Analysis of gene expression using simian virus 40 vectors

Human retinoblastoma is not caused by known pRb-inactivating human DNA tumor viruses

Retinoblastomas occur as the consequence of inactivation of the tumor suppressor retinoblastoma protein (pRb), classically upon biallelic inactivation of the RB1 gene locus. Recently, human papillomavirus (HPV) genomic DNA has been detected in retinoblastomas. To investigate the possibility that oncoproteins encoded by pRb-inactivating DNA tumor viruses play a role in the pathogenesis of human retinoblastoma, 40 fresh-frozen tumors were analyzed for the presence of HPV, adenovirus (HAdV) and polyomavirus (BKV, JCV and SV40) genomic DNA sequences by real-time polymerase chain reaction (PCR). Tumors were screened for genetic and epigenetic alterations in all 27 exons of the RB1 gene locus and promoter by exonic copy number detection, sequencing and methylation-specific PCR of the promoter region. Retinoblastoma tumors from children with bilateral familial (n=1), bilateral nonfamilial (n=1) and unilateral nonfamilial (n=38) disease were analyzed. Inactivating modifications to the RB1 gene locus were identified on both the alleles in 27 tumors, one allele in 8, and neither allele in 5 cases. A median of over 107,000 tumor cells were analyzed for viral genomic DNA in each PCR reaction. All tumor samples were negative for 37 HPV types, 51 HAdV types, BKV and JCV genomic sequences. Very low copy number (0.2-260 copies per 100,000 tumor cells) SV40 genomic DNA detected in 8 of 39 samples was demonstrated to be consistent with an artifact of plasmid-derived SV40. In contrast to recent reports, we obtained substantial quantitative evidence indicating that neither HPV nor any other pRb-inactivating human DNA tumor viruses play a role in the development of retinoblastoma, regardless of RB1 genotype.

Control of lactotrop proliferation by dopamine: essential role of signaling through D2 receptors and ERKs

Dopamine is thought to exert a negative control on lactotrop cell proliferation and prolactin production. Indeed, mice lacking the D2 receptor develop pituitary tumors of lactotrop origin. Because lactotrops express two isoforms of D2R, D2L, and D2S, in a specific ratio, we decided to explore the physiological importance of their relative abundance in vivo. Thus, we generated transgenic animals overexpressing either D2L or D2S in lactotrops. Increased expression of D2S, but not of D2L, leads to mitogen-activated protein kinase (MAPK) induction, which results in pituitary hypoplasia. On the other hand, levels of phosphorylated MAPKs are drastically reduced in pituitary tumors generated by the absence of D2-dependent signaling. These results underline a critical role of D2-mediated MAPK activation in lactotrop proliferation. Furthermore, whereas D2S overexpression results to a drastic reduction of prolactin, D2L overexpression elevates it. Our findings underscore a different role of the two D2R isoforms in the pituitary gland physiology.

Expression and function of the Drosophila melanogaster ADH in male Ceratitis capitata adults: a potential strategy for medfly genetic sexing based on gene-transfer technology

The aim of development of a Mediterranean fruit fly Ceratitis capitata genetic sexing strain derives from the large scale SIT programmes being carried out to control this pest. Toward this direction, we present here the male-specific expression of the Drosophila melanogaster alcohol dehydrogenase (ADH) in medfly transgenic adults generated by Minos-mediated germ line transformation. This expression pattern is obtained by using a promoter fragment of the male-specific gene MSSP-alpha2 of the medfly. We show that the heterologous enzyme is functional in the medfly oxidizing both ethanol and 2-propanol. Although leading to an approximately twofold increase of total ADH activity in male compared to female transgenic adults, these expression levels are not enough for performing genetic sexing when high doses of environmental alcohol are applied. This could be achieved either by further enhancement of the transgene expression or by generating an Adh- line to host the Minos insertions.

Two medfly promoters that have originated by recent gene duplication drive distinct sex, tissue and temporal expression patterns

Genes encoding predominantly male-specific serum polypeptides (MSSPs) in the medfly Ceratitis capitata are members of a multigene family that are structurally similar to the genes encoding odorant binding proteins of insects. To study the transcriptional regulation of the genes MSSP-alpha2 and MSSP-beta2, overlapping fragments of their promoters, containing the 5' UTRs and 5' flanking regions, were fused to the lacZ reporter gene and introduced into the medfly genome via Minos-mediated germline transformation. Transgenic flies were functionally assayed for beta-galactosidase activity. Despite their extensive sequence similarity, the two gene promoters show distinct expression patterns of the reporter gene, consistent with previously reported evidence for analogous transcriptional activity of the corresponding endogenous genes. The MSSP-alpha2 promoter drives gene expression specifically in the fat body of the adult males, whereas the MSSP-beta2 promoter directs gene expression in the midgut of both sexes. In contrast, similar transformation experiments in Drosophila melanogaster showed that both promoters drive the expression of the reporter gene in the midgut of adult flies of both sexes. Thus, the very same MSSP-alpha2 promoter fragment directs expression in the adult male fat body in Ceratitis, but in the midgut of both sexes in Drosophila. Our data suggest that through the evolution of the MSSP gene family a limited number of mutations that occurred within certain cis-acting elements, in combination with new medfly-specific trans-acting factors, endowed these recently duplicated genes with distinct sex-, tissue-, and temporal-specific expression patterns.

Epidermal growth factor regulation of glutathione S-transferase gene expression in the rat is mediated by class Pi glutathione S-transferase enhancer I

Using chloramphenicol acetyltransferase assays we showed that epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), and 3,3',4,4',5-pentachlorobiphenyl (PenCB) induce class Pi glutathione S-transferase (GSTP1) in primary cultured rat liver parenchymal cells. GSTP1 enhancer I (GPEI), which is required for the stimulation of GSTP1 expression by PenCB, also mediates EGF and TGF alpha stimulation of GSTP1 gene expression. However, hepatocyte growth factor and insulin did not stimulate GPEI-mediated gene expression. On the other hand, the antioxidant reagents butylhydroxyanisole and t-butylhydroquinone, stimulated GPEI-mediated gene expression, but the level of GSTP1 mRNA was not elevated. Our observations suggest that EGF and TGF alpha induce GSTP1 by the same signal transduction pathway as PenCB. Since the sequence of GPEI is similar to that of the antioxidant responsive element (ARE), some factors which bind to ARE might play a role in GPEI-mediated gene expression.

