Biomedical subjects

P Ia Boĭkov

Publications and source records attributed to P Ia Boĭkov.

At least 19 recordsLinked to original sources

PubMed1994

[Change in the level of sphingosine in rat liver nuclei and cells during oncogene superexpression induced by cycloheximide].

Changes in the sphingosine content in rat liver cells and nuclei have been studied with reference to the level of nuclear oncogene expression, induced by cycloheximide (0.1, 0.5 and 3.0 mg/kg). It has been found that only the sublethal (3 mg/kg) dose of cycloheximide which induces the superexpression of c-fos and c-myc oncogenes can promote sphingosine accumulation in the cell. At the moment of enhanced expression of nuclear oncogenes, the maximum content of free sphingosine exceeds the control level 1.5- and 3-fold in the cell and in the nuclei, respectively. The difference in the sphingosine accumulation patterns in the cell and in the nuclei testifies to the fact that sphingomyelin metabolism is more active in the nuclei than in the cell. Sphingosine accumulation in the nuclei is characterized by coordination of sphingomyelinase activity and changes in the sphingomyelin content. A comparative analysis of activities of enzymes of sphingomyelin (sphingomyelinase) and phosphatidyl inositol (phosphatidyl inositol kinase) cycles indicates that in the nuclei the activation of the sphingomyelin cycle forestalls the cycloheximide-induced activation of the phosphatidyl inositol cycle and the maximal accumulation of nuclear oncogene mRNAs. A model of activation of oncogene expression with participation of sphingosine inhibiting protein kinase C and activating casein kinase II, the key enzymes of the signal transduction system of cell proliferation and differentiation, is proposed.

Animals↗

PubMed1992

[Structural changes of chromatin during proto-oncogene activation by cycloheximide: dose-effect].

The level of expression of cellular proto-oncogens c-myc and c-fos in rat liver has been studied as a function of protein synthesis rate (cycloheximide dose). Activation of proto-oncogens has been established to be initiated by 50% inhibition of nuclear protein synthesis. This promotes a certain level in chromatin structural rearrangements which is manifested, in particular, in decreasing activity of chromatin cleavage by Ca2+, Mg(2+)-DNAase and increasing degree of chromatin condensation. A role of topoisomerase II in chromatin structural rearrangements during proto-oncogen activation is postulated.

Animals↗

PubMed1990

[Effects of daunorubicin and its nitroxyl analog on the synthesis of nucleic acids].

The impact of daunorubicin, emoksil in sublethal doses and daunorubicin mixtures with a nitroxyl radical of 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (NR) on synthesis of DNA and RNA in some organs of rats was studied. Daunorubicin and emoksil induced marked (by 80 to 90%) inhibition of DNA synthesis in all the examined organs even within the first hours of administration. In the heart, DNA synthesis remained lower by the end of the experiment. In the spleen its partial recovery up to 40 to 60% of the control level was observed. In the liver the synthesis was stimulated in 24 hours. Its highest stimulation was recorded with the use of emoksil and daunorubicin in combination with NR. After administration of daunorubicin the maximum synthesis of DNA exceeded the control level 2.5 times. Addition of NR lowered 2-fold inhibition of DNA synthesis by daunorubicin within the first hours. It was of interest that the anthracyclines appeared to markedly stimulate RNA synthesis in the spleen, the fact not described in the literature. The stimulation of DNA synthesis in the liver was supposed to be one of the components of the compensatory mechanisms engaged by the cell in response to the drug's damaging effect.

Animals↗

PubMed1990

[Reorganization of chromatin superstructure during marked changes in the rate of protein synthesis].

The changes in the structure and RNA-polymerase activity of rat liver cell chromatin after a single injection of cycloheximide (3 mg/kg of body mass) were studied. The cycloheximide-induced fluctuations in protein synthesis rates are concomitant with episodes of drastic changes in the chromatin structure. The reorganization of the general protein structure is associated with an increase or a decrease of the RNA-polymerase II activity. The data obtained suggest that the activation-inactivation of RNA-polymerase II in cell nuclei is due to reorganization of chromatin infrastructures--from higher levels of the electron-dense chromatin package to the unfolded nucleosomes of the transcriptionally active protein.

