[Whole-Genome Duplications in Evolution, Ontogeny, and Pathology: Complexity and Emergency Reserves].

Whole-genome duplication (WGD), or polyploidy, increases the amount of genetic information in the cell. WGDs of whole organisms are found in all branches of eukaryotes and act as a driving force of speciation, complication, and adaptations. Somatic-cell WGDs are observed in all types of tissues and can result from normal or altered ontogenetic programs, regeneration, pathological conditions, aging, malignancy, and metastasis. Despite the versatility of WGDs, their functional significance, general properties, and causes of their higher adaptive potential are unclear. Comparisons of whole-transcriptome data and information from various fields of molecular biology, genomics, and molecular medicine showed several common features for polyploidy of organisms and somatic and cancer cells, making it possible to understand what WGD properties lead to the emergence of an adaptive phenotype. The adaptation potential of WGDs may be associated with an increase in the complexity of the regulation of networks and signaling systems; a higher resistance to stress; and activation of ancient evolutionary programs of unicellularity and pathways of morphogenesis, survival, and life extension. A balance between the cell and organismal levels in controlling gene regulation may shift in stress towards the priority of cell survival, and the shift can lead to cardiovascular diseases and carcinogenesis. The presented information helps to understand how polyploidy creates new phenotypes and why it acts as a driving force of evolution and an important regulator of biological processes in somatic cells during ontogeny, pathogenesis, regeneration, and transformation.

Evolutionary framework of the human interactome: Unicellular and multicellular giant clusters.

The main contradiction of multicellularity (MCM) is between the unicellular (UC) and multicellular (MC) levels. In human interactome we revealed two giant clusters with MC and UC medians (and several smaller ones with MC medians). The enrichment of these clusters by phylostrata and by functions support the MC versus UC division. The total interactome and the giant clusters show a core-periphery evolutionary growth. From viewpoint of the MCM, the most important is the placement of genes, appearing at UC evolutionary stage, in the MC clusters. Thus, genes involved in vesicle-mediated transport, cell cycle, cellular responses to stress, post-translational modifications and many diseases appeared at UC evolutionary stage but are placed mostly in MC clusters. Genes downregulated with age are enriched in UC cluster, whereas the upregulated genes are preferentially placed in MC giant cluster. The tumor suppressor and pluripotency regulating pathways are also enriched in MC giant cluster. Therefore, this cluster probably operates as 'internal manager' constraining runaway unicellularity. The clusters have denser interactions within than between them, therefore they can serve as attractors (stable states of dynamic systems) of cellular programs. Importantly, the UC cluster have a higher inside/outside connection ratio compared with MC clusters, which suggests a stronger attractor effect and may explain why cells of MC organisms are prone to oncogenesis. The evolutionary clustering of human interactome elucidates the MC control over functions appearing at UC evolutionary stage and can build a framework for biosystems studies focusing on the interplay between UC and MC levels.

Natural killer cell activity irreversibly decreases after Cryptosporidium gastroenteritis in neonatal mice.

Cryptosporidiosis causes persistent diarrhoea in infants, immunocompromised patients and elderly persons. Long-term consequences of the disease include increased risk of malignancy, cardiomyopathy and gastrointestinal inflammation. This study aimed to investigate prolonged effects of cryptosporidiosis on innate immunity and growth in neonatal C3HA mice. The disease was challenged by Cryptosporidium parvum oocyst inoculation into 7-day-old animals. The mice whose intestine smears contained 3-5 or 6 and more oocysts per microscopic field at the day 5 after infection were considered as mildly or severely infected, correspondingly. To determine natural killer cell (NK) activity, we applied 3 H-uridine cytotoxic assay to the animals at 5-68 days after infection using K562 cells as targets. At severe infection, there was a statistically significant 1.5-2.0 fold decline of body mass, spleen mass and spleen cellularity that persisted in animals of all ages. Accordingly, NK cytotoxicity showed even more drastic drop reaching 2.7-3.0 folds that was statistically significant in all animals. At mild infection, the discovered effects were less pronounced and reached significance only in some age groups. Thus, our study provides evidence that NK cells show long-term cytotoxic activity decrease following Cryptosporidium infection in neonatal mice, particularly in severe disease.

DNA helix: the importance of being AT-rich.

