Transmodulation of cell surface regulatory molecules via ectodomain shedding

Dysregulation of angiopoietin-Tie-2 axis in ugandan children hospitalized with pneumonia

OBJECTIVE

Pneumonia is the leading cause of death in children under 5, with the highest burden in resource-limited countries. Endothelial activation occurs in pneumonia and can be assessed using quantitative levels of biomarkers angiopoietin (Ang)-1 and Ang-2. We examined admission levels of Ang-1 and Ang-2 in pediatric pneumonia and their association with disease severity and outcome.

METHODS

Prospective cohort study of children with hypoxemic pneumonia admitted to two hospitals in Uganda. Clinical, radiographic, and microbiologic characteristics were measured at admission. Disease severity was assessed using the Respiratory Index of Severity in Children (RISC). Plasma levels of Ang-1 and Ang-2 were quantified by enzyme-linked immunosorbent assay. Vital signs, oxygen supplementation, and mortality were assessed prospectively.

RESULTS

We included 65 patients (43% female) with median age 19 months (IQR 8-24). Admission Ang-2/Ang-1 ratio directly correlated with RISC (ρ = 0.32, p = 0.008) and lactate level (ρ = 0.48, p < 0.001). Ang-2/Ang-1 ratio was higher in pneumococcal pneumonia than viral RTI (0.19 [IQR: 0.076-0.54] vs. 0.078 [IQR: 0.027-0.11]; p = 0.03). Elevated Ang-2/Ang-1 ratio (>0.084) was associated with prolonged tachypnea (HR 0.50 (95%CI 0.29-0.87), p = 0.02), fever (HR 0.56 (95%CI 0.33 to 0.96), p = 0.02), longer duration of oxygen therapy (HR 0.59 (95%CI 0.35-0.99), p = 0.04), and hospital stay (HR 0.43 (95%CI 0.25-0.74), p = 0.001). The Ang-2/Ang-1 ratio at admission was higher in fatal cases relative to survivors (0.36 [IQR: 0.17-0.58] vs. 0.077 [IQR: 0.025-0.19]; p = 0.05) CONCLUSION: Endothelial activation in hypoxemic pediatric pneumonia, reflected by high plasma Ang-2/Ang-1 ratio, is associated with disease severity, prolonged recovery time, and mortality.

Long-term viability and function of transplanted islets macroencapsulated at high density are achieved by enhanced oxygen supply

Transplantation of encapsulated islets can cure diabetes without immunosuppression, but oxygen supply limitations can cause failure. We investigated a retrievable macroencapsulation device wherein islets are encapsulated in a planar alginate slab and supplied with exogenous oxygen from a replenishable gas chamber. Translation to clinically-useful devices entails reduction of device size by increasing islet surface density, which requires increased gas chamber pO2. Here we show that islet surface density can be substantially increased safely by increasing gas chamber pO2 to a supraphysiological level that maintains all islets viable and functional. These levels were determined from measurements of pO2 profiles in islet-alginate slabs. Encapsulated islets implanted with surface density as high as 4,800 islet equivalents/cm3 in diabetic rats maintained normoglycemia for more than 7 months and provided near-normal intravenous glucose tolerance tests. Nearly 90% of the original viable tissue was recovered after device explantation. Damaged islets failed after progressively shorter times. The required values of gas chamber pO2 were predictable from a mathematical model of oxygen consumption and diffusion in the device. These results demonstrate feasibility of developing retrievable macroencapsulated devices small enough for clinical use and provide a firm basis for design of devices for testing in large animals and humans.

Metalloprotease ADAM17 regulates porcine epidemic diarrhea virus infection by modifying aminopeptidase N

Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea (PED). PED, characterized by acute diarrhea, vomiting, dehydration, has caused serious economic losses in pig industry worldwide. Here, we demonstrate that activation of a disintergrin and metalloprotease 17 (ADAM17) induced the decrease of PEDV infection in HEK293 and IPEC-J2 cells and the downregulation of cell surface aminopeptidase N (APN) expression, an important entry factor for PEDV infection. Furthermore, overexpression of ADAM17 suppressed PEDV infection in HEK293 and IPEC-J2 cells, whereas ablation of ADAM17 expression using ADAM17 specific siRNA resulted in a corresponding increase of PEDV infection and an upregulation of cell surface APN expression. Taken together, these data demonstrate that modulation of APN expression by metalloprotease ADAM17 regulates PEDV infection. Hence, the reduction in APN expression represents another component of the anti-PEDV infection response initiated by ADAM17.

Pharmacokinetic Considerations for Antibody-Drug Conjugates against Cancer

Antibody-drug conjugates (ADCs) are ushering in the next era of targeted therapy against cancer. An ADC for cancer therapy consists of a potent cytotoxic payload that is attached to a tumour-targeted antibody by a chemical linker, usually with an average drug-to-antibody ratio (DAR) of 3.5-4. The theory is to deliver potent cytotoxic payloads directly to tumour cells while sparing healthy cells. However, practical application has proven to be more difficult. At present there are only two ADCs approved for clinical use. Nevertheless, in the last decade there has been an explosion of options for ADC engineering to optimize target selection, Fc receptor interactions, linker, payload and more. Evaluation of these strategies requires an understanding of the mechanistic underpinnings of ADC pharmacokinetics. Development of ADCs for use in cancer further requires an understanding of tumour properties and kinetics within the tumour environment, and how the presence of cancer as a disease will impact distribution and elimination. Key pharmacokinetic considerations for the successful design and clinical application of ADCs in oncology are explored in this review, with a focus on the mechanistic determinants of distribution and elimination.

Effect of antigen shedding on targeted delivery of immunotoxins in solid tumors from a mathematical model

Most cancer-specific antigens used as targets of antibody-drug conjugates and immunotoxins are shed from the cell surface (Zhang & Pastan (2008) Clin. Cancer Res. 14: 7981-7986), although at widely varying rates and by different mechanisms (Dello Sbarba & Rovida (2002) Biol. Chem. 383: 69–83). Why many cancer-specific antigens are shed and how the shedding affects delivery efficiency of antibody-based protein drugs are poorly understood questions at present. Before a detailed numerical study, it was assumed that antigen shedding would reduce the efficacy of antibody-drug conjugates and immunotoxins. However, our previous study using a comprehensive mathematical model showed that antigen shedding can significantly improve the efficacy of the mesothelin-binding immunotoxin, SS1P (anti-mesothelin-Fv-PE38), and suggested that receptor shedding can be a general mechanism for enhancing the effect of inter-cellular signaling molecules. Here, we improved this model and applied it to both SS1P and another recombinant immunotoxin, LMB-2, which targets CD25. We show that the effect of antigen shedding is influenced by a number of factors including the number of antigen molecules on the cell surface and the endocytosis rate. The high shedding rate of mesothelin is beneficial for SS1P, for which the antigen is large in number and endocytosed rapidly. On the other hand, the slow shedding of CD25 is beneficial for LMB-2, for which the antigen is small in number and endocytosed slowly.

