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

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

The dendritic cell (DC) lineage of white blood cells specializes in capturing antigens and stimulating T-dependent immunity. Because of their efficacy in inducing T cell responses in vivo without other adjuvants, DCs can be considered "nature's adjuvant." DCs are the least abundant of leukocytes, but methods for generating large numbers of DCs are being developed. Ex vivo, DCs develop from CD34+ progenitors cultured in the presence of a combination of granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha). This kind of work is stimulating interest in charging DCs with clinically relevant antigens and inducing active immunity in patients. Targeting antigens to DCs may become feasible also because of the identification of distinct antigen receptors such as DEC-205, a DECalectin with 10 contiguous, C-type lectin domains. DEC-205 can mediate adsorptive uptake and presentation via DCs. AIDS is another disease for which DCs should be considered in designing new therapies, since DCs can play a major role in promoting HIV-1 replication. Many HIV-1 isolates induce syncytia between DCs and CD4+ memory T cells. These syncytia in turn are the site for a productive infection with HIV-1, possibly because requisite transcription factors like NF-kappaB and Sp1 are separately provided by DCs and T cells, respectively. Further attention to the DC lineage should provide new avenues for manipulating the immune system in several clinical contexts.
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PMID:Dendritic cells and immune-based therapies. 869 42

The regulation of HIV expression is controlled by the activity of the Long Terminal Repeat (LTR). Trans-activation by the virally encoded Tat protein is one of the main mechanisms of LTR activation. Tat binds to its target, TAR RNA, and cellular proteins that bind the LTR, Tat, or TAR RNA are important components of the trans-activation process. We will review the factors that have been characterized for a possible involvement in this mechanism. Whereas LTR binding proteins consist of Sp1 and TBP, a large number of factors that bind TAR RNA have been isolated. We have previously cloned two of them by RNA probe recognition: TRBP and La. We have shown that the in vitro and in vivo binding of TRBP to TAR RNA correlates with a constant expression of the protein during HIV-1 infection. Several proteins that interact with Tat have mainly positive, but some negative, effects on trans-activation. Genetic studies have defined that human chromosome 12 encodes a protein that will allow trans-activation in rodent cells. The binding and the functional data about these proteins suggest sequential steps for the Tat trans-activation mechanism. Each of these intracellular molecular events could be the target for molecular intervention against the virus.
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PMID:Sequential steps in Tat trans-activation of HIV-1 mediated through cellular DNA, RNA, and protein binding factors. 872 88

In order to understand the regulation of HIV genome transcription induced by cell stimulation through transmembrane receptors, we have transfected cells with polyoma middle T antigen (PyMT) expression vectors, thus mimicking activated receptor-dependent cell stimulation. PyMT-expressing Cos7 cells provided an environment where transcription of an HIV provirus was activated. PyMT expression induced the activity of both enhancer- and promoter-dependent HIV-LTR luciferase vectors. Induction of the HIV promoter domain depended on Sp1-binding sites and could be blocked by Wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K). This indicates that PyMT-induced HIV transcription and replication are controlled by both the enhancer and promoter domains of the HIV-LTR. The latter, but not the former, was induced in a PI3K-dependent way. Thus at least 2 different transduction pathways appear to collaborate for induction of full HIV genome transcription in activated cells.
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PMID:HIV genome transcription induced by polyoma virus middle T antigen through both enhancer- and promoter-dependent LTR activation. 874 37

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

The understanding of early events in the expression of genes has vastly improved in recent years with the identification of a variety of gene- and sequence-specific DNA binding transcription factors. One such protein, Sp1, has been implicated in activating transcription of various cellular and viral genes including those of HIV, and SIV types of retroviruses. The basic recognition site for Sp1 has been identified as variants of a 10 base-pairs long GC-rich DNA, often containing a hexanucleotide segment 5'-GGGCGG (termed GC-box). However, variations in both the relative protein-DNA binding affinity and the nature of binding sequences have been noted. Two-dimensional 1H-NMR experiments (500 MHz) were employed for conformational studies of two decadeoxyribonucleotide duplexes, d(GAGGCGTGGC).d(GCCACGCCTC), termed Sp1-III, and d(GGGAGTGGCG).d(CGCCACTCCC), termed Sp1-I. These are two of the highest affinity Sp1 binding sites and consist of diverse positioning of the tri- and tetranucleotide segments GAG, GTG, GCG, GGCG, GTGG and GGAG, that occur frequently in other Sp1 binding sites as well, and may form specific contacts with the protein. Phase-sensitive nuclear Overhauser enhancement (2D-NOESY and MINSY) and correlation (COSY) spectra were obtained for the assignment of the exchangeable and nonexchangeable protons in a sequence-specific fashion. As a prelude to determination of the detailed solution structures of the selected sequences, numerous structural constraints were obtained from angle-dependent coupling constants and relative intensities of distance-dependent intra- and internucleotide NOEs. Overall, each duplex adopts a structure similar to B-DNA with predominantly C2'-endo/S-type sugar conformation and anti-glycosidic torsion angles. A selective disruption of sequential NOE connectivities at the GAG.CAC and GTG.CAC steps, irrespective of the flanking sequence, suggests that conformational changes at these sites may act as unique determinants of sequence specific recognition/binding of Sp1. Implications for a specific inhibition of Sp1-mediated transcription by minor groove binding class of drugs, designed to recognize GC-rich sequences, are also briefly discussed.
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PMID:Conformational characteristics of high affinity Sp1 binding enhancer elements of HIV-LTR by high resolution 2D-NMR. 882 36

