Membrane-anchored CD40 is processed by the tumor necrosis factor-alpha-converting enzyme. Implications for CD40 signaling

ADAM17 deletion in thymic epithelial cells alters aire expression without affecting T cell developmental progression

Background

Cellular interactions between thymocytes and thymic stromal cells are critical for normal T cell development. Thymic epithelial cells (TECs) are important stromal niche cells that provide essential growth factors, cytokines, and present self-antigens to developing thymocytes. The identification of genes that mediate cellular crosstalk in the thymus is ongoing. One candidate gene, Adam17, encodes a metalloprotease that functions by cleaving the ectodomain of several transmembrane proteins and regulates various developmental processes. In conventional Adam17 knockout mice, a non-cell autonomous role for ADAM17 in adult T cell development was reported, which strongly suggested that expression of ADAM17 in TECs was required for normal T cell development. However, knockdown of Adam17 results in multisystem developmental defects and perinatal lethality, which has made study of the role of Adam17 in specific cell types difficult. Here, we examined T cell and thymic epithelial cell development using a conditional knockout approach.

Methodology/Principal Findings

We generated an Adam17 conditional knockout mouse in which floxed Adam17 is deleted specifically in TECs by Cre recombinase under the control of the Foxn1 promoter. Normal T cell lineage choice and development through the canonical αβ T cell stages was observed. Interestingly, Adam17 deficiency in TECs resulted in reduced expression of the transcription factor Aire. However, no alterations in the patterns of TEC phenotypic marker expression and thymus morphology were noted.

Conclusions/Significance

In contrast to expectation, our data clearly shows that absence of Adam17 in TECs is dispensable for normal T cell development. Differentiation of TECs is also unaffected by loss of Adam17 based on phenotypic markers. Surprisingly, we have uncovered a novel genetic link between Adam17and Aire expression in vivo. The cell type in which ADAM17 mediates its non-cell autonomous impact and the mechanisms by which it regulates intrathymic T cell development remain to be identified.

The pattern of inflammatory/anti-inflammatory cytokines and chemokines in type 1 diabetic patients over time

AIMS

To evaluate the profile of pro- and anti-inflammatory cytokines in type 1 diabetes mellitus (T1DM) and the way they are connected in co-regulated networks and determine whether disease duration influences their pattern.

METHODS

Plasma levels of 20 cytokines and soluble CD40 (sCD40) from 44 uncomplicated patients and 22 healthy controls (HCs) were measured using enzyme-linked immunosorbent assay (ELISA) and protein array technology.

RESULTS

Patients showed significantly higher levels of sCD40, IL-1a, IL-2, IL-4, IL-5, IL-10, granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage inflammatory protein (MIP)-1a, MIP-1b, regulated on activation normal T cell expressed and secreted (RANTES), matrix metalloproteinase (MMP)-9, and a trend to higher IL-6 than did HCs. RANTES and sCD40 discriminated significantly between diabetics and HCs. In patients with disease duration >6 months, cytokines were organized in two clusters mainly regulated by Th17 and Th1/Th2 cells respectively, while in those with disease duration <or=6 months a set of Th1-cytokines was separated apart from the second cluster. Monocyte chemotactic protein (MCP)-1 was revealed as the most discriminant factor between patients with disease duration of more than and less than 6 months.

CONCLUSIONS

A parallel elevation of both inflammatory and anti-inflammatory cytokines was observed in patients compared with HCs. In T1DM patients with disease duration <or=6 months, Th1-cytokines were organized on a separate cluster, suggesting a possible role of Th1 cells in the progress of beta-cell destruction during the first period of the disease.

Dialysis membrane: from convection to adsorption

Although patients undergoing dialysis have a complex illness, there are compelling reasons to believe that the inadequate removal of organic waste is an important contributing factor to the illness itself. This paper focuses on the transport phenomena that occur within a dialyser. An attempt is made to clarify how transport phenomena are related to the performance of a dialysis session and how they depend on the membrane characteristics. Our study offers some discussion points on the complex issue of defining what the best parameters could be in comparing the efficiency of different membranes. The new high-flux dialysers have improved larger-molecule clearance and biocompatibility. Membrane performance is a very hard process to evaluate, and different membranes can only be compared by establishing adequate points of comparison. At the same time, the points of comparison themselves may change depending on the type of co-morbidities of the specific patient who is considered for membrane selection. This editorial (together with all the papers presented in this issue) seeks to focus on the membrane's own merits in improving the dialysis therapy.

Potential role of the soluble form of CD40 in deficient immunological function of dialysis patients: new findings of its amelioration using polymethylmethacrylate (PMMA) membrane

Even though numerous studies have helped to better delineate abnormalities of either innate or adaptive immune system in end-stage renal disease (ESRD) patients, understanding immune dysfunctions in ESRD patients remains a very complex puzzle with missing pieces. In this context, we showed that the soluble form of CD40 (sCD40) is elevated in ESRD patients and is associated with a lack of response to hepatitis B vaccination. Interestingly, although most dialysis membranes are unable to clear sCD40, we demonstrated that polymethylmethacrylate (PMMA) BK-F membranes (Toray Medical Company, Japan) allow a dramatic diminution of the molecule. We took advantage of this observation to address the question of the potential usefulness of PMMA membrane (BK-F series) in the improvement of humoral immune response of ESRD patients. We, thus, present our recent data highlighting the potential role of BK-F membrane in the improvement of hepatitis B vaccination of ESRD patients who failed to mount a protective immune response despite one or more well-conducted anterior vaccination.

Taken as a whole, our findings reinforced the concept of seeing dialysis membranes not just as a simple diffusive device but as a tool to tailor dialysis procedure to improve the global quality of life of ESRD patients. This opens a wide area of investigation, notably for the management of immunological dysfunction of ESRD patients.

Full-length, membrane-anchored TWEAK can function as a juxtacrine signaling molecule and activate the NF-kappaB pathway

Tumor necrosis factor (TNF) family members are initially synthesized as type II transmembrane proteins, but some of these proteins are substrates for proteolytic enzymes that generate soluble cytokines with biological activity. TWEAK (TNF-like weak inducer of apoptosis), a member of the TNF family, is a multifunctional cytokine that acts via binding to a cell surface receptor named Fn14 (fibroblast growth factor-inducible 14). Studies conducted to date indicate that TWEAK-producing cells can co-express both membrane-anchored and soluble TWEAK isoforms, but there is little information on TWEAK proteolytic processing. Also, it is presently unclear whether membrane-anchored TWEAK, like soluble TWEAK, is biologically active. Here we show that full-length human TWEAK is processed intracellularly by the serine protease furin and identify TWEAK amino acid residues 90-93 as the predominant furin recognition site. In addition, we report that full-length, membrane-anchored TWEAK can bind the Fn14 receptor on neighboring cells and activate the NF-kappaB signaling pathway. Thus, TWEAK can act in a juxtacrine manner to initiate cellular responses, and this property may be important for TWEAK function during physiological wound repair and disease pathogenesis.

