Tissue inhibitor of metalloproteinases-3 inhibits shedding of L-selectin from leukocytes

Trafficking circuit of CD8+ T cells between the intestine and bone marrow governs antitumour immunity

Immunotherapy elicits a systemic antitumour immune response in peripheral circulating T cells. However, the T cell trafficking circuit between organs and their contributions to antitumour immunity remain largely unknown. Here we show in multiple mouse leukaemia models that high infiltration of leukaemic cells in bone marrow (BM) stimulates the transition of CD8+CD44+CD62L+ central memory T cells into CD8+CD44-CD62L- T cells, designated as inter-organ migratory T cells (TIM cells). TIM cells move from the BM to the intestine by upregulating integrin β7 and downregulating C-X-C motif chemokine receptor 3 during leukaemogenesis. Upon immunogenic chemotherapy, these BM-derived TIM cells return from the intestine to the BM through integrin α4-vascular cell adhesion molecule 1 interaction. Blocking C-X-C motif chemokine receptor 3 function boosts the immune response against leukaemia by enhancing T cell trafficking. This phenomenon can also be observed in patients with leukaemia. In summary, we identify an unrecognized intestine-BM trafficking circuit of T cells that contributes to the antitumour effects of immunogenic chemotherapy.

Tissue Inhibitor of Metalloproteases 3 (TIMP-3): In Vivo Analysis Underpins Its Role as a Master Regulator of Ectodomain Shedding

The proteolytical cleavage of transmembrane proteins with subsequent release of their extracellular domain, so-called ectodomain shedding, is a post-translational modification that plays an essential role in several biological processes, such as cell communication, adhesion and migration. Metalloproteases are major proteases in ectodomain shedding, especially the disintegrin metalloproteases (ADAMs) and the membrane-type matrix metalloproteases (MT-MMPs), which are considered to be canonical sheddases for their membrane-anchored topology and for the large number of proteins that they can release. The unique ability of TIMP-3 to inhibit different families of metalloproteases, including the canonical sheddases (ADAMs and MT-MMPs), renders it a master regulator of ectodomain shedding. This review provides an overview of the different functions of TIMP-3 in health and disease, with a major focus on the functional consequences in vivo related to its ability to control ectodomain shedding. Furthermore, herein we describe a collection of mass spectrometry-based approaches that have been used in recent years to identify new functions of sheddases and TIMP-3. These methods may be used in the future to elucidate the pathological mechanisms triggered by the Sorsby’s fundus dystrophy variants of TIMP-3 or to identify proteins released by less well characterized TIMP-3 target sheddases whose substrate repertoire is still limited, thus providing novel insights into the physiological and pathological functions of the inhibitor.

ADAM17-dependent proteolysis of L-selectin promotes early clonal expansion of cytotoxic T cells

L-selectin on T-cells is best known as an adhesion molecule that supports recruitment of blood-borne naïve and central memory cells into lymph nodes. Proteolytic shedding of the ectodomain is thought to redirect activated T-cells from lymph nodes to sites of infection. However, we have shown that activated T-cells re-express L-selectin before lymph node egress and use L-selectin to locate to virus-infected tissues. Therefore, we considered other roles for L-selectin proteolysis during T cell activation. In this study, we used T cells expressing cleavable or non-cleavable L-selectin and determined the impact of L-selectin proteolysis on T cell activation in virus-infected mice. We confirm an essential and non-redundant role for ADAM17 in TCR-induced proteolysis of L-selectin in mouse and human T cells and show that L-selectin cleavage does not regulate T cell activation measured by CD69 or TCR internalisation. Following virus infection of mice, L-selectin proteolysis promoted early clonal expansion of cytotoxic T cells resulting in an 8-fold increase over T cells unable to cleave L-selectin. T cells unable to cleave L-selectin showed delayed proliferation in vitro which correlated with lower CD25 expression. Based on these results, we propose that ADAM17-dependent proteolysis of L-selectin should be considered a regulator of T-cell activation at sites of immune activity.

Characterization of the catalytic properties of the membrane-anchored metalloproteinase ADAM9 in cell-based assays

ADAM9 (A Disintegrin And Metalloprotease 9) is a membrane-anchored metalloproteinase that has been implicated in pathological retinal neovascularization and in tumor progression. ADAM9 has constitutive catalytic activity in both biochemical and cell-based assays and can cleave several membrane proteins, including epidermal growth factor and Ephrin receptor B4; yet little is currently known about the catalytic properties of ADAM9 and its post-translational regulation and inhibitor profile in cell-based assays. To address this question, we monitored processing of the membrane-anchored Ephrin receptor B4 (EphB4) by co-expressing ADAM9, with the catalytically inactive ADAM9 E > A mutant serving as a negative control. We found that ADAM9-dependent shedding of EphB4 was not stimulated by three commonly employed activators of ADAM-dependent ectodomain shedding: phorbol esters, pervanadate or calcium ionophores. With respect to the inhibitor profile, we found that ADAM9 was inhibited by the hydroxamate-based metalloprotease inhibitors marimastat, TAPI-2, BB94, GM6001 and GW280264X, and by 10 nM of the tissue inhibitor of metalloproteinases (TIMP)-3, but not by up to 20 nM of TIMP-1 or -2. Additionally, we screened a non-hydroxamate small-molecule library for novel ADAM9 inhibitors and identified four compounds that selectively inhibited ADAM9-dependent proteolysis over ADAM10- or ADAM17-dependent processing. Taken together, the present study provides new information about the molecular fingerprint of ADAM9 in cell-based assays by showing that it is not stimulated by strong activators of ectodomain shedding and by defining a characteristic inhibitor profile. The identification of novel non-hydroxamate inhibitors of ADAM9 could provide the basis for designing more selective compounds that block the contribution of ADAM9 to pathological neovascularization and cancer.

Characterization of CD200 Ectodomain Shedding

We have previously reported the existence of a soluble form of CD200 (sCD200) in human plasma, and found sCD200 to be elevated in the plasma of Chronic Lymphocytic Leukemia (CLL) patients. CLL cells release CD200 at a constitutive level, which could be attenuated partially by ADAM28 silencing. In this study, we further explored mechanisms of CD200 shedding beyond that of ADAM28, and performed biochemical analysis of sCD200 using materials derived from purified CLL cells and Hek293 cells stably transfected with CD200, and antibodies generated specifically against either the extracellular or cytoplasmic regions of CD200. CD200 shedding was enhanced by PMA stimulation, and the loss of cell surface CD200 could be monitored as a reduction in CD200 cell surface expression by flow cytometry, in parallel with an increase in the detection of sCD200 in the supernatant. Western blot analyses and functional studies using CD200R1 expressing Hek293 cells showed that the shed CD200 detected in CLL and Hek293-hCD200 supernatants lacked the cytoplasmic domain of CD200 but retained the functional extracellular domain required for binding to, and phosphorylation of, CD200R. These data confirms that a functionally active CD200 extracellular moiety can be cleaved from the surface of CD200 expressing cells following ectodomain shedding.

ADAM17-mediated shedding of FcγRIIIA on human NK cells: identification of the cleavage site and relationship with activation

FcγRIIIA/CD16A, the low-affinity receptor for the IgG Fc portion expressed on human CD56(dim) NK cells and involved in Ab-dependent cell cytotoxicity, is shed upon NK cell activation. We found that recombinant a disintegrin and metalloprotease (ADAM) 17 cleaved the ectodomain of FcγRIIIA/CD16A and a peptide for which the sequence encompasses aa 191-201 of the FcγRIIIA/CD16A stalk region but not ADAM10. MALDI-TOF analysis revealed that the peptide was cleaved between Ala(195) and Val(196) (i.e., 1 aa upstream of the expected position). This location of the cleavage site was confirmed by the finding that ADAM17 failed to cleave a peptide in which Ala and Val were reversed. ADAM17 was found to be expressed on NK cells, and stimulation with PMA or N-ethyl-maleimide resulted in the shedding of FcγRIIIA/CD16A and CD62L, a specific substrate of ADAM17. Selective inhibition of ADAM17 prevented the shedding of both molecules. Moreover, the shedding of FcγRIIIA/CD16A was strongly correlated with degranulation when a wide range of CD56(dim) NK cell activating receptors were stimulated, whereas both ADAM17-dependent shedding and internalization were involved in FcγRIIIA/CD16A downmodulation when the latter was engaged. Finally, the shedding of FcγRIIIA/CD16A was restricted to activated cells, suggesting that ADAM17 acts mainly, if not exclusively, in cis. Taken together, our results demonstrated for the first time, to our knowledge, at the molecular level that ADAM17 cleaves the stalk region of FcγRIIIA/CD16A and identified its cleavage site. The shedding of FcγRIIIA/CD16A was at least partially ADAM17 dependent, and it may be considered as a marker of FcγRIIIA/CD16A-independent NK cell activation highly correlated with degranulation.

