Cell-specific activity of the human immunodeficiency virus enhancer repeat in vitro

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

A Simple and Rapid TAR-Dependent in vitro Transcription Assay Using T Cell Nuclear Extracts and Synthetic tat1-86 Protein

A 'G-less' cassette was cloned downstream of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) to facilitate rapid identification of authentic LTR-directed transcription in T cell nuclear extracts. Despite a high constitutive level of transcription, addition of chemically synthesized full-length HIV-1(bru) tat (amino acids 1-86) stimulated transcription 3-fold but only if the template included the TAR region of the LTR. Suppression of basal transcription in T cell nuclear extracts by sodium citrate increased the relative level of tat stimulation, but neither potassium chloride nor histone H1 had an effect. A mutant synthetic tat polypeptide, lacking residues 22-32 in the cysteine-rich domain, was inactive in uptake assays and failed to stimulate transcription. Short basic peptides that competed full-length tat from complexes with TAR RNA also inhibited tat stimulation of transcription, whereas short basic peptide unable to bind TAR or compete tat from complexes were also unable to inhibit tat stimulation of transcription. These data confirm that active HIV-1 tat must first interact with TAR RNA via basic amino acid residues in order to stimulate transcription of downstream sequences. Copyright 1995 S. Karger AG, Basel

Nuclear expression of the 50- and 65-kD Rel-related subunits of nuclear factor-kappa B is differentially regulated in human monocytic cells

The nuclear factor (NF)-kappa B transcription factor system is composed of at least four inducible nucleoprotein adducts termed p50, p55 (NF-kappa B p50), p75 (NF-kappa B p65), and p85 (c-Rel). These proteins are expressed in the nuclei of activated T cells in a distinctly biphasic fashion, with p55 and p75 induction occurring within minutes whereas the induction of p50 and p85 occurs after several hours. In contrast, p50 and p55 are constitutively expressed in the nuclei of U937 and THP-1 monocytic cells. However, cellular activation is required for the nuclear expression of p75 in these cells. Additionally, activation of monocytic cells does not result in a significant induction of p85. Tumor necrosis factor alpha induces the nuclear expression of p55 and p75 in these monocytic cells within 20 min, presumably reflecting the liberation of these proteins from I kappa B. In contrast, phorbol myristate acetate (PMA) induces the expression of these proteins with delayed kinetics, raising the possibility that PMA is incapable of mediating the efficient release of p55 and p75 from I kappa B in these cells. These findings highlight important differences in the regulation of these proteins in monocytic cells versus T cells and suggest that the induced expression of NF-kappa B p65 in monocytes may play a central role in the activation of HIV-1 gene expression.

Differential human immunodeficiency virus expression in CD4+ cloned lymphocytes: from viral latency to replication

By using cloning methodology, 13 CD4+, CD8-, CD45RO+, and CD29+ clones, isolated from human immunodeficiency virus (HIV)-negative donors, have been characterized and tested regarding their susceptibility to two strains of HIV type 1 (HIV-1). Infected clones possess integrated provirus. Only six are able to replicate HIV-1, while seven may normally grow without cytopathic effect and without viral replication. These results argue that all CD4+ lymphocyte clones may be infectable but that a heterogeneity exists regarding their abilities to replicate HIV-1.

Enhancement of RNA polymerase II initiation complexes by a novel DNA control domain downstream from the cap site of the cytomegalovirus major immediate-early promoter

The major immediate-early promoter (MIEP) of human cytomegalovirus is a remarkably strong RNA polymerase II transcription control unit. We have identified and characterized a novel regulatory domain associated with MIEP downstream from the initiation site of transcription. The downstream regulatory region was first identified by analyzing a series of mutations in the 5' untranslated leader exon. This regulatory domain was shown to enhance the number of functional initiation complexes without significantly altering the apparent elongation rate by RNA polymerase II transcription. In addition, run-off in vitro transcription and DNA-binding experiments identified two distinct downstream elements that specify the interaction of cellular transcription factors. One of these elements contains a reiterated sequence motif, present twice within the leader exon. The second element is an 18-bp sequence located at approximately nucleotide position +33 that is conserved between strains of cytomegalovirus from different species. On the basis of two criteria, an oligonucleotide competition assay and oligomerization upstream of the promoter, the binding of factors to the conserved box was shown to be critical for mediating the level of transcription from MIEP. Two discrete cellular nuclear proteins, designated LTF A and B (for leader transcription factor A and B binding factors), were found to specifically recognize the conserved element. This study of promoter-proximal elements within transcribed sequences demonstrates the recognition of the control domain at the DNA level that functions to increase the number of committed RNA polymerase II transcription complexes.

Human chromosome 12 is required for elevated HIV-1 expression in human-hamster hybrid cells

Host cell factors act together with regulatory genes of the human immunodeficiency virus (HIV) to control virus production. Human-Chinese hamster ovary hybrid cell clones were used to probe for human chromosomes involved in regulating HIV gene expression. DNA transfection experiments showed that 4 of 18 clones had high levels of HIV gene expression measured by both extracellular virus production and transactivation of the HIV long terminal repeat in the presence of the trans-activator (tat) gene. Karyotype analyses revealed a 94% concordance (17/18) between human chromosome 12 and HIV gene expression. Other chromosomes had an 11 to 72% concordance with virus production.

kappa B elements strongly activate gene expression in non-lymphoid cells and function synergistically with NF1 elements

kappa B elements have been described as lymphoid-specific transcriptional activators. Here we show that kappa B elements are able to stimulate expression from test promoters more than 100-fold in T47D and 3T3 non-lymphoid cells. We also demonstrate that nuclear proteins from T47D cells form two prominent complexes with HIV kappa B sites. Since the complexes formed in nuclear extracts from T47D and PHA/PMA stimulated Jurkat cells comigrate in polyacrylamide gels, we suggest that the respective binding protein in T47D cells is either NF-kappa B or a closely related family member. In addition we provide evidence that NF1 and kappa B elements can act synergistically to further increase transcriptional activity.

In vitro transcription of the mouse whey acidic protein promoter is affected by upstream sequences

The promoter sequences from -175 to +10 of the mouse whey acidic protein (WAP) gene are a target for sequence-specific binding of nuclear proteins [(1987) Nucleic Acids Res. 15, 2103-2121]. Using in vitro transcription assays based on nuclear extracts, transcription factors were shown to bind to these sequences and promoter upstream sequences were found to stimulate transcription.

Cell-specific activity of the modulator region in the human cytomegalovirus major immediate-early gene

In this paper we demonstrate that modulator sequences upstream of the enhancer of the major immediate-early promoter of human cytomegalovirus exert a differential effect on the level of transcription in a variety of cells and that this region has the capacity to interact with specific nuclear protein. Depending on the cell type, these modulator sequences increased or decreased transcriptional activation from the IE1 gene promoter-enhancer. The cell lines identified in this report should be useful to study the molecular mechanism of cell-specific transcriptional repression and activation exerted by the major immediate-early promoter upstream region.

Cell-specific activity of the modulator region in the human cytomegalovirus major immediate-early gene

In this paper we demonstrate that modulator sequences upstream of the enhancer of the major immediate-early promoter of human cytomegalovirus exert a differential effect on the level of transcription in a variety of cells and that this region has the capacity to interact with specific nuclear protein. Depending on the cell type, these modulator sequences increased or decreased transcriptional activation from the IE1 gene promoter-enhancer. The cell lines identified in this report should be useful to study the molecular mechanism of cell-specific transcriptional repression and activation exerted by the major immediate-early promoter upstream region.