Amino-terminal regions of polyomavirus middle T antigen are required for interactions with protein phosphatase 2A

Polyomavirus middle T antigen (MT) is the major transforming protein of the virus. It functions through interactions with a number of cellular proteins involved in cell proliferation. MT forms complexes with protein phosphatase 2A (PP2A), pp60c-src, phosphatidylinositol 3-kinase, and Shc. We introduced both deletion and point mutations into three regions of MT and examined their ability to associate with PP2A and pp60c-src. The first 25 amino acid residues of MT are required for association with PP2A and pp60c-src. Amino acids 105 to 111, comprising the sequence Cys-Arg-Met-Pro-Leu-Thr-Cys, is also required for complex formation between MT and PP2A. However, the sequence Asp-Lys-Gly-Gly (amino acids 44 to 47), also found in the B subunit of PP2A, is dispensable for complex formation between MT and PP2A. We find a strict correlation between the ability of MT to associate with PP2A and the ability of MT to associate with pp60c-src. One mutant, L5E, associates with a phosphatase other than PP2A, pp60c-src, and phosphatidylinositol 3-kinase in a manner similar to that of wild-type MT yet is reduced in its transforming ability on NIH 3T3 cells.

Acetaldehyde exposure causes growth inhibition in a Chinese hamster ovary cell line that expresses alcohol dehydrogenase

Chronic ethanol exposure causes many pathophysiological changes in cellular function due to ethanol itself and/or the effects of its metabolism (i.e., generation of acetaldehyde and redox equivalents). However, the role of each of these effects remains controversial. To address these questions, we have developed a cell line that expresses alcohol dehydrogenase. This cell line permits separate examination of the effects of ethanol and its metabolite acetaldehyde on cell function. An expression vector for the mouse liver alcohol dehydrogenase was constructed and transfected into Chinese hamster ovary cells. Cells expressing alcohol dehydrogenase were identified by screening with allyl alcohol, which is metabolized by alcohol dehydrogenase to the toxic aldehyde acrolein. A number of cell lines were identified that expressed alcohol dehydrogenase. A-10 cells were selected for further study because of their high sensitivity to allyl alcohol, suggesting a high level of alcohol dehydrogenase expression. These cells expressed a mRNA that hybridizes with the alcohol dehydrogenase cDNA and had an alcohol dehydrogenase activity comparable to murine liver. When cultures of these cells were exposed to ethanol, acetaldehyde was detected in both the medium and cells. The acetaldehyde concentration in the medium remained constant for at least 1 week in culture and was a function of the added ethanol concentration. Chronic exposure of A-10 cells to ethanol resulted in a dose-dependent reduction in the number of cells that accumulated over 7 days. Ethanol-treated cells remained viable, and growth inhibition was reversible. Growth inhibition was blocked by the alcohol dehydrogenase inhibitor 4-methylpyrazole, suggesting that acetaldehyde and not ethanol was responsible for growth inhibition in these cells.

Elements in the immunoglobulin heavy-chain enhancer directly regulate simian virus 40 ori-dependent DNA replication

In a previous study, we showed that the immunoglobulin heavy-chain (IgH) enhancer (IgHe) is near or in an initiation zone of chromosomal DNA replication, which is preferentially active in B cells (K. Ariizumi, Z. Wang, and P. W. Tucker, Proc. Natl. Acad. Sci. USA 90:3695-3699, 1993). This suggests the existence of a functional relationship between IgHe-mediated transcription and DNA replication. To test this theory, we utilized simian virus 40 (SV40) DNA replication as a model of chromosomal replication. IgHe or its operationally divisible domains (5'-En, core, and 3'-En) were introduced into SV40 minichromosomes (IgHe-SV40). Results of replication assays with IgHe-SV40 replicons indicated that the 5'-En and 3'-En activated or suppressed SV40 DNA replication regardless of the presence of SV40 enhancers or promoters in these replicons. The activity did not reside in IgHe core sequences. The results suggested that the 5'- and 3'-En regulated SV40 replication through direct interaction with the origin, not through suppression at the SV40 enhancer and/or promoter. In an effort to identify elements within the 5'-En motif that contributed to this effect, we found that the E site, but not microE5 and microE2 boxes, upregulated DNA replication. Our results provide another possible regulatory function for the 5'-En and 3'-En domains besides transcriptional suppression of IgHe.

Elements in the immunoglobulin heavy-chain enhancer directly regulate simian virus 40 ori-dependent DNA replication

In a previous study, we showed that the immunoglobulin heavy-chain (IgH) enhancer (IgHe) is near or in an initiation zone of chromosomal DNA replication, which is preferentially active in B cells (K. Ariizumi, Z. Wang, and P. W. Tucker, Proc. Natl. Acad. Sci. USA 90:3695-3699, 1993). This suggests the existence of a functional relationship between IgHe-mediated transcription and DNA replication. To test this theory, we utilized simian virus 40 (SV40) DNA replication as a model of chromosomal replication. IgHe or its operationally divisible domains (5'-En, core, and 3'-En) were introduced into SV40 minichromosomes (IgHe-SV40). Results of replication assays with IgHe-SV40 replicons indicated that the 5'-En and 3'-En activated or suppressed SV40 DNA replication regardless of the presence of SV40 enhancers or promoters in these replicons. The activity did not reside in IgHe core sequences. The results suggested that the 5'- and 3'-En regulated SV40 replication through direct interaction with the origin, not through suppression at the SV40 enhancer and/or promoter. In an effort to identify elements within the 5'-En motif that contributed to this effect, we found that the E site, but not microE5 and microE2 boxes, upregulated DNA replication. Our results provide another possible regulatory function for the 5'-En and 3'-En domains besides transcriptional suppression of IgHe.

