Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.108 (TAT)
 2,389 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Whereas glucocorticoids induce TAT, TRP, GPT in liver and only TAT in HTC cells, no hormonal effect on the synthesis of these enzymes was found in Zajdela hepatoma cells grown in vivo as an ascitic tumor, or in vitro as layer cultures. Although these cells remain uninducible, the hormone penetrates normally, but a strong decrease of the specific binding of cytosol and nuclear proteins with the hormone was observed. The impairment at the level of the hormone receptors could account for the non-inducibility of enzyme synthesis in ZHC cells.
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PMID:Impairment of enzyme induction by glucocorticoids in Zajdela hepatoma cells. 1 35

Visna virus is a pathogenic lentivirus of sheep that is distantly related to the primate lentiviruses, including the human immunodeficiency virus type 1 (HIV-1). Replication of HIV-1 in cell culture requires the expression of a virus-encoded protein, Tat, which is a potent trans-activator of viral gene expression. Visna virus encodes an analogous Tat protein that greatly increases gene expression directed by the visna viral LTR. This report uses a stable vero cell line that constitutively expresses visna virus Tat to investigate the molecular mechanism of action of Tat on viral gene expression. Transient expression assays, using the visna virus LTR to drive transcription of the bacterial gene for chloramphenicol acetyltransferase (CAT), demonstrate that Tat trans-activates gene expression by increasing steady-state mRNA levels. The increase in steady-state mRNA levels is sufficient to account for the increase in protein observed and is due, in part, to an increase in the rate of transcription initiation. Tat mediates the accumulation of mRNA through AP-4 and AP-1 binding sites located in the U3 region of the LTR. Deletion of the upstream AP-1 and AP-4 binding sites results in a residual low level of trans-activation by Tat. Further experiments, using LTRs with R-U5 sequences deleted to +10, demonstrate AP-1 and AP-4 mediated responses to TAT at the RNA level, but no increase was observed in CAT protein.
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PMID:Molecular mechanisms of visna virus Tat: identification of the targets for transcriptional activation and evidence for a post-transcriptional effect. 131 69

Human immunodeficiency virus type 1 (HIV-1) NEF protein has been demonstrated to be a negative regulator of HIV-1 replication and HIV-1 LTR transcription under transient expression conditions. The difficulty of several laboratories to reproduce these findings led us to reexamine the role of NEF in HIV-1 provirus expression and HIV-1 LTR transcription. Basal transcription from the HIV-1 LTR in the presence of a NEF expression vector was compared to that in the presence of a mutated NEF vector. NEF expression led to a greater than 10-fold repression of LTR transcription under these conditions. HeLa and Jurkat cell lines carrying the nef gene linked to the CMV promoter or the HIV-1 LTR were isolated by coselection for neomycin resistance. Single cell isolates were further selected for the expression of nef transcripts. With the exception of the anti-sense nef cell lines, all the nef cell lines expressed the 27-kDa NEF protein, detectable by immunoprecipitation. NEF+ HeLa cell lines were at least 5-fold less efficient than NEF- HeLa cell lines in transient proviral expression. Provirus expression was also repressed in the NEF+ Jurkat cell lines. TAT-activated LTR transcription from an HIV-1 LTR-linked CAT expression vector was repressed 10-fold in the NEF+ HeLa and NEF+ Jurkat cell lines. When infected with HIV-1, NEF expressing T lymphoid cell lines showed moderate delays in onset and peak of reverse transcriptase production. However, none of these cell lines completely arrested virus replication. Our data confirm a negative regulatory effect of NEF on both virus production and LTR driven CAT expression in the cell lines tested. It is possible that cell specific factors may influence NEF activity.
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PMID:Human immunodeficiency virus type 1 (HIV-1) provirus expression and LTR transcription are repressed in NEF-expressing cell lines. 202 88

