Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously shown that the Tat protein of the human immunodeficiency virus type 1 (HIV-1) is a modular transcriptional activator that can be targeted upstream of either a synthetic promoter or the intact HIV promoter to activate transcription. This activation was shown to be largely dependent on the presence of consensus binding sites for the cellular transcription factor Sp1. Since the use of heterologous promoters may provide further insight into Tat-mediated transactivation, we have analyzed the transactivation of the thymidine kinase promoter of herpes simplex virus by Tat and by the acidic transcriptional transactivator VP16. The effects of mutations of defined upstream promoter elements show that Tat transactivation is dependent on Sp1 binding sites in a site-specific manner. In contrast, transactivation by the acidic transactivator VP16 is completely independent of any of the defined promoter elements upstream of the TATA box. These results suggest that Tat and the classically defined modular acidic transcriptional activators have different modes of transactivation. In addition, the substitution of the HIV-1 TATA box for the thymidine kinase TATA box substantially increases Tat transactivation, indicating that Tat transactivation may also ultimately involve TATA box-associated cellular transcription factors.
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PMID:Activation of a heterologous promoter by human immunodeficiency virus type 1 Tat requires Sp1 and is distinct from the mode of activation by acidic transcriptional activators. 841 86

The human immunodeficiency virus (HIV) type 1 long terminal repeat (LTR) contains binding sites for nuclear factor kappa B (NF-kappa B) and the constitutively expressed transcription factor Sp1, both of which are highly conserved in HIV and simian immunodeficiency virus isolates. To delineate the effects of these motifs on the replicative capacity of HIV and to explore the possibility of extending the virus host range, known heterologous enhancer/promoters were inserted into the HIV-1 LTR in place of the NF-kappa B and Sp1 binding sites. The effects of these substitutions on viral replication in transfected HeLa cells and on HIV infection of human peripheral blood lymphocytes or continuous T-leukemia cell lines were evaluated. HIVs in which the NF-kappa B/Sp1 enhancer plus the downstream TATA element were replaced with heterologous enhancer/promoters were also constructed. Viruses containing the human cytomegalovirus immediate-early enhancer exhibited infectious kinetics similar to that of wild-type HIV in activated human peripheral blood lymphocytes and AA2 cells but replicated less efficiently in H9 and CEM cells. These studies indicate that heterologous enhancer elements are capable of restoring Tat responsiveness to the HIV LTR in the context of directing reporter gene expression as well as in the production of infectious progeny virions.
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PMID:Human immunodeficiency viruses containing heterologous enhancer/promoters are replication competent and exhibit different lymphocyte tropisms. 841 44

In previous transfection analyses using the chloramphenicol acetyltransferase reporter gene system, we determined that linker substitution (LS) mutations between -201 and -130 (relative to the transcription start site) of the human immunodeficiency virus type 1 long terminal repeat (LTR) caused moderate decreases in LTR transcriptional activity in a T-cell line (S. L. Zeichner, J. Y. H. Kim, and J. C. Alwine, J. Virol. 65:2436-2444, 1991). In order to confirm the significance of this region in the context of viral replication, we constructed several of these LS mutations (-201 to -184, -183 to -166, -165 to -148, and -148 to -130) in proviruses and prepared viral stocks by cocultivation of transfected RD cells with CEMx174 cells. In addition, two mutations between -93 and -76 and between -75 and -58 were utilized, since they affect the nuclear factor kappa B (NF-kappa B)- and Sp1-binding sites and were expected to diminish viral replication. Our results suggest that while transfection analyses offer an adequate approximation of the effects of the LS mutations, the analysis of viral replication using a mutant viral stock presents a more accurate picture, which is sometimes at variance with the transfection results. Three mutants (-201/-184 NXS, -165/-148 NXS, and -147/-130 NXS) had effects on viral replication that were much more severe than the effects predicted from their performance in transfection analyses, and the effects of two LS mutations (-201/-184 NXS and -183/-166 NXS) were not predicted by their effects in transfection. In addition, we observed cell type-specific permissiveness to replication of some mutant viruses. In the cell types tested, the LS mutations indicated an apparent requirement not only for the intact NF-kappa B and SP1-binding sites but also for several regions between -201 and -130 not previously associated with viral infectivity.
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PMID:Replication of type 1 human immunodeficiency viruses containing linker substitution mutations in the -201 to -130 region of the long terminal repeat. 843 35

