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PubMed1985

Expression of long terminal repeat (LTR) sequences in carcinogen-induced murine skin carcinomas.

RNA sequences homologous to the Long Terminal Repeat (LTR) sequence of Moloney Murine Leukemia Virus proviral DNA are expressed in murine squamous cell carcinomas of the skin induced by chemical carcinogens. These transcripts range in size from 8.2 to less than 2.4 kb but their size profile varies between individual tumors. These RNAs are not detected in the poly A+ RNA fraction obtained from the epidermis of control mice or carcinogen induced skin papillomas. The poly A+ RNAs from the livers and spleens of some of the mice with skin carcinomas also revealed LTR related sequences, whereas these RNAs were not detected in the livers and spleens of control mice or of carcinogen-treated mice that did not develop carcinomas. Thus, chemical carcinogenesis in mouse skin is associated with constitutive expression of endogenous retrovirus related sequences in the carcinomas as well as in certain apparently normal host tissues.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1987

Sodium butyrate activates human immunodeficiency virus long terminal repeat--directed expression.

To study the effect of sodium butyrate on human immunodeficiency virus (HIV) long terminal repeat (LTR)--directed expression, we constructed a chimeric plasmid (pLTR-CAT) in which the LTR sequences derived from a molecular clone of HIV were fused to the chloramphenicol acetyltransferase (CAT) gene. We used transient expression assays in transfected tissue culture cells to monitor the activity of the LTR. The expression of the pLTR-CAT plasmid was activated when the cells were exposed to butyrate after transfection. The magnitude of butyrate-induced increase was linear up to an 8 mM concentration and was different with regard to the target promoters used. Recombinant plasmids linked to marker genes may be useful models for studying the effects on HIV of various agents of chemical and biological origin.

Butyrates↗
PubMed1990

Silencing of human immunodeficiency virus long terminal repeat expression by an adenovirus E1a mutant.

Gene expression from the human immunodeficiency virus (HIV) long terminal repeat (LTR) is strongly stimulated by the viral tat gene. The HIV LTR is also activated by several physical and chemical agents and heterologous viral genes, including adenovirus E1a. As E1a has separable transcriptional activation and repression functions, we examined the negative regulatory effects of E1a on the expression of the HIV LTR by using a trans-dominant E1a mutant. Mutant hr5 strongly suppressed the basal activity of the LTR as well as trans-activation of the LTR by heterologous agents such as the cytomegalovirus immediate early gene or DNA-damaging agents such as mitomycin C and UV irradiation. In addition, hr5 also caused significant suppression of tat gene-mediated trans-activation. The suppression of HIV LTR expression by hr5 appears to be mediated, at least in part, by the repression of the HIV enhancer, as the activity of an enhancer test system composed of the human T-cell leukemia virus I LTR containing an HIV-1 enhancer substitution was severely repressed by hr5. Cotransfection of HIV-1 proviral DNA with hr5 DNA resulted in a significant reduction of HIV production.

Adenovirus Early Proteins↗
PubMed2000

Subtype-specific sequence variation of the HIV type 1 long terminal repeat and primer-binding site.

We studied sequence differences in regulatory elements of the long terminal repeat (LTR) and primer-binding site (PBS) among various human immunodeficiency virus type 1 (HIV-1) subtypes. Phylogenetic sequence analysis of a fragment of 729 base pairs (bp) covering the Gag-coding region for half of p24 and all of p17 revealed the gag subtype of all 60 viruses included in the study: A (n = 20), B (n = 12), C (n = 7), D (n = 10), E (n = 3), F (n = 4), G (n = 3), and H (n = 1). The subtype was also determined by analysis of a 689-bp fragment comprising the LTR and the PBS motif. Comparison of the LTR versus gag sequences showed a mosaic genome for seven isolates. After analysis of all sequences, we could describe subtype-specific differences in sequences encompassing the regulatory elements of the LTR and the PBS motif.

Base Sequence↗
PubMed1985

Trans activation of the bovine leukemia virus long terminal repeat in BLV-infected cells.

The transcription initiation signals for retroviruses lie within the long terminal repeat (LTR) sequences that flank the integrated provirus. This study shows that factors present in cells infected with bovine leukemia virus (BLV) mediate transcriptional trans activation of the BLV LTR. This phenomenon is similar to that reported for the human T-cell leukemia virus LTR and establishes both structural and functional criteria for inclusion of BLV and human T-cell leukemia viruses in the same family of transforming retroviruses.

Animals↗
PubMed2000

marY1, a member of the gypsy group of long terminal repeat retroelements from the ectomycorrhizal basidiomycete Tricholoma matsutake.

