The HIV-1 vpr protein acts as a negative regulator of apoptosis in a human lymphoblastoid T cell line: possible implications for the pathogenesis of AIDS.

Although apoptosis is considered one of the major mechanisms of CD4(+) T cell depletion in HIV-infected patients, the virus-infected cells somehow appear to be protected from apoptosis, which generally occurs in bystander cells. Vpr is an auxiliary HIV-1 protein, which, unlike the other regulatory gene products, is present at high copy number in virus particles. We established stable transfectants of CD4+ T Jurkat cells constitutively expressing low levels of vpr. These clones exhibited cell cycle characteristics similar to those of control-transfected cells. Treatment of control clones with apoptotic stimuli (i.e., cycloheximide/tumor necrosis factor alpha (TNF-alpha), anti-Fas antibody, or serum starvation) resulted in a massive cell death by apoptosis. In contrast, all the vpr-expressing clones showed an impressive protection from apoptosis independently of the inducer. Notably, vpr antisense phosphorothioate oligodeoxynucleotides render vpr-expressing cells as susceptible to apoptosis induced by cycloheximide and TNF-alpha as the control clones. Moreover, the constitutive expression of HIV-1 vpr resulted in the upregulation of bcl-2, an oncogene endowed with antiapoptotic activities, and in the downmodulation of bax, a proapoptotic factor of the bcl-2 family. Altogether, these results suggest that low levels of the endogenous vpr protein can interfere with the physiological turnover of T lymphocytes at early stages of virus infection, thus facilitating HIV persistence and, subsequently, viral spread. This might explain why apoptosis mostly occurs in bystander uninfected cells in AIDS patients.

The relationship between 1H-NMR mobile lipid intensity and cholesterol in two human tumor multidrug resistant cell lines (MCF-7 and LoVo).

The high resolution proton nuclear magnetic resonance (1H-NMR) spectra of two different cell lines exhibiting multidrug resistance (MDR) as demonstrated by the expression of the well-known energy-driven, membrane-bound 170 kDa P-glycoprotein pump known as Pgp were investigated. In particular, the mobile lipid (ML) profile, and the growth and biochemical characteristics of MCF-7 (human mammary carcinoma) and LoVo (human colon adenocarcinoma) sensitive and resistant tumor cells were compared. The results indicate that both MCF-7 and LoVo resistant cells have a higher ML intensity than their respective sensitive counterparts. However, since sensitive and resistant cells of each pair grow in the same manner, variations in growth characteristics do not appear to be the cause of the ML changes as has been suggested by other authors in non-resistant tumor cells. In order to investigate further the origin of the ML changes, lipid analyses were conducted in sensitive and resistant cell types. The results of these experiments show that resistant cells of both cell types have a greater amount of esterified cholesterol and saturated cholesteryl ester and triglyceride fatty acid than their sensitive counterparts. From a thorough analysis of the data obtained in this paper utilizing numerous techniques including biological, biophysical and biochemical ones, it is hypothesized that cholesterol and triglyceride play a pivotal role in inducing changes in NMR ML signals. The importance of these lipid variations in MDR is discussed in view of the controversy regarding the origin of ML signals and the paramount role played by the Pgp pump in resistance.

Synthetic hammerhead ribozymes as therapeutic tools to control disease genes.

Ribozymes are RNA molecules that have the ability to catalyse the cleavage and formation of covalent bonds in RNA strands at specific sites. The "hammerhead" motif, approximately 30-nucleotide long, is the smallest endonucleolytic cis-acting ribozyme structure found in natural circular RNAs of some plant viroids. Hammerhead ribozymes became appealing when it was shown that it is possible to produce trans-acting ribozymes directed against RNA sequences of interest. Since then, gene-tailored ribozymes have been designed, produced and given to cells to knock down the expression of specific genes. At present, this technology has advanced so much that many hammerhead ribozymes are being used in clinical trials. With this work we would provide some guidelines to design efficient trans-acting hammerhead ribozymes as well as review the recent results obtained with them as gene therapy tools.

Extremely low frequency (ELF) magnetic fields and apoptosis: a review.

