Isolation of High-Molecular-Weight Activation Complexes of Initiator Caspases in DNA Damage.

Initiation of apoptosis by chemotherapeutic drugs is one of the most effective approaches to the treatment of cancers. Caspases, the main enzymes of apoptosis, undergo activation to initiate cell death. Activation of initiator caspases requires their binding to special protein complexes. For elucidation of the mechanisms of apoptosis, these complexes should be isolated. However, their purification is challenging because they are formed in the cell in negligible amounts and rapidly degrade. We have developed an effective way to isolate caspase activation complexes formed in tumor cells in response to DNA damage. The method is based on combination of gel filtration with immunoprecipitation. The first stage is aimed at the separation of the high-molecular-weight caspase activation complexes and their monomeric forms, which allows increasing the efficiency of isolation of complexes at the second stage.

[Caspase-2 as an Oncosupressor and Metabolism Regulator: What Life Will Bring over the Long Run?]

Programmed cell death is governed by a set of gene networks, which define a variety of distinct molecular mechanisms essential for the maintenance of multicellular organisms. The most studied modality of programmed cell death is known as apoptosis. Caspase-2, as a member of the family of the cysteine-dependent protease, demonstrates both proapoptotic and tumor suppressive functions. This protease plays an essential role in the maintenance of genomic stability and induces apoptotic cell death in response to geno-toxic stress. Here we discuss the molecular mechanisms of caspase-2 regulation and its physiological role as a tumor suppressor and metabolic regulator.

Inhibition of P-glycoprotein stimulates cell death under Hypoxia-mimicking conditions.

The most common drug resistance mechanism in tumor cells is expression on their surface of the energy-dependent pump like P-glycoprotein (P-gp) that expels chemotherapeutic agents from the interior. An imitation of the hypoxic condition by the iron chelator deferoxamine caused Hypoxia-inducible factor 1-alpha (HIF-1α) stabilization and inhibition of doxorubicin-induced apoptosis in colon cancer НСТ116 cells. P-gp blocker verapamil suppressed doxorubicin accumulation leading to cell death induction. Considering these results, P-gp may be used as a potential target to stimulate chemotherapeutic drugs activity that will contribute to more efficient tumor cells elimination.

[Nutrient restriction in combinatory therapy of tumors].

The main objective of anticancer treatment is the elimination of degenerated cells by the induction of programmed cell death. Various chemotherapy drugs and radiation are able to activate cell death mechanisms in tumors. However, unfortunately, monotherapy will always be insufficiently effective because of the variety and virulence of tumors, as well as their ability to develop resistance to drugs. Moreover, monotherapy might constrain many negative side effects. Therefore, the combination of different approaches and/or drugs will increase the efficiency of treatment. One such promising approach is the combination of nutrient restriction (NR) and various chemotherapeutic drugs. This approach may not only affect the autophagy but also influence apoptotic cell death. This review is focused on the potential of NR use in anticancer therapy, as well as the molecular mechanisms underlying this approach.

Cellular Energetics as a Target for Tumor Cell Elimination.

Investigation of cancer cell metabolism has revealed variability of the metabolic profiles among different types of tumors. According to the most classical model of cancer bioenergetics, malignant cells primarily use glycolysis as the major metabolic pathway and produce large quantities of lactate with suppressed oxidative phosphorylation even in the presence of ample oxygen. This is referred to as aerobic glycolysis, or the Warburg effect. However, a growing number of recent studies provide evidence that not all cancer cells depend on glycolysis, and, moreover, oxidative phosphorylation is essential for tumorigenesis. Thus, it is necessary to consider distinctive patterns of cancer metabolism in each specific case. Chemoresistance of cancer cells is associated with decreased sensitivity to different types of antitumor agents. Stimulation of apoptosis is a major strategy for elimination of cancer cells, and therefore activation of mitochondrial functions with direct impact on mitochondria to destabilize them appears to be an important approach to the induction of cell death. Consequently, the design of combination therapies using acclaimed cytotoxic agents directed to induction of apoptosis and metabolic agents affecting cancer cell bioenergetics are prospective strategies for antineoplastic therapy.

Mechanism of caspase-2 activation upon DNA damage.

The mechanism of caspase-2 activation in response to DNA damage was studied using human ovarian cancer cells Caov-4 treated with chemotherapeutic agent cisplatin. It was shown that mutations of the three cleavage sites of caspase-2 do not affect the assembly of the macromolecular complex of caspase-2 and its activation, but, conversely, stabilize this complex, most likely, via the inhibition of the dissociation of the active caspase-2.

[Induction of Unspecific Permeabilization of Mitochondrial Membrane and Its Role in Cell Death].

Mitochondria participate in various vital cellular processes. Violation of their functions can lead to the development of cardiovascular and neurodegenerative diseases and malignancies. One of the key events responsible for mitochondrial damage-induction of Ca^(2+)-dependent mitochondrial permeability transition, due to the opening of a nonspecific pore in the inner mitochondrial membrane. Despite active studies of pore components, its detailed structure has not yet been established. This review analyzes possible constituents and regulators of the pore, the role of the pore in various pathologies, and hypotheses that explain the organization of the pores. Elucidation of these questions can help developing strategies for the treatment of a wide range of pathologies-from Alzheimer and Parkinson's disease to cancer.

Etoposide and hypoxia do not activate apoptosis of multipotent mesenchymal stromal cells in vitro.

