Engagement of CD44 up-regulates Fas ligand expression on T cells leading to activation-induced cell death

Identification the role of necroptosis in rheumatoid arthritis by WGCNA network

Rheumatoid arthritis (RA) is the predominant manifestation of inflammatory arthritis, distinguished by an increasing burden of morbidity and mortality. The intricate interplay of genes and signalling pathways involved in synovial inflammation in patients with RA remains inadequately comprehended. This study aimed to ascertain the role of necroptosis in RA, as along with their associations with immune cell infiltration. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were employed to identify central genes for RA. In this study, identified total of 28 differentially expressed genes (DEGs) were identified in RA. Utilising WGCNA, two co-expression modules were generated, with one module demonstrating the strongest correlation with RA. Through the integration of differential gene expression analysis, a total of 5 intersecting genes were discovered. These 5 hub genes, namely fused in sarcoma (FUS), transformer 2 beta homolog (TRA2B), eukaryotic translation elongation factor 2 (EEF2), cleavage and polyadenylation specific factor 6 (CPSF6) and signal transducer and activator of transcription 3 (STAT3) were found to possess significant diagnostic value as determined by receiver operating characteristic (ROC) curve analysis. The close association between the concentrations of various immune cells is anticipated to contribute to the diagnosis and treatment of RA. Furthermore, the infiltration of immune cells mentioned earlier is likely to exert a substantial influence on the initiation of this disease.

A multivalent CD44 glycoconjugate vaccine candidate for cancer immunotherapy

Cancer presents a high mortality rate due to ineffective treatments and tumour relapse with progression. Cancer vaccines hold tremendous potential due to their capability to eradicate tumour and prevent relapse. In this study, we present a novel glycovaccine for precise targeting and immunotherapy of aggressive solid tumours that overexpress CD44 standard isoform (CD44s) carrying immature Tn and sialyl-Tn (sTn) O-glycans. We describe an enzymatic method and an enrichment strategy to generate libraries of well-characterized cancer-specific CD44s-Tn and/or sTn glycoproteoforms, which mimic the heterogeneity found in tumours. We conjugated CD44-Tn-derived glycopeptides with carrier proteins making them more immunogenic, with further demonstration of the importance of this conjugation to overcome the glycopeptides' intrinsic toxicity. We have optimized the glycopeptide-protein maleimide-thiol conjugation chemistry to avoid undesirable cross-linking between carrier proteins and CD44s glycopeptides. The resulting glycovaccines candidates were well-tolerated in vivo, inducing both humoral and cellular immunity, including immunological memory. The generated antibodies exhibited specific reactivity against synthetic CD44s-Tn glycopeptides, CD44s-Tn glycoengineered cells, and human tumours. In summary, we present a promising prototype of a cancer glycovaccine for future therapeutical pre-clinical efficacy validation.

Primary and Secondary micro-RNA Modulation the Extrinsic Pathway of Apoptosis in Hepatocellular Carcinoma

Abstract-One of the most common malignant liver diseases is hepatocellular carcinoma, which has a high recurrence rate and a low five-year survival rate. It is very heterogeneous both in structure and between patients, which complicates the diagnosis, prognosis and response to treatment. In this regard, an individualized, patient-centered approach becomes important, in which the use of mimetics and hsa-miRNA inhibitors involved in the pathogenesis of the disease may be determinative. From this point of view hsa-miRNAs are of interest, their aberrant expression is associated with poor prognosis for patients and is associated with tumor progression due to dysregulation of programmed cell death (apoptosis). However, the effect of hsa-miRNA on tumor development depends not only on its direct effect on expression of genes, the primary targets, but also on secondary targets mediated by regulatory pathways. While the former are actively studied, the role of secondary targets of these hsa-miRNAs in modulating apoptosis is still unclear. The present work summarizes data on hsa-miRNAs whose primary targets are key genes of the extrinsic pathway of apoptosis. Their aberrant expression is associated with early disease relapse and poor patient outcome. For these hsa-miRNAs, using the software package ANDSystem, we reconstructed the regulation of the expression of secondary targets and analyzed their impact on the activity of the extrinsic pathway of apoptosis. The potential effect of hsa-miRNAs mediated by action on secondary targets is shown to negatively correlate with the number of primary targets. It is also shown that hsa-miR-373, hsa-miR-106b and hsa-miR-96 have the highest priority as markers of hepatocellular carcinoma, whose action on secondary targets enhances their anti-apoptotic effect.