In recent years, there has been increasing evidence that extremely low frequency magnetic fields might be linked to tumours, particularly with childhood leukaemia. In the same period, the role of apoptosis in the tumour process has also gained increasing importance. It is the purpose of this review to describe the apoptotic process, discuss selected papers in which apoptosis is examined in cells exposed to magnetic fields and describe the possible biophysical mechanisms responsible for changes in the apoptotic process in exposed cells. Despite some differences, as a whole, the literature seems to demonstrate that magnetic fields induce changes in apoptosis in cells exposed to different experimental protocols. In addition, the important role of ions, particularly of Ca2+, in the apoptotic process is also discussed, and one possible model for magnetic field action on apoptosis that brings together experimental observations of different nature is suggested and discussed.

A 700 MHz 1H-NMR study reveals apoptosis-like behavior in human K562 erythroleukemic cells exposed to a 50 Hz sinusoidal magnetic field.

PURPOSE: To study cell damage and possible apoptosis in K562 human erythroleukemic cells exposed for 2 h to an extremely low frequency (ELF) 50 Hz sinusoidal magnetic field with a magnetic induction of either 1 or 5 mT using high resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy. MATERIALS AND METHODS: One-dimensional 1H-NMR spectra were obtained on whole K562 cells and perchloric acid extracts of these cells. In addition, two-dimensional 1H-NMR spectra were also acquired. Cell damage was examined by lactate dehydrogenase release and changes in cell growth were monitored by growth curve analyses, bromodeoxyuridine incorporation and Ki67 antigen localization. Cell death (necrosis and apoptosis) were also studied by using the chromatin dye Hoechst 33258. RESULTS: The variations in numerous metabolites observed with 1H-NMR reveal apoptosis-like behavior in response of K562 cells to ELF fields. CONCLUSION: 1H-NMR can be extremely useful in studying the effects of ELF fields on cells. In particular, the variations in metabolites which suggest apoptosis-like behavior occur when the cells are not identifiable as apoptotic by more traditional techniques.

Accumulation of anchorage independent cells showing amplified genes (CAD) during the in vitro propagation of CHEF18 Chinese hamster cells.

Anchorage independence and gene amplification have frequently been associated with a transformed or tumorigenic phenotype in cultured mammalian cells. However, it is unknown whether these two traits occur as related events during transformation, or are independent features of the transformed phenotype. To clarify this point, immortalized, untransformed CHEF18 Chinese hamster cells were propagated in culture until they became transformed and tumorigenic. The frequencies with which CHEF18 cells formed colonies either in soft agar, in medium containing N-phosphonacetyl-L-aspartate or in the two selective media simultaneously, were determined. The results indicate that anchorage independence and CAD gene amplification spontaneously arose during the propagation of the cells and that their concurrent emergence was not the consequence of independent events. However, the kinetics of their appearance suggests that anchorage independence is the early event whereas gene amplification might represent one of the numerous events which can be dynamically selected in anchorage-independent cells.

A novel gene order in the Paracentrotus lividus mitochondrial genome.

The mitochondrial DNA (mtDNA) from Paracentrotus lividus (sea urchin) eggs, a circular molecule of about 15,500 bp, has been cloned in plasmid vectors after cleavage with various restriction enzymes. By a combination of Northern blot hybridization and nucleotide sequence analysis we have characterized most of the P. lividus mitochondrial transcripts and determined the basic gene organization of the mtDNA. The nucleotide sequence of a gene for one NADH dehydrogenase (ND) subunit, ND4L, has also been determined. Our results show the existence of a novel gene order. The 12S and 16S rRNA genes are not contiguous but are separated from each other by ND1 and ND2 genes. The ND4L gene is not adjacent to ND4 but is located between the tRNAArg gene and the gene for subunit II of cytochrome oxidase (CoII). The tRNA genes are reshuffled and contrary to all vertebrate mitochondrial genomes studied so far, there are no intergenic regions between the tRNAPhe and the cytochrome b genes. These characteristics suggest a peculiar mechanism for the regulation of gene expression in this organism and provide information on the evolution of the mitochondrial genetic system in animal cells.

