Right Heart Failure in Mice Upon Pressure Overload Is Promoted by Mitochondrial Oxidative Stress.

We sought to unravel pathomechanisms of the transition of maladaptive right ventricular (RV) remodeling to right heart failure (RHF) upon pressure overload. Exposure of C57BL/6J and C57BL/6N mice to pulmonary artery banding disclosed a tight relation of structural remodeling with afterload, but a dissociation from RV systolic function. Reduced release of mitochondrial reactive oxygen species in C57BL/6J mice prevented the development of RHF. In patients with left heart failure, increased oxidative damage in RV sections was associated with severely impaired RV function. In conclusion, reactive oxygen species are involved in the transition of maladaptive RV remodeling to RHF.

The Metalloprotease-Disintegrin ADAM8 Alters the Tumor Suppressor miR-181a-5p Expression Profile in Glioblastoma Thereby Contributing to Its Aggressiveness.

Glioblastoma (GBM) as the most common and aggressive brain tumor is characterized by genetic heterogeneity, invasiveness, radio-/chemoresistance, and occurrence of GBM stem-like cells. The metalloprotease-disintegrin ADAM8 is highly expressed in GBM tumor and immune cells and correlates with poor survival. In GBM, ADAM8 affects intracellular kinase signaling and increases expression levels of osteopontin/SPP1 and matrix metalloproteinase 9 (MMP9) by an unknown mechanism. Here we explored whether microRNA (miRNA) expression levels could be regulators of MMP9 expression in GBM cells expressing ADAM8. Initially, we identified several miRNAs as dysregulated in ADAM8-deficient U87 GBM cells. Among these, the tumor suppressor miR-181a-5p was significantly upregulated in ADAM8 knockout clones. By inhibiting kinase signaling, we found that ADAM8 downregulates expression of miR-181a-5p via activation of signal transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinase (MAPK) signaling suggesting an ADAM8-dependent silencing of miR-181a-5p. In turn, mimic miR-181a-5p transfection caused decreased cell proliferation and lower MMP9 expression in GBM cells. Furthermore, miR-181a-5p was detected in GBM cell-derived extracellular vesicles (EVs) as well as patient serum-derived EVs. We identified miR-181a-5p downregulating MMP9 expression via targeting the MAPK pathway. Analysis of patient tissue samples (n=22) revealed that in GBM, miR-181a-5p is strongly downregulated compared to ADAM8 and MMP9 mRNA expression, even in localized tumor areas. Taken together, we provide evidence for a functional axis involving ADAM8/miR-181a-5p/MAPK/MMP9 in GBM tumor cells.

ADAM8-Dependent Extracellular Signaling in the Tumor Microenvironment Involves Regulated Release of Lipocalin 2 and MMP-9.

The metalloprotease-disintegrin ADAM8 is critically involved in the progression of pancreatic cancer. Under malignant conditions, ADAM8 is highly expressed and could play an important role in cell-cell communication as expression has been observed in tumor and immune cells of the tumor microenvironment (TME) such as macrophages. To analyze the potential role of ADAM8 in the TME, ADAM8 knockout PDAC tumor cells were generated, and their release of extracellular vesicles (EVs) was analyzed. In EVs, ADAM8 is present as an active protease and associated with lipocalin 2 (LCN2) and matrix metalloprotease 9 (MMP-9) in an ADAM8-dependent manner, as ADAM8 KO cells show a lower abundance of LCN2 and MMP-9. Sorting of ADAM8 occurs independent of TSG101, even though ADAM8 contains the recognition motif PTAP for the ESCRTI protein TSG101 within the cytoplasmic domain (CD). When tumor cells were co-cultured with macrophages (THP-1 cells), expression of LCN2 and MMP-9 in ADAM8 KO cells was induced, suggesting that macrophage signaling can overcome ADAM8-dependent intracellular signaling in PDAC cells. In co-culture with macrophages, regulation of MMP-9 is independent of the M1/M2 polarization state, whereas LCN2 expression is preferentially affected by M1-like macrophages. From these data, we conclude that ADAM8 has a systemic effect in the tumor microenvironment, and its expression in distinct cell types has to be considered for ADAM8 targeting in tumors.

ADAM8 signaling drives neutrophil migration and ARDS severity.

