Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Specific binding of radiolabelled FSH and LH to rat ovaries was demonstrated at the age of 7 days. However, when the biological response to LH and FSH was monitored by cAMP production in vitro, the FSH response appeared earlier than that of LH, on days 4 and 7, respectively. Cholera toxin stimulated cAMP production even in fetal ovaries, suggesting the presence of functional post-receptor machinery of cAMP production. Hence, the appearance of the functional gonadotropin receptor probably plays a key role in the onset of postnatal ovarian steroidogenesis. To test the effect of gonadotropin suppression during postnatal ovarian development, a potent GnRH antagonist was administered to neonatal animals between days 1-6 or 1-9 of life. The ovarian responsiveness to FSH developed even in the absence of normal gonadotropin levels, but that to LH was suppressed after the longer antagonist treatment. The temporal relationship between the onset of LHR gene expression, i.e. transcription, and translation to functional receptor protein was thereafter investigated using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. The measurements revealed the existence only of truncated versions of LHR mRNA in the fetal ovary from day 17 of gestation up to day 7 of postnatal life. With the onset of the receptor function around day 7, also larger mRNA transcripts, corresponding to the full-length receptor protein appeared. Our findings suggest that the LHR gene may be constitutively expressed in the ovary and a change in the alternative splicing pattern may cause the onset of translation of a functional receptor protein.
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PMID:Ontogeny of gonadotropin action in the rat ovary. 134 71

HIV infection is associated with qualitative and functional immune deficiencies. It has been shown that the in vitro infection of CD4+ cells with HIV was associated with sustained elevation of cAMP and cGMP. In the present report the role of cAMP on HIV replication in MT-4 cells was investigated. The MT-4 cells were infected with HIV (strain 3b), in the presence or absence of agents that increase intracellular levels of cAMP, through different mechanisms. At selected times postinfection, HIV replication was measured by reverse transcriptase activity or HIV P24Ag in culture supernatants. Forskolin (FK, an activator of adenylate cyclase 1-100 microM), Isobutyl-methylxanthine (IBMX, a phosphodiesterase inhibitor, which indirectly increases intracellular levels of cAMP, 30-100 microM) and dibutyryl (db) cAMP (0.1-10 microM) enhanced HIV replication, in a dose-dependent manner. FK, IBMX, and db cAMP enhanced HIV replication by 2- to 10-fold, 4- to 7-fold, and 2- to 6-fold, respectively. Intracellular levels of cAMP were measured by radioimmunoassay and were also enhanced. Since cAMP exerts its catalytic effects through activation of protein kinase (PK) A the effect of H-8 (a specific inhibitor of the cAMP dependent PK A) on HIV replication was simultaneously examined. The H8 at doses of 0.1 to 10 microns inhibited HIV replication by 25 to 99.9%. Moreover H9 inhibited HIV replication in peripheral blood mononuclear cells by more than 90%. The replication of HIV appears to be a cAMP-dependent event, and PK A could possibly be a target for the development of anti-HIV therapies.
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PMID:Human immunodeficiency virus replication: modulation by cellular levels of cAMP. 138

The 20 S RNA genome is a circular single-stranded replicon, present in most laboratory yeast strains, whose copy number is induced 10,000-fold by transfer of cells to acetate medium without a carbon source. We have sequenced most of the 20 S RNA genome, and the (+) strand has a long open reading frame with the potential to encode a protein with homology to viral RNA-dependent RNA polymerases. The presence of a typical cAMP-dependent phosphorylation site in the putative RNA polymerase suggests that the acetate amplification of the 20 S RNA genome might be mediated by cAMP, a signal known to transmit the same nutritional status information to the sporulation-control system. Our inability to clone across the gap in the sequence suggests either autocatalytic cleavage of the RNA in the reverse transcriptase reaction, an unusual linkage of 5' and 3' ends of a fundamentally linear molecule, or a structure unusually resistant to reverse transcription. The identity of our sequence with that of the accompanying paper (Rodriguez-Cousino, N., Esteban, L.M., and Esteban, R. (1991) J. Biol. Chem. 266, 12772-12778) for W double-stranded RNA (dsRNA) suggests that W is the replicative form of 20 S RNA. The presence of single-stranded (+) and (-) strands and greater than unit length molecules suggests a rolling circle mode of replication as has been suggested for viroids.
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PMID:Yeast 20 S RNA replicon. Replication intermediates and encoded putative RNA polymerase. 164 4

