Collagen XII interacts with avian tenascin-X through its NC3 domain

Development of the zebrafish myoseptum with emphasis on the myotendinous junction

Zebrafish myosepta connect two adjacent muscle cells and transmit muscular forces to axial structures during swimming via the myotendinous junction (MTJ). The MTJ establishes transmembrane linkages system consisting of extracellular matrix molecules (ECM) surrounding the basement membrane, cytoskeletal elements anchored to sarcolema, and all intermediate proteins that link ECM to actin filaments. Using a series of zebrafish specimens aged between 24 h post-fertilization and 2 years old, the present paper describes at the transmission electron microscope level the development of extracellular and intracellular elements of the MTJ. The transverse myoseptum development starts during the segmentation period by deposition of sparse and loosely organized collagen fibrils. During the hatching period, a link between actin filaments and sarcolemma is established. The basal lamina underlining sarcolemma is well differentiated. Later, collagen fibrils display an orthogonal orientation and fibroblast-like cells invade the myoseptal stroma. A dense network of collagen fibrils is progressively formed that both anchor myoseptal fibroblasts and sarcolemmal basement membrane. The differentiation of a functional MTJ is achieved when sarcolemma interacts with both cytoskeletal filaments and extracellular components. This solid structural link between contractile apparatus and ECM leads to sarcolemma deformations resulting in the formation of regular invaginations, and allows force transmission during muscle contraction. This paper presents the first ultrastructural atlas of the zebrafish MTJ development, which represents an useful tool to analyse the mechanisms of the myotendinous system formation and their disruption in muscle disorders.

Phosphorylation of extracellular matrix tenascin-X detected by differential mass tagging followed by nanoLC-MALDI-TOF/TOF-MS/MS using ProteinPilot software

Reversible protein phosphorylation represents a major mechanism of signal transduction in a variety of cellular functions. An understanding of proteome-wide phosphorylation dynamics is important to obtain an overview of the whole signal transduction network. However, a systematic analysis for differentially expressed phosphoproteins under serum-stimulated response is lacking. Here, an easy and fast approach for the identification of differentially expressed phosphoproteins was used. After enrichment of phosphoproteins from serum-stimulated cell lysates by immobilized metal affinity chromatography, a quantitative proteomic approach with isobaric tag for absolute and relative quantitation labeling in combination with nanoLC-MALDI-TOF/TOF-MS/MS followed by ProteinPilot analysis was used. Consequently, 506 differentially expressed phosphoproteins were identified. Among them, 22 proteins that had a reproducible phosphorylation site at Ser or Thr were identified. Out of these 22 phosphoproteins, 7 are mainly involved in splicing. Among the 22 proteins, it was found that extracellular matrix tenascin-X is phosphorylated, although there is little quantitative change by the serum stimulation. MS/MS analysis revealed a novel phosphorylation site of tenascin-X, Thr1841, located in the loop region between the 10th and 11th fibronectin type III repeats. The phosphorylation of tenascin-X would be considered in clarifying its function in the future.

Type XII collagen regulates osteoblast polarity and communication during bone formation

Type XII collagen–null mice have fragile bones with disorganized collagen fiber arrangement, decreased bone matrix formation, and delayed osteoblast differentiation.

Differentiated osteoblasts are polarized in regions of bone deposition, demonstrate extensive cell interaction and communication, and are responsible for bone formation and quality. Type XII collagen is a fibril-associated collagen with interrupted triple helices and has been implicated in the osteoblast response to mechanical forces. Type XII collagen is expressed by osteoblasts and localizes to areas of bone formation. A transgenic mouse null for type XII collagen exhibits skeletal abnormalities including shorter, more slender long bones with decreased mechanical strength as well as altered vertebrae structure compared with wild-type mice. Col12a^−/− osteoblasts have decreased bone matrix deposition with delayed maturation indicated by decreased bone matrix protein expression. Compared with controls, Col12a^−/− osteoblasts are disorganized and less polarized with disrupted cell–cell interactions, decreased connexin43 expression, and impaired gap junction function. The data demonstrate important regulatory roles for type XII collagen in osteoblast differentiation and bone matrix formation.