Acute respiratory distress syndrome (ARDS) results in catastrophic lung failure and has an urgent, unmet need for improved early recognition and therapeutic development. Neutrophil influx is a hallmark of ARDS and is associated with the release of tissue-destructive immune effectors, such as matrix metalloproteinases (MMPs) and membrane-anchored metalloproteinase disintegrins (ADAMs). Here, we observed using intravital microscopy that Adam8-/- mice had impaired neutrophil transmigration. In mouse pneumonia models, both genetic deletion and pharmacologic inhibition of ADAM8 attenuated neutrophil infiltration and lung injury while improving bacterial containment. Unexpectedly, the alterations of neutrophil function were not attributable to impaired proteolysis but resulted from reduced intracellular interactions of ADAM8 with the actin-based motor molecule Myosin1f that suppressed neutrophil motility. In 2 ARDS cohorts, we analyzed lung fluid proteolytic signatures and identified that ADAM8 activity was positively correlated with disease severity. We propose that in acute inflammatory lung diseases such as pneumonia and ARDS, ADAM8 inhibition might allow fine-tuning of neutrophil responses for therapeutic gain.

ADAM8 affects glioblastoma progression by regulating osteopontin-mediated angiogenesis.

Glioblastoma multiforme (GBM) is the most aggressive type of brain cancer with a median survival of only 15 months. To complement standard treatments including surgery, radiation and chemotherapy, it is essential to understand the contribution of the GBM tumor microenvironment. Brain macrophages and microglia particularly contribute to tumor angiogenesis, a major hallmark of GBM. ADAM8, a metalloprotease-disintegrin strongly expressed in tumor cells and associated immune cells of GBMs, is related to angiogenesis and correlates with poor clinical prognosis. However, the specific contribution of ADAM8 to GBM tumorigenesis remains elusive. Knockdown of ADAM8 in U87 glioma cells led to significantly decreased angiogenesis and tumor volumes of these cells after stereotactic injection into striate body of mice. We found that the angiogenic potential of ADAM8 in GBM cells and in primary macrophages is mediated by the regulation of osteopontin (OPN), an important inducer of tumor angiogenesis. By in vitro cell signaling analyses, we demonstrate that ADAM8 regulates OPN via JAK/STAT3 pathway in U87 cells and in primary macrophages. As ADAM8 is a dispensable protease for physiological homeostasis, we conclude that ADAM8 could be a tractable target to modulate angiogenesis in GBM with minor side-effects.

Degradome of soluble ADAM10 and ADAM17 metalloproteases.

Disintegrin and metalloproteinases (ADAMs) 10 and 17 can release the extracellular part of a variety of membrane-bound proteins via ectodomain shedding important for many biological functions. So far, substrate identification focused exclusively on membrane-anchored ADAM10 and ADAM17. However, besides known shedding of ADAM10, we identified ADAM8 as a protease capable of releasing the ADAM17 ectodomain. Therefore, we investigated whether the soluble ectodomains of ADAM10/17 (sADAM10/17) exhibit an altered substrate spectrum compared to their membrane-bound counterparts. A mass spectrometry-based N-terminomics approach identified 134 protein cleavage events in total and 45 common substrates for sADAM10/17 within the secretome of murine cardiomyocytes. Analysis of these cleavage sites confirmed previously identified amino acid preferences. Further in vitro studies verified fibronectin, cystatin C, sN-cadherin, PCPE-1 as well as sAPP as direct substrates of sADAM10 and/or sADAM17. Overall, we present the first degradome study for sADAM10/17, thereby introducing a new mode of proteolytic activity within the protease web.

Metalloprotease inhibitor profiles of human ADAM8 in vitro and in cell-based assays.

ADAM8 as a membrane-anchored metalloproteinase-disintegrin is upregulated under pathological conditions such as inflammation and cancer. As active sheddase, ADAM8 can cleave several membrane proteins, among them the low-affinity receptor FcεRII CD23. Hydroxamate-based inhibitors are routinely used to define relevant proteinases involved in ectodomain shedding of membrane proteins. However, for ADAM proteinases, common hydroxamates have variable profiles in their inhibition properties, commonly known for ADAM proteinases 9, 10 and 17. Here, we determined the inhibitor profile of human ADAM8 for eight ADAM/MMP inhibitors by in vitro assays using recombinant ADAM8 as well as the in vivo inhibition in cell-based assays using HEK293 cells to monitor the release of soluble CD23 by ADAM8. ADAM8 activity is inhibited by BB94 (Batimastat), GW280264, FC387 and FC143 (two ADAM17 inhibitors), made weaker by GM6001, TAPI2 and BB2516 (Marimastat), while no inhibition was observed for GI254023, an ADAM10 specific inhibitor. Modeling of inhibitor FC143 bound to the catalytic sites of ADAM8 and ADAM17 reveals similar geometries in the pharmacophoric regions of both proteinases, which is different in ADAM10 due to replacement in the S1 position of T300 (ADAM8) and T347 (ADAM17) by V327 (ADAM10). We conclude that ADAM8 inhibitors require maximum selectivity over ADAM17 to achieve specific ADAM8 inhibition.

