The Mechanisms of Regulation of Aerobic Glycolysis (Warburg Effect) by Oncoproteins in Carcinogenesis.

According to modern concepts, tumor formation is associated with impairments in the structure of protooncogenes and/or deactivation of suppressor genes, regardless of the nature of carcinogenic factor. As a consequence, unregulated oncoproteins activate extracellular proteases, resulting in the destruction of the extracellular matrix, which facilitates cell invasion, deterioration of the cell-cell contacts, and metastasis. Tumor development requires activation of certain transcription factors; however, many oncoproteins are not transcription factors. It can be assumed that these oncoproteins are not the ultimate effectors of tumor development, but rather transmitters of the carcinogenic signal to the transcription factors promoting tumorigenesis. Here, we describe the mechanisms of carcinogenesis caused by various oncogenes/oncoproteins. We conclude that the common feature of these mechanisms is stimulation of aerobic glycolysis (Warburg effect) regulated, as a rule, through the activation of the HIFα transcription factor. The role of aerobic glycolysis at the early stages of carcinogenesis is discussed.

Role of Proton Pumps in Tumorigenesis.

One of the differences between normal and cancer cells is lower pH of the extracellular space in tumors. Low pH in the extracellular space activates proteases and stimulates tumor invasion and metastasis. Tumor cells display higher level of the HIF1α transcription factor that promotes cell switch from mitochondrial respiration to glycolysis. The terminal product of glycolysis is lactate. Lactate formation from pyruvate is catalyzed by the specific HIF1α-dependent isoform of lactate dehydrogenase A. Because lactate accumulation is deleterious for the cell, it is actively exported by monocarboxylate transporters. Lactate is cotransported with proton, which acidifies the extracellular space. Another protein that contributes to proton concentration increase in the extracellular space is tumor-specific HIF1α-dependent carbonic anhydrase IX, which generates a proton in the reaction between carbon dioxide and water. The activity of Na+/H+ exchanger (another protein pump) is stimulated by stress factors (e.g. osmotic shock) and proliferation stimuli. This review describes the mechanisms of proton pump activation and reviews results of studies on effects of various proton pump inhibitors on tumor functioning and growth in cell culture and in vivo. The prospects of combined application of proton pump inhibitors and cytostatics in cancer therapy are discussed.

HYPOXIA AND GLYCOLYSIS AS FACTORS DETERMINING THE MALIGNANT PHENOTYPE.

The review deals with the role of hypoxia and glycolysis in the development of cancer. Experimental results demonstrate that the function of glycolysis in tumour cells is not limited to providing energy. Glycolysis stimulates the activity of transcription factor HIF1a. HIF1a in complex with protein ARNT stimulates expression of numerous genes. There are genes encoding proteins of glycolysis, telomerase, P-glycoproteins, antiapoptotic proteins belonging to bcl2 family, inhibitor of pyruvate dehydrogenase­pyruvate dehydrogenase kynase, dedifferentiation genes and others. Inhibition of mitochondria respiratory chain by inhibiting of pyruvate dehydrogenase stimulates accumulation of pyruvate in the cell. Lactate dehydrogenase transforms pyruvate on lactate. Accumulation of lactate in tumour cells activates monocarboxylate transporter. As a result, lactate and proton are displayed in the intercellular space. There is a drop in the pH in tumour tissue. The low pH promotes the activity of various proteases that degrade intercellular matrix. The enhancement of invasion is observed in tumours area with low pH level. The restoration of normal pH level in tumour tissue inhibits invasion and metastasis. Thus, it is possible to conclude that hypoxia is a physiological state of cells that stimulates and mantaines tumour process. Aerobic glycolisis (Warburg effect) stimulates tumour growth even in the case of sufficient oxygenation of the cells. Modern views on the mechanism of the Warburg effect is given. The possibility of using inhibitors of different stages of glycolysis as mono anticancer agents or in combination with conventional anticancer compounds is discussed.

[Effect of cell microenvironment on cell functions associated with tumour promotion and progression].