Cell surface-bound TIMP3 induces apoptosis in mesenchymal Cal78 cells through ligand-independent activation of death receptor signaling and blockade of survival pathways

Background

The matrix metalloproteinases (MMPs) and their endogenous regulators, the tissue inhibitor of metalloproteinases (TIMPs 1–4) are responsible for the physiological remodeling of the extracellular matrix (ECM). Among all TIMPs, TIMP3 appears to play a unique role since TIMP3 is a secreted protein and, unlike the other TIMP family members, is tightly bound to the ECM. Moreover TIMP3 has been shown to be able to induce apoptotic cell death. As little is known about the underlying mechanisms, we set out to investigate the pro-apoptotic effect of TIMP3 in human mesenchymal cells.

Methodology/Principal Findings

Lentiviral overexpression of TIMP3 in mesenchymal cells led to a strong dose-dependent induction of ligand-independent apoptosis as reflected by a five-fold increase in caspase 3 and 7 activity compared to control (pLenti6/V5-GW/lacZ) or uninfected cells, whereas exogenous TIMP3 failed to induce apoptosis. Concordantly, increased cleavage of death substrate PARP and the caspases 3 and 7 was observed in TIMP3 overexpressing cultures. Notably, activation of caspase-8 but not caspase-9 was observed in TIMP3-overexpressing cells, indicating a death receptor-dependent mechanism. Moreover, overexpression of TIMP3 led to a further induction of apoptosis after stimulation with TNF-alpha, FasL and TRAIL. Most interestingly, TIMP3-overexpression was associated with a decrease in phosphorylation of cRaf, extracellular signal-regulated protein kinase (Erk1/2), ribosomal S6 kinase (RSK1) and Akt and serum deprivation of TIMP3-overexpressing cells resulted in a distinct enhancement of apoptosis, pointing to an impaired signaling of serum-derived survival factors. Finally, heparinase treatment of heparan sulfate proteoglycans led to the release of TIMP3 from the surface of overexpressing cells and to a significant decrease in apoptosis indicating that the binding of TIMP3 is necessary for apoptosis induction.

Conclusion

The results demonstrate that exclusively cell surface-bound endogenous TIMP3 induces apoptosis in mesenchymal Cal78 cells through ligand-independent activation of death receptor signaling and blockade of survival signaling pathways.

Stromal TIMP3 regulates liver lymphocyte populations and provides protection against Th1 T cell-driven autoimmune hepatitis

Lymphocyte infiltration into epithelial tissues and proinflammatory cytokine release are key steps in autoimmune disease. Although cell-autonomous roles of lymphocytes are well studied in autoimmunity, much less is understood about the stromal factors that dictate immune cell function. Tissue inhibitor of metalloproteinases 3 (TIMP3) controls systemic cytokine bioavailability and signaling by inhibiting the ectodomain shedding of cytokines and their receptors. The role of TIMP3 in cytokine biology is emerging; however, its contribution to cellular immunology remains unknown. In this study, we show that TIMP3 produced by the hepatic stroma regulates the basal lymphocyte populations in the liver and prevents autoimmune hepatitis. TIMP3 deficiency in mice led to spontaneous accumulation and activation of hepatic CD4(+), CD8(+), and NKT cells. Treatment with Con A in a model of polyclonal T lymphocyte activation resulted in a greatly enhanced Th1 cytokine response and acute liver failure, which mechanistically depended on TNF signaling. Bone marrow chimeras demonstrated that TIMP3 derived from the stromal rather than hematopoietic compartment provided protection against autoimmunity. Finally, we identified hepatocytes as the major source of Timp3 in a resting liver, whereas significant Timp3 gene transcription was induced by hepatic stellate cells in the inflamed liver. These results uncover metalloproteinase inhibitors as critical stromal factors in regulating cellular immunity during autoimmune hepatitis.

Characterization of TIMP-3 in human articular talar cartilage

Tissue inhibitor of matrix metalloproteinase 3 (TIMP-3) is an inhibitor of matrix degradation; however, little else is known about the role(s) of this protein in articular cartilage. In this study we compared levels of TIMP-3 in human knee and ankle cartilages and in normal and degraded cartilages. In addition, our studies focused on the compartmentalization of TIMP-3 in human adult articular cartilage matrix, identification of its potential binding partners, and determining the effects of cytokines on its matrix compartment deposition. We extracted TIMP-3 from cartilage and found that while TIMP-3 was localized throughout the matrix, it was predominately associated with the chondrocyte. We also found that more TIMP-3 was extracted from normal compared to degraded cartilage and more in ankle than knee cartilage suggesting the potential of this inhibitor as a protective agent. Our data suggest that TIMP-3 interacts with heparan sulfate and heparan sulfate proteoglycans and to a lesser extent with heparin and chondroitin sulfate. Stimulation with Interleukin-1β and osteogenic protein-1 decreased while tumor necrosis factor alpha and transforming growth factor beta increased TIMP-3 protein levels; however, TIMP-3 mRNA was not significantly affected by any of these treatments. These characteristics indicate the chondroprotective nature of TIMP-3 and its potential as a therapeutic agent for osteoarthritis.

TLR-mediated loss of CD62L focuses B cell traffic to the spleen during Salmonella typhimurium infection

B cells recognize Ags on microorganisms both with their BCRs and TLRs. This innate recognition has the potential to alter the behavior of whole populations of B cells. We show in this study that in culture and in mice, MyD88-dependent activation of B cells via TLR2 or TLR9 causes the rapid loss of expression of CD62L by metalloproteinase-dependent shedding. Adoptive transfer of in vitro CpG-activated B cells showed them to be excluded from lymph nodes and Peyer's patches, but not the spleen. In vivo, both injection of CpG and systemic infection with Salmonella typhimurium caused the shedding of CD62L and the consequent focusing of B cell migration to the spleen and away from lymph nodes. We propose that wholesale TLR-mediated changes to B cell migration influence the development of immunity to pathogens carrying appropriate ligands.

G protein-coupled receptor 43 is essential for neutrophil recruitment during intestinal inflammation

Molecular danger signals attract neutrophilic granulocytes (polymorphonuclear leukocytes (PMNs)) to sites of infection. The G protein-coupled receptor (GPR) 43 recognizes propionate and butyrate and is abundantly expressed on PMNs. The functional role of GPR43 activation for in vivo orchestration of immune response is unclear. We examined dextrane sodium sulfate (DSS)-induced acute and chronic intestinal inflammatory response in wild-type and Gpr43-deficient mice. The severity of colonic inflammation was assessed by clinical signs, histological scoring, and cytokine production. Chemotaxis of wild-type and Gpr43-deficient PMNs was assessed through transwell cell chemotactic assay. A reduced invasion of PMNs and increased mortality due to septic complications were observed in acute DSS colitis. In chronic DSS colitis, Gpr43(-/-) animals showed diminished PMN intestinal migration, but protection against inflammatory tissue destruction. No significant difference in PMN migration and cytokine secretion was detected in a sterile inflammatory model. Ex vivo experiments show that GPR43-induced migration is dependent on activation of the protein kinase p38alpha, and that this signal acts in cooperation with the chemotactic cytokine keratinocyte chemoattractant. Interestingly, shedding of L-selectin in response to propionate and butyrate was compromised in Gpr43(-/-) mice. These results indicate a critical role for GPR43-mediated recruitment of PMNs in containing intestinal bacterial translocation, yet also emphasize the bipotential role of PMNs in mediating tissue destruction in chronic intestinal inflammation.

