Transcriptional activation of cloned human beta-globin genes by viral immediate-early gene products

Expression of the immediate early IE180 protein under the control of the hTERT and CEA tumor-specific promoters in recombinant pseudorabies viruses: Effects of IE180 protein on promoter activity and apoptosis induction

Since the pseudorabies virus (PRV) genome encodes for a single immediate-early protein, IE180, we reasoned that this strong transactivating protein could represent a key regulatory switch that could be genetically manipulated in order to alter its tropism towards cancer cells. We therefore initiated studies to test whether the human telomerase reverse transcriptase (hTERT) and carcinoembryonic antigen (CEA) tumor promoters could functionally replace the IE180 promoter. We show that both promoters can functionally substitute the IE180 promoter in plasmid constructs and recombinant viruses, and observed that IE180 differentially auto-regulated each promoter tested, with PRV IE180 negatively regulating the hTERT promoter but positively hyper-activating the CEA promoter. Interestingly, we also observed that the recombinant PRV-TER and PRV-CEA viruses preferentially replicated in diverse cancer cell lines compared to control non-cancer cells, and the PRV-CEA was capable of additionally inducing a profound apoptotic phenotype which we correlated to the overexpression of IE180.

Anti pseudorabies virus activity of kumazasa extract

Sasa veitchii or "kumazasa" has been used for the preservation of food, or preventing bacterial activity. However, the antiviral activity of kumazasa is poorly understood. In the present study, the antiviral activity of kumazasa extract (KE) was assessed by the plaque reduction assay for the pseudorabies virus (PRV). KE reduced 99% of the plaque formation of PRV at concentrations of 1.2%, showing that KE inhibited PRV adsorption to cells and IE180 expression. The polysaccharide fraction of KE showed a concentration dependent inhibition of PRV plaque formation. We conclude that KE possesses potent anti PRV activity, and the candidate responsible for the antiviral property was the polysaccharide fraction.

Motor-coordination-dependent learning, more than others, is impaired in transgenic mice expressing pseudorabies virus immediate-early protein IE180

The cerebellum in transgenic mice expressing pseudorabies virus immediate-early protein IE180 (TgIE96) was substantially diminished in size, and its histoarchitecture was severely disorganized, resulting in severe ataxia. TgIE96 mice can therefore be used as an experimental model to study the involvement of cerebellar circuits in different learning tasks. The performance of three-month-old TgIE96 mice was studied in various behavioral tests, including associative learning (classical eyeblink conditioning), object recognition, spatial orientation (water maze), startle response and prepulse inhibition, and passive avoidance, and compared with that of wild-type mice. Wild-type and TgIE96 mice presented similar reflexively evoked eyeblinks, and acquired classical conditioned eyelid responses with similar learning curves for both trace and delay conditioning paradigms. The two groups of mice also had similar performances during the object recognition test. However, they showed significant differences for the other three tests included in this study. Although both groups of animals were capable of swimming, TgIE96 mice failed to learn the water maze task during the allowed time. The startle response to a severe tone was similar in both control and TgIE96 mice, but the latter were unable to produce a significant prepulse inhibition. TgIE96 mice also presented evident deficits for the proper accomplishment of a passive avoidance test. These results suggest that the cerebellum is not indispensable for the performance of classical eyeblink conditioning and for object recognition tasks, but seems to be necessary for the proper performance of water maze, prepulse inhibition, and passive avoidance tests.

Cerebellar pathology in transgenic mice expressing the pseudorabies virus immediate-early protein IE180

Pseudorabies virus is an alphaherpesvirus causing fatal neurological diseases in animals. Pseudorabies virus carries a gene encoding immediate-early (IE) protein IE180, which controls the transcription of other viral and host cell genes. Previously, we reported that transgenic expression of IE180 in mice causes severe ataxia and cerebellar deformity. Here we identified profound abnormalities in adult IE180 transgenic mice, including malpositioning of Purkinje cells (PCs), granule cells (GCs) and Bergmann glia (BG), impaired dendritogenesis and synaptogenesis in PCs, disoriented BG fibers, absence of molecular layer interneurons, and increased apoptosis of neurons and glia. In accordance with the cellular defects, we found the expression of IE180 in PCs, GCs and astrocytes during cerebellar development. We next examined transgenic mice expressing truncated IE180 mutants: dlN132 lacking the acidic transcriptional active domain, dlC629 lacking the nuclear localization signal and dlC1081 having all known domains but lacking the carboxyl-terminal sequence. Despite similar expression levels of the transgenes, ataxia and cerebellar defects were only manifested in the dlC1081 transgenic mice but their phenotypes were milder compared with the IE180 transgenic mice. In the dlC1081 transgenic mice, cerebellar neurons and glia were normally positioned but cerebellar size was severely reduced due to GC deficits. Interestingly, dlC1081 was mainly expressed in the GCs with low expression in a few BG. Taken together, the present findings clarified a causal relationship between cerebellar pathology and cellular expression of IE180, and further afforded an experimental insight into different symptomatic severity as a consequence of different cellular defects caused by such cytotoxic viral agents.

Tumor necrosis factor (TNF) protects resistant C57BL/6 mice against herpes simplex virus-induced encephalitis independently of signaling via TNF receptor 1 or 2

Tumor necrosis factor (TNF) is a multifunctional cytokine that has a role in induction and regulation of host innate and adaptive immune responses. The importance of TNF antiviral mechanisms is reflected by the diverse strategies adopted by different viruses, particularly members of the herpesvirus family, to block TNF responses. TNF binds and signals through two receptors, Tnfrsf1a (TNF receptor 1 [TNFR1], or p55) and Tnfrsf1b (TNFR2, or p75). We report here that herpes simplex virus 1 (HSV-1) infection of TNF-/- mice on the resistant C57BL/6 genetic background results in significantly increased susceptibility (P < 0.0001, log rank test) to fatal HSV encephalitis (HSE) and prolonged persistence of elevated levels of virus in neural tissues. In contrast, although virus titers in neural tissues of p55-/- N13 mice were elevated to levels comparable to what was found for the TNF-/- mice, the p55-/- N13 mice were as resistant as control C57BL/6 mice (P > 0.05). The incidence of fatal HSE was significantly increased by in vivo neutralization of TNF using soluble TNFR1 (sTNFR1) or depletion of macrophages in C57BL/6 mice (P = 0.0038 and P = 0.0071, respectively). Strikingly, in vivo neutralization of TNF in HSV-1-infected p55-/- p75-/- mice by use of three independent approaches (treatment with soluble p55 receptor, anti-TNF monoclonal antibody, or in vivo small interfering RNA against TNF) resulted in significantly increased mortality rates (P = 0.005), comparable in magnitude to those for C57BL/6 mice treated with sTNFR1 (P = 0.0018). Overall, these results indicate that while TNF is required for resistance to fatal HSE, both p55 and p75 receptors are dispensable. Precisely how TNF mediates protection against HSV-1 mortality in p55-/- p75-/- mice remains to be determined.