We cloned an intact copy of a long terminal repeat retroelement designated marY1 from the ectomycorrhizal basidiomycete Tricholoma matsutake. The reverse transcriptase domain is found in T. matsutake and Tricholoma magnivelare worldwide. This finding suggests that retroelements associate with ectomycorrhizal basidiomycetes and may be useful as genetic markers for identification, phylogenetic analysis, and mutagenesis of this fungal group.

Basidiomycota↗
PubMed1989

Functional characterization of a complex protein-DNA-binding domain located within the human immunodeficiency virus type 1 long terminal repeat leader region.

Transcriptional trans activation of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) by the viral tat trans activator is mediated by an LTR-specific sequence located immediately 3' to the start of transcription initiation. We have used a range of molecular techniques to examine DNA-protein interactions that occur in the vicinity of this cis-acting sequence. Our results demonstrate the existence of a sequence-specific DNA-protein interaction involving the HIV-1 leader DNA and map this binding event to between -2 and +21 base pairs relative to the HIV-1 LTR transcription start site. Evidence suggesting that this interaction involves three distinct protein-DNA contact sites extending along one side of the DNA helix is presented. Mutation of these sites was found to ablate protein-DNA binding yet was observed to have no effect on either the basal or tat trans-activated level of HIV-1 LTR-specific gene expression. We therefore conclude that this DNA-protein interaction has a function distinct from the regulation of HIV-1 LTR-specific gene expression.

Base Sequence↗
PubMed1992

a1/EBP: a leucine zipper protein that binds CCAAT/enhancer elements in the avian leukosis virus long terminal repeat enhancer.

Avian leukosis virus (ALV) induces bursal lymphoma in chickens after integration of proviral long terminal repeat (LTR) enhancer sequences next to the c-myc proto-oncogene. Labile LTR-binding proteins appear to be essential for c-myc hyperexpression, since both LTR-enhanced transcription and the activities of LTR-binding proteins are specifically decreased after inhibition of protein synthesis (A. Ruddell, M. Linial, W. Schubach, and M. Groudine, J. Virol. 62:2728-2735, 1988). This lability is restricted to hematopoietic cells from ALV-susceptible chicken strains, suggesting that the labile proteins play an important role in lymphomagenesis. The major labile activity binding to the a1 LTR region (A. Ruddell, M. Linial, and M. Groudine, Mol. Cell. Biol. 12:5660-5668, 1989) was purified from bursal lymphoma cells by conventional and oligonucleotide affinity chromatography, yielding three proteins of 35, 40, and 42 kDa. More than one of these species binds the a1 LTR region, as judged by gel shift analysis. A gene encoding an a1-binding protein (designated a1/EBP) was cloned by screening a bursal lymphoma cDNA library for fusion proteins binding the a1 LTR site. DNase I footprinting and gel shift assays indicate that the a1/EBP fusion protein binds multiple LTR CCAAT/enhancer elements in a pattern similar to that of the purified B-cell protein. DNA sequence analysis shows that this 2.2-kb cDNA encodes a 209-amino-acid open reading frame containing carboxy-terminal basic and leucine zipper motifs, indicating that a1/EBP encodes a novel member of the leucine zipper family of transcription factors.

Amino Acid Sequence↗
PubMed1992

Transformation of chicken myelomonocytic cells by a retrovirus expressing the v-myb oncogene from the long terminal repeats of avian myeloblastosis virus but not Rous sarcoma virus.

To test the effect of long terminal repeat (LTR) regulatory sequences on the transforming capability of the v-myb oncogene from avian myeloblastosis virus (AMV), we have constructed replication-competent avian retroviral vectors with nearly identical structural genes that express v-myb from either AMV or Rous sarcoma virus (RSV) LTRs. After transfection into chicken embryo fibroblasts, virus-containing cell supernatants were used to infect chicken myelomonocytic target cells from preparations of 16-day-old embryonic spleen cells. Both wild-type AMV and the virus expressing v-myb from AMV LTRs (RCAMV-v-myb) were able to transform the splenocyte cultures into a population of immature myelomonocytic cells. The transformed cells expressed the p48v-Myb oncoprotein and formed compact foci when grown in soft agar. In contrast, the virus expressing v-myb from RSV LTRs (RCAS-v-myb) was repeatedly unable to transform the same splenocyte cells, despite being able to infect fibroblasts with high efficiency. This difference in the transforming activities of v-myb-expressing viruses with different LTRs most likely results from the presence of a factor (or factors) within the appropriate myelomonocytic target cell that promotes specific expression from the AMV but not from the RSV LTR.