Modulation of CD163 expression by metalloprotease ADAM17 regulates porcine reproductive and respiratory syndrome virus entry

As a consequence of their effects on ectodomain shedding, members of the A disintegrin and metalloprotease (ADAM) family have been implicated in the control of various cellular processes. Although ADAM family members are also involved in cancer, inflammation, and other pathologies, it is unclear whether they affect porcine reproductive and respiratory syndrome virus (PRRSV) infection. Here, we demonstrate for the first time that inhibition of ADAM17 enhances PRRSV entry in Marc-145 and porcine alveolar macrophages (PAMs). We also demonstrate that the inhibition of ADAM17 upregulates membrane CD163 expression, a putative PRRSV receptor that is exogenously expressed in BHK-21 and endogenously expressed in Marc-145 and PAMs. Furthermore, overexpression of ADAM17 induced downregulation of CD163 expression and a reduction in PRRSV infection, whereas ablation of ADAM17 expression using specific small interfering RNA resulted in upregulation of CD163 expression with a corresponding increase in PRRSV infection. These ADAM17-mediated effects were confirmed with PRRSV nonpermissive BHK-21 cells transfected with CD163 cDNA. Overall, these findings indicate that ADAM17 downregulates CD163 expression and hinders PRRSV entry. Hence, downregulation of ADAM17 particular substrates may be an additional component of the anti-infection defenses.

IMPORTANCE

ADAM17 is one of the important membrane-associated metalloproteases that mediate various cellular events, as well as inflammation, cancer, and other pathologies. Here, we investigate for the first time the role of the metalloprotease ADAM17 in PRRSV infection. By using inhibitor and genetic modification methods, we demonstrate that ADAM17 negatively regulate PRRSV entry by regulating its substrate(s). More specifically, ADAM 17 mediates the downregulation of the PRRSV cellular receptor CD163. The reduction in CD163 expression represents another component of the anti-infection response initiated by ADAM17.

The cytosolic domain of protein-tyrosine kinase 7 (PTK7), generated from sequential cleavage by a disintegrin and metalloprotease 17 (ADAM17) and γ-secretase, enhances cell proliferation and migration in colon cancer cells

Protein-tyrosine kinase 7 (PTK7) is a member of the defective receptor protein-tyrosine kinases and is known to function as a regulator of planar cell polarity during development. Its expression is up-regulated in some cancers including colon carcinomas. A 100-kDa fragment of PTK7 was detected in the culture media from colon cancer cells and HEK293 cells. The shed fragment was named sPTK7-Ig1-7 because its molecular mass was very similar to that of the entire extracellular domain of PTK7 that contains immunoglobulin-like loops 1 to 7 (Ig1-7). The shedding of sPTK7-Ig1-7 was enhanced by treatment with phorbol 12-myristate 13-acetate. In addition to the sPTK7-Ig1-7 found in the culture medium, two C-terminal fragments of PTK7 were detected in the cell lysates: PTK7-CTF1, which includes a transmembrane segment and a cytoplasmic domain, and PTK7-CTF2, which lacks most of the transmembrane segment from PTK7-CTF1. Analysis of PTK7 processing in the presence of various protease inhibitors or after knockdown of potential proteases suggests that shedding of PTK7 into sPTK7-Ig1-7 and PTK7-CTF1 is catalyzed by ADAM17, and further cleavage of PTK7-CTF1 into PTK7-CTF2 is mediated by the γ-secretase complex. PTK7-CTF2 localizes to the nucleus and enhances proliferation, migration, and anchorage-independent colony formation. Our findings demonstrate a novel role for PTK7 in the tumorigenesis via generation of PTK7-CTF2 by sequential cleavage of ADAM17 and γ-secretase.

The association of endothelial cell signaling, severity of illness, and organ dysfunction in sepsis

Introduction

Previous reports suggest that endothelial activation is an important process in sepsis pathogenesis. We investigated the association between biomarkers of endothelial cell activation and sepsis severity, organ dysfunction sequential organ failure assessment (SOFA) score, and death.

Methods

This is a prospective, observational study including adult patients (age 18 years or older) presenting with clinical suspicion of infection to the emergency department (ED) of an urban, academic medical center between February 2005 and November 2008. Blood was sampled during the ED visit and biomarkers of endothelial cell activation, namely soluble fms-like tyrosine kinase-1 (sFlt-1), plasminogen activator inhibitors -1 (PAI-1), sE-selectin, soluble intercellular adhesion molecule (sICAM-1), and soluble vascular cell adhesion molecule (sVCAM-1), were assayed. The association between biomarkers and the outcomes of sepsis severity, organ dysfunction, and in-hospital mortality were analyzed.

Results

A total of 221 patients were included: sepsis without organ dysfunction was present in 32%, severe sepsis without shock in 30%, septic shock in 32%, and 6% were non-infected control ED patients. There was a relationship between all target biomarkers (sFlt-1, PAI-1, sE-selectin, sICAM-1, and sVCAM-1) and sepsis severity, P < 0.05. We found a significant inter-correlation between all biomarkers, including the strongest correlations between sFlt-1 and sE-selectin (r = 0.55, P < 0.001), and between sFlt-1 and PAI-1 (0.56, P < 0.001). Among the endothelial cell activation biomarkers, sFlt-1 had the strongest association with SOFA score (r = 0.66, P < 0.001), the highest area under the receiver operator characteristic curve for severe sepsis of 0.82, and for mortality of 0.91.

Conclusions

Markers of endothelial cell activation are associated with sepsis severity, organ dysfunction and mortality. An improved understanding of endothelial response and associated biomarkers may lead to strategies to more accurately predict outcome and develop novel endothelium-directed therapies in sepsis.

A tandem scFv-based fusion protein and its enediyne-energized analogue show intensified therapeutic efficacy against lung carcinoma xenograft in athymic mice

Gelatinases play important roles in tumor progression and are abundantly expressed in a variety of malignant tumors. Antibody targeting gelatinases is a possible avenue to fight against cancer. However, antibody alone can not achieve curative efficacy. Herein, we demonstrated the intensified targeting therapy of a tandem scFv-based fusion protein and its enediyne-energized analogue against gelatinases-overexpressed tumor. A fusion protein dFv-LDP, comprising a tandem scFv of anti-gelatinases linked to the apoprotein (LDP) of lidamycin, was generated and showed strong tumor targeting capability in three different tumor xenografts. In PG-BE1 lung carcinoma xenograft, the tumor inhibition rate was 77.5% by dFv-LDP versus 94.2% by dFv-LDP-AE, the product of dFv-LDP assembled with the active enediyne chromophore (AE) of lidamycin. Moreover, the combination of dFv-LDP with dFv-LDP-AE further augmented the therapeutic efficacy, producing initial tumor shrinkage in five of six mice. The microvessel density (P<0.05) and proliferation index (P<0.05) were also stepwise decreased in groups of dFv-LDP, dFv-LDP-AE and the combination. In conclusion, our results demonstrated that the antibody-based therapy against gelatinases was stepwise intensified in use of dFv-LDP, dFv-LDP-AE and dFv-LDP plus dFv-LDP-AE, and indicated that the combination of an antibody with its drug-armed analogue might be of interest as a new approach to augment antitumor efficacy.