Myeloid-derived suppressor cells down-regulate L-selectin expression on CD4+ and CD8+ T cells

Effective cell-mediated antitumor immunity requires the activation of tumor-reactive T cells and the trafficking of activated T cells to tumor sites. These processes involve the extravasation of lymphocytes from the blood and lymphatics, and their homing to lymph nodes and tumors. L-selectin (CD62L) is an important molecule in these processes. It directs naive lymphocytes to peripheral lymph nodes where they become activated and it traffics naive lymphocytes to inflammatory environments, such as tumors. Individuals with advanced cancer are immune suppressed due to myeloid-derived suppressor cells (MDSC), a population of immature myeloid cells that accumulate to high levels in response to tumor-secreted and proinflammatory factors. We now demonstrate that the reduction in T cell levels of L-selectin that is commonly seen in individuals with cancer inversely correlates with MDSC levels. Three lines of evidence demonstrate that MDSC directly down-regulate L-selectin on naive T cells: 1) naive T cells cocultured with tumor-induced MDSC have reduced L-selectin; 2) T cells in tumor-free aged mice with elevated levels of MDSC have reduced L-selectin, and 3) peritoneal exudate T cells of tumor-free mice treated with plasminogen activator urokinase to elevate MDSC have reduced levels of L-selectin. MDSC are likely to down-regulate L-selectin through their plasma membrane expression of ADAM17 (a disintegrin and metalloproteinase domain 17), an enzyme that cleaves the ectodomain of L-selectin. Therefore, MDSC down-regulate L-selectin levels on naive T cells, decreasing their ability to home to sites where they would be activated. This is another mechanism by which MDSC inhibit antitumor immunity.

S156C mutation in tissue inhibitor of metalloproteinases-3 induces increased angiogenesis

Tissue Inhibitor of metalloproteinases-3 (TIMP-3) is a potent matrix-bound angiogenesis inhibitor. Mutations in TIMP-3 cause Sorsby Fundus Dystrophy, a dominant inherited, early onset macular degenerative disease, with choroidal neovascularization causing a loss of vision in the majority of patients. Here we report that expression of S156C TIMP-3 mutation in endothelial cells results in an abnormal localization of the protein, increased glycosylation, decreased matrix metalloproteinase inhibitory activity, and increased vascular endothelial growth factor (VEGF) binding with a consequent increase in VEGF-dependent migration and tube formation. These enhanced signaling events appear to be mediated as a consequence of a post-transcriptionally regulated increase in the expression of membrane-associated VEGFR-2 in endothelial cells of Timp-3(156/156) mutant mice as well as in human Sorsby fundus dystrophy eyes. Understanding the mechanism(s) by which mutant TIMP-3 can induce abnormal neovascularization provides important insight into the pathophysiology of a number of diseases with increased angiogenesis.

L-selectin shedding in sepsis limits leukocyte mediated microvascular injury at remote sites

BACKGROUND

Increased soluble L-selectin levels have been shown to attenuate local inflammation-mediated microvascular leakage, and failure to generate high levels has been associated with increased risk of acute respiratory distress syndrome in septic patients. We hypothesized that failure to shed L-selectin in systemic inflammation would result in increased local inflammation-induced leukocyte adherence and microvascular leakage.

METHODS

Using intraperitoneal lipopolysaccharide (LPS) or control bicarbonate buffered saline (BBS) and intrascrotal TNFalpha or BBS, mice were randomized to systemic inflammation (LPSip + BBSis), local inflammation (BBSip + TNFis), both (LPSip + TNFis), or control (BBSip+BBSis). Furthermore, mice received intraperitoneal L-selectin Sheddase inhibitor (Ro31-9790) or control vector. With intravital microscopy on cremaster muscle, we measured leukocyte-endothelial cell interactions and microvascular leakage (permeability index). Surface L-selectin was measured by flow cytometry (MCF).

RESULTS

Without Ro31-9790, systemic inflammation attenuated increases induced by local inflammation in leukocyte adherence and vascular leakage. Ro31-9790 significantly increased adherence and leakage in systemic and systemic + local inflammation. L-selectin was shed progressively by increasing degrees of inflammation. Ro31-9790 limited this shedding of L-selectin.

CONCLUSION

In systemic inflammation, L-selectin shedding is required to limit local inflammation-mediated leukocyte adherence and microvascular leakage. Failure to shed L-selectin may increase leukocyte-mediated end-organ injury in septic patients.

Aldose reductase regulates high glucose-induced ectodomain shedding of tumor necrosis factor (TNF)-alpha via protein kinase C-delta and TNF-alpha converting enzyme in vascular smooth muscle cells

Chronic low-grade inflammation has emerged as a key contributor to the cardiovascular complications of diabetes, however, the mechanisms by which diabetes increases inflammation remain poorly understood. Here, we report that exposure to high glucose (HG) stimulates ectodomain shedding of TNF-alpha from rat aortic smooth muscle cells in culture. Our results show that exposure to HG decreases membrane-associated TNF-alpha. This decrease in unprocessed TNF-alpha was prevented by the aldose reductase (AR) inhibitor sorbinil and AR small interference RNA. Treatment with HG, but not equimolar mannitol or 3-O-methyl glucose, resulted in phosphorylation and activation of TNF-alpha converting enzyme (TACE) (ADAM17), which were attenuated by sorbinil or AR-specific small interference RNA. HG-induced TACE phosphorylation and TNF-alpha processing were also prevented by TNF-alpha protease inhibitor-1, an inhibitor of TACE. Inhibition of protein kinase C (PKC)-delta by rottlerin prevented HG-induced TACE activation and the accumulation of unprocessed TNF-alpha. Treatment with sorbinil decreased elevated levels of circulating TNF-alpha in streptozotocin-treated diabetic rats. Sorbinil treatment also decreased the expression of TNF-alpha, matrix metalloproteinase-2, matrix metalloproteinase-9, and increased tissue inhibitor of metalloproteinase-3 in vascular smooth muscle cells treated with HG and in balloon-injured carotid arteries of diabetic rats. These results indicate that HG-induced TNF-alpha shedding could be attributed to TACE activation, which is regulated, in part, by PKC-delta and AR. Therefore, inhibition of TACE by TNF-alpha protease inhibitor-1, or pharmacological inhibition of PKC-delta or AR may represent useful strategies for treating vascular inflammation associated with diabetes.

Cutting edge: soluble IL-6R is produced by IL-6R ectodomain shedding in activated CD4 T cells

IL-6 trans-signaling via the soluble IL-6R (sIL-6R) plays an important role in the progression of several autoimmune diseases and cancer by providing IL-6-responsiveness to cells lacking IL-6R. However, the potential sources of sIL-6R are less understood. In this study we show that sIL-6R is produced by both naive and memory CD4 T cells upon TCR activation. The production of sIL-6R by activated CD4 T cells is mediated by shedding of the membrane-bound IL-6R, and this process correlates with the expression of the metalloproteinase ADAM17 in these cells. In contrast to CD4 T cells, CD8 T cells do not express ADAM17 and their production of sIL-6R is negligible. Thus, during an immune response CD4 T cells are an important source of sIL-6R. Production of sIL-6R by autoreactive CD4 T cells may contribute to their role in the development of autoimmune disease by conferring IL-6-responsiveness to cells lacking IL-6R such as synoviocytes.

Molecular dissection of TIMP3 mutation S156C associated with Sorsby fundus dystrophy

Sorsby fundus dystrophy (SFD) is an autosomal dominant macular degeneration of late onset. A key feature of the disease is the thickening of Bruch's membrane, an ECM structure located between the RPE and the choroid. SFD is caused by mutations in the gene encoding the ECM-associated tissue inhibitor of metalloproteases-3 (TIMP3). We have recently generated two Timp3 gene-targeted mouse lines, one deficient for the murine gene (Timp3-/-) and one carrying an SFD-related S156C mutation. Based on extracts and cell cultures derived from tissues of these animals we now evaluated TIMP3 functionality and its contribution to SFD. We show that the activity levels of TIMP3 target proteases including TACE, ADAMTS4/5 and aggrecan-cleaving MMPs are similar in Timp3S156/+ and Timp3S156C/S156C mice when compared to controls. In Timp3-/- mice, a significant enhancement of enzyme activity was observed for TACE but not for ADAMTS4/5 and MMPs indicating a compensatory effect of other inhibitors regulating the latter two groups of proteases. Fibrin bead assays show that angiogenesis in Timp3S156/+ and Timp3S156C/S156C mice is not altered whereas increased formation of capillary tubes was observed in Timp3-/- animals over controls. Rescue experiments using recombinant proteins demonstrate that the inhibitory activities of TIMP3 towards TACE and aggrecan-cleaving MMPs as well as the anti-angiogenic properties of TIMP3 are not impaired by SFD mutation S156C. We finally demonstrate that wild-type and S156C-TIMP3 proteins block the binding of VEGF to its receptor VEGFR2 to a similar extent. Taken together, this study shows that S156C-TIMP3 retains its known functional properties suggesting that causes other than an imbalance in protease or angiogenic activities represent the primary molecular defect underlying SFD.

