Distinct roles for ADAM10 and ADAM17 in ectodomain shedding of six EGFR ligands

Angiotensin II and EGF receptor cross-talk in chronic kidney diseases: a new therapeutic approach

Mechanisms of progression of chronic renal diseases, a major healthcare burden, are poorly understood. Angiotensin II (AngII), the major renin-angiotensin system effector, is known to be involved in renal deterioration, but the molecular pathways are still unknown. Here, we show that mice overexpressing a dominant negative isoform of epidermal growth factor receptor (EGFR) were protected from renal lesions during chronic AngII infusion. Transforming growth factor-alpha (TGF-alpha) and its sheddase, TACE (also known as ADAM17), were induced by AngII treatment, TACE was redistributed to apical membranes and EGFR was phosphorylated. AngII-induced lesions were substantially reduced in mice lacking TGF-alpha or in mice given a specific TACE inhibitor. Pharmacologic inhibition of AngII prevented TGF-alpha and TACE accumulation as well as renal lesions after nephron reduction. These findings indicate a crucial role for AngII-dependent EGFR transactivation in renal deterioration and identify in TACE inhibitors a new therapeutic strategy for preventing progression of chronic renal diseases.

Metalloproteinases and their inhibitors in tumor angiogenesis

Angiogenesis is the process by which new blood vessels are formed from preexisting vasculature. It is an essential feature of the female reproductive cycle, embryonic development and wound repair. Angiogenesis has also been identified as a causal or contributing factor in several pathologies, including cancer, where it is a rate-limiting step during tumor progression. Matrix metalloproteinases (MMPs) are a family of soluble and membrane-anchored proteolytic enzymes that can degrade components of the extracellular matrix (ECM) as well as a growing number of modulators of cell function. Several of the MMPs, in particular the gelatinases and membrane-type 1 MMP (MT1-MMP), have been linked to angiogenesis. Potential roles for these proteases during the angiogenic process include degradation of the basement membrane and perivascular ECM components, unmasking of cryptic biologically relevant sites in ECM components, modulation of angiogenic factors and production of endogenous angiogenic inhibitors. This review brings together what is currently known about the functions of the MMPs and the closely related ADAM (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) families in angiogenesis and considers how this information might be useful in manipulation of the angiogenic process, with a view to constraining tumor progression.

ADAM proteases, ErbB pathways and cancer

A disintegrin and metalloproteases (ADAMs) are zinc-dependent trans-membrane metalloproteases that shed the extracellular domains of membrane-bound growth factors, cytokines and receptors. Key functions of ADAMs have emerged in ErbB signalling pathways as being sheddases for multiple ErbB ligands. As the ErbB pathway is a validated target for anti-cancer drugs, the upstream activators of ErbB ligands, their sheddases, now enter the spotlight as new drug targets in the ErbB pathway. ADAMs are involved not only in tumour cell proliferation but also in angiogenesis and metastasis. Therefore, strategies targeting ADAMs might be an important complement to existing anti-ErbB approaches.

Shedding light on ADAM metalloproteinases

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

Biological significance of c-erbB family oncogenes in head and neck cancer

Squamous cell carcinoma of the head and neck (SCCHN) tends to run an aggressive course and the prognosis has remained virtually unchanged in recent decades. The development of novel therapeutic strategies to improve patient outcome centres on the biology of the disease, namely the pivotal c-erbB family of growth factor receptors. c-erbB1 (or epidermal growth factor receptor, EGFR), is key to the pathogenesis of SCCHN and plays a central role in a complex network of downstream integrated signalling pathways. EGFR overexpression, detected in up to 90% of SCCHN, correlates with an increased risk of locoregional tumour relapse following primary therapy and relative resistance to treatment. The biological sequelae of erbB receptor activation are not simply cell proliferation, but also inhibition of apoptosis, enhanced migration, invasion, angiogenesis and metastasis: the 'hallmarks of cancer' [1]. As EGFR overexpression is associated with a poor clinical outcome in SCCHN, this receptor is attractive as a therapeutic target and the successful development of targeted therapies represents a paradigm shift in the medical approach to head and neck cancer. However, the extensive cross talk between signalling pathways, the multiple molecular aberrations and genetic plasticity in SCCHN all contribute to inherent and acquired resistance to both conventional and novel therapies. Understanding the cancer cell biology, in particular the significance of co-expression of c-erbB (and other) receptors, and the cell survival stimuli from (for example) activation of the phosphoinositide 3-kinase (PI3-kinase) cascade is fundamental to overcome current limitations in biologically targeted therapies.

