Katia Fettucciari

Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells

Notch signaling is involved in tumorigenesis, but its role in B-chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor-kappa B (NF-kappaB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the gamma-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-kappaB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.

Group B Streptococcus Induces Apoptosis in Macrophages

Group B Streptococcus (GBS) is a pathogen that has developed some strategies to resist host immune defenses. Because phagocytic killing is an important pathogenetic mechanism for bacteria, we investigated whether GBS induces apoptosis in murine macrophages. GBS type III strain COH31 r/s (GBS-III) first causes a defect in cell membrane permeability, then at 24 h, apoptosis. Apoptosis was confirmed by several techniques based on morphological changes and DNA fragmentation. Cytochalasin D does not affect apoptosis, suggesting that GBS-III needs not be within the macrophage cytoplasm to promote apoptosis. Inhibition of host protein synthesis prevents apoptosis, whereas inhibition of caspase-1 or -3, does not. Therefore, GBS can trigger an apoptotic pathway independent of caspase-1 and -3, but dependent on protein synthesis. Inhibition of apoptosis by EGTA and PMA, and enhancement of apoptosis by calphostin C and GF109203X suggests that an increase in the cytosolic calcium level and protein kinase C activity status are important in GBS-induced apoptosis. Neither alteration of plasma membrane permeability nor apoptosis were induced by GBS grown in conditions impeding hemolysin expression or when we used dipalmitoylphosphatidylcholine, which inhibited GBS β-hemolytic activity, suggesting that GBS β-hemolysin could be involved in apoptosis. β-Hemolysin, by causing membrane permeability defects, could allow calcium influx, which initiates macrophage apoptosis. GBS also induces apoptosis in human monocytes but not in tumor lines demonstrating the specificity of its activity. This study suggests that induction of macrophage apoptosis by GBS is a novel strategy to overcome host immune defenses.

Group B Streptococcus Induces Macrophage Apoptosis by Calpain Activation

Group B Streptococcus (GBS) has developed several strategies to evade immune defenses. We show that GBS induces macrophage (Mφ) membrane permeability defects and apoptosis, prevented by inhibition of calcium influx but not caspases. We analyze the molecular mechanisms of GBS-induced murine Mφ apoptosis. GBS causes a massive intracellular calcium increase, strictly correlated to membrane permeability defects and apoptosis onset. Calcium increase was associated with activation of calcium-dependent protease calpain, demonstrated by casein zymography, α-spectrin cleavage to a calpain-specific fragment, fluorogenic calpain-substrate cleavage, and inhibition of these proteolyses by calpain inhibitors targeting the calcium-binding, 3-(4-Iodophenyl)-2-mercapto-(Z)-2-propenoic acid, or active site (four different inhibitors), by calpain small-interfering-RNA (siRNA) and EGTA. GBS-induced Mφ apoptosis was inhibited by all micro- and m-calpain inhibitors used and m-calpain siRNA, but not 3-(5-Fluoro-3-indolyl)-2-mercapto-(Z)-2-propenoic acid (micro-calpain inhibitor) and micro-calpain siRNA indicating that m-calpain plays a central role in apoptosis. Calpain activation is followed by Bax and Bid cleavage, cytochrome c, apoptosis-inducing factor, and endonuclease G release from mitochondria. In GBS-induced apoptosis, cytochrome c did not induce caspase-3 and -7 activation because they and APAF-1 were degraded by calpains. Therefore, apoptosis-inducing factor and endonuclease G seem the main mediators of the calpain-dependent but caspase-independent pathway of GBS-induced apoptosis. Proapoptotic mediator degradations do not occur with nonhemolytic GBS, not inducing Mφ apoptosis. Apoptosis was reduced by Bax siRNA and Bid siRNA suggesting Bax and Bid degradation is apoptosis correlated. This signaling pathway, different from that of most pathogens, could represent a GBS strategy to evade immune defenses.