Klf4 cooperates with Oct3/4 and Sox2 to activate the Lefty1 core promoter in embryonic stem cells

Although the POU transcription factor Oct3/4 is pivotal in maintaining self renewal of embryonic stem (ES) cells, little is known of its molecular mechanisms. We previously reported that the N-terminal transactivation domain of Oct3/4 is required for activation of Lefty1 expression (H. Niwa, S. Masui, I. Chambers, A. G. Smith, and J. Miyazaki, Mol. Cell. Biol. 22:1526-1536, 2002). Here we test whether Lefty1 is a direct target of Oct3/4. We identified an ES cell-specific enhancer upstream of the Lefty1 promoter that contains binding sites for Oct3/4 and Sox2. Unlike other known Oct3/4-Sox2-dependent enhancers, however, this enhancer element could not be activated by Oct3/4 and Sox2 in differentiated cells. By functional screening of ES-specific transcription factors, we found that Krüppel-like factor 4 (Klf4) cooperates with Oct3/4 and Sox2 to activate Lefty1 expression, and that Klf4 acts as a mediating factor that specifically binds to the proximal element of the Lefty1 promoter. DNA microarray analysis revealed that a subset of putative Oct3/4 target genes may be regulated in the same manner. Our findings shed light on a novel function of Oct3/4 in ES cells.

Cellular gene expression survey of PseudoRabies Virus (PRV) infected Human Embryonic Kidney cells (HEK-293)

Pseudorabies virus (PRV) is an alpha herpesvirus that causes Aujezsky disease in the pig. To characterize the impact of PRV infection on cellular expression, we used microarrays consisting of 9850 oligonucleotides corresponding to human genes and examined the expression levels of mRNA isolated 0.5, 3, 6, and 9 h post infection (hpi) from cultures of infected HEK-293 cells. Very few changes were observed during the first 3 h of infection but significant modifications in the cell expression of more than 1000 genes were clearly apparent by 6 hpi. More than 2400 genes were either up- or down-regulated during the 9 h experiment. These results were then analyzed using gene ontology and the MAPP and MAPPFinder software. This comprehensive analysis clearly shows that the down-regulated genes were mainly involved in macromolecular synthesis (DNA, RNA and proteins) and the cell cycle. The up-regulated genes primarily concerned the regulation of DNA transcription, developmental processes (central nervous system development, neurogenesis, angiogenesis), cell adhesion and potassium transport. This study is the first qualitative analysis of a gene expression survey in a human cell line following PRV infection. It demonstrates global changes in the cell expression profile, and identifies the main biological processes that are altered during virus replication.

Molecular biology of pseudorabies virus: impact on neurovirology and veterinary medicine

Pseudorabies virus (PRV) is a herpesvirus of swine, a member of the Alphaherpesvirinae subfamily, and the etiological agent of Aujeszky's disease. This review describes the contributions of PRV research to herpesvirus biology, neurobiology, and viral pathogenesis by focusing on (i) the molecular biology of PRV, (ii) model systems to study PRV pathogenesis and neurovirulence, (iii) PRV transsynaptic tracing of neuronal circuits, and (iv) veterinary aspects of pseudorabies disease. The structure of the enveloped infectious particle, the content of the viral DNA genome, and a step-by-step overview of the viral replication cycle are presented. PRV infection is initiated by binding to cellular receptors to allow penetration into the cell. After reaching the nucleus, the viral genome directs a regulated gene expression cascade that culminates with viral DNA replication and production of new virion constituents. Finally, progeny virions self-assemble and exit the host cells. Animal models and neuronal culture systems developed for the study of PRV pathogenesis and neurovirulence are discussed. PRV serves asa self-perpetuating transsynaptic tracer of neuronal circuitry, and we detail the original studies of PRV circuitry mapping, the biology underlying this application, and the development of the next generation of tracer viruses. The basic veterinary aspects of pseudorabies management and disease in swine are discussed. PRV infection progresses from acute infection of the respiratory epithelium to latent infection in the peripheral nervous system. Sporadic reactivation from latency can transmit PRV to new hosts. The successful management of PRV disease has relied on vaccination, prevention, and testing.

Regulation of RNA Polymerase II Transcription by Sequence-Specific DNA Binding Factors

In eukaryotes, transcription of the diverse array of tens of thousands of protein-coding genes is carried out by RNA polymerase II. The control of this process is predominantly mediated by a network of thousands of sequence-specific DNA binding transcription factors that interpret the genetic regulatory information, such as in transcriptional enhancers and promoters, and transmit the appropriate response to the RNA polymerase II transcriptional machinery. This review will describe some early advances in the discovery and characterization of the sequence-specific DNA binding transcription factors as well as some of the properties of these regulatory proteins.

Impaired development of the cerebellum in transgenic mice expressing the immediate-early protein IE180 of pseudorabies virus

Pseudorabies virus (PRV) infection in animals other than its natural host almost always gives rise to fatal diseases in the central nervous system as a result of infection of peripheral neurons and subsequently to the brain. PRV immediate-early protein (IE180) activates transcription of the PRV early and late genes, and other viral and cellular genes, and represses its own transcription. To examine specific effects of IE180 in neuropathogenicity, we have generated four transgenic mouse lines expressing IE180 in a tetracycline-regulated system. In the transgenic mouse lines, cerebellar symptoms such as ataxic gait, tremor and motor discoordination were observed. Histopathology of the cerebella in the transgenic mouse lines showing severe symptoms was remarkable for a failure of layer formation and a reduction in cerebellar size. These findings suggest that IE180 affects the cascade of gene expression for development of the murine cerebellum, resulting in the impairment of the cerebellar development and differentiation.

