Biomedical subjects

Benjamin M Chain

Publications and source records attributed to Benjamin M Chain.

28 records · Page 2Linked to original sources

PubMed2003

Staurosporine induces rapid homotypic intercellular adhesion of U937 cells via multiple kinase activation.

1. Staurosporine is a broad-specificity kinase inhibitor, which has acted as lead compound for the development of some novel cytotoxic compounds for treatment of cancer. This study investigates the unexpected observation that staurosporine can also induce homotypic cellular aggregation. 2. In this study, staurosporine is shown to activate rapid homotypic aggregation of U937 cells, at concentrations below those required to induce cell death. This activity is a particular feature of staurosporine, and is not shared by a number of other kinase inhibitors. The proaggregating activity of staurosporine is inhibited by deoxyglucose, cytochalasin B and colchicine. Staurosporine-induced aggregation can be distinguished from that induced by the phorbol 12-myristate 13-acetate by faster kinetics and insensitivity to cycloheximide. Staurosporine induces translocation of conventional and novel, but not atypical isoforms of protein kinase C (PKC). Aggregation induced by staurosporine is inhibited by a number of inhibitors of PKC isoforms, and by inhibitors of protein tyrosine kinases. Staurosporine also induces rapid phosphorylation of ERK and p38, and inhibitors of both these enzymes block aggregation. 3. Staurosporine induces dysregulated activation of multiple kinase signaling pathways in U937 cells, and the combined activity of several of these pathways is essential for the induction of aggregation.

Acetophenones↗

PubMed2003

The differential influence of allogeneic tumor cell death via DNA damage on dendritic cell maturation and antigen presentation.

Dendritic cells (DCs) respond to danger signals from tissue injury by amplifying their immune-inducing capacity. In the cancer context, this may lead to in vivo antitumor synergism between DCs and DNA-damaging chemotherapeutic agents. Neither the interaction between DCs and dying tumor cells nor whether different ways of inducing cell injury can deliver danger signals of different strength to DCs nor the potential role of damaged DNA as a danger signal has been studied rigorously. Here we report that coculture of immature DCs with tumor cells treated with the alkylating agents melphalan and chlorambucil leads to enhanced autologous and allogeneic T-cell activation, up-regulation of surface expression of MHC and costimulatory molecules, and increased interleukin (IL)-12 secretion. Exposure of the same DCs to tumor cells killed by cytarabine or by freeze-thaw (primary necrosis) resulted in significantly less T-cell proliferation and IL-12 production, indicating that DCs are able to sense and respond differentially to the mode of cell death. Exposure of DCs to DNA purified from tumor cells treated with alkylating agents also increased their T-cell-stimulating capacity, expression of CD86, and IL-12 secretion, supporting the hypothesis that the activating effects of tumor cells are linked to the nature of the DNA damage. This is the first study that shows that DCs respond differentially to killed tumor cells, depending upon the mechanism of DNA damage and consequent cell death.

Antigen Presentation↗

PubMed2003

Local cooperation dominates over competition between CD4+ T cells of different antigen/MHC specificity.

Interactions between CD4(+) T cells in vivo are controlled by a balance between cooperation and competition. In this study the interaction between two populations of CD4(+) T cells of different MHC/peptide specificity was probed at different precursor frequencies, delivering one or both Ags to APC using particle-mediated DNA delivery. Expansion of clonal populations of Ag (OVA and pigeon cytochrome c-specific) CD4(+) T cells was limited at higher precursor frequencies, presumably reflecting intraclonal competition. In contrast, a strong enhancement of the number of cells expressing IFN-gamma, IL-4, and IL-2 was observed in populations of cells at low precursor frequency in the presence of a high frequency of activated cells of a different Ag specificity. The helper effect was most potent when both Ags were delivered to the same dendritic cell (i.e., linked). This reflects the requirement of epicrine or paracrine help for optimal activation of T cell clones at low frequency. A measure of help was also delivered in an endocrine manner (unlinked), especially for Th1 responses, suggesting that there is also limited diffusion of cytokines between dendritic cell clusters. The dominant effects of cooperation over competition between CD4(+) T cells responding to different Ags may have important implications in terms of the efficacy of multivalent vaccines.

Adoptive Transfer↗

PubMed2003

CD98-dependent homotypic aggregation is associated with translocation of protein kinase Cdelta and activation of mitogen-activated protein kinases.