ADAM10 is essential for Notch2-dependent marginal zone B cell development and CD23 cleavage in vivo

The proteolytic activity of a disintegrin and metalloproteinase 10 (ADAM10) regulates cell-fate decisions in Drosophila and mouse embryos. However, in utero lethality of ADAM10^−/− mice has prevented examination of ADAM10 cleavage events in lymphocytes. To investigate their role in B cell development, we generated B cell–specific ADAM10 knockout mice. Intriguingly, deletion of ADAM10 prevented development of the entire marginal zone B cell (MZB) lineage. Additionally, cleavage of the low affinity IgE receptor, CD23, was profoundly impaired, but subsequent experiments demonstrated that ADAM10 regulates CD23 cleavage and MZB development by independent mechanisms. Development of MZBs is dependent on Notch2 signaling, which requires proteolysis of the Notch2 receptor by a previously unidentified proteinase. Further experiments revealed that Notch2 signaling is severely impaired in ADAM10-null B cells. Thus, ADAM10 critically regulates MZB development by initiating Notch2 signaling. This study identifies ADAM10 as the in vivo CD23 sheddase and an important regulator of B cell development. Moreover, it has important implications for the treatment of numerous CD23- and Notch-mediated pathologies, ranging from allergy to cancer.

CD40/CD40L signaling and its implication in health and disease

CD40, a transmembrane receptor of the tumor necrosis factor gene superfamily is expressed on a variety of cells, such as monocytes, B-cells, antigen presenting cells, endothelial, smooth muscle cells, and fibroblasts. The interaction between CD40 and CD40 ligand (CD40L) enhances the expression of cytokines, chemokines, matrix metalloproteinases, growth factors, and adhesion molecules, mainly through the stimulation of nuclear factor kappa B. The aim of this review is to summarize the molecular and cellular characteristics of CD40 and CD40L, the mechanisms that regulate their expression, the cellular responses they stimulate and finally their implication in the pathophysiology of inflammatory and autoimmune diseases.

Plasma-soluble CD40 is related to cholesterol metabolism in patients with moderate hypercholesterolemia

OBJECTIVES

CD40 is a marker of immunological activation and is expressed in the atherosclerotic lesions. We studied whether CD40 and cholesterol synthesis pathways are associated with each other.

DESIGN

Forty-three subjects were randomly assigned to receive either simvastatin (n = 14), atorvastatin (n = 15), or placebo (n = 14) for eight weeks. Plasma samples were obtained before and at the end of the follow-up. sCD40 levels were measured in duplicate using an enzyme-linked immunosorbent assay. Cholesterol, its precursor lathosterol, the plant sterols campesterol and sitosterol as well as 27-hydroxycholesterol were quantified by gas-liquid chromatography-mass spectrometry.

RESULTS

sCD40 was inversely correlated with the lathosterol to cholesterol ratio (r = - 0.47, p = 0.002), an indicator of cholesterol synthesis rate, as well as apolipoprotein A-I (r = - 0.38, p = 0.01) in addition to being directly correlated with 27-hydroxycholesterol (r = 0.40, p = 0.008). In multivariate linear regression analysis these three predictors explained 37% of the total variability of sCD40 levels. Simvastatin or atorvastatin treatment had no significant effect on sCD40 levels.

CONCLUSION

These results indirectly suggest that sCD40 concentrations are related to cellular cholesterol levels. This may be a novel indication for the relationship between immunological processes and cholesterol metabolism.

High plasma levels of CD40 are associated with low coenzyme Q and vitamin E content of low‐density lipoprotein in healthy men

OBJECTIVE

There is a growing body of evidence to suggest that low-density lipoprotein (LDL) cholesterol, inflammation and oxidative stress are pivotal in the development of cardiovascular disease, but their interconnections are not well known. The objective of this study was to determine whether immunological activation, reflected by the plasma levels of soluble CD40 (sCD40), interleukin (IL)-1beta, tumor necrosis factor-alpha and IL-6 are associated with the antioxidant potential of LDL particles or with common lipid, immunological or thrombotic markers in 51 young healthy men.

MATERIAL AND METHODS

We determined the coenzyme Q level from an oxidized LDL fraction, obtaining the concentration for ubiquinone, which indicates total coenzyme Q levels.

RESULTS

The plasma level of sCD40 was negatively correlated with LDL ubiquinone (r=-0.45, p=0.001) and E vitamin (r=-0.37, p=0.008) and positively correlated with plasma concentration of plasminogen activator inhibitor-1 (PAI-1, r=0.52, p=0.002) and caspase-1 (r=0.40, p=0.004). No correlation was detected between sCD40 and plasma lipid or C-reactive protein concentrations. As sCD40 was strongly correlated with the content of LDL ubiquinone and vitamin E, their values were compared according to groups formed by sCD40 tertiles. Analysis of variance showed that there were significant differences in LDL ubiquinone (p<0.0001) and vitamin E (p=0.004) concentrations between sCD40 tertiles.

CONCLUSIONS

The data indicate that increased activation of the CD40 system is related to low levels of LDL ubiquinone and vitamin E. This suggests that chronic or increased immunological activation may consume the antioxidant potential of LDL particles.

Proinflammatory and prothrombotic effects on human vascular endothelial cells of immune-cell-derived LIGHT

Objective

LIGHT (TNFSF 14) belongs to the tumor necrosis factor superfamily and is expressed by activated T cells as well as various types of antigen presenting cells. LIGHT binds to its cellular receptors TR2 and LTßR and has a co-stimulatory role in T cell activation. Here, we compared the relative expression of LIGHT in different immune cells and the biological activity of immune cell-derived LIGHT on endothelial cells.

Methods and Results

Surface expression of LIGHT and mRNA production by PBMC and isolated T cells (CD4⁺ or CD8⁺) significantly increased after stimulation with PMA (Phorbolester-12-Myristat-13-Acetat) + ionomycin. No LIGHT expression on PMA stimulated monocytes or monocytic-like THP-1 cells could be detected; differentiation of monocytes and THP-1 cells into macrophages, however, resulted in up-regulation of LIGHT. Supernatants of stimulated T cells contained higher concentrations of soluble LIGHT than macrophage supernatants normalized to cell numbers; release of soluble LIGHT was found to be dependent on metalloproteinase activity. Size determination of released soluble LIGHT by size exclusion chromatography revealed a molecular mass of ~60 kDa, suggesting a trimeric form. Released soluble LIGHT induced expression of proinflammatory antigens ICAM-1, tissue factor and IL-8 in human endothelial cells and caused apoptosis of IFN-γ pretreated endothelial cells. Soluble LIGHT was detected at low levels in sera of healthy controls and was significantly enhanced in sera of patients with chronic hepatitis C and rheumatoid arthritis (24.93 ± 9.41 vs.129.53 ± 49.14 and 172.13 ± 77.64; p < 0.0005).

Conclusion

These findings suggest that among immune cells activated T lymphocytes are the main source of soluble LIGHT with released amounts of soluble LIGHT markedly higher compared to platelets. Immune cell-derived membrane-bound and soluble trimeric LIGHT is biologically active, inducing proinflammatory changes in endothelial cells. Enhanced plasma levels of soluble LIGHT in patients with chronic infections suggest a role of LIGHT in systemic inflammatory activation.