The systemic inflammatory response syndrome induces functional changes and relative hyporesponsiveness in neutrophils

PURPOSE

To study the effects of systemic inflammatory response syndrome (SIRS) on polymorhonuclear neutrophil (PMN) function and phenotype by comparing neutrophils from critically ill patients with SIRS against those from healthy blood donors.

MATERIAL AND METHODS

Intensive care unit patients (n = 110) who met at least one SIRS criterion were recruited to the study. One hundred healthy blood donors were recruited as normal controls.

RESULTS

Polymorphonuclear cells from critically ill patients with SIRS were more resistant to activation than PMNs from healthy donors, but when stimulated had an exaggerated microbicidal response. Buffer-treated PMNs from patients with SIRS had significantly higher CD43 surface expression that may inhibit heterotypic cellular contact or ligand stimulation of membrane receptors, had significantly lower expression of IgG receptor CD16, demonstrated resistance to shedding of L-selectin when primed by platelet-activating factor which could be pro-inflammatory, and had reduced respiratory burst when primed by platelet-activating factor than activated by formyl-Met-Leu-Phe.

CONCLUSION

The phenotypic and functional changes observed in neutrophils in the critically ill indicate that they require a higher level of stimulus to become activated. This may represent an auto-protective mechanism where the neutrophils in the already inflamed host may, by this mechanism, avoid excessive inflammation reducing the risk of further host cell injury and death.

Characterisation of endothelin converting enzyme-1 shedding from endothelial cells

The aim of this study was to determine if endothelin converting enzyme-1 (ECE-1) like other members of this metalloprotease family undergoes ectodomain shedding. The release/shedding of catalytically active ECE-1 was measured by monitoring the fluorescence resulting from the cleavage of a specific quenched fluorescent substrate. Catalytically active ECE-1 was detected in the media of human umbilical vein endothelial cells, and was confirmed by mass spectrometry based assays. Specificity of cleavage was confirmed by using both narrow and broad specificity inhibitors. In conclusion we demonstrate and characterize for the first time, ECE-1 shedding from the surface of endothelial cells.

The biochemical, biological, and pathological kaleidoscope of cell surface substrates processed by matrix metalloproteinases

Matrix metalloproteinases (MMPs) constitute a family of more than 20 endopeptidases. Identification of specific matrix and non-matrix components as MMP substrates showed that, aside from their initial role as extracellular matrix modifiers, MMPs play significant roles in highly complex processes such as the regulation of cell behavior, cell-cell communication, and tumor progression. Thanks to the comprehensive examination of the expanded MMP action radius, the initial view of proteases acting in the soluble phase has evolved into a kaleidoscope of proteolytic reactions connected to the cell surface. Important classes of cell surface molecules include adhesion molecules, mediators of apoptosis, receptors, chemokines, cytokines, growth factors, proteases, intercellular junction proteins, and structural molecules. Proteolysis of cell surface proteins by MMPs may have extremely diverse biological implications, ranging from maturation and activation, to inactivation or degradation of substrates. In this way, modification of membrane-associated proteins by MMPs is crucial for communication between cells and the extracellular milieu, and determines cell fate and the integrity of tissues. Hence, insights into the processing of cell surface proteins by MMPs and the concomitant effects on physiological processes as well as on disease onset and evolution, leads the way to innovative therapeutic approaches for cancer, as well as degenerative and inflammatory diseases.

Increase in Adhesion Molecules in Cerebrospinal Fluid of Children with Mumps and Mumps Meningitis

Adhesion molecules play a key role in leucocyte migration into the central nervous system (CNS). Concentrations of endothelial-derived soluble intercellular adhesion molecule-1 (sICAM-1) and leucocyte-originated soluble L-selectin (sL-selectin) in cerebrospinal fluid (CSF) of children with mumps meningitis (mononuclear pleocytosis, n = 33) and mumps (absence of pleocytosis, n = 9) were compared with values from age-matched control group (n = 19). In 14 patients from the meningitis group, adhesion molecule levels together with albumin concentration were estimated in paired CSF/serum samples to calculate concentration quotients and determine molecule intrathecal release. Both sICAM-1 (median 3.44 versus 0.86 ng/ml; P < 0.0001) and sL-selectin (median 29.91 versus 8.52 ng/ml; P < 0.0001) concentrations in CSF were increased in mumps meningitis patients compared with controls. Increased levels of the selected adhesion molecules were also observed in mumps patients without CNS involvement when compared with controls (median sICAM-1: 1.14 versus 0.86 ng/ml, sL-selectin: 13.54 versus 8.52 ng/ml; P < 0.01). Additionally, the concentration of adhesion molecules was found to correlate with CSF leucocyte count. Considerable correlation of sICAM-1 and sL-selectin quotients and corresponding albumin quotients suggests that a majority of the soluble adhesion molecules originated from the bloodstream. Analysis of adhesion molecule levels demonstrated indirect evidence of brain-derived fractions. Our results suggest the involvement of adhesion molecules during the early phase of mumps meningitis.

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.

Ectodomain shedding of preadipocyte factor 1 (Pref-1) by tumor necrosis factor alpha converting enzyme (TACE) and inhibition of adipocyte differentiation

Preadipocyte factor 1 (Pref-1), an epidermal growth factor repeat containing transmembrane protein found in the preadipocytes, inhibits adipocyte differentiation in vitro and in vivo. Here, we examined the processing of membrane form of Pref-1A to release the 50-kDa soluble form that inhibits adipocyte differentiation. The ectodomain cleavage of Pref-1 is markedly enhanced by phorbol 12-myristate 13-acetate in a dose- and time-dependent manner. The basal and stimulated cleavage is inhibited by the broad metalloproteinase inhibitor GM6001, a fact that suggests that cleavage of membrane Pref-1A is dependent on a metalloproteinase. Next, we showed that release of soluble Pref-1A is inhibited by TAPI-0 and by a tissue inhibitor of metalloproteinase-3, TIMP-3, that can inhibit tumor necrosis factor alpha converting enzyme (TACE), but not by TIMP-1 or TIMP-2. On the other hand, overexpression of TACE increases Pref-1 cleavage to produce the 50-kDa soluble form. Furthermore, this cleavage was not detected in cells with TACE mutation or with TACE small interfering RNA. TACE-mediated shedding of Pref-1 ectodomain inhibits adipocyte differentiation of 3T3-L1 cells and in Pref-1-null mouse embryo fibroblasts transduced with Pref-1A. Identification of TACE as the major protease responsible for conversion of membrane-bound Pref-1 to the biologically active diffusible form provides a new insight into Pref-1 function in adipocyte differentiation.

CD21 and CD62L shedding are both inducible via P2X7Rs

Neutrophils and lymphocytes are recruited to sites of inflammation and require the adhesion molecule L-selectin (CD62L) for adherence to endothelial cells. Nucleotides released from activated or dying cells at sites of inflammation can mediate signaling through purinergic receptor family II, resulting in CD62L shedding. Activation of B lymphocytes requires the complement receptor type II (CD21) and at the same time leads to shedding of CD21. Both CD62L and CD21 shedding possibly depends on the same families of proteases. In the present study, we characterized peripheral blood naive and memory cells and neutrophils for CD62L surface expression and analyzed benzoyl-benzoyl triphosphate (BzATP)-induced shedding. BzATP is able to induce CD62L shedding in naive and memory lymphocytes, but not in neutrophils. CD21 shedding can be induced through activation of the B cell receptor (BCR) or with mitogens. Here we show that CD21 is also susceptible to BzATP-induced shedding on peripheral B cells. In addition, using receptor inhibitors, we show that shedding of CD21 and CD62L is mediated via the P2X7R. P2X7R-mediated CD62L and CD21 shedding could occur as a result of extracellular accumulated ATP and may have an influence on leukocyte migrational behavior and BCR-mediated signaling.

