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D Ivanov

Publications and source records attributed to D Ivanov.

At least 37 records · Page 2Linked to original sources
PubMed2001

Mus cervicolor murine leukemia virus isolate M813 belongs to a unique receptor interference group.

Murine leukemia virus (MuLV) M813 was originally isolated from the Southeast Asian rodent Mus cervicolor. As with the ecotropic MuLVs derived from Mus musculus, its host range is limited to rodent cells. Earlier studies have mapped its receptor to chromosome 2, but it has not been established whether M813 shares a common receptor with any other MuLVs. In this study, we have performed interference assays with M813 and viruses from four interference groups of MuLV. The infection efficiency of M813 was not compromised in cells expressing any one of the other MuLVs, demonstrating that M813 must use a distinct receptor for cell entry. The entire M813 env coding region was molecularly cloned. Sequence analysis revealed high similarity with other MuLVs but with a unique receptor-binding domain. Substitution of M813 env sequences in Moloney MuLV resulted in a replication-competent virus with a host range and interference profile similar to those of the biological clone M813. M813 thus defines a novel receptor interference group of type C MuLVs.

3T3 Cells↗
PubMed2001

[Laparoscopic resection of the rectum].

Improving the laparoscopic equipments and the techniques have spreaded the repertoire of the laparoscopic procedures. In the beginning, it was performed the laparoscopic-assisted resection of the rectum, and later was performed the entire laparoscopic procedures on the colon. It had presented a patient, 71 years old man with diagnosis of the adenocarcinoma recti. After preoperately prepare carried out the laparoscopic procedure with T-T anastomosis by EEA stapler. We presented the first case of the laparoscopical performed resection of the rectum with desire to show possibilities and advantages of the laparoscopic surgery in the relation with conventional surgery and with hope that this techniques would be found the application in our land.

Adenocarcinoma↗
PubMed2000

Domains in the SPT5 protein that modulate its transcriptional regulatory properties.

SPT5 and its binding partner SPT4 regulate transcriptional elongation by RNA polymerase II. SPT4 and SPT5 are involved in both 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB)-mediated transcriptional inhibition and the activation of transcriptional elongation by the human immunodeficiency virus type 1 (HIV-1) Tat protein. Recent data suggest that P-TEFb, which is composed of CDK9 and cyclin T1, is also critical in regulating transcriptional elongation by SPT4 and SPT5. In this study, we analyze the domains of SPT5 that regulate transcriptional elongation in the presence of either DRB or the HIV-1 Tat protein. We demonstrate that SPT5 domains that bind SPT4 and RNA polymerase II, in addition to a region in the C terminus of SPT5 that contains multiple heptad repeats and is designated CTR1, are critical for in vitro transcriptional repression by DRB and activation by the Tat protein. Furthermore, the SPT5 CTR1 domain is a substrate for P-TEFb phosphorylation. These results suggest that C-terminal repeats in SPT5, like those in the RNA polymerase II C-terminal domain, are sites for P-TEFb phosphorylation and function in modulating its transcriptional elongation properties.

Amino Acid Sequence↗
PubMed1999

Cyclin T1 domains involved in complex formation with Tat and TAR RNA are critical for tat-activation.

Tat activates transcription from the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) by increasing the processivity of RNA polymerase II. Recently, it has been demonstrated that the cellular kinase CDK9 and its binding partner cyclin T1 are involved in regulating transcriptional elongation and tat-activation. Cyclin T1, CDK9 and Tat bind as a complex to elements in TAR RNA that are required for tat-activation. Here, we used cyclin T1 mutants to define domains in this protein that bind to both CDK9 and Tat and are involved in stimulating tat-activation. The region of cyclin T1 extending from amino acid residues 1 to 263 is necessary for complex formation with Tat bound to TAR RNA and for stimulation of tat-activation in murine cells that are normally poorly responsive to the actions of Tat. In contrast, a smaller region of cyclin T1 was required to bind to CDK9 and stimulate its kinase activity. Recombinant cyclin T1 and CDK9 stimulated both basal and tat-induced in vitro transcriptional elongation from the HIV-1 LTR. The effects of Tat on transcriptional elongation may be mediated by its ability to increase CDK9 phosphorylation of the RNA polymerase II C-terminal domain. These results demonstrate that cyclin T1 interactions with Tat and TAR RNA are critical for activation of HIV-1 gene expression.

