An enhanced EBNA1 variant with reduced IR3 domain for long-term episomal maintenance and transgene expression of oriP-based plasmids in human cells

The latent replication of oriP-based plasmids in human cells depends on the viral oriP-binding transactivator EBNA1. In this report, the effect of the internal repeat 3 (IR3 or GlyAla repeat) domain of EBNA1 on long-term maintenance and transgene expression of OriP-based plasmids was examined in dividing human cells. To assess the potential contribution of different isoforms of EBNA1 specifically, the long-term stability of oriP-based plasmids was determined after stable transfection of various CMV-driven EBNA1 genes in EBV-negative human B cells. Episome copy number was quantified using a novel sensitive assay based on human mitochondrial DNA as an internal extrachromosomal control. Using this assay, the standard B95.8-derived EBNA1 was compared with its truncated IR3-deleted, form, as well as a new EBNA1 isoform cloned from Raji. The results of a 6-month study indicate that the isoforms of EBNA1 differ with respect to their efficiency of plasmid maintenance. While the EBNA-1 Raji encoding plasmid was the most stable, the oriP-based vector expressing the truncated EBNA1 (IR3del) gene was lost at a much higher rate than those transducing full size EBNA1s. In parallel, long-term reporter gene expression in various human B cell lines was shown to persist at the highest level with the oriP-based Raji EBNA-1 construct. These results show that the GlyAla domain can positively influence long-term plasmid stability and episomal transgene expression.     

Stimulation of gene expression by introns: conversion of an inhibitory intron to a stimulatory intron by alteration of the splice donor sequence

Efficient expression of many mammalian genes depends on the presence of at least one intron. We previously showed that addition of almost any of the introns from the mouse thymidylate synthase (TS) gene to an intronless TS minigene led to a large increase in expression. However, addition of intron 4 led to a reduction in minigene expression. The goal of the present study was to determine why TS intron 4 was unable to stimulate expression. Insertion of intron 4 into an intron-dependent derivative of the ribosomal protein L32 gene did not lead to a significant increase in expression, suggesting that its inability to stimulate expression was due to sequences within the intron. Deleting most of the interior of intron 4, improving the putative branch point, removing purines from the pyrimidine stretch at the 3' end of the intron, or removing possible alternative splice acceptor or donor sites within the intron each had little effect on the level of expression. However, when the splice donor sequence of intron 4 was modified so that it was perfectly complementary to U1 snRNA, the modified intron 4 stimulated expression approximately 6-fold. When the splice donor site of TS intron 1 (a stimulatory intron) was changed to that of TS intron 4, the modified intron 1 was spliced very inefficiently and lost the ability to stimulate mRNA production. Our observations support the idea that introns can stimulate gene expression by a process that depends directly on the splicing reaction.     

Epstein-Barr virus nuclear antigen 2 transactivates the long terminal repeat of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1)-infected subjects show a high incidence of Epstein-Barr virus (EBV) infection. This suggests that EBV may function as a cofactor that affects HIV-1 activation and may play a major role in the progression of AIDS. To test this hypothesis, we generated two EBV-negative human B-cell lines that stably express the EBNA2 gene of EBV. These EBNA2-positive cell lines were transiently transfected with plasmids that carry either the wild type or deletion mutants of the HIV-1 long terminal repeat (LTR) fused to the chloramphenicol acetyltransferase (CAT) gene. There was a consistently higher HIV-1 LTR activation in EBNA2-expressing cells than in control cells, which suggested that EBNA2 proteins could activate the HIV-1 promoter, possibly by inducing nuclear factors binding to HIV-1 cis-regulatory sequences. To test this possibility, we used CAT-based plasmids carrying deletions of the NF-kappa B (pNFA-CAT), Sp1 (pSpA-CAT), or TAR (pTAR-CAT) region of the HIV-1 LTR and retardation assays in which nuclear proteins from EBNA2-expressing cells were challenged with oligonucleotides encompassing the NF-kappa B or Sp1 region of the HIV-1 LTR. We found that both the NF-kappa B and the Sp1 sites of the HIV-1 LTR are necessary for EBNA2 transactivation and that increased expression resulted from the induction of NF-kappa B-like factors. Moreover, experiments with the TAR-deleted pTAR-CAT and with the tat-expressing pAR-TAT plasmids indicated that endogenous Tat-like proteins could participate in EBNA2-mediated activation of the HIV-1 LTR and that EBNA2 proteins can synergize with the viral tat transactivator. Transfection experiments with plasmids expressing the EBNA1, EBNA3, and EBNALP genes did not cause a significant HIV-1 LTR activation. Thus, it appears that among the latent EBV genes tested, EBNA2 was the only EBV gene active on the HIV-1 LTR. The transactivation function of EBNA2 was also observed in the HeLa epithelial cell line, which suggests that EBV and HIV-1 infection of non-B cells may result in HIV-1 promoter activation. Therefore, a specific gene product of EBV, EBNA2, can transactivate HIV-1 and possibly contribute to the clinical progression of AIDS.     