Long terminal repeat (LTR) of human immunodeficiency virus (HIV) type 1 is activated by thyroid hormone (T3) receptor alpha (T3R alpha) in the absence of ligand. Addition of T3 reverses this effect. This activity is mediated by a high affinity T3 response element (T3RE) within the HIV-1 LTR, termed the HIV-T3RE (bases -74 to -50), which coincides with the Sp1 element as demonstrated by mobility shift, DNaseI footprinting, and methylation interference analyses. HIV-T3RE mediates ligand-independent activation of transcription by T3R alpha when linked to a heterologous promoter. In addition, the viral transactivator Tat synergizes with T3R alpha to activate the HIV-1 LTR in the absence of T3, which is relieved in its presence. These findings have implications for the possible control of HIV-1 LTR activity by T3.
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PMID:A unique thyroid hormone response element in the human immunodeficiency virus type 1 long terminal repeat that overlaps the Sp1 binding sites. 853 64

The 72 kDa 1E1 protein of human cytomegalovirus (HCMV) is one of a few viral regulatory proteins expressed immediately after infection of a host cell. Although it is now well-established that 1E1 is a potent transcriptional activator of the human immunodeficiency virus (HIV) long terminal repeat (LTR), the identity of the nucleotide sequence responsive to 1E1 remains elusive and the molecular mechanism of this interaction is not well-understood. We have constructed various LTR mutants and tested them for their ability to be activated by 1E1 using transient transfection assays. Mutations in the NF-kappa B sites, of either a few changes in the nucleotide sequence or a deletion of the entire region, abrogated 1E1-driven transactivation. Deletion of the Tat-responsive element (TAR) had no significant effect on reporter expression. Mutations in the Sp1 sites or the TATA box significantly lowered LTR activity, but this is probably due to an effect on the general transcription system, as these elements are also required for the transactivation of the LTR by many stimulators including Tat, tumour necrosis factor alpha (TNF-alpha). E1A/E1B and phorbol myristate acetate (PMA). In addition, gel retardation analysis demonstrated that NF- kappa B activity was significantly increased in human T lymphoid H9 and monocytic U937 cell lines constitutively expressing 1E1. Taken together, these data suggest that NF- kappa B plays a central role in the 1E1 transactivation of the HIV LTR.
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PMID:Essential role of NF-kappa B in transactivation of the human immunodeficiency virus long terminal repeat by the human cytomegalovirus 1E1 protein. 855 31

Ten mutants of the simian immunodeficiency virus (SIV) SIVmac239 bearing deletions (delta) or substitutions (subst) in the NF-kappaB and/or Sp1 binding elements were created, and the replicative capacities of the mutants were analyzed. All mutants, including one extensively mutagenized strain entirely missing the NF-kappaB and four Spl binding elements, replicated with wild-type kinetics and to a wild-type level in peripheral blood mononuclear cell cultures in 50 to 100% of the experiments. One group of mutants replicated very similarly to SIVmac239 in kinetics and yield in CEMxl74 cells (2xNFKappaB > or = SlVmac239 approximately deltaNFkappaB approximately deltaSpl234 approximately substNFkappaB approximately substSpl2 approximately substSp23), while a second group replicated with delayed or slightly delayed kinetics in CEMxl74 cells (SIVmac239 > substSp34 > deltaNFkappaBdeltaSpl234 approximately deltaNFkappaBdeltaSp1 > substSpl234). Reversions or additional mutations were not detected in the U3 and R regions of proviral DNA from CEMxl74 cells infected with the SIVmac239 mutants. Similar results were obtained when mutants of SIVmacMER (a macrophage-competent derivative of SIVmac239) were tested in peripheral blood mononuclear cell and CEMx174 cultures. However, the growth of most mutated viruses was suppressed in primary rhesus monkey alveolar macrophages (SIVmacMER approximately 2xNFkappaB approximately substNFkappaB > deltaNFkappaB > deltaNFkappaBdeltaSpl234 approximately deltaNFkappaBdeltaSpl > deltaSpl234 approximately substSpl2 > substSp23 approximately substSp34 approximately substSpl234 > or = SIVmac239). Thus, changes in the Sp1 binding sites had the most dramatic effects on SIVmac replication in primary macrophage cultures. Analysis of long terminal repeat-driven secreted alkaline phosphatase activity in transient assays showed that, unlike human immunodeficiency virus type 1, the SIV long terminal repeat possesses an enhancer region just upstream of the NF-kappaB element which maintains significant levels of basal transcription in the absence of NF-kappaB and Sp1 sites. This region is responsive to transactivation by Tat. In addition, the SIV TATA box was shown to be stronger than that of human immunodeficiency virus type 1. Therefore, the surprisingly high replicative capacity of NF-kappaB and Sp1 binding site mutants of SIVmac is due to unique features or the enhancer/promoter region.
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PMID:Efficient transcription and replication of simian immunodeficiency virus in the absence of NF-kappaB and Sp1 binding elements. 862 91

