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Cosima T Baldari

Publications and source records attributed to Cosima T Baldari.

At least 19 recordsLinked to original sources
PubMed2007

p66Shc is involved in promoting HIF-1alpha accumulation and cell death in hypoxic T cells.

Hypoxia results in adaptationally appropriate alterations of gene expression through the activation of hypoxia-inducible factor (HIF)-1 to overcome any shortage of oxygen. Peripheral blood mononuclear cells may be exposed to low oxygen tensions for different times as they migrate between blood and various tissues. We and others have previously shown that T-cell adaptation to hypoxia is characterized by a modulation of cytokine expression and an inhibition of T-cell activation. We have recently demonstrated that the adaptor protein p66Shc negatively regulates T-cell activation and survival. We here show that hypoxia enhances HIF-1alpha accumulation and vascular endothelial growth factor production in T cells. Hypoxic T cells expressed high levels of p21(WAF1/CIP1), of the pro-apoptotic molecules BNIP3, a classic HIF target gene, and BAX, as well as low levels of the anti-apoptotic molecule BCLxl, associated with an induction of cell death. We found out that hypoxic T cells expressed p66Shc. Furthermore, using T-cell transfectants expressing p66Shc, as well as T cells derived from mice p66Shc-/-, we defined a role of p66Shc in T-cell responses to hypoxia. Of interest, hypoxic p66Shc-positive transfectants expressed higher level of HIF-1alpha than negative controls. Thus, p66Shc may play an important role in downstream hypoxic signaling, involving HIF-1alpha protein accumulation and cell death in T lymphocytes.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Anthrax toxins inhibit immune cell chemotaxis by perturbing chemokine receptor signalling.

Pathogenic strains of Bacillus anthracis produce two potent toxins, lethal toxin (LT), a metalloprotease that cleaves mitogen-activated protein kinase kinases, and oedema toxin (ET), a calcium/calmodulin-dependent adenylate cyclase. Emerging evidence indicates a role for both toxins in suppressing the initiation of both innate and adaptive immune responses, which are essential to keep the infection under control. Here we show that LT and ET inhibit chemotaxis of T-cells and macrophages by subverting signalling by both CXC and CC chemokine receptors. The data highlight a novel strategy of immunosuppression by B. anthracis based on inhibition of immune cell homing.

Antigens, Bacterial↗
PubMed2006

Expression in T-cells of the proapoptotic protein p66SHC is controlled by promoter demethylation.

p66Shc plays a key role in oxidative stress-induced apoptosis. p66Shc gene expression is tissue-specific and controlled by promoter methylation. In T-cells p66Shc expression is induced by a variety of apoptotic stimuli. We have addressed the mechanisms regulating p66Shc expression in T-cells. We show that the increase in p66Shc protein following stimulation with a Ca2+ ionophore results from enhanced gene expression, which is primarily dependent on DNA replication-independent promoter demethylation. Our data underline the role of CpG methylation in the control of p66Shc gene expression and provide evidence that Ca2+ signaling may lead to epigenetic modifications in nondividing cells.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Anthrax toxins: A paradigm of bacterial immune suppression.

Several species of microorganism have developed immune evasion and/or immunosuppression strategies. Bacillus anthracis secretes two toxins, edema toxin and lethal toxin, that enter the cytosol of almost every cell type, including the cells of the innate and adaptive immune systems, and subvert cell signaling. Edema toxin causes a consistent elevation of cyclic adenosine monophosphate, whereas lethal toxin cleaves most isoforms of mitogen-activated protein kinase kinases. In a concerted manner, these toxins alter major signaling pathways involved in the development of immune-cell effector functions, with the inhibition of bacterial clearance by phagocytes and of B. anthracis-specific responses. Thus, B. anthracis can invade the host, with ensuing massive bacteremia and toxemia. Here, we review the specific effects of B. anthracis on neutrophils, macrophages, dendritic cells, T- and B-lymphocytes.