Cyclin T↗
PubMed1999

Role of the human and murine cyclin T proteins in regulating HIV-1 tat-activation.

Human cyclin T1 markedly stimulates tat-activation in rodent cells which are normally poorly responsive to the effects of Tat. This result suggests that there are likely to be critical differences in the murine and human cyclin T1 proteins. Here, we analyzed the role of the murine and human cyclin T1 proteins in addition to the human cyclin T2a and T2b proteins on regulating tat-activation. Only the human cyclin T1 protein efficiently formed a complex with Tat bound to TAR RNA. This difference in function was due to the presence of a cysteine residue in human cyclin T1 at position 261 rather than a tyrosine or asparagine residue which are found in the murine cyclin T1 protein and the human cyclin T2a and T2b proteins, respectively. A mouse cyclin T1 protein containing a substitution of tyrosine residue 261 with a cysteine residue, was able to interact with Tat and stimulate tat-transactivation in rodent cells. Likewise, substitution of a cysteine residue for an asparagine residue at position 260 of the cyclin T2a and T2b proteins also resulted in their ability to interact with Tat and stimulate tat-activation in rodent cells. The data indicate that a specific residue in the cyclin T proteins is required for their in vitro interaction with Tat and their ability to stimulate in vivo tat-activation.

Animals↗
PubMed1999

Training astronauts using three-dimensional visualisations of the International Space Station.

Recent advances in personal computer technology have led to the development of relatively low-cost software to generate high-resolution three-dimensional images. The capability both to rotate and zoom in on these images superposed on appropriate background images enables high-quality movies to be created. These developments have been used to produce realistic simulations of the International Space Station on CD-ROM. This product is described and its potentialities demonstrated. With successive launches, the ISS is gradually built up, and visualised over a rotating Earth against the star background. It is anticipated that this product's capability will be useful when training astronauts to carry out EVAs around the ISS. Simulations inside the ISS are also very realistic. These should prove invaluable when familiarising the ISS crew with their future workplace and home. Operating procedures can be taught and perfected. "What if" scenario models can be explored and this facility should be useful when training the crew to deal with emergency situations which might arise. This CD-ROM product will also be used to make the general public more aware of, and hence enthusiastic about, the International Space Station programme.

Astronauts↗
PubMed1998

Isolation and characterization of [3H]fucose-labeled glycoproteins from the serum of normal rats and rats bearing Zajdela hepatoma.

Specific [3H]fucose-labeled glycoproteins were found in the serum of rats bearing Zajdela hepatoma, which possess different isoelectric points in comparison with serum glycoproteins from normal rats. The electrophoretic profile of the serum glycoproteins is significantly altered. There is approximately a 2.5 times increase of [3H]fucose incorporation into serum glycoproteins from rats with an ascitic form of hepatoma, compared with normal rats and to animals bearing a solid form of the tumor (which have a considerably greater survival). Serum fucoproteins identical for the two forms of hepatoma were isolated, as well as glycoproteins strongly specific for each of the forms.

Animals↗
PubMed1998

Synthesis, toxicological, pharmacological assessment, and in vitro bronchodilating activity of some 7-theophyllinylacetyloxyglycols.

The synthesis of four ester derivatives of 7-theophylline-acetic acid and glycols by DCC/DMAP-mediated esterification under mild conditions was studied. The structures of the synthesized compounds were proved by microanalyses, UV-, IR-, and 1H-NMR data. Acute toxicity assessment of the compounds in mice showed that compounds 2a-d are less toxic than aminophylline. It was shown by in vivo experiments that 2a-d had depressive action on CNS (increasing of hexobarbital sleeping time and decreasing of spontaneous locomotor activity), and they did not influence to a statistically significant extent the normal 24 hour diuresis of rats (except 2c). The results of cardiovascular screening in rats show that compounds 2a and 2c decreased the heart rate of rats. A pharmacological study of the in vitro broncholytic effect (IC50 and pD2 values) of the derivatives and aminophylline showed that 2c exhibited good broncholytic effect in vitro especially in acetylcholine and serotonin induced guinea pig tracheal contraction. It was demonstrated that compounds 2b,c exerted a stronger inhibitory effect on the enzymic activity of phosphodiesterase in concentration 2 x 10(-3) M than aminophylline.