v-representability for noninteracting systems

The Epstein-Barr virus (EBV) induces unlimited growth of B lymphocytes in vitro, a phenomenon known as immortalization. The elucidation of the mechanisms by which EBV de-regulates B-cell proliferation in vitro will permit an understanding of how the virus contributes in vivo to the genesis of Burkitt's lymphoma (BL) and of lymphoproliferations in immunosuppressed patients. At present, no single EBV immortalizing gene has been identified, and the hypothesis has been made that many viral genes cooperate in establishing an autocrine loop of secretion leading to immortalization. Constitutive expression of B-cell surface molecules such as CD21 and CD23, specifically implicated in the control of B-cell proliferation, is indeed induced at the surface of immortalized B lymphocytes. The expression of the viral nuclear antigen 2 (EBNA2) has been shown to be in part responsible for CD21 and CD23 up-regulation, and EBNA2 is suspected to be a transactivator of cellular genes, although this point remains to be demonstrated. The role of EBNA2 gene, independently of other viral genes, has been investigated by transfection into B-lymphoma lines, but conflicting results have been reported. To further investigate its role in the regulation of CD21 and CD23 molecules, we have compared the effects of EBNA2 expression in 2 sets of B-lymphoma lines infected with P3HR1 EBV strain, and/or transfected with EBNA2 gene. We report here that: (i) EBNA2 expression is not a sufficient condition to induce CD21 and CD23 upregulation, EBNA2's effects are highly dependent on the cellular context, and moreover can be modified by infection with P3HR1 virus; (ii) EBNA2 induces activation of CD23 expression in a very particular way, namely, an increased quantity of CD23 steady-state RNA coding for the form A of the protein, which is not detectable at the cell surface but directly secreted.     

Role of endoplasmic reticulum-derived vesicles in the formation of Golgi elements in sec23 and sec18 Saccharomyces Cerevisiae mutants