POU/TBP cooperativity: a mechanism for enhancer action from a distance

Enhancers when functioning at a distance cannot effectively stimulate transcription from core promoters. We demonstrate that this is due to the inability of enhancer-bound activators to recruit TBP to a distal TATA box. Surprisingly, binding of a transcriptionally inert Oct-1 POU domain near a core promoter enables an enhancer to function from a distance. POU activity neither requires the coactivator OCA-B nor the interaction of TBP with TFIIA. Instead, the POU domain directly facilitates TBP recruitment to the promoter utilizing a bipartite interaction surface. These results establish that an interaction between the DNA binding domain of an activator and TBP can be used to stimulate transcription. Furthermore, they suggest a mechanism for long-range enhancer function in which a TBP complex is preassembled on a promoter via localized recruitment and then acted upon by distal activators.

Inhibition of pseudorabies virus replication by a dominant-negative mutant of early protein 0 expressed in a tetracycline-regulated system

Pseudorabies virus (PRV) early protein 0 (EP0) consisting of 410 amino acids is a transactivator of viral genes. A mutant consisting of amino acids 1-113 exhibits dominant-negative properties. In order to assess the antiviral potential of the EP0 mutant, Vero cells were transformed with the EP0 mutant gene expressed in a tetracycline-regulated system. The transformed cell lines showed marked resistance to PRV infection when expression of the EP0 mutant gene was induced. In the transformed cell line infected with PRV, synthesis of the immediate-early protein (IE180) and of EP0 was inhibited, whereas the levels of IE and EP0 messenger RNA (mRNA) were not decreased, as compared with those of the control cell line. The present results suggest that the EP0 mutant may not alter the efficiency of the viral gene transcription but rather translation efficiency of the viral mRNA.

Granulocytic differentiation of myeloid progenitor cells by p130, the retinoblastoma tumor suppressor homologue

The retinoblastoma protein (pRB) and the related pocket proteins, p107 and p130, play crucial roles in mammalian cell cycle control. Recent studies indicate that these pocket proteins are also involved in cellular differentiation processes. We demonstrate in this work that the pRB-related p130 selectively accumulates during the in vitro differentiation of the myeloid progenitor cell, 32Dcl3, into granulocyte in response to granulocyte-colony stimulating factor (G-CSF). This G-CSF-dependent granulocytic differentiation is blocked by the adenovirus E1A oncoprotein, which binds to and inactivates the pRB family of pocket proteins including p130. Furthermore, enforced overexpression of p130 but not pRB inhibits the myeloid cell proliferation that is concomitantly associated with granulocytic differentiation morphologically characterized by nuclear segmentation. However, simple G1-cell cycle arrest induced by cytokine deprivation or ectopic overexpression of the p27 cyclin-dependent kinase inhibitor, or inhibition of E2F activities by dominant negative DP-1 is not sufficient to trigger granulocytic differentiation. The differentiation-promoting activity of p130 in myeloid cells requires both the pocket domain and the spacer domain. Our results indicate that the pRB-related p130 plays a critical role in myeloid cell differentiation and suggest that coupling of cell cycle exit with the cellular differentiation program may be specifically achieved by p130.

Induction of erythrocyte protein 4.2 gene expression during differentiation of murine erythroleukemia cells

Protein 4.2 (P4.2) is an important component in the erythrocyte membrane skeletal network that regulates the stability and flexibility of erythrocytes. Recently, we provided the evidence for specific P4.2 expression in erythroid cells during development (L. Zhu et al., 1998, Blood 91, 695-705). Using dimethyl sulfoxide (DMSO)-induced differentiation of murine erythroleukemia (MEL) cells as a model, transcription of the P4.2 gene was found to be induced during erythroid differentiation. To examine the mechanism for this induction, we isolated the mouse P4.2 genomic DNA containing the 5' flanking sequence and defined the location of the P4.2 promoter. Transcription of the mouse P4.2 gene initiates at multiple sites, with the major initiation site mapped at 174 nucleotides upstream of the ATG start codon. The mouse P4.2 promoter is TATA-less and contains multiple potential binding sites for erythroid transcription factors GATA-1, NF-E2, EKLF, and tal-1/SCL. Transient transfection experiments demonstrated that a 1.7-kb mouse P4.2 promoter fused with the luciferase coding regions was induced in DMSO-treated MEL cells. Deletion analysis showed that a 259-bp P4.2 promoter DNA (nucleotide position -88 to +171 relative to the major transcription initiation site designated +1), containing a GATA-binding site at position -29 to -24, could still respond to the induction in differentiated MEL cells. Importantly, mutations in the -29/-24 GATA motif rendered the promoter unresponsive to DMSO induction. Electrophoretic mobility shift assay revealed that GATA-1 could bind to the -29/-24 GATA motif and this was confirmed by the observation that the nuclear protein bound to the motif was supershifted by an anti-GATA-1 monoclonal antibody. Taken together, these results suggest that the erythroid transcription factor GATA-1 plays an important role in the induction of P4.2 gene expression during erythroid cell differentiation.

Long-distance transcriptional enhancement by the histone acetyltransferase PCAF

Enhancers are defined by their ability to stimulate gene activity from remote sites and their requirement for promoter-proximal upstream activators to activate transcription. Here we demonstrate that recruitment of the p300/CBP-associated factor PCAF to a reporter gene is sufficient to stimulate promoter activity. The PCAF-mediated stimulation of transcription from either a distant or promoter-proximal position depends on the presence of an upstream activator (Sp1). These data suggest that acetyltransferase activity may be a primary component of enhancer function, and that recruitment of polymerase and enhancement of transcription are separable. Transcriptional activation by PCAF requires both its acetyltransferase activity and an additional activity within its N terminus. We also show that the simian virus 40 enhancer and PCAF itself are sufficient to counteract Mad-mediated repression. These results are compatible with recent models in which gene activity is regulated by the competition between deacetylase-mediated repression and enhancer-mediated recruitment of acetyltransferases.