Animals↗

PubMed1990

[Circadian rhythm of tRNA aminoacylation in hepatocyte culture].

In the monolayer of rat hepatocytes in vitro, the circadian rhythms were revealed of 3H-leucine incorporation in proteins and in aminoacyl-tRNA(Leu) fraction. The oscillations were mainly synphasic, though coordination between aminoacylation and protein synthesis was not stable in the coarse of time. In cell free system with the excess of ATP and aa-tRNA, the rhythm of 3H-leucine incorporation was also clear. This means, that oscillatory kinetics of the protein synthesis rate is not caused by oscillation of ATP which has been revealed earlier in the hepatocyte monolayer.

Acylation↗

PubMed1989

[Effect of cycloheximide on lipid metabolism in cells, nuclei and subcellular fractions in the rat liver].

Well coordinated stages of inhibition, restoration and stimulation of protein, DNA and RNA synthesis were observed after administration of cycloheximide (3 mg/kg). The changes in lipid synthesis and composition in the nuclei and intranuclear structures were studied at different stages of cycloheximide action. The accumulation and stimulation of lipid synthesis in the nuclei during the inhibition and restoration of protein and DNA syntheses were followed by electron microscopy and labeled precursors methods. Dramatic changes were observed in the phospholipid composition of chromatin and nuclear matrix. The accumulation of minor phospholipid fractions in intranuclear structures was observed during DNA synthesis. The sphingomyelin concentration was predominant and commensurable with those of phosphatidylcholine and phosphatidylethanolamine.

Animals↗

PubMed1987

[Phase-specific protein synthesis in human fibroblasts after synchronization by a double thymidine block].

Kinetics of acid-insoluble non-histone protein synthesis during S and G2 cell cycle phases of diploid human fibroblasts and heteroploid transformed cells was investigated. Two distinct groups of protein with different kinetic pattern depending on the cell culture type were revealed. Export of one group of protein and turnover of the other group of acid-insoluble non-histone protein is arrested in heteroploid transformed cells.

Cell Cycle↗

PubMed1987

[Characteristics of [3H]cycloheximide distribution, protein and DNA biosynthesis in rat organs after sublethal blocking of translation].

The kinetics of accumulation and release of [3H]cycloheximide (CHI) as well as protein and DNA biosyntheses in some organs of the rats injected with sublethal doses of CHI were studied. It was shown that in the majority of organs under study (especially in the liver, kidneys and adrenals) the inhibition is completed within 12 hours after CHI injection followed by the resumption of protein and DNA syntheses. In the thymus and pancreas the levels of these biosyntheses remain below control values up to the 72nd hour. A positive correlation was observed between the decrease of CHI (or its metabolites) concentration and the beginning of protein and DNA syntheses in different organs. However, there was a reverse correlation between the high values of squares below the kinetic curves of CHI release from the liver, kidneys and adrenals and the intensive resumption of protein and DNA biosyntheses in these organs. It was thus assumed that in these particular organs CHI is subjected to intensive biotransformations. The contribution of the endocrine system to the induction of intensive compensatory protein and DNA syntheses in the liver were estimated from the viewpoint of the nature of reconstructive processes occurring in the appropriate organs.

Animals↗

PubMed1986

[Glucose metabolism and template synthesis in the mitotic cycle of human diploid fibroblasts].

The correlation between the rates of protein and nucleic acid synthesis and the activity of the key enzymes of glycolysis (hexokinase, phosphofructokinase) and pentose phosphate cycle (glucose-6-phosphate dehydrogenase) in the mitotic cycle of human diploid fibroblasts synchronized by double thymidine block was studied. It was found that the removal of the thymidine block is followed by short-term (presumably, non-specific) simultaneous stimulation of matrix syntheses, as well as by glycolytic and pentose phosphate cycle enzyme syntheses. By the beginning of the S-phase, all the processes appear to be inhibited, followed by gradual activation of glycolysis and pentose phosphate cycle reactions. The implementation of the cell cycle is concomitant with stepwise transitions of protein and hexokinase synthesis rates and ATP content to one of the following levels--basal, intermediate or maximal. Changes in the activity of glucose-6-phosphate dehydrogenase in the course of the cell cycle appear as oscillations, those in phosphofructokinase as alternative states. At stage M, the oscillatory processes are temporarily quenched, whereas the ATP content occupies an intermediate level. In contrast with diploid fibroblasts, in transformed T9 cells the enzyme activity is much higher, and the fluctuations in activity throughout the cell cycle are less noticeable. Presumably, in transformed cells the enzyme activity is at the maximum level and is not prone to effector regulation.