Opening and refolding of simian virus 40 and in vitro packaging of foreign DNA

Simian virus 40 (SV40) can be disassembled under mild conditions by reducing disulfide bonds in the capsid and removing calcium ions. The nucleoprotein complexes formed, analyzed by electron microscopy, were circular and made up of 59 +/- 4 subunits, each with a diameter of about 10 nm. The complexes contained the viral DNA, histones, and the viral capsid proteins. The complexes had much-reduced infectivities compared with intact SV40. Addition of calcium ions to the disrupted virus caused the nucleoprotein complexes to refold into virus-like structures which sedimented at the same rate as intact SV40 and regained infectivity. Treatment of the disrupted SV40 with a high concentration of salt dissociated the viral proteins from the DNA. Lowering stepwise the salt concentration, removing the reducing agent, and adding calcium ions allowed structures to be reformed, and these structures sedimented, like SV40, at 240S and were infectious. The plaque-forming ability of the reconstituted particles was between that of the dissociated components and that of intact SV40. The addition of purified DNA of polyomavirus to the dissociated SV40 before the lowering of the salt concentration showed that virus-like structures could be formed from SV40 proteins and a foreign DNA.

Different pathways for chromosomal integration of transfected circular pSVneo plasmids in normal and established rodent cells

The chromosomal integration of transfected circular plasmid pSV2neo molecules was investigated in normal and established mammalian fibroblasts, including two secondary cultures of normal mouse fibroblast lines, one established mouse-hamster hybrid cell line, R44, and the human fibrosarcoma line, HT1080. The physical organization of the integrated molecules was studied by restriction analysis. The results showed that whereas the normal fibroblasts predominantly integrated one head-to-tail partial dimeric molecule, the established cells predominantly integrated distinctly different molecular forms including deleted monomeres (HT1080) and various complex concatemeric molecules (R44), and frequently at more than one chromosomal site (R44). We also constructed a head-to-tail dimeric version of the plasmid, which in the case of the normal fibroblasts again integrated as a partial dimeric molecule in at least 50% of these cells. This result excluded the possibility that the normal mouse transfectants were selected for the integration of two functional neo genes. Thus, it is concluded that the distinctly different molecular forms integrated in normal and established cells demonstrate the operation of different integration pathways, the possible nature of which is discussed.

Complete rescue of photoreceptor dysplasia and degeneration in transgenic retinal degeneration slow (rds) mice

retinal degeneration slow (rds) is a semidominant mutation of mice with the phenotype of abnormal development of rod and cone photoreceptors, followed by their slow degeneration. The rds gene has been putatively cloned and its novel protein product initially characterized biochemically. In the present study we undertook to correct in vivo the retinal phenotype of mice with the rds mutation. We assembled a transgene containing a regulatory segment of the opsin gene positioned upstream of the wild-type rds coding region. Mice from three transgenic lines, homozygous for the rds mutation, were analyzed for expression of the transgene and for their retinal phenotypes. In two high expressing lines, we observed complete reversion to wild-type retinal morphology. In a third, low expressing line, we observed a retinal phenotype intermediate between wild type and rds/rds, suggesting partial rescue of the mutation. These results constitute formal proof that we have cloned the rds gene.

A cDNA construct of tissue inhibitor of metalloproteinases (TIMP) linked to the last exon of Thy-1 confers glycophospholipid anchorage on this naturally secreted protein

A naturally secreted protein, tissue inhibitor of metalloproteinases (TIMP), has been transiently expressed on the surface of transfected COS cells and stably on transfected murine BW 5147 thymoma cells, by linkage of the entire coding sequence of the cDNA to the last exon of Thy-1. Thy-1 is a glycophospholipid-linked protein. In COS cells the chimaeric protein can be labelled by [3H]ethanolamine, which is a component of glycophospholipid anchors. Ltk- cells cannot anchor proteins by glycan phosphatidylinositol linkage and were found to be unable to express the engineered protein extracellularly on their plasma membranes. Phosphatidylinositol-specific phospholipase C treatment released 90% of the protein from all BW 5147 cells, but very little from the COS-1 cells. It is concluded that the last exon of Thy-1 has conferred the property of glycophospholipid anchorage on the normally secreted protein TIMP.

Expression of a gene encoding a rabbit sperm membrane protein in mammalian cells

A general mammalian expression vector designated pSV2-EP was reconstructed by inserting an oligonucleotide fragment into pSV2-dhfr. This vector allowed insertion of cDNAs with EcoRI cohesive ends. The pSV2-EP contains a simian virus 40 (SV40) early promoter, origin for DNA replication, SV40 poly-A site, splicing site, an initiator ATG downstream from the promoter and an EcoRI site for the insertion of cDNA fragment screened from lambda gt11 expression libraries. A recombinant plasmid (pS-VRS-1) was constructed by inserting RSD-1, a cDNA encoding a rabbit sperm tail protein, into the EcoRI site of the pSV2-EP vector. Chinese hamster ovarian (CHO) dhfr-negative cells were cotransformed with pSV2-dhfr and pSVRS-1 by the calcium phosphate method. In selective culture medium without thymidine and hypoxanthine, several cell lines were obtained containing mRNA and DNA that hybridized with RSD-1. One of these transformed cell lines stained intensely with anti-rSMP-B antibodies, demonstrating that the RSD-1 was expressed in the transformed CHO cells.

Transformation mapping of the regulatory elements of the ecdysone-inducible P1 gene of Drosophila melanogaster

The transcription of the P1 gene is induced by 20-hydroxyecdysone in fat bodies of third-instar larvae. Germ line transformation showed that sequences between -138 to +276 contain elements required for a qualitatively correct developmental and hormonal regulation of P1 transcription. Sequences from -138 to -68 are essential for this expression.

Transformation mapping of the regulatory elements of the ecdysone-inducible P1 gene of Drosophila melanogaster

The transcription of the P1 gene is induced by 20-hydroxyecdysone in fat bodies of third-instar larvae. Germ line transformation showed that sequences between -138 to +276 contain elements required for a qualitatively correct developmental and hormonal regulation of P1 transcription. Sequences from -138 to -68 are essential for this expression.

Comparison of the estrogen responsiveness of the rat and bovine oxytocin gene promoters

DNA sequences in the 5'-flanking region of rat and bovine oxytocin genes were examined for their capacity to confer estrogen responsiveness to their homologous promoters. In contrast to the 5'-flanking region of the rat oxytocin gene, upstream promoter sequences up to 3200 bp of the bovine gene linked to the chloramphenicol acetyltransferase (CAT) reporter gene which were transfected in estrogen receptor expressing MCF-7 cells did not respond to estrogen. Testing 5'-deletion mutants of the rat upstream region linked to the luciferase gene in P19 embryocarcinoma cells co-transfected with an estrogen receptor expression plasmid showed that two regions each associated with approximately 15-fold stimulation of promoter activity were located between nucleotides -172 and -149 and between -148 and +16 in the rat gene. The former region contains the imperfect palindrome GGTGACCTTGACC which differs in one nucleotide from the estrogen response element (ERE) consensus. It is concluded that the corresponding motive CATAACCTTGACC of the bovine gene is not a functional ERE. Thus, the estrogen responsiveness of oxytocin genes is species-dependent.