To study the tumour-promotion activity of cell environment the transformed embryonic rat fibroblasts (clone CL-1-1) were transfect to immunodeficient mice then the cells of the formed tumour were cultivated (clone CL-1-1). The cells before and after transplantation were compared by morphology, proliferation activity and gap junction intracellular communications. The clone CL-1 cells proliferated much faster than clone CL-1 cells. The CL-1-1 cells had changed morphology structure and unlike CL-1 the contract inhibition was absent in CL-1-1. The number of CL-1 cells in phase G1 was significantly greater than that of CL-1-1 cells, while the number of CL-1-1 cells in G2/M phases was much more the number of CL-1 cells. The activity of gap junction intercellular communications in both cell types was near the same. It was concluded that cell microenvironment act as a tumour-promoter and tumour progression factor in the case of cell transplantation to immunodeficient mice.

[Inhibitory effect of human lactoferrin (neolactoferrin) on the growth of transplantable tumor in the uterine cervix of mice].

There was studied effect of recombinant form of human breast milk component-lactoferrin, received from milk of goats-producers (neolactoferrin), on growth of transplantable tumor of the cervix in mice (TTC-5). Neolactoferrin in dose of 100 mg/kg and 200 mg/kg of animals' mass inhibited the rate of tumor growth. The most effective was the dose of 200 mg/kg, which was entered a week before transplantation. In contrast to the control group, in groups where neolactoferrin was entered it was fixed resorption of TTC-5 in 6 mice. Repeated transplantation TTC-5 to these mice led to reducing of the rate of tumor growth and increasing of duration of their lives. To investigate if tumor-braking effect neolactoferrin connected with direct effect on the tumor or due to the general effect of the organism, TTC-5 cells were transformed in culture and they were exposed by neolactoferrin in dose of 10 and 100 mkg/ml. In investigated doses neolactoferrin did not influence on tumor cells growth. There is discussed possible mechanism of anti-tumor effect of neolactoferrin.

[Activation of transcription factor NF-kappaB by carcinogenic polycyclic aromatic hydricarbons].

Effect of carcinogenic polycyclic aromatic hydrocarbons (PAH) benzo(a)pyrene (BP) and 3-methylcholanthrene (MC) on transcription factor NF-kappaB activation was studied. The determination of NF-kappaB activity was performed by two different methods: determination of mRNA expression of NF-kappaB-dependent I-kappaB gene, and determination of transcription activity of co-transfected with the plasmid containing the luciferase reporter gene under the NF-kappaB-sensitive promoter. As a subject of inquiry the hepatoma cell cultures HepG2 expressed Ah receptor and G27 not expressed Ah receptor were used. BP and MC weekly enhanced NF-kappaB activity in proliferating HepG2 cells. The enhance of NF-kappaB activity was significantly higher in resting cells. NF-kappaB activation by BP and MC in hepatoma G27 cells was significantly higher in hepatima G27 cells than in HepG2 cells both in proliferating and resting cells. The role of Ah receptor in PAH action on NF-kappaB activation is discussed.

Mechanisms of tumor promotion by reactive oxygen species.

This review analyzes the available information concerning mechanisms of non-genotoxic action of reactive oxygen species (ROS) during tumor promotion and pathways of their generation under the influence of chemical compounds. Special attention is given to the ability of ROS to induce pseudohypoxia through inhibition of prolyl oxidase, which is an oxygen sensor in the cell. Functions of HIF-1alpha as a main contributor to the ROS-induced promotion are analyzed. Data suggest that an unregulated high level of HIF-1alpha in the cell could induce the development of tumors. Hypothetical possibilities of ROS production under the influence of different environmental pollutants, which are promoters of tumorigenesis, include functioning of cytochrome P450 during oxidation of substrates, functioning of the mitochondrial respiratory chain, and action of peroxisome proliferators.

Appearance of differentiation characteristics (induction of Ah-receptor-dependent genes) during cultivation of transformed cell clone K8 from embryonic rat fibroblasts.