We have studied the abilities of different transactivation domains to stimulate the initiation and elongation (postinitiation) steps of RNA polymerase II transcription in vivo. Nuclear run-on and RNase protection analyses revealed three classes of activation domains: Sp1 and CTF stimulated initiation (type I); human immunodeficiency virus type 1 Tat fused to a DNA binding domain stimulated predominantly elongation (type IIA); and VP16, p53, and E2F1 stimulated both initiation and elongation (type IIB). A quadruple point mutation of VP16 converted it from a type IIB to a type I activator. Type I and type IIA activators synergized with one another but not with type IIB activators. This observation implies that synergy can result from the concerted action of factors stimulating two different steps in transcription: initiation and elongation. The functional differences between activators may be explained by the different contacts they make with general transcription factors. In support of this idea, we found a correlation between the abilities of activators, including Tat, to stimulate elongation and their abilities to bind TFIIH.
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PMID:Three functional classes of transcriptional activation domain. 862 70

We have examined the roles of AP-1, AP-3-like, DBF1, and Sp1 binding sites, which are located downstream of the human immunodeficiency virus type 1 (HIV-1) promoter, in regulating basal transcriptional activity directed by the integrated viral long terminal repeat (LTR). Point mutations affecting all four of these elements functionally inactivated the HIV-1 LTR when it was constrained in a chromatin configuration. Analyses of the chromatin structures of the transcriptionally active wild-type and inactive mutated HIV-1 promoters revealed several differences. In the active promoter, the 3' half of the U3 region, including the basal promoter, the enhancer, and the putative upstream regulatory sequences are situated within a nuclease-hypersensitive region. However, the far upstream U3 region appears to be packaged into a nuclease-resistant nucleosomal structure, whereas the R, U5, and gag leader sequences are associated with a region of altered chromatin that is sensitive to restriction endonucleases. In the inactive template, only the basal promoter and enhancer element remain sensitive to nucleases, and the adjacent upstream and downstream regions are incorporated into nuclease-resistant nucleosomal structures. Taken together, these results indicate that the chromatin structure of the integrated HIV-1 LTR plays a critical role in modulating basal transcriptional activity.
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PMID:cis-acting sequences located downstream of the human immunodeficiency virus type 1 promoter affect its chromatin structure and transcriptional activity. 864 7

A recombinant Tat protein was used to investigate the molecular mechanisms of transcriptional activation of the human immunodeficiency virus type 1 long terminal repeat (LTR). Liposome-mediated delivery of this protein to responsive cells results in dose-dependent LTR activation. As evaluated by mRNA quantitation with competitive PCR, the activation response is rapid and transient, peaking at 5 h after the beginning of Tat treatment. In vivo footprinting experiments at the LTR showed that transcriptional activation is concomitant with a modification of the protein-DNA interaction pattern at the downstream kappaB site of the enhancer and at the adjacent Sp1 boxes. The effects of Tat on the enhancer are mediated by Tat-induced nuclear translocation of NF-kappaB, which parallels the kinetics of transcriptional activation. This induction results from degradation of the inhibitor IkappaB-alpha, is blocked under antioxidant conditions and by a protease inhibitor, and occurs as a rapid response in different cell types. The functional response to Tat is impaired upon cell treatment with a kappaB site decoy or with sodium salicylate, an inhibitor of NF-kappaB activation. These results show that NF-kappaB activation by Tat is important for LTR transcriptional activation. Furthermore, they suggest that some of the pleiotropic effects of Tat on cellular functions can be mediated by induction of NF-kappaB.
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PMID:Activation of transcription factor NF-kappaB by the Tat protein of human immunodeficiency virus type 1. 867 66

We report the discovery of a fourth Sp1 binding site at the 5' end of the U3 region of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (HIV-1 Sp1 IV), localized to HXB2 nucleotides -433 to -441. This site is shown to bind Sp1 protein specifically in electrophoretic mobility shift assays. Sp1 protein appears to bind to HIV-1 Spl IV with 5 to 10 times lower affinity than to a consensus Sp1 site. Mutation of HIV-1 Sp1 IV in an HXB2-derived long terminal repeat-chloramphenicol acetyltransferase reporter construct gave no significant change in positive-sense transcription but abolished both basal and phorbol myristate acetate-activated negative-sense transcription. Taken together, the results further define the HIV-1 negative-sense promoter as an Sp1-dependent, phorbol myristate acetate-responsive, and Tat-inhibited promoter initiating at HXB2 nucleotide -450.
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PMID:A fourth Sp1 site in the human immunodeficiency virus type 1 long terminal repeat is essential for negative-sense transcription. 879 2


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