ADAM17 activity and other mechanisms of soluble L-selectin production during death receptor-induced leukocyte apoptosis

L-selectin is an adhesion molecule expressed by neutrophils that broadly directs their infiltration in to sites of inflammation. It is also present at relatively high levels in the serum of normal individuals. It is well established that L-selectin is efficiently shed from the surface of neutrophils upon their activation, a process that regulates its density and binding activity. Neutrophil programmed cell death is critical for the resolution of inflammation, and L-selectin downregulation is induced during this process as well. The mechanisms underpinning this latter process are much less understood, and were investigated in this study. Using a disintegrin and metalloprotease (ADAM)-17 radiation chimeric mice, we demonstrate for the first time that during early events of death receptor-mediated neutrophil apoptosis, L-selectin downregulation occurs primarily by ADAM17-mediated shedding. This was observed as well upon using shRNA to knock down ADAM17 expression in Jurkat cells, a well-studied cell line in terms of the molecular processes involved in the induction of apoptosis. These findings directly reveal that ADAM17 activity occurs during programmed cell death. Hence, the cleavage of particular ADAM17 substrates may be an additional component of the anti-inflammatory program initiated by apoptotic neutrophils. Of interest was that during later stages of induced leukocyte apoptosis, soluble L-selectin production occurred independent of ADAM17, as well as membrane events, such as blebbing and microparticle production. This process may provide an explanation for the lack of diminished serum L-selectin levels in ADAM17-null mice, and suggests a mechanism for the homeostatic maintenance of soluble L-selectin levels in the blood of healthy individuals.

Matrilysin (Matrix Metalloproteinase-7) regulates anti-inflammatory and antifibrotic pulmonary dendritic cells that express CD103 (alpha(E)beta(7)-integrin)

The E-cadherin receptor CD103 (alpha(E)beta(7)-integrin) is expressed on specific populations of pulmonary dendritic cells (DC) and T cells. However, CD103 function in the lung is not well understood. Matrilysin (MMP-7) expression is increased in lung injury and cleaves E-cadherin from injured lung epithelium. Thus, to assess matrilysin effects on CD103-E-cadherin interactions in lung injury, wild-type, CD103(-/-), and Mmp7(-/-) mice, in which E-cadherin isn't cleaved in the lung, were treated with bleomycin or bleomycin with nFMLP to reverse the defect in acute neutrophil influx seen in Mmp7(-/-) mice. Pulmonary CD103(+) DC were significantly increased in injured wild-type compared with Mmp7(-/-) mice, and CD103(+) leukocytes showed significantly enhanced interaction with E-cadherin on injured wild-type epithelium than with Mmp7(-/-) epithelium in vitro and in vivo. Bleomycin-treated CD103(-/-) mice had persistent neutrophilic inflammation, increased fibrosis, and increased mortality compared with wild-type mice, a phenotype that was partially recapitulated in bleomycin/nFMLP-treated Mmp7(-/-) mice. Soluble E-cadherin increased IL-12 and IL-10 and reduced IL-6 mRNA expression in wild-type bone marrow-derived DC but not in CD103(-/-) bone marrow-derived DC. Similar mRNA patterns were seen in lungs of bleomycin-injured wild-type, but not CD103(-/-) or Mmp7(-/-), mice. In conclusion, matrilysin regulates pulmonary localization of DC that express CD103, and E-cadherin cleavage may activate CD103(+) DC to limit inflammation and inhibit fibrosis.

Soluble CD146 is generated by ectodomain shedding of membrane CD146 in a calcium-induced, matrix metalloprotease-dependent process

CD146 is a cell adhesion molecule localized at the endothelial junction and is involved in the control of cell-cell cohesion. In this study, we showed that calcium influx in human microvascular lung endothelial cells results in the loss of surface CD146 and the release of soluble CD146. This calcium-induced CD146 shedding could be prevented with inhibitors of matrix metalloproteases indicating a central role of matrix metalloproteases in this process. We also investigated if CD146 shedding influences vascular permeability. Endothelial cell monolayers cultured on filter membranes showed an increased permeability for albumin when stimulated with ionomycin. This calcium-induced increase in permeability was inhibited when CD146 shedding was prevented by a matrix metalloprotease inhibitor. Our data indicate that surface CD146 plays a central role in the regulation of vascular permeability and demonstrate that CD146 and matrix metalloproteases are potential targets to modify endothelial barrier function.

Identification of ligand-induced proteolytic cleavage and ectodomain shedding of VEGFR-1/FLT1 in leukemic cancer cells

Vascular endothelial growth factor receptor-1/fms-related tyrosine kinase 1 (VEGFR-1/FLT1) is expressed as a membrane-bound receptor tyrosine kinase and as an alternatively spliced soluble protein (sVEGFR-1) containing the 1-6 IgG-like domain of its ectodomain. sVEGFR-1 is known as a naturally occurring inhibitor of angiogenesis and as a surrogate marker for cancer progression; it is also linked to pregnancy-induced hypertension called preeclampsia and to avascularity of normal cornea. It remains an open question whether alternative mRNA splicing is the only mechanism by which sVEGFR-1 is generated. In this study, we show that in leukemic cancer cells, PlGF and VEGF-A both induce tyrosine phosphorylation of VEGFR-1 and render it susceptible to ectodomain shedding, resulting in the generation of sVEGFR-1 and an intracellular cytoplasmic fragment. Activation of protein kinase C and tumor necrosis factor-alpha-converting enzyme family metalloproteases are critically required for the occurrence of sVEGFR-1. Following the removal of the ectodomain, the remnant of VEGFR-1 remains attached to the membrane, and the activity of gamma-secretase/presenilin is required for its release from the cell membrane. We propose that sVEGFR-1 produced via ectodomain shedding plays a prominent role in the VEGF receptor system by antagonizing VEGF receptor signaling by acting as a dominant-negative form and/or forming a nonsignaling dimerizing complex with VEGF receptors.

High shed antigen levels within tumors: an additional barrier to immunoconjugate therapy

Shedding of cell surface antigens is an important biological process that is used by cells to modulate responses to signals in the extracellular environment. Because antibody-based therapies of cancer target cell surface antigens, it is important to understand more about the shedding process and how it affects tumor responses to this type of therapy. Up to now most attention has been focused on measuring the concentration of shed antigens in the blood and using these to determine the presence of a tumor and as a measure of response. The recent finding that the concentration of the tumor antigen mesothelin is extremely high within the interstitial space of tumors, where it can block antibody action, and that the concentration of shed mesothelin within the tumor is lowered by chemotherapy has important implications for the successful treatment of solid tumors by immunoconjugates and whole antibodies.