Quantitative glycoproteomic analysis of optimal cutting temperature-embedded frozen tissues identifying glycoproteins associated with aggressive prostate cancer

Prostate cancer is the most common malignancy in men in the United States, and one in seven men with prostate cancer dies of the disease. A major issue of prostate diagnosis is that there is no good method to reliably distinguish aggressive prostate cancer from nonaggressive prostate cancer. This leads to significant unnecessary suffering among prostate cancer patients and massive unnecessary health care expenditures. In this study, we aim to identify glycoproteins associated with aggressive prostate cancer using optimal cutting temperature (OCT)-embedded frozen tissues obtained from patients with known clinical outcome. To eliminate the interference of mass spectrometric analysis by the compounds in OCT and identify extracellular proteins that are likely to serve as biomarkers in body fluids, we employed glycoproteomic analysis using solid-phase extraction of glycopeptides, which allowed the immobilization of glycopeptides to solid support and removal of OCT from sample proteins before releasing the glycopeptides from the solid support for mass spectrometry analysis. Tumor tissues were cryostat microdissected from four cases of aggressive and four cases of nonaggressive prostate tumors, and glycopeptides were isolated and labeled with iTRAQ reagents before the samples were analyzed with LTQ Orbitrap Velos. From the aggressive prostate cancer tissues, we identified the overexpression of three glycoproteins involved in an extracellular matrix remodeling and further examined two glycoproteins, cathepsin L and periostin, using Western blot and immunohistochemistry analyses. This is the first proteomic study to identify proteins potentially associated with aggressive prostate cancer using OCT-embedded frozen tissues. Further study of these proteins will be needed to understand the roles of extracellular matrix proteins in cancer progression and their potential clinical utility in improving diagnosis of aggressive prostate cancer.

SMOC1 is a tenascin-C interacting protein over-expressed in brain tumors

Tenascin-C is an extracellular matrix protein over-expressed in a large variety of cancers. In the present study, we aimed at identifying new interactors of tenascin-C by purifying secreted proteins on a tenascin-C affinity column. Analysis of eluates by mass spectrometry revealed phosphoglycerate kinase 1, clusterin, fibronectin, SPARC-related modular calcium-binding protein 1 (SMOC1) and nidogen-2 as potential interactors of tenascin-C. The interaction between tenascin-C and SMOC1 was confirmed by co-immunoprecipitation and further analyzed by Surface Plasmon Resonance Spectroscopy, which revealed an apparent dissociation constant (K(D)) value of 2.59∗10(-9)M. Further analyses showed that this binding is reduced in the presence of EDTA. To investigate whether SMOC1 itself could be over-expressed in the context of tumorigenesis, we analyzed data of two independent RNA profiling studies and found that mRNA levels of SMOC1 are significantly increased in oligodendrogliomas compared to control brain samples. In support of these data, western blot analysis of protein extracts from 12 oligodendrogliomas, 4 astrocytomas and 13 glioblastomas revealed elevated levels compared to healthy brain extract. Interestingly, cell migration experiments revealed that SMOC1 can counteract the chemo-attractive effect of tenascin-C on U87 glioma cells. The present study thus identified SMOC1 as a new cancer-associated protein capable of interacting with tenascin-C in vitro.

Phenotypic effects of Ehlers-Danlos syndrome-associated mutation on the FnIII domain of tenascin-X

Tenascin-X (TNX) is an extracellular matrix (ECM) protein and interacts with a wide variety of molecules in the ECM as well as on the membrane. Deficiency of TNX causes a recessive form of Ehlers-Danlos syndrome (EDS) characterized by hyperelastic and fragile skin, easy bruising, and hypermobile joints. Three point mutations in TNX gene were found to be associated with hypermobility type EDS and one of such mutations is the V1195M mutation at the 7th fibronectin Type III domain (TNXfn7). To help elucidate the underlying molecular mechanism connecting this mutation to EDS, here we combined homology modeling, chemical denaturation, single molecule atomic force microscopy, and molecular dynamics (MD) simulation techniques to investigate the phenotypic effects of V1195M on TNXfn7. We found that the V1195M mutation does not alter the three-dimensional structure of TNXfn7 and had only mild destabilization effects on the thermodynamic and mechanical stability of TNXfn7. However, MD simulations revealed that the mutation V1195M significantly alters the flexibility of the C'E loop of TNXfn7. As loops play important roles in protein-protein and protein-ligand interactions, we hypothesize that the decreased loop flexibility by V1195M mutation may affect the binding of TNX to ECM molecules and thus adversely affect collagen deposition and fibrillogenesis. Our results may provide new insights in understanding the molecular basis for the pathogenesis of V1195M-resulted EDS.