The "a disintegrin and metalloprotease" (ADAM) family of sheddases: physiological and cellular functions

There is an exciting increase of evidence that members of the disintegrin and metalloprotease (ADAM) family critically regulate cell adhesion, migration, development and signalling. ADAMs are involved in "ectodomain shedding" of various cell surface proteins such as growth factors, receptors and their ligands, cytokines, and cell adhesion molecules. The regulation of these proteases is complex and still poorly understood. Studies in ADAM knockout mice revealed their partially redundant roles in angiogenesis, neurogenesis, tissue development and cancer. ADAMs usually trigger the first step in regulated intramembrane proteolysis leading to activation of intracellular signalling pathways and the release of functional soluble ectodomains.

ADAM function in embryogenesis

Cleavage of proteins inserted into the plasma membrane (shedding) is an essential process controlling many biological functions including cell signaling, cell adhesion and migration as well as proliferation and differentiation. ADAM surface metalloproteases have been shown to play an essential role in these processes. Gene inactivation during embryonic development have provided evidence of the central role of ADAM proteins in nematodes, flies, frogs, birds and mammals. The relative contribution of four subfamilies of ADAM proteins to developmental processes is the focus of this review.

The ADAM metalloproteinases

The ADAMs (a disintegrin and metalloproteinase) are a fascinating family of transmembrane and secreted proteins with important roles in regulating cell phenotype via their effects on cell adhesion, migration, proteolysis and signalling. Though all ADAMs contain metalloproteinase domains, in humans only 13 of the 21 genes in the family encode functional proteases, indicating that at least for the other eight members, protein–protein interactions are critical aspects of their biological functions. The functional ADAM metalloproteinases are involved in “ectodomain shedding” of diverse growth factors, cytokines, receptors and adhesion molecules. The archetypal activity is shown by ADAM-17 (tumour necrosis factor-α convertase, TACE), which is the principal protease involved in the activation of pro-TNF-α, but whose sheddase functions cover a broad range of cell surface molecules. In particular, ADAM-17 is required for generation of the active forms of Epidermal Growth Factor Receptor (EGFR) ligands, and its function is essential for the development of epithelial tissues. Several other ADAMs have important sheddase functions in particular tissue contexts. Another major family member, ADAM-10, is a principal player in signalling via the Notch and Eph/ephrin pathways. For a growing number of substrates, foremost among them being Notch, cleavage by ADAM sheddases is essential for their subsequent “regulated intramembrane proteolysis” (RIP), which generates cleaved intracellular domains that translocate to the nucleus and regulate gene transcription. Several ADAMs play roles in spermatogenesis and sperm function, potentially by effecting maturation of sperm and their adhesion and migration in the uterus. Other non-catalytic ADAMs function in the CNS via effects on guidance mechanisms. The ADAM family are thus fundamental to many control processes in development and homeostasis, and unsurprisingly they are also linked to pathological states when their functions are dysregulated, including cancer, cardiovascular disease, asthma, Alzheimer’s disease. This review will provide an overview of current knowledge of the human ADAMs, discussing their structure, function, regulation and disease involvement.

Drug insight: tumor necrosis factor-converting enzyme as a pharmaceutical target for rheumatoid arthritis

The success of agents that inhibit tumor necrosis factor (TNF), such as infliximab, adalimumab and etanercept, has led to a desire for orally available small molecules that have a better safety profile and are less costly to produce than current agents. One target for anti-TNF therapy that is currently under investigation is TNF-converting enzyme, which promotes the release of soluble TNF from its membrane-bound precursor. Inhibitors of this enzyme with drug-like properties have been made and tested in the clinic. These inhibitors include TMI-005 and BMS-561392, both of which have entered into phase II clinical trials. This article summarizes preclinical and clinical findings regarding the use of inhibitors of TNF-converting enzyme for the treatment of rheumatoid arthritis.

A functional TNFRSF5 gene variant is associated with risk of lymphoma

CD40 and its ligand, CD154, are major costimulatory molecules whose interactions are important in humoral and cellular immunity. We hypothesized that single nucleotide polymorphisms (SNPs) in TNFRSF5 and TNFSF5 encoding the CD40 and CD154 proteins, respectively, influence lymphoma risk, particularly a functional TNFRSF5 SNP (-1C>T, rs1883832) associated with reduced B-cell CD40 expression. TNFRSF5 and TNFSF5 SNPs were examined in a population-based case-control study of non-Hodgkin lymphoma (376 cases/801 controls with DNA), and compelling findings were followed up in 2 independent populations. Pooled analyses of all 3 case-control studies (total N = 1776 non-Hodgkin lymphoma cases, N = 2482 controls) revealed an increased risk of follicular lymphoma (FL) associated with the TNFRSF5 -1TT genotype (odds ratio = 1.6; 95% confidence interval, 1.1-2.4). In addition, among women, an inverse association was found between the variant A allele for a TNFSF5 6809G>A SNP and FL risk (OR = .61; 95% CI, 0.36-0.98). In genotype-phenotype studies, significantly reduced circulating soluble CD40 was observed in TNFRSF5 -1TT compared with -1CC carriers. Further, dendritic cells from those with -1TT versus -1CC genotypes exhibited lower CD40 cell surface expression. These results suggest that the TNFRSF5 -1C>T polymorphism may increase FL susceptibility through mechanisms that hinder cellular immune responses. Further studies are needed to explore these findings.

Clipping, shedding and RIPping keep immunity on cue

Exposure to infectious agents elicits defense mechanisms that necessitate a timely immune response. The immediate delivery of essential cues for immune activation is provided, in part, by proteolytic processing. A large repertoire of molecules orchestrates the activation, migration, and effector function of immune cells. The diversity of this repertoire matches well with the broad array of substrates that can be cleaved by proteinases, and many of these substrates are proving to be essential for proper immune-cell function. Here, we discuss how two specific classes of metal-dependent proteinases, the matrix metalloproteinases and the disintegrin metalloproteinases, have consequences well beyond classical cell-matrix and cell-cell interactions and motility, and we review their roles in immune-cell maturation, clonal expansion, and cytotoxic functions.

Non-Cell Autonomous Expression of TNF-α-Converting Enzyme ADAM17 Is Required for Normal Lymphocyte Development

TNF-alpha converting enzyme (TACE; ADAM17), a member of the ADAM (a disintegrin and metalloprotease) family of metalloproteases, has been shown to cleave a wide variety of cell surface proteins of immunological importance. Due to the broad expression of TACE and the early postnatal lethality of TACE-deficient mice, it has been difficult to assess the role of TACE in lymphocyte development. Indeed, it is not known whether hemopoietic and/or nonhemopoietic expression of TACE is required for normal lymphocyte development. In the current study, we analyzed the lymphoid system of tace(DeltaZn/DeltaZn) mice and tace(DeltaZn/DeltaZn) bone marrow RAG1(-/-) recipients. Our results clearly show that nonlymphocyte expression of TACE is required for normal lymphocyte development and lymphoid organ structure. Lack of TACE function resulted in a partial block in T cell development at the double-negative 4:double-positive transition in the thymus, a loss of B cell development/maturation in the spleen, and a lack of B cell follicle and germinal center formation in the spleen. Thus, TACE serves as a lymphocyte extrinsic factor that is essential for normal T development and peripheral B cell maturation.

