A "humanized" green fluorescent protein cDNA adapted for high-level expression in mammalian cells

Presence of replicating virus in recombinant hepadnavirus stocks results from recombination and can be eliminated by the use of a packaging cell line

Mutant hepatitis B viruses are useful tools to study the viral life cycle and viral pathogenesis. Furthermore, recombinant hepatitis B viruses are candidate vectors for liver-directed gene therapy. Because wild-type viruses present in recombinant or mutant virus stocks may falsify experimental results and are detrimental for a viral vector, we investigated whether and to what extent wild-type virus is present in recombinant virus stocks and where it originates from. We took advantage of the duck model of hepatitis B virus infection which allows very sensitive detection of replication-competent viruses by infection of primary duck hepatocytes or of ducklings in vivo. Recombinant hepatitis B virus stocks contained significant amounts of wild-type viruses, which were most probably generated by homologous recombination between plasmids containing homologous viral sequences. In addition, replication-competent viral genomes were reconstituted from plasmids which contained replication-deficient but redundant viral sequences. Using a stable cell line for packaging of deficient viral genomes, no wild-type virus was detected, neither by infection of primary hepatocytes nor in vivo.

Chimeric and pseudotyped parvoviruses minimize the contamination of recombinant stocks with replication-competent viruses and identify a DNA sequence that restricts parvovirus H-1 in mouse cells

Recent studies demonstrated the ability of the recombinant autonomous parvoviruses MVMp (fibrotropic variant of the minute virus of mice) and H-1 to transduce therapeutic genes in tumor cells. However, recombinant vector stocks are contaminated by replication-competent viruses (RCVs) generated during the production procedure. To reduce the levels of RCVs, chimeric recombinant vector genomes were designed by replacing the right-hand region of H-1 virus DNA with that of the closely related MVMp virus DNA and conversely. Recombinant H-1 and MVMp virus pseudotypes were also produced with this aim. In both cases, the levels of RCVs contaminating the virus stocks were considerably reduced (virus was not detected in pseudotyped virus stocks, even after two amplification steps), while the yields of vector viruses produced were not affected. H-1 virus could be distinguished from MVMp virus by its restriction in mouse cells at an early stage of infection prior to detectable viral DNA replication and gene expression. The analysis of the composite viruses showed that this restriction could be assigned to a specific genomic determinant(s). Unlike MVMp virus, H-1 virus capsids were found to be a major determinant of the greater permissiveness of various human cell lines for this virus.

A naturally enhanced green fluorescent protein from magnificent sea anemone (Heteractis magnifica) and its functional analysis

A novel fluorescent protein termed hmGFP homologous to the green fluorescent protein (GFP) from Aequorea victoria was cloned from the tentacles of sea anemone Heteractis magnifica by EST sequencing and analysis of cDNA library and followed by using RT-PCR. The sequence analysis suggested that the chromophore, consensus amino acids, and secondary structure of 11 beta-strands of hmGFP were similar to those of GFP from other species. The recombinant hmGFP protein with high purity was obtained by the fusion expression of pETTRX-hmGFP in Escherichia coli and subsequent purification. The pH sensitivity and fluorescence spectroscopy of recombinant hmGFP were characterized. The excitation spectrum of recombinant hmGFP has a rather wide major peak with a maximum at 490 nm and a shoulder at 420 nm, and its emission spectrum at 510 nm. The expression of hmGFP and the chimera IPL through hmGFP in CHO cells has shown that the fusion protein IPL through hmGFP has retained the normal membrane targeting of the IPL from Dasyatis akajei, as well as maintaining fluorescent properties similar to those of native hmGFP, suggesting a promising prospect of the application in biotechnology research for the new protein.

hRUL138, a novel human RNA-binding RING-H2 ubiquitin-protein ligase

Cellular as well as viral RNAs are usually found complexed with proteins. In an attempt to identify proteins that interact with transcripts of hepatitis B virus (HBV), a DNA virus that replicates through reverse transcription, a partial cDNA was isolated from a human cDNA expression library whose gene product bound to an HBV-derived RNA. Using an overlapping clone from a molecular hybridization screen a full-length cDNA was assembled. It contained a large open reading frame for a 1208 amino-acid protein of 138 kDa identical to the hypothetical product of the KIAA0675 clone. Closely related sequences are present in mouse cDNA libraries but not in the genomes of lower organisms. The protein sequence contained no known RNA-binding domain and, apart from a probable coiled-coil domain, the only significant homology involved a complete RING-H2 motif. This suggested that the protein might be a novel RNA-binding RING-dependent ubiquitin-protein ligase or E3 enzyme. A motif critical for RNA binding was experimentally mapped to a central Lys-rich region. Binding specificity is either broad or the protein has as yet unknown physiological targets; hence, at present, a potential importance for HBV biology remains open. The RING-H2 domain was functional in and essential for self- and trans-ubiquitylation in vitro and for proteasome-mediated turnover of the protein in vivo. We therefore termed it hRUL138 for human RNA-binding ubiquitin ligase of 138 kDa. hRUL138 mRNAs are expressed at low levels in most tissues. GFP-tagged hRUL138 derivatives were found associated with cytoplasmic structures, possibly the ER, but excluded from the nucleus. The combined presence of RNA binding and E3 activity in hRUL138 raises the possibility that both are mechanistically linked.

Effects of virion host shut-off activity of bovine herpesvirus 1 on MHC class I expression

Previously, we have shown that bovine herpesvirus 1 (BHV-1) down-regulates the expression of major histocompatibility complex class I molecules by interfering with transport of peptides by the transporter associated with antigen processing (TAP). Further studies revealed that BHV-1 down-regulates the expression of mRNA for class I molecules and other cellular proteins. To further elucidate the mechanisms of down-regulation of class I molecules, a virion host shut-off (vhs) deletion mutant was generated. The mutant, like the wildtype (wt) virus, interfered with transport of peptides by the TAP, and down-regulated cell surface expression of class I molecules. However, unlike the wt virus, the mutant did not impair the synthesis of class I molecules. These results indicate that down-regulation of class I molecules by BHV-1 is mediated by vhs activity of the virus, as well as mechanisms specifically directed at the class I pathway. Absence of vhs activity should result in decreased pathogenicity and enhanced immunogenicity of BHV-1 vhs deletion mutant, making it a better vaccine candidate.

The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor has broad signaling effects in primary effusion lymphoma cells

Kaposi's sarcoma-associated herpesvirus (KSHV/human herpesvirus 8 [HHV-8]) is a gamma-2-herpesvirus responsible for Kaposi's sarcoma as well as primary effusion lymphoma (PEL). KSHV is a lymphotropic virus that has pirated many mammalian genes involved in inflammation, cell cycle control, and angiogenesis. Among these is the early lytic viral G protein-coupled receptor (vGPCR), a homologue of the human interleukin-8 (IL-8) receptor. When expressed, vGPCR is constitutively active and can signal via mitogen- and stress-activated kinases. In certain models it activates the transcriptional potential of NF-kappaB and activator protein 1 (AP-1) and induces vascular endothelial growth factor (VEGF) production. Despite its importance to the pathogenesis of all KSHV-mediated disease, little is known about vGPCR activity in hematopoietic cells. To study the signaling potential and downstream effects of vGPCR in such cells, we have developed PEL cell lines that express vGPCR under the control of an inducible promoter. The sequences required for tetracycline-mediated induction were cloned into a plasmid containing adeno-associated virus type 2 elements to enhance integration efficiency. This novel plasmid permitted studies of vGPCR activity in naturally infected KSHV-positive lymphocytes. We show that vGPCR activates ERK-2 and p38 in PEL cells. In addition, it increases the transcription of reporter genes under the control of AP-1, NF-kappaB, CREB, and NFAT, a Ca(2+)-dependent transcription factor important to KSHV lytic gene expression. vGPCR also increases the transcription of KSHV open reading frames 50 and 57, thereby displaying broad potential to affect viral transcription patterns. Finally, vGPCR signaling results in increased PEL cell elaboration of KSHV vIL-6 and VEGF, two growth factors involved in KSHV-mediated disease pathogenesis.