Eicosapentaenoic Acid Demethylates a Single CpG That Mediates Expression of Tumor Suppressor CCAAT/Enhancer-binding Protein δ in U937 Leukemia Cells

Polyunsaturated fatty acids (PUFAs) inhibit proliferation and induce differentiation in leukemia cells. To investigate the molecular mechanisms whereby fatty acids affect these processes, U937 leukemia cells were conditioned with stearic, oleic, linolenic, α-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids. PUFAs affected proliferation; eicosapentaenoic acid (EPA) was the most potent on cell cycle progression. EPA enhanced the expression of the myeloid lineage-specific transcription factors CCAAT/enhancer-binding proteins (C/EBPβ and C/EBPδ), PU.1, and c-Jun, resulting in increased expression of the monocyte lineage-specific target gene, the macrophage colony-stimulating factor receptor. Indeed, it is known that PU.1 and C/EBPs interact with their consensus sequences on a small DNA fragment of macrophage colony-stimulating factor receptor promoter, which is a determinant for expression. We demonstrated that C/EBPβ and C/EBPδ bind the same response element as a heterodimer. We focused on the enhanced expression of C/EBPδ, which has been reported to be a tumor suppressor gene silenced by promoter hypermethylation in U937 cells. After U937 conditioning with EPA and bisulfite sequencing of the −370/−20 CpG island on the C/EBPδ promoter region, we found a site-specific CpG demethylation that was a determinant for the binding activity of Sp1, an essential factor for C/EBPδ gene basal expression. Our results provide evidence for a new role of PUFAs in the regulation of gene expression. Moreover, we demonstrated for the first time that re-expression of the tumor suppressor C/EBPδ is controlled by the methylation state of a site-specific CpG dinucleotide.

Novel targets for endoplasmic reticulum stress-induced apoptosis in B-CLL

A better understanding of apoptotic signaling in B-chronic lymphocytic leukemia (B-CLL) cells may help to define new therapeutic strategies. This study investigated endoplasmic reticulum (ER) stress signaling in spontaneous apoptosis of B-CLL cells and whether manipulating ER stress increases their apoptosis. Results show that a novel ER stress-triggered caspase cascade, initiated by caspase-4 and involving caspase-8 and -3, plays an important role in spontaneous B-CLL cell apoptosis. ER stress-induced apoptosis in B-CLL cells also involves CHOP/GADD153 up-regulation, increased JNK1/2 phosphorylation, and caspase-8-mediated cleavage of Bap31 to Bap20, known to propagate apoptotic signals from ER to mitochondria. In ex vivo B-CLL cells, some apoptotic events associated with mitochondrial pathway also occur, including mitochondrial cytochrome c release and caspase-9 processing. However, pharmacologic inhibition studies show that caspase-9 plays a minor role in B-CLL cell apoptosis. ER stress also triggers survival signals in B-CLL cells by increasing BiP/GRP78 expression. Manipulating ER signaling by siRNA down-regulation of BiP/GRP78 or treating B-CLL cells with 2 well-known ER stress-inducers, tunicamycin and thapsigargin, increases their apoptosis. Overall, our findings show that ER triggers an essential pathway for B-CLL cell apoptosis and suggest that genetic and pharmacologic manipulation of ER signaling could represent an important therapeutic strategy.

GITR-GITRL System, A Novel Player in Shock and Inflammation

Glucocorticoid-induced TNFR-Related (GITR) protein is a member of the tumor necrosis factor receptor superfamily that modulates acquired and natural immune response. It is expressed in several cells and tissues, including T cells, natural killer cells, and, at lower levels, in cells of innate immunity. GITR is activated by its ligand, GITRL, mainly expressed on antigen presenting and endothelial cells. Recent evidence suggests that the GITR/GITRL system participates in the development of inflammatory responses, including shock, either due to early response of neutrophils and macrophages, or together with autoimmune/allergic pathogenesis. The pro-inflammatory role of the GITR/GITRL system is due to: 1) modulation of the extravasation process, 2) activation of innate immunity cells, 3) activation of effector T cells also favored by partial inhibition of suppressor T cells and modulation of dendritic function. This review summarizes the in vivo role of the GITR/GITRL system in inflammation and shock, explaining the mechanisms responsible for their effects, considering the interplay among the different cells of the immune system and transduction pathways activated by GITR and GITRL triggering. The hidden aspects about GITR/GITRL function, crucial for treatment planning of inflammatory diseases and shock by modulation of this system is stressed.