An essential role for Akt1 in dendritic cell function and tumor immunotherapy

Current dendritic cell (DC) vaccine preparations involving ex vivo differentiation and maturation produce short-lived, transiently active DCs that may curtail T-cell responses in vivo. We demonstrate that Akt1, downregulation of which decreases DC lifespan, is critical for proinflammatory signal-mediated DC survival and maturation. Lipopolysaccharide or CD40 signaling stabilizes Akt1, promoting both activation and Bcl-2-dependent survival of DCs. Expression of a potent allele encoding a lipid raft-targeted Akt1, M(F)-DeltaAkt, is sufficient for maturation and survival of murine bone marrow-derived DCs in vivo. M(F)-DeltaAkt-transduced DCs enhanced T-cell proliferation, activation and long-term memory responses, enabling eradication of large pre-established lymphomas and aggressive B16 melanomas. Human myeloid DCs expressing constitutively active M(F)-DeltahAkt also survived significantly longer and promoted antigen-specific T-cell responses. Thus, Akt1 is a critical regulator of DC lifespan, and its manipulation in DCs can improve the clinical efficacy of DC-based tumor vaccines.

Upregulation of ADAM-17 expression in active lesions in multiple sclerosis

ADAM-17, a disintegrin and metalloproteinase, is the major proteinase responsible for the cleavage of membrane-bound tumour necrosis factor (TNF) as well as being an active sheddase of other cytokines, cytokine receptors, growth factors and adhesion molecules. TNF is a major proinflammatory cytokine that has been identified as having a pathogenic role in inflammatory diseases within the CNS including multiple sclerosis (MS). Here we report the cellular origin and distribution of ADAM-17 expression within clinically and neuropathologically confirmed MS and normal control white matter, assessed by immunohistochemistry, western blotting and PCR. ADAM-17 expression was associated with the blood vessel endothelium, activated macrophages/microglia and parenchymal astrocytes in MS white matter. Increased levels of ADAM-17 immunoreactivity were displayed in active lesions with evidence of recent myelin breakdown. Further studies into the functional role of ADAM-17 in the pathogenesis of MS and other inflammatory conditions are required.

Differential regulation of soluble and membrane CD40L proteins in T cells

CD40 ligand is an important immunoregulatory protein expressed by T cells. This protein exists as two isoforms, a membrane glycoprotein and a truncated soluble form. Here we demonstrate that membrane and soluble CD40L (sCD40L) are differentially regulated depending upon the activation stimulus. In T cell receptor activated cells, both membrane and sCD40L proteins are expressed and CD28 costimulation further increases their expression. The dissection of TCR generated signals into calcium and PKC-dependent pathways demonstrates that calcium is sufficient to induce membrane CD40L yet insufficient for sCD40L. In contrast, sCD40L is preferentially induced by PKC. Moreover, sCD40L production is blocked by Zn(2+)-dependent metalloproteinase inhibitors while membrane CD40L is concurrently increased. This profile suggests the potential involvement of the ADAM-10 protease which was subsequently shown to cleave membrane CD40L to generate sCD40L. Given the role of sCD40L in numerous disease pathologies and its ability to activate proximal and distal immune responses, the regulated cleavage of CD40L may likely contribute to disease mechanisms.

ICOS-Induced B7h Shedding on B Cells Is Inhibited by TLR7/8 and TLR9

We report in this study that B7h, the ligand for the ICOS costimulatory receptor, is rapidly shed from mouse B cells following either ICOS binding or BCR engagement. Shedding occurs through proteolytic cleavage that releases the extracellular ICOS-binding region of B7h. Prior exposure of B7h-expressing APCs to ICOS-expressing cells inhibits their subsequent ability to costimulate IFN-gamma and IL-4 production from CD4+ T cells. Shedding is regulated as TLR7/8 and TLR9 ligands inhibit B7h shedding. A shedding-resistant B7h mutant elicits greater costimulation of IFN-gamma production from CD4+ T cells than does wild-type B7h. These data define shedding of B7h as a novel mechanism for controlling costimulatory signaling by B7-CD28 family members that is regulated on B cells by TLR signaling.

Circulating levels and clinical significance of soluble CD40 in patients with hematologic malignancies

BACKGROUND

CD40 plays a critical role in immunoregulation, and CD40 ligation is being investigated as a therapy for hematologic malignancies. Although soluble CD40 (sCD40) is a potential modulator of both antitumor responses and CD40-based therapies, the levels and significance of sCD40 in patients with hematologic malignancies are unknown.

METHODS

The authors evaluated serum/plasma sCD40 levels using an enzyme-linked immunoassay in patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), and multiple myeloma (MM).

RESULTS

Levels of sCD40 were elevated in serum (>1.697 ng/mL) or plasma (>0.649 ng/mL) from 73% of patients with CLL, 80% of patients with MCL, 40% of patients with AML, 43% of patients with MDS, and 33% of patients with MM. Multivariate analysis of patients with MM demonstrated that elevated sCD40 was a significant, independent predictor of poor survival. In multivariate analysis of patients with AML, sCD40 was a significant prognostic factor when the interaction of age and sCD40 was included as a variable. Further analysis demonstrated that elevated sCD86 levels were associated with significantly shorter survival only in AML patients younger than age 64 years. Release of sCD40 by CLL cells was induced by cross-linking with CD40 monoclonal antibody.

CONCLUSIONS

Many patients with hematologic malignancies have elevated circulating levels of sCD40, and these elevated levels are associated with a poor prognosis at least in patients with MM and AML, suggesting that sCD40 may have a role in modulating antitumor responses and also may be a useful prognostic marker. In addition, the findings suggested that further studies will be required to determine the effect of circulating sCD40 on the clinical effectiveness of CD40-ligating reagents used in the treatment of hematologic malignancies.

Components of the antigen processing and presentation pathway revealed by gene expression microarray analysis following B cell antigen receptor (BCR) stimulation

Background

Activation of naïve B lymphocytes by extracellular ligands, e.g. antigen, lipopolysaccharide (LPS) and CD40 ligand, induces a combination of common and ligand-specific phenotypic changes through complex signal transduction pathways. For example, although all three of these ligands induce proliferation, only stimulation through the B cell antigen receptor (BCR) induces apoptosis in resting splenic B cells. In order to define the common and unique biological responses to ligand stimulation, we compared the gene expression changes induced in normal primary B cells by a panel of ligands using cDNA microarrays and a statistical approach, CLASSIFI (Cluster Assignment for Biological Inference), which identifies significant co-clustering of genes with similar Gene Ontology™ annotation.

Results

CLASSIFI analysis revealed an overrepresentation of genes involved in ion and vesicle transport, including multiple components of the proton pump, in the BCR-specific gene cluster, suggesting that activation of antigen processing and presentation pathways is a major biological response to antigen receptor stimulation. Proton pump components that were not included in the initial microarray data set were also upregulated in response to BCR stimulation in follow up experiments. MHC Class II expression was found to be maintained specifically in response to BCR stimulation. Furthermore, ligand-specific internalization of the BCR, a first step in B cell antigen processing and presentation, was demonstrated.

