Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It is hypothesized that the immediate-early (IE) gene products of human cytomegalovirus (CMV) and the transactivator (TAT) of human immunodeficiency virus type 1 (HIV-1) regulate HIV-1 gene expression through mechanisms involving host cell factors. By using transient transfection assays with the gene for chloramphenicol acetyltransferase (CAT) under the transcriptional control of the HIV-1 long terminal repeat (LTR), we examined transactivation of the LTR by plasmids that express either the HIV-1 gene for TAT or human CMV IE. The ratio of the level of transactivation by CMV IE to the level of transactivation by TAT varied up to 1,000-fold between cell types. The difference in the activities of these transactivators in various cell types was not a consequence of differential expression of the transactivator gene. Analysis of RNA species initiated in the HIV-1 LTR supports the conclusion that cellular factors regulate the level of elongation of the transcription complex on the LTR. Furthermore, evidence that in some cell types the predominant mechanism of transactivation by HIV-1 TAT involves posttranscriptional processes is presented.
...
PMID:Cellular factors regulate transactivation of human immunodeficiency virus type 1. 199 49

We have compared the relative importance of transcription regulatory regions in the U3 and R regions of the human immunodeficiency virus type 1 long terminal repeat (LTR) by using linker-scanning mutational analysis. Twenty-six mutant LTR-chloramphenicol acetyltransferase (CAT) transient expression plasmids were prepared in which consecutive 18-bp regions of wild-type LTR were replaced with an NdeI-XhoI-SalI (NXS) polylinker. The mutant LTR-CAT plasmids were transfected into unstimulated Jurkat cells, Jurkat cells stimulated with phytohemagglutinin and tetradecanoylphorbol acetate, and Jurkat cells which constitutively express the human immunodeficiency virus type 1 trans-activator protein, Tat. Transcriptional activity was measured by analysis of CAT activity. The activities of these mutants identified one major and several minor transcription control elements in addition to previously identified elements. In addition, this fine-structure analysis identified differences in utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells. A significant regulatory region was indicated by linker-scanning mutations between nucleotides -183 and -130 (relative to the transcription start site, +1). These mutations caused marked decreases in activity of the LTR in unstimulated and especially in stimulated Jurkat cells but had no effect in Tat-expressing Jurkat cells. DNA mobility shift studies comparing probes of wild-type and mutant sequences in the -183 to -130 region indicated that alterations in specific DNA binding correspond to the altered transcriptional activity of the mutants. The effects of mutations in several regulatory regions, in addition to the -183 to -130 region described above, differ between Tat-expressing and -nonexpressing Jurkat cells. For example, the NF-kB sites are necessary for transcription in both Tat-expressing and -nonexpressing cells. However, Tat-expressing Jurkat cells primarily require only the 3'-proximal site, while both stimulated and unstimulated Jurkat cells appear to require both sites. Mutants downstream of the TATA element cause a more significant decrease in activity in Tat-expressing Jurkat cells than in the others. Finally, several mutations in the 5' half of the LTR (-453 to -184) show modest increases in transcription (1.5-fold or less) in unstimulated Jurkat cells only, suggesting possible negative regulatory sites. In summary, our studies have identified a control region (-183 to -130) upstream of the NF-kB sites and have more precisely defined significant differences in the utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells.
...
PMID:Linker-scanning mutational analysis of the transcriptional activity of the human immunodeficiency virus type 1 long terminal repeat. 201 66

The mechanism of induction of gene expression of the human immunodeficiency virus type 1 long terminal repeat (LTR) by the Tat transactivator protein was studied in a cell fusion assay. Tat causes a rapid activation of both transcription from the LTR and accumulation of hybrid LTR-chloramphenicol acetyltransferase mRNAs. Approximately 4 h after induction by Tat, expression from the LTR promoter is down-regulated, resulting in a decrease in the accumulation of LTR mRNA. This down-regulation of expression occurs in the continued presence of Tat. Protein synthesis inhibitors can block this down-regulation; therefore, the postinduction repression of expression is dependent upon de novo protein synthesis. We propose that a labile cellular protein(s) is responsible for the low levels of human immunodeficiency virus type 1 expression, possibly contributing to the establishment of a latent state of viral expression.
...
PMID:Rapid activation and subsequent down-regulation of the human immunodeficiency virus type 1 promoter in the presence of Tat: possible mechanisms contributing to latency. 203 65