T cell-specific constitutive active SHP2 enhances T cell memory formation and reduces T cell activation

Upon antigen recognition by the T cell receptor (TCR), a complex signaling network orchestrated by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs) regulates the transmission of the extracellular signal to the nucleus. The role of the PTPs Src-homology 2 (SH2) domain-containing phosphatase 1 (SHP1, Ptpn6) and Src-homology 2 (SH2) domain-containing phosphatase 2 (SHP2, Ptpn11) have been studied in various cell types including T cells. Whereas SHP1 acts as an essential negative regulator of the proximal steps in T cell signalling, the role of SHP2 in T cell activation is still a matter of debate. Here, we analyzed the role of the constitutively active SHP2-D61Y-mutant in T cell activation using knock-in mice expressing the mutant form Ptpn11D61Y in T cells. We observed reduced numbers of CD8+ and increased numbers of CD4+ T cells in the bone marrow and spleen of young and aged SHP2-D61Y-mutant mice as well as in Influenza A Virus (IAV)-infected mice compared to controls. In addition, we found elevated frequencies of effector memory CD8+ T cells and an upregulation of the programmed cell death protein 1 (PD-1)-receptor on both CD4+ and CD8+ T cells. Functional analysis of SHP2-D61Y-mutated T cells revealed an induction of late apoptosis/necrosis, a reduced proliferation and altered signaling upon TCR stimulation. However, the ability of D61Y-mutant mice to clear viral infection was not affected. In conclusion, our data indicate an important regulatory role of SHP2 in T cell function, where the effect is determined by the kinetics of SHP2 phosphatase activity and differs in the presence of the permanently active and the temporally regulated phosphatase. Due to interaction of SHP2 with the PD-1-receptor targeting the protein-tyrosine phosphatase might be a valuable tool to enhance T cell activities in immunotherapy.

Integrative Analysis Identifies Cell-Type-Specific Genes Within Tumor Microenvironment as Prognostic Indicators in Hepatocellular Carcinoma

Background

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality worldwide, but effective early detection and prognostication methods are lacking.

Methods

The Cox regression model was built to stratify the HCC patients. The single-cell RNA sequencing data analysis and gene set enrichment analysis were employed to investigate the biological function of identified markers. PLCB1 gain- or loss-of-function experiments were performed, and obtained HCC samples were analyzed using quantitative real-time PCR and immunohistochemistry assay to validate the biological function of identified markers.

Results

In this study, we developed a model using optimized markers for HCC recurrence prediction. Specifically, we screened out 8 genes through a series of data analyses, and built a multivariable Cox model based on their expression. The risk stratifications using the Eight-Gene Cox (EGC) model were closely associated with the recurrence-free survivals (RFS) in both training and three validation cohorts. We further demonstrated that this risk stratification could serve as an independent predictor in predicting HCC recurrence, and that the EGC model could outperform other models. Moreover, we also investigated the cell-type-specific expression patterns of the eight recurrence-related genes in tumor microenvironment using single-cell RNA sequencing data, and interpreted their functional roles from correlation and gene set enrichment analyses, in vitro and in vivo experiments. Particularly, PLCB1 and SLC22A7 were predominantly expressed in malignant cells, and they were predicted to promote angiogenesis and to help maintain normal metabolism in liver, respectively. In contrast, both FASLG and IL2RB were specifically expressed in T cells, and were highly correlated with T cell marker genes, suggesting that these two genes might assist in maintaining normal function of T cell-mediated immune response in tumor tissues.

Conclusion

In conclusion, the EGC model and eight identified marker genes could not only facilitate the accurate prediction of HCC recurrence, but also improve our understanding of the mechanisms behind HCC recurrence.