Conclusion

These observations provide experimental validation of the computational approach implemented in CLASSIFI, demonstrating that CLASSIFI-based gene expression cluster analysis is an effective data mining tool to identify biological processes that correlate with the experimental conditional variables. Furthermore, this analysis has identified at least thirty-eight candidate components of the B cell antigen processing and presentation pathway and sets the stage for future studies focused on a better understanding of the components involved in and unique to B cell antigen processing and presentation.

Generation of a multimeric form of CD40L with potent immunostimulatory activity using streptavidin as a chaperon

Effective aggregation of cell surface immune receptors with their ligands is critical in promoting humoral and cellular immune responses. Simulation of these interactions using soluble multimeric ligands having potent adjuvant effects may prove an effective alternative to agonistic antibodies as immunotherapeutics. Multimeric ligands may effectively engage their receptors, leading to aggregation and effective signal transduction. We exploited the structural characteristics of streptavidin (SA) for the generation of multimeric chimeric proteins. Streptavidin forms stable tetramers and oligomers under physiological conditions, and, as such, chimeric molecules with SA are expected to possess similar features. Two chimeric molecules consisting of the extracellular domains of human and mouse CD40L and a modified form of core streptavidin were generated. These proteins form stable oligomers that could only be dissociated into monomers by heating at 100 degrees C, but not 60 degrees C, under denaturing conditions. The chimeric proteins vigorously stimulated B cells, monocytes, and dendritic cells for the production of cytokines and chemokines and upregulation of immunostimulatory molecules. The use of SA as a chaperon presents a novel approach to generate multimeric immunological molecules with potent activities and their use as potential therapeutics for the treatment of cancer and other immune-based disorders.

Activation of mesangial cells by platelets in systemic lupus erythematosus via a CD154-dependent induction of CD40

BACKGROUND

Platelets are potential contributors to glomerular injury via the release of chemotactic and/or mitogenic mediators upon activation or through direct CD154/CD40-dependent interaction with cell components of the glomerulus. We examined whether platelets could activate mesangial cells and the potential role of the platelet-associated CD154.

METHODS

Thrombin-activated platelets from systemic lupus erythematosus (SLE) patients or from disease or healthy controls were grown with human mesangial cells in the presence or not of a neutralizing anti-CD154 antibody either in contact or in a noncontact setting, the platelets and mesangial cells being separated by a pore size semipermeable membrane. The induction of mesangial cell surface antigens was assayed by flow cytometry. The quantification of mesangial cell proliferation was performed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and the production of transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor (PDGF) and soluble CD40 were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Activated platelets from patients with SLE could induce an up-regulation of the expression of CD40 on mesangial cells with a concomitant release of soluble CD40. This induction required a direct contact between platelets and mesangial cells and was dependent upon the platelet-associated CD154. Pathologic consequences of the up-regulation of CD40 were a CD40-dependent stimulation of the proliferation of mesangial cells and a CD40-dependent increased production of TGF-beta1 by these cells.

CONCLUSION

Platelets from patients with SLE can activate mesangial cells through CD40/CD154 interactions, leading to an induction of proliferation of the mesangial cells and an enhanced production of TGF-beta1, a profibrotic cytokine.

Differential responses of human B-lymphocyte subpopulations to graded levels of CD40-CD154 interaction

Naïve and memory B-lymphocyte populations are activated by CD154 interaction through cell-surface CD40. This interaction plays an important role in the regulation of the humoral immune response, and increasing evidence indicates that fine variation in CD40 binding influences B lymphocytes, macrophages and dendritic cells in murine models. Here we have investigated whether and how variations in the intensity of the CD40-CD154 interaction could contribute to differential regulation of human B-lymphocyte populations. Proliferation and differentiation of B lymphocytes were monitored in response to graded levels of CD40 stimulation in the presence of interleukin (IL)-2, IL-4 and IL-10. Our results show that the level of CD154 binding to CD40 on B lymphocytes can directly influence the evolution of CD19(+) CD27(-) and CD19(+) CD27(+) cell populations. Furthermore, proliferation, global expansion of CD19(+) cells and emergence of CD38(++) CD138(+) cells, as well as immunoglobulin G (IgG) and IgM secretion, were affected by the level of exposure of B lymphocytes to CD154. These results suggest that the CD40-CD154 interaction is more like a rheostat than an on/off switch, and its variation of intensity may play a role in the regulation of B-lymphocyte activation following the primary and/or secondary humoral immune response.

Aspirin Induces Platelet Receptor Shedding via ADAM17 (TACE)

Aspirin is effective in the therapy of cardiovascular diseases, because it causes acetylation of cyclooxygenase 1 (COX-1) leading to irreversible inhibition of platelets. Additional mechanisms can be suspected, because patients treated with other platelet COX inhibitors such as indomethacin do not display an increased bleeding tendency as observed for aspirin-treated patients. Recently, aspirin and other anti-inflammatory drugs were shown to induce shedding of L-selectin in neutrophils in a metalloproteinase-dependent manner. Therefore, we investigated the effects of aspirin on the von Willebrand Factor receptor complex glycoprotein (GP) Ib-V-IX, whose lack or dysfunction causes bleeding in patients. As quantified by fluorescence-activated cell sorting analysis in whole blood, aspirin, but not its metabolite salicylic acid, induced dose-dependent shedding of human and murine GPIbalpha and GPV from the platelet surface, whereas other glycoproteins remained unaffected by this treatment. Biotinylated fragments of GPV were detected by immunoprecipitation in the supernatant of washed mouse platelets, and the expression level of GPIbalpha was decreased in these platelets as measured by Western blot analysis. Although shedding occurred normally in COX-1-deficient murine platelets, shedding was completely blocked by a broad-range metalloproteinase inhibitor and, more importantly, in mouse platelets expressing an inactive form of ADAM17. Shed fragments of GPIbalpha and GPV were elevated in the plasma of aspirin-injected mice compared with animals injected with control buffer. These data demonstrate that aspirin at high concentrations induces shedding of GPIbalpha and GPV by an ADAM17-dependent mechanism and that this process can occur in vivo.

Timp3 deficiency in insulin receptor-haploinsufficient mice promotes diabetes and vascular inflammation via increased TNF-alpha

Activation of inflammatory pathways may contribute to the beginning and the progression of both atherosclerosis and type 2 diabetes. Here we report a novel interaction between insulin action and control of inflammation, resulting in glucose intolerance and vascular inflammation and amenable to therapeutic modulation. In insulin receptor heterozygous (Insr+/-) mice, we identified the deficiency of tissue inhibitor of metalloproteinase 3 (Timp3, an inhibitor of both TNF-alpha-converting enzyme [TACE] and MMPs) as a common bond between glucose intolerance and vascular inflammation. Among Insr+/- mice, those that develop diabetes have reduced Timp3 and increased TACE activity. Unchecked TACE activity causes an increase in levels of soluble TNF-alpha, which subsequently promotes diabetes and vascular inflammation. Double heterozygous Insr+/-Timp3+/- mice develop mild hyperglycemia and hyperinsulinemia at 3 months and overt glucose intolerance and hyperinsulinemia at 6 months. A therapeutic role for Timp3/TACE modulation is supported by the observation that pharmacological inhibition of TACE led to marked reduction of hyperglycemia and vascular inflammation in Insr+/- diabetic mice, as well as by the observation of increased insulin sensitivity in Tace+/- mice compared with WT mice. Our results suggest that an interplay between reduced insulin action and unchecked TACE activity promotes diabetes and vascular inflammation.