Stable transformants of the Jurkat T-cell line have been obtained that express either of two distinct forms of the type 1 human immunodeficiency virus nef gene: the nef-1-encoded protein (Nef-1) contains alanine, glycine, and valine at positions 15, 29, and 33, respectively; the protein specified by nef-2 (Nef-2) has threonine, arginine, and alanine at the corresponding positions. When Jurkat cells or their Nef-2-expressing transformants are treated with phorbol 12-myristate 13-acetate (PMA) plus either phytohemagglutinin (PHA) or antibodies against CD3 epsilon, T-cell receptor beta chain, or CD2, there is a prompt increase in interleukin 2 (IL-2) mRNA and intracellular calcium and in the IL-2 receptor alpha chain on the cell surface. Although cells expressing Nef-1 also induce calcium mobilization and the production of IL-2 receptor alpha chain, the formation of IL-2 mRNA is blocked in response to these stimuli. Moreover, Nef-1-expressing cells transfected with a plasmid in which the IL-2 promoter is fused to the chloramphenicol acetyltransferase (CAT) gene fail to induce CAT following treatment with PMA and PHA. By contrast, the parental and Nef-2-containing cells induce CAT normally. Nef-1-expressing cells can produce IL-2 mRNA in response to a combination of PMA and ionomycin, although much less efficiently than the parental Jurkat cells or Nef-2-expressing cells. These findings, and others described herein, suggest that the virally encoded Nef protein interferes with a signal emanating from the T-cell receptor complex that induces IL-2 gene transcription.
...
PMID:Expression of the type 1 human immunodeficiency virus Nef protein in T cells prevents antigen receptor-mediated induction of interleukin 2 mRNA. 205 9

The binding of human immunodeficiency virus type 1 (HIV-1) gp120env to CD4 is the first event leading to infection and represents an important target for possible therapeutic intervention. To provide a tool for screening and quantitation of the effects of drugs inhibiting the Env-CD4 interaction, we developed a simple, fast and quantitative bioassay measuring the fusion between two cell lines generated by stable transfection: one expressing high levels of HIV-1 proteins but no infectious virus (HL2/3), and the other expressing the CD4 receptor and containing an inducible chloramphenicol acetyltransferase (CAT) gene linked to the HIV-1 long terminal repeat (HLCD4-CAT). Upon cocultivation of HL2/3 and HLCD4-CAT cells, efficient cell fusion is observed within 8 h. The efficiency of fusion can be evaluated visually and quantitated by measuring CAT enzyme. This novel bioassay allows testing for drugs capable of interfering with the CD4-Env interaction. HL2/3 cell line secretes gp120env in the medium and can be used for the production of Env protein.
...
PMID:A bioassay for HIV-1 based on Env-CD4 interaction. 207 9

Transfected gene constructs comprising the long terminal repeat (LTR) sequence of the human immunodeficiency virus (HIV) genome spliced to an assayable reporter gene have made possible the evaluation of a lipid mediator, platelet-activating factor (PAF), as a potential HIV transcriptional regulatory molecule. We assessed the activation of the HIV LTR promoter sequence linked to the chloramphenicol acetyltransferase (CAT) reporter gene (HIV-CAT) by PAF in both a human neural (SH-SY5Y neuroblastoma) and a human leukocytic (MOLT-4 T-lymphocyte) cell line. PAF activated expression of the HIV-CAT construct in both the SH-SY5Y and MOLT-4 T-cell lines. PAF-induced CAT activity was approximately six to seven times higher in the SH-SY5Y cells than in the MOLT-4 cells. Preincubation of cells with the specific PAF antagonist BN 52021 completely inhibited CAT expression in both cell lines. The biologically inactive PAF precursor lyso-PAF did not activate CAT expression. Assays for CAT mRNA demonstrated an increase after PAF treatment, an effect that was completely inhibited by BN 52021, and which was not elicited by lyso-PAF. These results show that PAF represents a potential cellular mediator evoking the expression of the HIV genome.
...
PMID:Platelet-activating factor activates HIV promoter in transfected SH-SY5Y neuroblastoma cells and MOLT-4 T lymphocytes. 207 79