ADAM8 in invasive cancers: links to tumor progression, metastasis, and chemoresistance.

Ectodomain shedding of extracellular and membrane proteins is of fundamental importance for cell-cell communication in neoplasias. A Disintegrin And Metalloproteinase (ADAM) proteases constitute a family of multifunctional, membrane-bound proteins with traditional sheddase functions. Their protumorigenic potential has been attributed to both, essential (ADAM10 and ADAM17) and 'dispensable' ADAM proteases (ADAM8, 9, 12, 15, and 19). Of specific interest in this review is the ADAM proteinase ADAM8 that has been identified as a significant player in aggressive malignancies including breast, pancreatic, and brain cancer. High expression levels of ADAM8 are associated with invasiveness and predict a poor patient outcome, indicating a prognostic and diagnostic potential of ADAM8. Current knowledge of substrates and interaction partners gave rise to the hypothesis that ADAM8 dysregulation affects diverse processes in tumor biology, attributable to different functional cores of the multidomain enzyme. Proteolytic degradation of extracellular matrix (ECM) components, cleavage of cell surface proteins, and subsequent release of soluble ectodomains promote cancer progression via induction of angiogenesis and metastasis. Moreover, there is increasing evidence for significance of a non-proteolytic function of ADAM8. With the disintegrin (DIS) domain ADAM8 binds integrins such as ß1 integrin, thereby activating integrin signaling pathways. The cytoplasmic domain is critical for that activation and involves focal adhesion kinase (FAK), extracellular regulated kinase (ERK1/2), and protein kinase B (AKT/PKB) signaling, further contributing to cancer progression and mediating chemoresistance against first-line therapies. This review highlights the remarkable effects of ADAM8 in tumor biology, concluding that pharmacological inhibition of ADAM8 represents a promising therapeutic approach not only for monotherapy, but also for combinatorial therapies.

ADAM8 expression in breast cancer derived brain metastases: Functional implications on MMP-9 expression and transendothelial migration in breast cancer cells.

Metastatic breast cancer affects long-term survival and is a major cause of cancer death for women worldwide. The Metalloprotease-Disintegrin ADAM8 promotes breast cancer development and brain metastasis in a mouse breast cancer model. Here, abundant ADAM8 expression was detected in primary human breast tumors and associated brain metastases. To investigate the function of ADAM8 in metastasis, MB-231 breast cancer cells with ADAM8 knockdown (MB-231_shA8) and scramble control cells (MB-231_shCtrl) were analyzed for their capability to develop metastases. In vitro, formation of metastatic complexes in hanging drops is dependent on ADAM8 and blocked by ADAM8 inhibition. MB-231_shA8 in contrast to MB-231_shCtrl cells were impaired in transmigration through an endothelial and a reconstituted blood-brain barrier. Out of 23 MMP and 22 ADAM genes, only the MMP-9 gene was affected by ADAM8 knockdown in MB-231_shA8 cells. Following re-expression of wild-type ADAM8 in contrast to ADAM8 lacking the cytoplasmic domain in MB-231_shA8 cells caused increased levels of activated pERK1/2 and pCREB (S133) that were associated with elevated MMP-9 transcription. Application of ADAM8 and MMP-9 antibodies reduced transmigration of MB-231 cells suggesting that ADAM8 affects transmigration of breast cancer cells by MMP-9 regulation. ADAM8-dependent transmigration was confirmed in Hs578t cells overexpressing ADAM8. Moreover, transmigration of MB-231 and Hs578t cells was significantly reduced for cells treated with an antibody directed against P-selectin glycoprotein ligand (PSGL-1), a substrate of ADAM8. From these data we conclude that ADAM8 promotes early metastatic processes such as transendothelial migration by upregulation of MMP-9 and shedding of PSGL-1 from breast cancer cells.