Apoptosis, cell adhesion and the extracellular matrix in the three-dimensional growth of multicellular tumor spheroids.

In the last few years, it has become increasingly apparent that cell survival and death, especially apoptosis, strongly depend on cell adhesion and the extracellular matrix. In addition, it has also become clear that the use of three-dimensional multicellular tumor spheroids, which mimick more closely solid tumors in vivo, are a realistic experimental model to investigate many aspects of tumor biology. In the present review, after a general overview of the current knowledge regarding apoptosis, cell adhesion and the extracellular matrix, the results obtained utilizing multicellular tumor spheroids in these types of studies are discussed. The main conclusion that may be drawn from a synthesis of the literature on these topics is that investigations with multicellular tumor spheroids yield much useful information that is sometimes in contradiction to that obtained with monolayer cultures, but is closer to that derived from in vivo studies. Consequently, the authors encourage that these three-dimensional systems be used in many studies in which cell death and adhesion are being examined.

The oxidizing agent menadione induces an increase in the intracellular molecular oxygen concentration in K562 and A431 cells: direct measurement using the new paramagnetic EPR probe fusinite.

The intracellular molecular oxygen concentration in control and menadione-treated K562 (an erythroleukemic cell line that grows in suspension) and A431 (an epidermal carcinoma that grows in monolayer) cells was measured directly by using the new electron paramagnetic resonance (EPR) probe fusinite. Because the oxidizing agent menadione is known to damage mitochondria and the cytoplasmic membrane in other cell systems, before conducting measurements of oxygen concentration in K562 and A431 cells, it was necessary to establish injury in these systems as well. Consequently, morphological and flow cytometric analyses were conducted after menadione treatment. The data presented here show that the two cell lines are heavily damaged by menadione. Once this menadione-induced injury was demonstrated, measurements of oxygen concentration were carried out in both K562 and A431 cells. Treatment with this quinone induces a sharp increase in intracytoplasmic molecular oxygen in both cell lines (from about 1% to about 10 and 15% in K562 and A431 cells, respectively). In addition, to gain a more complete understanding of the effects of menadione on cells, the extracellular molecular oxygen concentration and the oxygen consumption rate were also measured in control and menadione-treated K562 cells. These measurements demonstrate that menadione treatment results in an increase in the extracellular oxygen concentration (from about 5% in controls to 15% in treated cells) as well as a decrease in the oxygen consumption rate (from about 10 ng O/min/10(6) cells in controls to 3 ng O/min/10(6) cells after menadione exposure). The importance of the new EPR probe fusinite in monitoring directly cellular functions in which oxygen is involved and the effects of menadione on cellular oxygen balance are discussed.

Ribozyme and free alkylated base: a dual approach for sensitizing Mex+ cells to the alkylating antineoplastic drug.

N-alkyl-nitrosoureas and alkyl-triazenes are alkylating antineoplastic drugs, the efficacy of which is strongly affected by the level of expression of the DNA-repair enzyme O6-methylguanine-DNA methyltransferase (MGMT). In tumors, MGMT activity reduces the chemotherapeutic potential of alkylating drugs; therefore, efforts have been made to down-regulate the protein. A partial sensitization of Mex+ cells to alkylating drugs has been obtained using either free alkylated bases or oligonucleotides targeted against MGMT mRNA. In the present work, O6-methylguanine and a chemically modified ribozyme, without a cationic liposome as a carrier, were coadministered to CHO47 cells, which express a high level of human MGMT protein. The reduction of MGMT mRNA and protein enhanced the genotoxicity of the alkylating drug mitozolomide. Furthermore, the sensitivity of CHO47 cells is the same as that of CHO5 cells, which lack MGMT protein. These data indicate that a strategy in which both mRNA and protein are degradation targets can be successfully applied to down-regulate the MGMT gene.

Quantitation of in vitro activity of synthetic trans-acting ribozymes using HPLC.