In transient gene expression assays we observed an increase in expression of the bacterial chloramphenicol acetyl-transferase (CAT) gene, under the transcriptional control of the HIV-1 LTR (pLTR-CAT), when this plasmid was cotransfected into Vero or MRC-5 cells with a plasmid containing either the HCMV immediate early 1 and 2 (E1, IE2) genes (pRL43a) or just the IE2 gene (pMP18). When the HCMV IE1 gene (pMP12) was cotransfected with pLTR-CAT into Vero cells the level of measurable CAT gene activity was below the level observed when pLTR-CAT was cotransfected with a nonspecific carrier plasmid (pGEM3). The negative influence of the HCMV IE1 gene product on the HIV-1 LTR in Vero cells was also observed when the HIV-1 tat gene (pLTR-TAT) was contransfected into Vero cells with pLTR-CAT and pMP12. However, when the HCMV IE1 gene was cotransfected into rhabdomyosarcoma (RD) cells with proviral HIV-1 DNA, an increase in viral production, as monitored by measurement of HIV-1 reverse transcriptase activity, was observed. In electrophoretic mobility shift assays, nuclear extracts obtained 15 hr post-HCMV infection (hpi) were found to contain a lower level of interaction with an oligonucleotide which corresponded to the HIV-1 LTR Sp-1 binding motif. Nuclear extracts obtained 40 hpi of MRC-5 cells had a greater level of interaction with, and changed the mobility of, the Sp-1 oligonucleotide relative to the uninfected nuclear extracts. HCMV-infected MRC-5 cell nuclear extracts also contain a factor(s) which interacted with the HIV-1 LTR between nucleotide positions -15 to -2 relative to the HIV-1 mRNA start site.
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PMID:Characterization of multiple molecular interactions between human cytomegalovirus (HCMV) and human immunodeficiency virus type 1 (HIV-1). 215

A possible role of DNA methylation as a factor in HIV latency was studied by methylating a HIV1-LTR-CAT plasmid in vitro and measuring its expression after transfection on Vero cells. Methylation with a eukaryotic DNA methylase resulted in a 70% inhibition of chloramphenicol acetyltransferase expression, in the absence as well as in the presence of the HIV1 trans-activator protein TAT in the cell. A similar degree of transcription inhibition was obtained by methylation of the only Hpa II site at position-143 in the HIV1-LTR with the bacterial Hpa II methylase. In contrast to the effect by eukaryotic methylation, the inhibition by Hpa II methylation could be partially reversed by cotransfection of the TAT gene. The reason may lie in an about 40% demethylation at the Hpa II site which was concomitantly observed.
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PMID:Transcription of HIV1 is inhibited by DNA methylation. 232 94

A gene encoding the human immunodeficiency virus-1 (HIV-1) TAT protein was chemically synthesized and expressed in HeLa cells and in a cell-free system. To facilitate both the assembly of the synthetic gene and further mutagenesis and gene fusion studies, several unique restriction endonuclease cleavage sites were included in the coding sequence without altering the encoded protein sequence. The synthetic TAT coding sequence was fused to a translation start signal and placed under SV40 early transcriptional control. Co-transfection of the TAT-encoding synthetic gene together with a reporter gene (chloramphenical acetyl transferase or beta-galactosidase) linked to an HIV LTR confirmed that the synthetic gene product exhibits similar activity to TAT expressed from HIV genomic DNA in the transactivation of the LTR. TAT mRNA prepared by cell-free transcription of the synthetic TAT coding sequence was also shown to produce functional TAT following microinjection into HeLa-derived cells containing an integrated reporter gene with the HIV LTR linked to beta-galactosidase.
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PMID:Chemical synthesis and expression of a gene encoding HIV-1 TAT protein. 254

Replication of the human immunodeficiency virus (HIV-1) depends upon the viral TAT protein. TAT stimulates gene expression via a target response sequence (TAR) located within the HIV-1 LTR. As TAR is located in the transcribed region it could act as a signal in either the DNA, the RNA, or both. To test whether TAT acts on transcription and/or posttranscriptionally, we produced TAT in yeast and monitored its activity after microinjection into the nucleus or cytoplasm of Xenopus oocytes. The TAT protein stimulated TAR-dependent expression, but this activation was not inhibited by transcriptional inhibitors. Furthermore, TAR-containing RNA, produced in vitro, was "activated" by TAT after coinjection into oocytes. This activation only occurred, however, when the RNA was injected into the nucleus and not into the cytoplasm. Our data indicate, therefore, that in the Xenopus system TAT acts on presynthesized RNA and that the nucleus is involved in this action.
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PMID:HIV-1 TAT "activates" presynthesized RNA in the nucleus. 254 79