Regulation of the rat oxytocin gene by estradiol

Abstract Oxytocin (OT) plays a role in reproduction at the level of the pituitary and mammary glands and uterus. This OT is synthesized in the hypothalamo-neurohypophyseal system (HNS). A number of observations have suggested that estrogens regulate the production of OT in the HNS. In this study the effect of 17beta-estradiol on the activity of the OT gene promoter was examined as well as the effect of 17beta-estradiol in vivo on OT messenger ribonucleic acid (mRNA) and peptide revels in the rat HNS. Vasopressin (VP) and its mRNA were also determined in the in vivo studies. The direct transcriptional stimulation of OT gene expression by 17beta-estradiol was studied in two different heterologous expression systems. When a plasmid having nucleotides -363 to +16 of the rat OT gene fused to the firefly luciferase reporter gene was co-transfected with an estrogen receptor expression vector in P19 embryonal carcinoma cells, luciferase activity was stimulated 80-fold by 17beta-estradiol. In estrogen receptor containing MCF-7 cells transfected with a plasmid having nucleotides -188 to +16 of the rat OT gene fused to the chloramphenicol acetyl transferase gene, 17beta-estradiol induced the expression of the chloramphenicol acetyl transferase gene through the cloned promoter element. After in vivo treatment of ovariectomized rats with 17beta-estradiol, levels of OT mRNA and VP mRNA were measured in microdissected supraoptic and paraventricular nuclei as well as VP and OT levels in these nuclei and the pituitary gland. As compared to non-treated ovariectomized rats there was no difference in contents of OT mRNA and VP mRNA in these hypothalamic nuclei and in levels of the peptides in paraventricular nuclei and the pituitary gland. A 30% reduction of the OT content of the supraoptic nuclei only was found, while the VP content did not change. To explain the results immunocytochemical analyses of the hypothalamus were performed, showing that the estrogen receptor was absent in the magnocellular neurons of the supraoptic and paraventricular nuclei. The results demonstrate that the 5'flanking region of the OT gene confers estrogen-sensitivity to transcription of the OT gene. This potential to respond to estrogens is not used in the OT-producing neurons of supraoptic and paraventricular nuclei probably due to the absence of the estrogen receptor.

Aberrant expression of platelet-derived growth factor A-chain cDNAs due to cryptic splicing of RNA transcripts in COS-1 cells

Platelet-derived growth factor (PDGF) is a cationic dimer composed of two chains, designated A and B. All three dimeric isotypes of PDGF, PDGF-AA, -AB and -BB, are biologically active but may have distinct functional activities. Two A-chain precursors which differ by the presence of a highly basic 15 amino acid C-terminal extension are derived from the A-chain by alternative RNA splicing. To compare the functional properties of these two different forms of the A-chain, expression vectors were generated in which the cDNAs were placed under the transcriptional control of a viral promoter (pSV2). Surprisingly, cryptic RNA splice donor sites were identified in both forms of the PDGF A-chain which modify the A-chain open reading frame and alter the structure of the expressed protein. Recognition of this phenomenon appears to explain the discrepancies between previous results regarding the secretory properties of the PDGF A-chain and may explain difficulties in expression vectors containing splice acceptor sites between the inserted sequence and the polyadenylation site.

Stably expressed FIPV peplomer protein induces cell fusion and elicits neutralizing antibodies in mice

We have established bovine papilloma virus (BPV)-transformed mouse C127 cell lines that synthesize the peplomer protein of the feline infectious peritonitis virus (FIPV) strain 79-1146. For this purpose, a new cassette expression vector pHSL, which carries the Drosophila HSp70 promotor and the polyadenylation signal of the Moloney murine leukemia virus long terminal repeat, was constructed. Cocultivation of the BPV-transformed cell lines with FIPV-permissive feline fcwf-D cells resulted in polykaryocyte formation. Since it depended on the presence of fcwf-D cells, binding of E2 to the cell receptor may be required for membrane fusion. E2 was synthesized as a core-glycosylated protein of 180K which was only slowly transported from the endoplasmic reticulum to the medial Golgi: of the E2-molecules labeled during a 1-hr pulse about half was still completely sensitive to endoglycosidase H after a 2-hr chase, while the remaining E2 had been chased into multiple, partially endoglycosidase H-resistant forms. Immunofluorescence studies also indicated that most E2 was retained intracellularly. Mice immunized with whole lysates of the transformed cells produced FIPV-neutralizing antibodies as shown by plaque reduction.

Analysis of recombination in mammalian cells using SV40 and SV40-derived vectors

Viruses and viral vectors have played a crucial role in our understanding of the pathways of homologous and non-homologous recombination in mitotically dividing mammalian cells. In particular, they have allowed the confirmation of the preponderance of non-homologous over homologous recombination events and led to schemes for the selection and isolation of homologous recombination products. These studies have allowed an examination of the properties of reciprocal and non-reciprocal homologous recombination events extrachromosomally, in the chromosome and between plasmids and chromosomes. They suggest that it is feasible now to direct DNA segments to predetermined chromosomal locations by homologous recombination.

Larval fat body-specific gene expression in D. melanogaster

The Pl gene, together with the LSP-1 alpha, -1 beta, and -1 gamma, LSP-2, and P6 genes, is expressed exclusively in the larval fat body of D. melanogaster during the third instar. In vivo mapping of the cis-acting regulatory sequences of the P1 gene was carried out using hybrid constructs with three different reporter genes and a combination of transient and germline transformation assays. This revealed that regulatory elements involved in the setting up of the temporal and spatial specificities of transcription of the P1 gene are located in a short DNA region immediately upstream of the mRNA transcription start. This region includes an element that behaves as a fat-body transcriptional enhancer and element(s) required for ecdysone inducibility of transcription of the P1 gene.