Animals↗
PubMed1997

Purification of a Tat-associated kinase reveals a TFIIH complex that modulates HIV-1 transcription.

The Tat protein is a transcriptional activator which is required for efficient human immunodeficiency virus 1 (HIV-1) gene expression Tat stimulates HIV-1 transcriptional elongation by increasing the processivity of RNA polymerase II. To address whether Tat-mediated effects on HIV-1 gene expression are due to modulation in the phosphorylation of the RNA polymerase II C-terminal domain (CTD), we developed a purification protocol to identify cellular kinases that are capable of binding to Tat and hyperphosphorylating the RNA polymerase II CTD. A 600 kDa protein complex with these properties was isolated, and specific components were identified using peptide microsequence analysis. This analysis indicated that proteins comprising the multi-subunit TFIIH complex, in addition to several novel factors, were associated with Tat using both in vitro and in vivo analysis. The Tat-associated kinase bound to the activation domain of Tat, and its ability to hyperphosphorylate RNA polymerase II was markedly stimulated by Tat. Furthermore, the addition of the Tat-associated kinase to in vitro transcription assays stimulated the ability of Tat to activate HIV-1 transcription. These results define a cellular kinase complex whose activity is modulated by Tat to result in activation of HIV-1 trancription.

Cyclin-Dependent Kinases↗
PubMed1997

Association of Tat with purified HIV-1 and HIV-2 transcription preinitiation complexes.

The HIV-1 (human immunodeficiency virus type 1) and HIV-2 Tat proteins increase the level of transcription from their corresponding long terminal repeats. Tat activates transcription likely by interaction with components of the transcriptional initiation and elongation complexes during different stages of the transcription reaction. In the current study, two approaches were used to address the sites at which Tat becomes stably associated with the HIV transcription complex. First, we isolated column purified HIV-1 and HIV-2 transcription complexes that were competent for in vitro transcription and found that wild-type but not mutant Tat protein was specifically associated with this complex. An intact HIV TATA element and the presence of functional TATA-binding protein were necessary for Tat association. In contrast, the HIV-1 and HIV-2 TAR bulge sequences which serve as binding sites for Tat were not required for its association with the HIV preinitiation complex. A second complementary approach using immobilized HIV-1 and HIV-2 templates also demonstrated a functional association of Tat with HIV-1 and HIV-2 preinitiation complexes. Wild-type but not mutant Tat proteins associated with transcription complexes assembled on immobilized HIV-1 and HIV-2 templates and the association of Tat correlated with increases in the level of in vitro transcription. These results indicate that Tat can associate with HIV-1 and HIV-2 transcription complexes prior to the initiation of transcription by RNA polymerase II.

Gene Expression Regulation, Viral↗
PubMed1994

Comparative studies on the uridine-5'-diphosphate-galactose: glycoprotein galactosyltransferase activity in rat liver and Zajdela ascitic hepatoma.

We report here data on the galactosyltransferase activity in serum, liver and Zajdela ascitic hempatoma cells and about the rate of galactose attachment to appropriate acceptors by beta(1-4, beta(1-3) and alpha(1-3) linkages in liver and hepatoma cell homogenates. It was established that in serum of Zajdela bearing rats, in host liver and in Zajdela ascitic cells, galactosyltransferase activity towards ovomucoid was elevated in comparison with control serum and liver. The activity towards low molecular acceptor (N-acetylglucosamine) in liver and hepatoma was nearly the same. The predominant isomer synthesized in both tissues was beta 1-4-galactose-N-acetylglucosamine. When asialofetuin was used as acceptor the activity of alpha(1-3) galactosyltransferase was measured. In Zajdela ascitic hepatoma cells alpha(1-3) galactosyltransferase activity was 3 times higher than that in liver. The elevated ability of the tumor cells to attach galactose residues with alpha(1-3) linkage to Gal beta 1-4GlcNAc-R sequence should be considered as a characteristic feature of these malignant cells.

Acetylglucosamine↗
PubMed1989

Effects of some beta-adrenoceptor blockers on avoidance learning in rats.