Apoptosis, Autophagy, NETosis, Necroptosis, and Pyroptosis Mediated Programmed Cell Death as Targets for Innovative Therapy in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease that can lead to clinical manifestations of systemic diseases. Its leading features include chronic synovial inflammation and degeneration of the bones and joints. In the past decades, multiple susceptibilities for rheumatoid arthritis have been identified along with the development of a remarkable variety of drugs for its treatment; which include analgesics, glucocorticoids, nonsteroidal anti-inflammatory medications (NSAIDs), disease-modifying anti-rheumatic drugs (DMARDs), and biologic response modifiers (bDMARDs). Despite the existence of many clinical treatment options, the prognosis of some patients remains poor due to complex mechanism of the disease. Programmed cell death (PCD) has been extensively studied and ascertained to be one of the essential pathological mechanisms of RA. Its dysregulation in various associated cell types contributes to the development of RA. In this review, we summarize the role of apoptosis, cell death-associated neutrophil extracellular trap formation, necroptosis, pyroptosis, and autophagy in the pathophysiology of RA to provide a theoretical reference and insightful direction to the discovery and development of novel therapeutic targets for RA.

Effect of Lipopolysaccharide and Muramyl Dipeptide on Apoptosis of Bovine Mammary Gland Lymphocytes

Simple Summary

Inflammation of the mammary gland in dairy cattle is a global problem and causes huge financial loss to dairy farmers. Inflammation is caused by many species of bacteria penetrating through the teat canals into the udder. Those bacteria are usually eliminated by treatment with intramammary injection of antibiotics, while they are also eliminated by the immune cells of the cow. One of the immune cells are lymphocytes which are responsible for specific immunity. When viable, they are able to carry out their normal functions. The present study focused on the investigation of cell death of lymphocytes during bovine mammary gland inflammation. We analyzed apoptosis in mammary gland lymphocytes under the stimulation of lipopolysaccharides and muramyl dipeptide as the endotoxin of Gram-negative bacteria and the natural content of the cell wall of Gram-positive bacteria. We found that they induce lymphocyte apoptosis in the early phase of inflammation, which can be associated with the expression of CD44 receptors on lymphocytes. This receptor is important in many physiological processes, including apoptosis of cells. For a better understanding of immune responses in mammary glands and for developing of immunotherapy without antibiotics, the process of inflammation, including cell death of immune cells necessitates further holistic studies.

Abstract

The aim of this study was to evaluate whether apoptosis of lymphocytes is modulated by stimulation by lipopolysaccharide (LPS) of Escherichia coli or muramyl dipeptide (MDP). Cell populations were obtained by lavaging of the mammary glands 24, 48, 72, and 168 h following intramammary induced inflammation. The portion of apoptotic lymphocytes peaked at 48 h after treatment with LPS or MDP. The analysis of CD44 expression of the same cell populations showed a higher percentage of CD44-positive lymphocytes 24- and 48-h following induction of inflammation by LPS or MDP. The results demonstrate that during both experimental infection of bovine mammary glands with LPS or MDP, apoptosis of lymphocytes was induced in the initial phase of the inflammatory response and CD44 was also overexpressed at the beginning of inflammation. These data suggest a connection of lymphocyte apoptosis with the expression of CD44 receptors.

Modulation of intracellular calcium signaling by microRNA-34a-5p

Adjusting intracellular calcium signaling is an important feature in the regulation of immune cell function and survival. Here we show that miR-34a-5p, a small non-coding RNA that is deregulated in many common diseases, is a regulator of store-operated Ca²⁺ entry (SOCE) and calcineurin signaling. Upon miR-34a-5p overexpression, we observed both a decreased depletion of ER calcium content and a decreased Ca²⁺ influx through Ca²⁺ release-activated Ca²⁺ channels. Based on an in silico target prediction we identified multiple miR-34a-5p target genes within both pathways that are implicated in the balance between T-cell activation and apoptosis including ITPR2, CAMLG, STIM1, ORAI3, RCAN1, PPP3R1, and NFATC4. Functional analysis revealed a decrease in Ca²⁺ activated calcineurin pathway activity measured by a reduced IL-2 secretion due to miR-34a-5p overexpression. Impacting SOCE and/or downstream calcineurin/NFAT signaling by miR-34a-5p offers a possible future approach to manipulate immune cells for clinical interventions.