Vectors for Drosophila P-element-mediated transformation and tissue culture transfection

We describe nine P-element vectors that can be used to study gene regulation and function in Drosophila. These vectors were designed for use in germline transformation and cell culture transfection assays. One set consists of five P elements that can be used to study transcriptional regulatory sequences. These vectors contain several unique restriction sites for insertion of a foreign promoter upstream from either a cat or lacZ reporter gene. Two of the beta-galactosidase-coding vectors also require the insertion of a start codon for translation of the reporter enzyme and thus can be used to study translational regulatory sequences. The second set of P elements consists of four vectors that contain the Drosophila cytoplasmic actin 5C promoter and polyadenylation signals. Upon insertion of a foreign DNA segment, these vectors direct constitutive expression of the encoded RNA and protein.

Do transcriptional enhancers also augment DNA replication?

Enhancers are DNA elements that augment transcription in cis, independent of distance and orientation. Evidence such as hormone dependent neoplastic cell growth and the stimulation of viral replication by sequences present in enhancers suggests that enhancers may also directly affect DNA replication. We tested this hypothesis in recombinant plasmids by asking whether sequences that stimulated DNA replication shared the properties of transcriptional enhancers. The homologous simian virus 40 (SV40) core enhancer was ligated either adjacent to or 2.6 kb distant from the SV40 minimal origin of replication (ori) in both orientations. Plasmids were transfected into T antigen producing COS cells, and episomal DNA was harvested for quantitation of replication. Replication could be assessed either as accumulation of fmol of MboI sensitive progeny DNA, or as a transition in % DNA in replicated (MboI sensitive) versus unreplicated (DpnI sensitive) form. The two measures were related exponentially (r = 0.86). The SV40 enhancer augmented replication 1.5-10 fold. The effect was time dependent, distance dependent (only the adjacent enhancer locus stimulated replication), partially orientation dependent, and enhancer copy number independent. Phorbol ester did not affect replication. The heterologous glucocorticoid enhancer had no effect on replication. We conclude that the SV40 enhancer's cis-effect on replication seems to be dependent on the close proximity to the replication origin of specific homologous sequences within the enhancer, rather than a typical enhancer-like effect.

Transient expression in mammalian cells of the bacterial reporter gene encoding mercuric reductase: effects of various regulatory elements

The effect of several transcriptional regulatory elements on gene expression in mammalian cells was investigated. As a reporter gene we have used the bacterial gene merA coding for the enzyme mercuric reductase. Several plasmids were constructed with different promoter/enhancer sequences (pSV/E, pSV/L, pMT, pRSV or pAd) at the 5' end and different splicing (small intron of the T antigen of SV40 or the second intron of the rabbit beta-globin gene) and/or polyadenylation signals (AEn, ALn or AR beta Gn) at the 3' end of the merA gene. Expression was measured in five different mammalian cell lines. In COS cells the highest level of expression is obtained with pSV/L and the lowest level with pSV/E. In HeLa, CV-1, Ltk-, and CHO cells merA expression is relatively high, under control of pRSV and pMT and relatively low under control of pSV/L and pAd. The introns studied have a negative effect on the expression of merA. The presence of a polyadenylation signal downstream from the gene is essential for its expression. The three different polyadenylation signals studied give a similar stimulatory effect on the level of expression of the merA gene.

Excess antisense RNA from infectious recombinant SV40 fails to inhibit expression of a transfected, interferon-inducible gene

SV40-based infectious virus constructs were used to produce a high copy number of full-length antisense RNA in essentially every cell in a population. Chloramphenicol acetyltransferase (CAT) cDNA was placed in either the sense or antisense orientation relative to the SV40 early promoter in helper-free recombinant virus. RNA synthesized at high levels from the antisense virus was without effect on the expression of a stably-transfected CAT mini-gene controlled by an interferon-inducible promoter in monkey CV1 and large T antigen-expressing tsCOS cells. In double infection experiments the antisense RNA was similarly without effect on expression from CAT cDNA placed in the sense orientation in a second virus vector. No activation of the ppp(A2'p)nA(n greater than or equal to 2) system was observed after interferon treatment in either type of experiment. There was no evidence, therefore, for the formation of double-stranded (ds)RNA. It can be concluded that a large excess of a full-length antisense RNA is not necessarily sufficient to cause inhibition of gene expression even when interferon treatment is used to enhance any effect of dsRNA.

High-level transient expression of influenza virus proteins from a series of SV40 late and early replacement vectors

We have constructed a collection of simian virus 40 (SV40) plasmid vectors useful for transient or constitutive expression of cDNA or genomic DNA in animal cells. Most vectors contain several unique restriction sites downstream from the SV40 late or early promoter, and are available with or without the virus-specific splicing signals. The use of these vectors for transient expression in monkey cells of X47 (H3N2) influenza hemagglutinin (HA) and matrix protein (M1) was demonstrated. Membrane-bound (HAm) as well as secreted forms of the HA glycoprotein lacking the sequence of the C-terminal anchor (HA-) have been obtained. Depending on the insert, the type of vector and the amount of transfected DNA, HA levels in COS cells [Gething and Sambrook, Nature 293 (1981) 620-625] transfected with late replacement SV40 vectors vary from 10(9) (HAm) to 10(8) (HA-) molecules per transfected cell. The maximum expression levels with early replacement vectors in COS cells are at least 50 times lower. In addition to the optimalization and the characterization of the expression of each vector-coded influenza protein, cotransfections, including vectors expressing HAm, neuraminidase (NA) and M1, were undertaken. The latter experiments did not result in a measureable amount of HAm or NA in the cell culture medium, suggesting that expression of these three structural viral proteins does not result in budding of (empty) influenza particles from the cell surface.

Unexpected thymic hyperplasia in transgenic mice harboring a neuronal promoter fused with simian virus 40 large T antigen

The hypothalamic peptide growth hormone-releasing factor (GRF) regulates the secretion and production of growth hormone from the anterior pituitary (M. C. Gelato and G. R. Merriam, Annu. Rev. Physiol. 48:569-591). To study GRF gene regulation, transgenic mice were generated that harbor the human GRF promoter fused to the coding sequences from the simian virus 40 early region. These mice had normal hypothalamic functions but unexpectedly suffered from severe thymic hyperplasia. Immunohistochemical analysis revealed that large T antigen was expressed in the thymic epithelial cells. These cells have endocrine properties and are known to produce thymic hormones [corrected]. The thymic hyperplasia was the apparent consequence of inappropriate production of T-cell maturation factors by epithelial cells and could involve increased self renewal of apparently normal T stem cells in the thymus.