Metalloprotease-disintegrin ADAM8: expression analysis and targeted deletion in mice

ADAM8 (a disintegrin and metalloprotease 8, also referred to as MS2/CD156a) is a membrane-anchored metalloprotease that was first identified in a macrophage cell line and has been implicated in neurodegenerative diseases. Here, we evaluated the expression of ADAM8 during mouse development and generated mice lacking ADAM8 (Adam8-/- mice). During early mouse development, ADAM8 is expressed by maternal cells in the decidua and by trophoblast derivatives of the embryo but not in the derivatives of the inner cell mass. At later stages, prominent expression of ADAM8 is seen in the embryo proper, in the gonadal ridge, thymus, developing cartilage and bone, brain and spinal cord, and in the mesenchyme in close proximity to the branch point between the jugular vein and developing lymphatic vessels. Examination of Adam8-/- mice, however, revealed no major defects in these or other structures during development or in adult tissues and no evident pathological phenotypes.

Selective inhibition of TNF-alpha-induced activation of mitogen-activated protein kinases and metastatic activities by gefitinib

We have reported that the selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, gefitinib (‘Iressa’, ZD1839), suppressed intrahepatic metastasis of hepatocellular carcinoma CBO140C12 cells. In this study, we focused on the tumour necrosis factor-α (TNF-α) signalling pathways. Real-time reverse transcription–polymerase chain reaction showed that TNF-α mRNA was expressed in large quantities in the implanted tumour. Gefitinib inhibited EGF- but not hepatocyte growth factor (HGF)-induced activation of mitogen-activated protein kinase (MAPK) cascades, suggesting selectivity of the inhibitor. However, gefitinib inhibited the TNF-α-induced activation of MAPKs and Akt. In addition, TNF-α-induced metastatic properties including adhesion to fibronectin, mRNA expression of integrin αv, production of matrix metalloproteinase-9 and invasion were inhibited by gefitinib without affecting cell proliferation. Furthermore, the TNF-α-induced responses except for NF-κB activation were blocked by metalloprotease inhibitors, suggesting that gefitinib inhibited the transactivation of EGFR induced by TNF-α. These results suggest that the TNF-α signalling pathway is a possible target of gefitinib in suppressing the intrahepatic metastasis of hepatocellular carcinoma.

G protein coupling and second messenger generation are indispensable for metalloprotease-dependent, heparin-binding epidermal growth factor shedding through angiotensin II type-1 receptor

A G protein-coupled receptor agonist, angiotensin II (AngII), induces epidermal growth factor (EGF) receptor (EGFR) transactivation possibly through metalloprotease-dependent, heparin-binding EGF (HB-EGF) shedding. Here, we have investigated signal transduction of this process by using COS7 cells expressing an AngII receptor, AT1. In these cells AngII-induced EGFR transactivation was completely inhibited by pretreatment with a selective HB-EGF inhibitor, or with a metalloprotease inhibitor. We also developed a COS7 cell line permanently expressing a HB-EGF construct tagged with alkaline phosphatase, which enabled us to measure HB-EGF shedding quantitatively. In the COS7 cell line AngII stimulated release of HB-EGF. This effect was mimicked by treatment either with a phospholipase C activator, a Ca2+ ionophore, a metalloprotease activator, or H2O2. Conversely, pretreatment with an intracellular Ca2+ antagonist or an antioxidant blocked AngII-induced HB-EGF shedding. Moreover, infection of an adenovirus encoding an inhibitor of G(q) markedly reduced EGFR transactivation and HB-EGF shedding through AT1. In this regard, AngII-stimulated HB-EGF shedding was abolished in an AT1 mutant that lacks G(q) protein coupling. However, in cells expressing AT1 mutants that retain G(q) protein coupling, AngII is still able to induce HB-EGF shedding. Finally, the AngII-induced EGFR transactivation was attenuated in COS7 cells overexpressing a catalytically inactive mutant of ADAM17. From these data we conclude that AngII stimulates a metalloprotease ADAM17-dependent HB-EGF shedding through AT1/G(q)/phospholipase C-mediated elevation of intracellular Ca2+ and reactive oxygen species production, representing a key mechanism indispensable for EGFR transactivation.

A disintegrin and metalloprotease 33 polymorphisms and lung function decline in the general population

RATIONALE

A disintegrin and metalloprotease 33 (ADAM33) has been identified as a susceptibility gene for asthma and single nucleotide polymorphisms (SNPs) in this gene have been associated with excessive decline of lung function in individuals with asthma.