Visualization of molecular and cellular events with green fluorescent proteins in developing embryos: a review

During the past 5 years, green fluorescent protein (GFP) has become one of the most widely used in vivo protein markers for studying a number of different molecular processes during development, such as promoter activation, gene expression, protein trafficking and cell lineage determination. GFP fluorescence allows observation of dynamic developmental processes in real time, in both transiently and stably transformed cells, as well as in live embryos. In this review, we include the most up-to-date use of GFP during embryonic development and point out the unique contribution of GFP visualization, which resulted in novel discoveries.

Real-time imaging of individual fluorescent-protein color-coded metastatic colonies in vivo

We have established stable, bright green fluorescent protein (GFP)- or red fluorescent protein (RFP)-expressing HT-1080 human fibrosarcoma clones. These cell lines showed similar cell proliferation rates and high-frequency experimental lung metastasis. The HT-1080-GFP and -RFP clones enable simultaneous real-time dual-color imaging in the live animal. HT-1080 cells were transduced with retroviral vectors containing GFP or RFP and the neomycin resistance gene. Stable transformants were selected stepwise with G418 up to 800 microl/ml. Subsequently, high GFP- or RFP-expressing clones, HT-1080-GFP or HT-1080-RFP, respectively, were selected. 3 x 10(6) cells from each clone were mixed and injected into the tail vein of SCID mice. The cells seeded the lung at high frequency with subsequent formation of pure green and pure red colonies as well as mixed yellow colonies with different patterns visualized directly on excised lungs. The lung metastases were also visualized by external fluorescence imaging in live animals through skin-flap windows over the chest wall. Lung metastases were observed on the lung surface of all mice. SCID mice well tolerated multiple surgical procedures for direct-view imaging via skin-flap windows. Real-time metastatic growth of the two different colored clones in the same lung was externally imaged with resolution and quantification of green, red, or yellow colonies in live animals. The color coding enabled determination of whether the colonies grew clonally or were seeded as a mixture with one cell type eventually dominating, or whether the colonies grew as a mixture. The simultaneous real-time dual-color imaging of metastatic colonies described in this report gives rise to the possibility of color-coded imaging of clones of cancer cells carrying various forms of gene of interest.

In vivo introduction of unpreferred synonymous codons into the Drosophila Adh gene results in reduced levels of ADH protein

The evolution of codon bias, the unequal usage of synonymous codons, is thought to be due to natural selection for the use of preferred codons that match the most abundant species of isoaccepting tRNA, resulting in increased translational efficiency and accuracy. We examined this hypothesis by introducing 1, 6, and 10 unpreferred codons into the Drosophila alcohol dehydrogenase gene (Adh). We observed a significant decrease in ADH protein production with number of unpreferred codons, confirming the importance of natural selection as a mechanism leading to codon bias. We then used this empirical relationship to estimate the selection coefficient (s) against unpreferred synonymous mutations and found the value (s >or= 10(-5)) to be approximately one order of magnitude greater than previous estimates from population genetics theory. The observed differences in protein production appear to be too large to be consistent with current estimates of the strength of selection on synonymous sites in D. melanogaster.

Tetracycline-inducible transgene expression mediated by a single AAV vector

Regulated gene delivery systems are usually made of two elements: an inducible promoter and a transactivator. In order to optimize gene delivery and regulation, a single viral vector ensuring adequate stoichiometry of the two elements is required. However, efficient regulation is hampered by interferences between the inducible promoter and (i) the promoter used to express the transactivator and/or (ii) promoter/enhancer elements present in the viral vector backbone. We describe a single AAV vector in which transcription of both the reverse tetracycline transactivator (rtTA) and the transgene is initiated from a bidirectional tetracycline-responsive promoter and terminated at bidirectional SV40 polyadenylation sites flanking both ITRs. Up to 50-fold induction of gene expression in human tumor cell lines and 100-fold in primary cultures of rat Schwann cells was demonstrated. In addition an 80-fold induction in vivo in the rat brain has been obtained. In vitro, the autoregulatory vector exhibits an induced expression level superior to that obtained using the constitutive CMV promoter. Although extinction of the transgene after removal of tetracycline was rapid (less than 3 days), inducibility after addition of tetracycline was slow (about 14 days). This kinetics is suitable for therapeutic gene expression in slowly progressive diseases while allowing rapid switch-off in case of undesirable effects. As compared to previously described autoregulatory tet-repressible (tetOFF) AAV vectors, the tet-inducible (tetON) vector prevents chronic antibiotic administration in the uninduced state.

Construction of recombinant pseudorabies viruses optimized for labeling and neurochemical characterization of neural circuitry

In this study we have modified the neuroinvasiveness of pseudorabies virus strain Bartha, a commonly utilized trans-synaptic tract-tracer. In addition, we sought to facilitate detection of cellular mRNAs in neurons infected with the virus. In order to modify spreading characteristics, we inserted the lacZ or the GFP (green fluorescent protein) genes into the genomic loci containing the putative latency-associated transcript promoter (P(LAT2)), resulting in the disruption of the promoter function. Following rat kidney injection, mutant viruses labeled central autonomic neurons in a slower and much more restricted manner than the parent Bartha strain. Since both reporter genes were controlled by the human cytomegalovirus immediate early (IE) 1 promoter, they exhibited IE expression kinetics. This property proved to be important for the co-detection of reporter proteins with neuronal mRNAs, readily detected at early but not at late stage of infection, as shown in tyrosine-hydroxylase expressing A5 catecholaminergic neurons and in serotonin transporter expressing raphe magnus neurons.

Production of recombinant H1 parvovirus stocks devoid of replication-competent viruses

Vector and helper plasmids for the production of recombinant H1 (rH1) parvovirus, an oncolytic virus and candidate vector for cancer gene therapy, were constructed with the aim of reducing the contamination of these preparations with replication-competent viruses (RCV). Split-helper plasmids were constructed by manipulating the splicing signals for the capsid proteins such that VP1 and VP2 were expressed from separate plasmids. H1 vectors with similarly mutated splice sites were packaged, using the split-helper plasmids, and the resulting recombinant H1 viruses were completely free of RCV because the generation of recombinants expressing both capsid proteins was prevented. Vector yields of rH1 produced with split-helper plasmids in combination with splice site-modified vectors were similar (in the range of 10(7) replication units/ml) to yields of rH1 produced with the standard vector/helper pair, in which case significant levels of RCV were generated (10(4)-10(5) plaque-forming units/ml). To assess the functionality of this approach in vivo, rH1 was produced that contained the human interleukin 2 (IL-2) transgene and that was devoid of RCV. This IL-2-carrying rH1 vector expressed IL-2 efficiently in human tumor cells (HeLa) in vitro and generated antitumor responses in nude mice xenografted with HeLa cells that had been infected ex vivo with this virus. These results should allow the large-scale production of recombinant oncotropic parvoviruses and their assessment for the gene therapy of cancer in a clinical setting.

