Giuseppe Arancia

Induction of Lymphocyte Apoptosis by Tumor Cell Secretion of FasL-bearing Microvesicles

The hypothesis that FasL expression by tumor cells may impair the in vivo efficacy of antitumor immune responses, through a mechanism known as ‘Fas tumor counterattack,’ has been recently questioned, becoming the object of an intense debate based on conflicting results. Here we definitely show that FasL is indeed detectable in the cytoplasm of melanoma cells and its expression is confined to multivesicular bodies that contain melanosomes. In these structures FasL colocalizes with both melanosomal (i.e., gp100) and lysosomal (i.e., CD63) antigens. Isolated melanosomes express FasL, as detected by Western blot and cytofluorimetry, and they can exert Fas-mediated apoptosis in Jurkat cells. We additionally show that melanosome-containing multivesicular bodies degranulate extracellularly and release FasL-bearing microvesicles, that coexpress both gp100 and CD63 and retain their functional activity in triggering Fas-dependent apoptosis of lymphoid cells. Hence our data provide evidence for a novel mechanism potentially operating in Fas tumor counterattack through the secretion of subcellular particles expressing functional FasL. Such vesicles may form a sort of front line hindering lymphocytes and other immunocompetent cells from entering neoplastic lesions and exert their antitumor activity.

Immunity to cancer: attack and escape in T lymphocyte–tumor cell interaction

Summary: Tumor cells may express antigens which are recognized in a form of HLA/peptide complexes by T cells. The frequency at which different antigens are seen by T cells of melanoma patients and healthy donors was evaluated by human leukocyte antigen (HLA)/peptide tetramer technology which stains T cells bearing the specific receptor for a given epitope. By this technique, it was found that the majority of metastatic melanoma patients can recognize differentiation antigens (particularly Melan‐A/MART‐1), whereas such a recognition is scanty in the early phase of the disease and in healthy subjects. Despite the presence of melanoma‐specific T cells infiltrating tumor lesions, tumor rejection rarely occurs. Among the different mechanisms of such inefficient antitumor response, this review discusses the possible anti‐T‐cell counterattack mediated by FasL‐positive tumor cells, and shows that FasL is located in the cytoplasm of melanoma cells and is transported in the tumor microenvironment through the release of melanosomes. Additionally, mechanisms of suboptimal T cell activation through tumor cell expression of peptide analogs with antagonist activity are described, together with the possibility of overcoming such anergy induction by the usage of optimized tumor epitopes. Down‐modulation of HLA expression by target tumor cells and its multiple mechanisms is also considered. Finally, we discuss the role of inducible nitric oxide synthases in determining the inhibition of apoptosis in melanoma cells, which can make such tumor cells resistant to the T‐cell attack.

Exposure to ZnO nanoparticles induces oxidative stress and cytotoxicity in human colon carcinoma cells

Engineered nanoparticles offer great promise in many industrial and biomedical applications, however little information is available about gastrointestinal toxicity. The purpose of this study was to assess the cytotoxicity, oxidative stress, apoptosis and proinflammatory mediator release induced by ZnO nanoparticles on human colon carcinoma LoVo cells. The biological activity of these particles was related to their physico-chemical characteristics. The physico-chemical characteristics were evaluated by analytical electron microscopy. The cytotoxicity was determined by growth curves and water-soluble tetrazolium assay. The reactive oxygen species production, cellular glutathione content, changes of mitochondrial membrane potential and apoptosis cell death were quantified by flow cytometry. The inflammatory cytokines were evaluated by enzyme-linked immunoadsorbent assay. Treatment with ZnO (5μg/cm(2) corresponding to 11.5μg/ml) for 24h induced on LoVo cells a significant decrease of cell viability, H2O2/OH increase, O2(-) and GSH decrease, depolarization of inner mitochondrial membranes, apoptosis and IL-8 release. Higher doses induced about 98% of cytotoxicity already after 24h of treatment. The experimental data show that oxidative stress may be a key route in inducing the cytotoxicity of ZnO nanoparticles in colon carcinoma cells. Moreover, the study of the relationship between toxicological effects and physico-chemical characteristics of particles suggests that surface area does not play a primary role in the cytotoxicity.

Direct binding of human NK cell natural cytotoxicity receptor NKp44 to the surfaces of mycobacteria and other bacteria.