Bioengineered gold nanoparticles targeted to mesenchymal cells from patients with bronchiolitis obliterans syndrome does not rise the inflammatory response and can be safely inhaled by rodents

The use of gold nanoparticles (GNPs) as drug delivery system represents a promising issue for diseases without effective pharmacological treatment due to insufficient local drug accumulation and excessive systemic toxicity. Bronchiolitis obliterans syndrome (BOS) represents about 70% of cases of chronic lung allograft dysfunction, the main challenge to long-term lung transplantation. It is believed that due to repeated insults to epithelial bronchiolar cells local inflammatory response creates a milieu that favors epithelial-mesenchymal transition and activation of local mesenchymal cells (MCs) leading to airway fibro-obliteration. In a previous work, we engineered GNPs loaded with the mammalian target of rapamycin inhibitor everolimus, specifically decorated with an antibody against CD44, a surface receptor expressed by primary MCs isolated from bronchoalveolar lavage of BOS patients. We proved in vitro that these GNPs (GNP-HCe) were able to specifically inhibit primary MCs without affecting the bronchial epithelial cell. In the present work, we investigated the effect of these bioengineered nanoconstructs on inflammatory cells, given that a stimulating effect on macrophages, neutrophils or lymphocytes is strongly unwanted in graft airways since it would foster fibrogenesis. In addition, we administered GNP-HCe by the inhalatory route to normal mice for a preliminary assessment of their pulmonary and peripheral (liver, spleen and kidney) uptake. By these experiments, an evaluation of tissue toxicity was also performed. The present study proves that our bioengineered nanotools do not rise an inflammatory response and, under the tested inhalatory conditions that were used, are non-toxic.

Cancer microenvironment and inflammation: role of hyaluronan

The role of inflammation in the development of cancer was described as early as the nineteenth century. Abundant evidence supports the preposition that various cancers are triggered by infection and chronic inflammatory disease whereas, evading immune destruction has been proposed as one of the new “hallmarks of cancer.” Changes of the tumor microenvironment have been closely correlated to cancer-mediated inflammation. Hyaluronan (HA), an important extracellular matrices component, has become recognized as an active participant in inflammatory, angiogenic, fibrotic, and cancer promoting processes. This review discusses how HA and specific HA-binding proteins participate in and regulate cancer-related inflammatory processes.

Genetic deletion of Mst1 alters T cell function and protects against autoimmunity

Mammalian sterile 20-like kinase 1 (Mst1) is a MAPK kinase kinase kinase which is involved in a wide range of cellular responses, including apoptosis, lymphocyte adhesion and trafficking. The contribution of Mst1 to Ag-specific immune responses and autoimmunity has not been well defined. In this study, we provide evidence for the essential role of Mst1 in T cell differentiation and autoimmunity, using both genetic and pharmacologic approaches. Absence of Mst1 in mice reduced T cell proliferation and IL-2 production in vitro, blocked cell cycle progression, and elevated activation-induced cell death in Th1 cells. Mst1 deficiency led to a CD4⁺ T cell development path that was biased toward Th2 and immunoregulatory cytokine production with suppressed Th1 responses. In addition, Mst1^−/− B cells showed decreased stimulation to B cell mitogens in vitro and deficient Ag-specific Ig production in vivo. Consistent with altered lymphocyte function, deletion of Mst1 reduced the severity of experimental autoimmune encephalomyelitis (EAE) and protected against collagen-induced arthritis development. Mst1^−/− CD4⁺ T cells displayed an intrinsic defect in their ability to respond to encephalitogenic antigens and deletion of Mst1 in the CD4⁺ T cell compartment was sufficient to alleviate CNS inflammation during EAE. These findings have prompted the discovery of novel compounds that are potent inhibitors of Mst1 and exhibit desirable pharmacokinetic properties. In conclusion, this report implicates Mst1 as a critical regulator of adaptive immune responses, Th1/Th2-dependent cytokine production, and as a potential therapeutic target for immune disorders.