Transfer of T cell surface molecules to dendritic cells upon CD4+ T cell priming involves two distinct mechanisms

Activation of CD4(+) T cells by APCs occurs by multiple Ag recognition events including the exchange of costimulatory signals and cytokines. Additionally, the T cells acquire APC-derived surface molecules. Herein, we describe for the first time the transfer of human and murine T cell surface receptors to APCs after Ag-specific interaction. This transfer occurs in two qualitatively different phases. The first group of molecules (e.g., CD2) derived from the T cell surface was transferred rapidly after 2 h of interaction, was strongly bound on the DC surface (acid wash-resistant), was strictly dependent on dendritic cell-T cell contact, and transferred independently of T cell activation. The second group, including the CD3/TCR complex, CD27, and OX40, was of intracellular origin, transferred later after 10-16 h in a cell-cell contact-independent fashion, was noncovalently bound, and was strictly dependent on Ag-specific T cell activation. Functionally, murine dendritic cells that received TCR molecules from OVA-specific CD4(+) T cells after Ag-specific interaction were less efficient in priming naive CD4(+) T cells of the same specificity without losing their ability for CD8(+) T cell stimulation, indicating that the transferred TCR molecules mask the Ag-bearing MHC II molecules, thereby reducing their accessibility to following Ag-specific CD4(+) T cells. While the first group of transferred T cell surface molecules might facilitate the detachment of the CD4(+) T cell from the dendritic cell during the early scanning phases, the second group could play an important immunomodulatory role in intraclonal competition of T cells for APC access, making the physical presence of CD4(+) T cells unnecessary.

The role of alpha 6 integrin in prostate cancer migration and bone pain in a novel xenograft model

Of the estimated 565,650 people in the U.S. who will die of cancer in 2008, almost all will have metastasis. Breast, prostate, kidney, thyroid and lung cancers metastasize to the bone. Tumor cells reside within the bone using integrin type cell adhesion receptors and elicit incapacitating bone pain and fractures. In particular, metastatic human prostate tumors express and cleave the integrin A6, a receptor for extracellular matrix components of the bone, i.e., laminin 332 and laminin 511. More than 50% of all prostate cancer patients develop severe bone pain during their remaining lifetime. One major goal is to prevent or delay cancer induced bone pain. We used a novel xenograft mouse model to directly determine if bone pain could be prevented by blocking the known cleavage of the A6 integrin adhesion receptor. Human tumor cells expressing either the wildtype or mutated A6 integrin were placed within the living bone matrix and 21 days later, integrin expression was confirmed by RT-PCR, radiographs were collected and behavioral measurements of spontaneous and evoked pain performed. All animals independent of integrin status had indistinguishable tumor burden and developed bone loss 21 days after surgery. A comparison of animals containing the wild type or mutated integrin revealed that tumor cells expressing the mutated integrin resulted in a dramatic decrease in bone loss, unicortical or bicortical fractures and a decrease in the ability of tumor cells to reach the epiphyseal plate of the bone. Further, tumor cells within the bone expressing the integrin mutation prevented cancer induced spontaneous flinching, tactile allodynia, and movement evoked pain. Preventing A6 integrin cleavage on the prostate tumor cell surface decreased the migration of tumor cells within the bone and the onset and degree of bone pain and fractures. These results suggest that strategies for blocking the cleavage of the adhesion receptors on the tumor cell surface can significantly prevent cancer induced bone pain and slow disease progression within the bone. Since integrin cleavage is mediated by Urokinase-type Plasminogen Activator (uPA), further work is warranted to test the efficacy of uPA inhibitors for prevention or delay of cancer induced bone pain.

Differential dose-dependent effects of prednisolone on shedding of endothelial adhesion molecules during human endotoxemia

Low dose prednisolone was shown to be beneficial in the treatment of the Acute respiratory distress syndrome (ARDS) and septic shock. One corticosteroid-induced effect, postulated to mediate corticosteroid-induced anti-inflammatory effects, is decreased expression of adhesion molecules on endothelial cells, thereby preventing leukocyte recruitment at inflammatory sites. The current study aimed to investigate the effect of increasing doses of prednisolone on the release of soluble adhesion molecules in healthy volunteers challenged with endotoxin. Therefore, 32 healthy, male volunteers received prednisolone orally at doses of 0mg, 3mg, 10mg or 30 mg at 2h before injection of endotoxin prepared from Escherichia coli (4 ng/kg) and levels of soluble E-selectin (sE-selectin), soluble VCAM-1 (sVCAM-1) and soluble ICAM-1 (sICAM-1) were measured. Levels of all markers were increased after induction of endotoxemia. Levels of sE-selectin were inhibited by a dose of 3mg prednisolone and levels of sVCAM-1 were decreased after a dose of 10mg. Maximal inhibition of both sE-selectin and sVCAM-1 levels was achieved by the highest dose of prednisolone 30 mg. Remarkably, prednisolone 3mg potentiated endotoxin-induced sVCAM-1 release. Levels of sICAM-1 were not affected by prednisolone. Together, the data suggest that prednisolone differentially and dose-dependently influences the release of soluble endothelial adhesion molecules during human endotoxemia.

Pervanadate-induced shedding of the intercellular adhesion molecule (ICAM)-1 ectodomain is mediated by membrane type-1 matrix metalloproteinase (MT1-MMP)

In several vascular diseases, the ectodomain of intercellular adhesion molecule (ICAM)-1 is shed by the proteolytic activity of a zinc-dependent endopeptidase, releasing a soluble form of the protein (sICAM-1), a common marker for inflammatory diseases. Since reactive oxygen species (ROS) generated during prolonged inflammation are known to induce shedding or cleavage of several transmembrane proteins, we sought to explore the cleavage and enzymatic effects that the pervanadate, via oxidation and subsequent inactivation of protein tyrosine phosphatase, has on ICAM-1 cleavage. In these studies, we used endothelial cells (ECs) and 293 human embryonic kidney (HEK) cells expressing high-levels of surface ICAM-1. In addition, use of specific tissue inhibitors of metalloproteinases (TIMPs), small interfering (si)RNA designed to knockdown endopeptidase activity, and an immunocolocalization assay were employed to determine the identity of a specific metalloproteinase mediating pervanadate-induced sICAM-1 shedding. Our data indicate that membrane type-1 matrix metalloproteinase (MT1-MMP) is involved in pervanadate-mediated shedding of the sICAM-1 ectodomain in both cell types. Immunostaining and confocal microscopy provide visual evidence that ICAM-1 and MT1-MMP colocalize at the cellular surface following pervanadate treatment, further implicating the involvement of MT1-MMP activity in this mode of ICAM-1 shedding.

Pharmacologically enhanced expression of GPNMB increases the sensitivity of melanoma cells to the CR011-vcMMAE antibody-drug conjugate

GPNMB is a melanoma-associated glycoprotein that is targeted by the CR011-vcMMAE antibody-drug conjugate (ADC). Previous studies have shown that CR011-vcMMAE induces the apoptosis of GPNMB-expressing tumor cells in vitro and tumor regression in xenograft models. This ADC is currently in clinical trials for melanoma. In the present investigation, a variety of compounds were examined for their ability to increase the expression of GPNMB by cancer cells. These experiments lead to the identification of three distinct groups of compounds that increased GPNMB, some of which were shown to enhance the sensitivity of melanoma cells to CR011-vcMMAE. These data indicate that it may be possible to increase the anticancer activity of CR011-vcMMAE through pharmacological enhancement of GPNMB expression for potential therapeutic benefit.