Simultaneous Detection of Metalloprotease Activities in Complex Biological Samples Using the PrAMA (Proteolytic Activity Matrix Assay) Method.

Proteolytic Activity Matrix Analysis (PrAMA) is a method for simultaneously determining the activities of specific Matrix Metalloproteinases (MMPs) and A Disintegrin and Metalloproteinases (ADAMs) in complex biological samples. In mixtures of unknown proteases, PrAMA infers selective metalloproteinase activities by using a panel of moderately specific FRET-based polypeptide protease substrates in parallel, typically monitored by a plate-reader in a 96-well format. Fluorescence measurements are then quantitatively compared to a standard table of catalytic efficiencies measured from purified mixtures of individual metalloproteinases and FRET substrates. Computational inference of specific activities is performed with an easily used Matlab program, which is provided herein. Thus, we describe PrAMA as a combined experimental and mathematical approach to determine real-time metalloproteinase activities, which has previously been applied to live-cell cultures, cellular lysates, cell culture supernatants, and body fluids from patients.

Expression of the zinc importer protein ZIP9/SLC39A9 in glioblastoma cells affects phosphorylation states of p53 and GSK-3ß and causes increased cell migration.

Zinc importer proteins (ZIPs) have been proven as important molecular regulators in different cancers. As a member of the solute carrier family, ZIP9/SLC39A9 is overexpressed in prostate and breast cancer and affects B-cell receptor signaling. Here, we present data indicating that changes in intracellular zinc levels in glioblastoma cells can cause enhanced cell survival and cell migration, both hallmarks of the disease process. In particular, treatment of human glioblastoma cells with sublethal doses of cell-permeable heavy metal (Zn2+ > Fe2+ > Mn2+) chelator (N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN)) induced ZIP9 expression. Either TPEN treatment or expression of ZIP9 cDNA causes enhanced migration behavior of glioblastoma cells. Compared to untreated glioblastoma cells TPEN treatment or expression of ZIP9 results in activation of the tumor suppressor p53 by phosphorylation at serine residue 46 (Ser46) and in inactivation of the migration relevant glycogen synthase kinase 3 beta (GSK-3ß) by phosphorylation at serine residue 9 (Ser9). Whilst p53 activation affects cell survival in response to TPEN, GSK-3ß inactivation directly affects glioblastoma cell migration. Therefore, ZIP9 expression could regulate the migratory behavior of glioblastoma cells, so that ZIP9 may be of biological, but not of clinical relevance for glioblastomas, since in GBM tumor tissues, ZIP9 expression is not significantly increased compared to normal brain.

Synthesis and biological evaluation of analogues of the potent ADAM8 inhibitor cyclo(RLsKDK) for the treatment of inflammatory diseases and cancer metastasis.

The metalloproteinase ADAM8 serves as a pivotal catalyst in the development of inflammatory diseases and cancer metastasis. The cyclic peptide cyclo(RLsKDK) has been shown to inhibit the enzymatic activity of ADAM8 with high specificity and potency. Herein we report a structure-activity relationship (SAR) study of cyclo(RLsKDK) that involves the synthesis and biological evaluation of the lead compound and structural analogues thereof. This study provides insight into the ligand-receptor interactions that govern the binding of cyclo(RLsKDK) to the ADAM8 disintegrin domain and represents a stepping stone for the development of new treatments for inflammatory diseases and cancer metastasis.

Metalloproteinases ADAM12 and MMP-14 are associated with cavernous sinus invasion in pituitary adenomas.

Invasion of tumor cells critically depends on cell-cell or cell-extracellular matrix interactions. Enzymes capable of modulating these interactions belong to the proteinase families of ADAM (a disintegrin and metalloprotease) and MMP (matrix metalloprotease) proteins. Our objective is to examine their expression levels and evaluate the relationship between expression levels and cavernous sinus invasion in pituitary adenomas. Tissue samples from 35 patients with pituitary adenomas were analyzed. Quantitative real-time polymerase chain reaction (qPCR) was employed to assess mRNA expression levels for ADAM and MMP genes. Protein levels were examined using immunohistochemistry and Western Blot. Correlation analyses between expression levels and clinical parameters were performed. By silencing ADAM12 and MMP-14 with siRNA in a mouse pituitary adenoma cell line (TtT/GF), their cellular effects were investigated. In our study, nine women and 26 men were included, with a mean age of 53.1 years (range 15-84 years) at the time of surgery. There were 19 cases with cavernous sinus invasion. The proteins ADAM12 and MMP-14 were significantly up-regulated in invasive adenomas compared to noninvasive adenomas. Both human isoforms of ADAM12 (ADAM12L and ADAM12s) were involved in tumor invasion; moreover, ADAM12L was found to correlate positively with Ki-67 proliferation index in pituitary adenomas. In TtT/GF pituitary adenoma cells, silencing of ADAM12 and MMP-14 significantly inhibited cell invasion and migration, respectively, whereas only silencing of ADAM12 suppressed cell proliferation. We conclude that ADAM12 and MMP-14 are associated with cavernous sinus invasion in pituitary adenomas, which qualifies these proteins in diagnosis and therapy.