Dilated capillaries, disorganized collagen fibers and differential gene expression in periodontal ligaments of hypomorphic fibrillin-1 mice

The periodontal ligaments (PDLs) are soft connective tissue between the cementum covering the tooth root surface and alveolar bone. PDLs are composed of collagen and elastic system fibers, blood vessels, nerves, and various types of cells. Elastic system fibers are generally formed by elastin and microfibrils, but PDLs are mainly composed of the latter. Compared with the well-known function of collagen fibers to support teeth, little is known about the role of elastic system fibers in PDLs. To clarify their role, we examined PDLs of mice under-expressing fibrillin-1 (mgR mice), which is one of the major microfibrillar proteins. The PDLs of homozygous mgR mice showed one-quarter of the elastic system fibers of wild-type (WT) mice. A close association between the elastic system fibers and the capillaries was noted in WT, homozygous and heterozygous mgR mice. Interestingly, capillaries in PDLs of homozygous mice were dilated or enlarged compared with those of WT mice. A comparable level of type I collagen, which is the major collagen in PDLs, was expressed in PDL-cells of mice with three genotypes. However, multi-oriented collagen fiber bundles with a thinner appearance were noted in homozygous mice, whereas well-organized collagen fiber bundles were seen in WT mice. Moreover, there was a marked decrease in periostin expression, which is known to regulate the fibrillogenesis and crosslinking of collagen. These observations suggest that the microfibrillar protein, fibrillin-1, is indispensable for normal tissue architecture and gene expression of PDLs.

The initiation of embryonic-like collagen fibrillogenesis by adult human tendon fibroblasts when cultured under tension

Tendon fibroblasts synthesize collagen and form fibrils during embryonic development, but to what extent mature fibroblasts are able to recapitulate embryonic development and develop normal tendon structure is unknown. The present study examined the capability of mature human tendon fibroblasts to initiate collagen fibrillogenesis when cultured in fixed-length fibrin gels. Fibroblasts were dissected from semitendinosus and gracilis tendons from healthy humans and cultured in 3D linear fibrin gels. The fibroblasts synthesized an extracellular matrix of parallel collagen fibrils that were aligned along the axis of tension. The fibrils had a homogeneous narrow diameter that was similar to collagen fibrils occurring in embryonic tendon. Immunostaining showed colocalization of collagen type I with collagen III, XII and XIV. A fibronectin network was formed in parallel with the collagen, and fibroblasts stained positive for integrin α₅. Finally, the presence of cell extensions into the extracellular space with membrane-enclosed fibrils in fibripositors indicated characteristics of embryonic tendon. We conclude that mature human tendon fibroblasts retain an intrinsic capability to perform collagen fibrillogenesis similar to that of developing tendon, which implies that the hormonal/mechanical milieu, rather than intrinsic cellular function, inhibits regenerative potential in mature tendon.

Tenascin-X induces cell detachment through p38 mitogen-activated protein kinase activation

Extracellular matrix glycoprotein tenascin-X (TNX) is the largest member of the tenascin family. In this study, we investigated the adhesive properties of TNX and the signaling pathway to be induced to mouse fibroblast L cells on TNX substrate. Approximately 45% of evaluable cells used in the cell adhesion assay were attached to purified TNX but did not spread and were rounded on TNX. The remaining 55% of cells were detached from the TNX substrate and were floating in the conditioned medium. In rounded cells on TNX, phosphorylation of focal adhesion kinase (FAK) was diminished compared with that in cells on control phosphate buffered saline (PBS). To better understand the pathways that lead to the detachment of cells on the TNX substrate, we examined phosphorylation of p38 mitogen-activated protein (MAP) kinase. Phosphorylation of p38 MAP kinase was observed in the rounded cells on TNX in a dose-dependent manner, and the maximum effect was observed at 30 min on TNX. Inhibition of p38 MAP kinase alpha expression by RNA interference partially suppressed the TNX-induced cell detachment. These results suggest that the p38 MAP kinase is a major mediator of TNX-induced cell detachment.

