1,720,992 research outputs found
The Bcl-2 family as a rational target for the treatment of B-cell chronic lymphocytic leukaemia
No full textB-cell chronic lymphocytic leukaemia (B-CLL) is the most common lymphoid malignancy in the Western world, characterized by clonal growth and accumulation of monoclonal CD5+ B-cells in peripheral blood, bone marrow and peripheral lymphoid organs. Although the clinical course in B-CLL patients is highly variable, the most conserved feature is the prolonged survival of malignant B-cells, which has been associated to defects in the apoptotic machinery. The apoptosis defects are mainly determined by a defective balance among pro- and anti-apoptotic members of the Bcl-2 family, often related to resistance of CLL B-cells to chemotherapy. Purine nucleoside analogs or alkylating agents, alone or in combination, are the first-line treatment for B-CLL patients. Alternative, more specifically tailored therapeutics have been developed in recent years, including humanized monoclonal antibodies and kinase inhibitors. Here we shall review the drugs which are commonly used or are currently being assessed in clinical trials on B-CLL patients, their chemical structure, mechanisms of action, pharmacological properties, molecular targets, clinical efficacy and side effects, with a focus on drugs designed to promote apoptosis of malignant B-cells by targeting the Bcl-2 family
Abnormalities in chemokine receptor recycling in chronic lymphocytic leukemia
No full textIn addition to their modulation through de novo expression and degradation, surface levels of chemokine receptors are tuned by their ligand-dependent recycling to the plasma membrane, which ensures that engaged receptors become rapidly available for further rounds of signaling. Dysregulation of this process contributes to the pathogenesis of chronic lymphocytic leukemia (CLL) by enhancing surface expression of chemokine receptors, thereby favoring leukemic cell accumulation in the protective niche of lymphoid organs. In this review, we summarize our current understanding of the process of chemokine receptor recycling, focusing on the impact of its dysregulation in CLL
The Immunological Synapse: An Emerging Target for Immune Evasion by Bacterial Pathogens
Full text linkSimilar to other pathogens, bacteria have developed during their evolution a variety of mechanisms to overcome both innate and acquired immunity, accounting for their ability to cause disease or chronic infections. The mechanisms exploited for this critical function act by targeting conserved structures or pathways that regulate the host immune response. A strategic potential target is the immunological synapse (IS), a highly specialized structure that forms at the interface between antigen presenting cells (APC) and T lymphocytes and is required for the establishment of an effective T cell response to the infectious agent and for the development of long-lasting T cell memory. While a variety of bacterial pathogens are known to impair or subvert cellular processes essential for antigen processing and presentation, on which IS assembly depends, it is only recently that the possibility that IS may be a direct target of bacterial virulence factors has been considered. Emerging evidence strongly supports this notion, highlighting IS targeting as a powerful, novel means of immune evasion by bacterial pathogens. In this review we will present a brief overview of the mechanisms used by bacteria to affect IS assembly by targeting APCs. We will then summarize what has emerged from the current handful of studies that have addressed the direct impact of bacterial virulence factors on IS assembly in T cells and, based on the strategic cellular processes targeted by these factors in other cell types, highlight potential IS-related vulnerabilities that could be exploited by these pathogens to evade T cell mediated immunity
Nature vs. Nurture: The Two Opposing Behaviors of Cytotoxic T Lymphocytes in the Tumor Microenvironment
Full text linkSimilar to Janus, the two-faced god of Roman mythology, the tumor microenvironment operates two opposing and often conflicting activities, on the one hand fighting against tumor cells, while on the other hand, favoring their proliferation, survival and migration to other sites to establish metastases. In the tumor microenvironment, cytotoxic T cells-the specialized tumor-cell killers-also show this dual nature, operating their tumor-cell directed killing activities until they become exhausted and dysfunctional, a process promoted by cancer cells themselves. Here, we discuss the opposing activities of immune cells populating the tumor microenvironment in both cancer progression and anti-cancer responses, with a focus on cytotoxic T cells and on the molecular mechanisms responsible for the efficient suppression of their killing activities as a paradigm of the power of cancer cells to shape the microenvironment for their own survival and expansion
Negative regulation of immunoreceptor signaling by protein adapters: Shc proteins join the club
