Cancer patients are at an increased risk of developing thromboembolic complications. Several mechanisms have been proposed to explain cancer-associated thrombosis including the release of tumor-derived extracellular vesicles and the activation of host vascular cells. It was proposed that neutrophil extracellular traps (NETs) contribute to the prothrombotic phenotype in cancer. In this study, we evaluated the possible cooperation between tumor-derived exosomes and NETs in cancer-associated thrombosis. Female BALB/c mice were orthotopically injected with 4T1 breast cancer cells. The tumor-bearing animals exhibited increased levels of plasma DNA and myeloperoxidase in addition to significantly increased numbers of circulating neutrophils. Mice were subjected to either Rose Bengal/laser-induced venous thrombosis or ferric chloride-induced arterial thrombosis models. The tumor-bearing mice exhibited accelerated thrombus formation in both models compared to tumor-free animals. Treatment with recombinant human DNase 1 reversed the prothrombotic phenotype of tumor-bearing mice in both models. Remarkably, 4T1-derived exosomes induced NET formation in neutrophils from mice treated with granulocyte colony-stimulating factor (G-CSF). In addition, tumor-derived exosomes interacted with NETs under static conditions. Accordingly, the intravenous administration of 4T1-derived exosomes into G-CSF-treated mice significantly accelerated venous thrombosis in vivo. Taken together, our observations suggest that tumor-derived exosomes and neutrophils may act cooperatively in the establishment of cancer-associated thrombosis.

Microfibril-associated glycoprotein-1 (MAGP-1) is a small molecular weight component of the fibrillin-rich microfibril. Gene-targeted inactivation of MAGP-1 reveals a complex phenotype that includes increased body weight and size due to excess body fat, an altered wound healing response in bone and skin, and a bleeding diathesis. Elastic tissues rich in MAGP-1-containing microfibrils develop normally and show normal function. The penetrance of MAGP-1-null phenotypes is highly variable and mouse strain-dependent, suggesting the influence of modifier genes. MAGP-1 was found to bind active transforming growth factor-␤ (TGF-␤) and BMP-7 with high affinity, suggesting that it may be an important modulator of microfibrilmediated growth factor signaling. Many of the phenotypic traits observed in MAGP-1-deficient mice are consistent with loss of TGF-␤ function and are generally opposite those associated with mutations in fibrillin-1 that result in enhanced TGF-␤ signaling. Increased body size and fat deposition in MAGP-1-mutant animals are particularly intriguing given the localization of obesity traits in humans to the region on chromosome 1 containing the MAGP-1 gene.Microfibrils are important contributors to the structural integrity of tissues and participate in the assembly of elastic fibers during development. They also serve to bind and sequester growth factors in the extracellular matrix (ECM) 3 (1, 2) and can directly signal cells through sequence motifs that interact with integrins and other cell-surface receptors (3-6). The major structural components of these microfibrils are the fibrillins, large glycoproteins rich in calcium binding epidermal growth factor-like domains (7), and the MAGPs, small, cysteine-rich proteins of unknown function. Other proteins can be localized to microfibrils, but it is not clear whether they are integral or associated proteins (8).MAGP-1, a ϳ20-kDa glycoprotein, is synthesized by most matrix-producing cells (9). The N-terminal half of the molecule contains sites for tyrosine sulfation and transglutaminase crosslinking as well as all of the tri-and tetrasaccharide O-linked sugars (10). The first 20 amino acids of the protein are enriched in acidic residues that, together with the sulfotyrosines, create a region of high negative charge capable of binding cationic proteins. The C-terminal half contains all of the molecule's thirteen cysteine residues and encodes a 54-amino acid sequence that defines a matrix-binding domain that targets MAGP-1 to the ECM. MAGP-1 binds to tropoelastin and type VI collagen (11, 12) and interacts with other molecules with defined structural roles in the ECM such as fibrillin-1 and -2 (13, 14), decorin (15), and biglycan (16). It does not, however, bind to the interstitial collagens I, III, or V (12). MAGP-1 also interacts with and facilitates the shedding of Notch1 (17), but there is no evidence for interaction with integrins.MAGP-2 is the other member of the MAGP family and, like MAGP-1, is covalently associated with fibrillin-containing microfibrils (...