Incubation of multipotent mesenchymal stromal cells from human adipose tissue with etoposide for 24, 48, and 72 h under standard conditions (20% O(2)), at "physiological" oxygen content (5% O(2)), and under hypoxic conditions (1% O(2)) did not induce cell apoptosis and only slightly increased the number of necrotic cells. The absence of growth factors in the culture medium did not potentiate the damaging effect of etoposide on multipotent mesenchymal stromal cells under standard and hypoxic conditions. We concluded that etoposide produced no pro-apoptotic effect on multipotent mesenchymal stromal cells from the human adipose tissue.

Determination of some nuclear deoxyribonucleases in X-irradiated rat thymocytes.

The spectrum of nuclear nucleases in control and irradiated (4 Gy) thymocytes has been investigated. Using the method of SDS electrophoresis of nuclear proteins in 3H-DNA-polyacrylamide gels a number of polypeptides of MW. 35, 32, 17.7, 17.2 and 16.4 kDa possessing nuclease activity were found. The 35 kDa enzyme is only active in the presence of Ca2+ and Mg2+ ions. In response to cycloheximide injection (3 mg/100 g body weight) and irradiation, we did not detect the 35 kDa nuclease activity. Nucleases of 32, 17.7, 17.2 and 16.4 kDa are active in the presence of Ca2+ ions. The activities of these nucleases increases 60 min after irradiation. These nucleases were also found in the fraction of polydeoxyribonucleotide (PDN).

Nuclear protein synthesis in thymocytes of X-irradiated rats.

The biosynthesis and phosphorylation of nuclear proteins of thymocytes were investigated in rats after 4.0 Gy whole-body X-irradiation during the period which precedes DNA degradation in lymphoid cells. Proteins were separated by two-dimensional gel-electrophoresis, detected by Coomassie blue staining. Incorporation of [35S]methionine into proteins and phosphorylation of proteins with [32P]inorganic phosphate were determined by scanning densitometry of autofluorograms and autoradiograms, respectively. No change in the quantity of proteins was observed 1 h after irradiation. Decrease in specific activity of [35S]methionine-labelled proteins was seen in most protein fractions. Significant enhancement of phosphorylation of three proteins was established, characterized by molecular weight and pH: MW 20 kD, pH 6.8; MW 35 kD, pH 5.8 and MW 48 kD, pH 5.8. These results suggest that immediately after X-irradiation a short-term increase of chromatin-bound non-histone protein phosphorylation occurs. This finding, along with the previously described enhancement of RNA polymerase II in thymocytes (Zhivotovsky et al. 1982) suggests a temporary gene activation shortly after X-irradiation of the rat.

Degree of chromatin fragmentation and frequency of nuclear pyknosis in Percoll-fractionated thymocytes of irradiated rats.

The relationship between nuclear chromatin degradation to polydeoxyribonucleotides (PDN) and other features of interphase death were studied using thymocytes of normal and X-irradiated rats. Fractionation of the thymic cells in Percoll gradients was performed in order to separate dead from intact cells. The degree of radiation-induced chromatin fragmentation, as assessed by electrophoresis, was similar for PDN from all Percoll bands. Following irradiation 87-98 per cent of 'heavy' thymocytes were pyknotic and almost devoid of receptors to autologous erythrocytes thus comprising a dead cell population. A direct relationship between PDN content and nuclear pyknosis was noted throughout the gradient. The loss of autologous rosette-forming ability was directly related to other indices of interphase death. The possibility of PDN originating from pyknosis-prone cells and the capacity of radiosensitive thymocytes to form autologous rosettes are discussed.

Distribution of nuclease attack sites and complexity of DNA in the products of post-irradiation degradation of rat thymus chromatin.

The distribution of nuclease attack sites in chromatin has been studied on the basis of the quantitative relationship of the single- and double-stranded fragments of various lengths in the products of post-irradiation degradation of chromatin (PDN). It has been shown that in irradiated thymocytes internucleosome degradation of chromatin occurs and the products of the enzymic digestion of chromatin derive from randomly distributed genome areas accumulate. Analysis of the reassociation curves has not shown any differences in the complexity of the PDN fractions and total DNA.

Effects of X-irradiation on the hybridization of rat thymus nuclear RNA with repeated and unique DNA sequences.

The kinetics of DNA hybridization with heterogeneous nuclear RNA (hnRNA) from normal and phytohaemagglutinin (PHA)-stimulated thymocytes has been studied in control rats and in animals 30 min after exposure to whole-body X-radiation with 400 rad. Irradiation results in a diminished ability of hnRNA to form hybrids with DNA at all C0t values ranging from 10(-3) to 10(4). Since this effect is most pronounced in the regions of low repetitive and unique DNA sequences, it is concluded that whole-body X-irradiation of animals may also suppress the transcription, particularly, in these regions.

Reassociation kinetics of DNA from x-irradiated ascites hepatoma cells of the rat.

The kinetics of the reassociation fo DNA from ascites hepatoma cells has been studied. The curve exhibited three zones corresponding to 'fast', 'intermediate' and 'slow' speeds of DNA reassociation. The difference was observed in the DNA reassociation curves of the control and irradiated (1500 rad) cells which was particularly expressed in the 'slow' zone (10(2) less than C0t less than 10(4). The same dose, however, does not qualitatively effect the secondary DNA structure, which was estimated by the method of thermal elution from the hydroxyapatite column.