OBJECTIVES

To assess whether SNPs in ADAM33 are associated with accelerated lung function loss in the general population and with chronic obstructive pulmonary disease (COPD).

METHODS

DNA was collected from subjects of the Vlagtwedde-Vlaardingen cohort participating in the last survey in 1989-1990 after a follow-up of 25 years. Information was collected every 3 years, including lung function measurements. We defined COPD as GOLD stage 2 or higher at the last survey. A total of 1,390 subjects from the cohort was genotyped for the following SNPs in ADAM33: F+1, Q-1, S_1, S_2, T_1, T_2, V_4, and ST+5. Differences in prevalence of SNPs were analyzed with chi(2) tests. Linear mixed effects models were used to analyze FEV(1) decline according to genotype.

MEASUREMENTS AND MAIN RESULTS

In the whole population, mean adjusted decline was 18.7 and 12.7 ml/year in females and males, respectively. Individuals homozygous for minor alleles of SNPs S_2 and Q-1 and heterozygous for SNP S_1 had a significantly accelerated decline in FEV(1) of, respectively, 4.9, 9.6, and 3.6 ml/year compared with wild type. We found a significantly higher prevalence of SNPs F+1, S_1, S_2, and T_2 in subjects with COPD.

CONCLUSIONS

We demonstrated that SNPs in ADAM33 are associated with accelerated lung function decline in the general population. These SNPs are also risk factors for COPD.

ADAMs: key components in EGFR signalling and development

ADAM (a disintegrin and metalloprotease) proteins are membrane-anchored metalloproteases that process and shed the ectodomains of membrane-anchored growth factors, cytokines and receptors. ADAMs also have essential roles in fertilization, angiogenesis, neurogenesis, heart development and cancer. Research on ADAMs and their role in protein ectodomain shedding is emerging as a fertile ground for gathering new insights into the functional regulation of membrane proteins.

Cytoplasmic Domain of proEGF Affects Distribution and Post-Translational Modification of Microtubuli and Increases Microtubule-Associated Proteins 1b and 2 Production in Human Thyroid Carcinoma Cells

We studied the distribution of transcripts encoding the cytoplasmic domain of the membrane-anchored precursor epidermal growth factor (proEGFcyt) and a novel cytoplasmic proEGF splice isoform with a deleted exon 23 and an out-of-frame fusion of exon 24 (proEGFdel23) in human normal and neoplastic thyroid tissues. In papillary thyroid carcinoma (PTC), coexpression of transcripts encoding for both proEGFcyt and proEGFdel23 correlated with poor differentiation of PTC. To determine potential roles of the cytoplasmic proEGF domain in human thyroid cells, we generated stable transfectants of the human follicular thyroid carcinoma cell line FTC-133 overexpressing the normal cytoplasmic domain proEGFcyt, a truncated proEGFcyt composed of the peptide sequence encoded by exons 22 and 23 (proEGF22.23) and proEGFdel23. The proEGFcyt and proEGF22.23 transfectants displayed significantly reduced proliferation rates, an enlarged cellular phenotype, and alterations in the distribution and post-translational modification of the microtubular system. These transfectants also displayed increased production of microtubule-associated proteins 1b and 2c, which was absent in FTC-133-proEGFdel23 or FTC-133-empty plasmid transfectants. This is the first evidence of an involvement of proEGF cytoplasmic domain in microtubular stability in the human thyroid carcinoma cell line FTC-133 and may suggest a specific role for the cytoplasmic domain of membrane-anchored proEGF, particularly exon 23, in thyroid carcinoma. The up-regulation of proEGFdel23 in poorly differentiated PTC and the exclusive detection of both proEGF isoforms in undifferentiated thyroid carcinoma may indicate an involvement of this novel truncated proEGFdel23 cytoplasmic domain during dedifferentiation processes of human thyroid cells.