Animals↗
PubMed2006

Conditional up-regulation of IL-2 production by p38 MAPK inactivation is mediated by increased Erk1/2 activity.

The p38 mitogen-activated protein kinase regulates many cellular processes in almost all eukaryotic cell types. In T cells, p38 was shown to regulate thymic development and cytokine production. Here, the role of p38 on interleukin-2 (IL-2) production by human peripheral blood CD4+ T cells was examined. When T cells were stimulated under weak stimulation conditions, pharmaceutical and molecular p38 inhibitors induced a dramatic increase of IL-2 production. In contrast, IL-2 levels were not affected significantly when strong stimulation was provided to T cells. The increase in IL-2 production, following p38 inhibition, was associated with a strong up-regulation of extracellular signal-regulated kinase (Erk)1/2 activity. Furthermore the Erk inhibitor U0126 was able to counteract the effect of p38 inhibition on IL-2 production, supporting the conclusion that p38 mediates its effect through Erk. These results suggest that the p38 kinase, through its ability to control Erk activation levels, acts as a gatekeeper, which prevents inappropriate IL-2 production. Also, the finding that p38 acts in a strength-of-stimulation-dependent way provides an explanation for previously reported, contradictory results regarding the role of this kinase in IL-2 expression.

CD4-Positive T-Lymphocytes↗
PubMed2006

Cytoskeleton rearrangement induced by tetraspanin engagement modulates the activation of T and NK cells.

The hepatitis C virus (HCV) binds to human cells through the interaction of its envelope glycoprotein E2 with the tetraspanin CD81. We have previously reported that engagement of CD81 has opposite effects on T and NK cell function, as it enhances T cell receptor-mediated T cell activation and inhibits CD16- or IL-12-mediated NK cell activation. We further investigated this dichotomy and found that another tetraspanin, CD82, induces the same opposing effects on human primary T and NK cells. Activation by other unrelated stimuli such as NKG2D- and beta-1 integrin is also reduced by CD81 ligation on NK cells. CD81 engagement by monoclonal antibody or HCV-E2 enhances zeta and Erk phosphorylation in T cells and reduces them in NK cells, reflecting the opposite functional outcomes. CD81 engagement induces dramatic morphological changes and local F-actin accumulation in both NK and T cells, indicating rearrangement of the actin cytoskeleton. Pharmacological inhibition of actin polymerization reduces T cell activation, whereas it greatly enhances NK cell activation. Importantly, treatment with actin blockers abolishes the inhibitory effect of CD81 ligation on NK cells. We propose that tetraspanin engagement leads to comparable cytoskeleton reorganization in T and NK cells, which in turn results in opposite functional outcomes.

Actins↗
PubMed2006

Simvastatin inhibits the MHC class II pathway of antigen presentation by impairing Ras superfamily GTPases.

Statins are widely used hypocholesterolemic drugs that inhibit 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, a rate-limiting enzyme of the mevalonate pathway whose biosynthetic endproduct is cholesterol. As a result of this activity, statins may perturb the composition of cell membranes, resulting in lipid raft disruption. Furthermore, by inhibiting protein prenylation, a process also dependent on mevalonate, statins block membrane targeting and activity of small GTPases. Antigen uptake, processing and presentation involve the interplay of Rab and Rho family GTPases. Furthermore, lipid rafts have been implicated both in antigen internalization by the BCR and in MHC class II clustering at the immunological synapse. Here we have addressed the effects of simvastatin on antigen processing and presentation by human B cells and dendritic cells. The results show that simvastatin potently suppresses tetanus toxoid processing and presentation to CD4+ T cells by HLA-DR by inhibiting protein antigen uptake through both receptor-mediated endocytosis and macropinocytosis. This effect can be largely accounted for by defective prenylation of Rho and Rab GTPases in the absence of any measurable perturbation of lipid rafts. In addition, simvastatin was found to preferentially affect the invariant chain-dependent MHC class II pathway, thereby identifying this route of antigen processing and presentation as a selective target of statins.