The -104G nucleotide of the human CYP21 gene is important for CYP21 transcription activity and protein interaction

CYP21 gene encodes the steroid 21-hydroxylase (P450c21) that is involved in steroidogenesis in the adrenal cortex. Mutations occurring on CYP21 which convert it to the neighboring pseudogene, CYP21P, are found in patients with congenital adrenal hyperplasia (CAH), an autosomal recessive disease. We previously reported that the CYP21P pseudogene had lower transcription activity when compared with the active CYP21 gene. The sequences determining the basal transcription activity of the human CYP21 gene are located within the 166 bp region upstream from the transcriptional start site. Within this region, only 4 nucleotides are different between the active CYP21 and the CYP21P pseudogene; they are located at the -117, -104, -101 and -94 positions from the start site of the gene. Here, we report that the CYP21 gene-specific G nucleotide sequence at the -104 position is required for its basal transcription activity driven by the native TATA box of the human CYP21 gene. When this single nucleotide is changed to the CYP21P sequence, the basal transcription activity decreases by approximately 80% in transient transfection assay. In addition, our data from gel retardation assay show that this sequence is also critical for interaction with nuclear proteins from adrenal cells. These results therefore suggest that the single G sequence of the human CYP21 gene is crucial for the expression of its basal transcription activity, and this may be influenced by the interaction with specific nuclear proteins from the adrenal gland.

Promoter activity of sequence located upstream of the pseudorabies virus early protein 0 gene

Promoter activity of the 5'-flanking region of the pseudorabies virus (PRV) early protein 0 (EP0) gene was analysed by transient transfection assays employing chloramphenicol acetyl transferase (CAT) reporter constructs. We identified a 213 bp segment of the viral genome that was capable of efficiently driving expression of the EPO gene and a linked reporter gene upon transient transfection into Vero cells. This segment lacked the typical TATA element, and possessed an initiator element and the putative binding sites for the transcription factor Sp1 and immediate-early protein IE180, a strong transactivator of PRV. By analysing 5'-deletion mutants of the segment, a 48 bp segment (from nucleotide positions -65 to -17), which possessed three Sp1 binding sites, was identified to be critical for the promoter activity. Cotransfection of Vero cells with the mutant constructs and an IE180 expression plasmid resulted in transactivation of only those constructs in which the Sp1 sites were present. These results indicate that the EP0 gene may be transcribed from the TATA-less promoter that responds to Sp1.

Viral transactivating proteins

Many viruses utilize the cellular transcription apparatus to express their genomes, and they encode transcriptional regulatory proteins that modulate the process. Here we review the current understanding of three viral regulatory proteins. The adenovirus E1A protein acts within the nucleus to regulate transcription through its ability to bind to other proteins. The herpes simplex type 1 virus VP16 protein acts within the nucleus to control transcription by binding to DNA in conjunction with cellular proteins. The human T-cell leukemia virus Tax protein influences transcription through interactions with cellular proteins in the nucleus as well as the cytoplasm.

Immunolocalization of the pseudorabies virus immediate-early protein IE180 by immunoperoxidase staining

The immediate-early (1E) gene of pseudorabies virus (PRV) expresses immediately upon infection, a phosphorylated protein (immediate-early protein, IE180) that can transactivate viral other genes and plays an essential role in regulating viral gene expression. In order to detect and localize IE180 in infected cells early on, this gene was cloned for overexpression, and the expressed products were applied to generate specific antibodies against IE180 protein. Two recombinant expression plasmids pN and pNB were constructed by cloning the IE gene onto pET 30a(+) expression vector via NcoI and BamHI sites. Plasmid pN contains the 1.8-kb NcoI-NcoI fragment of IE gene coding for the N-terminus of 616 amino acid residues, while pNB contains the 2.8-kb NcoI-Bam HI fragment coding for the rest of the IE180 protein. Both pN and pNB were transformed, respectively, into E. coli cells and produced large amounts of IE protein products during induction with 1 mM IPTG. The expressed IE proteins for pN and pNB were 60 kDa and 100 kDa in size, respectively. These expression products were purified and then used as antigens to immunize mice for preparing specific antibodies against PRV IE180 protein. The specificities of the mice immune sera were confirmed by their abilities to react with IE180 protein present in the PRV infected cells in the Western immunoblotting assay. Furthermore, immunoperoxidase staining of PRV infected cells undertaken with these antisera revealed the subcellular distribution of the IE proteins in the infected cells and also demonstrated their transportation from the cytoplasm to the nucleus during infection.

Herpes simplex virus immediate-early proteins ICP0 and ICP4 activate the endogenous human alpha-globin gene in nonerythroid cells

Globin genes are normally expressed only in erythroid cell lineages. However, we found that the endogenous alpha-globin gene is activated following infection of human fibroblasts and HeLa cells with herpes simplex virus (HSV), leading to accumulation of correctly initiated transcripts driven by the alpha-globin promoter. The alpha1- and alpha2-globin genes were both induced, but expression of beta- or zeta-globin genes could not be detected. Experiments using HSV mutants showed that null mutations in the genes encoding the viral immediate-early proteins ICP4 and ICP22 reduced induction approximately 10-fold, while loss of ICP0 function had a smaller inhibitory effect. Transient transfection experiments showed that ICP0 and ICP4 are each sufficient to trigger detectable expression of the endogenous gene, while ICP22 had no detectable effect in this assay. ICP4 also strongly enhanced expression of transfected copies of the alpha2-globin gene. In contrast, the adenovirus E1a protein did not activate the endogenous gene and inhibited expression of the plasmid-borne alpha2-globin gene. Previous studies have led to the hypothesis that chromosomal alpha-globin genes are subject to chromatin-dependent repression mechanism that prevents expression in nonerythroid cells. Our data suggest that HSV ICP0 and ICP4 either break or bypass this cellular gene silencing mechanism.