Adeno-associated viral vectors as agents for gene delivery: application in disorders and trauma of the central nervous system

The use of viral vectors as agents for gene delivery provides a direct approach to manipulate gene expression in the mammalian central nervous system (CNS). The present article describes in detail the methodology for the injection of viral vectors, in particular adeno-associated virus (AAV) vectors, into the adult rat brain and spinal cord to obtain reproducible and successful transduction of neural tissue. Surgical and injection procedures are based on the extensive experience of our laboratory to deliver viral vectors to the adult rat CNS and have been optimized over the years. First, a brief overview is presented on the use and potential of viral vectors to treat neurological disorders or trauma of the CNS. Next, methods to deliver AAV vectors to the rat brain and spinal cord are described in great detail with the intent of providing a practical guide to potential users. Finally, some data on the experimental outcomes following AAV vector-mediated gene transfer to the adult rat CNS are presented as is a brief discussion on both the advantages and limitations of AAV vectors as tools for somatic gene transfer.

Amelioration of chronic neuropathic pain after partial nerve injury by adeno-associated viral (AAV) vector-mediated over-expression of BDNF in the rat spinal cord

Changing the levels of neurotrophins in the spinal cord micro-environment after nervous system injury has been proposed to recover normal function, such that behavioral response to peripheral stimuli does not lead to chronic pain. We have investigated the effects of recombinant adeno-associated viral (rAAV)-mediated over-expression of brain-derived neurotrophic factor (BDNF) in the spinal cord on chronic neuropathic pain after unilateral chronic constriction injury (CCI) of the sciatic nerve. The rAAV-BDNF vector was injected into the dorsal horn at the thirteenth thoracic spinal cord vertebra (L(1) level) 1 week after CCI. Allodynia and hyperalgesia induced by CCI in the hindpaws were permanently reversed, beginning 1 week after vector injection, compared with a similar injection of a control rAAV-GFP vector (green fluorescent protein) or saline. In situ hybridization for BDNF demonstrated that both dorsal and ventral lumbar spinal neurons contained an intense signal for BDNF mRNA, at 1 to 8 weeks after vector injection. There was no similar BDNF mRNA over-expression associated with either injections of saline or rAAV-GFP. These data suggest that chronic neuropathic pain is sensitive to early spinal BDNF levels after partial nerve injury and that rAAV-mediated gene transfer could potentially be used to reverse chronic pain after nervous system injuries in humans.

Gene therapy for treatment of cerebral ischemia using defective recombinant adeno-associated virus vectors

In this review we present our results and experiences in performing gene therapy of cerebral stroke using recombinant adeno-associated virus (rAAV) vectors in a rat model. The methodologies involving the production of AAV vectors, gene transfer to the brain, and a trivessel ligation model of focal ischemic cerebral stroke in rats are described. Furthermore, a brief description of other viral vectors and candidates of therapeutic transgenes used for gene therapy of cerebral stroke are presented. The potential advantages and limitations of stroke gene therapy are also discussed with the intention of outlining the design of more appropriate experiments.

Synonymous codon usage bias and the expression of human glucocerebrosidase in the methylotrophic yeast, Pichia pastoris

The lysosomal hydrolase glucocerebrosidase catalyzes the penultimate step in the breakdown of membrane glycosphingolipids. An inherited deficiency in this enzyme leads to the onset of Gaucher disease, the most common lysosomal storage disorder. Exogenous sources of this protein are required for biochemical and biophysical investigations and enzyme replacement therapy of Gaucher disease. Heterologous expression of glucocerebrosidase has been successful in mammalian and insect cell lines and although its use in enzyme replacement therapy of Gaucher disease has proven efficacious, current production levels limit the availability of the enzyme. Initial attempts to express human glucocerebrosidase using the methylotrophic yeast Pichia pastoris had limited success, despite significant levels of transcription. Using fragments of the glucocerebrosidase cDNA fused to the luciferase cDNA as a translational read-through reporter, the impact of synonymous codon usage bias on protein expression in P. pastoris was examined. A table of preferred codons was determined for P. pastoris and the codon usage of a 186-bp fragment of the glucocerebrosidase gene was optimized to that of the P. pastoris preferred set. A second construct with altered G+C content but no codon optimization was created for comparison. While the native glucocerebrosidase coding region limited luciferase activity to baseline levels, the codon optimized and G+C altered constructs increased luciferase activity 10.6- and 7.5-fold, respectively. Optimized G+C content, regardless of corresponding codon optimization, appears to be the major contributor to increased translational efficiency in this heterologous expression host.

Production methods for gene transfer vectors based on adeno-associated virus serotypes

Vectors derived from adeno-associated virus serotype 2 (AAV-2) represent a most promising tool for human gene transfer because these vectors are neither pathogenic nor toxic to the target cell, and allow long-term gene expression in a large variety of tissues. However, they are rather inefficient at infecting a number of clinically relevant cell types, and transduction by these vectors is likely hampered by neutralizing antibodies that are highly prevalent in the human population. Therefore, an increasing number of researchers are currently turning their attention to the five other serotypes of AAV, to try and develop these as novel vectors for human gene transfer, hoping to overcome the problems associated with AAV-2 vectors. Here I describe and discuss the methodology to produce these alternative AAV vectors in tissue culture. In detail, two strategies are compared that rely on transfection of cells in culture with either two or three plasmids, containing the AAV vector genome and encoding AAV and adenoviral helper functions. Either of these protocols can be used to package a recombinant AAV genome into capsids of its own serotype (generation of "real" serotypes) or to "cross-package" this vector DNA into capsids derived from another AAV serotype ("pseudotyping"). As these approaches are still in their early stages, the existing limitations of current technology are discussed, and possible further improvements proposed.

Production and purification of serotype 1, 2, and 5 recombinant adeno-associated viral vectors

Recombinant adeno-associated viral (rAAV) vectors based on serotype 2 are currently being evaluated most extensively in animals and human clinical trials. rAAV vectors constructed from other AAV serotypes (serotypes 1, 3, 4, 5, and 6) can transduce certain tissues more efficiently and with different specificity than rAAV2 vectors in animal models. Here, we describe reagents and methods for the production and purification of AAV2 inverted terminal repeat-containing vectors pseudotyped with AAV1 or AAV5 capsids. To facilitate pseudotyping, AAV2rep/AAV1cap and AAV2rep/AAV5cap helper plasmids were constructed in an adenoviral plasmid backbone. The resultant plasmids, pXYZ1 and pXYZ5, were used to produce rAAV1 and rAAV5 vectors, respectively, by transient transfection. Since neither AAV5 nor AAV1 binds to the heparin affinity chromatography resin used to purify rAAV2 vectors, purification protocols were developed based on anion-exchange chromatography. The purified vector stocks are 99% pure with titers of 1 x 10(12) to 1 x 10(13)vector genomes/ml.

Application of adeno-associated viral vectors in behavioral research

Viral vectors afford the capability of genetically manipulating the expression of neurotransmitters, neuropeptides, hormones, and their receptors in specific brain sites of adult animals of any species. Hence, they are a powerful tool for investigating the neurochemistry underlying complex cognitive processes and behaviors. Here we discuss how the recombinant adeno-associated virus (rAAV) can be engineered for use in neurobehavioral studies, techniques for site-specific delivery of vector into the brain, characterization of expression profiles, and biosafety issues. Finally, we discuss issues of experimental design and interpretation of behavioral results in viral vector studies.