Anticholesteremic Agents↗
PubMed2005

Distinct spatial and temporal distribution of ZAP70 and Lck following stimulation of interferon and T-cell receptors.

T-cell receptor (TCR) stimulation results in the recruitment and activation of the proteins ZAP70 and Lck. These two proteins have been implicated in signalling derived from interferon receptors, although their precise role in this independent pathway has not been determined fully. These observations raise a fundamental question of how a given protein in a cell can be involved in more than one signalling pathway, yet each pathway is able to produce a highly specific downstream response to its own stimulant. To maintain exclusivity of response, each pathway must isolate its component molecules chemically, spatially or dynamically from other prevailing pathways. To address this question, the proteins ZAP70 and Lck were investigated following stimulation of the interferon-alpha receptor and the TCR in T cells by two different extracellular stimulants: interferon-alpha and the anti-CD3 antibody, OKT3, respectively. We first demonstrate that ZAP70 plays a pivotal role in interferon-stimulated MAPK activation, and that the tyrosine residue at position 319 of ZAP70 is important for interferon-stimulated ERK activation. Translocation of both ZAP70 and Lck to the nucleus following interferon receptor stimulation is demonstrated for the first time. Fluorescence resonance energy transfer microscopy revealed a high degree of spatial localization of the ZAP70/Lck complex within the cell following IFNalpha stimulation, in contrast to a diffuse presence following the application of OKT3. The difference in the spatio-temporal localization of these proteins following stimulation may eliminate signal crosstalk, and could explain the differentiation of the specific downstream responses of these pathways.

Active Transport, Cell Nucleus↗
PubMed2005

Defective Vav expression and impaired F-actin reorganization in a subset of patients with common variable immunodeficiency characterized by T-cell defects.

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T-cell function (T-CVID). We have previously identified a subset of patients with T-CVID characterized by defective T-cell receptor (TCR)-dependent protein tyrosine phosphorylation. In these patients, ZAP-70 fails to be recruited to the TCR as the result of impaired CD3zeta phosphorylation, which is, however, not dependent on defective Lck expression or activity. Here we show that neither Fyn nor CD45 is affected in these patients. On the other hand, T-CVID T cells show dramatic defects in the Vav/Rac pathway controlling F-actin dynamics. A significant deficiency in Vav protein was indeed observed; in 3 of 4 patients with T-CVID, it was associated with reduced VAV1 mRNA levels. The impairment in Vav expression correlated with defective F-actin reorganization in response to TCR/CD28 co-engagement. Furthermore, TCR/CD28-dependent up-regulation of lipid rafts at the cell surface, which requires F-actin dynamics, was impaired in these patients. The actin cytoskeleton defect could be reversed by reconstitution of Vav1 expression in the patients' T cells. Results demonstrate an essential role of Vav in human T cells and strongly suggest Vav insufficiency in T-CVID.

Actins↗
PubMed2005

Cooperation and selectivity of the two Grb2 binding sites of p52Shc in T-cell antigen receptor signaling to Ras family GTPases and Myc-dependent survival.

Shc proteins participate in a variety of processes regulating cell proliferation, survival and apoptosis. The two ubiquitously expressed isoforms, p52Shc/p46Shc, couple tyrosine kinase receptors to Ras by recruiting Grb2/Sos complexes to a membrane-proximal localization. Tyrosine residues 239/240 and 317 become phosphorylated following receptor engagement and, as such, form two Grb2 binding sites, which have been proposed to be differentially coupled to Myc-dependent survival and to fos-dependent proliferation, respectively. Here, we have addressed the individual function of YY239/240 and Y317 in T-cell antigen receptor (TCR) signaling. We show that p52Shc is phosphorylated on both YY239/240 and Y317 following TCR engagement. Mutation of either YY239/240 or Y317 results in impaired interaction with Grb2 and inhibition of Ras/MAP kinase activation and CD69 induction, supporting a role for both Grb2 binding sites in this function. Substitution of either YY239/240 or Y317 also results in a defective activation of Rac and the coupled stress kinases JNK and p38. Furthermore, mutation of Y317 or, to a larger extent, of YY239/240, results in increased activation-induced cell death, which in cells expressing the FF239/240 mutant is accompanied by impaired TCR-dependent c-myc transcription. The data underline a pleiotropic and nonredundant role of Shc, mediated by both YY239/240 and Y317, in T-cell activation and survival.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Anthrax toxins suppress T lymphocyte activation by disrupting antigen receptor signaling.