Mapping of a functional region conferring nuclear localization of pseudorabies virus immediate-early protein

The immediate-early protein (IE180) of pseudorabies virus (PrV) is localized predominantly in the nuclei of infected cells. To define the nuclear localization signals within IE180, we prepared truncated mutants of IE180 and analyzed their localization in the transfected cells by indirect immunofluorescence. Analysis of mutants truncated from the carboxy-terminal end of the 1460-amino acid polypeptide showed that two regions including a short sequence of basic amino acid residues were associated with the nuclear localization of IE180. To assess whether these regions substantially function as signals for nuclear localization of the IE180 molecule, we then constructed two deletion mutants lacking each region. A mutant lacking amino acids 333 to 575 was detected in the nuclei of the transfected cells, whereas the other mutant lacking amino acids 900 to 950 was detected mainly in the cytoplasm. These results suggest that the region of amino acids 900 to 950 is responsible for nuclear localization of IE180.

Induction of transcription by a viral regulatory protein depends on the relative strengths of functional TATA boxes

The mechanisms by which viral regulatory proteins activate the cellular transcription apparatus without binding to specific DNA elements are not fully understood. Several lines of evidence suggest that activation by one such regulatory protein, herpes simplex virus ICP4, could be mediated, at least in part, by TFIID. To test this model, we replaced the TATA box of the ICP4-responsive viral thymidine kinase gene with functional TATA boxes that displayed different apparent affinities for TATA-box-binding protein as measured by DNase I footprinting. We measured the effects of these TATA boxes on ICP4 induction by constructing ICP4-deficient recombinant viruses containing the different TATA alleles and comparing their expression in cells lacking or expressing ICP4. Overall, ICP4 induced weak TATA boxes (those that displayed low apparent affinity for TATA-box-binding protein and low basal expression) the most (18- to 41-fold) and strong TATA boxes the least (7- to 10-fold). Therefore, ICP4 induction correlated inversely with TATA box strength. Using a reconstituted in vitro transcription assay, we determined that the relative levels of induction by ICP4 of the different TATA alleles were similar to those measured in vivo, suggesting that ICP4 was the only viral protein required for induction. These results fit a model in which ICP4 acts in part to enhance binding of TFIID to the TATA box. We compare and contrast these results with those observed with the viral regulatory proteins adenovirus E1a and simian virus 40 large T antigen and the cellular coactivator PC4.

Induction by adenovirus-5 E1A of the differentiation phenotype of F9 teratocarcinoma cells involves a conserved region (CR1) of E1A

The effects of the E1A protein of adenovirus-5 on the differentiation program of F9 teratocarcinoma cells were examined by the stable introduction of plasmids that expressed wild-type or mutated forms of E1A. Constitutive expression of plasmids for most of the mutant E1As induced loss of expression of the cell-surface antigen SSEA-1 and the enhanced expression of genes specific for the differentiated phenotype of F9 cells, such as genes for laminin B1, tissue-type plasminogen activator (tPA) and type IV collagen, as well as the altered cell morphology that is associated with the differentiated state. However, such changes were not observed in the case of genes for mutant proteins from which a conserved region (CR1) of E1A had been deleted. Furthermore, no significant induction of expression of the c-jun gene or transactivation of the c-jun-CAT reporter gene were observed when the sequence that encodes CR1 of E1A had been deleted. A palindromic sequence element (DRE) of the c-jun promoter was essential for the E1A-mediated up-regulation of the c-jun gene. These results imply that CR1 is required for activation of the c-jun gene and that it is implicated in the growth arrest, expression of parietal endoderm-specific functions and the orderly differentiation of F9 cells.

Strong transcriptional activators isolated from viral DNA by the 'activator trap', a novel selection system in mammalian cells

Transcription factors often contain activation domains that interact with the basic transcription machinery. We have developed a functional screening strategy in mammalian cells to selectively isolate activation domains from a library of random DNA inserts. For this, sonicated DNA fragments are cloned next to the DNA binding domain of GAL4 factor in a plasmid that also contains the SV40 origin of replication. Pools of fusion protein clones are transfected into CV-1-5GT monkey cells containing an SV40 T antigen gene under the control of a promoter with GAL4 binding sites. Plasmids that express functional transactivating fusion proteins activate the T antigen gene, thus promoting selective amplification of the plasmid in the mammalian host cell line. Using this method, we were able to select strong enhancer-type activation domains from the immediate early regions of two herpesviruses, namely pseudorabies virus and bovine herpesvirus 1. In both cases, the activation domains selected were homologues of the ICP4 regulatory protein of herpes simplex virus. The activation domain from pseudorabies virus is four times stronger than the activation domain of herpes simplex virus protein VP16 (Vmw65), making it the strongest activation domain characterized so far. This activator trap method should be useful for precisely localizing activation domain(s) in known factors, or to identify mammalian transcriptional adaptors that do not bind DNA and which may escape conventional detection methods.

Mapping of transcriptional regulatory domains of pseudorabies virus immediate-early protein

The 180 kilodalton immediate-early protein (IE180) of pseudorabies virus functions as a strong transactivator of several different promoters and also as a repressor of its own transcription. To map the functional domains of IE180, we prepared various truncated mutants and analyzed their transcriptional regulatory activities using the chloramphenicol acetyl transferase (CAT) assay. Analysis of mutants truncated from the carboxy-terminal end of the 1,460-amino acid polypeptide showed that a polypeptide possessing amino acids 1 to 1,081 retained significant functions of transactivation and autoregulation potential. On the other hand, removing amino acids 1 to 131 resulted in a complete loss of transactivation potential, indicating that the domain responsible for transactivation is located in the amino-terminal end of IE180. Additional amino-terminal truncation up to amino acid 453 did not affect the autoregulation activity, indicating that the region between amino acids 454 and 1081 has autoregulation potential.