Cells, Cultured↗

PubMed1986

[Correlation of the activity of the key enzymes of glycolysis and respiration in hepatomas with different growth rates].

It is shown that an increase in the activity of glycolysis resulting from the rise of the hepatoma growth rate is accompanied by a decrease in the activity of the pentose-phosphate pathway and respiratory chain. It is supposed that variations in the activity both of different carbohydrate catabolism ways and the respiration with a rise of the hepatoma growth rate reflect changes in the relative content of cells at different phases of the cell cycle.

Animals↗

PubMed1985

[Sequential changes in the macrostructure and RNA-synthesizing activity of nucleolar and extranucleolar chromatin from rat liver cells during induction of DNA synthesis].

The dynamics of structural changes and RNA-polymerase activity in rat liver cell chromatin caused by drastic changes in the rates of protein synthesis was investigated. Inhibition of protein synthesis after a single injection of animals with cycloheximide (0.3 mg/100 g of body weight) increased the total condensibility of chromatin. Under these conditions, the stepwise activation of RNA-polymerases I and II correlated with decondensation of chromatin. By the 6-12th hour following cycloheximide injection, a chromatin fraction enriched with RNA-polymerase I and a RNA-polymerase II-rich fraction could be isolated from liver cell nuclei.

Animals↗

PubMed1985

[Sequence of activation of template biosynthesis in normal and transformed human cells after synchronization by a double thymidine block].

The sequence of matrix biosyntheses of DNA, RNA and various proteins in normal and transformed human fibroblasts in the first mitotic cycle after synchronization of cells by double thymidine block was studied. Two important regularities of synthesis of acid-soluble histone-like and acid-insoluble proteins in normal and transformed cells were established. In normal fibroblasts, the synthesis of both acid-soluble and acid-insoluble proteins is minimal before DNA replication and maximal in the G2-phase; that in transformed cells is maximal after removal of the thymidine block and decreased in the G2-phase. In normal fibroblasts, the synthesis of acid-insoluble proteins is maximal before, while that of acid-soluble ones--after the maximum of DNA synthesis. In transformed cells the situation is opposite. RNA synthesis in normal and transformed cells is stimulated at the end of the G2-phase. In normal cells, protein synthesis is coupled with the activation of RNA synthesis, whereas in transformed fibroblasts protein synthesis occurs, in all probability, in the next mitotic cycle. These differences are especially well-pronounced in the expression of some LMG proteins. It is concluded that in transformed cells the regulatory control over the coupling of matrix biosyntheses is impaired.

Cell Cycle↗

PubMed1985

[Activation of nuclear polypeptide synthesis in rat liver cells after inhibition of template protein synthesis. The role of nuclear polypeptide synthesis in the changes of the chromatin structure].

The correlation between the rates of nuclear polypeptide synthesis (NPS) and matrix protein synthesis in rat liver cells was investigated. It was shown that NPS is activated under conditions of protein synthesis inhibition in the cytoplasm. Model experiments revealed that the NPS and ADP ribosylation systems compete for chromatin structure: ADP ribosylation induces condensation, while NPS--decondensation of chromatin.

Adenosine Diphosphate Ribose↗

PubMed1984

[Correlation between the rate of protein and nucleic acid synthesis and the intensity of various glucose metabolic pathways in rat liver cells].

A sharp and strong suppression of protein synthesis by cycloheximide in liver cells of starving rats is paralleled with activation of RNA synthesis and glucose-6-phosphate dehydrogenase production. Subsequent reconstitution and stimulation of protein synthesis (6-12 hrs after cycloheximide injection) result in activation of hexokinase. Upon stimulation of DNA synthesis (48-60 hrs after cycloheximide injection) the activity of both enzymes is very low. Since glucose-6-phosphate dehydrogenase appears to be the limiting step of glucose decay via the pentose phosphate pathway, and hexokinase is the limiting step of glycolysis, it was assumed that RNA synthesis predominantly occurs via the pentose phosphate pathway, while that of proteins via glycolysis.