The differentiation status of fibroblasts can be characterized by their ability to induce Ah-receptor-dependent genes. The ability to induce Ah-receptor-dependent genes encoding cytochrome P450 isoforms, Ah-receptor repressor, and NADPH-quinine oxidoreductase were studied in the transformed cell clone K8 obtained from immortalized embryonic rat fibroblasts by treatment with benzo(a)pyrene and in the parental clone F27. Treatment with benz(a)anthracene did not induce the genes in the transformed clone K8 on passages 4-14, but the induction was recorded in the transformed clone beginning from the 16th passage and later, whereas in F27 cells the induction was observed throughout the experiment. Induction levels of mRNA of the induction-regulating genes encoding the Ah-receptor and Ah receptor nuclear translocator were similar in F27 cells and in the transformed cell clone K8 in both early and late passages. Electrophoretic mobility shift assay showed that in clone K8 transmission of the induction signal was disturbed in the early passages before interaction of the activated Ah-receptor with the recognizing region of DNA. Possible mechanisms responsible for the absence of induction in the early passages in the transformed cells are discussed.

[Ah receptor-independent inhibition of gap junction intercellular communications in hepatoma cell culture 27 by polycyclic aromatic hydrocarbons].

One of the systems that regulate tissue homeostatis is gap junction intercellular communications (GJIC). Inhibition of GJIC is widely used in experiments as a characteristic of tumor promotion. It is accepted that the down-regulation of GJIC is tightly related with the tumor-promoting properties of carcinogens. In this study, the effect of some carcinogenic polycyclic aromatic hydrocarbons on GJIC in cell cultures of hepatoma 27 lacking cytochrome P450 and Ah receptor was investigated. It was shown that inter 6 compounds studied only benzo/a/pyren and 3-methylcholanthrene were able to inhibit GJIC. We have concluded that an unknown factor is present in hepatoma cells and its interaction with some polycyclic aromatic hydrocarbons results in GJIC inhibition. The investigation of mutual effect of benzo/a/pyrene and non carcinogenic benzo/e/pyrene with similar structure has shown that GJIC inhibition by benzo/a/pyrene is at least double stepped.

Comparative analysis of family 1 cytochrome p-450 mRNA expression in human intestinal adenocarcinoma and intact portion of the intestine.

The expression of mRNA of proteins involved in the transformations of cytostatics (cytochrome P-450 1A1 and 1B1 isoforms) and genes encoding proteins participating in their regulation (Ah receptor, AHRR and ARNT) in intestinal tumors and intact portions of the intestine were studied. The expression of cytochrome P-450 1A1 increased in poorly differentiated tumors in comparison with its expression in intact portions of the intestine (tumor/intact tissue=1.65). The expression of cytochrome P-450 1B1 was higher in well-differentiated tumors (tumor/intact tissue=1.62). The possibility of practical use of high expression of cytochrome P-450 isoforms in tumors in comparison with intact intestinal tissue is discussed.

Benzo[a]pyrene-dependent activation of transcription factors NF-kappaB and AP-1 related to tumor promotion in hepatoma cell cultures.

The activation by the carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BP) of transcription factors NF-kappaB and AP-1 in hepatoma 27 and HepG2 cell cultures was studied. In contrast to the hepatoma HepG2 cells, cytochrome P450 isoforms and Ah-receptor are not expressed in the hepatoma 27 cells. The transcription factor NF-kappaB was activated only in the hepatoma 27 cells by BP treatment but not by its noncarcinogenic isomer benzo[e]pyrene (BeP). Conversely to NF-kappaB activation the transcription factor AP-1 was activated in the hepatoma HepG2 cells by cell treatment with BP but not in the hepatoma 27 cells. It is concluded that the NF-kappaB activation is caused by nonmetabolized BP molecule and not related to activation of the Ah-receptor. The transcription factor AP-1 seems to be activated as a result of the interaction of BP with the Ah-receptor. The realization of tumor promotion stage by carcinogenic PAHs treatment in dependence on the cytochrome P450 and Ah-receptor levels in the initiated cells is discussed.

Expression of mRNA for several enzymes of xenobiotic detoxification in normal and spontaneously transformed mesothelial cells and mesothelioma cells of rats.

Expression of mRNA for the mdr1 gene, cytochrome P450 isoforms 1A1 and 1B1, Ah receptor, and ARNT protein regulating the concentration of cytochrome P450 mRNA was compared in normal and spontaneously transformed mesothelial cells and mesothelioma cells from rats. Expression of cytochrome P450 1A1 and 1B1 mRNA decreased in transformed mesothelial and mesothelioma cells compared to normal mesothelial cells. mRNA for the mdr1 gene was undetected in normal mesothelial cells. Expression of mRNA for the Ah receptor and ARNT protein did not differ in cultured cells.

