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

Human immunodeficiency virus type 1 (HIV-1) encodes a transactivator protein, known as Tat, that stimulates transcription directed by the HIV-1 long terminal repeat sequences. Tat appears to bind directly to the TAR RNA element present at the 5' end of nascent HIV-1 transcripts and thereby stimulates the activity of transcription complexes. We have expressed Tat in simian COS cells by transfection of a mammalian expression vector. Using immunoblots to detect Tat, the results of gel filtration and velocity sedimentation analyses demonstrate that Tat is a monomer in COS cell extracts. These results agree with other studies which indicate that Tat is a monomeric protein.
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PMID:Tat protein of human immunodeficiency virus type 1 is a monomer when expressed in mammalian cells. 165 98

To determine whether HIV-1 tat can transactivate a heterologous promoter lacking HIV sequences other than the TAR element, TAR was placed downstream of the chicken beta-actin promoter. Tat increased expression directed by the actin-TAR promoter to a degree equal to tat induction of the HIV-1 LTR. Optimal transactivation was observed when TAR was positioned downstream of the actin promoter such that the expected cap site of transcripts from this promoter would be the same as in transcripts directed by the HIV-1 LTR. Tat was able to transactivate, though to a lesser extent, a promoter consisting solely of a TATA element fused to TAR. Thus, tat induction does not require HIV-1 LTR promoter sequences other than TAR. Tat, when fused to the DNA binding domain of BPV-1 E2, was able to transactivate a truncated SV40 promoter containing upstream E2 binding sites, indicating that tat may be capable of transactivation when directed by a DNA binding protein to an upstream site in a heterologous promoter lacking all HIV sequences. Substitution of Ala for Lys at position 41 of tat in the tat-E2 fusion, a mutation which dramatically decreases tat transactivation of the HIV-1 LTR, eliminated this transactivation.
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PMID:Transactivation of heterologous promoters by HIV-1 tat. 166 14

The TAR sequence of the 5' leader of HIV-1 long terminal repeat-directed mRNA was found to be able to bind to and to activate double-stranded RNA-dependent (2'-5')A synthetase. Binding of TAR to the purified synthetase in vitro was abolished by addition of HIV-1 Tat protein, which binds to this sequence with a high affinity. Inhibition of TAR-mediated activation of (2'-5')A synthetase by Tat was prevented in the presence of the Zn2+ and Cd2+ chelators o-phenanthroline and penicillamine, which did not impair TAR-synthetase interaction. Transient expression assays of bacterial chloramphenicol acetyltransferase (CAT) gene in HeLa cells revealed that the levels of both CAT mRNA and CAT protein decreased after treatment of the cells with interferon, if CAT gene was linked to HIV-1 TAR segment. Cotransfection of the cells with a tat sequence containing plasmid rendered CAT gene expression insensible to the action of interferon.
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PMID:Binding of Tat protein to TAR region of human immunodeficiency virus type 1 blocks TAR-mediated activation of (2'-5')oligoadenylate synthetase. 169 53

Short peptides that contain the basic region of the HIV-1 Tat protein bind specifically to a bulged region in TAR RNA. A peptide that contained nine arginines (R9) also bound specifically to TAR, and a mutant Tat protein that contained R9 was fully active for transactivation. In contrast, a peptide that contained nine lysines (K9) bound TAR poorly and the corresponding protein gave only marginal activity. By starting with the K9 mutant and replacing lysine residues with arginines, a single arginine was identified that is required for specific binding and transactivation. Ethylation interference experiments suggest that this arginine contacts two adjacent phosphates at the RNA bulge. Model building suggests that the arginine eta nitrogens and the epsilon nitrogen can form specific networks of hydrogen bonds with adjacent pairs of phosphates and that these arrangements are likely to occur near RNA loops and bulges and not within double-stranded A-form RNA. Thus, arginine side chains may be commonly used to recognize specific RNA structures.
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PMID:Arginine-mediated RNA recognition: the arginine fork. 170 22

The quantity and quality of HIV-1 gene expression is temporally controlled by a cascade of sequential regulatory interactions. Basal HIV-1 transcription is determined by interaction of cellular regulatory proteins with specific DNA target sequences within the HIV-1 long-terminal repeat. The most notable of these protein:DNA interactions involves NF-kappa B, a transcription factor that plays a pivotal role in the activation of genes important for cellular responses to infection and inflammation. A second level of control involves the virally encoded Tat trans-activator. Tat, in combination with as yet unidentified cellular proteins, activates HIV-1 gene expression through a specific interaction with the viral TAR RNA stem-loop target sequence. A final level of regulation is mediated by the viral Rev protein. Rev acts posttranscriptionally to induce the expression of HIV-1 structural proteins and thereby commits HIV-1 to the late, cytopathic phase of the viral replication cycle. Rev activity appears to require a critical, threshold level of Rev protein expression, thus preventing entry into this late phase in cells that are unable to support efficient HIV-1 gene expression. In total, this cascade of regulatory levels allows the HIV-1 provirus to respond appropriately to the intracellular milieu present in each infected cell. In activated cells, the combination of Tat and Rev can stimulate a very high level of viral gene expression and replication. In quiescent or resting cells, in contrast, these same regulatory proteins are predicted to maintain the HIV-1 provirus in a latent or nonproductive state.
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PMID:Regulation of HIV-1 gene expression. 171 25