The AT-rich DNA is mostly associated with condensed chromatin, whereas the GC-rich sequence is preferably located in the dispersed chromatin. The AT-rich genes are prone to be tissue-specific (silenced in most tissues), while the GC-rich genes tend to be housekeeping (expressed in many tissues). This paper reports another important property of DNA base composition, which can affect repertoire of genes with high AT content. The GC-rich sequence is more liable to mutation. We found that Spearman correlation between human gene GC content and mutation probability is above 0.9. The change of base composition even in synonymous sites affects mutation probability of nonsynonymous sites and thus of encoded proteins. There is a unique type of housekeeping genes, which are especially unsafe when prone to mutation. Natural selection which usually removes deleterious mutations, in the case of these genes only increases the hazard because it can descend to suborganismal (cellular) level. These are cell cycle-related genes. In accordance with the proposed concept, they have low GC content of synonymous sites (despite them being housekeeping). The gene-centred protein interaction enrichment analysis (PIEA) showed the core clusters of genes whose interactants are modularly enriched in genes with AT-rich synonymous codons. This interconnected network is involved in double-strand break repair, DNA integrity checkpoints and chromosome pairing at mitosis. The damage of these genes results in genome and chromosome instability leading to cancer and other 'error catastrophes'. Reducing the nonsynonymous mutations, the usage of AT-rich synonymous codons can decrease probability of cancer by above 20-fold.

Molecular Genetic Analysis of Human Endometrial Mesenchymal Stem Cells That Survived Sublethal Heat Shock.

High temperature is a critical environmental and personal factor. Although heat shock is a well-studied biological phenomenon, hyperthermia response of stem cells is poorly understood. Previously, we demonstrated that sublethal heat shock induced premature senescence in human endometrial mesenchymal stem cells (eMSC). This study aimed to investigate the fate of eMSC-survived sublethal heat shock (SHS) with special emphasis on their genetic stability and possible malignant transformation using methods of classic and molecular karyotyping, next-generation sequencing, and transcriptome functional analysis. G-banding revealed random chromosome breakages and aneuploidy in the SHS-treated eMSC. Molecular karyotyping found no genomic imbalance in these cells. Gene module and protein interaction network analysis of mRNA sequencing data showed that compared to untreated cells, SHS-survived progeny revealed some difference in gene expression. However, no hallmarks of cancer were found. Our data identified downregulation of oncogenic signaling, upregulation of tumor-suppressing and prosenescence signaling, induction of mismatch, and excision DNA repair. The common feature of heated eMSC is the silence of MYC, AKT1/PKB oncogenes, and hTERT telomerase. Overall, our data indicate that despite genetic instability, SHS-survived eMSC do not undergo transformation. After long-term cultivation, these cells like their unheated counterparts enter replicative senescence and die.

[PAIRWISE CROSS-SPECIES TRANSCRIPTOME ANALYSIS OF POLYPLOIDY-ASSOCIATED EXPRESSION CHANGES OF DEVELOPMENTAL GENE MODULES].

Design and development of highly sensitive method bioinformatics are important for investigation of casual relationships between epigenetic changes and gene activity. Cell polyploidy may trigger such changes. However, maintaining the balance of gene dosage, polyploidy may provide only a rather weak effect on their expression. Currently, there is no comprehensive and concordant data in regard to ploidy-associated transcriptomic changes. To find out how polypoidy affects gene activity, we have developed an integrative bioinformatic method of pairwise cross-species transcriptome analysis of mammalian tissues with various polyploidy degrees. The main benefit of this approach is its ability to separate species- and tissue-specific noises of evolutionary conserved effects. We demonstrat the application of the method for the analysis of gene modules and protein interactions networks coordinating programs of development, differentiation and pluripotency. The analysis was performed with transcriptomes of polyploid and diploid organs (human and mouse heart and liver). Our data indicate that ploidy-induced genes enrich Gene Ontology (GO) biological processes and KEGG pathways related to development, morphogenesis and stem cells biology (including Hippo, Pi3K, WNT, Hedgehog and TGF-ß pathways) with higher degree than ploidy-inhibited genes. Thas, our data are the first to show that polyploidy may induce and coordinate developmental modules.

[Threshold rat neonatal cardiomyocyte response to gradual cryptosporidial infection severity increase].