Disparate mechanisms of sICAM-1 production in the peripheral lung: contrast between alveolar epithelial cells and pulmonary microvascular endothelial cells

Membrane-associated intercellular adhesion molecule-1 (mICAM-1; CD54) is constitutively expressed on the surface of type I alveolar epithelial cells (AEC). Soluble ICAM-1 (sICAM-1) may be produced by proteolytic cleavage of mICAM-1 or by alternative splicing of ICAM-1 mRNA. In contrast to inducible expression seen in most cell types, sICAM-1 is constitutively released by type I AEC and is present in normal alveolar lining fluid. Therefore, we compared the mechanism of sICAM-1 production in primary cultures of two closely juxtaposed cells in the alveolar wall, AEC and pulmonary microvascular endothelial cells (PVEC). AEC, but not PVEC, demonstrated high-level baseline expression of sICAM-1. Stimulation of AEC with TNFalpha or LPS resulted in minimal increase in AEC sICAM-1, whereas PVEC sICAM-1 was briskly induced in response to these signals. AEC sICAM-1 shedding was significantly reduced by treatment with a serine protease inhibitor, but not by cysteine, metalloprotease, or aspartic protease inhibitors. In contrast, none of these inhibitors effected sICAM-1 expression in PVEC. RT-PCR, followed by gel analysis of total RNA, suggests that alternatively spliced fragments are present in both cell types. However, a 16-mer oligopeptide corresponding to the juxtamembrane region of mICAM-1 completely abrogated sICAM-1 shedding in AEC but reduced stimulated PVEC sICAM-1 release by only 20%. Based on these data, we conclude that the predominant mechanism of sICAM-1 production likely differs in the two cell types from opposite sides of the alveolar wall.

Immunotoxin and Taxol synergy results from a decrease in shed mesothelin levels in the extracellular space of tumors

Recombinant immunotoxins are chimeric proteins composed of the Fv portion of a tumor-specific antibody fused to a toxin. SS1P (CAT-5001) is an immunotoxin composed of an antimesothelin Fv fused to a 38-kDa portion of Pseudomonas exotoxin A. Immunotoxins have been shown to be active in lymphomas and leukemias, but are much less active against solid tumors. We recently reported that Taxol and other chemotherapeutic agents show striking synergistic antitumor activity in mice when immunotoxin SS1P, which targets the mesothelin antigen on solid tumors, is given with Taxol. Using a pair of Taxol-sensitive and Taxol-resistant KB tumors equally sensitive to immunotoxin SS1P, we examined the mechanism of synergy. We show that synergy is only observed with Taxol-sensitive tumors, ruling out an effect of Taxol on endothelial cells. We also show that the KB tumors have high levels of shed mesothelin in their extracellular space; these levels increase with tumor size and, after Taxol treatment, dramatically fall in the drug-sensitive but not the drug-resistant tumors. Because the mesothelin levels in the tumor exceed the levels of SS1P in the tumor, and because shed mesothelin is being continuously released into the circulation at a high rate, we propose that synergy is due to the Taxol-induced fall in shed antigen levels.

Isolation of a novel mouse gene, mSVS-1/SUSD2, reversing tumorigenic phenotypes of cancer cells in vitro

We report isolation of a novel tumor-reversing gene, tentatively named SVS-1, encoding a protein of 820 amino acids with localization on the plasma membrane as a type I transmembrane protein. The gene was found among those downregulated in the activated oncogene-v-K-ras-transformed NIH3T3 cells, Ki3T3, with tumorigenic phenotype. SVS-1 protein harbors several functional domains inherent to adhesion molecules. Histochemical staining of mouse tissues using antibody raised against the protein showed the expression of the protein in restricted regions and cells, for example, strongly positive in apical membranes of epithelial cells in renal tubules and bronchial tubes. The protein inducibly expressed in human fibrosarcoma HT1080 cells and cervical carcinoma HeLa cells was found to be localized primarily on the plasma membrane, as stained with antibodies against FLAG tag in the N-terminus and against the C-terminal peptide of the protein. Expression of the protein in cells induced a variety of biological effects on cancer cells: detachment from the substratum and aggregation of cells and growth inhibition in HeLa cells, but no inhibition in non-tumorigenic mouse NIH3T3 cells. Inhibition of clonogenicity, anchorage-independent growth, migration and invasion through Matrigel was also observed. Taken together these results suggest that the SVS-1 gene is a possible tumor-reversing gene.

Regulated proteolytic processing of LRP6 results in release of its intracellular domain

Low-density lipoprotein receptor-related protein 6 (LRP6) is a member of low-density lipoprotein receptor (LDLR) family which cooperates with Frizzled receptors to transduce the canonical Wnt signal. As a critical component of the canonical Wnt pathway, LRP6 is essential for appropriate brain development, however, the mechanism by which LRP6 facilitates Wnt canonical signaling has not been fully elucidated. Interestingly, LRP6 which lacks its extracellular domain can constitutively activate TCF/LEF and potentiate the Wnt signal. Further, the free cytosolic tail of LRP6 interacts directly with glycogen synthase kinase (GSK3) and inhibits GSK3's activity in the Wnt canonical pathway which results in increased TCF/LEF activation. However, whether these truncated forms of LRP6 are physiologically relevant is unclear. Recent studies have shown that other members of the LDLR family undergo gamma-secretase dependent regulated intramembrane proteolysis (RIP). Using independent experimental approaches, we show that LRP6 also undergoes RIP. The extracellular domain of LRP6 is shed and released into the surrounding milieu and the cytoplasmic tail is cleaved by gamma-secretase-like activity to release the intracellular domain. Furthermore, protein kinase C, Wnt 3a and Dickkopf-1 modulate this process. These findings suggest a novel mechanism for LRP6 in Wnt signaling: induction of ectodomain shedding of LRP6, followed by the gamma-secretase involved proteolytic releasing its intracellular domain (ICD) which then binds to GSK3 inhibiting its activity and thus activates the canonical Wnt signaling pathway.

ADAM10 inhibition of human CD30 shedding increases specificity of targeted immunotherapy in vitro

CD30 is a transmembrane protein selectively overexpressed on many human lymphoma cells and therefore an interesting target for antibody-based immunotherapy. However, binding of therapeutic antibodies stimulates a juxtamembrane cleavage of CD30 leading to a loss of target antigen and an enhanced release of the soluble ectodomain of CD30 (sCD30). Here, we show that sCD30 binds to CD30 ligand (CD153)-expressing non-target cells. Because antibodies bind to sCD30, this results in unwanted antibody binding to these cells via sCD30 bridging. To overcome shedding-dependent damage of normal cells in CD30-specific immunotherapy, we analyzed the mechanism involved in the release. Shedding of CD30 can be enhanced by protein kinase C (PKC) activation, implicating the disintegrin metalloproteinase ADAM17 but not free cytoplasmic calcium. However, antibody-induced CD30 shedding is calcium dependent and PKC independent. This shedding involved the related metalloproteinase ADAM10 as shown by the use of the preferential ADAM10 inhibitor GI254023X and by an ADAM10-deficient cell line generated from embryonically lethal ADAM10(-/-) mouse. In coculture experiments, the antibody-induced transfer of sCD30 from the human Hodgkin's lymphoma cell line L540 to the CD30-negative but CD153-expressing human mast cell line HMC-1 was inhibited by GI254023X. These findings suggest that selective metalloproteinase inhibitors blocking antibody-induced shedding of target antigens could be of therapeutic value to increase the specificity and reduce side effects of immunotherapy with monoclonal antibodies.

