Paola Matarrese

Galectin‐3 overexpression protects from apoptosis by improving cell adhesion properties

Galectin‐3 is a carbohydrate‐binding protein endowed with affinity for β‐galactosides. It plays a role in cell–cell and cell–matrix interactions. Furthermore, it has been hypothesized to be involved in tumor progression and metastasis. To address the role of galectin‐3 in the invasive and metastatic processes, we stably overexpressed galectin‐3 in human breast carcinoma cell lines, and we evaluated the influence of elevated galectin‐3 expression on several cell features, including cellular homotypic and heterotypic interactions and cell survival. No differences in various parameters related with cell growth features and proliferation were detected. By contrast, we found that galectin‐3 overexpressing cells, with respect to low galectin‐3 expressing cells, exerted: (1) a significantly enhanced adhesion to laminin, fibronectin and vitronectin exerted both directly or via increased expression of specific integrins, e.g., alpha‐4 and beta‐7; (2) a remodeling of those cytoskeletal elements associated with cell spreading, i.e., microfilaments; (3) an enhanced survival upon exposure to different apoptotic stimuli, such as cytokine and radiation. Collectively, our results indicate that overexpression of galectin‐3 may play a role in tumor cell invasion and metastasis by specifically influencing cell adhesion to the extracellular matrix. This may confer selective survival advantage and resistance to the particular homeless‐induced apoptosis called anoikia. Int. J. Cancer 85:545–554, 2000.

CD95 (APO‐1/Fas) linkage to the actin cytoskeleton through ezrin in human T lymphocytes: a novel regulatory mechanism of the CD95 apoptotic pathway

CD95 (APO‐1/Fas) is a member of the tumor necrosis factor receptor family, which can trigger apoptosis in a variety of cell types. However, little is known of the mechanisms underlying cell susceptibility to CD95‐mediated apoptosis. Here we show that human T cells that are susceptible to CD95‐mediated apoptosis, exhibit a constitutive polarized morphology, and that CD95 colocalizes with ezrin at the site of cellular polarization. In fact, CD95 co‐immunoprecipitates with ezrin exclusively in lymphoblastoid CD4+ T cells and primary long‐term activated T lymphocytes, which are prone to CD95‐mediated apoptosis, but not in short‐term activated T lymphocytes, which are refractory to the same stimuli, even expressing equal levels of CD95 on the cell membrane. Pre‐treatment with ezrin antisense oligonucleotides specifically protected from the CD95‐mediated apoptosis. Moreover, we show that the actin cytoskeleton integrity is essential for this function. These findings strongly suggest that the CD95 cell membrane polarization, through an ezrin‐mediated association with the actin cytoskeleton, is a key intracellular mechanism in rendering human T lymphocytes susceptible to the CD95‐mediated apoptosis.

Proton Pump Inhibitors Induce Apoptosis of Human B-Cell Tumors through a Caspase-Independent Mechanism Involving Reactive Oxygen Species

Proton pumps like the vacuolar-type H+ ATPase (V-ATPase) are involved in the control of cellular pH in normal and tumor cells. Treatment with proton pump inhibitors (PPI) induces sensitization of cancer cells to chemotherapeutics via modifications of cellular pH gradients. It is also known that low pH is the most suitable condition for a full PPI activation. Here, we tested whether PPI treatment in unbuffered culture conditions could affect survival and proliferation of human B-cell tumors. First, we showed that PPI treatment increased the sensitivity to vinblastine of a pre-B acute lymphoblastic leukemia (ALL) cell line. PPI, per se, induced a dose-dependent inhibition of proliferation of tumor B cells, which was associated with a dose- and time-dependent apoptotic-like cytotoxicity in B-cell lines and leukemic cells from patients with pre-B ALL. The effect of PPI was mediated by a very early production of reactive oxygen species (ROS), that preceded alkalinization of lysosomal pH, lysosomal membrane permeabilization, and cytosol acidification, suggesting an early destabilization of the acidic vesicular compartment. Lysosomal alterations were followed by mitochondrial membrane depolarization, release of cytochrome c, chromatin condensation, and caspase activation. However, inhibition of caspase activity did not affect PPI-induced cell death, whereas specific inhibition of ROS by an antioxidant (N-acetylcysteine) significantly delayed cell death and protected both lysosomal and mitochondrial membranes. The proapoptotic activity of PPI was consistent with a clear inhibition of tumor growth following PPI treatment of B-cell lymphoma in severe combined immunodeficient mice. This study further supports the importance of acidity and pH gradients in tumor cell homeostasis and suggests new therapeutic approaches for human B-cell tumors based on PPI.