CD98 is a protein found on the surface of many activated cell types, and is implicated in the regulation of cellular differentiation, adhesion, growth, and apoptosis. Despite many studies addressing CD98 function, there is little information on the intracellular signalling pathways that mediate its activity. In this study, we examine protein kinase pathways that are activated following ligation by the CD98 antibody AHN-18, an antibody that induces U937 homotypic aggregation and inhibits antigen presenting activity and T-cell activation. Ligation by CD98 antibody AHN-18 induces tyrosine kinase activity, but inhibition of this activity does not affect U937 aggregation. Ligation also induces membrane translocation of the serine/threonine kinase novel PKCdelta, but not other members of the PKC family. Translocation is blocked by rottlerin, and this inhibitor also blocks aggregation. PKCdelta activation in turn mediates activation of ERK1/2 and p38, as well as tyrosine phosphorylation of multiple proteins, and MAPK activation is essential for cellular aggregation. One of the targets of CD98-induced tyrosine phosphorylation is itself PKCdelta, suggesting that this phosphorylation may act as a negative feedback to limit the overall activation of the CD98 pathway.

Adrenergic beta-Antagonists↗

PubMed2003

Modulation of dendritic cell endocytosis and antigen processing pathways by Escherichia coli heat-labile enterotoxin and mutant derivatives.

Escherichia coli heat-labile enterotoxin (LT) is known to be a potent adjuvant of both the mucosal and systemic immune systems but the mechanism of action leading to adjuvant activity remains incompletely understood. This study investigates the action of LT and LT mutants with impaired enzymatic activity, on the function of dendritic cells. Wild-type LT and LTR72, which retains some ADP ribosyltransferase activity, induced a selective increase in cell surface expression of B7.1, and a selective decrease of CD40 expression on mouse bone marrow derived dendritic cells. LTK63 and LT-B had no obvious effect on the expression of these antigens on similar dendritic cells. LT-treated dendritic cells also showed a profoundly impaired ability to present protein antigen (ovalbumin) to cognate T cells, although this effect was not observed with non-toxic LT mutants. LT and LTR72-treated cells showed a slower rate of receptor-mediated endocytosis as measured by flow cytometric analysis of uptake of fluorescently labelled dextran. Furthermore, confocal microscopy showed changes in the intracellular distribution of endocytosed molecules, and of the class II containing acidic antigen processing compartments. This response of dendritic cells to toxin is likely to play an important role in determining the adjuvant activity of these molecules.

Adjuvants, Immunologic↗

PubMed2003

Instruction of naive CD4+ T cells by polarized CD4+ T cells within dendritic cell clusters.

Cooperation between CD4(+) T cells can enhance the response and modulate the cytokine profile, and defining these parameters has become a major issue for multivalent-vaccine strategies. We explored cooperation using adoptive transfer of two populations of TCR transgenic T cells of different specificity. One was transferred without prior activation, whereas the second was activated for five days by antigen stimulation under polarizing culture conditions. Both populations were transferred into a single adoptive host and then primed by particle-mediated DNA delivery. Polarized Th1 cells (inducers) raised the frequency of IFN-gamma(+) cells within a naive (target) population, whereas Th2 inducers raised the frequency of IL-4(+) and reduced that of IL-2(+) cells. These effects were obtained when the genes for both antigens were on the same particle, favoring presentation by the same dendritic cell, but not when on different particles delivered to different dendritic cells. Autonomy of DC clusters allows linked sets of antigens (e.g. from a single pathogen) to maintain cytokine bias, but allows other independent responses, each with their own set of autonomous clusters.

Adoptive Transfer↗

PubMed2003

Ribotoxic stress activates p38 and JNK kinases and modulates the antigen-presenting activity of dendritic cells.

Initiation of adaptive immunity requires activation of dendritic cells (DC) by "danger" signals. This study examines the functional consequences of activating a cellular stress response in human DC. Anisomycin, a potent inducer of this "stress" response, selectively activates p38 kinase in DC at low concentrations, and both p38 kinases and JNKs at higher concentrations. Activation of p38, was accompanied by an increase in the potency of dendritic cells to activate T cells. In contrast to LPS, anisomycin had no effect on the expression of several DC activation markers. Anisomycin synergised with LPS in driving release of IL-12 and TNF-alpha. Anisomycin also enhanced the formation of clusters between DC and T cells. Enhanced cytokine release and clustering were both inhibited by the selective p38 alpha and p38 beta inhibitor SB203580. This study demonstrates that the cellular stress response, mediated via p38 kinases, plays an important role in the regulation of several aspects of DC function.