Anthrax is an infection caused by pathogenic strains of Bacillus anthracis, which secretes a three-component toxic complex consisting of protective antigen (PA), edema factor (EF), and lethal factor (LF). PA forms binary complexes with either LF or EF and mediates their entry into host cells. Although the initial phases of bacterial growth occur in the lymph node, the host fails to mount an effective immune response. Here, we show that LT and ET are potent suppressors of human T cell activation and proliferation triggered through the antigen receptor. Both LT and ET inhibit the mitogen-activated protein and stress kinase pathways, and both toxins inhibit activation of NFAT and AP-1, two transcription factors essential for cytokine gene expression. These data identify a novel strategy of immune evasion by B. anthracis, based on both effector subunits of the toxic complex, and targeted to a key cellular component of adaptive immunity.

Anthrax↗
PubMed2005

Simvastatin inhibits T-cell activation by selectively impairing the function of Ras superfamily GTPases.

Statins are widely used hypocholesterolemic drugs that inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme of the mevalonate pathway whose biosynthetic end product is cholesterol. In addition to lowering circulating cholesterol, statins perturb the composition of cell membranes, resulting in disruption of lipid rafts, which function as signaling platforms in immunoreceptor signaling. Furthermore, by inhibiting protein prenylation, a process also dependent on mevalonate, statins block membrane targeting and hence activity of small GTPases, which control multiple pathways triggered by these receptors. T-cell activation is crucially dependent on Ras, Rho and Rab GTPases. Furthermore TCR signaling is orchestrated at lipid rafts, identifying T-cells as potential cellular targets of statins. Here we report that simvastatin suppresses T-cell activation and proliferation as the result of its capacity to inhibit HMG-CoA reductase. T-cell treatment with simvastatin does not affect intracellular cholesterol levels or raft integrity nor, accordingly, the initial tyrosine phosphorylation-dependent cascade. Conversely, inhibition of protein prenylation by simvastatin results in a dramatic impairment in the pathways regulated by small GTPases, including the Ras/MAP kinase pathway, the Rac/stress kinase pathway, and the Rab-dependent pathway of receptor endocytosis. The results identify Ras superfamily GTPases as strategic molecular targets in T-cell immunosuppression by statins.

Endocytosis↗
PubMed2005

Immune subversion by Helicobacter pylori.

To maintain prolonged colonization of the human gastric mucosa, Helicobacter pylori must avoid both innate and adaptive immune responses. During its long coexistence with humans, it has evolved complex strategies to maintain a mild inflammation of the gastric epithelium while limiting the extent of immune effector activity. Severe disease, associated with bacterial colonization, might reflect loss of this control. Several mechanisms and the bacterial factors involved in immune subversion have, in recent years, been elucidated, thus opening the possibility of a better understanding of the pathogenicity of this microorganism.

Antigen Presentation↗
PubMed2004

Nonsteroidal anti-inflammatory drugs inhibit a Fyn-dependent pathway coupled to Rac and stress kinase activation in TCR signaling.