In experiments on male Wistar rats, we studied the effects of some beta-adrenoceptor blockers: nonselective-propranolol, pindolol and 3b (a new aminotetraline derivative); and cardioselective (beta 1)-acebutolol and talinolol, on avoidance learning. The nonselective beta-adrenoceptor blockers failed to deteriorate and in some cases even facilitated learning, estimated by the number of avoidance responses and their latencies, while the cardioselective blockers significantly impaired learning process. A significant learning-impairing effect was shown by the beta 2-adrenoceptor agonist salbutamol. Similar was the effect of the mixed alpha- and beta-adrenoceptor blocker labetalol. The results are interpreted in connection with the functional role of beta 1- and beta 2- adrenoceptors in the CNS and with the importance of their balance for learning process.

Adrenergic alpha-Antagonists↗
PubMed1985

Changes in the adrenergic reactivity of spontaneously hypertensive rats after abrupt withdrawal of chronic clonidine treatment.

An experimental model of the "withdrawal syndrome" in chronic clonidine treatment is reproduced in spontaneously hypertensive rats (SHR). Medication is withdrawn abruptly after daily oral administration of 100 micrograms/kg clonidine for 12 days or after it has been received with the drinking water in a dose of approximately 250 micrograms/kg daily for 14 days. In the course of the treatment, as well as on the 24th and 48th hour after withdrawal, studies are carried out of the changes in the arterial pressure, heart rate, vascular resistance, the contractions of electrically stimulated m.anococcygeus and vas deferens, as well as some biochemical parameters (noradrenaline content in the brain and myocardium, the level of glucose and free fatty acids in the blood, the activity of phosphorylase "a" in the myocardium). In the course of clonidine treatment there is potentiation of the peripheral noradrenaline effects on the arterial pressure and vascular resistance, increasing hyperglycaemia, reduced noradrenaline content in the brain and myocardium, as well as potentiation of the inhibitory effect of clonidine on the contractions of electrically stimulated m.anococcygeus, as well as potentiation of the isoprenaline responses on the arterial pressure. The isoprenaline effects on electrically stimulated vas deferens, as well as the activity of the stimulated phosphorylase "a", decrease. No sharp increase in the arterial blood pressure was observed upon withdrawal of the clonidine treatment. The reactivity of the peripheral pre- and postsynaptic alpha-adrenergic receptors is intensified (the effects of noradrenaline on the arterial pressure and vascular resistance become even stronger, the noradrenaline content in the brain and myocardium and hyperglycaemia increase, and there is potentiation of the inhibitory effect of clonidine on electrically stimulated m.anococcygeus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Effects of a new 2-piperazinotetralin on alpha-1 and alpha-2 adrenergic receptors in isolated rat vas deferens.

The pharmacological action of a newly synthesized piperazine derivative of 2-aminotetralin (P11) on pre- and postsynaptic alpha-adrenoceptors of isolated rat vas deferens has been investigated. P11 shifted noradrenaline concentration-effect curves to the right. The pA2 value was 5.88 for P11, 5.38 for phentolamine, and 7.73 for prazosin. The maximum effect of the agonist was enhanced by P11 and phentolamine, but this enhancement was less pronounced in the presence of 1 X 10(-5) M cocaine and 1 X 10(-6) M propranolol. 1 X 10(-6) M to 1 X 10(-5) M P11 increased the contractions of a field-stimulated vas deferens and antagonized the effects of clonidine (1 X 10(-9) M on the same preparation. The IC50 values of P11, phentolamine and prazosin were 0.40 microM, 0.03 microM and greater than 10.0 microM, respectively. The results show that P11 possesses alpha 1-and alpha 2-adrenolytic activity. The effect of P11 on these receptors most likely participates in the mechanisms of its hypotensive action.

Animals↗
PubMed1985

[Treatment and prevention of paroxysmal atrial fibrillation and flutter with quinidine retard].

The ability of quinidine retard of restoring sinus rhythm and further maintenance after successful regulation were checked in 42 patients with flutter and fibrillation in an open clinical trial. Quinidine retard restores the sinus rhythm in less patients (60.0%) than quinidine sulphate (81,8%). At the same time, it maintains sinus rhythm in 91,4 per cent of the cases in anti-recurrence treatment. That makes quinidine retard adequate for long-term administration.

Adult↗