Galectin-1 sensitizes resting human T lymphocytes to Fas (CD95)-mediated cell death via mitochondrial hyperpolarization, budding, and fission

Galectins have emerged as a novel family of immunoregulatory proteins implicated in T cell homeostasis. Recent studies showed that galectin-1 (Gal-1) plays a key role in tumor-immune escape by killing antitumor effector T cells. Here we found that Gal-1 sensitizes human resting T cells to Fas (CD95)/caspase-8-mediated cell death. Furthermore, this protein triggers an apoptotic program involving an increase of mitochondrial membrane potential and participation of the ceramide pathway. In addition, Gal-1 induces mitochondrial coalescence, budding, and fission accompanied by an increase and/or redistribution of fission-associated molecules h-Fis and DRP-1. Importantly, these changes are detected in both resting and activated human T cells, suggesting that Gal-1-induced cell death might become an excellent model to analyze the morphogenetic changes of mitochondria during the execution of cell death. This is the first association among Gal-1, Fas/Fas ligand-mediated cell death, and the mitochondrial pathway, providing a rational basis for the immunoregulatory properties of Gal-1 in experimental models of chronic inflammation and cancer.

Galectin‐3 overexpression protects from cell damage and death by influencing mitochondrial homeostasis

Galectins are a family of proteins involved in several cell processes, including their survival and death. Galectin‐3 has in particular been described as an anti‐apoptotic molecule entangled with a number of subcellular activities including anoikis resistance. In this work we partially address the mechanisms underlying this activity pointing at two key factors in injury progression: the alteration of mitochondrial membrane potential and the formation of reactive oxygen species. Overexpression of galectin‐3 appears in fact to exert a protective effect towards both these events. On the basis of these data, we propose a reappraisal of the role of galectin‐3 as a regulator of mitochondrial homeostasis.

Transglutaminase overexpression sensitizes neuronal cell lines to apoptosis by increasing mitochondrial membrane potential and cellular oxidative stress

‘Tissue’ transglutaminase (tTG) selectively accumulates in cells undergoing apoptosis both in vivo and in vitro. Considering the central role played by mitochondria in apoptosis, we investigated the relationships existing amongst tTG expression, apoptosis and mitochondrial function. To this aim we studied the mechanisms of apoptosis in a neuronal cell line (SK‐N‐BE (2)) in which the tTG‐expression was driven by a constitutive promoter. Furthermore, a tet‐off inducible promoter was also used in 3T3 fibroblastic cells used as control. Both cell lines, when expressing tTG, appeared ‘sensitized’ to apoptosis. Strikingly, we found major differences in the morphological features of mitochondria among cell lines in the absence of apoptotic stimuli. In addition, these ultrastructural characteristics were associated with specific functional features: (i) constitutively hyperpolarized mitochondria and (ii) increased reactive oxygen intermediates production. Importantly, after mitochondrial‐mediated apoptosis by stauro‐ sporine, a rapid loss of mitochondrial membrane potential was found in tTG cells only. Taken together, these results seem to suggest that, via hyperpolarization, tTG might act as a ‘sensitizer’ towards apoptotic stimuli specifically targeted to mitochondria. These results could also be of pathogenetic relevance for those diseases that are characterized by increased tTG and apoptotic rate together with impaired mitochondrial function, e.g. in some neurodegenerative disease.