Fas ligand-expressing lymphocytes enhance alveolar macrophage apoptosis in the resolution of acute pulmonary inflammation

Apoptosis of alveolar macrophages and their subsequent clearance by neighboring phagocytes are necessary steps in the resolution of acute pulmonary inflammation. We have recently identified that activation of the Fas death receptor on the cell surface of macrophages drives macrophage apoptosis. However, the source of the cognate ligand for Fas (FasL) responsible for induction of alveolar macrophage apoptosis is not defined. Given their known role in the resolution of inflammation and ability to induce macrophage apoptosis ex vivo, we hypothesized that T lymphocytes represented a critical source of FasL. To address this hypothesis, C57BL/6J and lymphocyte-deficient (Rag-1(-/-)) mice were exposed to intratracheal lipopolysaccharide to induce pulmonary inflammation. Furthermore, utilizing mice expressing nonfunctional FasL, we adoptively transferred donor lymphocytes into inflamed lymphocyte-deficient mice to characterize the effect of lymphocyte-derived FasL on alveolar macrophage apoptosis in the resolution of inflammation. Herein, evidence is presented that lymphocytes expressing FasL enhance alveolar macrophage apoptosis during the resolution of LPS-induced inflammation. Moreover, lymphocyte induction of alveolar macrophage apoptosis results in contraction of the alveolar macrophage pool, which occurs in a FasL-dependent manner. Specifically, FasL-expressing CD8(+) T lymphocytes potently induce alveolar macrophage apoptosis and contraction of the alveolar macrophage pool. Together, these studies identify a novel role for CD8(+) T lymphocytes in the resolution of acute pulmonary inflammation.

Distinct effects of saracatinib on memory CD8+ T cell differentiation

Immunologic memory involving CD8(+) T cells is a hallmark of an adaptive Ag-specific immune response and constitutes a critical component of protective immunity. Designing approaches that enhance long-term T cell memory would, for the most part, fortify vaccines and enhance host protection against infectious diseases and, perhaps, cancer immunotherapy. A better understanding of the cellular programs involved in the Ag-specific T cell response has led to new approaches that target the magnitude and quality of the memory T cell response. In this article, we show that T cells from TCR transgenic mice for the nucleoprotein of influenza virus NP68 exhibit the distinct phases--priming, expansion, contraction, and memory--of an Ag-specific T cell response when exposed in vitro to the cognate peptide. Saracatinib, a specific inhibitor of Src family kinases, administered at low doses during the expansion or contraction phases, increased CD62L(high)/CD44(high) central memory CD8(+) T cells and IFN-γ production but suppressed immunity when added during the priming phase. These effects by saracatinib were not accompanied by the expected decline of Src family kinases but were accompanied by Akt-mammalian target of rapamycin suppression and/or mediated via another pathway. Increased central memory cells by saracatinib were recapitulated in mice using a poxvirus-based influenza vaccine, thus underscoring the importance of dose and timing of the inhibitor in the context of memory T cell differentiation. Finally, vaccine plus saracatinib treatment showed better protection against tumor challenge. The immune-potentiating effects on CD8(+) T cells by a low dose of saracatinib might afford better protection from pathogens or cancer when combined with vaccine.

Activation of CD44, a receptor for extracellular matrix components, protects chronic lymphocytic leukemia cells from spontaneous and drug induced apoptosis through MCL-1

Survival of chronic lymphocytic leukemia (CLL) cells in vivo is supported by the tissue microenvironment, which includes components of the extracellular matrix. Interactions between tumor cells and the extracellular matrix are in part mediated by CD44, whose principal ligand is hyaluronic acid. Here, we show that CD44 is more highly expressed on CLL cells of the clinically more progressive immunglobulin heavy chain variable gene (IGHV)-unmutated subtype than on cells of the IGHV-mutated type. Engagement of CD44 activated the phosphatidylinositol 3-kinase (PI3K)/AKT and mitogen activated protein kinase (MAPK)/ERK pathways and increased myeloid cell leukemia sequence 1 (MCL-1) protein expression. Consistent with the induction of these anti-apoptotic mechanisms, CD44 protected CLL cells from spontaneous and fludarabine-induced apoptosis. Obatoclax, an antagonist of MCL-1, blocked the pro-survival effect of CD44. In addition, obatoclax synergized with fludarabine to induce apoptosis of CLL cells. In conclusion, components of the extracellular matrix may provide survival signals to CLL cells through engagement of CD44. Inhibition of MCL-1 is a promising strategy to reduce the anti-apoptotic effect of the microenvironment on CLL cells.