A p5 integration efficiency element mediates Rep-dependent integration into AAVS1 at chromosome 19

Adeno-associated virus (AAV) undergoes site-specific integration into human chromosome 19 through a deletion-substitution mechanism at the well characterized AAVS1 site. We have shown previously that a cis element within the left end of the AAV genome enhances the efficiency of Rep-mediated site-specific integration into chromosome 19 when present in inverted terminal repeat-containing recombinant AAV (rAAV) plasmids. We now demonstrate that a 138-bp cis element, the p5 integration efficiency element (p5IEE), mediates efficient integration. The p5IEE is not only required for efficient site-specific integration, it is also sufficient. Integration mediated by the p5IEE occurs in the absence of the AAV inverted terminal-repeat elements. The data presented in this study demonstrate that the p5IEE is a multifunctional element, serving as the highly regulatable Rep promoter and the primary substrate for targeted integration.

Construction and functional characterization of feline foamy virus-based retroviral vectors

Replication-competent feline foamy or spuma virus (FFV) vectors were constructed and functionally tested. The unmodified FFV vector genome expressed by the strong human cytomegalovirus immediate early promoter encodes FFV particles that were replication-competent in cell cultures. Virus derived from the cloned FFV DNA replicated and persisted in experimentally infected cats similar to the FFV isolate FUV. A FFV vector partially deleted in the noncoding area of the U3 region was used to transduce the gene for the green fluorescent protein (Gfp) into cell cultures. Gfp was expressed either by an internal ribosomal entry site (IRES) or as C-terminal fusion protein linked to Bet that was recently shown to be essential for FFV replication. Whereas the genetic stability of the IRES-Gfp construct was comparably low, the Bet-Gfp fusion protein was detectable upon serial cell-free vector passages. However, genetic rearrangements also occurred leading to the concomitant loss of marker gene expression.

Intracellular localization of Herpes simplex virus type 1 thymidine kinase fused to different fluorescent proteins depends on choice of fluorescent tag

Gene therapy employing the suicide gene/prodrug activating system Herpes simplex virus type 1 thymidine kinase (HSV-TK)/ganciclovir (GCV) is effective in killing malignant tumor cells. Labeling of the HSV-TK enzyme with fluorescent proteins makes possible the non-invasive imaging of transduction efficiency, enzyme localization and activity in cell culture and in animal models of human cancers. Here we report the expression of HSV-TK tagged with different fluorescent proteins (EGFP, DSRed1, DsRed2, dsdrFP616) and show that intracellular localization of the fusion products depends on the nature of the fluorescent tag despite the presence of several nuclear targeting signals within the enzyme itself. Coexpression of red fluorescent HSV-TK fusion proteins with TK-EGFP or untagged HSV-TK allowed these proteins to enter the nucleus by inhibiting formation of red fluorescent protein oligomers. As enzyme localization may influence HSV-TK activity, this observation is of potential importance to gene therapy studies.

Intramuscular administration of recombinant adeno-associated virus 2 alpha-1 antitrypsin (rAAV-SERPINA1) vectors in a nonhuman primate model: safety and immunologic aspects

We performed a series of studies in baboons to evaluate the safety of intramuscular administration of rAAV vector expressing the alpha-1 antitrypsin (AAT) gene (SERPINA1) in a nonhuman primate model. Initial experiments performed with an rAAV vector expressing the human SERPINA1 gene (at doses of up to 5 x 10(12) vector genomes/kg) resulted in the generation of anti-human AAT antibodies, which correlated with a loss of detectable transgene expression. Subsequent studies made use of the baboon SERPINA1 gene tagged with a short (10-amino-acid) c-myc tag. When animals were sacrificed, 4 months after vector injection, transduced myofibers showed efficient transgene expression without detectable humoral immune responses. Mild inflammation was observed in and near the sites of injection in some vector- and saline-injected animals, but serum creatine kinase (CK) values were normal in nearly every case. Real-time PCR was also performed 4 months after injection on gonadal tissue to evaluate the risk of germline transmission. No vector sequences were detected in the gonadal tissues from these animals. These studies indicate that the risks of immune reaction and germline transmission after intramuscular injection of rAAV-SERPINA1 in nonhuman primates are relatively low within the range of vector doses studied.

Green fluorescent protein imaging of tumour growth, metastasis, and angiogenesis in mouse models

We have developed a way of imaging metastases in mice by use of tumour cells expressing green fluorescent protein (GFP) that can be used to examine fresh tissue, both in situ and externally. These mice present many new possibilities for research including real-time studies of tumour progression, metastasis, and drug-response evaluations. We have now also introduced the GFP gene, cloned from bioluminescent organisms, into a series of human and rodent cancer-cell lines in vitro, which stably express GFP after transplantation to rodents with metastatic cancer. Techniques were also developed for transduction of tumours by GFP in vivo. With this fluorescent tool, single cells from tumours and metastases can be imaged. GFP-expressing tumours of the colon, prostate, breast, brain, liver, lymph nodes, lung, pancreas, bone, and other organs have also been visualised externally by use of quantitative transcutaneous whole-body fluorescence imaging. GFP technology has also been used for real-time imaging and quantification of angiogenesis.

Development and optimization of a real-time quantitative PCR-based method for the titration of AAV-2 vector stocks

Despite the clinical application of adeno-associated virus (AAV) gene therapy, the titration of viral stocks has not yet been standardized. This complicates the comparison of viral stocks between laboratories. Functional titering of AAV is time-consuming, requires the manipulation of hazardous material, and often has a high degree of variability. We established an optimized real-time quantitative polymerase chain reaction (RQ-PCR) titration assay to determine viral titers and compared it with a functional green fluorescent protein (GFP)-based titration method. With a combination of improved lysis procedures and RQ-PCR protocols we could decrease the intraexperimental coefficient of variation (CV) from 0.24 +/- 0.03 to 0.042 +/- 0.004 and the interexperimental CV from 0.34 +/- 0.06 to 0.093 +/- 0.028 following functional and RQPCR-based titration, respectively. This low variability conforms to even the strictest quality standards required, for example, in clinical laboratories. The highly standardized titration by RQPCR described here will be especially advantageous for groups working on AAV-based gene therapy in a good manufacturing practice setting.

Thixotropic solutions enhance viral-mediated gene transfer to airway epithelia

Adenovirus-mediated gene transfer to airway epithelia is inefficient in part because its receptor is absent on the apical surface of the airways. Targeting adenovirus to other receptors, increasing the viral concentration, and even prolonging the incubation time with adenovirus vectors can partially overcome the lack of receptors and facilitate gene transfer. Unfortunately, mucociliary clearance would prevent prolonged incubation time in vivo. Thixotropic solutions (TS) are gels that upon a vigorous shearing force reversibly become liquid. We hypothesized that formulating recombinant adenoviruses in TS would decrease virus clearance and thus enhance gene transfer to the airway epithelia. We found that clearance of virus-sized fluorescent beads by human airway epithelia in vitro and by monkey trachea in vivo were markedly decreased when the beads were formulated in TS compared with phosphate-buffered saline (PBS). Adenovirus formulated in TS significantly increased adenovirus-mediated gene transfer of a reporter gene in human airway epithelia in vitro and in murine airway epithelia in vivo. Furthermore, an adenovirus encoding the cystic fibrosis transmembrane regulator (CFTR) gene (AdCFTR) formulated in TS was more efficient in correcting the chloride transport defect in cystic fibrosis airway epithelia than AdCFTR formulated in PBS. These data indicate a novel strategy to augment the efficiency of gene transfer to the airways that may be applicable to a number of different gene transfer vectors and could be of value in gene transfer to cystic fibrosis (CF) airway epithelia in vivo.