The human airway trypsin-like protease modulates the urokinase receptor (uPAR, CD87) structure and functions

The human airway trypsin-like protease (HAT) is a respiratory epithelium-associated, type II transmembrane serine protease, which is also detected as an extracellular enzyme in lung fluids during airway inflammatory disorders. We have evaluated its capacity to affect the urokinase-type plasminogen activator receptor (uPAR), a membrane glycolipid-anchored, three-domain (D1D2D3) glycoprotein that plays a crucial role in innate immunity and inflammation by supporting cell migration and matrix degradation, with structure and biological properties that can be regulated via limited endoproteolysis. With the use of immunoblotting, flow immunocytometry, and ELISA analyses applied to a recombinant uPAR protein and to uPAR-expressing monocytic and human bronchial epithelial cells, it was shown that exposure of uPAR to soluble HAT in the range of 10-500 nM resulted in the proteolytic processing of the full-length (D1D2D3) into the truncated (D2D3) species, with cleavage occurring in the D1 to D2 linker sequence after arginine residues at position 83 and 89. Using immunohistochemistry, we found that both HAT and uPAR were expressed in the human bronchial epithelium. Moreover, transient cotransfection in epithelial cells showed that membrane coexpression of the two partners produced a constitutive and extensive shedding of the D1 domain, occurring for membrane-associated HAT concentrations in the nanomolar range. Because the truncated receptor was found to be unable to bind two of the major uPAR ligands, the adhesive matrix protein vitronectin and the serine protease urokinase, it thus appears that proteolytic regulation of uPAR by HAT is likely to modulate cell adherence and motility, as well as tissue remodeling during the inflammatory response in the airways.

Exosomes: from biogenesis and secretion to biological function

Exosomes are small microvesicles that are released from late endosomal compartments of cultured cells. Recent work has shown that exosome-like vesicles are also found in many body fluids such as blood, urine, ascites and amnionic fluid. Although the biological function of exosomes is far from being fully understood, exosomes may have general importance in cell biology and immunology. The present review aims to address some of the facets of exosome research with particular emphasis on the immunologist's perspective: (i) exosomes as a novel platform for the ectodomain shedding of membrane proteins by ADAMs and (ii) recent findings on the role of exosomes in tumor biology and immune regulation.

ADAM10-mediated Release of Complement Membrane Cofactor Protein during Apoptosis of Epithelial Cells

Membrane cofactor protein CD46 controls complement activation on cells, is a receptor for several pathogens, and modulates immune responses by affecting CD8(+) T cells. Cells can release CD46 in an intact form on membrane vesicles and in a truncated form by a metalloproteolytic cleavage. The mechanism of shedding and its relationship to cell physiology has remained unclear. We have found using RNA interference analysis that a disintegrin and metalloproteinase (ADAM) 10 is responsible for the regulated shedding of the ectodomain of CD46 in apoptotic cells. The shedding of CD46 was initiated with staurosporine and UVB. Exposure of cell cultures to either UVB or staurosporine resulted in changes of cell morphology and detachment of cells from their matrices within 8-24 h. During this process CD46 was released both in apoptotic vesicles (vCD46) and proteolytically (sCD46) into the medium. Both the metalloproteinase inhibitor GM6001 and RNA interference of ADAM10 completely prevented the release of sCD46 and increased the expression of vCD46 on HaCaT cell vesicles, suggesting that ADAM10 releases sCD46 from the apoptotic vesicles. To explore whether the release of sCD46 is associated with apoptosis we analyzed the effects of caspase inhibitors. As expected, the inhibition of caspase activity attenuated the characteristic features of apoptosis and also decreased the release of sCD46. Our results reveal ADAM10 as an important regulator of CD46 expression during apoptosis. The ADAM10-mediated release of CD46 from apoptotic vesicles may represent a form of strategy to allow restricted complement activation to deal with modified self.

Redox regulation of CD21 shedding involves signaling via PKC and indicates the formation of a juxtamembrane stalk

Soluble CD21 (sCD21), released from the plasma membrane by proteolytic cleavage (shedding) of its extracellular domain (ectodomain) blocks B cell/follicular dendritic cell interaction and activates monocytes. We show here that both serine- and metalloproteases are involved in CD21 shedding. Using the oxidant pervanadate to mimic B cell receptor activation and thiol antioxidants such as N-acetylcysteine (NAC) and glutathione (GSH) we show that CD21 shedding is a redox-regulated process inducible by oxidation presumably through activation of a tyrosine kinase-mediated signal pathway involving protein kinase C (PKC), and by reducing agents that either directly activate the metalloprotease and/or modify intramolecular disulfide bridges within CD21 and thereby facilitate access to the cleavage site. Lack of short consensus repeat 16 (SCR16) abolishes CD21 shedding, and opening of the disulfide bridge between cys-2 (Cys941) and cys-4 (Cys968) of SCR16 is a prerequisite for CD21 shedding. Replacing these cysteines with selenocysteines (thereby changing the redox potential from -180 to -381 mV) results in a loss of inducible CD21 shedding, and removing this bridge by exchanging these cysteines with methionines increases CD21 shedding.

Tumour necrosis factor alpha-converting enzyme mediates ectodomain shedding of Vps10p-domain receptor family members

Several transmembrane molecules are cleaved at juxtamembrane extracellular sites leading to shedding of ectodomains. We analysed shedding of members of the Vps10p-D (Vps10p domain; where Vps is vacuolar protein sorting) family of neuronal type-I receptors with partially overlapping functions, and additional proteolytic events initiated by the shedding. When transfected into CHO (Chinese-hamster ovary) cells (CHO-K1), sorCS1a-sorCS1c isoforms were shed at high rates (approximately 0.61% x min(-1)) that were increased approx. 3-fold upon stimulation with phorbol ester. sorCS1c identified in the cultured neuroblastoma cell line SH-SY5Y was shed similarly. In CHO-K1 transfectants, constitutive and stimulated shedding of sorCS3 also occurred at high rates (0.29% and 1.03% x min(-1)). By comparison, constitutive and stimulated shedding of sorLA occurred at somewhat lower rates (0.07% and 0.48% x min(-1)), whereas sorCS2 and sortilin were shed at very low rates even when stimulated (approximately 0.01% x min(-1)). Except for sorCS2, shedding of the receptors was dramatically reduced in mutant CHO cells (CHO-M2) devoid of active TACE (tumour necrosis factor alpha-converting enzyme), demonstrating that this enzyme accounts for most sheddase activity. The release of sorCS1 and sorLA ectodomains initiated rapid cleavage of the membrane-tethered C-terminal stubs that accumulated only in the presence of gamma-secretase inhibitors. Purified shed sorLA bound several ligands similarly to the entire luminal domain of the receptor, including PDGF-BB (platelet-derived growth factor-BB) and amyloid-beta precursor protein. In addition, PDGF-BB also bound to the luminal domains of sorCS1 and sorCS3. The results suggest that ectodomains shed from a subset of Vps10p-D receptors can function as carrier proteins.