Infectious gastroenteritis is one of the common causes of tachyarrythmia, malabsorbtion and growth retardation in children. Our recent studies have indicated that neonatal.cryptosporidial gastroenteritis is associated with long-term cardiomyocyte abnormalities. The aim of the present study was to find out how neonatal cryptosporidiosis of various severities affects cardiac anatomy and cardiomyocyte polyploidization, remodeling and HIF-1α expression. Using real-time PCR, cytometry, immunohistochemistry, image analysis and interatrial septum visual examination, we revealed that gradual increase in cryptosporidial invasion was associated with threshold changes. At weak parasitic infection, interatrial septum was entire and there was no statistically significant change in cardiomyocytes. At moderate and severe infection, all changes in cardiac anatomy and cardiomyocytes were statistically significant and demonstrated approximately similar degree. Compared to control, heart were atrophied and elongated, interatrial septum contained a small window (patentforamrn ovale), and cardiomyocytes lost protein, became elongated, thin and accumulated additional genomes. Also we found HIF-1α mRNA hyperexpression. Notable, the threshold response to gradual stimulus is an important criterion of development programming since such a response is commonly a consequence of abnormal anatomic structure formation and cell differentiation failure. Our results can be interesting for physicians because they indicate that even moderate cryptosporidiosis can be dangerous for neonatal heart and can trigger neonatal programming of cardiovascular pathology. Also, our results for the first time demonstrate the association between gastroenteritis, patent foramen ovale and cardiomyocyte malfunction.

[Rat cardiomyocyte remodeling after neonatal cryptosporidiosis. II. Elongation, excessive polyploidization and HIF-1alpha overexpression].

Retrospective epidemyological studies evidence that infant diseases leave survivors with an increased susceptibility to cardiovascular diseases in later life. At the same time, the mechanisms of this link remain poorly understood. Based on medical statistics reporting that infectious gastroenteritis is the most common cause of maladies in babies, infants and children, we analysed the effects of moderate cryptosporidial gastroenteritis on the heart and ventricular cardiomyocyte remodelling in rats of the first month of life. The disease was challenged by a worldwide human protozoic pathogen Cryptosporidium parvum (Apicomplexa, Sporozoa). The main symptoms manifested in the growth retardation moderate diarrhea. Using real-time PCR, cytophotometry, confocal microscopy and image analysis, we indicated that cryptosporidiosis was associated, with the atrophy heart and the elongation, narrowing, protein content decrease and hyperpolyploidization of cardiomyocytes and the moderate overexpression of hypoxia inducible factor 1alpha (HIF-1alpha) mRNA. Cardiomyocyte shape remodeling and heart atrophy presented in all age groups. The severity of these changes, hovewer, declined gradually from younger to older groups. In contrast, hyperpolyploidization and HIF-1alpha mRNA overexpression were registered mainly among animals aged between 6 and 13 days, and were barely detected and non-significant in older age groups. In the rat the time period covering 6-13 days after birth is known to coincide with the intensive cardiomyocyte polyploidization and the switch from proliferation to hypertrophy. Thus, our data indicate that neonatal cryptosporidiosis may be potential cardiovascular diseases risk factor and that one of the critical time windows for the growing heart covers the time period when cardiomyocyte undergo polyploidization.

[Somatic polyploidy associated metabolic changes revealed by modular biology].

Excessive somatic polyploidy usually accompanies physiologic and pathologic overload and it is generally accepted as a symptom of pathology. At the same time, polyploidy cells exist in most fungal, plant, mollusk, fish, bird and mammalian tissues confirming their great evolutionary success. The secret of this success remains enigmatic. Since transcriptome rearrangements usually start with metabolic flux redistribution, we decided to investigate firstly the effects of polyploidy on cell metabolism. Using multitest approach of modular biology and databases Entrez Gene, RefSeq, GNF SymAtlas, Gene Ontology, KEGG, BioCarta; MsigDb, Reactome, GenMAPP, and HumanCyc, we performed detailed comparison of metabolic genes expression in human and mouse organs with reciprocal pattern of polyploidy (i. e. in the heart and in the liver). Pairwise criss-cross comparison of diploid vs. polyploid organs allowed removing species- and tissue-specific effects. From our results, polyploidy is associated with rearrangements of main metabolic pathways. We found deep depression of mitochondrial processes, features of autophagia, and increased carbohydrate degradation and lipid biosynthesis. Taken together, these changes pointed to the energy and oxygen deprivation. We also found clear indications of enhanced oxidative stress protection. The major of them are triggering of pentose-phosphate pathway, depression of mitochondria-cytoplasm electron shuttles, and impartment of electron flows across 1 (NADH dehydrogenase) and IV (cytochrome c-oxydase) breath complexes. We suggest that all these changes are necessary for the increase in metabolic plasticity and for the protection of replicating DNA from oxidative damage.