Inflammatory effects of BaP1 a metalloproteinase isolated from Bothrops asper snake venom: leukocyte recruitment and release of cytokines

The inflammatory events induced by BaP1, a 22.7 kDa metalloproteinase isolated from Bothrops asper snake venom, were studied. BaP1 i.p. injection in mice induced a marked inflammatory cell infiltrate into peritoneal cavity of animals with predominance of neutrophils in the early phase followed by mononuclear cells in the late period. Inhibition of enzymatic activity of BaP1 by chelation with EDTA resulted in a drastic reduction of this effect. In addition, BaP1 induced a significant increase of blood neutrophil numbers before its accumulation in peritoneal cavity, thus suggesting a stimulatory action of BaP1 on mechanisms of cell mobilization from bone marrow reserve compartments. A reduction in the number of neutrophils was observed in the exudate when antibodies against LECAM-1, CD18 and LFA-1 were used, suggesting the involvement of these adhesion molecules in the effects of BaP1. In contrast, there was no effect with antibodies against ICAM-1 and PECAM-1. Moreover, a conspicuous increment in the levels of IL-1 and TNF-alpha, but not of LTB4, was observed in peritoneal washes collected from mice injected with BaP1. It is concluded that BaP1 induces in vivo a marked leukocyte influx, which parallels an increased number of these cells in the blood, and is associated to the expression of specific leukocyte adhesion molecules and release of chemotactic inflammatory cytokines. Since BaP1 is a P-I class metalloproteinase, these results indicate that the proteolytic domain of metalloproteinases per se can trigger specific inflammatory events.

Cutting Edge: Tissue Inhibitor of Metalloproteinase 3 Regulates TNF-Dependent Systemic Inflammation

Host response to infectious agents must be rapid and powerful. One mechanism is the release of presynthesized membrane-bound TNF. TNF shedding is mediated by TNF-alpha converting enzyme, which is selectively inhibited by the tissue inhibitor of metalloproteinase 3 (TIMP3). We show that loss of TIMP3 impacts innate immunity by dysregulating cleavage of TNF and its receptors. Cultured timp3-/- macrophages release more TNF in response to LPS than wild-type macrophages. In timp3-/- mice, LPS causes serum levels of TNF and its receptors to rise more rapidly and remain higher compared with wild-type mice. The altered kinetics of ligand and receptor shedding enhances TNF signaling in timp3-/- mice, indicated by elevated serum IL-6. Physiologically, timp3-/- mice are more susceptible to LPS-induced mortality. Ablation of the TNF receptor gene p55 (Tnfrsf1a) or treatment with a synthetic metalloproteinase inhibitor rescues timp3-/- mice. Thus, TIMP3 is essential for normal innate immune function.

A disintegrin and metalloprotease 21 (ADAM21) is associated with neurogenesis and axonal growth in developing and adult rodent CNS

We have reported that alpha6beta1 integrin regulates the directed migration of neuroblasts from the adult rodent subventricular zone (SVZ) through the rostral migratory stream (RMS). ADAM (a disintegrin and metalloprotease) proteins bind integrins. Here, we show that ADAM21, but not ADAM2, -3, -9, -10, -12, -15, or -17, is expressed in adult rats and mice by ependyma and SVZ cells with long basal processes, and in radial glia at early postnatal times. ADAM21-positive processes projected into the RMS, contacted blood vessels, and were present within the RMS intermingled with neuroblasts up to where neuroblasts start their radial migration and differentiation in the olfactory bulb. Tissue inhibitors of metalloproteases (TIMPs) 1, 2, and 3 are present in the ependymal layer but not in the SVZ and RMS. Thus, ADAM21 could regulate neurogenesis and guide neuroblast migration through cleavage-dependent activation of proteins and integrin binding. ADAM21 is also present in growing axonal tracts during postnatal development and in growing primary olfactory axons in adults. In the olfactory nerve layer, ADAM21 often, but not always, colocalizes with OMP, a marker of mature olfactory neurons, but is not colocalized with the immature marker betaIII-tubulin. This suggests that ADAM21 is involved in the final axonal outgrowth phase and/or synapse formation. TIMP3 is present in periglomerular neurons, where it could restrict ADAM21-mediated axonal growth to the glomeruli. ADAM21's unique disintegrin and metalloprotease sequences and its restricted expression suggest that it might be a good target for influencing neurogenesis and neuronal plasticity.

ERK-mediated phosphorylation of Thr735 in TNFalpha-converting enzyme and its potential role in TACE protein trafficking

Tumor necrosis factor alpha-converting enzyme (TACE/ADAM17) has been implicated in the inducible shedding of numerous cell surface proteins. In light of this, the regulation of TACE catalytic activation and protein maturation has recently received considerable interest in the context of extracellular signal-regulated kinase activation and the subsequent phosphorylation of TACE at residue Thr735. In this study, we analysed the subcellular localisation of TACE derivatives using laser-scanning confocal microscopy and cell surface biotinylation. Whereas WT.TACE- and T735A.TACE-enhanced green fluorescent protein (-eGFP) fusion derivatives of TACE were both found to localise with the endoplasmic reticulum, a phosphomimicking form of TACE (T735E.TACE-eGFP) was found to colocalise predominantly with components of the protein secretory pathway (COPII vesicles and trans-Golgi network). Additionally, upon analysis of biotinylated ectopic TACE, we observed that inducible trafficking of TACE to the cell surface was dependent upon extracellular signal-regulated kinase activation and phosphorylation of Thr735. We conclude from our observations that phosphorylation of TACE at Thr735 highlights a key step in inducible TACE protein trafficking and maturation.

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.

Lack of tissue inhibitor of metalloproteinases-3 results in an enhanced inflammatory response in antigen-induced arthritis

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is known to inhibit matrix metalloproteinases, aggrecanases, and tumor necrosis factor (TNF)-alpha-converting enzyme (TACE, ADAM17). These metalloproteases participate in different aspects of joint destruction in inflammatory arthritis. To determine the relative importance of this inhibitor in joint pathology, wild-type and Timp3-/- mice were immunized with methylated bovine serum albumin followed by arthritis induction by intra-articular injection of the same antigen. Animals were monitored for up to 14 days after challenge, and joint tissues were analyzed by routine and Safranin O staining and for the presence of aggrecan neoepitopes produced by metalloprotease cleavage. Serum TNF-alpha was measured by immunoassay. Compared to wild-type animals, Timp3-/- mice showed a dramatic increase in the initial inflammatory response to intra-articular antigen injection, and serum TNF-alpha levels were greatly elevated in the Timp3-/- animals after immunization. However, these differences in clinical features disappeared by days 7 to 14. No difference in Safranin O staining or aggrecan cleavage site neoepitope abundance was seen. Thus, in inflammatory joint disease TIMP-3 likely dampens the inflammatory response of TNF-alpha by reducing ADAM17 activity.

Synthetic glycoprotein mimics inhibit L-selectin-mediated rolling and promote L-selectin shedding

L-selectin is a leukocyte cell-surface protein that facilitates the rolling of leukocytes along the endothelium, a process that leads to leukocyte migration to a site of infection. Preventing L-selectin-mediated rolling minimizes leukocyte adhesion and extravasation; therefore, compounds that inhibit rolling may act as anti-inflammatory agents. To investigate the potential role of multivalent ligands as rolling inhibitors, compounds termed neoglycopolymers were synthesized that possess key structural features of physiological L-selectin ligands. Sulfated neoglycopolymers substituted with sialyl Lewis x derivatives (3',6-disulfo Lewis x or 6-sulfo sialyl Lewis x) or a sulfatide analog (3,6-disulfo galactose) inhibited L-selectin-mediated rolling of lymphoid cells. Functional analysis of the inhibitory ligands indicates that they also induce proteolytic release of L-selectin. Thus, their inhibitory potency may arise from their ability to induce shedding. Our data indicate that screening for compounds that promote L-selectin release can identify ligands that inhibit rolling.

Prognostic Value of an Early Soluble L-Selectin (sCD62L) Assay for Risk Assessment in Blunt Multiple Trauma: A Metaanalysis

Background: After severe trauma, decreased plasma concentrations of the soluble adhesion molecule L-selectin (sCD62L) have been linked to an increased incidence of lung failure and multiorgan dysfunction syndrome (MODS). Individual studies have had conflicting results, however. We examined multiple studies in an attempt to determine whether early sCD62L concentrations are predictive of major complications after severe trauma.