T-cells from human immunodeficiency virus (HIV)-infected patients are characterized by a number of qualitative deficiencies including defective T-cell activation. The latter has previously been shown to be normally regulated by cAMP. In this study the patterns of cAMP and cGMP induction in MT-4 cells following HIV infection were investigated. The MT-4 cells were infected with HIV (strain IIIb) and at selected times postinfection (p.i.), culture supernatants were tested for HIV replication by reverse transcriptase activity or HIV P24 Ag. The cells were also examined for their intracellular levels of cAMP and cGMP by radioimmunoassay. HIV infection was associated with an increase in intracellular levels of cAMP and cGMP. The cAMP was increased 40-fold by Day 8 and cGMP 4-fold by Day 4 Pl. The increase in intracellular levels of the cyclic nucleotides (CN) were virus specific, dependent on virus dosage, genetically conserved among the two fresh patient isolates tested, and were abolished by uv inactivation. An increase in cAMP and cGMP was also observed in other cell lines infected with HIV. The sustained elevation in CN level observed could certainly influence cell activation and HIV replication and may potentially have clinical relevance.
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PMID:Human immunodeficiency virus infection: association with altered intracellular levels of cAMP and cGMP in MT-4 cells. 170 57

By genetic analysis, we have localized a new mutation, isolated from rho-crp background, responsible for a carbohydrate-positive phenotype. The mutation maps in the rpoB gene coding for the beta-subunit of Escherichia coli RNA polymerase. Using reverse transcriptase analysis of transcripts obtained in vivo and transcription assays in vitro, we have shown that this altered RNA polymerase can efficiently initiate the transcription of the lactose operon in the absence of the cAMP-CRP complex both in vivo and in vitro.
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PMID:RNA polymerase mutant able to express in vivo and in vitro the lactose operon in the absence of the cAMP-CRP complex. 241 69

The regulation of murine mammary tumor virus (MuMTV) production by mammotropic hormones, hormonomimetic substances, and cyclic nucleotides was investigated. The virus produced in control and treated mammary tumor cell cultures was quantitated by measuring the supernatant reverse transcriptase activity in exogenous reaction using poly(rC).oligo(dG) as template-primer. Two days after exposure, the synthetic glucocorticoid, dexamethasone (DXMT), increased spontaneous MuMTV production at optimal concentration (0.1 mumol) up to ten times. Dibutyryl derivative of cyclic AMP had no effect on spontaneous MuMTV production, whereas the drug potentiated suboptimal concentrations of the glucocorticoid. Natural prostaglandins, potent agonists of adenylate cyclase catalyzing intracellular synthesis of cyclic AMP, enhanced both basal (up to five times) and DXMT-stimulated (up to 1.6 times) MuMTV replication. The MuMTV-stimulating activity of prostaglandins decreased in the order of PGA1 greater than PGE1 greater than PGB1 greater than PGF2 alpha. Prostaglandins can be replaced partially by norepinephrine and isoproterenol by enhancing the DXMT-mediated MuMTV stimulation, whereas these drugs remained without effect on spontaneous MuMTV production. Theophylline, an antagonist of cAMP-phosphodiesterase converting cAMP to AMP, enhanced the virus-stimulating activity of DXMT as well as of prostaglandins. The enhancement of MuMTV production by adenylate cyclase agonists do not correlate absolutely with the estimates of intracellular cAMP levels, since the highest amounts of cAMP has been repeatedly observed in cells treated with PGE1 and norepinephrine. The results indicate that besides hormones, other hormone-like substances and cyclic nucleotides may be involved in the complex mechanism of hormone-regulated MuMTV genome expression.
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PMID:Role of natural prostaglandins in the control of murine mammary tumor virus expression. 628 Dec 84

Osteoblasts express calcium channels that are thought to be involved in the transduction of extracellular signals regulating bone metabolism. The molecular identity of the pore-forming subunit (alpha 1) of L-type calcium channel(s) was determined in rat osteosarcoma UMR-106 cells, which express an osteoblast phenotype. A homology-based reverse transcriptase-polymerase chain reaction cloning strategy was employed that used primers spanning the fourth domain. Three types of cDNAs were isolated, corresponding to the alpha 1S (skeletal), alpha 1C (cardiac), and alpha 1D (neuroendocrine) isoforms. In the transmembrane segment IVS3 and the extracellular loop formed by the IVS3-S4 linker, a single pattern of mRNA splicing was found that occurs in all three types of calcium channel transcripts. Northern blot analysis revealed an 8.6-kb mRNA that hybridized to the alpha 1C probe and 4.8- and 11.7-kb mRNAs that hybridized to the alpha 1S and alpha 1D probes. Antisense oligonucleotides directed to the calcium channel alpha 1D transcript, but not those directed to alpha 1S or alpha 1C transcripts, inhibited the rise of intracellular calcium induced by parathyroid hormone. However, alpha 1D antisense oligonucleotides had no effect on the accumulation of cAMP induced by parathyroid hormone. When L-type calcium channels were activated with Bay K 8644, antisense oligonucleotides to each of the three isoforms partially inhibited the rise of intracellular calcium. The present results provide evidence for the expression of three distinct calcium channel alpha 1-subunit isoforms in an osteoblast-like cell line. We conclude that the alpha 1D isoform is selectively activated by parathyroid hormone.
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PMID:Multiple calcium channel transcripts in rat osteosarcoma cells: selective activation of alpha 1D isoform by parathyroid hormone. 747 9