Optimizing gene expression in BPV-transformed cells: effects of cell type on enhancer/promoter interaction

We have compared several combinations of enhancers and promoters in expressing the chloramphenicol acetyl transferase gene in transient assays, in mouse C127, the most widely used host cell for the bovine papilloma virus (BPV) expression vector. Of the various combinations tested, the unit comprised of the SV40 enhancer and adenovirus type 2 major late promoter (MLP) was the most active in BPV transformed C127 cells. We further demonstrate that untransformed and BPV transformed C127 cells respond differently to the various enhancer/promoter combinations tested. Moving the SV40 enhancer closer to the cap site of a complete MLP (from -414 to -107) reduced potentiation to less than half in BPV transformed cells. The level of potentiation with enhancer at either site was similar in human HeLa cells. In BPV transformed C127 cells, the SV40 enhancer and the MLP (at the -414 site) supports 4-5 fold greater levels of expression than the murine sarcoma virus (MSV) enhancer/mouse metallothionein (MT) promoter which has previously been extremely effective in BPV vectors. Our findings provide a basis for the improvement of the BPV vector system in supporting increased levels of expression of proteins of important therapeutic application.

Unexpected thymic hyperplasia in transgenic mice harboring a neuronal promoter fused with simian virus 40 large T antigen

The hypothalamic peptide growth hormone-releasing factor (GRF) regulates the secretion and production of growth hormone from the anterior pituitary (M. C. Gelato and G. R. Merriam, Annu. Rev. Physiol. 48:569-591). To study GRF gene regulation, transgenic mice were generated that harbor the human GRF promoter fused to the coding sequences from the simian virus 40 early region. These mice had normal hypothalamic functions but unexpectedly suffered from severe thymic hyperplasia. Immunohistochemical analysis revealed that large T antigen was expressed in the thymic epithelial cells. These cells have endocrine properties and are known to produce thymic hormones [corrected]. The thymic hyperplasia was the apparent consequence of inappropriate production of T-cell maturation factors by epithelial cells and could involve increased self renewal of apparently normal T stem cells in the thymus.

Firefly luciferase gene: structure and expression in mammalian cells

The nucleotide sequence of the luciferase gene from the firefly Photinus pyralis was determined from the analysis of cDNA and genomic clones. The gene contains six introns, all less than 60 bases in length. The 5' end of the luciferase mRNA was determined by both S1 nuclease analysis and primer extension. Although the luciferase cDNA clone lacked the six N-terminal codons of the open reading frame, we were able to reconstruct the equivalent of a full-length cDNA using the genomic clone as a source of the missing 5' sequence. The full-length, intronless luciferase gene was inserted into mammalian expression vectors and introduced into monkey (CV-1) cells in which enzymatically active firefly luciferase was transiently expressed. In addition, cell lines stably expressing firefly luciferase were isolated. Deleting a portion of the 5'-untranslated region of the luciferase gene removed an upstream initiation (AUG) codon and resulted in a twofold increase in the level of luciferase expression. The ability of the full-length luciferase gene to activate cryptic or enhancerless promoters was also greatly reduced or eliminated by this 5' deletion. Assaying the expression of luciferase provides a rapid and inexpensive method for monitoring promoter activity. Depending on the instrumentation employed to detect luciferase activity, we estimate this assay to be from 30- to 1,000-fold more sensitive than assaying chloramphenicol acetyltransferase expression.

Firefly luciferase gene: structure and expression in mammalian cells

The nucleotide sequence of the luciferase gene from the firefly Photinus pyralis was determined from the analysis of cDNA and genomic clones. The gene contains six introns, all less than 60 bases in length. The 5' end of the luciferase mRNA was determined by both S1 nuclease analysis and primer extension. Although the luciferase cDNA clone lacked the six N-terminal codons of the open reading frame, we were able to reconstruct the equivalent of a full-length cDNA using the genomic clone as a source of the missing 5' sequence. The full-length, intronless luciferase gene was inserted into mammalian expression vectors and introduced into monkey (CV-1) cells in which enzymatically active firefly luciferase was transiently expressed. In addition, cell lines stably expressing firefly luciferase were isolated. Deleting a portion of the 5'-untranslated region of the luciferase gene removed an upstream initiation (AUG) codon and resulted in a twofold increase in the level of luciferase expression. The ability of the full-length luciferase gene to activate cryptic or enhancerless promoters was also greatly reduced or eliminated by this 5' deletion. Assaying the expression of luciferase provides a rapid and inexpensive method for monitoring promoter activity. Depending on the instrumentation employed to detect luciferase activity, we estimate this assay to be from 30- to 1,000-fold more sensitive than assaying chloramphenicol acetyltransferase expression.

SV40-based Escherichia coli shuttle vectors infectious for monkey cells

We describe SV40-based Escherichia coli shuttle vectors which can be packaged as pseudovirions without excision of plasmid sequences and which can be rescued in bacteria. These vectors replicate and are transmitted as virus in monkey COS cells without requiring a helper virus. Extrachromosomal vector DNA isolated from infected cells can be rescued in E. coli, so that DNA alterations can be easily screened. Indeed, some of the constructions give rise to very stable plasmids with no detectable rearrangements after multiple lytic cycles in COS cells. The spontaneous mutation frequency measured in bacteria, on the lacO target, is smaller than those usually found with shuttle vectors. We also constructed an expression vector derived from one of our infectious viruses by inserting the chloramphenicol acetyl transferase gene, expressed from the SV40 early promoter, which is efficiently transduced to cells by infection. In this system, the shuttle virus combines the convenience of plasmid rescue and analysis in bacteria, with the advantages of infectious virus.