Animals↗
PubMed1997

Localized sequence heterogeneity in the long terminal repeats of in vivo isolates of equine infectious anemia virus.

The role of in vivo long terminal repeat (LTR) sequence variation of the lentivirus equine infectious anemia virus (EIAV) has not been explored. In this study, we investigated the heterogeneity found in the LTR sequences from seven EIAV-seropositive horses: three horses with clinical disease and four horses without any detectable signs of disease. LTR sequences were targeted in this study because the LTR U3 enhancer region of tissue culture-derived isolates has been identified as one of the few hypervariable regions of the EIAV genome. Furthermore, LTR variation may regulate EIAV expression in vivo. Both intra- and interanimal sequence variations were investigated. The intra-animal variation was low in seropositive, healthy horses (on average 0.44%). Intra-animal variation was consistently higher in clinically ill horses (0.99%), suggesting that greater numbers of quasispecies of EIAV are present when active virus replication is ongoing. Interanimal comparisons of consensus sequences generated from each horse demonstrated that the enhancer region is a hotspot of sequence variation in vivo. Thirty-seven of the 83 nucleotides that compose the U3 enhancer region were variable between the different in vivo-derived LTRs. The remainder of the LTR that was analyzed was more conserved, 8 of 195 nucleotide positions being variable. Results of electrophoretic mobility shift assays demonstrated that some nucleotide substitutions that occurred in the enhancer region eliminated or altered transcription factor binding motifs that are known to be important for EIAV LTR expression. These data suggested that the selective pressures exerted on the EIAV LTR enhancer sequences are different from those exerted on the remainder of the LTR. Our findings are consistent with the possibility that enhancer sequence hypervariability can alter expression of the virus in tissue macrophages and therefore contribute to clinical disease in infected horses.

Animals↗
PubMed1989

Isolation and analysis of a rat genomic clone containing a long terminal repeat with high similarity to the oncomodulin mRNA leader sequence.

The structure of a novel long terminal repeat (LTR) from an intracisternal A particle (IAP) DNA element in the rat (Sprague-Dawley) genome was determined. This LTR has a total length of 313 base pairs (bp). Several structural features typical for retroviral LTR promoters were identified, including a "CCAAT" box, a "TATA" box, a polyadenylation signal, and a polyadenylation site. The LTR is flanked by 3-bp inverted repeats, and it consists of the three typical LTR regions, U3, R, and U5. U3 contains 213 bp, R 46 bp, and U5 54 bp, which is within the usual size range of IAP LTRs. A sequence of 60 bp in the U3 region reveals considerable similarity to a murine IAP LTR U3 element, which is known to interact with nuclear proteins. A sequence of 69 bp in the U5 and R regions has 83 and 93% similarities to an endogenous retroviral LTR from Syrian hamster and to the cDNA leader sequence of (Buffalo) rat oncomodulin, respectively. Oncomodulin is an "EF-hand" Ca2+-binding protein and appears in many human and rodent tumors and in cells with tumor-like properties but not in normal tissues. We postulate that in the rat the tumor-specific expression of oncomodulin is controlled by a retroviral LTR promoter.

Animals↗
PubMed1985

Retroviral characteristics of the long terminal repeat of murine E.Tn sequences.

E.Tn sequences form a family of long moderately repeated sequences which are abundantly transcribed in the pluripotent cell lineage between day 3.5 and 7.5 of early mouse embryogenesis. The structure of the long terminal repeat (LTR) bordering the E.Tn sequences has been investigated by nucleotide sequencing, primer extension and S1 mapping experiments. This has allowed the identification of U3, R and U5 domains, and of several other structural features all of which are characteristics of retroviral LTRs.

Animals↗
PubMed1994

Activation of the human immunodeficiency virus long terminal repeat by abrasion of the skin in transgenic mice.

Mechanical wounding was shown to activate the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in the skin of transgenic mice. Both noninvasive rubbing and scratching of the skin resulted in a range of 4- to 44-fold increased levels of luciferase reporter gene activities when assayed 24-48 h after wounding. Moreover, long-term noninvasive rubbing each day for 17 days resulted in similar increased levels of luciferase activity. Experiments were done to determine whether the HIV-1 LTR-luciferase transgene might be activated when pups were nursed on the mammary tissues of transgenic mice. Luciferase reporter gene activity in mammary glands skin following nursing was significantly higher than in skin from non-pregnant transgenic mice or transgenic mice 20 days post-conception, which suggests that the natural abrasive action of nursing resulted in activation of the LTR. These results may have implications for sexual transmission and maternal-to-infant transmission of HIV-1.