Multiple regulatory elements in the human immunodeficiency virus long terminal repeat (HIV LTR) are required for activation of HIV gene expression. Previous transfection studies of HIV LTR constructs linked to the chloramphenicol acetyltransferase gene indicated that multiple regulatory regions including the enhancer, SP1, TATA and TAR regions were important for HIV gene expression. To characterize these regulatory elements further, mutations in these regions were inserted into both the 5' and 3' HIV LTRs and infectious proviral constructs were assembled. These constructs were transfected into either HeLa cells, Jurkat cells or U937 cells in both the presence and absence of phorbol esters which have previously been demonstrated to activate HIV gene expression. Viral gene expression was assayed by the level of p24 gag protein released from cultures transfected with the proviral constructs. Results in all cell lines indicated that mutations of the SP1, TATA and the TAR loop and stem secondary structure resulted in marked decreases in gene expression while mutations of the enhancer motif or TAR primary sequence resulted in only slight decreases. However, viruses containing mutations in either the TAR loop sequences or stem secondary structure which were very defective for gene expression in untreated Jurkat cells, gave nearly wild-type levels of gene expression in phorbol ester-treated Jurkat cells but not in phorbol ester-treated HeLa or U937 cells. High level gene expression of these TAR mutant constructs in phorbol ester-treated Jurkat cells was eliminated by second site mutations in the enhancer region or by disruption of the tat gene.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:TAR independent activation of the human immunodeficiency virus in phorbol ester stimulated T lymphocytes. 212 73

Biological interactions between human cytomegalovirus (HCMV) and the human immunodeficiency virus type 1 (HIV-1) were analysed in transfection and infection experiments, carried out in a human osteogenic sarcoma cell line (HOS) and in the same cell line chronically infected with HCMV (E155). When HOS and E155 cells were transfected with recombinant plasmids containing the HIV long terminal repeat (LTR) linked to the bacterial chloramphenicol acetyltransferase (CAT) gene, LTR-directed CAT expression was 20 times higher in E155 cells than in HOS cells. HOS cells co-infected with HCMV and HIV-1 showed enhanced production of the HIV-1 p24 antigen. In reciprocal experiments, an increase in HCMV immediate early gene expression was observed when HCMV-infected HOS cells and E155 cells were either transfected with a recombinant plasmid containing the HIV transactivator gene (pTAT), or when infected with HIV-1. DNA hybridization analysis of E155 and HCMV-infected HOS cells revealed higher levels of HCMV DNA in cells transfected with pTAT than in cells transfected with other non-specific recombinant plasmids. E155 cells transfected with pTAT also produced higher titres of infectious HCMV than control cultures of E155 cells transfected with other recombinant plasmids, including pMTAT carrying a mutant tat gene. The functional reciprocity in vitro between HCMV and HIV is discussed with respect to its possible implications for the clinical development of AIDS.
...
PMID:Reciprocal enhancement of gene expression and viral replication between human cytomegalovirus and human immunodeficiency virus type 1. 215 40

Proteins encoded by a variety of DNA viruses activate gene expression from the promoter within the long terminal repeat (LTR) of the human immunodeficiency virus type 1 (HIV-1). The mechanism by which immediate-early (IE) gene products of human cytomegalovirus (CMV) activate expression from the HIV-1 LTR was examined in transient expression assays in cultures of human cells by using plasmids containing the LTR linked to the bacterial chloramphenicol acetyltransferase (CAT) gene and a plasmid expressing the CMV IE gene. Analysis of clustered site mutations within the HIV-1 LTR revealed that sequences from nucleotides -6 to +20 (relative to the start site of transcription) are critical for responsiveness to transactivation by CMV IE gene products. This region partially overlaps the trans-acting response element (+19 to +42) required for function of the HIV-1 transactivator. The CMV IE gene was shown to increase the steady-state levels of both prematurely terminated and full-length transcripts initiated within the LTR. These results support a model in which CMV IE gene products act through a specific regulatory element in the HIV-1 LTR to increase viral transcription.
...
PMID:Cytomegalovirus activates transcription directed by the long terminal repeat of human immunodeficiency virus type 1. 215 54

Since human immunodeficiency virus (HIV) nef has been suggested to exert regulatory effects on HIV long terminal repeat (LTR) activity, we transiently transfected HIV LTR chloramphenicol acetyltransferase or luciferase expression vectors into a human astrocytoma clone (U-373nef) that constitutively expresses the HIV nef gene. In these cells, basal HIV LTR activity, as well as tumor necrosis factor-induced or tat-driven activity, was similar to that in control cells. Lack of any detectable effect of HIV nef on LTR activity was not the result of mutations in integrated nef DNA, as was shown by polymerase chain reaction. These data suggest that the role of nef in HIV genome transcription does not necessarily involve a direct influence on HIV LTR activity.
...
PMID:Constitutive expression of human immunodeficiency virus (HIV) nef protein in human astrocytes does not influence basal or induced HIV long terminal repeat activity. 218 77


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---