Up regulated expression of tumour necrosis factor {alpha} converting enzyme in peripheral monocytes of patients with early systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is accompanied by abnormalities in humoral and cellular immune systems.

OBJECTIVE

To determine the genes specifically expressed in the immune system in SSc by analysis of the gene expression profile of peripheral blood mononuclear cells (PBMC) from patients with SSc, including those treated with haematopoietic stem cell transplantation (HSCT). Additionally, to investigate the clinical significance of the up regulation of tumour necrosis factor alpha (TNFalpha) converting enzyme (TACE).

METHODS

PBMC from patients with SSc (n = 23) and other autoimmune diseases (systemic lupus erythematosus (SLE, n = 16), rheumatoid arthritis (RA, n = 29)), and from disease-free controls (n = 36) were examined. Complementary DNA arrays were used to evaluate gene expression of PBMC, in combination with real time quantitative polymerase chain reactions. TACE protein expression in PBMC was examined by fluorescence activated cell sorter (FACS).

RESULTS

In patients with SSc 118 genes were down regulated after HSCT. Subsequent comparative analysis of SSc without HSCT and healthy controls indicated SSc-specific up regulation for three genes: monocyte chemoattractant protein-3 (p = 0.0015), macrophage inflammatory protein 3alpha (p = 0.0339), and TACE (p = 0.0251). In the FACS analysis, TACE protein was mainly expressed on CD14(+) monocytes both in patients with SSc and controls. TACE expression on CD14(+) cells was significantly increased in patients with early SSc (p = 0.0096), but not in those with chronic SSc, SLE, or RA. TACE protein levels in SSc monocytes correlated with the intracellular CD68 levels (p = 0.0016).

CONCLUSIONS

Up regulation of TACE expression was a unique profile in early SSc, and may affect the function of TNFalpha and other immunoregulatory molecules.

L-selectin: mechanisms and physiological significance of ectodomain cleavage

L-selectin is a cell adhesion molecule consisting of a large, highly glycosylated, extracellular domain, a single spanning transmembrane domain and a small cytoplasmic tail. It is expressed on most leukocytes and is involved in their rolling on inflamed vascular endothelium prior to firm adhesion and transmigration. It is also required for the constitutive trafficking of lymphocytes through secondary lymphoid organs. Like most adhesion molecules, L-selectin function is regulated by a variety of mechanisms including gene transcription, post-translational modifications, association with the actin cytoskeleton, and topographic distribution. In addition, it is rapidly downregulated by proteolytic cleavage near the cell surface by ADAM-17 (TACE) and at least one other "sheddase". This process of "ectodomain shedding" results in the release of most of the extracellular portion of L-selectin from the cell surface while retaining the cytoplasmic, transmembrane, and eleven amino acids of the extracellular domain on the cell. This review will examine the mechanism(s) of L-selectin ectodomain shedding and discuss the physiological implications.

ADAM-17 and TIMP3 protein and mRNA expression in spinal cord white matter of rats with acute experimental autoimmune encephalomyelitis

Tumour necrosis factor (TNF) is a major immunomodulatory and proinflammatory cytokine implicated in the pathogenesis of multiple sclerosis (MS) and the animal model experimental autoimmune encephalomyelitis (EAE). ADAM-17 cleaves membrane-bound TNF into its soluble form. The distribution and level of ADAM-17 expression within spinal cords of Lewis rats with EAE was investigated. ADAM-17 was associated with endothelial cells in the naïve and pre-disease spinal cords. In peak disease astrocytic and inflammatory cells expressed ADAM-17. Upregulation of ADAM-17 mRNA expression was coupled with a decrease in mRNA levels of its inhibitor TIMP3 suggesting a role for ADAM-17 in EAE pathogenesis.

Shedding light on ADAM metalloproteinases

ADAM metalloproteinase disintegrins have emerged as the major proteinase family that mediates ectodomain shedding, the proteolytic release of extracellular domains from their membrane-bound precursors. Recent gene-manipulation studies have established the role of ADAM-mediated shedding in mammalian physiology and, in addition, raised the issue of functional redundancy among ADAM sheddases. ADAM sheddases activate, for example, growth factors and cytokines, thus regulating signalling pathways that are important in development and pathological processes such as cancer. The recent studies have also begun to elucidate the substrate specificity and the mechanisms that control ADAM-mediated shedding events that regulate, for example, growth-factor and Notch signalling, and the processing of the amyloid precursor protein.

Genes transactivated by hepatitis C virus core protein, a microarray assay

AIM: To explore the new target genes transactivated by hepatitis C virus (HCV) core protein and to elucidate the pathogenesis of HCV infection.

METHODS: Reverse transcribed cDNA was subjected to microarray assay. The coding gene transactivated by HCV core protein was cloned and analyzed with bioinformatics methods.

RESULTS: The expressive vector of pcDNA3.1(-)-core was constructed and confirmed by restriction enzyme digestion and DNA sequencing and approved correct. mRNA was purified from HepG2 and HepG2 cells transfected with pcDNA3.1(-)-core, respectively. The cDNA derived was subjected to microarray assay. A new gene named HCTP4 was cloned with molecular biological method in combination with bioinformatics method.

CONCLUSION: HCV core is a potential transactivator. Microarray is an efficient and convenient method for analysis of differentially expressed genes.

Nectin-4, a new serological breast cancer marker, is a substrate for tumor necrosis factor-alpha-converting enzyme (TACE)/ADAM-17

Serum markers are extensively used in diagnostic and follow-up of cancer patients. We recently described Nectin-4, a 66-kDa adhesion molecule of the Nectin family, which is a valuable new histological and serological marker for breast carcinoma. In vivo, Nectin-4 is re-expressed in breast carcinoma, and a circulating form of Nectin-4 is detected in the sera of patients with metastatic breast cancer. In vitro, a soluble form of Nectin-4 is produced in the supernatant of breast tumor cell lines (S. Fabre-Lafay, C. Ginestier, S. Garrido-Urbani, C. Berruyer, R. Sauvan, N. Reymond, J. Adelaide, J. Geneix, P. Dubreuil, J. Jacquemier, D. Birnbaum, and M. Lopez, manuscript in preparation). We have investigated the mechanisms that regulate the production of this soluble form. It was found that the soluble form of Nectin-4 detected in the sera of patients and the supernatant of breast tumor cell lines share similar biochemical and immunological features. The soluble Nectin-4 form (43 kDa) is formed by the entire Nectin-4 ectodomain. Nectin-4 shedding is constitutive, strongly enhanced by 12-O-tetradecanoylphorbol-13-acetate activation, and reduced tumor necrosis factor-alpha protease inhibitor TAPI-1 or by the tissue inhibitor of metalloproteinase-3 (TIMP-3). TAPI-1 and TIMP-3 are inhibitors of the endoprotease tumor necrosis factor-alpha-converting enzyme (TACE)/ADAM-17. Overexpression or small interfering RNA-mediated silencing of TACE enhanced or reduced Nectin-4 shedding, respectively. Nectin-4 is not shed when expressed in TACE-deficient fibroblasts. Interestingly, the active form of TACE is overexpressed in breast tumors and may indicate that TACE is responsible for Nectin-4 shedding not only in vitro but also in vivo.