Serum tenascin-X strongly binds to vascular endothelial growth factor

Interstitial extracellular matrix tenascin-X (iTNX) with about 450 kDa is prominently present in various tissues. Previously, we identified the serum form of TNX (sTNX) with 200 kDa in the mouse. In the present study, in order to investigate distinctive features and functions of sTNX, a plasmid encoding the recombinant mouse sTNX was constructed. As a control, we also constructed a plasmid encoding mouse 450-kDa iTNX and a plasmid encoding 250-kDa iTNX, which lacks the region of 200-kDa sTNX from 450-kDa iTNX. In cells stably expressing each recombinant TNX, a more than 7-fold larger amount of 200-kDa sTNX was released into conditioned medium than the amounts of 250-kDa iTNX and 450-kDa iTNX released into the medium. We previously reported that a splice isoform of iTNX (340-kDa iTNX) binds to vascular endothelial growth factor B (VEGF-B) as well as to VEGF-A. Therefore, the ability of VEGF-A and VEGF-B to bind to 200-kDa sTNX was examined by a co-immunoprecipitation assay in comparison with the binding abilities to 250-kDa iTNX and 450-kDa iTNX. It was found that sTNX strongly bound to VEGF-A and VEGF-B, compared with the binding abilities of other iTNX proteins. Based on the results of assays of incorporation of 5-ethynyl-2'-deoxyuridine (EdU), we found that purified recombinant 200-kDa sTNX both alone and in combination with VEGF-A or basic fibroblast growth factor (bFGF) can weakly promote DNA synthesis in proliferating vascular endothelial cells (UVfemale symbol2 cells). These results suggest that sTNX possesses weak activity for proliferation of endothelial cells.

Tenascins and their implications in diseases and tissue mechanics

Tenascins are glycoproteins found in the extracellular matrix (ECM) of many tissues. Their role is not only to support the tissue structurally but also to regulate the fate of the different cell types populating the ECM. For instance, tenascins are required when active tissue modeling during embryogenesis or re-modeling after injury occurs. Interestingly, the four members of the tenascin family, tenascin-C, -X, -R and -W, show different and often mutually exclusive expression patterns. As a consequence, these structurally related proteins display distinct functions and are associated with distinct pathologies. The present review aims at presenting the four members of the tenascin family with respect to their structure, expression patterns and implications in diseases and tissue mechanics.

Type XIV Collagen Regulates Fibrillogenesis: PREMATURE COLLAGEN FIBRIL GROWTH AND TISSUE DYSFUNCTION IN NULL MICE

Type XIV collagen is a fibril-associated collagen with an interrupted triple helix. This collagen interacts with the fibril surface and has been implicated as a regulator of fibrillogenesis; however, a specific role has not been elucidated. Functional roles for type XIV collagen were defined utilizing a new type XIV collagen-deficient mouse line. This line was produced using a conventional targeted knock-out approach. Col14a1(-/-) mice were devoid of type XIV collagen, whereas heterozygous mice had reduced synthesis. Both mutant Col14a1 genotypes were viable with a grossly normal phenotype; however, mature skin exhibited altered mechanical properties. Prior to evaluating tendon fibrillogenesis in type XIV collagen-deficient mice, the developmental expression patterns were analyzed in wild-type flexor digitorum longus (FDL) tendons. Analyses of mRNA and protein expression indicated tissue-specific temporal expression that was associated with the early stages in fibrillogenesis. Ultrastructural analyses of wild-type and null tendons demonstrated premature fibril growth and larger fibril diameters in tendons from null mice at postnatal day 4 (P4). However, fibril structure in mature tendons was normal. Biomechanical studies established a direct structure/function relationship with reduced strength in P7-null tendons. However, the biomechanical properties in P60 tendons were comparable in null and wild-type mice. Our results indicate a regulatory function for type XIV collagen in early stages of collagen fibrillogenesis with tissue differences.

Mechanical strain increases expression of type XII collagen in murine osteoblastic MC3T3-E1 cells

In adult mouse, the mRNA corresponding to the alpha1 chain of type XII collagen (alpha 1(XII)) is predominantly detected in the bone. Additionally, murine osteoblastic cells, MC3T3-E1, increased the mRNA level of alpha 1(XII) response to the mechanical strain in the stretch culture system. Cyclic stretch stress resulted in a threefold increase in mRNA level of alpha 1(XII) as compared to the control experiment in MC3T3-E1. Transient transfection assays employing a reporter construct, together with site-directed mutagenesis studies, suggested that the AP-1 binding site in the first exon of mouse alpha 1(XII) gene is important for stretch stress-mediated upregulation of alpha 1(XII) expression. Electrophoretic mobility shift assay and associated antibody supershift experiments showed that stretch stress promotes the binding of c-Jun and JunD. Further chromatin immunoprecipitation experiments confirmed the participation of these transcription factors in the region. Also, the exogenous induction of the dominant negative form of c-Jun canceled the effect of stretch stress on the stimulation of the alpha 1(XII) gene. Here, we reported a potential responsive element to the stretch stress in mouse alpha 1(XII) gene. These data will provide new information on the mechanical strain-mediated transcriptional control of alpha 1(XII)-mediated fibrillogenesis in the bone.