The cleavage activity of synthetic ribozymes needs to be characterized by reliable and rapid methods. A chromatographic method to simultaneously quantitate the amounts of substrate, cleavage fragments and ribozyme is described. The method allows the rapid normalization of analytical data because the sum of the 260-nm peak areas of remaining substrate and obtained fragments is essentially equal to the initial substrate peak area. Moreover, the simultaneous determination of the ribozyme content improves the accuracy of the evaluation of kinetic parameters compared with conventional densitometric methods. Finally, the characterization of two different hammerhead motifs indicated that the method is suitable for a rapid screening of synthetic ribozyme activity.

Efficacy of an amphipathic oligopeptide to shuttle and release a cis-acting DNA decoy into human cells.

We investigated the ability of an amphipathic oligopeptide to carry a synthetic dsDNA oligonucleotide inside human cells. The oligonucleotide was designed as a decoy binding site for the transcriptional activator of the methylguanine-DNA methyltransferase (MGMT) gene. The complex oligopeptide and decoy were administered to MCF10A exponentially growing cells, and the uptake was monitored by flow cytometry. After a 1-h exposure, almost all of the MCF10A cells were fluorescent, indicating that all of the cells had been transfected. By increasing the time, the fluorescence intensity per cell rapidly increased to a plateau at the 8-h time point. RT-PCR analysis of the MGMT gene was used as the molecular readout of the intracellular activity of the DNA decoy. MCF10A cells transfected with the oligopeptide/decoy complex showed a strong reduction in MGMT mRNA. Here, we discuss the advantages of using amphipathic oligopeptides as carriers of short DNA sequences.

Thiol supplier N-acetylcysteine enhances conjugate formation between natural killer cells and K562 or U937 targets but increases the lytic function only against the latter.

In this in vitro study, an evaluation of the importance of intracellular oxidative balance on cell-mediated cytotoxicity was performed by analyzing the effects of the antioxidant N-acetylcysteine (NAC), a specific thiol supplier, on natural killer (NK) cell-mediated cytotoxicity. The results obtained indicate that an enhancement of target cell (TC) killing can be detected when a pre-exposure of effector cells (EC) to NAC was performed. However, this effect seems to depend upon the TC type used. In fact, the increase of EC activity was detected against the differentiated U937 TC while no changes were detected by the same effectors against K562 cells. The mechanism of this enhancement seems to be ascribable to an increased ability of NAC-exposed NK cells to form conjugates (binding) which, in turn, appears to be due to a specific effect of NAC on actin microfilaments. A role for NAC as a cytoskeleton thiol-modifier contributing to the activation of effector cells can thus be hypothesized.

A new, striking morphological alteration of P-glycoprotein expression in NK cells from AIDS patients.

Natural killer cells from healthy donors express P-glycoprotein on their surface. This molecule is rearranged during the process of cell-mediated cytotoxicity and it appears to be clustered in the cell-to-cell contact regions. By contrast, in HIV-infected subjects this rearrangement is hindered. These results seem to be associated with cytoskeleton network alterations of the cell-mediated killing process occurring in AIDS patients and can contribute to the comprehension of the mechanisms of the natural killer cell deficiency found in these patients.

P-170 glycoprotein (P-170) is involved in the impairment of natural killer cell-mediated cytotoxicity in HIV+ patients.

In the present study we analyze peripheral blood lymphocytes (PBL) from patients with human immunodeficiency virus (HIV) infection for both phenotypic expression and function of P-glycoprotein (P-170). This transmembrane efflux pump is known to be one of the mechanisms responsible for the multidrug resistance (MDR) in cancer therapy and it is also constitutively expressed in normal PBL. P-170 function, evaluated as Rhodamine 123 (Rh123) efflux in flow cytometry, was found to be significantly reduced in CD16+ natural killer (NK) cells from patients with HIV infection. Interestingly, this reduced efflux significantly correlates with the decreased NK cytotoxicity observed in HIV+ patients, as evaluated against the NK-specific K562 target cell line. These results support a possible role of the P-170-related pump in specific immunological lymphocyte function such as NK cell-mediated cytotoxicity.

RNA-based drugs: from RNA interference to short interfering RNAs.