Methods: We performed a systematic review of six electronic databases and a manual search for clinical studies comparing outcomes of multiply injured patients (Injury Severity Score ≥16) depending on their early sCD62L blood concentrations. Because of various outcome definitions, acute lung injury (ALI) and adult respiratory distress syndrome (ARDS) were studied as a composite endpoint. Weighted mean differences (WMDs) in sCD62L concentrations were calculated between individuals with and without complications by fixed- and random-effects models.

Results: Altogether, 3370 citations were identified. Seven prospective studies including 350 patients were eligible for data synthesis. Published data showed the discriminatory features of sCD62L but did not allow for calculation of measures of test accuracy. Three of four studies showed lower early sCD62L concentrations among individuals progressing to ALI and ARDS (WMD = −229 μg/L; 95% confidence interval, −476 to 18 μg/L). No differences in sCD62L concentrations were noted among patients with or without later MODS. Nonsurvivors had significantly lower early sCD62L plasma concentrations (WMD = 121 μg/L; 95% confidence interval, 63–179 μg/L), but little information was available on potential confounders in this group.

Conclusions: Early decreased soluble L-selectin concentrations after multiple trauma may signal an increased likelihood of lung injury and ARDS. The findings of this metaanalysis warrant a large cohort study to develop selectin-based models targeting the risk of inflammatory complications.

Tumor necrosis factor alpha stimulates MUC1 synthesis and ectodomain release in a human uterine epithelial cell line

Regulation of MUC1 expression and removal is a salient feature of embryo implantation, bacterial clearance, and tumor progression. In some species, embryo implantation is accompanied by a transcriptional decline in uterine epithelial expression of MUC1. In other species, MUC1 is locally removed at blastocyst attachment sites, suggesting a proteolytic activity. Previously, we demonstrated that MUC1 is proteolytically released from the surface of a human uterine epithelial cell line, HES, and identified TNFalpha converting enzyme/a disintegrin and metalloprotease 17 as a constitutive and phorbol ester-stimulated MUC1 sheddase. The aims of the current study were to test the ability of soluble factors elevated during the periimplantation interval in vivo to stimulate ectodomain shedding of MUC1 from HES uterine epithelial cells and to characterize the nature of this proteolytic activity(ies). We identified TNFalpha as a prospective endogenous stimulus of MUC1 ectodomain release and of MUC1 and TNFalpha converting enzyme/a disintegrin and metalloprotease 17 expression. Moreover, we established that TNFalpha-stimulated MUC1 shedding occurs independently of increased de novo protein synthesis and demonstrated that the TNFalpha-induced increase in MUC1 gene expression is mediated through the kappaB site in the MUC1 promoter. Finally, we determined that the TNFalpha-sensitive MUC1 sheddase is inhibited by the metalloprotease inhibitor, TNFalpha protease inhibitor (TAPI), and the endogenous tissue inhibitor of metalloprotease-3. Collectively, these studies provide the initial in vitro characterization of a putative physiological stimulus of MUC1 ectodomain release and establish the nature of the metalloproteolytic activity(ies) involved.

Mutagenesis of the Ezrin-Radixin-Moesin Binding Domain of L-selectin Tail Affects Shedding, Microvillar Positioning, and Leukocyte Tethering

L-selectin is a cell adhesion molecule that mediates the initial capture (tethering) and subsequent rolling of leukocytes along ligands expressed on endothelial cells. We have previously identified ezrin and moesin as novel binding partners of the 17-amino acid L-selectin tail, but the biological role of this interaction is not known. Here we identify two basic amino acid residues within the L-selectin tail that are required for binding to ezrin-radixinmoesin (ERM) proteins: arginine 357 and lysine 362. L-selectin mutants defective for ERM binding show reduced localization to microvilli and decreased phorbol 12-myristate 13-acetate-induced shedding of the L-selectin ectodomain. Cells expressing these L-selectin mutants have reduced tethering to the L-selectin ligand P-selectin glycoprotein ligand-1, but rolling velocity on P-selectin glycoprotein ligand-1 is not affected. These results suggest that ERM proteins are required for microvillar positioning of L-selectin and that this is important both for leukocyte tethering and L-selectin shedding.

Dystroglycan in skin and cutaneous cells: beta-subunit is shed from the cell surface

In skin, hemidesmosomal protein complexes attach the epidermis to the dermis and are critical for stable connection of the basal epithelial cell cytoskeleton with the basement membrane (BM). In muscle, a similar supramolecular aggregate, the dystrophin glycoprotein complex links the inside of muscle cells with the BM. A component of the muscle complex, dystroglycan (DG), also occurs in epithelia. In this study, we characterized the expression and biochemical properties of authentic and recombinant DG in human skin and cutaneous cells in vitro. We show that DG is present at the epidermal BM zone, and it is produced by both keratinocytes and fibroblasts in vitro. The biosynthetic precursor is efficiently processed to the alpha- and beta-DG subunits; and, in addition, a distinct extracellular segment of the transmembranous beta-subunit is shed from the cell surface by metalloproteinases. Shedding of the beta-subunit releases the alpha-subunit from the DG complex on the cell surface into the extracellular space. The shedding is enhanced by IL-1beta and phorbol esters, and inhibited by metalloproteinase inhibitors. Deficiency of perlecan, a major ligand of alpha-DG, enhanced shedding suggesting that lack of a binding partner destabilizes the epithelial DG complex and makes it accessible to proteolytic processing.

Glu496 to Ala polymorphism in the P2X7 receptor impairs ATP-induced IL-1 beta release from human monocytes

Priming of monocytes with LPS produces large quantities of intracellular, biologically inactive IL-1beta that can be processed and released by subsequent activation of the P2X7 receptor by extracellular ATP. We examined whether a loss-of-function polymorphism of the human P2X7 receptor (Glu496Ala) impairs this process. Both ATP-induced ethidium+ uptake and ATP-induced shedding of L-selectin (CD62L) were nearly absent in monocytes from four subjects homozygous for Glu496Ala confirming that this polymorphism impairs P2X7 function. The level of ATP-induced IL-1beta released in 2 h from LPS-activated whole blood from homozygous subjects was 50% of that from wild-type samples. A more marked defect in IL-1beta release was observed from LPS-activated monocytes of homozygous subjects which was only 22% of that released from wild-type monocytes after a 30-min incubation with ATP. However, after a 60-min incubation with ATP, the amount of IL-1beta released from homozygous monocytes was 70% of that released from wild-type monocytes. Incubation of monocytes of either genotype with nigericin resulted in a similar release of IL-1beta. Western blotting demonstrated that ATP induced the release of mature 17-kDa IL-1beta from monocytes, and confirmed that this process was impaired in homozygous monocytes. Finally, ATP-induced 86Rb+ efflux was 9-fold lower from homozygous monocytes than from wild-type monocytes. The results indicate that ATP-induced release of IL-1beta is slower in monocytes from subjects homozygous for the Glu496Ala polymorphism in the P2X7 receptor and that this reduced rate of IL-1beta release is associated with a lower ATP-induced K+ efflux.

Agonists of proteinase-activated receptor-2 modulate human neutrophil cytokine secretion, expression of cell adhesion molecules, and migration within 3-D collagen lattices

Proteinase-activated receptor-2 (PAR2) belongs to a novel subfamily of G-protein-coupled receptors with seven-transmembrane domains. PAR2 can be activated by serine proteases such as trypsin, mast cell tryptase, and allergic or bacterial proteases. This receptor is expressed by various cells and seems to be crucially involved during inflammation and the immune response. As previously reported, human neutrophils express functional PAR2. However, the precise physiological role of PAR2 on human neutrophils and its implication in human diseases remain unclear. We demonstrate that PAR2 agonist-stimulated human neutrophils show significantly enhanced migration in 3-D collagen lattices. PAR2 agonist stimulation also induced down-regulation of L-selectin display and up-regulation of membrane-activated complex-1 very late antigen-4 integrin expression on the neutrophil cell surface. Moreover, PAR2 stimulation results in an increased secretion of the cytokines interleukin (IL)-1beta, IL-8, and IL-6 by human neutrophils. These data indicate that PAR2 plays an important role in human neutrophil activation and may affect key neutrophil functions by regulating cell motility in the extracellular matrix, selectin shedding, and up-regulation of integrin expression and by stimulating the secretion of inflammatory mediators. Thus, PAR2 may represent a potential therapeutic target for the treatment of diseases involving activated neutrophils.