The expression of different myocardial regulatory proteins is altered in human heart failure, e.g., beta 1-adrenoceptors, G-proteins and others. Similar changes in rats after 4 days treatment with isoproterenol led to the hypothesis of the cAMP pathway involved in these changes. In different cell types cAMP-dependent transcriptional activation is mediated by the cAMP-response element binding protein (CREB) which was recently shown to be expressed and phosphorylated in the human heart. Here, by the reverse transcriptase-polymerase chain reaction two alternatively spliced isoforms of CREB mRNA were found to be expressed in rat ventricles. Both isoforms were down-regulated in the ventricles of rats treated in vivo with isoproterenol (2.4 mg/kg per day) for 4 days proposing a possible mechanism involved in expressional changes mentioned above.
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PMID:In vivo isoproterenol treatment leads to downregulation of the mRNA encoding the cAMP response element binding protein in the rat heart. 748 29

Recent studies in a cultured model of the intestinal epithelium (HT-29cl.19A) have shown that somatostatin-14 (SS-14) inhibits the Cl- secretory process by acting at multiple G protein-dependent sites. These actions may underlie the antidiarrheal properties of SS peptides. This study has investigated the expression of specific SS receptor subtypes (SSTR) in HT-29cl.19A and examined their role in mediating SS antisecretory actions. Two predominant SSTR, SSTR1 and SSTR2, were identified by reverse transcriptase-polymerase chain reaction (RT-PCR) of mRNA from polarized HT-29cl.19A monolayers. Receptor binding studies showed evidence of two distinct populations of binding sites consistent with the known properties of SSTR1 and SSTR2. The role of SSTR in inhibition of secretion was investigated by comparing the effectiveness of native and synthetic SS peptides on adenosine 3',5'-cyclic monophosphate (cAMP)-dependent Cl- secretion. Secretion stimulated by the receptor-mediated agonist prostaglandin E2 (PGE2) was inhibited > 70% by SS-14 with a 50% effective concentration (EC50) of 32 nM. In contrast, SMS-201-995 (SMS) and RC-160 exhibited little or no antisecretory activity (maximum inhibition of 15 +/- 1.9 and 2.8 +/- 1.9%, respectively, at 100 microM; EC50 > 1.5 microM). Similar effects on PGE2-stimulated cAMP accumulation were also observed. SS-14, but not SMS, also inhibited secretion stimulated by dibutyryl cAMP, which acts independently of changes in cellular cAMP. Pretreatment with pertussis toxin reversed the antisecretory effects of SS peptides.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Expression of somatostatin receptor genes and their role in inhibiting Cl- secretion in HT-29cl.19A colonocytes. 749 65

Papaverine hydrochloride (PAP) has previously been shown to have a potent inhibitory effect on the replication of viruses such as cytomegalovirus (CMV) and measles. In this report the effect of PAP on human immunodeficiency virus (HIV) replication and T lymphocyte cell function were examined. MT4 cells infected with HIV strain 3b were incubated with serial dilutions of PAP (1-30 microM). At selected times postinfection HIV replication was measured by reverse transcriptase activity (RT) or HIV p24 Ag. PAP significantly inhibited HIV replication by more than 99% at doses of 30 microM with an CD50 and ED50 of 32 microM and 5.8 microM respectively. The mechanism of inhibition of HIV caused by PAP appeared independent form its ability to increase intracellular levels of cAMP and was not mediated via a direct effect on RT activity. To examine T cell function, peripheral blood mononuclear cells (PBMC) from normal donors were stimulated with phytohemagglutinin (PHA) or CMV Ag in the presence or absence of PAP (1-30 microM). At selected times proliferative response to PHA and CMV Ag were determined by [3H]thymidine uptake. In addition, interferon (IFN) gamma and interleukin 2 (IL2) response to mitogens were measured by radioimmunoassay (RIA). PAP enhanced PHA induced IFN production at doses of 1-10 microM and CMV Ag induced IFN production at doses of 1-3 microM. Higher doses were inhibitory. PAP did not affect IL-2 production or IL2 receptor expression and had an inhibitory effect on mitogenic responses.
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PMID:Papaverine hydrochloride: effects on HIV replication and T-lymphocyte cell function. 750 1


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