ABSTRACT Our previous studies demonstrated that Mycobacterium bovis bacillus Calmette-Guérin (BCG) can directly interact with human NK cells and induce the proliferation, gamma interferon production, and cytotoxic activity of such cells without the need for accessory cells. Thus, the aim of the present study was to identify the putative receptor(s) responsible for the recognition of BCG by human NK cells and potentially involved in the activation of NK cells. To this end, we first investigated the surface expression of three NK cell-activating receptors belonging to the natural cytoxicity receptor (NCR) family on highly purified human NK cells upon in vitro direct stimulation with BCG. An induction of the surface expression of NKp44, but not of NKp30 or NKp46, was observed after 3 and 4 days of in vitro stimulation with live BCG. The NKp44 induction involved mainly a particular NK cell subset expressing the CD56 marker at high density, CD56bright. In order to establish whether NKp44 could directly bind to BCG, whole BCG cells were stained with soluble forms of the three NCRs chimeric for the human immunoglobulin G (IgG) Fc fragment (NKp30-Fc, NKp44-Fc, NKp46-Fc), followed by incubation with a phycoerythrin (PE)-conjugated goat anti-human IgG antibody. Analysis by flow cytometry of the complexes revealed a higher PE fluorescence intensity for BCG incubated with NKp44-Fc than for BCG incubated with NKp30-Fc, NKp46-Fc, or negative controls. The binding of NKp44-Fc to the BCG surface was confirmed with immunogold labeling using transmission electron microscopy, suggesting the presence of a putative ligand(s) for human NKp44 on the BCG cell wall. Similar binding assays performed on a number of gram-positive and gram-negative bacteria revealed a pattern of NKp44-Fc binding restricted to members of the genus Mycobacterium, to the mycobacterium-related species Nocardia farcinica, and to Pseudomonas aeruginosa. Altogether, the results obtained indicate, for the first time, that at least one member of the NCR family (NKp44) may be involved in the direct recognition of bacterial pathogens by human NK cells.

The biological functions of polyamine oxidation products by amine oxidases: perspectives of clinical applications.

Summary.The polyamines spermine, spermidine and putrescine are ubiquitous cell components. If they accumulate excessively within the cells, due either to very high extracellular concentrations or to deregulation of the systems which control polyamine homeostasis, they can induce toxic effects. These molecules are substrates of a class of enzymes that includes monoamine oxidases, diamine oxidases, polyamine oxidases and copper containing amine oxidases. Polyamine concentrations are high in growing tissues such as tumors. Amine oxidases are important because they contribute to regulate levels of mono- and polyamines. These enzymes catalyze the oxidative deamination of biogenic amines and polyamines to generate the reaction products H2O2 and aldehyde(s) that are able to induce cell death in several cultured human tumor cell lines. H2O2 generated by the oxidation reaction is able to cross the inner membrane of mitochondria and directly interact with endogenous molecules and structures, inducing an intense oxidative stress. Since amine oxidases are involved in many crucial physiopathological processes, investigations on their involvement in human diseases offer great opportunities to enter novel classes of therapeutic agents.

Cytoskeletal changes induced in HEp-2 cells by the cytotoxic necrotizing factor of Escherichia coli

The effect of the cytotoxic necrotizing factor of Escherichia coli on HEp-2 cells was studied by fluorescence and scanning electron microscopy. This cytotoxin, known for inducing the formation of giant multinucleated cells in several cell lines, caused changes in actin and tubulin organization. The presence of membrane ruffles at the cell border and of numerous thick bundles of actin crossing the cell body, suggests that the factor promotes cell spreading; this probably interferes with cytokinesis, ultimately leading to the formation of very large flattened multinucleated cells. Moreover, the nuclear segmentation observed in treated cells seems to be associated with a rearrangement of actin in the perinuclear region and with the presence of tubulin bundles in proximity to nuclear clefts. Although the primary target is still unknown, these findings suggest that the cytoskeleton is affected accounting for the multinucleation process induced by the factor.

PE is a functional domain responsible for protein translocation and localization on mycobacterial cell wall.

The PE family of Mycobacterium tuberculosis includes 98 proteins which share a highly homologous N‐terminus sequence of about 110 amino acids (PE domain). Depending on the C‐terminal domain, the PE family can be divided in three subfamilies, the largest of which is the PE_PGRS with 61 members. In this study, we determined the cellular localization of three PE proteins by cell fractionation and immunoelectron microscopy by expressing chimeric epitope‐tagged recombinant proteins in Mycobacterium smegmatis. We demonstrate that the PE domain of PE_PGRS33 and PE11 (a protein constituted by the only PE domain) contains the information necessary for cell wall localization, and that they can be used as N‐terminal fusion partners to deliver a sufficiently long C‐terminus‐linked protein domain on the mycobacterial cell surface. Indeed, we demonstrate that PE_PGRS33 and Rv3097c (a lipase belonging to the PE family) are surface exposed and localize in the mycobacterial cell wall. Moreover, we found that PE_PGRS33 is easily extractable by detergents suggesting its localization in the mycobacterial outer membrane. Beyond defining the cellular localization of these proteins, and a function for their PE domains, these data open the interesting possibility to construct recombinant mycobacteria expressing heterologous antigens on their surface for vaccine purposes.