No full textProtein adapters couple surface receptors to multiple intracellular signaling modules by acting as scaffolds for the assembly of multimolecular complexes responsible for the coordination and amplification of signals. Through the spatiotemporally controlled recruitment of mediators with opposite activities (e.g. protein tyrosine kinases and phosphatases), adapters are implicated not only in signal initiation and propagation, but also in feedback loops for signal extinction. Moreover, adaptors specialized in preventing or dampening signaling have been more recently discovered. Here we shall present of brief overview of the principal adaptors which act as negative regulators of TCR and BCR signaling, with a focus of the mechanisms underlying this function. We shall then discuss our recent findings implicating p66Shc and Rai, two members of the Shc family of cytosolic protein adapters, in the negative control of antigen receptor signaling, and their role as gatekeepers of autoimmunity and leukemia. © 2010 Federation of European Biochemical Societies
Glycerophosphoinositol-4-phosphate enhances SDF-1?-stimulated T-cell chemotaxis through PTK-dependent activation of Vav
No full textGlycerophosphoinositols (GPIs) are water-soluble phosphoinosite metabolites produced by all cell types, whose levels increase in response to a variety of extracellular stimuli, and are particularly high in Ras-transformed cells. GPIs are released to the extracellular space, wherefrom they can be taken up by other cells through a specific transporter. Exogenous GPIs affect a plethora of cellular functions. Among these compounds the most active is GroPIns4P, which affects cAMP levels and PKA-dependent functions through the inhibition of heterotrimeric Gs proteins. GroPIns4P has also recently been found to promote actin cytoskeleton reorganization by inducing Rho and Rac activation through an as yet unidentified mechanism. Here we have assessed the potential effects of GroPIns4P on T-cells. We found that GroPIns4P enhances CXCR4-dependent chemotaxis. This activity results from the capacity of GroPIns4P to activate the Rho GTPase exchange factor, Vav, through an Lck-dependent pathway which also results in activation of the stress kinases JNK and p38. GroPIns4P was also found to activate with a delayed kinetics the Lck-dependent activation of ZAP-70, Shc and Erk1/2. The activities of GroPIns4P were found to be dependent on its capacity to inhibit cAMP production and PKA activation. Collectively, the data provide the first evidence of a role of glycerophosphoinositols as modulators of T-cell signaling and establish a mechanistic basis for the effects of this phosphoinositide derivative on F-actin dynamics
Expression in T-cells of the proapoptotic protein p66SHC is controlled by promoter demethylation.
No full textp66Shc 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.
Ó 2006 Elsevier Inc. All rights reserved
Impaired T(H)2 response in patients with Vav1-deficient common variable immunodeficiency with T-cell defects
No full textVav1 haploinsufficiency in a common variable immunodeficiency patient with defective T-cell function.
No full textCommon 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 previously identified a subset of T-CVID patients characterized by defective expression of Vav1, a guanine nucleotide exchanger which couples the T-cell antigen receptor to reorganization of the actin cytoskeleton. Here we have addressed the possibility that an intrinsic defect in the Vav1 gene might underlie the reduction in Vav protein observed in T cells from these patients. We report the identification in one T-CVID patient of a heterozygous deletion in Vav1. The gene deletion, spanning exons 2-27, accounts for the reduction in Vav1 mRNA and protein in T cells from this patient. The disease-related pedigree of this patient suggests a de novo origin of the Vav1 deletion. The findings highlights Vav1 as an autosomal dominant disease gene associated with CVID with defective T-cell function
Expression of the p66Shc protein adaptor is regulated by the activator of transcription STAT4 in normal and chronic lymphocytic leukemia B cells
Full text linkp66Shc attenuates mitogenic, prosurvival and chemotactic signaling and promotes apoptosis in lymphocytes. Consistently, p66Shc deficiency contributes to the survival and trafficking abnormalities of chronic lymphocytic leukemia (CLL) B cells. The mechanism of p66shc silencing in CLL B cells is methylation-independent, at variance with other cancer cell types. Here we identify STAT4 as a novel transcriptional regulator of p66Shc in B cells. Chromatin immunoprecipitation and reporter gene assays showed that STAT4 binds to and activates the p66shc promoter. Silencing or overexpression of STAT4 resulted in a co-modulation of p66Shc. IL-12-dependent STAT4 activation caused a coordinate increase in STAT4 and p66Shc expression, which correlated with enhanced B cell apoptosis. Treatment with the STAT4 inhibitor lisofylline reverted partly this effect, suggesting that STAT4 phosphorylation is not essential for but enhances p66shc transcription. Additionally, we demonstrate that CLL B lymphocytes have a STAT4 expression defect which partly accounts for their p66Shc deficiency, as supported by reconstitution experiments. Finally, we show that p66Shc participates in a positive feedback loop to promote STAT4 expression. These results provide new insights into the mechanism of p66Shc expression in B cells and its defect in CLL, identifying the STAT4/IL-12 pathway as a potential therapeutic target in this neoplasia
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