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a binding partner of epithelial growth factor-containing fibulin-like extracellular matrix protein 1 (EFEMP1). Implications for macular degenerations

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a matrix-bound inhibitor of matrix metalloproteinases. Mutations in the Timp-3 gene cause Sorsby fundus dystrophy (SFD), a hereditary macular degenerative disease. The pathogenic mechanisms responsible for the disease phenotype are unknown. In an in vivo quest for binding partners of the TIMP-3 protein in the subretina, we identified epidermal growth factor-containing fibulin-like extracellular matrix protein 1 (EFEMP1, also known as fibulin 3) as a strong interacting protein. The COOH-terminal end of TIMP-3 was involved in the interaction. Interestingly, a missense mutation in EFEMP1 is responsible for another hereditary macular degenerative disease, Malattia Leventinese (ML). Both SFD and ML have strong similarities to age-related macular degeneration (AMD), a major cause of blindness in the elderly population of the Western hemisphere. Our results were supported by significant accumulation and expression overlap of both TIMP-3 and EFEMP1 between the retinal pigment epithelia and Bruch membrane in the eyes of ML and AMD patients. These results provide the first link between two different macular degenerative disease genes and imply the possibility of a common pathogenic mechanism behind different forms of macular degeneration.

Tumor necrosis factor alpha-converting enzyme mediates MUC5AC mucin expression in cultured human airway epithelial cells

Ectodomain shedding of epidermal growth factor receptor (EGFR) ligands [e.g., transforming growth factor type alpha (TGF-alpha)] and EGFR phosphorylation are implicated in mucin production in airway epithelial cells. Tumor necrosis factor alpha-converting enzyme (TACE) is reported to cleave precursor of TGF-alpha, with release of soluble mature TGF-alpha in various epithelial tissues. We hypothesized that TACE increases the shedding of TGF-alpha, resulting in EGFR phosphorylation and inducing mucin production in human airway epithelial (NCI-H292) cells. To examine this hypothesis, we stimulated NCI-H292 cells with phorbol 12-myristate 13-acetate (PMA, an activator of TACE) and pathophysiologic stimuli [lipopolysaccharide (LPS) and supernatant from the Gram-negative bacterium Pseudomonas aeruginosa (PA sup)]. PMA, PA sup, and LPS increased MUC5AC gene expression and mucin protein production, effects that were prevented by pretreatment with AG1478, a selective inhibitor of EGFR phosphorylation and by preincubation with an EGFR-neutralizing Ab or with a TGF-alpha-neutralizing Ab, implicating ligand (TGF-alpha)-dependent EGFR phosphorylation in mucin production. These stimuli induced release of soluble TGF-alpha, EGFR phosphorylation, and MUC5AC expression, which were blocked by the metalloprotease inhibitors tumor necrosis factor-alpha protease inhibitor-1 and tissue inhibitor of metalloprotease-3. We specifically knocked down the expression of metalloprotease TACE by using small interfering RNA for TACE. Knockdown of TACE inhibited PMA-, PA sup-, and LPS-induced TGF-alpha shedding, EGFR phosphorylation, and mucin production. From these results, we conclude that TACE plays a critical role in mucin production by airway epithelial cells by means of a TACE ligand-EGFR cascade in response to various stimuli.

Tissue inhibitor of metalloproteinases-3 and matrix metalloproteinase-3 regulate neuronal sensitivity to doxorubicin-induced apoptosis

Metalloproteinase activity at the cell surface influences cellular sensitivity to extrinsic death vs. survival signals in a variety of cell types, through proteolytic shedding of cell surface signalling molecules. Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a unique natural metalloproteinase inhibitor that plays a pro-apoptotic role through its ability to inhibit metalloproteinases that proteolytically cleave death receptors and their ligands from the cell surface. To study the convergence of metalloproteinase activity and death receptor signalling in neurons, we established an in vitro model of neuronal apoptosis utilizing the chemotherapeutic drug, doxorubicin (Dox). Primary cultures established from embryonic rat cerebral cortices displayed robust and selective neuronal apoptosis in response to Dox, an effect that was dependent on the activation of the death receptor, Fas. We demonstrate that both TIMP-3 and matrix metalloproteinase-3 (MMP-3) are constitutively expressed by primary cortical neurons in culture, and selectively modulated Fas-mediated neuronal apoptosis induced by Dox. Metalloproteinase inhibition by TIMP-3 was found to be necessary for Dox-induced neuronal death, whereas addition of active MMP-3 markedly attenuated apoptosis and diminished Fas-Fas ligand interaction at the cell surface. These observations implicate a physiological role for the balance of TIMP-3 and MMP-3 activity at the neuronal surface in regulating death receptor sensitivity. The convergence of metalloproteinase activity and death receptor signalling at the cell surface may influence neuronal cell death vs. survival decisions.

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

The soluble form of CD40 (sCD40), which co-exists with the membrane-anchored form (mCD40), is a natural antagonist of mCD40/CD154 interaction. However, the mechanism leading to the production of sCD40 has never been investigated. Here, we show that the engagement of mCD40 on the surface of B lymphocytes by anti-CD40 antibody led to enhanced sCD40 release associated with decreased amounts of mCD40. This sCD40 production was not affected by vesicular traffic inhibitors but was completely blocked by a broad-spectrum synthetic metalloproteinase (MP) inhibitor (GM6001) or a membrane-anchored MP-specific inhibitor (dec-RVKR-cmk). Recombinant MP disintegrin tumor necrosis factor-alpha converting enzyme (TACE) cleaved the purified CD40 ectodomain/Fc chimeric protein in vitro, giving rise to an sCD40 form similar to that shed from B cell cultures. Moreover, spontaneous production of sCD40 by mCD40-transfected human embryonic kidney cells (constitutively expressing TACE) was enhanced by the overexpression of TACE and abrogated by co-transfection with a dominant-negative TACE mutant. These results provide strong evidence that sCD40 production is an active process regulated by the engagement of mCD40 and its proteolytic cleavage by TACE or a related MP disintegrin. Given the antagonistic activity of sCD40 on the CD40/CD154 interaction, this shedding mechanism might represent an important negative feedback control of CD40 functions.

TACE/ADAM-17 enzymatic activity is increased in response to cellular stimulation

Tumor necrosis factor-alpha converting enzyme (TACE/ADAM-17) is a metalloprotease disintegrin that cleaves a variety of membrane proteins, releasing ("shedding") their extracellular domains from cells. Most TACE-mediated shedding events occur at low basal rates that are enhanced by treatment of cells with a variety of stimuli. To study the mechanism of induced shedding, we developed a peptide-cleavage assay that measures the cellular TACE activity. In unstimulated cells, cleavage of a TNFalpha processing-site peptide was mediated mainly by enzymes other than TACE. However, stimulation of cells with phorbol-12-myristate-13-acetate (PMA) increased peptide cleavage in a TACE-dependent manner. PMA treatment did not increase the amount of TACE on the cell surface. Moreover, the cytoplasmic domain of TACE was not required for the induced activity. Based on these observations, induction of TACE-mediated shedding events occurs at least in part via an increase in the enzymatic activity of cellular TACE, independent of its cytoplasmic domain.

Diminished adhesion of Anaplasma phagocytophilum-infected neutrophils to endothelial cells is associated with reduced expression of leukocyte surface selectin

Anaplasma phagocytophilum propagates within neutrophils and causes a disease marked by inflammatory tissue injury or complicated by opportunistic infections. We hypothesized that infection with A. phagocytophilum modifies the binding of neutrophils to endothelial cells and the expression of neutrophil adhesion molecules and studied these changes in vitro. Infected dimethyl sulfoxide-differentiated HL-60 cells and neutrophils showed reduced binding to cultured brain and systemic endothelial cells and lost expression of P-selectin glycoprotein ligand 1 (PSGL-1, CD162) and L-selectin (CD62L) (to 33 and 5% of control values, respectively), at a time when the levels of beta(2) integrin and immunoglobulin superfamily adhesion molecules and activation markers Mac-1 and intercellular adhesion molecule 1 increased (5 to 10 times that of the control). The loss of CD162 and CD62L expression was inhibited by EDTA, which suggests that neutrophil activation and sheddase cleavage occurred. The loss of selectin expression and the retained viability of the neutrophils persisted for at least 18 h with A. phagocytophilum infection, whereas Escherichia coli and Staphylococcus aureus rapidly killed neutrophils. The adhesion defect might increase the numbers of infected cells and their persistence in the blood prior to tick bites. However, decreased CD162 expression and poor endothelial cell binding may partly explain impaired host defenses, while simultaneous neutrophil activation may aggravate inflammation. These observations may help us to understand the modified biological responses, host inflammation, and immune response that occur with A. phagocytophilum infections.

