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Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A eukaryotic vector-host cell system is described where the additive transactivating effects of HIV-1 tat and adenovirus E1A on HIV-1 long terminal repeat (LTR) are exploited to increase expression of exogenous cDNAs. Human 143B and 293 cells, the latter constitutively producing E1A, were used as host cell lines. The bacterial gene chloramphenicol acetyltransferase (CAT) and the hepatitis B surface antigen (HBs-Ag) gene were employed as reporter genes inserted in pRPneoU3R, an episomal vector containing BK virus replication origin and early region, where cDNAs are expressed under control of HIV-1 LTR. The 293 cells were transformed by tat expression vectors to constitutively express tat. Stable cell clones of 293tat cells, constitutively expressing CAT after transformation with pRPneoU3R-CAT, show a CAT activity 600-fold higher than normal 293 transformed cells. CAT expression obtained in normal 293 cells can be transiently increased 10-fold by transfection by vectors expressing tat. The 293tat cells transformed by pRPneoU3R-HBs, an episomal vector expressing HBs-Ag from HIV LTR, yielded stable cell clones secreting HBs-Ag in the culture medium at a concentration up to 744 ng/ml or 44 ng/10(6) cells/24 h, 48-fold more than normal 293 cells. The use of this system for constitutive or inducible expression of sequences under control of HIV-1 LTR is discussed in view of possible applications for diagnostic, vaccinal and therapeutic purposes.
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PMID:High expression of exogenous cDNAs directed by HIV-1 long terminal repeat in human cells constitutively producing HIV-1 tat and adenovirus E1A/E1B. 182 15

The TAR element extending from -17 to +80 in the human immunodeficiency virus long terminal repeat (HIV LTR) is required for activation of gene expression by the tat trans-activator protein. TAR RNA forms a stable stem-loop structure, and mutagenesis studies indicate that the stem structure, the primary sequence of the loop, and the bulge element are the major determinants for tat activation. RNA gel retardation analysis demonstrates that both tat and cellular proteins bind to TAR RNA, but the mechanism by which these proteins increase HIV gene expression is unknown. We have fractionated HeLa cell nuclear extracts in an attempt to identify cellular proteins that bind to TAR RNA and are involved in regulating HIV gene expression. RNA gel retardation and UV cross-linking reveal that a cellular protein of 185 kD, which we designate TAR RNA-binding protein 185 (TRP-185), binds with both high affinity and marked specificity to TAR RNA. RNA gel retardation and competition analyses indicate that TRP-185 binding is strongly dependent on the TAR RNA loop sequences. The binding of TRP-185 is modulated by both a set of cellular cofactors and the tat protein. Highly purified preparations of TRP-185 are capable of activating in vitro transcription of wild-type, but not mutated, HIV LTR chloramphenicol acetyltransferase (CAT) constructs. These results characterize a positively acting cellular RNA-binding factor, TRP-185, which is involved in the regulation of HIV gene expression.
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PMID:tat regulates binding of the human immunodeficiency virus trans-activating region RNA loop-binding protein TRP-185. 193 97

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.
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PMID:Cellular factors regulate transactivation of human immunodeficiency virus type 1. 199 49

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.
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PMID:A bioassay for HIV-1 based on Env-CD4 interaction. 207 9

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)
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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.
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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.
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PMID:Cytomegalovirus activates transcription directed by the long terminal repeat of human immunodeficiency virus type 1. 215 54

In HuT 78 cells chronically infected with SIV, super-infection with rhesus cytomegalovirus (rhCMV) stimulated an increase in SIV replication. Utilizing transient expression assays with the SIV long terminal repeat (LTR) driving expression of the chloramphenicol acetyltransferase (CAT) reporter gene, the increase in SIV replication, by coinfection with CMV, was due to transactivation of the SIV LTR by the immediate early gene products (IE) of rhesus CMV. Similarly, IE of human CMV stimulated expression from both the SIV and HIV LTRs.
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PMID:Molecular interactions of cytomegalovirus and the human and simian immunodeficiency viruses. 217 42

We compared the ability of HIV-1 tat protein and JCV T-antigen in inducing transcription from the JCV late promoter, JCVL. A JCVL promoter-chloramphenicol acetyltransferase plasmid (pJCL-CAT) was transfected into human glial cells alone or together with plasmids producing T-antigen and tat protein. CAT enzyme activity obtained from the transfected cells indicated that both JCV T-antigen and HIV-1 tat proteins stimulated JCV late gene expression. However, the level of induction mediated by tat protein was significantly higher than that obtained with T-antigen. Moreover, in contrast to JCV T-antigen, tat stimulated JCVL-promoter activity over a narrow range of ptat expressor plasmid concentration. Co-transfection of both T-antigen and tat plasmids at optimal concentrations resulted in greater than additive CAT activity from the JCVL promoter. This synergism suggests that the two activator proteins utilize alternative mechanisms to exert their effects. Using deletion mutations from the 5' end of the JCVL promoter, we demonstrated that different regions within the JCV enhancer/promoter are important for T-antigen and tat induction, implying that these activators function through distinct targets to increase JCVL promoter activity.
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PMID:Regulation of the human neurotropic virus promoter by JCV-T antigen and HIV-1 tat protein. 217 36

The transient expression of hepatitis B virus (HBV) surface and "eJ" antigens caused by transfection of human hepatoblastoma HepG2 cells with HBV DNA was markedly inhibited by cotransfection with poly(I):poly(C). Cotransfection with poly(I):poly(C) also inhibited the expression of bacterial chloramphenicol acetyltransferase (CAT) gene which was under the control of either the HBV core promoter or the human immunodeficiency virus (HIV-1) long terminal repeat. This inhibition was much more pronounced on the expression of HBV-promoted CAT than HIV-promoted CAT. The uptake of reporter plasmid was not affected by cotransfected poly(I):poly(C). The inhibition was found to be at the steady-state CAT mRNA level and appeared to be specific for HBV and HIV regulatory sequences since CAT expression directed by other viral and cellular regulatory sequences was not inhibited. Cotransfection with a mixture of equal amounts of poly(I) and poly(C) had similar inhibitory effects whereas cotransfection with poly(l) or poly(C) alone, or other double-stranded ribo- or deoxyribonucleotides, did not have such strong effects. The addition of poly(l):poly(C) to the culture medium of cells transfected with these reporter plasmids caused little inhibition. Transfection with poly(l):poly(C) induced a minimal amount of intracellular interferon-alpha in HepG2 cells which may be involved in selective inhibition of HBV-and HIV-1-directed gene expression. 2-Aminopurine, an inhibitor of double-stranded RNA activated protein kinase known to block interferon gene induction by poly(l):poly(C), partially reversed the poly(l):poly(C)-induced inhibitory effect on HBV-CAT expression.
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PMID:Selective inhibition of hepatitis B virus and human immunodeficiency virus sequence-promoted gene expression by cotransfected poly(I):poly(C). 221 31


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