ADAM10 cleavage of N-cadherin and regulation of cell-cell adhesion and beta-catenin nuclear signalling

Cadherins are critically involved in tissue development and tissue homeostasis. We demonstrate here that neuronal cadherin (N-cadherin) is cleaved specifically by the disintegrin and metalloproteinase ADAM10 in its ectodomain. ADAM10 is not only responsible for the constitutive, but also for the regulated, shedding of this adhesion molecule in fibroblasts and neuronal cells directly regulating the overall levels of N-cadherin expression at the cell surface. The ADAM10-induced N-cadherin cleavage resulted in changes in the adhesive behaviour of cells and also in a dramatic redistribution of beta-catenin from the cell surface to the cytoplasmic pool, thereby influencing the expression of beta-catenin target genes. Our data therefore demonstrate a crucial role of ADAM10 in the regulation of cell-cell adhesion and on beta-catenin signalling, leading to the conclusion that this protease constitutes a central switch in the signalling pathway from N-cadherin at the cell surface to beta-catenin/LEF-1-regulated gene expression in the nucleus.

Expression of mRNAs encoding for growth factors, ECM molecules, and MMP13 in mono-cultures and co-cultures of human periodontal ligament fibroblasts and alveolar bone cells

Although the function and effects of many growth factors and extracellular matrix (ECM) molecules have been described for several periodontal tissues in vivo and in vitro, the molecular interactions involved in the communication between cells of the periodontal ligament and the alveolar bone are poorly understood. To contribute to the identification of such interactions, we have generated co-cultures (CCs) of periodontal ligament fibroblasts (PDLs) and alveolar bone cells (ABCs) and compared mRNA expression for various growth factors, ECM molecules, and matrix metalloproteinase13 (MMP13) after 1 and 2 weeks with matched mono-cultures (MCs) by reverse transcription/polymerase chain reaction. Compared with CCs of 1 week, PDLs and ABCs after 2 weeks revealed relatively high levels of all analyzed mRNAs, viz., for EGF, HGF, VEGF, TGFbeta1, collagen-I (COL1), osteonectin (ON), fibronectin (FN1), and MMP13. At week 2, when compared with MCs, CCs showed an elevation of all tested mRNAs in PDLs and ABCs, except for TGFbeta1 and FN1, which only increased in PDLs. After 1 week, when CCs were compared with MCs, mRNAs for HGF and TGFbeta1 were less abundant in PDLs and ABCs, whereas the other genes exhibited lower expression levels in only one of the cell types. Analysis of our data indicated that the expression of mRNAs for growth factors and for COL1, ON, FN1, and MMP13 was modulated in the distinct cell types with respect to culture time and culture type. The differences in the mRNA expression patterns between CCs and MCs suggest that the respective genes are involved in the molecular interactions of PDLs and ABCs.

Abundance of ADAM-8, -9, -10, -12, -15 and -17 and ADAMTS-1 in mouse uterus during the oestrous cycle

The aim of the present study was to determine whether a disintegrin and metalloproteinase (ADAM)-8, -9, -10, -12, -15 and -17 and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-1 are involved in the remodelling process of the mouse uterus during the oestrous cycle. The mRNA expression of ADAM was observed in all uterine tissues throughout the entire cycle. The levels of ADAM-8 mRNA were maximal at pro-oestrus, whereas the expression of ADAM-9 and ADAMTS-1 mRNA was maximal at oestrus. The minimum mRNA level of all ADAM genes always occurred at dioestrus. The mRNA levels of ADAM-10, -12, -15 and -17 did not vary significantly, regardless of the stage of the oestrous cycle. Immunoblot analyses demonstrated the presence of all ADAM proteins throughout the cycle. In terms of protein intensities, ADAM-8, -12 and -17 were maximal at pro-oestrus, whereas ADAM-10 and ADAMTS-1 were maximal at metoestrus and ADAM-9 was maximal at oestrus. Regardless of the ADAM species, minimal protein expression always occurred at dioestrus. Immunohistochemical studies showed ADAM protein expression in luminal and glandular epithelial layers, but not in the stromal layer. Moreover, ADAM proteins were found to be heterogeneously localised and their individual localisations depended on the stage of the oestrous cycle. From these observations, we suggest that the ADAM genes play an important role in mouse uterine tissue remodelling during the oestrous cycle.