Peroxynitrite induces senescence and apoptosis of red blood cells through the activation of aspartyl and cysteinyl proteases

Changes in the oxidative status of erythrocytes can reduce cell lifetime, oxygen transport, and delivery capacity to peripheral tissues and have been associated with a plethora of human diseases. Among reactive oxygen and nitrogen species of importance in red blood cell (RBC) homeostasis, superoxide and nitric oxide radicals play a key role. In the present work, we evaluated subcellular effects induced by peroxynitrite, the product of the fast reaction between superoxide and nitric oxide. Peroxynitrite induced 1) oxidation of oxyhemoglobin to methemoglobin, 2) cytoskeleton rearrangement, 3) ultrastructural alterations, and 4) altered expression of band‐3 and decreased expression of glycophorin A. With respect to control cells, this occurred in a significantly higher percentage of human RBC (∼40%). The presence of antioxidants inhibited these modifications. Furthermore, besides these senescence‐associated changes, other important modifications, absent in control RBC and usually associated with apoptotic cell death, were detected in a small but significant subset of peroxynitrite‐exposed RBC (∼7%). Active protease cathepsin E and μ‐calpain increased; activation of caspase 2 and caspase 3 was detected; and phosphatidylserine externalization, an early marker of apoptosis, was observed. Conversely, inhibition of cathepsin E, μ‐calpain, as well as caspase 2 and 3 by specific inhibitors resulted in a significant impairment of erythrocyte “apoptosis.” Altogether, these results indicate that peroxynitrite, a milestone of redox‐mediated damage in human pathology, can hijack human RBC toward senescence and apoptosis by a mechanism involving both cysteinyl and aspartyl proteases.

Escherichia coli Cytotoxic Necrotizing Factor 1 (CNF1), a Toxin That Activates the Rho GTPase

Cytotoxic necrotizing factor 1 (CNF1), a 110-kDa protein toxin from pathogenic Escherichia coli induces actin reorganization into stress fibers and retraction fibers in human epithelial cultured cells allowing them to spread. CNF1 is acting in the cytosol since microinjection of the toxin into HEp-2 cells mimics the effects of the externally applied CNF1. Incubation in vitro of CNF1 with recombinant small GTPases induces a modification of Rho (but not of Rac, Cdc42, Ras, or Rab6) as demonstrated by a discrete increase in the apparent molecular weight of the molecule. Preincubation of cells with CNF1 impairs the cytotoxic effects of Clostridium difficile toxin B, which inactivates Rho but not those of Clostridium sordellii LT toxin, which inhibits Ras and Rac. As shown for Rho-GTP, CNF1 activates, in a time- and dose-dependent manner, a cytoskeleton-associated phosphatidylinositol 4-phosphate 5-kinase. However, neither the phosphatidylinositol 4,5-bisphosphate (PIP2) nor the phosphatidylinositol 3,4-bisphosphate (PI 3,4-P2) or 3,4,5-trisphosphate (PIP3) cellular content were found increased in CNF1 treated HEp-2 cells. Cellular effects of CNF1 were not blocked by LY294002, a stable inhibitor of the phosphoinositide 3-kinase. Incubation of HEp-2 cells with CNF1 induces relocalization of myosin 2 in stress fibers but not in retraction fibers. Altogether, our data indicate that CNF1 is a toxin that selectively activates the Rho GTP-binding protein, thus inducing contractility and cell spreading.

Redox state, cell death and autoimmune diseases: a gender perspective.

Autoimmune disorders, redox balance and gender differences are closely connected. In fact, activation, proliferation and death of cells of different histotype, including blood and vascular cells, are under control of oxidative balance and are key players in autoimmune disease pathogenesis and progression. However, cells from male and female appear characterized by a huge series of differences in terms of reactive oxygen species production and oxidative stress susceptibility. In this review, we briefly summarize the possible implications of the redox state in the onset and progression of autoimmune diseases in a gender perspective.

Cardiolipin‐enriched raft‐like microdomains are essential activating platforms for apoptotic signals on mitochondria

Cardiolipin (CL) has recently been shown to provide an anchor and an essential activating platform for caspase‐8 on mitochondria. We hypothesize that these platforms may correspond to “raft‐like” microdomains, which have demonstrated to be detectable on mitochondrial membrane of cells undergoing apoptosis. The role for CL in “raft‐like” microdomains could be to anchor caspase‐8 at contact sites between inner and outer membranes, facilitating its self‐activation, Bid cleavage and apoptosis execution. The role played by “raft‐like” microdomains in the apoptotic program could introduce a new task in the pathogenetic studies on human diseases associated with cardiolipin dismetabolism.