Control of membrane permeability in animal cells by divalent cations

Extracellular vesicles of Trypanosoma cruzi tissue-culture cell-derived trypomastigotes: Induction of physiological changes in non-parasitized culture cells

BACKGROUND

Trypanosoma cruzi is the obligate intracellular parasite that causes Chagas disease. The pathogenesis of this disease is a multifactorial complex process that involves a large number of molecules and particles, including the extracellular vesicles. The presence of EVs of T. cruzi was first described in 1979 and, since then, research regarding these particles has been increasing. Some of the functions described for these EVs include the increase in heart parasitism and the immunomodulation and evasion of the host immune response. Also, EVs may be involved in parasite adhesion to host cells and host cell invasion.

METHODOLOGY/PRINCIPAL FINDINGS

EVs (exosomes) of the Pan4 strain of T. cruzi were isolated by differential centrifugation, and measured and quantified by TEM, NTA and DLS. The effect of EVs in increasing the parasitization of Vero cells was evaluated and the ED50 was calculated. Changes in cell permeability induced by EVs were evaluated in Vero and HL-1 cardiomyocyte cells using cell viability techniques such as trypan blue and MTT assays, and by confocal microscopy. The intracellular mobilization of Ca2+ and the disruption of the actin cytoskeleton induced by EVs over Vero cells were followed-up in time using confocal microscopy. To evaluate the effect of EVs over the cell cycle, cell cycle analyses using flow cytometry and Western blotting of the phosphorylated and non-phosphorylated protein of Retinoblastoma were performed.

CONCLUSION/SIGNIFICANCE

The incubation of cells with EVs of trypomastigotes of the Pan4 strain of T. cruzi induce a number of changes in the host cells that include a change in cell permeability and higher intracellular levels of Ca2+ that can alter the dynamics of the actin cytoskeleton and arrest the cell cycle at G0/G1 prior to the DNA synthesis necessary to complete mitosis. These changes aid the invasion of host cells and augment the percentage of cell parasitization.

EDTA enhances the antitumor efficacy of intratumoral cisplatin in s.c. grafted rat colon tumors

We have investigated whether EDTA, a calcium chelator, could improve the accumulation of platinum in tumors and enhance the antitumor efficacy by increasing drug diffusion through the extracellular tumor matrix. Intratumoral injection of 0.3 mg/kg cisplatin combined with 10 mg/ml EDTA in 2 ml saline serum led to tumor cure in four of eight rats and produced major tumor regression in the other animals. In contrast, intratumoral injection of cisplatin alone or EDTA alone had no antitumoral effect. EDTA increased platinum accumulation both in vivo and ex vivo in the PROb tumors. EDTA alone was cytotoxic at a concentration of 10 mg/ml, but neither increased platinum accumulation nor cisplatin toxicity on cultured PROb colonic cancer cells. We conclude that EDTA could be a useful and well-tolerated adjuvant for enhancing intratumoral cisplatin chemotherapy.

Measurement of the relative hydrophobicity of organic compounds without organic solvent. Effects of salt composition and pH on organic acids and nonionic compounds

Partitioning of a variety of nonionic and acidic organic compounds was examined in aqueous dextran-poly(ethylene glycol) (PEG) two-phase systems of different ionic composition at pH 2.00 and 7.40. Relative hydrophobicity of the compounds was estimated in terms of equivalent numbers of methylene units. Effect of the ionic composition and pH of aqueous media on the relative hydrophobicity of organic compounds was established and described quantitatively. The results obtained indicate that the ionic composition affects the relative hydrophobicity of ionized compounds and has no effect on that of nonionic compounds and ionizable compounds in the undissociated state. Ionization of a given ionic group seems to bring about a constant change in the relative hydrophobicity of a compound. This result supports the applicability of the additivity principle to the relative hydrophobicity estimates obtained with the aqueous two-phase partitioning technique.

Translocation of alpha-sarcin across the lipid bilayer of asolectin vesicles

alpha-Sarcin is a cytotoxic protein produced by the mould Aspergillus giganteus. Insertion of alpha-sarcin into asolectin membranes has been demonstrated by protein labelling with photoreactive phospholipids. alpha-Sarcin added externally to tRNA-containing asolectin liposomes degrades the entrapped tRNA. Trypsin-containing asolectin liposomes were also prepared. Encapsulated trypsin degrades alpha-sarcin, even in the presence of a large excess of external hen egg-white trypsin inhibitor to prevent any alpha-sarin degradation outside the vesicles. These processes occur only with acidic phospholipids and were not observed when phosphatidylcholine vesicles were used. These results indicate that alpha-sarcin penetrates the lipid bilayer and becomes exposed to the lumen of negatively charged liposomes.