RNA interference consists of a sequence specific post-transcriptional gene silencing phenomenon triggered by a double strand RNA molecule homologous to the silenced gene. The dsRNA is cleaved by DICER enzyme in small dsRNA pieces, named short interfering RNAs (siRNAs). These fragments are thereafter associated to RISC complex where the cleavage of target RNA occurs. The observation that siRNAs can trigger the RNA interference mechanism in mammalian cells represents a fundamental discovery that discloses new horizons in genetic researches in that theoretically each gene can be silenced. The relative simplicity by which active short interfering RNAs can be designed and synthesized explains their widespread use in basic and applied researches, even if appropriate controls that exclude off-target effects are strictly required. The findings that siRNAs are active even when expressed in viral vectors open the possibility that they can be very soon used for gene therapy of several human diseases.

The HIV-1 gp120 causes ultrastructural changes typical of apoptosis in the rat cerebral cortex.

We used transmission electron microscopy (TEM) and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labelling (TUNEL) techniques to study the neuropathological effects of intracerebroventricular (i.c.v.) injection of recombinant HIV-1 gp 120 in rats. In brain cortical tissue sections from rats treated with a single daily dose of gp120 (100 ng day-1 for 7 or 14 consecutive days) TEM analysis showed chromatin compaction and marginalization along the inner surface of the nuclear envelope followed by masses of condensed chromatin, ultrastructural signs demonstrating the occurrence of apoptotic cell death. These effects were paralleled by in situ DNA fragmentation, as revealed by application of TUNEL technique to cryostat brain tissue sections from rats treated likewise with the viral coat protein. In no instance was apoptosis seen in the brain cortex of control rats. The present data demonstrate that gp120 given i.c.v. produces apoptosis in the neocortex of rats.

Folate-sensitive fragile sites in Chinese hamster cell lines.

The expression of fragile sites in three different Chinese hamster cell lines was studied. Results showed that folate-sensitive fragile sites were expressed in the pericentromeric regions of chromosomes 1, 3, 4, 6, and 7 and in band 1q22. A comparison of the breakpoints involved in formation of chromosome rearrangements in some established Chinese hamster cell lines was also made. Results showed that while the specific type of rearrangement was random, the breakpoints were not. Three of the chromosomal sites most frequently involved in breaks were regions in which fragile sites were expressed.

Specific chromosomal aberrations correlated to transformation in Chinese hamster cells.

Cytogenetic changes were investigated during the spontaneous progression of CHEF18 Chinese hamster cells towards tumorigenicity. We further report the chromosomal characterization of a series of spontaneous anchorage-independent clones, as well as of a series of tumor-derived cell lines resulting from injection of late passage cells in nude mice. The high karyotypic homogeneity (presence of four marker chromosomes strictly associated in all the metaphases analyzed) in all clones and tumor-derived cell lines prompted us to alter the specific pattern of chromosomal aberrations in order to identify which if any of the aberrations were more strictly related to transformation. For this purpose we treated a tumor-derived cell line with Colcemid and analyzed the reversion of anchorage-independent phenotype in the subclones showing an altered association of the four marker chromosomes. We conclude that two of four marker chromosomes contribute to anchorage independence.

The genotoxicity of the chloroethylating agent mitozolomide is enhanced in CHO mex+ cells by the administration of antimessenger oligonucleotide targeted against methylguanine-DNA methyltransferase gene (MGMT).

The alkylating drug resistance is frequently related to the DNA repair activity 0(6)-alkylguanine-DNA alkyltransferase (0(6)-AT), a protein coded by the methylguanine-DNA methyltransferase gene (MGMT). We synthesized one antisense oligodeoxyribonucleotide (AS-ODN) targeted against the mRNA of the MGMT gene. The administration of this "antimessenger" sequence to a Chinese hamster ovary cell line, expressing the transfected human MGMT gene, caused a moderate decrease of the resistance to the chloroethylating drug mitozolomide (MTZ), measured as induction of sister chromatid exchanges (SCE). The AS-ODN administration combined with depletion and recovery of 0(6)-AT by 0(6)-methylguanine inhibitor treatment showed an enhancement of SCE induction. The results support the inhibition of the MGMT translation mechanism by AS-ODN and suggest that the pre-existing protein could compromise the reversion of the resistant phenotype if is still active during the administration of the "antimessenger" sequence.