Complementary functions of E1a conserved region 1 cooperate with conserved region 3 to activate adenovirus serotype 5 early promoters

The amino-terminal region of the adenovirus type 5 E1a protein including conserved regions (CRs) 1 and 2 binds the 105-kDa retinoblastoma protein and a second, 300-kDa, cellular protein. We show that mutant viruses with deletions of CR1 which release the binding of either p105 or p300 still activate early promoters and infect cells productively. However, mutations which disrupt binding of both proteins disrupt early promoter activity and block the viral life cycle. Ela CR3, which has an established role in early promoter activation, can act in trans to the amino-terminal functions. This suggests that the amino terminus provides distinct, redundant functions related to p300 and Rb binding that synergize with CR3 to transactivate early genes.

An early history of gene transfer and therapy

The term "gene therapy" was coined to distinguish it from the Orwellian connotations of "human genetic engineering," which, in turn, was derived from the term "genetic engineering." Genetic engineering was first used at the Sixth International Congress of Genetics held in 1932 and was taken to mean "the application of genetic principles to animal and plant breeding." Once the basics of molecular genetics and gene transfer in bacteria were established in the 1960s, gene transfer into animals and humans using either viral vectors and/or genetically modified cultured cells became inevitable. Despite the early exposition of the concept of gene therapy, progress awaited the advent of recombinant DNA technology. The lack of trustworthy techniques did not stop many researchers from attempting to transfer genes into cells in culture, animals, and humans. Viral genomes were used for the development of the first relatively efficient methods for gene transfer into mammalian cells in culture. In the late 1970s, early transfection techniques were combined with selection systems for cultured cells and recombinant DNA technology. With the development of retroviral vectors in the early 1980s, the possibility of efficient gene transfer into mammalian cells for the purpose of gene therapy became widely accepted.

Identification of a functional initiator sequence in the human MDR1 promoter

The sequence requirements for proper transcriptional initiation of the downstream human multidrug resistance MDR1 (P1) promoter were determined using a transient expression system in HeLa cells. The MDR1 promoter has no TATA box and the transcription start site has a strong homology with the initiator (Inr) sequence identified in the murine terminal deoxynucleotidyltransferase (TdT) gene. A deletion analysis showed that sequences from -6 to +11 relative to the P1 transcription start site were sufficient for proper transcriptional initiation, whereas deletion of sequences downstream of +11 resulted in a strong reduction of properly initiated transcripts. In this transient assay system, both the MDR1 and TdT initiator require in Hela cells the presence of an upstream activating sequence such as the SV40 enhancer. This is in contrast to the transcription in in vitro systems, in which the initiator sequence is able to direct transcription in the absence of an enhancer. Analysis of mutations in the initiator sequence from -8 to +10 showed that the A and T nucleotides at position +1 and +3, respectively, were essential, whereas other substitutions in this region had little effect on promoter activity.

A brief history of gene therapy

The concepts of gene therapy arose initially during the 1960s and early 1970s whilst the development of genetically marked cells lines and the clarification of mechanisms of cell transformation by the papaovaviruses polyoma and SV40 was in progress. With the arrival of recombinant DNA techniques, cloned genes became available and were used to demonstrate that foreign genes could indeed correct genetic defects and disease phenotypes in mammalian cells in vitro. Efficient retroviral vectors and other gene transfer methods have permitted convincing demonstrations of efficient phenotype correction in vitro and in vivo, now making gene therapy a broadly accepted approach to therapy and justifying clinically applied studies with human patients.

Promoter specificity of basal transcription factors

Regulation of expression of protein-encoding genes in eukaryotes is frequently mediated by sequence-specific transcription factors that control the activities of the basal factors and RNA polymerase II. Basal factors have been considered to be essential for all polymerase II promoters. Studies of the basal factor requirements for transcription from the immunoglobulin heavy chain gene (IgH) core promoter and the adenovirus major late gene core promoter (MLP) suggest that this paradigm is too simple. Basal transcription from the IgH promoter was reconstituted by TFIID, TFIIB, TFIIF, and polymerase, whereas basal transcription from the MLP is highly dependent upon TFIIE in addition to the above factors. Two novel protein activities, referred to as 700 kd and 90 kd, further stimulated the basal reaction from the MLP. Thus, these data indicate that not all basal factors are in fact general.

Characterization of the regulatory functions of the equine herpesvirus 1 immediate-early gene product

Use of the translation-inhibiting drug cycloheximide has indicated that the equine herpesvirus 1 (EHV-1) immediate-early (IE) gene, the sole EHV-1 IE gene, encodes a major viral regulatory protein since IE mRNA translation is a prerequisite for all further viral gene expression (W.L. Gray, R. P. Baumann, A. T. Robertson, G. B. Caughman, D. J. O'Callaghan, and J. Staczek, Virology 158:79-87, 1987). An EHV-1 IE gene expression vector (pSVIE) in combination with chimeric EHV-1 promoter-chloramphenicol acetyltransferase (CAT) reporter constructs was used in transient transfection assays to characterize the regulatory functions of the IE gene product. These experiments demonstrated that (i) the EHV-1 IE gene product is a bifunctional protein capable of both positive and negative modulation of gene expression; (ii) the IE gene product possesses an autoregulatory function which represses the IE promoter; (iii) IE autoregulation is dependent on IE promoter sequences mapping within positions -288 to +73 relative to the transcription initiation site (+1) of the IE gene; (iv) the IE gene product can independently activate the EHV-1 tk promoter (an early promoter) by as much as 60-fold; (v) two EHV-1 beta-gamma (leaky late) promoters, those of IR5 (gene 5 in the inverted repeat) and the glycoprotein D gene, demonstrate a requirement for both the IE gene product as well as a gene product encoded within the EHV-1 XbaI G fragment for significant activation; and (vi) the IE gene product is capable of activating heterologous viral promoters.

Functional roles for the TATA promoter and enhancers in basal and Tat-induced expression of the human immunodeficiency virus type 1 long terminal repeat

We have analyzed the contributory role of the human immunodeficiency virus type 1 (HIV-1) promoter and enhancers in basal and Tat-induced transcription. We found that a minimal promoter competent for basal expression is contained within sequences spanning nucleotides -43 to +80. Basal expression from this HIV-1 promoter was boosted more by the additional presence of the NF-kappa B elements than by the Sp1 elements. The minimal long terminal repeat promoter (-43 to +80), while having an intact TAR sequence, was not Tat inducible. However, the simple addition of short synthetic enhancer motifs (AP1, Oct, Sp1, and NF-kappa B) conferred Tat responsiveness. This ability to respond to Tat was in part dependent on the presence of the HIV-1 promoter. Changing the HIV-1 TATA to other eucaryotic TATA or non-TATA initiators minimally affected basal expression but altered Tat inducibility. Our findings suggest a specific context of functional promoter and enhancer elements that is optimal for Tat trans activation of the HIV-1 long terminal repeat. Our results do not allow conclusions about whether Tat acts at the level of initiation or at the level of elongation to be drawn.