In vitro and in vivo assessment of the ability of adeno-associated virus-brain-derived neurotrophic factor to enhance spiral ganglion cell survival following ototoxic insult

OBJECTIVES/HYPOTHESIS

Auditory dysfunction following ototoxic insult results from loss of cochlear hair cells. Secondary degeneration of auditory neurons ensues from withdrawal of neurotrophic support from hair cells and can be prevented with administration of neurotrophins. Administration of adeno-associated virus containing the gene for brain-derived neurotrophic factor will promote spiral ganglion neuron survival after the destruction of hair cells.

METHODS

Prevention of aminoglycoside-induced spiral ganglion neuron loss through the expression of brain-derived neurotrophic factor mediated by means of the adeno-associated virus was tested in vitro in cochlear explants and in vivo in mammalian cochlea.

RESULTS

Neuronal survival was significantly enhanced in adeno-associated virus-brain-derived neurotrophic factor transfected rat cochlear explants compared with control samples (30% vs. 19%, P <.05) following exposure to aminoglycoside. Following deafening with aminoglycoside and loop diuretic and introduction of adeno-associated virus-brain-derived neurotrophic factor through osmotic minipump, the experimental group of animals infused with adeno-associated virus-brain-derived neurotrophic factor displayed enhanced spiral ganglion neuron survival in the basal turn of the cochlea when compared with the control group infused with adeno-associated virus containing green fluorescent protein reporter gene.

CONCLUSIONS

Administration of adeno-associated virus-brain-derived neurotrophic factor enhances spiral ganglion neuron survival following ototoxic exposure in vitro and in vivo. These studies lay the groundwork for further exploration of its application as an adjunct therapy for patients undergoing cochlear implantation because the success of implantation depends directly on the population of neurons available for electrical stimulation.

Monitoring receptor-mediated activation of heterotrimeric G-proteins by fluorescence resonance energy transfer

Green fluorescent protein (GFP)-centered fluorescence resonance energy transfer (FRET) relies on a distance-dependent transfer of energy from a donor fluorophore to an acceptor fluorophore and can be used to examine protein interactions in living cells. Here we describe a method to monitor the association and disassociation of heterotrimeric GTP-binding (G-proteins) from one another before and after stimulation of coupled receptors in living Dictyostelium discoideum cells. The Galpha(2)and Gbetagamma proteins were tagged with cyan and yellow fluorescent proteins and used to observe the state of the G-protein heterotrimer. Data from emission spectra were used to detect the FRET fluorescence and to determine kinetics and dose-response curves of bound ligand and analogs. Extending G-protein FRET to mammalian G-proteins should enable direct in situ mechanistic studies and applications such as drug screening and identifying ligands of new G-protein-coupled receptors.

RNA 3' readthrough of oncoretrovirus and lentivirus: implications for vector safety and efficacy

The expression of reporter genes driven by the same human elongation factor 1alpha (EF1alpha) promoter in murine leukemia virus (MLV)- and human immunodeficiency virus type 1 (HIV-1)-based vectors was studied in either transfected or virally transduced cells. The HIV-1 vectors consistently expressed 3 to 10 times higher activity than the MLV vectors at both the RNA and protein levels. The difference was not attributable to transcriptional interference, alternative enhancer/silencer, or differential EF1alpha intron splicing. Based on nuclear run-on assays, both vectors exhibited similar EF1alpha transcriptional activity. The reduced RNA levels of MLV vectors could not be explained by the decrease in RNA half-lives. Southern analysis of proviral DNA indicated that both HIV-1 and MLV vectors efficiently propagated the EF1alpha intron in the transduced cells. To decipher the discrepancy in transgene expression between MLV and HIV-1 vectors, the role of RNA 3'-end processing was examined using a sensitive Cre/lox reporter assay. The results showed that MLV vectors, but not HIV-1 vectors, displayed high frequencies of readthrough of the 3' polyadenylation signal. Interestingly, the polyadenylation signal of a self-inactivating (SIN) HIV-1 vector was as leaky as that of the MLV vectors, suggesting a potential risk of oncogene activation by the lentiviral SIN vectors. Together, our results suggest that an efficient polyadenylation signal would improve both the efficacy and the safety of these vectors.

Efficient integration of recombinant adeno-associated virus DNA vectors requires a p5-rep sequence in cis

The initial aim of this study was to combine attributes of adeno-associated virus (AAV) and adenovirus (Ad) gene therapy vectors to generate an Ad-AAV hybrid vector allowing efficient site-specific integration with Ad vectors. In executing our experimental strategy, we found that, in addition to the known incompatibility of Rep expression and Ad growth, an equally large obstacle was presented by the inefficiency of the integration event when using traditional recombinant AAV (rAAV) vectors. This study has addressed both of these problems. We have shown that a first-generation Ad can be generated that expresses Rep proteins at levels consistent with those found in wild-type AAV (wtAAV) infections and that Rep-mediated AAV persistence can occur in the presence of first-generation Ad vectors. Our finding that traditional rAAV plasmid vectors lack integration potency compared to wtAAV plasmid constructs (10- to 100-fold differences) was unexpected but led to the discovery of a previously unidentified AAV integration enhancer sequence element which functions in cis to an AAV inverted terminal repeat-flanked target gene. rAAV constructs containing left-end AAV sequence, including the p5-rep promoter sequence, integrate efficiently in a site-specific manner. The identification of this novel AAV integration enhancer element is consistent with previous studies, which have indicated that a high frequency of wtAAV recombinant junction formation occurs in the vicinity of the p5 promoter, and recent studies have demonstrated a role for this region in AAV DNA replication. Understanding the contribution of this element to the mechanism of AAV integration will be critical to the use of AAV vectors for targeted gene transfer applications.

Effects of adeno-associated virus-vectored ciliary neurotrophic factor on retinal structure and function in mice with a P216L rds/peripherin mutation

Past studies have shown that acute administration of ciliary neurotrophic factor (CNTF) can prolong the survival of retinal photoreceptor cells that have undergone phototoxic injury or that express gene mutations. Adenovirus-vectored CNTF has also been effective but for all of these treatments, the effect has been transient. On the other hand, adeno-associated virus-vectored minigenes offer considerable promise for long-term survival. The authors sought to provide long-term, CNTF-based protection of mouse photoreceptors expressing a dominant-negative point mutation in the rds gene by using recombinant adeno-associated virus (rAAV) to deliver minigenes that code for a secreted form of CNTF.Secreted CNTF, under control of a cytomegalovirus (CMV) or chick beta actin (CBA) promoter provided long-term, panretinal rescue of photoreceptors following single injections of rAAV vectors into the subretinal compartment. Rescue was much less effective and less reproducible when the vectors were placed in the vitreous compartment. However, there were unexpected side effects that appeared to be dose-related. One side effect was a change in rod photoreceptor nucleus phenotype, featuring an increase in euchromatin and an increase in nuclear size following subretinal injections but not intravitreal injections. These nuclear changes were panretinal when the putatively stronger CBA promoter was used but not panretinal when the CMV promoter was used. In the latter case, the nuclear changes were much more pronounced at the site of injection. Thus, chronic hyperstimulation of retinal cells with CNTF may up-regulate gene expression in photoreceptors. Based on current knowledge of retinal cell targets for CNTF, this effect may be indirect and may not represent direct stimulation of photoreceptors by CNTF.A second side effect was a paradoxical decrease in scotopic a- and b-wave amplitudes and a decrease in photopic b-wave amplitudes in the injected, rescued retina when compared to its contralateral, uninjected counterpart, in spite of the fact that these retinas had more photoreceptors than their untreated mates. The basis for these decreased ERG amplitudes may be related to changes in gene expression. The mechanisms for these side effects and proper doses of CNTF administration should be determined before human clinical trials are considered for the amelioration of inherited retinal degenerations with CNTF.