Bone morphogenetic protein receptors and bone morphogenetic protein signaling are controlled by tumor necrosis factor-α in human bone cells

Bone morphogenetic proteins (BMP) stimulate osteoblast differentiation by signal transduction via three BMP receptors (BMPR-IA, -IB and -II), whereas the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) has been shown to suppress osteoblast differentiation. Although the mechanisms which regulate the BMPR are not yet known, it is possible that they may be negatively controlled by TNF-alpha, thereby inhibiting BMP-induced osteoblast differentiation. To test this hypothesis, we have examined the effects of TNF-alpha on BMPR-IA, -IB and -II expression and the functional consequences of this cytokine on BMPR-mediated functions in human bone cells. The results showed that although TNF-alpha down-regulated BMPR-IA and -II transcripts, it increased the level of BMPR-IB mRNA via a MAPK-dependent pathway. In marked contrast, however, TNF-alpha nevertheless caused marked down-regulation of the expression of the BMPR-IB surface antigen specifically. Moreover, the cytokine-induced decrease in BMPR-IB expression was found to be associated with the concurrent presence of a 'soluble' form of this antigen in supernatants of TNF-alpha-treated cultures. Furthermore, the TNF-alpha-induced loss of BMPR-IB was found to ablate BMP-2-stimulated bone cell functions, including phosphorylation of Smad1/5/8, alkaline phosphatase activity and osteocalcin expression. In conclusion, our study has provided evidence, for the first time, that BMPR can be differentially modulated by TNF-alpha at both the post-transcriptional and post-translational levels, with the TNF-alpha-induced shedding of the BMPR-IB antigen associated with a significantly diminished response to BMP-2 in vitro.

Tumor necrosis factor-alpha-converting enzyme (TACE/ADAM-17) mediates the ectodomain cleavage of intercellular adhesion molecule-1 (ICAM-1)

Ectodomain shedding has emerged as an important regulatory step in the function of transmembrane proteins. Intercellular adhesion molecule-1 (ICAM-1), an adhesion receptor that mediates inflammatory and immune responses, undergoes shedding in the presence of inflammatory mediators and phorbol 12-myristate 13-acetate (PMA). The shedding of ICAM-1 in ICAM-1-transfected 293 cells upon PMA stimulation and in endothelial cells upon tumor necrosis factor-alpha stimulation was blocked by metalloproteinase inhibitors, whereas serine protease inhibitors were ineffective. p-Aminophenylmercuric acetate, a mercuric compound that is known to activate matrix metalloproteinases, up-regulated ICAM-1 shedding. TIMP-3 (but not TIMP-1 or -2) effectively blocked cleavage. This profile suggests the involvement of the ADAM family of proteases in the cleavage of ICAM-1. The introduction of enzymatically active tumor necrosis factor-alpha-converting enzyme (TACE) into ICAM-1-expressing cells up-regulated cleavage. Small interfering RNA directed against TACE blocked ICAM-1 cleavage. ICAM-1 transfected into TACE-/- fibroblasts did not show increased shedding over constitutive levels in the presence of PMA, whereas cleavage did occur in ICAM-1-transfected TACE+/+ cells. These results indicate that ICAM-1 shedding is mediated by TACE. Blocking the shedding of ICAM-1 altered the cell adhesive function, as ICAM-1-mediated cell adhesion was up-regulated in the presence of TACE small interfering RNA and TIMP-3, but not TIMP-1. However, cleavage was found to occur at multiple sites within the stalk domain of ICAM-1, and numerous point mutations within the region did not affect cleavage, indicating that TACE-mediated cleavage of ICAM-1 may not be sequence-specific.

Matrilysin (MMP-7) expression in renal tubular damage: association with Wnt4

BACKGROUND

Matrilysin, a secreted matrix metalloproteinase and target gene of Wnt signaling, functions in epithelial repair and host defense, but no role in renal injury has been described.

METHODS

Matrilysin expression was assessed in human kidney specimens by immunohistochemistry, and in experimental renal injury in mice by immunohistochemistry, Northern blotting, and RNase protection assays (RPA). A relationship to Wnt4, which is also induced in renal injury, was determined by RPA and in situ hybridization.

RESULTS

Matrilysin was not detected in the normal human renal tubular epithelium by immunohistochemistry. However, prominent staining was detected in sections from autosomal-dominant polycystic kidney disease in the cyst lining epithelium, atrophic tubules, and cyst micropolyps, and from hydronephrosis in dilated and atrophic tubules. Matrilysin expression was also induced by acute folic acid nephropathy and unilateral ureteral obstruction (UUO) in the mouse, and expression increased as acute injury progressed to tubulointerstitial fibrosis. Matrilysin staining was primarily localized to epithelium of distal tubule/collecting duct origin in both human and murine renal disease. Wnt signaling can induce matrilysin expression, and we found that the pattern of matrilysin expression during progression of renal fibrosis in the mouse after UUO or folic acid nephropathy, and in the jck model of murine polycystic kidney disease, closely paralleled that of Wnt4.

CONCLUSION

These observations suggest that matrilysin may have a role in renal tubular injury and progression of tubulointerstitial fibrosis, and that Wnt4 may regulate matrilysin expression in the kidney.

The ectodomain shedding of CD30 is specifically regulated by peptide motifs in its cysteine-rich domains 2 and 5

Tumor necrosis factor (TNF)-alpha converting enzyme (TACE) is responsible for the ectodomain release of various membrane proteins by proteolytic cleavage in close proximity to the cell membrane. Despite the wide spectrum of possible substrates, selective cleavage can be achieved by substrate cross-linking. To explore the underlying mechanism, we studied the TACE-mediated shedding of CD30. Whereas the constitutive release of the soluble ectodomain of CD30 (sCD30) from the lymphoma cell line Karpas 299 was enhanced by most anti-CD30 antibodies, it was inhibited by antibodies Ber-H2 and Ki-4. On the basis of the recognized epitopes, shedding seemed to depend on the availability of the cysteine-rich domains (CRD) 2 and 5 of the CD30 ectodomain. CRD2 and 5 have almost identical amino acid sequences and are localized distant from the TACE-targeted cleavage site. Soluble CD30, the product of this enzyme reaction, did not inhibit, but on the contrary, it stimulated CD30 shedding in a CRD2/5-dependent manner. This process could also be induced by CRD2/5-derived peptides but not by a CRD1-derived control peptide. This example of a product-activation was CD30 selective since other TACE substrates such as TNFR1 or TNF-alpha were not affected. These data suggest that CD30 shedding is stimulated by an elevated local availability of CRD2 or 5, possibly by forming a docking station for the releasing enzyme through substrate aggregation.