Zebrafish collagen XII is present in embryonic connective tissue sheaths (fascia) and basement membranes

Connective tissues ensure the cohesion of the tissues of the body, but also form specialized structures such as tendon and bone. Collagen XII may enhance the stability of connective tissues by bridging collagen fibrils, but its function is still unclear. Here, we used the zebrafish model to visualize its expression pattern in the whole organism. The zebrafish col12a1 gene is homologous to the small isoform of the tetrapod col12a1 gene. In agreement with the biochemical data reported for the small isoform, the zebrafish collagen XII alpha1 chain was characterized as a collagenase sensitive band migrating at approximately 200 kDa. Using newly generated polyclonal antibodies and anti-sense probes, we performed a comprehensive analysis of its expression in developing zebrafish. Collagen XII exhibited a much broader expression pattern than previously thought: it was ubiquitously expressed in the connective tissue sheaths (fascia) that encase the tissues and organs of the body. For example, it was found in sclera, meninges, epimysia and horizontal and vertical myosepta. Collagen XII was also detected in head mesenchyme, pharyngeal arches and within the spinal cord, where it was first expressed within and then at the lateral borders of the floor plate and at the dorsal midline. Furthermore, double immunofluorescence staining with laminin and immunogold electron microscopy revealed that collagen XII is associated with basement membranes. These data suggest that collagen XII is implicated in tissue cohesion by stabilizing fascia and by linking fascia to basement membranes.

Evidence for the evolution of tenascin and fibronectin early in the chordate lineage

Fibronectin and tenascin are extracellular matrix glycoproteins that play important roles in cell adhesion and motility. In a previous study we provided evidence that tenascin first appeared early in the chordate lineage. As tenascin has been proposed to act, in part, through modulation of cell-fibronectin interactions, we sought here to identify fibronectin genes in non-vertebrate chordates and other invertebrates to determine if tenascin and fibronectin evolved separately or together, and to identify phylogenetically conserved features of both proteins. We found that the genome of the urochordate Ciona savignyi contains both a tenascin gene and a gene encoding a fibronectin-like protein with fibronectin type 1, 2 and 3 repeats. The genome of the cephalochordate Branchiostoma floridae (amphioxus) also has a tenascin gene. However, we could not identify a fibronectin-like gene in B. floridae, nor could we identify fibronectin or tenascin genes in echinoderms, protostomes or cnidarians. If urochordates are more closely related to vertebrates, tenascin may have evolved before fibronectin in an ancestor common to tunicates and amphioxus. Alternatively, tenascin and fibronectin may have evolved in an ancestor common to B. floridae and C. savignyi and the fibronectin gene was subsequently lost in the cephalochordate lineage. The fibronectin-like gene from C. savignyi does not encode the RGD motif for integrin binding found in all vertebrate fibronectins, and it lacks most of the fibronectin type 1 domains believed to be critical for fibrillogenesis. In contrast, the tenascin gene in B. floridae encodes multiple RGD motifs, suggesting that integrin binding is fundamental to tenascin function.

Analysis of obstetric complications and uterine connective tissue in tenascin-X-deficient humans and mice

Tenascin-X (TNX) is a large, multi-domain, extracellular matrix glycoprotein. Complete deficiency of TNX in humans leads to a recessive form of Ehlers-Danlos syndrome (EDS), and TNX haploinsufficiency is a cause of hypermobility type EDS. EDS patients appear to have a higher risk of several complications during pregnancy, such as pelvic instability, premature rupture of membranes, and postpartum hemorrhage. Here, we present a study of genitourinary and obstetric complications in TNX-deficient women of reproductive age. We have found complications, such as uterus prolapses, that are in agreement with previous findings in other EDS types. In TNX knockout (KO) mice, we have observed mild pregnancy-related abnormalities. Morphological and immunohistological analysis of uterine tissues has not revealed obvious quantitative or spatial differences between TNX KO and wildtype mice with respect to collagen types I, III, V, and XII or elastic fibers. We conclude that TNX-deficient women are at risk of obstetric complications, but that TNX KO mice show only a mild phenotype. Furthermore, we show that TNX is involved in the stability of elastic fibers rather than in their initial deposition.