A novel mechanism of methylglyoxal cytotoxicity in prostate cancer cells

Methylglyoxal is one of the most powerful glycating agents of proteins and other important cellular components and has been shown to be toxic to cultured cells. Methylglyoxal cytotoxicity appears to occur through cell-cycle arrest but, more often, through induction of apoptosis. In this study we examined whether, and through which molecular mechanism, methylglyoxal affects the growth of poorly aggressive LNCaP and invasive PC3 human prostate cancer cells, where its role has not been exhaustively investigated yet. We demonstrated that methylglyoxal is cytotoxic on LNCaP and PC3 and that such cytotoxicity occurs not via cell proliferation but apoptosis control. Moreover, we demonstrated that methylglyoxal cytotoxicity, potentiated by the silencing of its major scavenging enzyme Glyoxalase I, occurred via different apoptotic responses in LNCaP and PC3 cells that also showed a different susceptibility to this metabolite. Finally, we showed that the observed methylglyoxal apoptogenic role involved different molecular pathways, specifically mediated by methylglyoxal or methylglyoxal-derived argpyrimidine intracellular accumulation and NF-kB signaling-pathway. In particular, in LNCaP cells, methylglyoxal, through the accumulation of argpyrimidine, desensitized the key cell survival NF-kB signaling pathway, which was consistent with the modulation of NF-kB-regulated genes, triggering a mitochondrial apoptotic pathway. The results suggest that this physiological compound merits investigation as a potential chemo-preventive/-therapeutic agent, in differently aggressive prostate cancers.

Notch1 modulates mesenchymal stem cells mediated regulatory T-cell induction.

Notch1 signaling is involved in regulatory T (Treg)‐cell differentiation. We previously demonstrated that, when cocultured with CD3+ cells, mesenchymal stem cells (MSCs) induced a T‐cell population with a regulatory phenotype. Here, we investigated the molecular mechanism underlying MSC induction of human Treg cells. We show that the Notch1 pathway is activated in CD4+ T cells cocultured with MSCs. Inhibition of Notch1 signaling through GSI‐I or the Notch1 neutralizing antibody reduced expression of HES1 (the Notch1 downstream target) and the percentage of MSC‐induced CD4+CD25highFOXP3+ cells in vitro. Moreover, we demonstrate that FOXP3 is a downstream target of Notch signaling in human cells. No crosstalk between Notch1 and TGF‐β signaling pathways was observed in our experimental system. Together, these findings indicate that activation of the Notch1 pathway is a novel mechanism in the human Treg‐cell induction mediated by MSCs.

Modulation of Pro- and Antiapoptotic Molecules in Double-Positive (CD4+CD8+) Thymocytes following Dexamethasone Treatment

Glucocorticoids play a role in regulation of T lymphocytes homeostasis and development. In particular, glucocorticoid treatment induces massive apoptosis of CD4+CD8+ double-positive (DP) thymocytes. This effect is due to many mechanisms, mainly driven by modulation of gene transcription. To find out which genes are modulated, we analyzed DP thymocytes treated for 3 h with dexamethasone (a synthetic glucocorticoid) by global gene expression profiling. Results indicate modulation of 163 genes, also confirmed by either RNase protection assay or real-time polymerase chain reaction. In particular, dexamethasone caused down-regulation of genes promoting DP thymocyte survival (e.g., Notch1, suppressor of cytokine signaling 1, and inhibitor of DNA binding 3) or modulation of genes activating cell death through the ceramide pathway (UDP-glucose ceramide glucosyltransferase, sphingosine 1-phosphate phosphatase, dihydroceramide desaturase, isoform 1, and G protein-coupled receptor 65) or through the mitochondrial machinery. Among the latter, there are Bcl-2 family members (Bim, Bfl-1, Bcl-xL, and Bcl-xβ), genes involved in the control of redox status (thioredoxin reductase, thioredoxin reductase inhibitor, and NADP+-dependent isocitrate dehydrogenase) and genes belonging to Tis11 family that are involved in mRNA stability. Our study suggests that dexamethasone treatment of DP thymocytes modulates several genes belonging to apoptosis-related systems that can contribute to their apoptosis.

Role of glyoxalase I in the proliferation and apoptosis control of human LNCaP and PC3 prostate cancer cells

Glyoxalase I (GLOI) detoxifies reactive dicarbonyls, as methylglyoxal (MG) that, directly or through the formation of MG‐derived adducts, is a growth inhibitor and apoptosis inducer. GLOI has been considered a general marker of cell proliferation, but a direct link between the two has yet to be demonstrated. The aim of the present work was to clarify whether GLOI was involved in the proliferation control of LNCaP and PC3 human prostate cancer cells or might play a different role in the growth regulation of these cells.