A purified adenovirus 289-amino-acid E1A protein activates RNA polymerase III transcription in vitro and alters transcription factor TFIIIC

We have previously demonstrated that a purified bacterially synthesized E1A 289-amino-acid protein is capable of stimulating transcription from the promoters of genes transcribed by RNA polymerase II in vitro (R. Spangler, M. Bruner, B. Dalie, and M. L. Harter, Science 237:1044-1046, 1987). In this study, we show that this protein is also capable of transactivating in vitro the adenovirus virus-associated (VA1) RNA gene transcribed by RNA polymerase III. Pertinent to the transcription of this gene is the rate-limiting component, TFIIIC, which appears to be of two distinct forms in uninfected HeLa cells. The addition of an oligonucleotide containing a TFIIIC binding site to HeLa whole-cell extracts inhibits VA1 transcription by sequestering TFIIIC. However, the addition of purified E1A to extracts previously challenged with the TFIIIC oligonucleotide restores the level of VA1 transcription. When included in the same reaction, an E1A-specific monoclonal antibody reverses the restoration. Incubation of purified E1A with either HeLa cell nuclear or whole-cell extracts alters the DNA-binding properties of TFIIIC as detected by gel shift assays. This alteration does not occur if E1A-specific antibody and E1A protein are added simultaneously to the extract. In contrast, the addition of this antibody to extracts at a later time does not reverse the alteration observed in the TFIIIC binding activities. Never at any time did we note the formation of novel TFIIIC-promoter complexes after the addition of E1A to nuclear extracts. These results clearly establish that E1A mediates its effect on VA1 transcription through TFIIIC in a very rapid yet indirect manner.(ABSTRACT TRUNCATED AT 250 WORDS)

A nexus between Oct-4 and E1A: implications for gene regulation in embryonic stem cells

Oct-4 is a transcription factor expressed in the pluripotent progenitor cells of the early mouse embryo. Additional factors are required for the distal activation of genes in differentiated cells containing ectopically expressed Oct-4. Here we show that Oct-4 and E1A are sufficient for distance-independent activation of the basal transcription machinery. The ratio of Oct-4 to E1A is critical for transcriptional activation, because higher levels of either factor are less efficient. Activation depends on a transactivation domain linked to the POU domain of Oct-4 and also on the conserved domain 3 of the 289RE1A protein. This domain is required for binding to the C-terminal part of Oct-4 including the POU domain. Our results indicate that E1A can serve as a bridging factor between Oct-4 and the basal initiation complex, and we postulate that an E1A-like factor acts as a cellular bridging factor of Oct-4 in pluripotent cells.

The functional domains of the murine Thy-1 gene promoter

The Thy-1 gene promoter resembles a "housekeeping" promoter in that it is located within a methylation-free island, lacks a canonical TATA box, and displays heterogeneity in the 5'-end termini of the mRNA. Using transgenic mice, we show that this promoter does not confer any tissue specificity and is active only in a position-dependent manner. It can only be activated in a tissue-specific manner by elements that lie downstream of the initiation site. We have analyzed the functional domains of the minimal Thy-1 promoter and show that the dominant promoter elements consist of multiple binding sites for the transcription factor Sp1, an inverted CCAAT box, and sequences proximal to the transcription start site. DNase I and gel mobility shift assays show the binding of a number of nuclear factors to these elements, including Sp1 and CP1. Our results show that the structure of this promoter only permits productive interactions of the two transcription factors Sp1 and CP1 with the basal transcription machinery in the presence of enhancer sequences.

Adenovirus E1A protein activates transcription of the E1A gene subsequent to transcription complex formation

The mechanism of transcriptional activation of the adenovirus E1A and E3 genes by E1A protein during infection was examined by using transcription-competition assays. Infection of HeLa cells with one virus led to inhibition of mRNA accumulation from a superinfecting virus. Synthesis of the E1A 289R protein by the first virus to infect reduced inhibition of transcription of the superinfecting virus, indicating that the E1A 289R protein was limiting for E1A-activated transcription. Infection with an E1A- virus, followed 6 h later by superinfection with a wild-type virus, led to preferential transcriptional activation of the E1A gene of the first virus, suggesting that a host transcription component(s) stably associated with the E1A promoter in the absence of E1A protein and that this complex was the substrate for transcriptional activation by E1A protein. The limiting host transcription component(s) bound to the E1A promoter to form a complex with a half-life greater than 24 h in the absence of E1A 289R protein, as demonstrated in a challenge assay with a large excess of superinfecting virus. In the presence of the E1A 289R protein, the E1A gene of the superinfecting virus was gradually activated with a reduction in E1A mRNA accumulation from the first virus. The kinetics of the activation suggest that this was due to an indirect effect rather than to destabilization of stable transcription complexes by the 289R protein.

The functional domains of the murine Thy-1 gene promoter

The Thy-1 gene promoter resembles a "housekeeping" promoter in that it is located within a methylation-free island, lacks a canonical TATA box, and displays heterogeneity in the 5'-end termini of the mRNA. Using transgenic mice, we show that this promoter does not confer any tissue specificity and is active only in a position-dependent manner. It can only be activated in a tissue-specific manner by elements that lie downstream of the initiation site. We have analyzed the functional domains of the minimal Thy-1 promoter and show that the dominant promoter elements consist of multiple binding sites for the transcription factor Sp1, an inverted CCAAT box, and sequences proximal to the transcription start site. DNase I and gel mobility shift assays show the binding of a number of nuclear factors to these elements, including Sp1 and CP1. Our results show that the structure of this promoter only permits productive interactions of the two transcription factors Sp1 and CP1 with the basal transcription machinery in the presence of enhancer sequences.