Recombinant AAV vector encoding human VEGF165 enhances wound healing

Delivery of therapeutic genes represents an appealing possibility to accelerate healing of wounds that are otherwise difficult to treat, such as those in patients with metabolic disorders or infections. Experimental evidence indicates that in such conditions potentiation of neo-angiogenesis at the wound site might represent an important therapeutic target. Here we explore the efficacy of gene therapy of wound healing with an adeno-associated virus (AAV) vector expressing the 165 amino acid isoform of vascular endothelial growth factor-A (VEGF-A). By gene marker studies, we found that AAV vectors are highly efficient for gene transfer to the rat skin, displaying an exquisite tropism for the panniculus carnosus. Gene expression from these vectors is sustained and persistent over time. Delivery of VEGF165 to full thickness excisional wounds in rats resulted in remarkable induction of new vessel formation, with consequent reduction of the healing time. Histological examination of treated wounds revealed accelerated remodeling of epidermis and dermis, with formation of a thick granular layer, containing numerous newly formed capillaries, as well as vessels of larger size. These data underline the importance of neo-angiogenesis in the healing process and indicate that VEGF gene transfer might represent a novel approach to treat wound healing disorders.

TrkB gene transfer protects retinal ganglion cells from axotomy-induced death in vivo

Injury-induced downregulation of neurotrophin receptors may limit the response of neurons to trophic factors, compromising their ability to survive. We tested this hypothesis in a model of CNS injury: retinal ganglion cell (RGC) death after transection of the adult rat optic nerve. TrkB mRNA rapidly decreased in axotomized RGCs to approximately 50% of the level in intact retinas. TrkB gene transfer into RGCs combined with exogenous BDNF administration markedly increased neuronal survival: 76% of RGCs remained alive at 2 weeks after axotomy, a time when >90% of these neurons are lost without treatment. Activation of mitogen-activated protein kinase, but not phosphatidylinositol-3 kinase, was required for TrkB-induced survival. These data provide proof-of-principle that enhancing the capacity of injured neurons to respond to trophic factors can be an effective neuroprotective strategy in the adult CNS.

Adenoviral vectors can impair adrenocortical steroidogenesis: clinical implications for natural infections and gene therapy

Recombinant adenoviral vectors are effective in transferring foreign genes to a variety of cells and tissue types, both in vitro and in vivo. However, during the gene transfer, they may alter the principal function and local environment of transfected cells. Increasing evidence exists for a selective adrenotropism of adenovirus during infections and gene transfer. Therefore, using bovine adrenocortical cells in primary culture, we analyzed the influence of different adenoviral deletion mutants on cell morphology and physiology. Transfection of cells with an E1/E3-deleted adenoviral vector, engineered to express a modified form of the Aequorea victoria green fluorescent protein, was highly efficient, as documented by fluorescent microscopy. Ultrastructural analysis, however, demonstrated nuclear fragmentation and mitochondrial alterations in addition to intranuclear viral particles. Basal secretion of 17-OH-progesterone, 11-deoxycortisol, and cortisol was significantly increased by E1/E3-deleted vectors; yet, the corticotropin-stimulated release of these steroids was decreased. Interestingly, neither purified viral capsids nor E3/E4-deleted adenoviral mutants altered basal and stimulated steroidogenesis of adrenocortical cells. An intact adrenal response is crucial for adaptation to stress and survival. Therefore, the implications of our findings need to be considered in patients with adenoviral infections and those undergoing clinical studies using adenoviral gene transfer. At the same time, the high level of transfection in adrenocortical cells might make appropriately modified adenoviral vectors suitable for gene therapy of adrenocortical carcinomas with poor prognosis.

Gene therapy for hypertension: the preclinical data

In spite of several drugs for the treatment of hypertension, there are many patients with poorly controlled high blood pressure. This is partly due to the fact that all available drugs are short-lasting (24 hr or less), have side effects, and are not highly specific. Gene therapy offers the possibility of producing longer-lasting effects with precise specificity from the genetic design. Preclinical studies on gene therapy for hypertension have taken two approaches. Chao et al. have carried out extensive studies on gene transfer to increase vasodilator proteins. They have transferred kallikrein, atrial natriuretic peptide, adrenomedullin, and endothelin nitric oxide synthase into different rat models. Their results show that blood pressure can be lowered for 3-12 weeks with the expression of these genes. The antisense approach, which we began by targeting angiotensinogen and the angiotensin type 1 receptor, has now been tested independently by several different groups in multiple models of hypertension. Other genes targeted include the beta 1-adrenoceptor, TRH, angiotensin gene activating elements, carboxypeptidase Y, c-fos, and CYP4A1. There have been two methods of delivery antisense; one is short oligodeoxynucleotides, and the other is full-length DNA in viral vectors. All the studies show a decrease in blood pressure lasting several days to weeks or months. Oligonucleotides are safe and nontoxic. The adeno-associated virus delivery antisense to AT1 receptors is systemic and in adult rodents decreases hypertension for up to 6 months. We conclude that there is sufficient preclinical data to give serious consideration to Phase I trials for testing the antisense ODNs, first and later the AAV.

Pseudorabies virus-based gene delivery to rat embryonic spinal cord grafts

The construction and application of recombinant pseudorabies viruses (PrVs) for the delivery of beta-galactosidase and/or green fluorescent protein (GFP) genes to rat embryonic spinal cord cells are reported here. These viruses were specifically designed to infect embryonic spinal cord neurons, which can be grafted into a lesioned spinal cord in order to restore the lost functions of the host cord. The recombinant viruses were constructed in two steps. The small subunit of the ribonucleotide reductase (RR) gene was first abolished by a frameshift mutation and an expression cassette containing the lacZ gene alone or together with the GFP gene was then inserted in place of the early protein 0 (EP0) gene of PrV. The reporter gene cassettes were positioned downstream from the PrV latency-associated promoter. Using an ex vivo system, we infected embryonic spinal cord explants with these viruses and found that neither vRREP0lac nor vRREP0lacgfp exerted any cytotoxic effect at all. It was also revealed that these viruses infect embryonic cells with high efficiency, and that infected neurons grafted into the spinal cord express the inserted reporter genes for periods of up to 12 weeks. This system offers a new approach for foreign gene transfer to neurons grafted into the CNS.