Amino-terminal TACE prodomain attenuates TNFR2 cleavage independently of the cysteine switch

TNF-alpha-converting enzyme (TACE, ADAM17) cleaves membrane-associated cytokines and receptors and thereby regulates inflammatory and immune events, as well as lung development and mucin production. For example, the TACE-mediated cleavage of the type II 75-kDa TNF receptor (TNFR2) generates a soluble TNF-binding protein that modulates TNF bioactivity. TACE is synthesized as a latent proenzyme that is retained in an inactive state via an interaction between its prodomain and catalytic domain. Although the formation of an intramolecular bond between a cysteine in the prodomain and a zinc atom in the catalytic site had been thought to mediate this inhibitory activity, it was recently reported that the cysteine-switch motif is not required. Here, we hypothesized that the amino terminus of the TACE prodomain might contribute to the ability of the prodomain to maintain TACE in an inactive state independently of a cysteine-switch mechanism. We synthesized a 37-amino acid peptide corresponding to TACE amino acids 18-54 (N-TACE(18-54)) and assessed whether it possessed TACE inhibitory activity. In an in vitro model assay system, N-TACE(18-54) attenuated TACE-catalyzed cleavage of a TNFR2:Fc substrate. Furthermore, N-TACE(18-54) inhibited constitutive TNFR2 shedding from a human monocytic cell line by 42%. A 19-amino acid, leucine-rich domain, corresponding to TACE amino acids 30-48, demonstrated partial inhibitory activity. In summary, we have identified a subdomain within the amino terminus of the TACE prodomain that attenuates TACE catalytic activity independently of a cysteine-switch mechanism, which provides new insight into the regulation of TACE enzymatic activity.

Expression of membrane-bound and soluble receptor activator of NF-kappaB ligand (RANKL) in human T cells

The receptor activator of NF-kappaB ligand (RANKL) and its receptor RANK are critical regulators for immune responses as well as bone remodeling. RANKL is a type II transmembrane protein that has two forms-a membrane-anchored protein and a secreted protein. In this report, we demonstrate for the first time the kinetical expression of two forms of RANKL in human T cells using two monoclonal antibodies (mAbs) against human RANKL, which we newly derived. Freshly isolated T cells rarely expressed mRANKL, while the activation of T cells induced a substantial but minimal level of mRANKL as well as the accumulation of considerable amounts of sRANKL. The addition of the metalloprotease inhibitor KB-R8301 efficiently suppressed the release of sRANKL from activated T cells or RANKL-transfectants, and reciprocally enhanced the mRANKL expression. The membrane form of RANKL was also expressed on the infiltrating T cells in the rheumatoid synovial fluid and in the gingival tissues of patients with periodontitis. Our results demonstrate that the expression of mRANKL on T cells is strictly limited, and the majority of RANKL protein produced by T cells may be active in the soluble form after shedding. The mAbs that were derived in this study may be useful for investigating the regulation and function of RANKL in immune responses and bone remodeling.

Re-engineered CD40 receptor enables potent pharmacological activation of dendritic-cell cancer vaccines in vivo

Modest clinical outcomes of dendritic-cell (DC) vaccine trials call for the refinement of DC vaccine design. Although many potential antigens have been identified, development of methods to enhance antigen presentation by DCs has lagged. We have engineered a potent, drug-inducible CD40 (iCD40) receptor that permits temporally controlled, lymphoid-localized, DC-specific activation. iCD40 is comprised of a membrane-localized cytoplasmic domain of CD40 fused to drug-binding domains. This allows it to respond to a lipid-permeable, high-affinity dimerizer drug while circumventing ectodomain-dependent negative-feedback mechanisms. These modifications permit prolonged activation of iCD40-expressing DCs in vivo, resulting in more potent CD8(+) T-cell effector responses, including the eradication of previously established solid tumors, relative to activation of DCs ex vivo (P < 0.01), typical of most clinical DC protocols. In addition, iCD40-mediated DC activation exceeded that achieved by stimulating the full-length, endogenous CD40 receptor both in vitro and in vivo. Because iCD40 is insulated from the extracellular environment and can be activated within the context of an immunological synapse, iCD40-expressing DCs have a prolonged lifespan and should lead to more potent vaccines, perhaps even in immune-compromised patients.

A novel blocking monoclonal antibody recognizing a distinct epitope of human CD40 molecule

CD40, a member of the tumor necrosis factor receptor superfamily, is an important costimulatory molecule during the immune response. Here, we report a blocking mouse antihuman CD40 monoclonal antibody, mAb 3G3, of which the specificity was verified by flow cytometry and Western blot. It was shown by competition test that 3G3 bound to a different site (epitope) of CD40 from the reported CD40 mAbs, including clone mAb89, 3B2, and 5C11. It was also found that mAb 3G3 could inhibit homotypic aggregation of Daudi cells induced by the agonistic anti-CD40 mAb 5C11. Furthermore, mAb 3G3 effectively inhibited the proliferation of peripheral blood mononuclear cells in mixed lymphocyte reaction assay. Finally, a sensitive and specific soluble CD40 (sCD40) ELISA kit was established by matching mAb 3G3 with 5C11, and it was found that the levels of sCD40 in sera from patients with immune disorders such as hyperthyroidism, chronic nephritis, and rheumatoid arthritis were obviously higher than those from normal individuals. Thus, this blocking anti-CD40 mAb provides a novel tool for the study of CD40.

Regulation of platelet membrane levels of glycoprotein VI by a platelet-derived metalloproteinase

Thrombosis can be initiated when activated platelets adhere to injured blood vessels via the interaction of subendothelial collagen with its platelet receptor, glycoprotein (GP) VI. Here we observed that incubation of platelets with convulxin, collagen, or collagen-related peptide (CRP) resulted in GPVI signaling-dependent loss of surface GPVI and the appearance of an approximately 55-kDa soluble fragment of GPVI as revealed by immunoblotting. Ethylenediaminetetraacetic acid (EDTA) or GM6001 (a metalloproteinase inhibitor with broad specificity) prevented this loss. In other receptor systems, calmodulin binding to membrane-proximal cytoplasmic sequences regulates metalloproteinase-mediated ectodomain shedding. In this regard, we have previously shown that calmodulin binds to a positively charged, membrane-proximal sequence within the cytoplasmic tail of GPVI. Incubation of platelets with calmodulin inhibitor W7 (150 μM) resulted in a time-dependent loss of GPVI from the platelet surface. Both EDTA and GM6001 prevented this loss. Surface plasmon resonance demonstrated that W7 specifically blocked the association of calmodulin with an immobilized synthetic peptide corresponding to the calmodulin-binding sequence of GPVI. These findings suggest that disruption of calmodulin binding to receptor cytoplasmic tails by agonist binding to the receptor triggers metalloproteinase-mediated loss of GPVI from the platelet surface. This process may represent a potential mechanism to regulate GPVI-dependent platelet adhesion.