Previous mutations associated with lecithin:cholesteryl acyltransferase (LCAT) deficiency syndromes have been identified in the coding regions of the LCAT gene. However, recently, an intron mutation was found in a family in which three sisters presented with fish-eye disease (FED). The probands were shown to be heterozygotes for a mutation in intron 4. The respective T-->C nucleotide substitution, 22 bases upstream of the 3'-splice site, causes a null allele as the result of complete intron retention. Since the natural mutation occurs in a putative branchpoint consensus sequence of the intron, it was hypothesized that the point mutation may disrupt the splicing of the pre-mRNA. To further study the functional significance of the above thymine residue in the branchpoint sequence, we introduced other nucleotides at this position, i.e., LCAT Int-4 MUT-1 (T-->G) and LCAT Int-4 MUT-2 (T-->A). After stable transfection of the mutated pNUT-LCAT minigenes into BHK cells, we could detect neither LCAT activity nor LCAT protein in the culture medium of the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines, as was previously described for the natural mutation. To determine the effects of the introduced mutations on pre-mRNA splicing, total RNA from transfected BHK cells was used for RT-PCR analysis. All BHK cell lines were shown to transcribe the integrated LCAT minigenes. However, the sizes of these LCAT messengers indicated that intron 4 was retained in the pNUT-LCAT Int-4 MUT-1 and pNUT-LCAT Int-4 MUT-2 cell lines. Subsequent sequence analysis of the RT-PCR products demonstrated that the unspliced intronic sequences contained the introduced mutations. In conclusion, the observed retention of intron 4 of the LCAT gene is the result of the specific loss of a thymine residue two bases upstream of the branchpoint adenosine residue in the putative branchpoint consensus sequence. The results confirm that a single base change in the branchpoint consensus sequence of an intron can cause human disease although this sequence is poorly conserved in mammals.     

Molecular cloning of a cDNA from Brassica napus L. for a homologue of acyl-CoA-binding protein

A cDNA encoding an acyl-CoA-binding protein (ACBP) homologue has been cloned from a lambda gt11 library made from mRNA isolated from developing seeds of oilseed rape (Brassica napus L.). The derived amino acid sequence reveals a protein 92 amino acids in length which is highly conserved when compared with ACBP sequences from yeast, cow, man and fruit fly. Southern blot analysis of Brassica napus genomic DNA revealed the presence of 6 genes, 3 derived from the Brassica rapa parent and 3 from Brassica oleracea. Northern blot analysis showed that ACBP genes are expressed strongly in developing embryo, flowers and cotyledons of seedlings and to a lesser extent in leaves and roots.     

Genomic organization of IFI16, an interferon-inducible gene whose expression is associated with human myeloid cell differentiation: correlation of predicted protein domains with exon organization

The human IFI16 gene is a member of an interferon-inducible family of mouse and human genes closely linked on syntenic regions of chromosome 1. Expression of these genes is largely restricted to hemopoietic cells, and is associated with the differentiation of cells of the myeloid lineages. As a prelude to defining the mechanisms governing IFI16 expression, we have deduced its genomic organization using a combination of genomic cloning and polymerase chain reaction amplification of genomic DNA. IFI16 consists of ten exons and nine intervening introns spanning at least 28 kilobases (kb) of DNA. The reiterated domain structure of IFI16 protein is closely reflected in its intron/exon boundaries, and may represent the evolutionary fusion of several independent functional domains. Thus, exon 1 consists of 5' untranslated (UT) sequences and contains sequence motifs that may confer interferon-inducibility, and exon 2 encodes the lysine-rich amino-terminal ("K") region, which possesses DNA-binding activity. Exon 3 codes for a domain which is poorly conserved between family members, except for a strongly retained basic motif likely to provide localization. The first of two 200 amino acid repeat domains that are the hallmark of this family (domain A) is represented jointly on exons 4 and 5, which are reiterated as exons 8 and 9, respectively, to encode the second 200 amino acid domain (B). Two intervening serine-threonine-rich domains (C and C'), unique to IFI16, are each encoded by single exons of identical length (exons 5 and 6). These domains are predicted to encode semi-rigid "spacer" domains between the 200 amino acid repeats. The reiterated nature of exons 4 to 6 and the insertion of introns into a single reading frame strongly suggest that IFI16 and related genes arose by a series of exon duplications, some of which antedated speciation into mouse and humans. Several alternative mRNA cap sites downstream of a TATA consensus sequence were defined, using primer extension analysis of mRNA. Sequencing of approximately 1.7 kb of DNA upstream of this region revealed no recognizable consensus elements for induction by interferon-alpha (interferon-alpha/beta-stimulated response elements), but two motifs resembling interferon-gamma activation sites were located. IFNs alpha and gamma both induce IFI16 mRNA expression in myeloid cells. Interferon-alpha inducibility of IFI16 may be regulated by an interferon-alpha/beta-stimulated response consensus element in the 5' UT exon, as a similar motif is conserved in the corresponding position in the related myeloid cell nuclear differentiation antigen gene.(ABSTRACT TRUNCATED AT 400 WORDS)     