CD44 in hematological neoplasias

The CD44 protein family spans a large group of transmembrane glycoproteins acquired by alternative splicing and post-translational modifications. The great heterogeneity in molecular structure is reflected in its various important functions: CD44 mediates (1) interaction between cell and extracellular matrix, (2) signal submission, e.g., by acting as co-receptor for membrane-spanning receptor tyrosine kinases or by association with intracellular molecules initiating several signaling pathways, and (3) anchor function connecting to the cytoskeleton via the ezrin-radixin-moesin protein family. The expression pattern of the different CD44 isoforms display strong variations dependent on cell type, state of activation, and differentiation stage. In hematopoietic cells, CD44 mediates interaction of progenitor cells and bone marrow stroma during hematopoiesis, regulates maturation, and activation-induced cell death in T cells, influences neutrophil and macrophage migration as well as cytokine production, and participates in lymphocyte extravasation and migration. CD44 is involved in development and progress of hematological neoplasias by enhancement of apoptotic resistance, invasiveness, as well as regulation of bone marrow homing, and mobilization of leukemia-initiating cells into the peripheral blood. Thereby altered CD44 expression functions as marker for worse prognosis in most hematological malignancies. Additionally, CD44 expression levels can be used to distinguish between different hematological neoplasias and subtypes. Concerning new treatment strategies, CD44 displays promising potential either by direct targeting of CD44 expressed on the malignant cells or reversing an acquired resistance to primary treatment mediated through altered CD44 expression. The former can be achieved by antibody or hyaluronan-based immunotherapy.

Multifaceted regulation of T cells by CD44

CD44 is a widely-expressed adhesion receptor that is associated with diverse biological processes involving migrating cells, including inflammation, angiogenesis, bone metabolism and wound healing. In the immune system, CD44 is upregulated after activation of naive T lymphocytes during their responses against invading microbes. Once an infection is cleared, elevated levels of CD44 remain on the surface of memory T cells that mediate protection against re-infection. While this has led to the use of highly sustained CD44 expression on T cells as an indicator of a previous immune response, the relevance to T-cell responses or homeostasis has been largely unexplored. Our recent studies demonstrate that CD44 selectively regulates the survival of the Th1 subset of CD4 T cells, but not other T-cell subpopulations. These findings, together with studies of CD44 in other cell types, suggest that differences in the engagement of signaling mechanisms are likely to underlie differential regulation of T-cell responses and underscore the importance of this adhesion receptor to immune cell regulation and protection against viruses and intracellular bacteria.

An activation marker finds a function

In this issue of Immunity, Baaten et al. (2010) describe a previously unknown role for CD44 in counteracting Fas-mediated apoptosis of Th1 effector cells during clonal expansion and allowing their entry into the memory pool.

CD44 regulates survival and memory development in Th1 cells

Optimal immunity to microorganisms depends upon the regulated death of clonally expanded effector cells and the survival of a cohort of cells that become memory cells. After activation of naive T cells, CD44, a widely expressed receptor for extracellular matrix components, is upregulated. High expression of CD44 remains on memory cells and despite its wide usage as a "memory marker," its function is unknown. Here we report that CD44 was essential for the generation of memory T helper 1 (Th1) cells by promoting effector cell survival. This dependency was not found in Th2, Th17, or CD8(+) T cells despite similar expression of CD44 and the absence of splice variants in all subsets. CD44 limited Fas-mediated death in Th1 cells and its ligation engaged the phosphoinositide 3-kinase-Akt kinase signaling pathway that regulates cell survival. The difference in CD44-regulated apoptosis resistance in T cell subpopulations has important implications in a broad spectrum of diseases.