Tyrosine phosphatase activity in mitochondria: presence of Shp-2 phosphatase in mitochondria

Tyrosine phosphorylation by unidentified enzymes has been observed in mitochondria, with recent evidence indicating that non-receptorial tyrosine kinases belonging to the Src family, which represent key players in several transduction pathways, are constitutively present in mitochondria. The extent of protein phosphorylation reflects a coordination balance between the activities of specific kinases and phophatases. The present study demonstrates that purified rat brain mitochondria possess endogenous tyrosine phosphatase activity. Mitochondrial phosphatases were found to be capable of dephosphorylating different exogenous substrates, including paranitrophenylphosphate, 32P-poly(Glu-Tyr)4:1 and 32P-angiotensin. These activities are strongly inhibited by peroxovanadate, a well-known inhibitor of tyrosine phosphatases, but not by inhibitors of alkali or Ser/Thr phosphatases, and mainly take place in the intermembrane space and outer mitochondrial membrane. Using a combination of approaches, we identified the tyrosine phosphatase Shp-2 in mitochondria. Shp-2 plays a crucial role in a number of intracellular signalling cascades and is probably involved in several human diseases. It thus represents the first tyrosine phosphatase shown to be present in mitochondria.

Biophysical and structural characterization of 1H-NMR-detectable mobile lipid domains in NIH-3T3 fibroblasts

Nature and subcellular localization of 1H-NMR-detectable mobile lipid domains (ML) were investigated by NMR, Nile red fluorescence and electron microscopy, in NIH-3T3 fibroblasts and their H-ras transformants (3T3ras) transfected with a high number of oncogene copies. Substantial ML levels (ratio of (CH2)n/CH3 peak areas R=1. 56+/-0.33) were associated in untransformed fibroblasts with both (a) intramembrane amorphous lipid vesicles, about 60 nm in diameter, distinct from caveolae; and (b) cytoplasmic, osmiophilic lipid bodies surrounded by own membrane, endowed of intramembrane particles. 2D NMR maps demonstrated that ML comprised both mono- and polyunsaturated fatty chains. Lower ML signals were detected in 3T3ras (R=0.76+/-0.37), under various conditions of cell growth. Very few (if any) lipid bodies and vesicles were detected in the cytoplasmic or membrane compartments of 3T3ras cells with R<0.4, while only intramembrane lipid vesicles were associated with moderate R values. Involvement of phosphatidylcholine hydrolysis in ML generation was demonstrated by selective inhibition of endogenous phospholipase C (PC-plc) or by exposure to bacterial PC-plc. This study indicates that: (1) both cytoplasmic lipid bodies and membrane vesicles (possibly in mutual dynamic exchange) may contribute (although to a different extent) to ML signals; and (2) high levels of ras-transfection either inhibit ML formation or facilitate their extrusion from the cell.

The PPAR-γ agonist troglitazone antagonizes survival pathways induced by STAT-3 in recombinant interferon-β treated pancreatic cancer cells.

We have previously shown that cancer cells can protect themselves from apoptosis induced by type I interferons (IFNs) through a ras→MAPK-mediated pathway. In addition, since IFN-mediated signalling components STATs are controlled by PPAR gamma we studied the pharmacological interaction between recombinant IFN-β and the PPAR-γ agonist troglitazone (TGZ). This combination induced a synergistic effect on the growth inhibition of BxPC-3, a pancreatic cancer cell line, through the counteraction of the IFN-β-induced activation of STAT-3, MAPK and AKT and the increase in the binding of both STAT-1 related complexes and PPAR-γ with specific DNA responsive elements. The synergism on cell growth inhibition correlated with a cell cycle arrest in G0/G1 phase, secondary to a long-lasting increase of both p21 and p27 expressions. Blockade of MAPK activation and the effect on p21 and p27 expressions, induced by IFN-β and TGZ combination, were due to the decreased activation of STAT-3 secondary to TGZ. IFN-β alone also increased p21 and p27 expression through STAT-1 phosphorylation and this effect was attenuated by the concomitant activation of IFNbeta-induced STAT-3-activation. The combination induced also an increase in autophagy and a decrease in anti-autophagic bcl-2/beclin-1 complex formation. This effect was mediated by the inactivation of the AKT→mTOR-dependent pathway. To the best of our knowledge this is the first evidence that PPAR-γ activation can counteract STAT-3-dependent escape pathways to IFN-β-induced growth inhibition through cell cycle perturbation and increased autophagic death in pancreatic cancer cells.