Reduced quantitative muscle function in tenascin-X deficient Ehlers-Danlos patients

The Ehlers-Danlos Syndrome (EDS) is a heterogeneous group of heritable connective tissue disorders. Skeletal muscle features belong to the clinical criteria of EDS and are generally interpreted to result from increased tendon distensibility or exercise avoidance. However, muscle function in EDS has hardly been investigated as such. We performed a pilot study consisting of clinical investigations, electromyography, muscle ultrasound, muscle biopsy, and quantitative muscle function tests on two EDS patients with deficiency of tenascin-X. Quantitative muscle function proved severely reduced despite normal findings on electromyography and muscle biopsy. These findings dispute the interpretation of increased tendon distensibility. We hypothesize that alterations in the extracellular matrix modify myofascial force transmission and thus influence muscle function in EDS.

Identification and characterization of multiple species of tenascin-X in human serum

We analysed the diversity of tenascin-X (TNX) species in serum and studied parameters that could affect determination of TNX levels in serum. Using western blot analysis we identified at least seven distinct TNX species, ranging from 75 kDa to the presumably full-length 450 kDa form. Purification of serum TNX followed by sequence analysis positively identified two major TNX species of 75 and 140 kDa. We found that serum TNX binds to tropoelastin but not to fibrillar collagens. We conclude that serum TNX is composed of distinct molecular species that retain functional activity.

Wound healing in tenascin-X deficient mice suggests that tenascin-X is involved in matrix maturation rather than matrix deposition

Tenascin-X (TNX) is an extracellular matrix glycoprotein whose absence in humans leads to a recessive form of Ehlers-Danlos Syndrome (EDS). TNX deficient patients have hypermobile joints and fragile skin, but unlike the classical type of EDS, no atrophic scars were observed. Anecdotal evidence suggested that wound healing in TNX deficient patients is abnormal, but no detailed study has been performed so far. To address the role of TNX in wound healing, we analyzed skin wound morphology and mechanical properties of scars in TNX knockout (KO) mice. Breaking strength of unwounded skin of KO mice is significantly lower (<50%) than that of wild-type (WT) mice. In the early stage of wound healing when TNX is hardly expressed in WT wounds (day 7), WT and KO skin are of similar strength. After 14 days, when TNX starts to be expressed at moderate levels in wounds of WT mice, the WT scars gain a further increase in breaking strength, whereas KO scars do not progress beyond the mechanical strength of uninjured KO skin. No obvious differences between KO and WT mice were noted in the rate of wound closure, or in expression of fibrillar collagens during wound healing. We conclude that TNX is unlikely to be involved in matrix deposition in the early phase of wound healing, but it is required in the later phase when remodeling and maturation of the matrix establishes and improves its biomechanical properties.

The cysteine-rich domain of snake venom metalloproteinases is a ligand for von Willebrand factor A domains: role in substrate targeting

Snake venom metalloproteinases (SVMPs) are members of the Reprolysin family of metalloproteinases to which the ADAM (a disintegrin and metalloproteinase) proteins also belong. The disintegrin-like/cysteine-rich domains of the ADAMs have been implicated in their function. In the case of the SVMPs, we hypothesized that these domains could function to target the metalloproteinases to key extracellular matrix proteins or cell surface proteins. Initially we detected interaction of collagen XIV, a fibril-associated collagen with interrupted triple helices containing von Willebrand factor A (VWA) domains, with the PIII SVMP catrocollastatin. Next we investigated whether other VWA domain-containing matrix proteins could support the binding of PIII SVMPs. Using surface plasmon resonance, the PIII SVMP jararhagin and a recombinant cysteine-rich domain from a PIII SVMP were demonstrated to bind to collagen XIV, collagen XII, and matrilins 1, 3, and 4. Jararhagin was shown to cleave these proteins predominantly at sites localized at or near the VWA domains suggesting that it is the VWA domains to which the PIII SVMPs are binding via their cysteine-rich domain. In light of the fact that these extracellular matrix proteins function to stabilize matrix, targeting the SVMPs to these proteins followed by their specific cleavage could promote the destabilization of extracellular matrix and cell-matrix interactions and in the case of capillaries could contribute to their disruption and hemorrhage. Although there is only limited structural homology shared by the cysteine-rich domains of the PIII SVMPs and the ADAMs our results suggest an analogous function for the cysteine-rich domains in certain members of the expanded ADAM family of proteins to target them to VWA domain-containing proteins.