Animals↗
PubMed1991

Anti-CD2 receptor antibodies activate the HIV long terminal repeat in T lymphocytes.

The CD2 T lymphocyte glycoprotein surface molecule mediates both cell to cell adhesion and T cell activation, two processes that are involved in the spread of HIV infection. Treatment of chronically HIV-infected PBMC with anti-CD2 mAb has been shown to induce the expression of infectious virus from these cultures. In this study we investigated the mechanisms whereby anti-CD2 antibodies stimulate viral production. We demonstrate that treatment of transiently transfected T lymphocytes with anti-CD2 antibodies results in activation of the HIV long terminal repeat. Furthermore, CAT assays using mutated HIV long terminal repeat-CAT constructs and gel shift assays demonstrate that this activation is dependent on the NF-kappa B enhancer. These studies suggest that interaction of CD2 with its natural ligand, LFA-3, may play a role in regulation of HIV expression.

Antibodies, Monoclonal↗
PubMed1987

The 3' long terminal repeat of a transcribed yet defective endogenous retroviral sequence is a competent promoter of transcription.

Although actively transcribed and present as multiple genomic copies, a distinct class of endogenous murine leukemia virus-related sequence does not give rise to infectious virus. Since the long terminal repeat at the 3' terminus provides the transcriptional start site after reintegration, we determined the structure and potential promoter activity of that sequence obtained from cDNA of endogenous retroviral transcripts. These studies demonstrate that the distinctive 3' long terminal repeat sequence of these transcripts could serve as an effective promoter of transcription and, therefore, may not be the primary defect in the infectious cycle of retroviral replication but may result in the propagation of these endogenous retroviral sequences in the genome as retrotransposons.

Animals↗
PubMed1984

The envelope gene and long terminal repeat sequences contribute to the pathogenic phenotype of helper-independent Friend viruses.

Friend murine leukemia virus (F-MuLV) and Friend mink cell focus-inducing virus (Fr-MCF) are helper-independent murine retroviruses which induce a rapidly fatal erytholeukemia in NIH Swiss mice. Amphotropic clone 4070 (Ampho) is a murine retrovirus which does not cause leukemia in these animals. Mice inoculated with Ampho, an Fr-MCF/Ampho pseudotype, or F-MuLV developed leukemia in 0, 50, and 100% of animals, respectively. To identify the F-MuLV and Fr-MCF sequences responsible for leukemia, we constructed hybrid viral genomes between these viruses and Ampho, using subgenomic fragments of molecularly cloned viral DNA. Transfection of these hybrid viral DNAs into fibroblasts produces recombinant retroviruses. These new viruses are assayed in vivo for their ability to cause leukemia. Recombinant viruses constructed between the Ampho genome and the Fr-MCF envelope gene do not cause leukemia. Similarly, viruses constructed by using either the Fr-MCF long terminal repeat U3 region or the F-MuLV long terminal repeat U3 region and the remainder of the Ampho genome do not cause leukemia. However, if the Fr-MCF envelope gene plus the Fr-MCF U3 region are joined to Ampho, the resulting virus causes erythroleukemia in 14% of mice. Recombinant viruses made between the Fr-MCF envelope gene, the F-MuLV U3 region, and the remainder of the Ampho genome cause erythroleukemia in 38% of mice. This study demonstrates that both the envelope gene of Fr-MCF and the U3 regions of Fr-MCF and F-MuLV contain sequences which contribute to the leukemic phenotype of helper-independent Friend viruses.

Animals↗
PubMed1992

Functional roles for the TATA promoter and enhancers in basal and Tat-induced expression of the human immunodeficiency virus type 1 long terminal repeat.

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.

Base Sequence↗
PubMed1995

p53 and Sp1 interact and cooperate in the tumor necrosis factor-induced transcriptional activation of the HIV-1 long terminal repeat.

Tumor necrosis factor alpha (TNF) is a potent activator of transcription directed by the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). We have recently reported that the p53 tumor suppressor gene product binds to a site within the Sp1 binding region of the HIV-1 LTR and contributes to the TNF induction of this promoter. In this study we show that the transcription factor Sp1 cooperates with p53 in the transcriptional activation directed by the HIV-1 LTR. The presence of Sp1 increased p53 binding to its recognition sequence in the HIV-1 LTR, and experiments in Drosophila cells show that Sp1 is necessary for full transactivation by mutant p53. Importantly, TNF induced the association between p53 and Sp1 in Jurkat T cells. These data demonstrate a synergistic role for these proteins in the mechanism of TNF induction of HIV-1 LTR-mediated transcription and suggest that Sp1 may play an important role in modulating certain functions of p53.

Base Sequence↗