Expression of BCL-2 via adeno-associated virus vectors rescues thalamic neurons after visual cortex lesion in the adult rat

Lesions of the mammalian visual cortex cause the retrograde degeneration of the thalamic neurons projecting to the damaged cortex. The proto-oncogene bcl-2 is known to inhibit neuronal apoptosis induced by a variety of noxious stimuli and preserve the functional integrity of the injured cells. Here we have tested whether the overexpression of bcl-2 via adeno-associated virus (AAV) vectors is able to protect the neurons in the lateral geniculate nucleus after visual cortex ablation in adult rats. Recombinant AAV vectors encoding Bcl-2 (AAV-Bcl-2) or green fluorescent protein (AAV-GFP) as a control were stereotaxically injected into the geniculate. Three weeks after vector injection, the ipsilateral visual cortex was removed by aspiration, and cell survival was assessed 2 weeks later. We found that 20% of the geniculate neurons were transduced by the Bcl-2 vector. These cells were completely protected from death following cortical ablation. Delivery of AAV-GFP transduced an identical number of geniculate neurons but had no effect on cell survival after lesion. The total number of surviving geniculate neurons was found to be significantly higher in animals injected with AAV-Bcl-2 than in rats injected with AAV-GFP or in control lesioned rats. These data indicate that Bcl-2 gene therapy with AAV vectors represents an effective treatment to promote neuronal survival after central nervous system insults.

Rescue of a deficiency in ATP synthesis by transfer of MTATP6, a mitochondrial DNA-encoded gene, to the nucleus

A T-->G transversion at nt 8993 in mitochondrial DNA of MTATP6 (encoding ATPase 6 of complex V of the respiratory chain) causes impaired mitochondrial ATP synthesis in two related mitochondrial disorders: neuropathy, ataxia and retinitis pigmentosa and maternally inherited Leigh syndrome. To overcome the biochemical defect, we expressed wildtype ATPase 6 protein allotopically from nucleus-transfected constructs encoding an amino-terminal mitochondrial targeting signal appended to a recoded ATPase 6 gene (made compatible with the universal genetic code) that also contained a carboxy-terminal FLAG epitope tag. After transfection of human cells, the precursor polypeptide was expressed, imported into and processed within mitochondria, and incorporated into complex V. Allotopic expression of stably transfected constructs in cytoplasmic hybrids (cybrids) homoplasmic with respect to the 8993T-->G mutation showed a significantly improved recovery after growth in selective medium as well as a significant increase in ATP synthesis. This is the first successful demonstration of allotopic expression of an mtDNA-encoded polypeptide in mammalian cells and could form the basis of a genetic approach to treat a number of human mitochondrial disorders.

Budding of equine infectious anemia virus is insensitive to proteasome inhibitors

The only retrovirus protein required for the budding of virus-like particles is the Gag protein; however, recent studies of Rous sarcoma virus (RSV) and human immunodeficiency virus have suggested that modification of Gag with ubiquitin (Ub) is also required. As a consequence, the release of these viruses is reduced in the presence of proteasome inhibitors, which indirectly reduce the levels of free Ub within the cell. Here we show that the budding of equine infectious anemia virus (EIAV) from infected equine cells is largely unaffected by these drugs, although use of one inhibitor (MG-132) resulted in a dramatic block to proteolytic processing of Gag. This lack of sensitivity was also observed in transiently transfected avian cells under conditions that greatly reduce RSV budding. Moreover, insensitivity was observed when the EIAV Gag protein was expressed in the absence of all the other virus products, indicating that they are not required for this phenotype. An activity that enables EIAV to tolerate exposure to proteasome inhibitors was mapped to the C-terminal p9 sequence, as demonstrated by the ability of an RSV Gag-p9 chimera to bud in the presence of the drugs. Intriguingly, the p9 sequence contains a short sequence motif that is similar to a surface-exposed helix of Ub, suggesting that EIAV Gag may have captured a function that allows it to bypass the need for ubiquitination. Thus, the mechanism of EIAV budding may not be substantially different from that of other retroviruses, even though it behaves differently in the presence of proteasome inhibitors.

Restoration of UV sensitivity in UV-resistant HeLa cells by antisense-mediated depletion of damaged DNA-binding protein 2 (DDB2)

Damaged DNA-binding activity comprises two major protein components, DDB1 and DDB2, which are implicated in the repair of ultraviolet (UV) radiation-induced DNA damage. The possible role of DDB2 as a determinant of cellular sensitivity to UV was investigated. The abundance of DDB2 in UV-resistant HeLa cell lines was increased compared with that in the parental UV-sensitive cells. Stable transfection of the resistant cells with DDB2 antisense cDNA resulted in marked depletion of DDB2 protein and restored cellular sensitivity to UV-induced apoptosis. Whereas the extent of UV-induced activation of apoptosis executioners, including DNA fragmentation factor, and caspase-3 were reduced in the UV-resistant cells compared with those apparent in the sensitive cells, depletion of DDB2 from the resistant cells restored the normal activation patterns for these proteins. In contrast, overexpressing DDB2 in DDB2-depleted cells with recombinant adenovirus, which carries ddb2 cDNA, markedly inhibited the extent of UV-induced activation of DNA fragmentation factor, and caspase-3. Interestingly, a mutated form of DDB2, which is defective in interacting with DDB1 and binding to UV-damaged DNA, also markedly inhibited the activation of apoptosis executioners. These results indicate that DDB2 is a modulator of UV-induced apoptosis, and that UV resistance can be overcome by inhibition of DDB2. The findings also suggest that modulation of UV-induced apoptosis by DDB2 may be independent of DNA repair.

Transduction of human and mouse pancreatic islet cells using a bicistronic recombinant adeno-associated viral vector

Recent reports indicate successful transduction of pancreatic islets using recombinant adeno-associated viral (rAAV) vectors. This advance offers new possibilities in rendering islets resistant to rejection and recurrence of autoimmune destruction in the setting of islet transplantation as treatment of type 1 diabetes. Most gene delivery approaches using islets have thus far involved transduction with a single gene. However, the concomitant delivery of more than one gene encoding cytoprotective and/or immunoregulatory molecules may offer superior clinical utility. Here, we have generated a bicistronic rAAV (serotype 2) vector incorporating a viral internal ribosome entry site (IRES), derived from polio virus type 1, to allow for translation of two coupled cDNAs from a single mRNA transcript. Our study demonstrates the ability of this vector to produce significant expression of two reporter proteins in human and mouse islets in vitro. This expression did not interfere with beta-cell function. Transduction was maintained in vivo following transplantation of mouse islets. These data are the first report of efficient islet cell transduction with two genes using a single bicistronic rAAV vector and have direct implications for strategies aimed at enhancing islet transplant survival.

Focal adhesions require catalytic activity of Src family kinases to mediate integrin-matrix adhesion

Members of the Src family of tyrosine kinases function to phosphorylate focal adhesion (FA) proteins. To explore the overlapping functions of Src kinases, we have targeted Csk, a negative regulator of the Src family, to FA structures. Expression of FA-targeted Csk (FA-Csk) effectively reduced the active form (nonphosphorylated at the C-terminal regulatory tyrosine) of Src members in the cell. We found that fibroblasts expressing FA-Csk lost integrin-mediated adhesion. Activated Src (SrcY529F) as well as activation of putative Src signaling mediators (Fak, Cas, Crk/CrkL, C3G, and Rap1) blocked the effect of FA-Csk in a manner dependent on Rap1. SrcY529F also inhibited activated Ras-induced cell detachment but failed to rescue detachment caused by an activated mutant of Raf1 (Raf-BXB) that Rap1 cannot inhibit. Although normal spreading onto fibronectin was restored by the beta(1) integrin affinity-activating antibody TS2/16 in cells expressing FA-Csk or Raf-BXB, FAs were lost in these cells. On the other hand, Rap1 activation could restore FAs in cells expressing FA-Csk. Activation of the executioner caspase, caspase 3, is essential for many forms of apoptosis. While a caspase 3 inhibitor (Z-DEVD-FMK) inhibited cell detachment triggered by activation of caspase 8, this inhibitor had no effect on cell detachment caused by FA-Csk. Likewise, overexpression of an activated Akt made cells resistant to the effect of caspase 8 activation, but not to the effect of FA-Csk. It is therefore likely that the primary cause of cell rounding and detachment induced by FA-Csk involves dysfunction of FAs rather than caspase-mediated apoptosis that may result from possible loss of survival signals mediated by Src family kinases. We suggest that endogenous Src family kinases are essential for FAs through activation of Rap1 in fibroblasts.