[Neonatal gastroenteritis triggers long-term cardiomyocyte atrophy, remodeling and irreversible hyperpolyploidization].

Growth retardation, inflammation and cardiac overload in early childhood are linked with hypertension and infarction in adults. This link was termed as developmental programming. Exact mechanisms and critical time frames for development of the heart are still unknown. To elucidate these questions, we developed a model of moderate cryptosporidial gastroenteritis triggering main programming factors. Sliding the time point of infection day by day (from day 4 to day 18), we tested complete rat neonatal period. Also, we repeated all experiments 30 days after infection. Using methods of cytometry, immunocytochemistry and confocal microscopy, we compared sensitivity of ventricular cardiomyocyte shape, protein content and ploidy. Our data indicated that gastroenteritis lasting four days triggered cardiomyocyte atrophy, almost doubling cell length to width ratio, and premature and excessive polyploidization. Surprisingly, nucleus and cytoplasm reacted to the disease differently. Cardiomyocytes accumulated genomes only when the disease covered the time period between 6 and 14 days after birth, when cells substitute proliferative growth with hypertrophy. Contractile proteins and cell shape on the contrary, showed high sensitivity in the course of complete neonatal period. After restoration, ploidy did not regress, whereas cell shape and protein content revealed moderate restoration. Taking into account that somatic polyploidy is irreversible and that it alters global gene expression pattern, we may suggest that genome duplication is one of the instruments of developmental programming and that gastroenteritis is one if the triggers of this programming.

[Polyploidy: significance for cardiomyocyte function and heart aerobic capacity]. / Poliploidiia: znachenie dlia funktsii kardiomiotsitov i potentsiala raboty serdtsa.

Somatic polyploidy, defined as genome multiplication, was found in all differentiated mammalian tissues. The highest level of such a polyploidy was found in the myocardium. This phenomenon was shown to be associated with changes in the pattern of gene expression. Hence, polyploidization may create cells with new physiology. The effect of polyploidy on the heart function has never been studied. The aim of the present study was to investigate the effect of polyploidy on cardiomyocyte functioning and heart aerobic capacity. DNA and the total protein content, nucleolar activity reflecting the rate of rRNA synthesis and, consequently, ribosome biogenesis, were measured in ventricular myocytes isolated from the human and from 21 mammalian species by image cytometry and microscopic morphometry. The total protein content was estimated after staining slides with naphtol-yellow dye. For measurement of DNA and nucleolar area, staining with Hoechst and AgNO3 was applied. Cardiac aerobic capacity was evaluated by the heart mass to body mass ratio. A negative correlation between the heart index and the average cell ploidy was revealed (r = -0.79; P < 0.0001). The average genome number per myocyte was registered to be higher by approximately 35% in the sedentary mammals, with the heart index about 0.4% from body mass, than in the athletes with heart index about 0.6% of body mass. Polyploidization was shown to be associated with a sharp decrease in the protein/DNA ratio in cardiomyocytes. As a result, cardiomyocytes in the athletic mammals with poorly polyploid hearts have much higher protein content per genome than do cells in the sedentary species with highly polyploid hearts. Surprisingly, despite decreased protein/DNA ratio, the nucleolar area per genome significantly increased with polyploidization, indicating the imbalance between the cellular protein content and the rate of ribosome biogenesis. Such an imbalance should obviously impair cardiac function, because the additional genomes take some valuable space and biological resources from the cell, which could have been otherwise directed to the maintenance of cardiomyocyte contractile machinery. It is generally accepted that somatic polyploidy is associated with oxidative stress and energetic starvation. Thus, we suppose that additional genomes may serve for cardiomyocyte protection from oxidative damage in the hearts.

[Morphofunctional changes in hepatocytes during the early postnatal development of rats experimentally infected with the intestinal protozoan pathogen, Cryptosporidium parvum (Coccidia, Sporozoa)]. / Morfofunktsional'nye izmeneniia pecheni v rannem postnatal'nom razvitii u krys, éksperimental'no zarazhennykh kishechnym protozoinym patogenom Cryptosporidium parvum (Coccidia, Sporozoa).