Previous studies have shown that in human T-cells (Jurkat) and hepatoma cells (HepG2), exogenous NF-IL6 can activate HIV-1 gene expression even in the absence of its consensus binding elements in the viral long terminal repeat (LTR). To identify the LTR elements that mediate this response, we have analysed constructs containing mutated and deleted LTR sequences. We have also examined heterologous plasmids to evaluate a potential requirement for the natural LTR sequences in producing HIV-1 gene activation by NF-IL6. As observed for Jurkat and HepG2 cells, we find that in the absence of NF-IL6 binding elements, NF-IL6 can elicit LTR-mediated gene expression in cotransient expression assays performed in monocytic (U937) cells. However, we detect distinct modes of regulation depending on cell type. In U937 cells, the basal LTR sequences retain a significant fraction (42%) of NF-IL6 responsiveness in the absence of upstream regulatory elements in the LTR while these elements are required for maximal response. In HepG2 cells, NF-IL6 elicits a relatively low level of gene activation from the basal LTR elements; response to NF-IL6 is restored with either the Sp1 binding sequences or the other upstream regulatory elements in the LTR. In addition, even though NF-IL6 induces a relatively low gene activity from the basal LTR sequences analysed in HepG2 cells, study of a heterologous construct indicates that these sequences are required for the responsiveness of Sp1 elements to NF-IL6 in this cellular background.
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PMID:Regulation of HIV-1 gene expression by NF-IL6. 884 98

MSSP proteins have been identified by their binding to an upstream element of c-myc. Independently, two different approaches yielded two cDNA clones highly homologous to the MSSP cDNAs, suggesting an involvement of MSSP in the regulation of the cell cycle (scr2) and in the repression of HIV-1 and ILR2 alpha-promoter transcription (human YC1). Screening human genomic libraries, we have isolated clones belonging to two different gene loci. Whereas the human MSSP gene 1 turned out to be intronless, the organization of the coding sequence within gene 2 is more complex. It spans more than 60 kb and contains 16 exons (including two alternative first exons), ranging from 48 to 287 bp, respectively. The intron sizes vary from 0.1 to more than 13 kb. Gene 1 has been completely sequenced. A deletion series of its upstream region was conjugated to the luciferase gene, but the transfection of the constructs did not display any promoter activity. Moreover, compared with gene 2 and the cDNA sequences known so far, about 20 point mutations as well as flanking direct repeats have been detected in the MSSP gene 1, showing that it possesses all the characteristics of processed retropseudogenes. Sequence analysis of a 1.7 kb fragment of the 5' flanking region of the MSSP gene 2 revealed that the promoter of gene 2 lacks consensus sequences for TATA and CCAAT boxes, is GC-rich, and contains numerous potential transcription factor binding elements including an Sp1 binding site. DNase I footprinting experiments showed that the putative Sp1 site was bound by proteins. The results of primer extension and S1 mapping analyses suggested the transcription of the gene starts at multiple positions upstream from the initiator methionine codon. Luciferase assays employing progressive deletions of the 1.7 kb promoter region allowed us to define the minimal promoter region of 428 bp (-488/+) and revealed a complex pattern of the transcriptional regulation the human MSSP gene 2. Furthermore, it can be concluded that the MSSP gene 2 encodes both MSSP-1 and MSSP-2, and moreover scr2 and human YC1.
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PMID:Cloning and characterization of the genomic DNA of the human MSSP genes. 887 67

A new restriction endonuclease, named Splase, was constructed by genetically fusing the DNA-cleavage domain of the restriction endonuclease Fok1 with the zinc-finger DNA-binding domain of the transcription factor Sp1. The resulting protein was expressed in Escherichia coli., partially purified, and shown to selectively digest plasmid DNA harboring consensus Sp1 sites. Splase was also shown to selectively digest the long terminal repeat of the HIV-1 DNA at Sp1 sites. Splase recognizes a 10-bp DNA sequence and hydrolyzes phosphodiester bonds upstream of the binding sequence. The binding specificity of Splase makes this a "rare cutter" restriction enzyme which could be valuable in creating large DNA fragments for genome sequencing projects. The result also presents the opportunity to create other restriction enzymes by altering the binding specificity of the zinc-finger recognition helix.
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PMID:Splase: a new class IIS zinc-finger restriction endonuclease with specificity for Sp1 binding sites. 889 94

Adeno-associated virus (AAV) Rep78 is a multifunctional protein that is required for AAV transcriptional activity, AAV DNA replication, and possibly for site-specific integration of AAV into human chromosome 19. Rep78 is also able to inhibit a variety of heterologous promoters, including those of c-H-ras, human papillomavirus types 16 and 18, and HIV type 1. However, Rep78 is unable to significantly affect murine osteosarcomavirus (MSV). It was noticed that promoters that are inhibited possess binding motifs for the cellular transcription factor Sp1, whereas the MSV long terminal repeat promoter did not. These data stimulated the hypothesis that Rep78 may recognize and interact with cellular Sp1. Here, we demonstrate that Rep78 is able to interact with Sp1 in vitro as analyzed by West(far)-Western, electrophoretic mobility shift assay-supershift, and coimmunoprecipitation analyses. Furthermore, in support of an in vivo biological effect from this interaction, Rep78 is demonstrated to inhibit a synthetic, Sp1-dependent promoter. Further still, the insertion of Sp1 DNA binding motifs into the Rep78-resistant MSV long terminal repeat results in a promoter that has increased sensitivity to inhibition by Rep78. Finally, it is demonstrated that the Sp1-Rep78 interaction requires the amino half of Rep78. The interaction of Rep78 with Sp1, along with possible downstream effects on the transcription initiation process of RNA polymerase II, may partially explain the rather broad-based antitumor abilities of AAV.
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PMID:The adeno-associated virus Rep78 major regulatory/transformation suppressor protein binds cellular Sp1 in vitro and evidence of a biological effect. 891 72


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