Vaccine-induced immune responses in rodents and nonhuman primates by use of a humanized human immunodeficiency virus type 1 pol gene

A synthetic gene consisting of the reverse transcriptase (RT) and integrase (IN) domains of human immunodeficiency virus type 1 (HIV-1) pol was constructed using codons most frequently used in humans. The humanized pol gave dramatically improved levels of Rev-independent, in vitro protein production in mammalian cells and elicited much stronger cellular immunity in rodents than did virus-derived gene. Specifically, BALB/c mice were immunized with plasmids and/or recombinant vaccinia virus constructs expressing the synthetic gene. High frequencies of Pol-specific T lymphocytes were detected in these animals by the gamma interferon enzyme-linked immunospot assay against pools of short overlapping peptides. Characterization of the stimulatory peptides from these pools indicates that the optimized gene constructs are able to effectively activate both CD4+ and CD8+ T cells. Immunization of rhesus macaques with DNA vaccines expressing the humanized pol coupled to a human tissue plasminogen activator leader sequence led to pronounced in vitro cytotoxic T-lymphocyte killing activities and enhanced levels of circulating Pol-specific T cells, comparable to those observed in HIV-1-infected human subjects. Thus, optimizing the immunogenic properties of HIV-1 Pol at the level of the gene sequence validates it as an antigen and provides an important step toward the construction of a potent pol-based HIV-1 vaccine component.

Codon-improved Cre recombinase (iCre) expression in the mouse

By applying the mammalian codon usage to Cre recombinase, we improved Cre expression, as determined by immunoblot and functional analysis, in three different mammalian cell lines. The improved Cre (iCre) gene was also designed to reduce the high CpG content of the prokaryotic coding sequence, thereby reducing the chances of epigenetic silencing in mammals. Transgenic iCre expressing mice were obtained with good frequency, and in these mice loxP-mediated DNA recombination was observed in all cells expressing iCre. Moreover, iCre fused to two estrogen receptor hormone binding domains for temporal control of Cre activity could also be expressed in transgenic mice. However, Cre induction after administration of tamoxifen yielded only low Cre activity. Thus, whereas efficient activation of Cre fusion proteins in the brain needs further improvements, our studies indicate that iCre should facilitate genetic experiments in the mouse.

Activation of cAMP-dependent protein kinase increases the protein level of steroidogenic factor-1

The orphan nuclear receptor steroidogenic factor 1 (SF-1) is an essential regulator of endocrine organogenesis, sexual differentiation, and steroidogenesis. SF-1 is a transcriptional regulator of cAMP responsive genes, but the exact mechanisms by which cAMP-dependent PKA modulates SF-1 dependent transcription leading to increased steroidogenic output have not been determined. In this report the effects of PKA activation on SF-1 in living cells have been examined by the use of full-length SF-1 cDNA fused to the cDNA encoding green fluorescent protein (GFP). The GFP-SF-1 fusion protein localized to the nucleus of both steroidogenic Y1 cells and nonsteroidogenic COS-1 cells, and the functional properties of wild-type SF-1 were conserved. When the catalytic subunit of PKA was coexpressed with GFP-SF-1, we observed that the fluorescence emission was markedly elevated. These findings were confirmed by Western blot analysis, showing that stimulation of PKA increased SF-1 protein levels. The PKA- induced expression of SF-1 protein was not accompanied by an increase in SF-1 mRNA levels. However, pulse-chase studies showed a decrease in SF-1 degradation rate in response to activation of PKA, indicating that PKA elevates the level of SF-1 by increasing the stability of SF-1 protein.

MuSK induces in vivo acetylcholine receptor clusters in a ligand-independent manner

Muscle-specific receptor tyrosine kinase (MuSK) is required for the formation of the neuromuscular junction. Using direct gene transfer into single fibers, MuSK was expressed extrasynaptically in innervated rat muscle in vivo to identify its contribution to synapse formation. Spontaneous MuSK kinase activity leads, in the absence of its putative ligand neural agrin, to the appearance of epsilon-subunit-specific transcripts, the formation of acetylcholine receptor clusters, and acetylcholinesterase aggregates. Expression of kinase-inactive MuSK did not result in the formation of acetylcholine receptor (AChR) clusters, whereas a mutant MuSK lacking the ectodomain did induce AChR clusters. The contribution of endogenous MuSK was excluded by using genetically altered mice, where the kinase domain of the MuSK gene was flanked by loxP sequences and could be deleted upon expression of Cre recombinase. This allowed the conditional inactivation of endogenous MuSK in single muscle fibers and prevented the induction of ectopic AChR clusters. Thus, the kinase activity of MuSK initiates signals that are sufficient to induce the formation of AChR clusters. This process does not require additional determinants located in the ectodomain.

Involvement of cellular double-stranded DNA break binding proteins in processing of the recombinant adeno-associated virus genome

Unlike postmitotic tissues in vivo, transduction of cultured cells is poor with recombinant adeno-associated virus (rAAV). The ability of rAAV to transduce cells is greatly enhanced by a variety of agents that induce DNA damage and is elevated in cells defective in the ataxia telangiectasia gene product (ATM), showing increased genomic instability. Here we show that DNA double-stranded break (DSB) repair pathways are involved in the regulation of rAAV transduction efficiency. By quantitative chromatin immunoprecipitation, we found that Ku86 and Rad52 proteins associate with viral DNA inside transduced cells. Both proteins are known to competitively recognize hairpin structures and DNA termini and to promote repair of DSBs, the former by facilitating nonhomologous end joining and the latter by initiating homologous recombination. We found that rAAV transduction is increased in Ku86-defective cells while it is inhibited in Rad52 knockout cells. These results suggest that binding of Rad52 to the rAAV genome might be involved in processing of the vector genome through a homologous recombination pathway.

Codon usage bias covaries with expression breadth and the rate of synonymous evolution in humans, but this is not evidence for selection

In numerous species, from bacteria to Drosophila, evidence suggests that selection acts even on synonymous codon usage: codon bias is greater in more abundantly expressed genes, the rate of synonymous evolution is lower in genes with greater codon bias, and there is consistency between genes in the same species in which codons are preferred. In contrast, in mammals, while nonequal use of alternative codons is observed, the bias is attributed to the background variance in nucleotide concentrations, reflected in the similar nucleotide composition of flanking noncoding and exonic third sites. However, a systematic examination of the covariants of codon usage controlling for background nucleotide content has yet to be performed. Here we present a new method to measure codon bias that corrects for background nucleotide content and apply this to 2396 human genes. Nearly all (99%) exhibit a higher amount of codon bias than expected by chance. The patterns associated with selectively driven codon bias are weakly recovered: Broadly expressed genes have a higher level of bias than do tissue-specific genes, the bias is higher for genes with lower rates of synonymous substitutions, and certain codons are repeatedly preferred. However, while these patterns are suggestive, the first two patterns appear to be methodological artifacts. The last pattern reflects in part biases in usage of nucleotide pairs. We conclude that we find no evidence for selection on codon usage in humans.