ADAM10 Mediates Ectodomain Shedding of the Betacellulin Precursor Activated by p-Aminophenylmercuric Acetate and Extracellular Calcium Influx

Betacellulin belongs to the family of epidermal growth factor-like growth factors that are expressed as transmembrane precursors and undergo proteolytic ectodomain shedding to release a soluble mature growth factor. In this study, we investigated the ectodomain shedding of the betacellulin precursor (pro-BTC) in conditionally immortalized wild-type (WT) and ADAM-deficient cell lines. Sequential ectodomain cleavage of the predominant cell-surface 40-kDa form of pro-BTC generated a major (26-28 kDa) and two minor (20 and 15 kDa) soluble forms and a cellular remnant lacking the ectodomain (12 kDa). Pro-BTC shedding was activated by calcium ionophore (A23187) and by the metalloprotease activator p-aminophenylmercuric acetate (APMA), but not by phorbol esters. Culturing cells in calcium-free medium or with the protein kinase Cdelta inhibitor rottlerin, but not with broad-based protein kinase C inhibitors, blocked A23187-activated pro-BTC shedding. These same treatments were without effect for constitutive and APMA-induced cleavage events. All pro-BTC shedding was blocked by treatment with a broad-spectrum metalloprotease inhibitor (GM6001). In addition, constitutive and activated pro-BTC shedding was differentially blocked by TIMP-1 or TIMP-3, but was insensitive to treatment with TIMP-2. Pro-BTC shedding was functional in cells from ADAM17- and ADAM9-deficient mice and in cells overexpressing WT or catalytically inactive ADAM17. In contrast, overexpression of WT ADAM10 enhanced constitutive and activated shedding of pro-BTC, whereas overexpression of catalytically inactive ADAM10 reduced shedding. These results demonstrate, for the first time, activated pro-BTC shedding in response to extracellular calcium influx and APMA and provide evidence that ADAM10 mediates constitutive and activated pro-BTC shedding.

ADAM-mediated ectodomain shedding of HB-EGF in receptor cross-talk

All ligands of the epidermal growth factor receptor (EGFR) which has important roles in development and disease, are shed from the plasma membrane by metalloproteases. The ectodomain shedding of EGFR ligands has emerged as a critical component in the functional activation of EGFR in the interreceptor cross-talk. Identification of the sheddases for EGFR ligands using mouse embryonic cells lacking candidate sheddases (a disintegrin and metalloprotease; ADAM) has revealed that ADAM10, -12 and -17 are the sheddases of the EGFR ligands in response to various shedding stimulants such as GPCR agonists, growth factors, cytokines, osmotic stress, wounding and phorbol ester. Among the EGFR ligands, heparin-binding EGF-like growth factor (HB-EGF) is a representative ligand to understand the pathophysiological roles of the ectodomain shedding in wound healing, cardiac diseases, etc. Here we focus on the ectodomain shedding of HB-EGF by ADAMs, which is not only a key event of receptor cross-talk but also a novel intercellular signaling by the carboxy-terminal fragment (CTF signal).

Fringe glycosyltransferases differentially modulate Notch1 proteolysis induced by Delta1 and Jagged1

Fringe O-fucose-beta1,3-N-acetylglucosaminyltransferases modulate Notch signaling by potentiating signaling induced by Delta-like ligands, while inhibiting signaling induced by Serrate/Jagged1 ligands. Based on binding studies, the differential effects of Drosophila fringe (DFng) on Notch signaling are thought to result from alterations in Notch glycosylation that enhance binding of Delta to Notch but reduce Serrate binding. Here, we report that expression of mammalian fringe proteins (Lunatic [LFng], Manic [MFng], or Radical [RFng] Fringe) increased Delta1 binding and activation of Notch1 signaling in 293T and NIH 3T3 cells. Although Jagged1-induced signaling was suppressed by LFng and MFng, RFng enhanced signaling induced by either Delta1 or Jagged1, underscoring the diversity of mammalian fringe glycosyltransferases in regulating signaling downstream of different ligand-receptor combinations. Interestingly, suppression of Jagged1-induced Notch1 signaling did not correlate with changes in Jagged1 binding as found for Delta1. Our data support the idea that fringe glycosylation increases Delta1 binding to potentiate signaling, but we propose that although fringe glycosylation does not reduce Jagged1 binding to Notch1, the resultant ligand-receptor interactions do not effectively promote Notch1 proteolysis required for activation of downstream signaling events.