Morphofunctional changes in hepatocytes of 10-14-day old rats were followed in norm and after experimental infection with different doses of oocysts of Cryptosporidium parvum. The liver index (ratio between the liver and body masses) varied with the intensity of invasion on the background of slowing down up to the total cessation of animal growth rates, and all this obviously pointed to severe pathology. In the infected rats, some cytological indices were shifted compared to the norm: protein amount and the average number of genomes per hepatocyte were seen to increase, the normal ratio between cells with different ploidy levels being violated. The particular correlation analysis was employed to distinguish between the ontogenetic (animal growth related) and pathologic (related to the infection intensity) polyploidization and hypertrophy in hepatocytes. In 10-14-day old rats, the former is affected primarily by the increase in the share of multinuclear hepatocytes, whereas the latter is accomplished by the increase in the number of cells with polyploid nuclei (4c and 4c x 2 cells). In the heavily infected rats, the ontogenetic polyploidy was almost totally suppressed due, presumably, to their growth rate inhibition, the rise in hepatocyte ploidy resulting form the obvious pathological changes in the liver. In the infected rats, the ontogenetic hypertrophy of hepatic parenchymatous cells was not manifested, and the observed protein accumulation in hepatocytes also resulted from the pathological changes in the liver. It is obvious that changes in cell hypertrophy (protein content) may serve as a more susceptible tool that readily perceives the host's stress experienced due to the parasitic infection (cryptosporidiosis), than cell ploidy: the levels of the respective responses of these two parameters differing by 4 times. However, due to the known reversible nature of hypertrophy, it cannot be used for the aims of a long-term prediction about the future mode of liver functioning in the animal that survived cryptosporidiosis. Unlike, such a parameter as frequencies of hepatocytes with different ploidy levels is much more useful in this respect.

Relationship of hepatocyte ploidy levels with body size and growth rate in mammals.

To elucidate possible causes of the elevation of genome number in somatic cells, hepatocyte ploidy levels were measured cytofluorimetrically and related to the organismal parameters (body size, postnatal growth rate, and postnatal development type) in 53 mammalian species. Metabolic scope (ratio of maximal metabolic rate to basal metabolic rate) was also included in 23 species. Body masses ranged 10(5) times, and growth rate more than 30 times. Postnatal growth rate was found to have the strongest effect on the hepatocyte ploidy. At a fixed body mass the growth rate closely correlates (partial correlation analysis) with the cell ploidy level (r = 0.85, P < 10(-6)), whereas at a fixed growth rate body mass correlates poorly with ploidy level (r = -0.38, P < 0.01). The mature young (precocial mammals) of the species have, on average, a higher cell ploidy level than the immature-born (altricial) animals. However, the relationship between precocity of young and cell ploidy levels disappears when the influences of growth rate and body mass are removed. Interspecies variability of the hepatocyte ploidy levels may be explained by different levels of competition between the processes of proliferation and differentiation in cells. In turn, the animal differences in the levels of this competition are due to differences in growth rate. A high negative correlation between the hepatocyte ploidy level and the metabolic scope indicates a low safety margin of organs with a high number of polyploid cells. This fact allows us to challenge a common opinion that increasing ploidy enhances the functional capability of cells or is necessary for cell differentiation. Somatic polyploidy can be considered a "cheap" solution of growth problems that appear when an organ is working at the limit of its capabilities.

Cardiomyocyte ploidy levels in birds with different growth rates.

Cytofluorimetric study of ploidy levels in ventricular cardiomyocytes was carried out on 36 adult bird species belonging to 10 orders as well as on the quail Coturnix coturnix, of different ages. It was shown that polyploidization of quail cardiomyocytes occurs during the first 40 days after hatching and ends by the time growth is completed. In adult birds, the cardiomyocyte ploidy hardly changed at all. Interspecies comparison revealed that in the adult bird myocardium 2cx2 myocytes are predominant, accounting for at least 50% of the cell population. Multinuclear cells with three to eight diploid nuclei were widespread. The percentage of such cells was five to six times higher in precocial species than in altricial birds of the same weight. Myocytes with polyploid nuclei were rare. A significant interspecies variability of cardiomyocyte ploidy levels was observed. The most prominent differences were found between the precocial and the altricial birds. The mean number of genomes in cells correlated both with the body mass and with the growth rate of the birds. The differences between the precocial and altricial birds disappeared when a statistical method was used to eliminate the effect of the growth rate, but did not when the effect of body mass was eliminated. Among the altricial birds, which are generally immobile during growth, the cardiomyocyte ploidy levels also correlated more closely with growth rate than with body mass. The opposite was observed in the precocial birds, which are highly mobile from the first minutes of life. We conclude that the interspecies variability of bird cardiomyocyte ploidy levels is a result of changes in the balance between the cardiac functional load and the growth rate; this is manifested at the cellular level as a competition between the proliferation and differentiation of cardiomyocytes. J. Exp. Zool. 289:48-58, 2001.