Mechanisms of soluble cytokine receptor generation

Soluble cytokine receptors regulate inflammatory and immune events by functioning as agonists or antagonists of cytokine signaling. As such, they act within complex receptor systems that include signaling receptors, nonsignaling decoy receptors, receptor-associated proteins, and soluble receptor antagonists. Soluble cytokine receptors can be generated by several mechanisms, which include proteolytic cleavage of receptor ectodomains, alternative splicing of mRNA transcripts, transcription of distinct genes that encode soluble cytokine-binding proteins, release of full-length receptors within the context of exosome-like vesicles, and cleavage of GPI-anchored receptors. Furthermore, the important role of soluble cytokine receptors in regulating host defense mechanisms is evidenced by viruses that encode soluble homologues of mammalian receptors and thereby evade innate host immune responses via the sequestration of essential cytokines.

N/A

N/A

Natural Soluble Interleukin-15Rα Is Generated by Cleavage That Involves the Tumor Necrosis Factor-α-converting Enzyme (TACE/ADAM17)

This study shows that the high affinity alpha-chain of the interleukin (IL)-15 receptor exists not only in membrane-anchored but also in soluble form. Soluble IL-15Ralpha (sIL-15Ralpha) can be detected in mouse sera and cell-conditioned media by enzyme-linked immunosorbent assay and by immunoprecipitation and Western blotting. This protein has a molecular mass of about 30 kDa because of the presence of a single N-glycosylation site, which is reduced to 26 kDa after N-glycosidase treatment. Transmembrane IL-15Ralpha is constitutively converted into its soluble form by proteolytic cleavage that involves tumor necrosis factor-alpha-converting enzyme (TACE), and this process is further enhanced by phorbol 12-myristate 13-acetate (PMA) stimulation. The hydroxamate GW280264X, which is capable of blocking TACE and the closely related disintegrin-like metalloproteinase 10 (ADAM10), effectively inhibited both spontaneous and PMA-inducible cleavage of IL-15Ralpha, whereas GI254023X, which preferentially blocks ADAM10, was ineffective. Overexpression of TACE but not ADAM10 in COS-7 cells enhanced the constitutive and PMA-inducible cleavage of IL-15Ralpha. Moreover, murine fibroblasts deficient in TACE but not ADAM10 expression exhibited a significant reduction in the spontaneous and inducible IL-15Ralpha shedding, whereas a reconstitution of TACE in these cells restored the release of sIL-15Ralpha, thereby suggesting that TACE-mediated proteolysis may represent a major mechanism for sIL-15Ralpha generation in mice. The existence of natural sIL-15Ralpha offers novel insights into the complex biology of IL-15 and envisages a new level for therapeutic intervention.

Abnormal TNF activity in Timp3-/- mice leads to chronic hepatic inflammation and failure of liver regeneration

Tumor-necrosis factor (TNF), a pleiotropic cytokine, triggers physiological and pathological responses in several organs. Here we show that deletion of the mouse gene Timp3 resulted in an increase in TNF-alpha converting enzyme activity, constitutive release of TNF and activation of TNF signaling in the liver. The increase in TNF in Timp3(-/-) mice culminated in hepatic lymphocyte infiltration and necrosis, features that are also seen in chronic active hepatitis in humans. This pathology was prevented when deletion of Timp3 was combined with Tnfrsf1a deficiency. In a liver regeneration model that requires TNF signaling, Timp3(-/-) mice succumbed to liver failure. Hepatocytes from Timp3(-/-) mice completed the cell cycle but then underwent cell death owing to sustained activation of TNF. This hepatocyte cell death was completely rescued by a neutralizing antibody to TNF. Dysregulation of TNF occurred specifically in Timp3(-/-), and not Timp1(-/-) mice. These data indicate that TIMP3 is a crucial innate negative regulator of TNF in both tissue homeostasis and tissue response to injury.

The CD40/CD40L costimulatory pathway in inflammatory bowel disease

The CD154-CD40 ligand pair interaction plays a central role in both induction of the immune response and in immune effector functions. Indeed, many animal disease models and human autoimmune diseases have demonstrated a central role for CD154 expression. The expression of CD154 is very tightly regulated by the immune system through a number of non-redundant overlapping mechanisms that ensure its limited initial induction, along with its temporal maintenance and rapid elimination from the cell surface, and its functional neutralization by the release of soluble CD40. In this review, we discuss the current state of understanding of CD154 regulation during the activation of the immune system and describe numerous strategic mechanisms by which modulation of CD154-CD40 interactions may be applied to treat autoimmune disease.

Wound-induced HB-EGF ectodomain shedding and EGFR activation in corneal epithelial cells

PURPOSE

Epithelial wound healing is, at least in part, mediated in an autocrine fashion by epidermal growth factor (EGF) receptor (EGFR)-ligand interactions. This study sought to identify the endogenous EGFR ligand and the mechanism by which it is generated in response to wounding in cultured porcine corneas and human corneal epithelial cells.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence of tyrphostin AG1478 (an EGFR inhibitor), GM6001 (a matrix metalloproteinase [MMP] inhibitor), or CRM197 (a diphtheria toxin mutant), with or without HB-EGF. The activation of EGFR and extracellular signal-regulated kinase (ERK) was analyzed by immunoprecipitation using EGFR antibodies and Western blot analysis with phosphotyrosine antibody. Wound induced HB-EGF shedding was assessed by isolation of secreted HB-EGF from wounded THCE cells and by measuring the release of alkaline phosphatase (AP) in THCE stable cell lines expressing HB-EGF-AP.

RESULTS

In THCE cells, wound-induced EGFR phosphorylation and ERK activation. In both organ and cell culture models, epithelial wounds were healed in basal media and inhibition of EGFR activation by AG1478 blocked wound closure with or without exogenously added HB-EGF. GM6001 delayed wound closure. Its effects diminished in the presence of exogenous EGF or HB-EGF, suggesting that the MMP inhibitor primarily blocks the release of EGFR ligands. CRM197, a highly specific antagonist of HB-EGF, impaired epithelial wound closure, suggesting that HB-EGF is an endogenous ligand released on epithelial wounding. Consistent with the effects on epithelial migration, all inhibitors as well as HB-EGF function-blocking antibodies retarded wound-induced EGFR phosphorylation in cultured THCE cells. The release of HB-EGF in response to wounding was demonstrated by the fact that heparin-binding proteins isolated from wounded, but not control, THCE-conditioned medium stimulated EGFR and ERK phosphorylation and by the expression of HB-EGF-AP in THCE cells, in which wounding induced the release of AP activity in an MMP-inhibitor-sensitive manner.

CONCLUSIONS

HB-EGF released on wounding acts as an autocrine-paracrine EGFR ligand. HB-EGF shedding and EGFR activation represent a critical event during corneal epithelial wound healing, suggesting a possible manipulation of wound healing during the early phases.