Mechanisms of soluble cytokine receptor generation

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

Activation of the epidermal growth factor receptor by respiratory syncytial virus results in increased inflammation and delayed apoptosis

Respiratory syncytial virus (RSV) preferentially infects lung epithelial cells. Infection by RSV leads to an extended inflammatory response, characterized by the release of interleukin-8 (IL-8). Activation of ERK MAP kinase is required for both RSV-induced inflammation and the extended survival of infected cells. In this study, we analyzed the role of the epidermal growth factor receptor (EGFR) in RSV activation of ERK. We demonstrate for the first time that RSV activates EGFR in lung epithelial cells. Activation of EGFR results in increased ERK activity, contributing to both the inflammatory response (IL-8 release) and prolonging the survival of RSV-infected cells. Inhibition of EGFR with siRNA decreased both ERK activation and IL-8 production after RSV. In analyzing the effect of EGFR activation on survival of RSV-infected cells, we found that EGFR activation by RSV resulted in ERK-dependent alterations in the balance of pro- versus anti-apoptotic Bcl2 proteins. RSV altered the balance between pro- and anti-apoptotic Bcl2 proteins (increased BclxL and decreased BimEL) increasing the relative amount of pro-survival proteins. This occurred in an EGFR-dependent manner. This study supports an important role for EGFR activity in the lifespan and inflammatory potential of RSV-infected epithelial cells.

Transactivation of epidermal growth factor receptor mediates catecholamine-induced growth of vascular smooth muscle

Stimulation of alpha1-adrenoceptors induces proliferation of vascular smooth muscle cells (SMCs) and contributes to arterial remodeling. Although activation of NAD(P)H oxidase and generation of reactive oxygen species (ROS) are required, little is known about this pathway. In this study, we examined the hypothesis that epidermal growth factor receptor (EGFR) transactivation and extracellular regulated kinases (ERK) are involved in alpha1-adrenoceptor-mediated SMC growth. Phenylephrine increased protein synthesis in association with a rapid (< or =5 minutes) and sustained (> or =60 minutes) doubling of phosphorylation of EGFR and ERK1/2, but not p38 or JNK in the media of rat aorta maintained in organ culture. Antagonists of EGFR phosphotyrosine activity (AG-1478) and ERK phosphorylation (PD-98059, U-0126) abolished phenylephrine-induced protein synthesis, whereas antagonists of p38 or JNK phosphorylation had no specific effect. A competitive antagonist (P22) for heparin binding EGF-like growth factor (HB-EGF) blocked phenylephrine-induced protein synthesis, as did downregulation of pro-HB-EGF (CRM197). Phenylephrine-induced protein synthesis was inhibited by neutralizing antibody to HB-EGF and absent in HB-EGF-/- SMCs. Inhibitors of metalloproteinases (BiPS, KB-R7785) also blocked adrenergic growth. The neutralizing antibody against HB-EGF had no effect on the two-fold increase in ROS generation induced by phenylephrine (DCF fluorescence), suggesting that stimulation of NAD(P)H oxidase by alpha1-adrenoceptor occupation precedes HB-EGF release. Cell culture studies confirmed and extended these findings. These data suggest that alpha1-adrenoceptor-mediated SMC growth requires ROS-dependent shedding of HB-EGF, transactivation of EGFR, and activation of the MEK1/2-dependent MAP kinase pathway. This trophic pathway may link sympathetic activity to arterial wall growth in adaptive remodeling and hypertrophic disease.

Evaluation of the contribution of different ADAMs to tumor necrosis factor alpha (TNFalpha) shedding and of the function of the TNFalpha ectodomain in ensuring selective stimulated shedding by the TNFalpha convertase (TACE/ADAM17)

Tumor necrosis factor-alpha (TNFalpha), a potent pro-inflammatory cytokine, is released from cells by proteolytic cleavage of a membrane-anchored precursor. The TNF-alpha converting enzyme (TACE; a disintegrin and metalloprotease17; ADAM17) is known to have a key role in the ectodomain shedding of TNFalpha in several cell types. However, because purified ADAMs 9, 10, and 19 can also cleave a peptide corresponding to the TNFalpha cleavage site in vitro, these enzymes are considered to be candidate TNFalpha sheddases as well. In this study we used cells lacking ADAMs 9, 10, 17 (TACE), or 19 to address the relative contribution of these ADAMs to TNFalpha shedding in cell-based assays. Our results corroborate that ADAM17, but not ADAM9, -10, or -19, is critical for phorbol ester- and pervanadate-stimulated release of TNFalpha in mouse embryonic fibroblasts. However, overexpression of ADAM19 increased the constitutive release of TNFalpha, whereas overexpression of ADAM9 or ADAM10 did not. This suggests that ADAM19 may contribute to TNFalpha shedding, especially in cells or tissues where it is highly expressed. Furthermore, we used mutagenesis of TNFalpha to explore which domains are important for its stimulated processing by ADAM17. We found that the cleavage site of TNFalpha is necessary and sufficient for cleavage by ADAM17. In addition, the ectodomain of TNFalpha makes an unexpected contribution to the selective cleavage of TNFalpha by ADAM17: it prevents one or more other enzymes from cleaving TNFalpha following PMA stimulation. Thus, selective stimulated processing of TNFalpha by ADAM17 in cells depends on the presence of an appropriate cleavage site as well as the inhibitory role of the TNF ectodomain toward other enzymes that can process this site.