Using a biochemical and cell biological approach, we have identified a cell interaction site at the carboxyl terminus of tropoelastin. Cell interactions with the COOH-terminal sequence are not through the elastin-binding protein (EBP67) because neither VGVAPG-like peptides nor galactoside sugars altered adhesion. Our results also show that cell adhesion to tropoelastin is not promoted by integrins. Through the use of mutant Chinese hamster ovary cell lines defective in glycosaminoglycan biosynthesis, as well as competition studies and enzymatic removal of specific cell-surface glycosaminoglycans, the tropoelastin-binding moieties on the cell surface were identified as heparan and chondroitin sulfate-containing glycosaminoglycans, with heparan sulfate being greatly preferred. Heparin affinity chromatography combined with cell adhesion assays identified the last 17 amino acids as the sequence element at the carboxyl terminus of tropoelastin responsible for the adhesive activity.The ability to interact with receptors or binding proteins on the cell surface is a property of all proteins of the extracellular matrix. This interaction provides important temporal and spatial signals to cells and influences such cellular processes as adhesion, migration, gene expression, proliferation, and apoptosis. In addition, several receptors function in ECM 2 assembly to directly or indirectly assemble monomers of ECM proteins into their functional polymeric form.Elastin is the major extracellular matrix protein capable of elastic recoil in tissues repeatedly subjected to cycles of reversible extension (1-3). It functions as an insoluble polymer made up of cross-linked tropoelastin molecules enmeshed in a network of filamentous microfibrils (4 -6). The secreted form of elastin, tropoelastin, is a highly cationic protein because of an enrichment of lysine residues that serve as precursors to covalent cross-links that form between and within tropoelastin monomers. Lysine side chains are modified through oxidative deamination of ⑀-amino groups that then condense with unmodified lysines or with other modified side chains to form a covalent linkage. It is important to note that almost all of the lysine residues in tropoelastin are modified to form cross-links in the mature protein. This changes the physical character of the protein from cationic to slightly anionic and hydrophobic in nature. In this respect, mature elastin has very different chemical and physical properties than does the precursor molecule tropoelastin.Like other ECM proteins, elastin has been shown to specifically interact with binding proteins on the cell surface (7-10). Binding occurs with high affinity and to multiple cell types, including bacteria (11). In responsive cells, elastin has been shown to alter gene expression, influence mobilization of intracellular ions, modulate cell adhesion and movement, effect cell proliferation, and to induce actin polymerization (7,(12)(13)(14)(15)(16)(17)(18). There is evidence from multiple studies that implicate changes in cal...

These studies were undertaken to determine how lysyl oxidase (LOX) and lysyl oxidase like-1 (LOXL) enzymes are targeted to their substrates in the extracellular matrix. Full-length LOX/LOXL and constructs containing just the pro-regions of each enzyme localized to elastic fibers when expressed in cultured cells. However, the LOXL catalytic domain without the pro-region was secreted into the medium but did not associate with matrix. Ligand blot and mammalian two-hybrid assays confirmed an interaction between tropoelastin and the pro-regions of both LOX and LOXL. Immunofluorescence studies localized both enzymes to elastin at the earliest stages of elastic fiber assembly. Our results showed that the proregions of LOX and LOXL play a significant role in directing the deposition of both enzymes onto elastic fibers by mediating interactions with tropoelastin. These findings confirmed that an important element of substrate recognition lies in the pro-domain region of the molecule and that the pro-form of the enzyme is what initially interacts with the matrix substrate. These results have raised the interesting possibility that sequence differences between the prodomain of LOX and LOXL account for some of the functional differences observed for the two enzymes.Production of a mature and functional elastic fiber is a complex process that is only partially understood. Monomers of elastin (tropoelastin) are cross-linked in the extracellular space by one or more members of the lysyl oxidase (LO) 3 gene family to form an elastin polymer, which is the functional form of the mature protein. Fibrillin-containing microfibrils are thought to play an important role in the assembly process by serving as a scaffold for aligning cross-linking domains within tropoelastin. Recently, several other proteins, such as members of the fibulin and emilin families, have been suggested to play a role in elastic fiber formation, although their exact function has not yet been determined (1).LOs are extracellular copper-requiring enzymes that catalyze the cross-linking of collagen and elastin through oxidative deamination of lysine or hydroxylysine side chains. The resultant allysine residues can then spontaneously condense with vicinal peptidyl aldehydes or with ⑀-amino groups of peptidyl lysines to generate covalent cross-linkages.There are five members of the LO family: lysyl oxidase (LOX) and lysyl oxidase-like 1-4 (LOXL 1-4) (reviewed in Ref.2). The C-terminal region of all of the LO family members contains the elements required for catalytic activity (the copper binding site, tyrosyl and lysyl residues that contribute to the carbonyl cofactor, and 10 cysteine residues), and the high sequence homology in this region suggests that all family members share a common enzymatic mechanism. The N-terminal regions, in contrast, show the greatest variability in size and sequence.The genes for LOX and LOXL have a similar exon structure consisting of seven exons, five of which (exons 2-6) are of similar size and encode proteins with 76% amino acid iden...

Fibrillin-1 and -2 are large modular extracellular matrix glycoproteins found in many vertebrate organ systems and are known to be key components of the elastic fibre. In the present study, we identify a new heparin-binding region in fibrillin-2 between exons 18 and 24. Additionally, we have narrowed the location of heparin-binding activity previously identified in fibrillin-1 to the last 17 residues of the mature proteolytically processed protein. This domain demonstrated higher activity as a multimer than as a monomer. The fibrillin-1 C-terminal site supported cell attachment in each of nine cell types tested. Attachment was shown to be mediated by cell-surface heparan sulphate proteoglycans. Fibrillin-1 has been shown previously to have heparin-binding activity that is important for matrix deposition of the molecule by fibroblasts. This function in deposition was confirmed in two additional fibrillin-producing cell types (osteosarcoma and epithelial cells) for the deposition of both fibrillin-1 and -2 into the extracellular matrix.