In addition to their anti-inflammatory properties, nonsteroidal anti-inflammatory drugs (NSAIDs) harbor immunosuppressive activities related to their capacity both to inhibit cyclooxygenases (COXs) and to act as peroxisome proliferator-activated receptor (PPAR) ligands. We have previously shown that the stress-activated kinase p38 is a selective target of NSAIDs in T cells. Here we have investigated the effect of NSAIDs on the signaling pathway triggered by the T-cell antigen receptor (TCR) and leading to stress kinase activation. The results show that nonselective and COX-1-selective NSAIDs also block activation of the stress kinase c-Jun N-terminal kinase (JNK) and that prostaglandin-E2 (PGE2) reverses this block and enhances TCR-dependent JNK activation. Analysis of the activation state of the components upstream of p38 and JNK showed that NSAIDs inhibit the serine-threonine kinase p21-activated protein kinase 1 (Pak1) and the small guanosine 5'-triphosphatase (GTPase) Rac, as well as the Rac-specific guanine nucleotide exchanger, Vav. Furthermore, activation of Fyn, which controls Vav phosphorylation, is inhibited by NSAIDs, whereas activation of lymphocyte-specific protein tyrosine kinase (Lck) and of the Lck-dependent tyrosine kinase cascade is unaffected. Accordingly, constitutively active Fyn reverses the NSAID-dependent stress kinase inhibition. The data identify COX-1 as an important early modulator of TCR signaling and highlight a TCR proximal pathway selectively coupling the TCR to stress kinase activation.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2004

Inhibition of ShcA isoforms p46/p52Shc enhances HIV-1 replication in CD4+ T-lymphocytes.

HIV-1 infection decreases the number of CD4(+) T-cells, and apoptosis has been suggested among the mechanisms. Proteins of the Shc family are involved in a complex network of signal transduction, differentiation, and apoptotic response to stress in many different cell types. Out of three homologous gene products (ShcA, ShcB, and ShcC), only two splicing variants of ShA are expressed in T-lymphocytes, namely p46Shc and p52Shc. In the present study, we report that inhibition of p46Shc and p52Shc by a dominant negative mutant enhances the yield of HIV-1 particles production without affecting efficiency of viral gene expression in CD4(+)-infected cells. The increase in HIV-1 replication in cells expressing the dominant negative mutant isoform ultimately correlates with a decrease in the percentage of cells entering apoptosis. The data presented suggest that ShcA proteins can play a role in committing CD4(+) T-cells to apoptosis, as a response to HIV-1 infection.

Adaptor Proteins, Signal Transducing↗
PubMed2004

The thrombin peptide, TP508, enhances cytokine release and activates signaling events.

The thrombin peptide, TP508, accelerates tissue repair and initiates a cascade of cellular events. We have previously shown that alpha-thrombin induces cytokine expression in human mononuclear cells. We, therefore, investigated the possibility that TP508 might activate cytokine production and intracellular signaling pathways associated with cytokine activation. Our results show that TP508 induces cytokine expression in human mononuclear cells. TP508 treatment enhances extracellular signal-regulated kinase (Erk1/2) activities in U937 cells, as well as Erk1/2 and p38 activation in Jurkat T cells. These data support the hypothesis that TP508 may accelerate tissue repair through the activation of the inflammatory response.

Cell Survival↗
PubMed2004

p66SHC promotes apoptosis and antagonizes mitogenic signaling in T cells.

Of the three Shc isoforms, p66Shc is responsible for fine-tuning p52/p46Shc signaling to Ras and has been implicated in apoptotic responses to oxidative stress. Here we show that human peripheral blood lymphocytes and mouse thymocytes and splenic T cells acquire the capacity to express p66Shc in response to apoptogenic stimulation. Using a panel of T-cell transfectants and p66Shc(-/-) T cells, we show that p66Shc expression results in increased susceptibility to apoptogenic stimuli, which depends on Ser36 phosphorylation and correlates with an altered balance in apoptosis-regulating gene expression. Furthermore, p66Shc blunts mitogenic responses to T-cell receptor engagement, at least in part by transdominant inhibition of p52Shc signaling to Ras/mitogen-activated protein kinases, in an S36-dependent manner. The data highlight a novel interplay between p66Shc and p52Shc in the control of T-cell fate.

Adaptor Proteins, Signal Transducing↗