ADAM binding protein Eve-1 is required for ectodomain shedding of epidermal growth factor receptor ligands

A disintegrin and metalloproteases (ADAMs) are implicated in the ectodomain shedding of epidermal growth factor receptor (EGFR) ligands in EGFR transactivation. However, the activation mechanisms of ADAMs remain elusive. To analyze the regulatory mechanisms of ADAM activation, we performed yeast two-hybrid screening using the cytoplasmic domain of ADAM12 as bait, and identified a protein that we designated Eve-1. Two cDNAs were cloned and characterized. They encode alternatively spliced isoforms of Eve-1, called Eve-1a and Eve-1b, that have four and five tandem Src homology 3 (SH3) domains in the carboxyl-terminal region, respectively, and seven proline-rich SH3 domain binding motifs in the amino-terminal region. The short forms of Eve-1, Eve-1c and Eve-1d, translated at Met-371 are human counterparts of mouse Sh3d19. Northern blot analysis demonstrated that Eve-1 is abundantly expressed in skeletal muscle and heart. Western blot analysis revealed the dominant production of Eve-1c in human cancer cell lines. Knockdown of Eve-1 by small interfering RNA in HT1080 cells reduced the shedding of proHB-EGF induced by angiotensin II and 12-O-tetradecanoylphorbol-13-acetate, as well as the shedding of pro-transforming growth factor-alpha, promphiregulin, and proepiregulin by 12-O-tetradecanoylphorbol-13-acetate, suggesting that Eve-1 plays a role in positively regulating the activity of ADAMs in the signaling of EGFR-ligand shedding.

Extracellular calcium-sensing receptor transactivates the epidermal growth factor receptor by a triple-membrane-spanning signaling mechanism

Activation of the extracellular calcium-sensing receptor (CaR) stimulates mitogen-activated protein kinases to upregulate the synthesis and secretion of parathyroid hormone related peptide (PTHrP) from cells expressing the CaR heterologously or endogenously. The current experiments demonstrate that this occurs because CaR activation "transactivates" the EGF receptor (EGFR). Time dependent increases in tyrosine phosphorylation of the EGFR after addition of extracellular calcium ([Ca2+]o, 3 mM) occurred in stably CaR-transfected HEK293 cells but not in non-transfected HEK293 cells. AG1478, an EGFR kinase inhibitor, prevented the CaR-mediated increases of pERK and PTHrP release, while AG1296, a PDGFR kinase inhibitor, had no effect. Inhibitors of matrix metalloproteinase and heparin bound-EGF prevented the CaR-mediated increases of pERK and PTHrP, consistent with a "triple-membrane-spanning signaling" requirement for transactivation of the EGFR by the CaR. Proximal and distal signal transduction cascades activated by the CaR may reflect transactivation of the EGFR by the extracellular calcium-sensing receptor.

Amyloid at the cutting edge: activation of alpha-secretase prevents amyloidogenesis in an Alzheimer disease mouse model

The amyloid beta-peptide (A beta peptide) is assumed to play a crucial and early role in the pathogenesis of Alzheimer disease. Thus, strategies for a pharmacotherapy aim at reducing A beta peptide generation, which proteolytically derives from the amyloid precursor protein (APP). The main targets so far have been beta- and gamma-secretase, the two proteases that cleave APP at the N- and C-terminus of the A beta peptide and are thus directly responsible for A beta peptide generation. A different strategy, namely the activation of alpha-secretase, has barely been investigated for its therapeutic potential. alpha-Secretase cleaves within the A beta peptide domain and thus precludes A beta peptide generation. Now, new results demonstrate that activation of alpha-secretase indeed reduces A beta peptide generation and toxicity in vivo.