Animals↗

PubMed1984

[Structural changes in chromatin during activation of transcription coupled with translation inhibition by cycloheximide].

A chromatin preparation isolated one hour after cycloheximide injection possesses a higher RNA-synthesizing activity and is split by DNAase I to a greater extent as compared to chromatin of control hepatocytes. Thermal denaturation of this preparation causes a considerable increase (about 2-fold) in the content of the thermolabile fraction melting in the free DNA denaturation zone. The relative content of fast repetitions in the thermolabile fraction (1 hour after the beginning of experiment) is lower than that in control. The type of changes in the viscosity of chromatin in the predenaturation zone isolated one hour later suggests a more labile binding of DNA to the protein. Chromatin preparation isolated 3 hours after cycloheximide injection is characterized by intermediate values of all parameters under study, as compared to the two other preparations used in this experiment. It is assumed that the activation of transcription coupled with the inhibition of translation by cycloheximide is determined by the appearance of elongated segments of free or weakly bound DNA in the chromatin preparation.

Animals↗

PubMed1984

[Relation of the biosynthesis of intracellular and export proteins in rat liver cells during induction of proliferation by cycloheximide].

After a single injection of a sublethal dose of cycloheximide (CHI) the biosynthesis of extracellular proteins in rat hepatocytes was rapidly suppressed, the reconstitution being very slow. On the contrast, the biosynthesis of intracellular proteins (e.g., histones, and other acid-soluble liver proteins) was more resistant to CHI. The activation of biosynthesis of acid-soluble and acid-insoluble proteins was found to occur stepwise. It was assumed that the activation of synthesis and accumulation of intracellular proteins after CHI release accompanied by a decreased synthesis of extracellular proteins is one of possible causes of stimulation of DNA synthesis in the hepatocytes following a single injection of CHI.

Animals↗

PubMed1984

[Sequential activation of various types of nuclear RNA polymerases of rat liver cells during the process of DNA synthesis induction by cycloheximide].

The dynamics of changes in the activity of RNA polymerases I and II (EC 2.7.7.6) and the activities of free and bound forms of RNA polymerase II in isolated rat liver nuclei after a singular injection of sublethal dose of cycloheximide (CHI) was studied. Activation of RNA polymerases occurs in three steps. The first step (1--2 hours after CHI injection) coincides with inhibition of protein synthesis and predominant activation of both forms of RNA polymerase II. The second step (6--24 hours after CHI injection) is characterized by de novo protein synthesis and activation of RNA polymerase I and RNA polymerase II. The third step (36--48 hours after CHI injection) witnesses activation of both RNA polymerases which coincides with the beginning of stimulation of DNA replication. It is assumed that this step is coupled with the synthesis of a special form of RNA polymerase, RNA polymerase IV, which is responsible for transcription of genes synthesizing various chromatin components (histones, NHB, RNA prime). At all steps the activity of free RNA polymerase II remains at a sufficiently high level. Consequently, the activity of chromatin is limited by chromatin structure rather than by RNA polymerase II content in it. Presumably, such activation of various forms of RNA polymerase is essential for cell preparation for DNA replication.

Animals↗

PubMed1983

[Degradation of 18S and 28S ribosomal RNA in the cytoplasm of rat liver cells after inhibition of protein synthesis].

Inhibition of protein synthesis (up to 95%) in starved rat liver cells after a single injection of a sublethal dose of cycloheximide (0.3 mg per 100 g of body weight) results in degradation of 18S rRNA during the first 3 hours, whereas the 28S rRNA remains unaffected. However, the increase of 28S rRNA degradation products was observed by the 6th and 12th hours. The rapid decay of 18S rRNA is due to the degradation of this RNA in 40S ribosomal subunits. In contrast to 28S rRNA the specific radioactivity of 18S rRNA is increased by the 6th hour. Presumably the synthesis and processing of 18S rRNA impaired during the 1st hour are recovered partially or completely by this time. A molecular mechanism underlying 18S rRNA degradation in 40S ribosomal subunits is proposed.

Animals↗