Kinetic study of the cytotoxic effect of alpha-sarcin, a ribosome inactivating protein from Aspergillus giganteus, on tumour cell lines: protein biosynthesis inhibition and cell binding

alpha-Sarcin is a ribosome inactivating protein produced by the mould Aspergillus giganteus. The effect of this protein on eight different tumour cell lines has been studied in the absence of any agent affecting membrane permeability. The protein is cytotoxic for all the tumour cell lines considered. alpha-Sarcin modifies the cell proliferation pattern by inhibiting the protein biosynthesis of the cultured cells. No membrane damage produced by alpha-sarcin has been observed by measuring lactic dehydrogenase leakage. Alteration on the cell mitochondrial activity has not been detected upon treatment with alpha-sarcin. Differences on the extent of the protein binding to the cells have been observed by flow cytometric measurements. The kinetic analysis of the protein biosynthesis inhibition produced by alpha-sarcin reveals an alpha-sarcin concentration-dependent lag phase followed by a first order decrease of the protein synthesis rate. This parameter is dependent on the external alpha-sarcin concentration. A saturable component for the action of alpha-sarcin is also deduced from these experiments. Results are discussed in terms of the protein passage across the cell membrane as the potential rate-limiting step for the action of alpha-sarcin.

Measurement of hygromycin B phosphotransferase activity in crude mammalian cell extracts by a simple dot-blot assay

Hygromycin B (Hy) resistance, encoded by the prokaryotic gene hph, is commonly used as a dominant selectable marker for gene transfer experiments in mammalian cells. We describe a simple, quantitative dot-blot assay for measuring the activity in crude mammalian cell extracts of Hy phosphotransferase, the product of the hph gene. The assay shows no cross interference with substrates for neomycin phosphotransferase II, the product of the commonly used marker gene neo; hph and neo may thus be useful as a set of two non-interfering selectable marker and reporter genes for gene transfer experiments in mammalian cells.

Modification of membrane permeability by animal viruses

Animal viruses modify membrane permeability during lytic infection. There is a co-entry of macromolecules and virion particules during virus penetration and a drastic change in transport and membrane permeability at the late stages of the lytic cycle. Both events are of importance to understand different molecular aspects of viral infection, as virus entry into the cell and the interference of virus infection with cellular metabolism. Other methods of cell permeabilization of potential relevance to understand the mechanism of viral damage of the membrane are also discussed.

Exogenous phospholipase C permeabilizes mammalian cells to proteins

Mammalian cells treated with low concentrations of phospholipase C become permeable to the protein toxin alpha-sarcin. A similar permeabilization is not induced upon treatment with other lipases such as phospholipase A2, sphingomyelinase, or cholesterol esterase. Concentrations of 10 micrograms/ml alpha-sarcin almost completely blocked translation in HeLa cells treated with 0.3 U/ml phospholipase C (PL-C) for 1 h. In contrast, 200 micrograms/ml of alpha-sarcin had no effect at all on protein synthesis in untreated cells. Other macromolecules such as horseradish peroxidase and luciferase also enter into cells if they are treated with phospholipase C. This permeabilization method is fully reversible. As soon as 5 min after PL-C removal, the cells become impermeable to alpha-sarcin. Other metabolites such as uridine nucleotides are partially released after PL-C incubation, whereas the content of 86Rb+ remains at control levels, probably because the Na+/K+ ATPase activity increases.

Inhibition of natural killer cytotoxicity by extracellular ppp(A2'p5')nA oligonucleotides

The effect of purified 2'-5' linked polyadenylated oligomers on the human natural killer (NK) activity has been investigated. Permeabilization of NK cells to ppp(A2'p5')2A did not enhance their NK activity at any concentration tested. Furthermore, concentrations higher than 0.1 mM inhibited their NK activity. Similar results were obtained by pre-incubating non-permeabilized intact cells, indicating an extracellular effect of these compounds on cell membranes, which was further investigated. This inhibition by the oligomers was greater (50% inhibition was obtained with 50 micron), when they were added directly to the NK assay, than when the NK cells were pre-incubated. Similar inhibitory effects were observed with ppp(A2'p5')A and ppp(A2'p5')3A oligomers but not with the dephosphorylated "core" molecules or other nucleotides. The inhibition was completely or partially reversed by phorbol esters and by interferon (IFN), respectively. The inhibition was temperature and extracellular Ca2+ dependent. The oligomers did not inhibit the binding of the effector cells to the target cells. The programming for lysis was the step of the lytic mechanism affected, possibly due to the alteration of the Ca2+ influx into the NK cells observed in presence of the ppp(A2'p5')nA.

Proteins are cointernalized with virion particles during early infection

Mammalian cells infected with enveloped or naked animal viruses become permeabilized to several proteins. The entry of alpha-sarcin, horseradish peroxidase, and luciferase is greatly increased during the early stages of viral infection. This process is promoted by uv-inactivated SFV, but not by heat-inactivated virions, suggesting that the process does not require viral gene expression. The entry of alpha-sarcin has been monitored both by its effects on protein synthesis and by indirect immunofluorescence. Increased entry of alpha-sarcin and luciferase is clearly observed in animal virus-infected cells by fluorescence microscopy. Chloroquine blocks the coentry of alpha-sarcin with enveloped, but not with naked, viruses. These results have implications to elucidate the mechanisms involved in virus entry.