Cell-matrix interaction via CD44 is independently regulated by different metalloproteinases activated in response to extracellular Ca(2+) influx and PKC activation

CD44 is an adhesion molecule that interacts with hyaluronic acid (HA) and undergoes sequential proteolytic cleavages in its ectodomain and intramembranous domain. The ectodomain cleavage is triggered by extracellular Ca(2+) influx or the activation of protein kinase C. Here we show that CD44-mediated cell-matrix adhesion is terminated by two independent ADAM family metalloproteinases, ADAM10 and ADAM17, differentially regulated in response to those stimuli. Ca(2+) influx activates ADAM10 by regulating the association between calmodulin and ADAM10, leading to CD44 ectodomain cleavage. Depletion of ADAM10 strongly inhibits the Ca(2+) influx-induced cell detachment from matrix. On the other hand, phorbol ester stimulation activates ADAM17 through the activation of PKC and small GTPase Rac, inducing proteolysis of CD44. Furthermore, depletion of ADAM10 or ADAM17 markedly suppressed CD44-dependent cancer cell migration on HA, but not on fibronectin. The spatio-temporal regulation of two independent signaling pathways for CD44 cleavage plays a crucial role in cell-matrix interaction and cell migration.

Loss of ectodomain shedding due to mutations in the metalloprotease and cysteine-rich/disintegrin domains of the tumor necrosis factor-alpha converting enzyme (TACE)

Tumor necrosis factor-alpha converting enzyme (TACE), a multidomain protease essential for development and disease, releases the ectodomains from many transmembrane proteins in a regulated fashion. To understand the mechanism underlying the regulation of TACE activity, we sought to identify the cause of ectodomain shedding deficiencies in two mutated CHO sublines designated M1 and M2. Transfection of expression vectors for human and mouse TACE restored ectodomain shedding of TNF-alpha and TGF-alpha, suggesting that defects in the TACE gene contribute to the phenotype of M1 and M2 cells. The overall levels of endogenous TACE forms in M1 cells were significantly lower than those found in their parental cells, whereas only TACE zymogen, but not its mature form, was detectable in M2 cells. Molecular analyses suggested that M1 cells contained only one expressible TACE allele encoding an M435I point mutation in the catalytic center of the protease, and M2 cells produced two TACE variants with distinct point mutations in the catalytic domain (C225Y) and the cysteinerich/disintegrin domain (C600Y). Overexpression of the C225Y and C600Y TACE by transient transfection largely compensated for maturation defects in the variants but failed to restore TNF-alpha and TGF-alpha release in the shedding-defective CHO cell lines and fibroblasts derived from TACE-null mouse embryo. Further mutagenesis and functional analyses demonstrated that Cys(600) was absolutely essential for ectodomain shedding, suggesting that Cys(600), similar to Cys(225), participates in disulfide bonding, which is critical for both the processing and catalysis of TACE.

Selective roles for tumor necrosis factor alpha-converting enzyme/ADAM17 in the shedding of the epidermal growth factor receptor ligand family: the juxtamembrane stalk determines cleavage efficiency

Epidermal growth factor (EGF) family ligands are derived by proteolytic cleavage of the ectodomains of integral membrane precursors. Previously, we established that tumor necrosis factor alpha-converting enzyme (TACE/ADAM17) is a physiologic transforming growth factor-alpha (TGF-alpha) sheddase, and we also demonstrated enhanced shedding of amphiregulin (AR) and heparin-binding (HB)-EGF upon restoration of TACE activity in TACE-deficient EC-2 fibroblasts. Here we extended these results by showing that purified soluble TACE cleaved single sites in the juxtamembrane stalks of mouse pro-HB-EGF and pro-AR ectodomains in vitro. For pro-HB-EGF, this site matched the C terminus of the purified human growth factor, and we speculate that the AR cleavage site is also physiologically relevant. In contrast, ADAM9 and -10, both implicated in HB-EGF shedding, failed to cleave the ectodomain or cleaved at a nonphysiologic site, respectively. Cotransfection of TACE in EC-2 cells enhanced phorbol myristate acetate-induced but not constitutive shedding of epiregulin and had no effect on betacellulin (BTC) processing. Additionally, soluble TACE did not cleave the juxtamembrane stalks of either pro-BTC or pro-epiregulin ectodomains in vitro. Substitution of the shorter pro-BTC juxtamembrane stalk or truncation of the pro-TGF-alpha stalk to match the pro-BTC length reduced TGF-alpha shedding from transfected cells to background levels, whereas substitution of the pro-BTC P2-P2' sequence reduced TGF-alpha shedding less dramatically. Conversely, substitution of the pro-TGF-alpha stalk or lengthening of the pro-BTC stalk, especially when combined with substitution of the pro-TGF-alpha P2-P2' sequence, markedly increased BTC shedding. These results indicate that efficient TACE cleavage is determined by a combination of stalk length and scissile bond sequence.