Anisomycin↗

PubMed2002

The role of advanced oxidation protein products in regulation of dendritic cell function.

The basis for this study was the "injury hypothesis," which holds that release of micro-environmental constituents, such as reactive oxygen species and oxidants, acts as a signal, and potential activator, of dendritic cell (DC)-mediated antigen presentation. Following this oxidative stress, dityrosine containing cross-linked proteins, advanced oxidation protein products (AOPP), are known to be generated, and we proposed that they may serve as moieties that mediate such signals. Therefore, the effect of AOPP on DCs has been examined in vitro. There were no AOPP-induced changes in DC phenotype as judged by expression of typical surface costimulatory molecules. However, at higher cell concentrations AOPP-treated DCs were more potent inducers in an oxidative mitogenesis assay than controls. Thus, AOPP may act like superantigens, allowing for bypass of upregulation of costimulation, and, either alone or in synergy with oxidants themselves, serving as amplifiers of DC function.

Animals↗

PubMed2002

Extension, retraction and contraction in the formation of a dendritic cell dendrite: distinct roles for Rho GTPases.

The morphology of antigen-presenting dendritic cells (DC) is characterized by the possession of numerous long arborizing processes known as dendrites. The formation of these processes by DC, both in the periphery and in lymphoid organs, is believed to contribute to the remarkable efficiency with which they take up, process and present antigen to T cells. However, the process of dendrite formation and the signaling pathways that lead to the formation of these dendrites remain obscure. In this study we describe an in vitro model in which human immature DC form long processes similar to those formed in vivo. The formation of these processes involves initial attachment of a cell protrusion to the extracellular matrix substrate, and subsequent movement of the cell body away from the adhesion site, leaving behind a long slender dendrite. Dendrite formation, but not their maintenance, was found to be dependent on the activity of Rho GTPases. More specifically, Cdc42 and Rac1 were both required for the migration step of process formation, promoting cell spreading and extension. In contrast, Rho, and its downstream effector p160ROCK, regulated the release of adhesions to the substratum, and associated cellular contraction. Consequently, inhibition of Rho/p160ROCK leads to the formation of longer dendrites. DC therefore coordinate adhesion and protrusion to perform a specialized process of cellular morphogenesis, which differentiates these cells from all other cells of the immune system and may contribute to their distinctive function.

Cell Adhesion↗

PubMed2002

Effects of oxidised low density lipoprotein on dendritic cells: a possible immunoregulatory component of the atherogenic micro-environment?

OBJECTIVE: The objective of this study was to explore the relationship between low density lipoprotein (LDL) and dendritic cell (DC) activation, based upon the hypothesis that reactive oxygen species (ROS)-mediated modification of proteins that may be present in local DC microenvironments could be important as mediators of this activation. Although LDL are known to be oxidised in vivo, and taken up by macrophages during atherogenesis; their effect on DC has not been explored previously. METHODS: Human DCs were prepared from peripheral blood monocytes using GM-CSF and IL-4. Plasma LDLs were isolated by sequential gradient centrifugation, oxidised in CuSO(4), and oxidation arrested to yield mild, moderate and highly oxidised LDL forms. DCs exposed to these LDLs were investigated using combined phenotypic, functional (autologous T cell activation), morphological and viability assays. RESULTS: Highly-oxidised LDL increased DC HLA-DR, CD40 and CD86 expression, corroborated by increased DC-induced T cell proliferation. Both native and oxidised LDL induced prominent DC clustering. However, high concentrations of highly-oxidised LDL inhibited DC function, due to increased DC apoptosis. CONCLUSIONS: This study supports the hypothesis that oxidised LDL are capable of triggering the transition from sentinel to messenger DC. Furthermore, the DC clustering-activation-apoptosis sequence in the presence of different LDL forms is consistent with a regulatory DC role in immunopathogenesis of atheroma. A sequence of initial accumulation of DC, increasing LDL oxidation, and DC-induced T cell activation, may explain why local breach of tolerance can occur. Above a threshold level, however, supervening DC apoptosis limits this, contributing instead to the central plaque core.

Apoptosis↗