Characterization of a human multilineage-colony-stimulating factor cDNA clone identified by a conserved noncoding sequence in mouse interleukin-3

Blood-cell production is regulated by hemopoietic growth factors, which act at specific stages of hemopoietic cell differentiation. Murine interleukin-3 (mIL-3)/multilineage colony-stimulating factor (multi-CSF) has been shown to stimulate colony formation in vitro by multipotent hemopoietic cells and production of spleen colony-forming units (CFU-S) in suspension cultures. The molecular cloning of the human counterpart of mIL-3 is described here. Hybridization of radiolabeled mIL-3 cDNA with a cDNA library obtained from mRNA of stimulated human lymphocytes resulted in the identification of a human (h)multi-CSF cDNA clone. Sequence homology (73%) in the 3'-noncoding region of mIL-3 enabled the detection of the hmulti-CSF cDNA clone. Whereas only 45% sequence homology was found in the coding region, specific A + T-rich domains in the 3'-noncoding region were highly conserved (93%). As far as we know, this is the first example of gene identification by sequence homology occurring only within the 3'-noncoding region. The protein encoded by this hmulti-CSF cDNA stimulates in vitro colony formation by multipotent human hemopoietic stem cells. In addition, the growth factor strongly stimulates the in vitro proliferation of human leukemic blast cells.

Escherichia coli aspartate transcarbamylase: a novel marker for studies of gene amplification and expression in mammalian cells

Eucaryotic expression vectors containing the Escherichia coli pyrB gene (pyrB encodes the catalytic subunit of aspartate transcarbamylase [ATCase]) and the Tn5 phosphotransferase gene (G418 resistance module) were transfected into a mutant Chinese hamster ovary cell line possessing a CAD multifunctional protein lacking ATCase activity. G418-resistant transformants were isolated and analyzed for ATCase activity, the ability to complement the CAD ATCase defect, and the ability to resist high concentrations of the ATCase inhibitor N-(phosphonacetyl)-L-aspartate (PALA) by amplifying the donated pyrB gene sequences. We report that bacterial ATCase is expressed in these lines, that it complements the CAD ATCase defect in trans, and that its amplification engenders PALA resistance. In addition, we derived rapid and sensitive assay conditions which enable the determination of bacterial ATCase enzyme activity in the presence of mammalian ATCase.

Escherichia coli aspartate transcarbamylase: a novel marker for studies of gene amplification and expression in mammalian cells

Eucaryotic expression vectors containing the Escherichia coli pyrB gene (pyrB encodes the catalytic subunit of aspartate transcarbamylase [ATCase]) and the Tn5 phosphotransferase gene (G418 resistance module) were transfected into a mutant Chinese hamster ovary cell line possessing a CAD multifunctional protein lacking ATCase activity. G418-resistant transformants were isolated and analyzed for ATCase activity, the ability to complement the CAD ATCase defect, and the ability to resist high concentrations of the ATCase inhibitor N-(phosphonacetyl)-L-aspartate (PALA) by amplifying the donated pyrB gene sequences. We report that bacterial ATCase is expressed in these lines, that it complements the CAD ATCase defect in trans, and that its amplification engenders PALA resistance. In addition, we derived rapid and sensitive assay conditions which enable the determination of bacterial ATCase enzyme activity in the presence of mammalian ATCase.

Regulation of gene amplification and expression in cells that constitutively express a temperature sensitive SV40 T-antigen

Simian cells have been transformed with SV40 origin-defective recombinant plasmids containing the tsA209 T-antigen gene. These plasmids contain deletions of either 5 or 52 nucleotides that include the BglI site at the SV40 ori, are defective for replication in COS-1 cells but retain a functional SV40 early promoter. Two cell lines transformed with these plasmids, U4 and S7, and their respective clonal derivatives E5 and F11, contain the tsA209 T-antigen gene integrated into the cell DNA and express T-antigen as detected by immunoprecipitation and immunofluorescence. These cells behave as ts-COS cells, since they complement in a temperature dependent manner the replication of an SV40 derived recombinant plasmid. When transfected with recombinant plasmids containing the chloramphenicol acetyl transferase (CAT) gene cloned into SV40 replicons, ts-COS cells were able to regulate the induction of the CAT activity by temperature. The ratios of CAT activity observed at permissive versus restrictive temperature were in the range of 20-400. Thus, these ts-COS cells are useful systems for the regulated expression of cloned genes in simian cells.

One pyrimidine dimer inactivates expression of a transfected gene in xeroderma pigmentosum cells

We have developed a host cell reactivation assay of DNA repair utilizing UV-treated plasmid vectors. The assay primarily reflects cellular repair of transcriptional activity of damaged DNA measured indirectly as enzyme activity of the transfected genes. We studied three plasmids (pSV2cat, 5020 base pairs; pSV2catSVgpt, 7268 base pairs; and pRSVcat, 5027 base pairs) with different sizes and promoters carrying the bacterial cat gene (CAT, chloramphenicol acetyltransferase) in a construction that permits cat expression in human cells. All human simian virus 40-transformed cells studied expressed high levels of the transfected cat gene. UV treatment of the plasmids prior to transfection resulted in differential decrease in CAT activity in different cell lines. With pSV2catSVgpt, UV inactivation of CAT expression was greater in the xeroderma pigmentosum group A and D lines (D0 = 56 J X m-2) than in the other human cell lines tested (normal, ataxia-telangiectasia, Lesch-Nyhan, retinoblastoma)(D0 = 680 J X m-2)(D0 is the dose that reduces the percentage of CAT activity by 63% along the exponential portion of the dose-response curve). The D0 of the CAT inactivation curve was 50 J X m-2 for pSV2cat and for pRSVcat in the xeroderma pigmentosum group A cells. The similarity of the D0 data in the xeroderma pigmentosum group A cells for three plasmids of different size and promoters implies they all have similar UV-inactivation target size. UV-induced pyrimidine dimer formation in the plasmids was quantified by assay of the number of UV-induced T4 endonuclease V-sensitive sites. In the most sensitive xeroderma pigmentosum cells, with all three plasmids, one UV-induced pyrimidine dimer inactivates a target of about 2 kilobases, close to the size of the putative CAT mRNA.