Membrane-type 1 matrix metalloproteinase: a key enzyme for tumor invasion

Matrix metalloproteinases (MMPs) are believed to play a pivotal role in malignant behavior of cancer cells such as rapid tumor growth, invasion, and metastasis by degrading extracellular matrix (ECM). Different types of synthetic inhibitors against MMPs (MMPIs) were developed as candidates for anti-cancer therapeutics and so far clinical trials had led to no significant success. However, this does not diminish the importance of MMPs in the malignancy of cells. Details about MMPs, specifically when and how they take part in the development of cancer are necessary for more advanced application of MMPIs. In this paper, we summarize recent knowledge about membrane-type 1 matrix metalloproteinase (MT1-MMP) which is expressed on cancer cell surface as an invasion-promoting proteinase. By localizing at the leading edge of invasive cancer cells, MT1-MMP degrades components of the tissue barriers. One of the major targets is type I collagen, the most abundant ECM component. Although MT1-MMP itself cannot degrade type IV collagen in the basement membrane, it binds to and activates proMMP-2, one of the type IV collagenases. However, degradation of the ECM is not the sole function of MT1-MMP. MT1-MMP also regulates cell-ECM interaction by processing cell adhesion molecules such as CD44 and integrin alphav chain, and eventually promotes cell migration as well. In addition to the transcriptional regulation, invasion-promoting activity of the MT1-MMP is also strictly monitored at the post-translational level. Precise knowledge about the regulation will give us insight to develop new methods for treating invasive cancer patients.

Tissue inhibitor of metalloproteinases-3 induces apoptosis in melanoma cells by stabilization of death receptors

Tissue inhibitors of metalloproteinases (TIMPs) are important regulators of matrix metalloproteinase (MMP) and adamalysin (ADAM) activity. We have previously shown that adenovirally expressed tissue inhibitor of metalloproteinases-3 (TIMP-3) induces apoptosis in melanoma cells and inhibits growth of human melanoma xenografts. Here, we have studied the role of death receptors in apoptosis of melanoma cells induced by TIMP-3. Our results show, that the exposure of three metastatic melanoma cell lines (A2058, SK-Mel-5, and WM-266-4) to recombinant TIMP-3, N-terminal MMP inhibitory domain of TIMP-3, as well as to adenovirally expressed TIMP-3 results in stabilization of tumor necrosis factor receptor-1 (TNF-RI), FAS, and TNF-related apoptosis inducing ligand receptor-1 (TRAIL-RI) on melanoma cell surface and sensitizes these cells to apoptosis induced by TNF-alpha, anti-Fas-antibody and TRAIL. Stabilization of death receptors by TIMP-3 results in activation of caspase-8 and caspase-3, and subsequent apoptosis is blocked by specific caspase-8 inhibitor (Z-IETD-FMK) and by pan-caspase inhibitor (Z-DEVD-FMK). Adenovirus-mediated expression of TIMP-3 in human melanoma xenografts in vivo resulted in increased immunostaining for TNF-RI, FAS, and cleaved caspase-3, and in apoptosis of melanoma cells. Taken together, these results show that TIMP-3 promotes apoptosis in melanoma cells through stabilization of three distinct death receptors and activation of their apoptotic signaling cascade through caspase-8.

A method to increase the number of growth hormone receptors at the surface of cells

The number of growth hormone receptors (GHRs) per cell are regulated and this feature plays a major role in the hormone responsiveness of the body. We previously observed in transfected Chinese hamster lung cells that GHR availability is determined by three factors: endocytosis (75%), shedding (10%), and other undetermined mechanisms (15%). The endocytosis depends on an active ubiquitin conjugation system. In addition, this process is ligand-independent. Here, we show that this principle is useful to increase the abundance of GHRs at the cell surface of cells using a combination of inhibitors. In theory, an inhibitor that targets the ubiquitin conjugation specific for the GHR, would suffice, as almost 80% of the removal rate depends on this mechanism. As the molecular mechanism is unknown yet, we used a general inhibitor of proteasome action. Unfortunately, such an inhibitor stimulates the shedding process severalfold. Our data show that the combination of a general proteasome inhibitor and a matrix metalloprotease inhibitor results in an almost twofold increase in functional GHRs at the cell surface, and generate new perspectives to increase the sensitivity of cells for growth hormone.

Tumor necrosis factor-alpha converting enzyme/ADAM 17 mediates MUC1 shedding

MUC1 clearance from the uterine epithelial cell surface is a prerequisite for the creation of an environment conducive to embryo implantation. In some species, reduced mRNA levels along with metabolic turnover account for loss of MUC1 during the receptive phase throughout the uterine epithelium. In other species, MUC1 is rapidly lost solely at the site of blastocyst attachment, suggesting the action of a protease. Correlative studies also indicate the presence of soluble forms of MUC1 in cell culture supernatants in vitro and in bodily fluids in vivo. To characterize the proteolytic activity mediating MUC1 release, shedding of MUC1 was analyzed in a human uterine epithelial cell line (HES) that abundantly expresses and readily sheds MUC1. MUC1 release was stimulated by phorbol 12-myristate 13-acetate and was markedly inhibited by the synthetic peptide hydroxamate metalloprotease inhibitor, tumor necrosis factor-alpha protease inhibitor (TAPI), as well as by an endogenous inhibitor of matrix metalloproteases, tissue inhibitor of metalloproteases (TIMP)-3. These characteristics along with studies conducted with cell lines genetically deficient in various ADAMs (for a disintegrin and metalloprotease) identified tumor necrosis factor-alpha converting enzyme (TACE)/ADAM 17 as a MUC1 sheddase. Furthermore, both TACE and MUC1 were expressed in human uterine epithelia during the receptive phase, and co-immunoprecipitation experiments revealed a physical interaction between TACE and MUC1 in HES cells. These studies establish a proteolytic mechanism for MUC1 clearance from a human uterine epithelial cell line and identify TACE as a MUC1 sheddase.

Molecular mechanisms of L-selectin-induced co-localization in rafts and shedding [corrected]

Leukocyte recruitment to lymph nodes or inflammatory sites is regulated by adhesion and activation. L-selectin (CD62L) is expressed on leukocytes and mediates tethering and rolling of leukocytes on endothelial cells. Upon stimulation L-selectin is down-regulated by proteolytic cleavage but the molecular mechanisms regulating this shedding step are poorly defined. To study intracellular mechanisms, we induced shedding of L-selectin by cross-linking with an immobilized L-selectin antibody (Dreg56) in Jurkat cells. The loss of surface expression was quantitated by flow cytometry and the increase of soluble L-selectin was determined by Western blot analysis. We find that Jurkat and p56(lck)-deficient JCaM1.6 cells released L-selectin to similar extent (18+/-4% and 17+/-3%, respectively) and revealed comparable inhibition with the src-tyrosine kinase inhibitor PP2. Glutathione (GSH), an inhibitor of the neutral sphingomyelinase, PD98059, a MAP-kinase (MAP-K) inhibitor and metalloprotease inhibitors (MPI) (TAPI, Ro 31-9790, and BB-3103) reduced significantly L-selectin-induced shedding by 60-80%. In Jurkat cells, L-selectin was present in Triton X-100 insoluble membrane rafts and was constitutively tyr-phosphorylated. Dreg56 cross-linking enhanced phosphorylation and recruitment of L-selectin into rafts which was significantly decreased by pretreatment of cells with PD98059. We conclude, that the metalloproteinase-mediated cleavage of L-selectin from cell surface is triggered by intracellular signaling pathways that are independent of p56(lck) tyrosine kinase activity, but require other tyrosine kinases and the neutral sphingomyelinase. The cleavage of L-selectin might involve membrane rafts as signaling platform.