To further document the role of interferons in the restriction of HIV1 replication in cells of the monocyte/macrophage lineage, the antiviral effects of alpha-interferon (IFN alpha) were studied in chronically HIV 1-infected promonocytic cells U937, in which IFN alpha was endogenously produced or to which recombinant IFN alpha was added. Protein analysis performed after immunoprecipitation of culture media revealed that the addition of anti-IFN alpha antibody led to an increase in the production of viral particles, whereas addition of IFN alpha caused its decrease in a dose-dependent manner, indicating that IFN alpha mainly affects viral assembly and virion release. However, the treatment of HIV 1-infected cells with IFN alpha did not cause an increase in the amount of intracellular viral proteins, suggesting that this cytokine might act on other steps in the viral life cycle. No decrease in the level of the 3 main types of viral RNA was observed by Northern blot analysis, indicating that proviral transcription was not restricted by IFN alpha. Furthermore, cotransfection experiments with TAR(trans-activation responsive)-element-containing expression plasmids demonstrated that viral replication appears to be restricted at either a post-transcriptional and/or a translational level. These experiments suggest that the double-stranded (ds) inverted repeat TAR sequence present in HIV1 leader RNA may inhibit viral protein synthesis by phosphorylating the dsRNA-activated protein kinase induced by IFN. These results provide an impetus for achieving antiretroviral therapy based on the constitutive expression of IFN in monocytes and macrophages.
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PMID:Interferon-regulated viral replication in chronically HIV1-infected promonocytic U937 cells. 171 78

We have analyzed the contributory role of the human immunodeficiency virus type 1 (HIV-1) promoter and enhancers in basal and Tat-induced transcription. We found that a minimal promoter competent for basal expression is contained within sequences spanning nucleotides -43 to +80. Basal expression from this HIV-1 promoter was boosted more by the additional presence of the NF-kappa B elements than by the Sp1 elements. The minimal long terminal repeat promoter (-43 to +80), while having an intact TAR sequence, was not Tat inducible. However, the simple addition of short synthetic enhancer motifs (AP1, Oct, Sp1, and NF-kappa B) conferred Tat responsiveness. This ability to respond to Tat was in part dependent on the presence of the HIV-1 promoter. Changing the HIV-1 TATA to other eucaryotic TATA or non-TATA initiators minimally affected basal expression but altered Tat inducibility. Our findings suggest a specific context of functional promoter and enhancer elements that is optimal for Tat trans activation of the HIV-1 long terminal repeat. Our results do not allow conclusions about whether Tat acts at the level of initiation or at the level of elongation to be drawn.
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PMID:Functional roles for the TATA promoter and enhancers in basal and Tat-induced expression of the human immunodeficiency virus type 1 long terminal repeat. 172 76

A comparative analysis of TAR RNA structures in human and simian immunodeficiency viruses reveals the conservation of certain structural features despite the divergence in sequence. Both the TAR elements of HIV-1 and SIV-chimpanzee can be folded into relatively simple one-stem hairpin structures. Chemical and RNAase probes were used to analyze the more complex structure of HIV-2 TAR RNA, which folds into a branched hairpin structure. A surprisingly similar RNA conformation can be proposed for SIV-mandrill, despite considerable divergence in nucleotide sequence. A third structural presentation of TAR sequences is seen for SIV-african green monkey. These results are generally consistent with the classification of HIV-SIV viruses in four subgroups based on sequence analyses (both nucleotide- and amino acid-sequences). However, some conserved TAR structures were detected for members of different virus subgroups. It is therefore proposed that RNA structure analysis might provide an additional tool for determining phylogenetic relationships among the HIV-SIV viruses.
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PMID:Structural features in TAR RNA of human and simian immunodeficiency viruses: a phylogenetic analysis. 173 99

Transcriptional activation by the HIV-1 Tat protein requires specific residues in the hexanucleotide loop and trinucleotide bulge of the TAR RNA stem-loop structure found in the 5'-untranslated leader of all viral transcripts. Tat directly contacts residue U22 in the bulge and is thought to act in concert with cellular factors bound to the loop. We find that HeLa nuclear extracts contain two specific TAR RNA-binding proteins, designated TRP-1 and TRP-2, which compete for binding to the upper portion of the TAR hairpin. Analysis of point mutants in TAR RNA reveals that TRP-1 contacts residues in the loop that are important for trans-activation, whereas TRP-2 contacts the bulge, including the same residue (U22) that is required for the Tat-TAR interaction. Glycerol gradient sedimentation and UV cross-linking experiments indicate that TRP-1 is a large heteromeric complex containing a 185-kD RNA-binding protein, whereas TRP-2 activity derives from a family of 110- to 70-kD proteins. Interestingly, both TRP-1 and TRP-2 promote TAR-dependent transcription in vitro in the presence of Tat, although mixing experiments indicate that each of the three proteins must bind independently to TAR RNA. These findings suggest that the TAR element is recognized by two different nuclear RNA-binding proteins that affect transcriptional regulation by Tat.
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PMID:Two distinct nuclear transcription factors recognize loop and bulge residues of the HIV-1 TAR RNA hairpin. 175 41

The human immunodeficiency virus-1 (HIV-1) trans-activator Tat is an attractive target for the development of antiviral drugs because inhibition of Tat would arrest the virus at an early stage. The drug Ro 5-3335 [7-chloro-5-(2-pyrryl)-3H-1,4-benzodiazepine-2(H)-one], inhibited gene expression by HIV-1 at the level of transcriptional trans-activation by Tat. The compound did not inhibit the basal activity of the promoter. Both Tat and its target sequence TAR were required for the observed inhibitory activity. Ro 5-3335 reduced the amount of cell-associated viral RNA and antigen in acutely, as well as in chronically infected cells in vitro (median inhibition concentration 0.1 to 1 micromolar). Effective inhibition of viral replication was also observed 24 hours after cells were transfected with infectious recombinant HIV-1 DNA. The compound was active against both HIV-1 and HIV-2 and against 3'-azido-3'-deoxythymidine (AZT)-resistant clinical isolates.
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PMID:Inhibition of HIV replication in acute and chronic infections in vitro by a Tat antagonist. 176 31


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