A colorimetric-based amplification system for proteinases including MMP2 and ADAM8.

We have developed a new amplification system for proteinases that is sensitive, simple, and inexpensive to run, exemplified by a horseradish peroxidase (HRP)-conjugated, dual MMP2 (matrix metalloproteinase 2) and ADAM8 (a disintegrin and metalloproteinase 8) peptide substrate assay presented herein. The HRP-conjugated substrate is attached to beads through a 6× histidine tag and then incubated with the target enzyme, cleaving the HRP reporter. This product is subsequently removed from the unreacted bound portions of the substrate by magnetic deposition of the beads. The amount of product is then quantified using a standard HRP color development assay employing 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2). This HRP amplification system represents a new approach to proteinase assays and could be applied to other enzymes, such as lipases, esterases, and kinases, as long as the unreacted substrate can be physically separated from the product and catalysis by the enzyme to be quantified is not impaired dramatically by steric hindrance from the HRP entity.

The metalloprotease-disintegrin ADAM8 contributes to temozolomide chemoresistance and enhanced invasiveness of human glioblastoma cells.

BACKGROUND: Despite multimodal treatment, glioblastoma (GBM) therapy with temozolomide (TMZ) remains inefficient due to chemoresistance. Matrix metalloproteinase (MMP) and a disintegrin and metalloprotease (ADAM), increased in GBM, could contribute to chemoresistance and TMZ-induced recurrence of glioblastoma. METHODS: TMZ inducibility of metalloproteases was determined in GBM cell lines, primary GBM cells, and tissues from GBM and recurrent GBM. TMZ sensitivity and invasiveness of GBM cells were assessed in the presence of the metalloprotease inhibitors batimastat (BB-94) and marimastat (BB-2516). Metalloprotease-dependent effects of TMZ on mitochondria and pAkt/phosphatidylinositol-3 kinase (PI3K) and phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) pathways were analyzed by fluorescence activated cell sorting, morphometry, and immunoblotting. Invasiveness of GBM cells was determined by Matrigel invasion assays. Potential metalloprotease substrates were identified by proteomics and tested for invasion using blocking antibodies. RESULTS: TMZ induces expression of MMP-1, -9, -14, and ADAM8 in GBM cells and in recurrent GBM tissues. BB-94, but not BB-2516 (ADAM8-sparing) increased TMZ sensitivity of TMZ-resistant and -nonresistant GBM cells with different O(6)-methylguanine-DNA methyltransferase states, suggesting that ADAM8 mediates chemoresistance, which was confirmed by ADAM8 knockdown, ADAM8 overexpression, or pharmacological inhibition of ADAM8. Levels of pAkt and pERK1/2 were increased in GBM cells and correlated with ADAM8 expression, cell survival, and invasiveness. Soluble hepatocyte growth factor (HGF) R/c-met and CD44 were identified as metalloprotease substrates in TMZ-treated GBM cells. Blocking of HGF R/c-met prevented TMZ-induced invasiveness. CONCLUSIONS: ADAM8 causes TMZ resistance in GBM cells by enhancing pAkt/PI3K, pERK1/2, and cleavage of CD44 and HGF R/c-met. Specific ADAM8 inhibition can optimize TMZ chemotherapy of GBM in order to prevent formation of recurrent GBM in patients.