Anti-CD44 induces apoptosis in T lymphoma via mitochondrial depolarization

A blockade of CD44 can interfere with haematopoietic and leukemic stem cell homing, the latter being considered as a therapeutic option in haematological malignancies. We here aimed to explore the molecular mechanism underlying the therapeutic efficacy of anti-CD44. We noted that in irradiated mice reconstituted with a bone marrow cell transplant, anti-CD44 exerts a stronger effect on haematopoietic reconstitution than on T lymphoma (EL4) growth. Nonetheless, in the non-reconstituted mouse anti-CD44 suffices for a prolonged survival of EL4-bearing mice, where anti-CD44-prohibited homing actively drives EL4 cells into apoptosis. In vitro, a CD44 occupancy results in a 2–4-fold increase in apoptotic EL4 cells. Death receptor expression (CD95, TRAIL, TNFRI) remains unaltered and CD95 cross-linking-mediated apoptosis is not affected. Instead, CD44 ligation promotes mitochondrial depolarization that is accompanied by caspase-9 cleavage and is inhibited in the presence of a caspase-9 inhibitor. Apoptosis becomes initiated by activation of CD44-associated phosphatase 2A (PP2A) and proceeds via ERK1/2 dephosphorylation without ERK1/2 degradation. Accordingly, CD44-induced apoptosis could be mimicked by ERK1/2 inhibition, that also promotes EL4 cell apoptosis through the mitochondrial pathway. Thus, during haematopoietic stem cell reconstitution care should be taken not to interfere by a blockade of CD44 with haematopoiesis, which could be circumvented by selectively targeting leukemic CD44 isoforms. Beyond homing/settlement in the bone marrow niche, anti-CD44 drives leukemic T cells into apoptosis via the mitochondrial death pathway by CD44 associating with PP2A. Uncovering this new pathway of CD44-induced leukemic cell death provides new options of therapeutic interference.

CD44 costimulation promotes FoxP3+ regulatory T cell persistence and function via production of IL-2, IL-10, and TGF-beta

Work by our group and others has demonstrated a role for the extracellular matrix receptor CD44 and its ligand hyaluronan in CD4(+)CD25(+) regulatory T cell (Treg) function. Herein, we explore the mechanistic basis for this observation. Using mouse FoxP3/GFP(+) Treg, we find that CD44 costimulation promotes expression of FoxP3, in part through production of IL-2. This promotion of IL-2 production was resistant to cyclosporin A treatment, suggesting that CD44 costimulation may promote IL-2 production through bypassing FoxP3-mediated suppression of NFAT. CD44 costimulation increased production of IL-10 in a partially IL-2-dependent manner and also promoted cell surface TGF-beta expression. Consistent with these findings, Treg from CD44 knockout mice demonstrated impaired regulatory function ex vivo and depressed production of IL-10 and cell surface TGF-beta. These data reveal a novel role for CD44 cross-linking in the production of regulatory cytokines. Similar salutary effects on FoxP3 expression were observed upon costimulation with hyaluronan, the primary natural ligand for CD44. This effect is dependent upon CD44 cross-linking; while both high-molecular-weight hyaluronan (HA) and plate-bound anti-CD44 Ab promoted FoxP3 expression, neither low-molecular weight HA nor soluble anti-CD44 Ab did so. The implication is that intact high-molecular weight HA can cross-link CD44 only in those settings where it predominates over fragmentary LMW-HA, namely, in uninflamed tissue. We propose that intact but not fragmented extracellular is capable of cross-linking CD44 and thereby maintains immunologic tolerance in uninjured or healing tissue.

FasL cross-linking inhibits activation of human peripheral T cells

Activation of resting T cells in vitro is triggered by combined TCR and CD28 engagement and can be modulated by simultaneous ligation of various other surface receptors. Although the Fas ligand (FasL) is best known for its capacity to initiate cell death in Fas-bearing cells, it has recently been implicated in the regulation of T cell activation. Thus, a cross-talk between the TCR and FasL is likely, but far from being biochemically elucidated. We now report that FasL engagement by immobilized but not soluble FasFc fusion protein and anti-FasL polyclonal antibody blocks the activation of human peripheral T cells even in the presence of CD28 co-stimulation. The data presented here stress the importance of the Fas/FasL system for signal initiation via the TCR-CD3 complex and provide further arguments for a retrograde signaling capacity of FasL or a crucial role of Fas as a co-stimulatory molecule.