[A comparative study of induction regulation in cytochromes family 1 P450 in cell cultures at different stages of tumor transformation].

Lipophilic xenobiotics, including some carcinogenic agents and cytostatics, are metabolized by cytochrome P450 isoforms (CYP). In tumours expression of CYP genes and their inducibility are lower than in a homologous normal tissue. This phenomenon determines the known higher cytostatic stability of tumour cells. To clarify, at which particular stage of tumour transformation the level of family 1 CYP may change, we compared mRNA expression of CYP1A1, CYP1B1 and also of proteins regulated CYP expression: Ah receptor, ARNT and AHRR. For this aim we studied embryonic and fibroblast-like cells, in addition to cells of the same types but immortalized by the Rausher virus, or spontaneously after crisis. Besides, we investigated transformed clones obtained by means of benzo/a/pyrene action on Rausher virus-immortalized cells. Constitutive expression of genes studied in all cell cultures was shown. Benzo/a/anthracene induction increases the mRNA expression of all inducible genes (CYP1A1, CYP1B1, AHRR) in the original embryonic cells, in Rausher virus-immortalized cells, and in transformed clone K2. In both spontaneously immortalized cells and transformed clone K1 only CYP1B1 was induced. In transformed clone K8 no inducible gene was induced. In summary, we have shown that: (1) the ability of immortalized cells to CYP induction is determined not only by their capacity for a non-limited persistence, but also by the nature of immortalization; (2) despite their common genesis, the transformed clones differ in their ability to induce CYP. In addition to Ah receptor and ARNT, some other, yet unknown factors may also take part in CYP induction.

Inhibition of gap junction intercellular communications in cell culture by polycyclic aromatic hydrocarbons (PAH) in the absence of PAH metabolism.

We have studied the effect of polycyclic aromatic hydrocarbons (PAH) on gap junction intercellular communications (GJIC) in culture of hepatoma cells Hep G2 and G27. Carcinogenic PAH inhibited GJIC in both cultures in contrast to non-carcinogenic PAH. We showed that both constitutive and inducible expressions of mRNAs of Ah receptor and cytochrome P4501A1 (the main isoform involved in PAH metabolism) were absent in hepatoma G27 cells. We concluded that the initial, non-metabolized molecules of carcinogenic PAH are responsible for changes in GJIC through interaction with an unknown factor in the cellular membrane.

Change in contents of biologically active sphingolipids modulating cell growth and survival in hepatoma 27 compared to rat liver.

The contents of bioactive sphingolipids (sphingomyelin, ceramide, glucosyl- and lactosylceramides, gangliosides) were studied in rat hepatoma 27 and rat liver. The amounts of sphingomyelin, ceramide, and glucosyl- and lactosylceramides were about twofold and that of gangliosides was about 3.5-fold increased in the tumor compared to normal tissue. Since sphingomyelin promotes angiogenesis, glucosyl- and lactosylceramides stimulate proliferation, gangliosides inhibit apoptosis, but ceramides suppress proliferation and stimulate apoptosis, it is obvious that the balance of these effectors in hepatoma 27 moves with the tumor growth.

Cytochrome P-450 family 1 in rat embryo cell culture immortalized by Rausher leukemia virus.

We studied comparative expression and activity of cytochrome P450 family 1 (CYP1) isoforms in rat embryo cells, both primary and immortalized by Rausher leukemia virus (RLV). In RLV-infected embryonal cells compared with the initial ones the expression levels of CYP1A1 and 1B1 mRNAs and benzo[a]pyrene (BP) hydroxylase activity were higher, regardless of their treatment with the CYP1 inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin. The sensitivity to BP and 7,12-dimethylbenzo[a]anthracene was higher in the cells immortalized with RLV. The expression level of mRNAs of induction-mediating proteins aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator was the same in both cell cultures tested. Higher sensitivity of cells immortalized with RLV compared with the initial embryo cells to transforming effect of BP, which was described previously, is possibly associated with elevated expression of CYP1 isoforms.