Signals mediating cleavage of intercellular adhesion molecule-1

ICAM-1, a membrane-bound receptor, is released as soluble ICAM-1 in inflammatory diseases. To delineate mechanisms regulating ICAM-1 cleavage, studies were performed in endothelial cells (EC), human embryonic kidney (HEK)-293 cells transfected with wild-type (WT) ICAM-1, and ICAM-1 containing single tyrosine-to-alanine substitutions (Y474A, Y476A, and Y485A) in the cytoplasmic region. Tyrosine residues at 474 and 485 become phosphorylated upon ICAM-1 ligation and associate with signaling modules. Cleavage was assessed by using an antibody against the cytoplasmic tail of ICAM-1, which recognizes intact ICAM-1 and the 7-kDa membrane-bound fragment remaining after cleavage. Cleavage in HEK-293 WT cells was accelerated by phorbol ester PMA, whereas in EC it was induced by tumor necrosis factor-alpha. In both cell types, a 7-kDa ICAM-1 remnant was detected. Tyrosine phosphatase inhibitors dephostatin and sodium orthovanadate augmented cleavage. PD-98059 (MEK kinase inhibitor), geldanamycin and PP2 (Src kinase inhibitors), and wortmannin (phosphatidylinositol 3-kinase inhibitor) dose-dependently inhibited cleavage in both cell types. SB-203580 (p38 inhibitor) was more effective in EC, and D609 (PLC inhibitor) mostly affected cleavage in HEK-293 cells. Cleavage was drastically decreased in Y474A and Y485A, whereas it was marginally reduced in Y476A. Surprisingly, phosphorylation was not detectable on the 7-kDa fragment of ICAM-1. These results implicate distinct pathways in the cleavage process and suggest a preferred signal transmission route for ICAM-1 shedding in the two cell systems tested. Tyrosine residues Y474 and Y485 within the cytoplasmic sequence of ICAM-1 regulate the cleavage process.

Phorbol 12-myristate 13-acetate-induced release of the colony-stimulating factor 1 receptor cytoplasmic domain into the cytosol involves two separate cleavage events

The colony-stimulating factor 1 (CSF-1) receptor is a protein-tyrosine kinase that regulates cell division, differentiation, and development. In response to phorbol 12-myristate 13-acetate (PMA), the CSF-1 receptor is subject to proteolytic processing. Use of chimeric receptors indicates that the CSF-1 receptor is cleaved at least two times, once in the extracellular domain and once in the transmembrane domain. Cleavage in the extracellular domain results in ectodomain shedding while the cytoplasmic domain remains associated with the membrane. Intramembrane cleavage depends on the sequence of the transmembrane domain and results in the release of the cytoplasmic domain. This process can be blocked by gamma-secretase inhibitors. The cytoplasmic domain localizes partially to the nucleus, displays limited stability, and is degraded by the proteosome. CSF-1 receptors are continuously subject to down-modulation and regulated intramembrane proteolysis (RIP). RIP is stimulated by granulocyte-macrophage-CSF, CSF-1, interleukin-2 (IL-2), IL-4, lipopolysaccharide, and PMA and may provide the CSF-1 receptor with an additional mechanism for signal transduction.

Amyloid-beta increases acetylcholinesterase expression in neuroblastoma cells by reducing enzyme degradation

Amyloid-beta (Abeta) is the principal protein constituent of 'senile plaques' and is a suspected mediator in Alzheimer's disease (AD). Senile plaques also contain acetylcholinesterase (AChE; EC 3.1.1.7), which may have a role in promoting Alphabeta-toxicity. We have found that Alphabeta can affect AChE expression in a neuron-like line, the N1E.115 neuroblastoma cell. When 1 micro mAlphabeta 1-42 or 25-35 was added for 24 h to differentiating N1E.115 in culture, AChE activity increased 30-40% in adherent cells, and 100% or more in nonadherent cells. The changes in both tetrameric (G4) and monomeric (G1) AChE forms were comparable. Turnover studies indicated that the elevation of AChE activity reflected slowed AChE degradation rather than accelerated synthesis. With a similar time course, Alphabeta also increased the quantity of muscarinic receptors on the plasma membrane. Immunocytochemistry for a lysosomal membrane protein (LAMP-1) indicated no change in abundance or localization of lysosomes in treated cells. But decreased labeling by pH-sensitive fluorescent dye pointed to an impairment of lysosomal acidification. We consider that the alteration of AChE expression after Alphabeta-exposure could reflect lysosomal dysfunction, and might itself enhance Alphabeta-toxicity.

Matrilysin (matrix metalloproteinase-7) mediates E-cadherin ectodomain shedding in injured lung epithelium

Matrilysin (matrix metalloproteinase-7) is highly expressed in lungs of patients with pulmonary fibrosis and other conditions associated with airway and alveolar injury. Although matrilysin is required for closure of epithelial wounds ex vivo, the mechanism of its action in repair is unknown. We demonstrate that matrilysin mediates shedding of E-cadherin ectodomain from injured lung epithelium both in vitro and in vivo. In alveolar-like epithelial cells, transfection of activated matrilysin resulted in shedding of E-cadherin and accelerated cell migration. In vivo, matrilysin co-localized with E-cadherin at the basolateral surfaces of migrating tracheal epithelium, and the reorganization of cell-cell junctions seen in wild-type injured tissue was absent in matrilysin-null samples. E-cadherin ectodomain was shed into the bronchoalveolar lavage fluid of bleomycin-injured wild-type mice, but was not shed in matrilysin-null mice. These findings identify E-cadherin as a novel substrate for matrilysin and indicate that shedding of E-cadherin ectodomain is required for epithelial repair.

Syndecans in inflammation

Cell surface heparan sulfate (HS) influences a multitude of molecules, cell types, and processes relevant to inflammation. HS binds to cell surface and matrix proteins, cytokines, and chemokines. These interactions modulate inflammatory cell maturation and activation, leukocyte rolling, and tight adhesion to endothelium, as well as extravasation and chemotaxis. The syndecan family of transmembrane proteoglycans is the major source of cell surface HS on all cell types. Recent in vitro and in vivo data suggest the involvement of syndecans in the modulation of leukocyte-endothelial interactions and extravasation, the formation of chemokine and kininogen gradients, participation in chemokine and growth factor signaling, as well as repair processes. Thus, the complex role of HS in inflammation is reflected by multiple functions of its physiological carriers, the syndecans. Individual and common functions of the four mammalian syndecan family members can be distinguished. Recently generated transgenic and knockout mouse models will facilitate analysis of the individual processes that each syndecan is involved in.

Long-range signal transmission in autocrine relays

Intracellular signaling induced by peptide growth factors can stimulate secretion of these molecules into the extracellular medium. In autocrine and paracrine networks, this can establish a positive feedback loop between ligand binding and ligand release. When coupled to intercellular communication by autocrine ligands, this positive feedback can generate constant-speed traveling waves. To demonstrate that, we propose a mechanistic model of autocrine relay systems. The model is relevant to the physiology of epithelial layers and to a number of in vitro experimental formats. Using asymptotic and numerical tools, we find that traveling waves in autocrine relays exist and have a number of unusual properties, such as an optimal ligand binding strength necessary for the maximal speed of propagation. We compare our results to recent observations of autocrine and paracrine systems and discuss the steps toward experimental tests of our predictions.