Tyrosine aminotransferase (TAT, EC 2.6.1.5) from the kinetoplastid, Crithidia fasciculata, was purified over 2000 fold to electrophoretic homogeneity. The native form of the enzyme had a molecular weight of approximately 100,000, whereas under denaturing conditions it produced two polypeptides of approximately 50,000 and 48,000, respectively. Absence of a reaction with the periodic acid-Schiff stain suggested that the crithidial enzyme was not a glycoprotein. It was relatively stable and remained active over a wide range of pH and temperature. It exhibited a broad substrate specificity and was able to utilize L-tyrosine, L-tryptophan, and L-phenylalanine as amino donors. Antiserum produced against partially purified crithidial tyrosine aminotransferase failed to inhibit the enzymatic activity. The same antiserum cross-reacted with a soluble extract from Trypanosoma brucei gambiense, but not with that from normal mouse liver, confirming evolutionary conservatism between the two protozoa.
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PMID:Purification and characterization of a tyrosine aminotransferase from Crithidia fasciculata. 289 Jan 1

Pregnant rats were fed six different diets from the first to the 15th, 17th or 19th day of pregnancy. Diets 1 to 5 contained the same amount of nitrogen (10% casein and unsupplemented or supplemented wheat or Bengalgram diets). Diet 6 contained 20% casein. Total placental protein, RNA, free alpha amino N contents and the activities of the enzymes arginase (EC 3.5.3.1), tyrosine amino transferase (TAT, EC 2.6.1.5) and lactate dehydrogenase (LDH, EC 1.1.1.27) were estimated. The fetal weight and placental weight, total placental protein, RNA and free alpha amino N and the activities of the enzymes increased with the gestational age, but the DNA content became constant after day 17 of gestation. The placental weight, protein, free alpha amino N and RNA contents were significantly reduced on wheat and Bengalgram diets as compared to 10% casein (control) diet. The low activities of arginase, TAT and LDH on these diets indicated impaired protein synthesis, as a result of reduction in the amino acid pool size. The fortification of wheat with lysine and Bengalgram with cystine, methionine and tryptophan showed significant improvement in the fetal weight and placental parameters. The values on the 20% casein diet were significantly higher than those observed on the 10% casein diet.
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PMID:Effect of dietary protein composition on placental protein, nucleic acid, free alpha amino N and enzymes in rats. 610 16

Human immunodeficiency virus 1 (HIV1) infection is associated with severe psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated production of interleukin 6 (IL-6) has been implicated in the pathogenesis of these diseases. The molecular mechanisms underlying the abnormal IL-6 secretion of HIV1-infected cells may include transactivation of the IL-6 gene by HIV1. To test this hypothesis, we used the pIL6Pr-chloramphenicol acetyltransferase (CAT) plasmid, an IL-6 promoter-CAT construct, as a target of the transactivating function of the HIV1 TAT protein. By cotransfecting the pIL6Pr-CAT and the tat-expressing pSVT8 plasmid in MC3 B-lymphoblastoid or in HeLa epithelial cells, we observed that TAT transactivates the human IL-6 promoter. These results were confirmed when pIL6Pr-CAT was transfected in MC3 or HeLa cells that constitutively expressed the tat gene in a sense (pSVT8 cells) or antisense (pSVT10 cells) orientation. 5' deletion plasmids of pIL6Pr-CAT, in which regions at -658, -287, and -172 were inserted 5' to the cat gene, were transiently transfected in pSVT10 and pSVT8 cells and showed that TAT-induced activation of the IL-6 promoter required a minimal region located between -287 and -54 bp. Moreover, experiments with plasmids carrying the -658, -287, and -172 bp regions of the IL-6 promoter inserted downstream to a TAR-deleted HIV1-LTR identified the sequence of -172 to -54 as the minimal region of the IL-6 promoter required for TAT to transactivate the TAR-deleted HIV1-LTR. By DNA-protein binding experiments, tat-transfected cells expressed a consistent increase in kappa B and nuclear factor (NF)-IL-6 binding activity. Accordingly, the pDRCAT and IL-1REK9CAT, carrying tandem repeats of NF-kappa B or NF-IL6 binding motifs, respectively, were activated in TAT-expressing cells. The biological relevance of the TAT-induced IL-6 secretion was addressed by generating 7TD1 cells, an IL-6-dependent mouse cell line, stably expressing the tat gene. These tat-positive cells expressed the endogenous IL-6 gene, secreted high amounts of murine IL-6, and grew efficiently in the absence of exogenous IL-6. Moreover, the tat-positive 7TD1 cells sustained the growth of parental 7TD1 cells and showed a dramatic increase in their tumorigenic potency. These results suggest that TAT protein may play a role in the pathogenesis of some HIV1-associated diseases by modulating the expression of host cellular genes.
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PMID:The expression of the interleukin 6 gene is induced by the human immunodeficiency virus 1 TAT protein. 811 88


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