Quantification of expression of linked cloned genes in a simian virus 40-transformed xeroderma pigmentosum cell line

We wished to determine whether simian virus 40 (SV40)-transformed xeroderma pigmentosum cells, despite their defective DNA repair, were suitable for DNA-mediated gene transfer experiments with linked genes. Expression of a nonselectable gene (cat, coding for chloramphenicol acetyltransferase [CAT]) linked to a selectable gene (gpt, coding for xanthine-guanine phosphoribosyltransferase [XPRT]) in the plasmid pSV2catSVgpt was quantified after transfection of SV40-transformed xeroderma pigmentosum [XP20s(SV40)] and normal human [GM0637(SV40)] fibroblast cell lines. A novel autoradiographic assay with [3H]xanthine incorporation showed 0.5 to 0.7% phenotypic expression of XPRT in both cell lines. Without selection, transient CAT activity was 20 times greater in the GM0637(SV40) than in the XP20s(SV40) cells, and transient XPRT activity was 5 times greater. Both of these transient activities were increased and equalized in both cell lines by transfection with pRSVcat or pRSVgpt. Genotypic transformation to gpt+ occurred at a frequency of 2 X 10(-4) to 4 X 10(-4) in both cell lines with pSV2catSVgpt. After 2 to 3 months in selective medium, stable expression of the (nonselected) cat gene was found in 11 (92%) of 12 gpt-containing clones derived from GM0637(SV40) cells and in 13 (81%) of 16 gpt-containing clones from XP20s(SV40) cells. However, the levels of CAT activity did not correlate with those of XPRT activity, and both of these activities varied more than 100-fold among different clones. Copies (1 to 4) of the gpt gene were integrated in four clones of the GM0637(SV40) cells having an XPRT activity of 1 to 5 nmol/min per mg, but 5 to 80 copies were integrated in four XP20s(SV40) clones with an XPRT activity of 0.8 to 1.8 nmol/min per mg. This study shows that XP20s(SV40) is as suitable for gene transfer experiments as the normal human line GM0637(SV40).

Quantification of expression of linked cloned genes in a simian virus 40-transformed xeroderma pigmentosum cell line

We wished to determine whether simian virus 40 (SV40)-transformed xeroderma pigmentosum cells, despite their defective DNA repair, were suitable for DNA-mediated gene transfer experiments with linked genes. Expression of a nonselectable gene (cat, coding for chloramphenicol acetyltransferase [CAT]) linked to a selectable gene (gpt, coding for xanthine-guanine phosphoribosyltransferase [XPRT]) in the plasmid pSV2catSVgpt was quantified after transfection of SV40-transformed xeroderma pigmentosum [XP20s(SV40)] and normal human [GM0637(SV40)] fibroblast cell lines. A novel autoradiographic assay with [3H]xanthine incorporation showed 0.5 to 0.7% phenotypic expression of XPRT in both cell lines. Without selection, transient CAT activity was 20 times greater in the GM0637(SV40) than in the XP20s(SV40) cells, and transient XPRT activity was 5 times greater. Both of these transient activities were increased and equalized in both cell lines by transfection with pRSVcat or pRSVgpt. Genotypic transformation to gpt+ occurred at a frequency of 2 X 10(-4) to 4 X 10(-4) in both cell lines with pSV2catSVgpt. After 2 to 3 months in selective medium, stable expression of the (nonselected) cat gene was found in 11 (92%) of 12 gpt-containing clones derived from GM0637(SV40) cells and in 13 (81%) of 16 gpt-containing clones from XP20s(SV40) cells. However, the levels of CAT activity did not correlate with those of XPRT activity, and both of these activities varied more than 100-fold among different clones. Copies (1 to 4) of the gpt gene were integrated in four clones of the GM0637(SV40) cells having an XPRT activity of 1 to 5 nmol/min per mg, but 5 to 80 copies were integrated in four XP20s(SV40) clones with an XPRT activity of 0.8 to 1.8 nmol/min per mg. This study shows that XP20s(SV40) is as suitable for gene transfer experiments as the normal human line GM0637(SV40).

Transient expression of human adenosine deaminase cDNAs: identification of a nonfunctional clone resulting from a single amino acid substitution

Human adenosine deaminase (ADA) is an important purine catabolic enzyme which irreversibly deaminates adenosine and deoxyadenosine. Severe genetic deficiency of ADA leads to an immunological deficiency state in which T-lymphoid cells are selectively destroyed by the accumulation of toxic levels of deoxyadenosine and deoxy-ATP. In preparation for transfer of ADA sequences into a variety of cell types, we explored expression of ADA cDNAs transfected into cultured cells within a simian virus 40-based expression vector. After transfection into monkey kidney (COS) cells, ADA cDNA encompassing the entire coding region of the protein generated human ADA activity. An unexpected finding, however, was the identification of a cDNA clone that failed to produce either human enzyme activity or immunoreactive ADA protein. As this pattern is typical of many naturally occurring mutant ADA alleles, we characterized the molecular defect in this clone. DNA sequence analysis revealed a single nucleotide substitution in amino acid position 50 (glycine-valine). Northern blotting with a unique 17-mer oligonucleotide demonstrated the absence of the mutant sequence in the mRNA from which the cDNA library giving rise to the mutant cDNA was constructed. Therefore, the substitution in the variant cDNA was created during cloning. These data define one critical region of the human ADA protein molecule and suggest a convenient strategy for characterization of the phenotypes associated with naturally occurring mutant alleles.

Transient expression of human adenosine deaminase cDNAs: identification of a nonfunctional clone resulting from a single amino acid substitution

Human adenosine deaminase (ADA) is an important purine catabolic enzyme which irreversibly deaminates adenosine and deoxyadenosine. Severe genetic deficiency of ADA leads to an immunological deficiency state in which T-lymphoid cells are selectively destroyed by the accumulation of toxic levels of deoxyadenosine and deoxy-ATP. In preparation for transfer of ADA sequences into a variety of cell types, we explored expression of ADA cDNAs transfected into cultured cells within a simian virus 40-based expression vector. After transfection into monkey kidney (COS) cells, ADA cDNA encompassing the entire coding region of the protein generated human ADA activity. An unexpected finding, however, was the identification of a cDNA clone that failed to produce either human enzyme activity or immunoreactive ADA protein. As this pattern is typical of many naturally occurring mutant ADA alleles, we characterized the molecular defect in this clone. DNA sequence analysis revealed a single nucleotide substitution in amino acid position 50 (glycine-valine). Northern blotting with a unique 17-mer oligonucleotide demonstrated the absence of the mutant sequence in the mRNA from which the cDNA library giving rise to the mutant cDNA was constructed. Therefore, the substitution in the variant cDNA was created during cloning. These data define one critical region of the human ADA protein molecule and suggest a convenient strategy for characterization of the phenotypes associated with naturally occurring mutant alleles.