Transition dependency: a gene-gene interaction measure for times series microarray data

Gene-Gene dependency plays a very important role in system biology as it pertains to the crucial understanding of different biological mechanisms. Time-course microarray data provides a new platform useful to reveal the dynamic mechanism of gene-gene dependencies. Existing interaction measures are mostly based on association measures, such as Pearson or Spearman correlations. However, it is well known that such interaction measures can only capture linear or monotonic dependency relationships but not for nonlinear combinatorial dependency relationships. With the invocation of hidden Markov models, we propose a new measure of pairwise dependency based on transition probabilities. The new dynamic interaction measure checks whether or not the joint transition kernel of the bivariate state variables is the product of two marginal transition kernels. This new measure enables us not only to evaluate the strength, but also to infer the details of gene dependencies. It reveals nonlinear combinatorial dependency structure in two aspects: between two genes and across adjacent time points. We conduct a bootstrap-based chi(2) test for presence/absence of the dependency between every pair of genes. Simulation studies and real biological data analysis demonstrate the application of the proposed method. The software package is available under request.

Hyaluronan induces cell death in activated T cells through CD44

In the immune system, leukocyte activation induces CD44 to bind hyaluronan, a component of the extracellular matrix. Here we used gain and loss of hyaluronan-binding mutants of CD44 to examine the consequence of hyaluronan binding in T cells. Jurkat T cells transfected with CD44 mutated at S180, which prevented the addition of chondroitin sulfate, displayed constitutively high levels of hyaluronan binding. These cells were more susceptible to activation-induced cell death, whereas cells expressing a CD44 mutant unable to bind hyaluronan (R41A) were resistant to cell death. In TCR or PMA activated Jurkat T cells, hyaluronan induced rapid cell death. This depended on the level of hyaluronan binding by the cell, and the amount and size of hyaluronan. High molecular mass hyaluronan had the greatest effect and cell death occurred independently of Fas and caspase activation. In splenic T cells, high hyaluronan binding occurred in a subpopulation of cells undergoing activation-induced cell death. In addition, hyaluronan induced cell death in approximately 10% of reactivated splenic T cells when Fas-dependent apoptosis was prevented by Ab blocking or in Fas negative MRL/lpr T cells. This demonstrates that hyaluronan can induce cell death in activated, high hyaluronan binding T cells via a Fas-independent mechanism.

Defective T-cell function leading to reduced antibody production in a kleisin-beta mutant mouse

The recently described nessy (Ncaph2nes/nes) mutant mouse strain has a defect in T-cell development caused by a mutation in the ubiquitous kleisin-beta (also known as Ncaph2). Kleisin-beta is a subunit of the condensin II complex involved in chromosome condensation during mitosis. The nessy phenotype is characterized by CD44hi CD8+ peripheral T cells, 10-20% of normal thymocyte numbers and 2.5-fold fewer alphabeta T cells in the spleen compared with wild-type mice. In this study we examined the effect of the nessy mutation in kleisin-beta on the immune response by challenging mice with an attenuated strain of Salmonella. Results showed that nessy mice control bacterial load as effectively as wild-type mice but exhibit a reduced antibody titre. Further experiments revealed that while the T-dependent antibody response was diminished in nessy mice the T-independent response was normal, suggesting that the defect was the result of T-cell function and not B-cell function. In vitro activation assays showed that nessy T cells have a lower capacity to up-regulate the early activation marker CD69 than wild-type T cells. Upon transfer into RAG-/- mice, nessy and wild-type CD4 T cells showed equivalent homeostatic proliferation, while nessy CD8 T cells proliferated more than their wild-type counterparts. When cultured with anti-T-cell receptor beta or concanavalin A, nessy T cells were found to die faster than wild-type T cells. These data indicate that kleisin-beta is required for a normal immune response, and represent the first demonstration of a role for kleisin-beta in T-cell function.