Regulated expression of human alpha- and beta-globin genes in transient heterokaryons

We have examined the expression of human alpha- and beta-like globin genes in transient heterokaryons formed by fusion of human nonerythroid cells with terminally differentiating mouse erythroleukemia (MEL) cells or with a MEL cell variant (GM979) in which the endogenous mouse embryonic beta-globin genes are activated. In both the parental MEL cells and the heterokaryons, the alpha-globin genes were activated at least 12 h earlier than the embryonic, fetal, and adult beta-globin genes. These results suggest that kinetic differences in the activation of alpha- and beta-like globin genes are not simply the result of different rates of accumulation of erythroid-specific regulatory factors but may reflect differences in the mechanisms governing the transcriptional activation of these genes during erythroid cell differentiation. In mouse GM979 x human nonerythroid heterokaryons, the human embryonic beta-globin gene was activated, consistent with our previous demonstration that erythroid cells contain stage-specific trans-acting regulators of globin gene expression. Moreover, a dramatic increase in the ratio of human fetal to adult beta-globin transcription was observed compared with that seen in MEL-human nonerythroid hybrids. This ratio change may reflect competition between the fetal and adult beta-globin genes for productive interactions with erythroid cell-specific regulatory elements. Finally, we demonstrate that the behavior of naturally occurring mutations that lead to aberrant hemoglobin switching in humans also leads to aberrant expression in transient heterokaryons. Therefore, erythroid cells must contain trans-acting factors that interact with mutated regulatory elements to induce high-level expression of the human fetal globin genes.

Effects of pseudorabies virus on the neuronal properties of PC12 cells

The effect of pseudorabies virus on neuronal functions was investigated in PC12 cells. During the period investigated, choline acetyltransferase was not affected, while the acetylcholinesterase activity declined steadily starting at 12 h post infection (p.i.), reaching its minimal level of 40% of the control value at 24 h p.i. In contrast, the activity of tyrosine hydroxylase, the key enzyme in catecholamine synthesis, increased to 150% of the control level by 15 h p.i., dropping off slowly with the appearance of viral cytopathology. In parallel, the infection induced, by a process independent of the extracellular Ca2+, an increased release of dopamine at 11 h p.i., followed by noradrenaline at 20 h p.i. In the infected cells, the intracellular content of catecholamine was maintained only in the presence of a high amount of catecholamine precursors in the culture medium. Three plaque-forming units per cell was the minimal multiplicity of infection required to obtain the maximal changes in enzyme activities; higher multiplicities induced more rapidly the maximal effects on tyrosine hydroxylase and acetylcholinesterase. Inhibition of DNA synthesis did not prevent the increase in tyrosine hydroxylase activity; however, protein synthesis was required. In conclusion, infection of the PC12 cells with pseudorabies virus induced significant changes in catecholaminergic and cholinergic metabolism, indicating the ability of this virus to interfere selectively with specialized neuronal functions.

Nucleotide sequence and regulation of the adenovirus type 3 E2A early promoter

The nucleotide sequence of the adenovirus serotype 3 E2A early promoter has been determined. In contrast to Ad2, the Ad3 E2A early promoter possessed only one TATA-like box and one nuclear transcription factor E2F binding site and lacked the silencer sequences; however, as in Ad2, the ATF binding site was present. Moreover, the Ad3 E2A promoter harbored a protein binding sequence recognized by the SP1 factor. By transient expression analysis in HeLa cells, we demonstrated that the E1A gene products of Ad3 and Ad2 stimulated Ad3 E2A transcription. In competition experiments, the Ad3 E2A promoter was used in preference to the Ad2 E2A promoter.

Regulated expression of human alpha- and beta-globin genes in transient heterokaryons

We have examined the expression of human alpha- and beta-like globin genes in transient heterokaryons formed by fusion of human nonerythroid cells with terminally differentiating mouse erythroleukemia (MEL) cells or with a MEL cell variant (GM979) in which the endogenous mouse embryonic beta-globin genes are activated. In both the parental MEL cells and the heterokaryons, the alpha-globin genes were activated at least 12 h earlier than the embryonic, fetal, and adult beta-globin genes. These results suggest that kinetic differences in the activation of alpha- and beta-like globin genes are not simply the result of different rates of accumulation of erythroid-specific regulatory factors but may reflect differences in the mechanisms governing the transcriptional activation of these genes during erythroid cell differentiation. In mouse GM979 x human nonerythroid heterokaryons, the human embryonic beta-globin gene was activated, consistent with our previous demonstration that erythroid cells contain stage-specific trans-acting regulators of globin gene expression. Moreover, a dramatic increase in the ratio of human fetal to adult beta-globin transcription was observed compared with that seen in MEL-human nonerythroid hybrids. This ratio change may reflect competition between the fetal and adult beta-globin genes for productive interactions with erythroid cell-specific regulatory elements. Finally, we demonstrate that the behavior of naturally occurring mutations that lead to aberrant hemoglobin switching in humans also leads to aberrant expression in transient heterokaryons. Therefore, erythroid cells must contain trans-acting factors that interact with mutated regulatory elements to induce high-level expression of the human fetal globin genes.

E1A gene products stimulate in vitro transcription from the adenovirus early region 4 promoter by enhancing a stable preinitiation complex

A cell-free transcription system using nuclear extracts prepared from adenovirus type 5 (Ad5)-infected and mock-infected cells were utilized to study the E1A-mediated transactivation of transcription from the Ad5 early region 4 (E4) promoter. The transcription activity of Ad-infected cell extracts was several times higher than that of mock-infected cell extracts when the E4 wild-type (WT) promoter was used. The increased activity required expression of E1A proteins. However, the transcription activities of both cell extracts were not different when the mutant promoter containing only the E4 TATA box was used. The formation of a stable preinitiation complex at the E4 WT promoter was facilitated by expression of E1A, whereas it was not facilitated at the mutant promoter. The results suggested that the E1A proteins stimulated transcription from the E4 promoter by enhancing the formation of a stable preinitiation complex through the upstream elements, together with the TATA box.