Hepatocyte polyploidy and metabolism/life-history traits: hypotheses testing.

Two alternate hypotheses explaining the causes of mammalian liver polyploidy have been tested by means of statistical analysis of more than 30 placental species. According to the first (general) hypothesis, the omission of mitosis is beneficial in rapidly growing and differentiating tissues that should early perform their specialized functions (economy on mitosis). In this case it is to be expected that the level of polyploidy is positively correlated to the rate of development. The second hypothesis suggests that hepatocyte polyploidy provides additional gene copies necessary under heavy chemical damage to metabolically active hepatocytes, which have to detoxicate noxious substances. In this case it is reasonable to expect that the level of liver ploidy is positively correlated with the rate of metabolism while inversely with the species lifespan (since it is usually assumed that DNA repair systems are more effective in more long-lived species). It is found that, if taken separately, the developmental rate, the rate of basal metabolism, the body weight (inversely), and the maximum lifespan (inversely) are all correlated with the level of hepatocyte polyploidy. However, all these parameters are intercorrelated. When the other parameters are fixed (in partial correlation analysis), only the developmental rate and the rate of basal metabolism remain significant predictors of the hepatocyte ploidy level, with only the former being a predictor of the nuclear ploidy level, while only the latter being positively correlated with the frequency of binucleated cells. These results suggest that relative importance of the two above explanations can differ for the different modes of liver cell polyploidy.(ABSTRACT TRUNCATED AT 250 WORDS)

Loosening of cell cycle controls of human lymphocytes under the action of tumour promoter TPA.

The effect of tumour promoter TPA (12-O-tetradecanoylphorbol-13-acetate) on the cell cycle of human peripheral blood lymphocytes stimulated by phytohaemagglutinin (PHA) in vitro was studied and it was found that TPA caused cells to accumulate in all the cell cycle phases. This accumulation took place preferentially at later culture passages, when lymphocytes stimulated by PHA alone stopped mainly in G0/G1 phases. Other effects of TPA were cell induction to enter higher DNA ploidy and to survive and even synthesize DNA under colchicine block of mitosis or under cytochalasin block of cytokinesis. In addition, in experiments in which a transitory block through the G1 phase of cell cycle was applied with use of aminopterin, we could show that a fraction of TPA-treated cells still entered the active phase of DNA synthesis. These findings suggest that TPA causes cell cycle controls to become loose, thereby enhancing adaptability of human lymphocytes to various hindrances in the course of cell cycle and eventually causing them to acquire characteristics known to be common for tumour cells.

[Effect of the tumor promoter TPA on the distribution of PHA-stimulated human lymphocytes by cell cycle phases]. / Vliianie opukholevogo promotora TFA na raspredelenie stimulirovannykh FGA limfotsitov chelovkea po fazam keltochnogo tsikla.

Patterns of the cell cycle distribution in human peripheral blood lymphocytes, stimulated by PHA alone and PHA plus 12-o-tetradecanoylphorbol-13-acetate (TPA), were studied using DNA cytometry in different times after PHA stimulation. In the first period (nearly 3 days after PHA stimulation) TPA induces no significant differences in the characters under consideration, but in the later period, when the proliferation of the cultures stimulated by PHA alone is reducing, in other cultures stimulated by PHA plus TPA the percentage of cells in S-phase does not reduce, whereas the percentage of cells in G2-phase is rising, which may suggest that this phase is blocked. Concurrently the tetraploid cells are appearing. Accumulation of cells in G2-phase can be overcome by the application of chlorpromazine, which is known to inhibit the membrane-associated protein kinase C.

[Possible role of protein kinase C in the T-lymphocyte cell cycle]. / Vozmozhnaia rol' proteinkinazy C v kletochnom tsikle T-limfotsitov.

Experimental results of induction of T-lymphocyte proliferation by means of tumor promotors-activators of protein kinase C (PKC) are reviewed. A hypothesis has been put forward that the discrepancy of the data so far available can be explained on the account of the difference in membrane-associated PKC activation patterns produced by tumor promotors and by interleukin 2. It is established that the former induce a permanent PKC activation, whereas the latter induces a transient one. Although enhancing DNA synthesis, the permanent (non-physiological) activation must induce an accumulation of cells in the cell cycle phases following the S-phase.