Epstein-Barr virus recombinants from overlapping cosmid fragments

Five overlapping type 1 Epstein-Barr virus (EBV) DNA fragments constituting a complete replication- and transformation-competent genome were cloned into cosmids and transfected together into P3HR-1 cells, along with a plasmid encoding the Z immediate-early activator of EBV replication. P3HR-1 cells harbor a type 2 EBV which is unable to transform primary B lymphocytes because of a deletion of DNA encoding EBNA LP and EBNA 2, but the P3HR-1 EBV can provide replication functions in trans and can recombine with the transfected cosmids. EBV recombinants which have the type 1 EBNA LP and 2 genes from the transfected EcoRI-A cosmid DNA were selectively and clonally recovered by exploiting the unique ability of the recombinants to transform primary B lymphocytes into lymphoblastoid cell lines. PCR and immunoblot analyses for seven distinguishing markers of the type 1 transfected DNAs identified cell lines infected with EBV recombinants which had incorporated EBV DNA fragments beyond the transformation marker-rescuing EcoRI-A fragment. Approximately 10% of the transforming virus recombinants had markers mapping at 7, 46 to 52, 93 to 100, 108 to 110, 122, and 152 kbp from the 172-kbp transfected genome. These recombinants probably result from recombination among the transfected cosmid-cloned EBV DNA fragments. The one recombinant virus examined in detail by Southern blot analysis has all the polymorphisms characteristic of the transfected type 1 cosmid DNA and none characteristic of the type 2 P3HR-1 EBV DNA. This recombinant was wild type in primary B-lymphocyte infection, growth transformation, and lytic replication. Overall, the type 1 EBNA 3A gene was incorporated into 26% of the transformation marker-rescued recombinants, a frequency which was considerably higher than that observed in previous experiments with two-cosmid EBV DNA cotransfections into P3HR-1 cells (B. Tomkinson and E. Kieff, J. Virol. 66:780-789, 1992). Of the recombinants which had incorporated the marker-rescuing cosmid DNA fragment and the fragment encoding the type 1 EBNA 3A gene, most had incorporated markers from at least two other transfected cosmid DNA fragments, indicating a propensity for multiple homologous recombinations. The frequency of incorporation of the nonselected transfected type 1 EBNA 3C gene, which is near the end of two of the transfected cosmids, was 26% overall, versus 3% in previous experiments using transfections with two EBV DNA cosmids. In contrast, the frequency of incorporation of a 12-kb EBV DNA deletion which was near the end of two of the transfected cosmids was only 13%.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mucin gene expression in biliary epithelial cells

BACKGROUND/AIMS: In recent years considerable advances have been made in our knowledge of human mucin genes. Although analysis of their genomic organization is still in progress, the pattern of their expression in different human mucosae is now fairly well established. However, little is known about their expression in the biliary tree. In this study we determined the pattern of expression of the different human mucin genes in gallbladder biliary epithelial cells, intrahepatic bile ducts and liver. METHODS: Two complementary methods were used: Northern-blot and in situ hybridization analyses. The experiments were performed with eight probes corresponding to MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6 and MUC7. RESULTS: Our results revealed a strong mRNA expression of MUC3, MUC6 and MUC5B, a weak expression of MUC1, MUC5AC and MUC2, and no expression of MUC4 and MUC7. Surprisingly, MUC3, which was the gene which was most expressed in the biliary tree, was also found in hepatocytes, suggesting another function for the MUC3 protein than that of a secreted mucin. CONCLUSIONS: We conclude that MUC3, MUC6 and MUC5B were the main mucin genes expressed in biliary epithelial cells.