ADAM8 as a drug target in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) has a grim prognosis with <5% survivors after 5 years. High expression levels of ADAM8, a metalloprotease disintegrin, are correlated with poor clinical outcome. We show that ADAM8 expression is associated with increased migration and invasiveness of PDAC cells caused by activation of ERK1/2 and higher MMP activities. For biological function, ADAM8 requires multimerization and associates with ß1 integrin on the cell surface. A peptidomimetic ADAM8 inhibitor, BK-1361, designed by structural modelling of the disintegrin domain, prevents ADAM8 multimerization. In PDAC cells, BK-1361 affects ADAM8 function leading to reduced invasiveness, and less ERK1/2 and MMP activation. BK-1361 application in mice decreased tumour burden and metastasis of implanted pancreatic tumour cells and provides improved metrics of clinical symptoms and survival in a Kras(G12D)-driven mouse model of PDAC. Thus, our data integrate ADAM8 in pancreatic cancer signalling and validate ADAM8 as a target for PDAC therapy.

ADAM8 expression in invasive breast cancer promotes tumor dissemination and metastasis.

The transmembrane metalloprotease-disintegrin ADAM8 mediates cell adhesion and shedding of ligands, receptors and extracellular matrix components. Here, we report that ADAM8 is abundantly expressed in breast tumors and derived metastases compared to normal tissue, especially in triple-negative breast cancers (TNBCs). Furthermore, high ADAM8 levels predicted poor patient outcome. Consistently, ADAM8 promoted an aggressive phenotype of TNBC cells in culture. In a mouse orthotopic model, tumors derived from TNBC cells with ADAM8 knockdown failed to grow beyond a palpable size and displayed poor vascularization. Circulating tumor cells and brain metastases were also significantly reduced. Mechanistically, ADAM8 stimulated both angiogenesis through release of VEGF-A and transendothelial cell migration via ß1-integrin activation. In vivo, treatment with an anti-ADAM8 antibody from the time of cell inoculation reduced primary tumor burden and metastases. Furthermore, antibody treatment of established tumors profoundly decreased metastases in a resection model. As a non-essential protein under physiological conditions, ADAM8 represents a promising novel target for treatment of TNBCs, which currently lack targeted therapies and frequently progress with fatal dissemination.

Axonal growth towards Xenopus skin in vitro is mediated by matrix metalloproteinase activity.

We have previously demonstrated that the growth of peripheral nervous system axons is strongly attracted towards limb buds and skin explants in vitro. Here, we show that directed axonal growth towards skin explants of Xenopus laevis in matrigel is associated with expression of matrix metalloproteinase (MMP)-18 and also other MMPs, and that this long-range neurotropic activity is inhibited by the broad-spectrum MMP inhibitors BB-94 and GM6001. We also show that forced expression of MMP-18 in COS-7 cell aggregates enhances axonal growth from Xenopus dorsal root ganglia explants. Nidogen is the target of MMPs released by cultured skin in matrigel, whereas other components remain intact. Our results suggest a novel link between MMP activity and extracellular matrix breakdown in the control of axonal growth.

ADAM9 inhibition increases membrane activity of ADAM10 and controls α-secretase processing of amyloid precursor protein.

Prodomains of A disintegrin and metalloproteinase (ADAM) metallopeptidases can act as highly specific intra- and intermolecular inhibitors of ADAM catalytic activity. The mouse ADAM9 prodomain (proA9; amino acids 24-204), expressed and characterized from Escherichia coli, is a competitive inhibitor of human ADAM9 catalytic/disintegrin domain with an overall inhibition constant of 280 ± 34 nM and high specificity toward ADAM9. In SY5Y neuroblastoma cells overexpressing amyloid precursor protein, proA9 treatment reduces the amount of endogenous ADAM10 enzyme in the medium while increasing membrane-bound ADAM10, as shown both by Western and activity assays with selective fluorescent peptide substrates using proteolytic activity matrix analysis. An increase in membrane-bound ADAM10 generates higher levels of soluble amyloid precursor protein α in the medium, whereas soluble amyloid precursor protein ß levels are decreased, demonstrating that inhibition of ADAM9 increases α-secretase activity on the cell membrane. Quantification of physiological ADAM10 substrates by a proteomic approach revealed that substrates, such as epidermal growth factor (EGF), HER2, osteoactivin, and CD40-ligand, are increased in the medium of BT474 breast tumor cells that were incubated with proA9, demonstrating that the regulation of ADAM10 by ADAM9 applies for many ADAM10 substrates. Taken together, our results demonstrate that ADAM10 activity is regulated by inhibition of ADAM9, and this regulation may be used to control shedding of amyloid precursor protein by enhancing α-secretase activity, a key regulatory step in the etiology of Alzheimer disease.