[Effect of some polycyclic aromatic hydrocarbons on gap junction intercellular communication in hepatoma Hep G2 cell culture]. / Deistvie riada politsiklicheskikh aromaticheskikh uglevodorodov na mezhkletochnye shchelevye kontakty v kul'ture kletok gepatomy Hep G2

Systems regulating tissue homeostasis are gap junction intercellular communications (GJIC). It is accepted that the down-regulation of GJIP has been due to tumor promoting properties of carcinogens. In this study, effects of some carcinogenic and noncarcinogenic polycyclic aromatic hydrocarbons (PAH) on GJIC were investigated. Noncarcinogenic PAHs do not influence GJIC function. In dose 5 microg/ml carcinogenic PAHs down-regulated GJIC by 70-100% after a 24 h treatment. Dependent on the structure of PAHs, down-regulation was observed after a 1 h treatment. The methyl group in PAH structure decreased down-regulation of GJIC in 1 h experiments, whereas after a 24 h treatment the down-regulation caused by methyl group either contained or not contained PAH was nearly the same. To clarify the role of Ah-receptor in PAH action on GJIC, the effect of 2,3,7,8-tetrachlorodibezdioxin, a specific ligand of Ah-receptor was studied, which appeared to be insignificant. Benzo/a/pyrene does not influence the functioning of gramicidine channels formed in the phospholipid membrane. This result indicates that PAH action on GJIC is not associated with non-specific destruction of the membrane. Thus, two steps are there in PAH action on GJIC: one is fast and caused by specific interaction of unchanged PAH molecule, the other develops in time and is presumably associated with the formation of active metabolites.

[The changes in the sphingenine/sphinganine ratio in sphingolipids of transplantable rat tumors depends on a transplantation organ]. / Izmenenie otnosheniia sfingenin/sfinganin v sfingolipidakh perevivaemykh opukholei krys v zavisimosti ot organa transplantatsii.

The content of sphingenine (sphingosine) and sphinganine was determined in the total pool of sphingomyelin and ceramide in the rat tumors transplanted subcutaneously and intrahepatically. The sphingenine/sphinganine ratio in the subcutaneously transplanted sarcoma M1 and cholangiocellular carcinoma RS1 was lower than that in the sphingolipids of the intrahepatically transplanted tumors. However, the sphingenine/sphinganine ratio in the subcutaneously transplanted rat hepatoma 27 was higher than in the intrahepatically transplanted hepatoma. These observations indicate that the sphingenine/sphinganine ratio in sphingolipids of tumors depends on the tumor type and its cellular microenvironment.

Comparative study of lipid composition and proliferative activity of rat cholangiocarcinoma RS1 and sarcoma M1 depending on the transplantation organ.

The proliferative activity and lipid composition (phospholipids, gangliosides) were studied in rat cholangiocarcinoma RS1 and sarcoma M1 transplanted subcutaneously or intrahepatically. The mitotic index was higher in the tumors transplanted into the heterologous organ. The total phospholipid and sphingomyelin contents were higher in the tumors transplanted intrahepatically. GM3 and GD3 were the main gangliosides in both variants of each tumor. A significant amount of GM3 ganglioside lactone was found in the intrahepatic variants whereas it was absent in the subcutaneous tumors. Both the mitotic index and lipid composition of the tumors studied depended on their microenvironment.

Dihydroceramide desaturase activity in tumors.

Dihydroceramide desaturase activity in the transplantable mouse hepatoma-22, rat hepatoma-27, M1 sarcoma, and RS1 rat cholangiocellular carcinoma has been investigated. It was found that the dihydroceramide desaturase activity in mouse hepatoma-22 is lower than that in normal mouse liver. However, the activity of this enzyme in subcutaneously and intrahepatically transplanted rat hepatoma-27 is increased compared to normal value. Dihydroceramide desaturase activity in subcutaneously and intrahepatically transplanted M1 sarcoma as well as in hepatoma-27 is dependent on the tumor microenvironment. The enzyme activity in RS1 tumor was not revealed. The data indicate that dihydroceramide desaturase activity depends on the tumor type and its microenvironment.