor effects on human melanoma xenografts of an amplicon vector transducing the herpes thymidine kinase gene followed by ganciclovir

Herpes simplex virus type-1 (HSV-1) has been demonstrated as a potentially useful gene delivery vector for gene therapy due to its high efficiency of in vivo transduction. The helper virus-dependent, HSV- 1 amplicon vectors were developed for easier operation and their larger capacity. In this study, the herpes simplex virus type-1 thymidine kinase (HSVtk) gene was cloned into the pHE700 amplicon vector to make an HE7tk vector and used for in vivo gene delivery. Human melanoma xenografts were established in athymic nude mice. Tumors were injected directly with HE7tk vector alone, HE7tk vector followed by ganciclovir (GCV), or a pHE700 amplicon vector carrying a green fluorescent protein (HE7GFP) gene followed by GCV. Efficient HSVtk transgene expression was found in the tumor 3 days after injection. Animals transduced with HE7tk followed by GCV had minimal tumor growth (P < .01 ). Animals that received either HE7tk vector without GCV or HE7GFP vector with GCV had some reduction in tumor growth compared to animals that were injected with buffer only. These data indicate that replication-defective HSV-1 amplicon vectors can be used effectively to deliver transgenes into solid tumors in vivo.