Publications by authors named "Rupert Timpl"

44 Publications

Laminin-121--recombinant expression and interactions with integrins.

Matrix Biol 2010 Jul 23;29(6):484-93. Epub 2010 May 23.

Max-Planck-Institut für Biochemie, Martinsried, Germany.

Laminin-121, previously referred as to laminin-3, was expressed recombinantly in human embryonic kidney (HEK) 293 cells by triple transfection of full-length cDNAs encoding mouse laminin α1, β2 and γ1 chains. The recombinant laminin-121 was purified using Heparin-Sepharose followed by molecular sieve chromatography and shown to be correctly folded by electron microscopy and circular dichroism (CD). The CD spectra of recombinant laminin-121 were very similar to those of laminin-111 isolated from Engelbreth-Holm-Swarm tumor (EHS-laminin) but its T(m) value was smaller than EHS-laminin and recombinant lamnin-111 suggesting that the replacement of the β chain reduced the stability of the coiled-coil structure of laminin-121. Its binding to integrins was compared with EHS-laminin, laminin-3A32 purified from murine epidermal cell line and recombinantly expressed laminins-111, -211 and -221. Laminin-121 showed the highest affinity to α6β1 and α7β1 integrins and furthermore, laminin-121 most effectively supported neurite outgrowth. Together, this suggests that the β2 laminins have higher affinity for integrins than the β1 laminins.
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http://dx.doi.org/10.1016/j.matbio.2010.05.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2939186PMC
July 2010

Expression of ECM proteins fibulin-1 and -2 in acute and chronic liver disease and in cultured rat liver cells.

Cell Tissue Res 2009 Sep 17;337(3):449-62. Epub 2009 Jul 17.

Department of Internal Medicine and Gastroenterology, University of Göttingen, Göttingen, Germany.

Fibulin-2 has previously been considered as a marker to distinguish rat liver myofibroblasts from hepatic stellate cells. The function of other fibulins in acute or chronic liver damage has not yet been investigated. The aim of this study has been to evaluate the expression of fibulin-1 and -2 in models of rat liver injury and in human liver cirrhosis. Their cellular sources have also been investigated. In normal rat liver, fibulin-1 and -2 were both mainly present in the portal field. Fibulin-1-coding transcripts were detected in total RNA of normal rat liver, whereas fibulin-2 mRNA was only detected by sensitive, real-time quantitative polymerase chain reaction. In acute liver injury, the expression of fibulin-1 was significantly increased (17.23-fold after 48 h), whereas that of fibulin-2 was not modified. The expression of both fibulin-1 and -2 was increased in experimental rat liver cirrhosis (19.16- and 26.47-fold, respectively). At the cellular level, fibulin-1 was detectable in hepatocytes, "activated" hepatic stellate cells, and liver myofibroblasts (2.71-, 122.65-, and 469.48-fold over the expression in normal rat liver), whereas fibulin-2 was restricted to liver myofibroblasts and was regulated by transforming growth factor beta-1 (TGF-beta1) in 2-day-old hepatocyte cultures and in liver myofibroblasts. Thus, fibulin-1 and -2 respond differentially to single and repeated damaging noxae, and their expression is differently present in liver cells. Expression of the fibulin-2 gene is regulated by TGF-beta1 in liver myofibroblasts.
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http://dx.doi.org/10.1007/s00441-009-0823-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2728066PMC
September 2009

Mapping of SPARC/BM-40/osteonectin-binding sites on fibrillar collagens.

J Biol Chem 2008 Jul 16;283(28):19551-60. Epub 2008 May 16.

Max-Planck-Institut für Biochemie, Am Klopferspitz 18, 82152 Martinsried, Germany.

The 33-kDa matrix protein SPARC (BM-40, osteonectin) binds several collagen types with moderate affinity. The collagen-binding site resides in helix alphaA of the extracellular calcium-binding domain of SPARC and is partially masked by helix alphaC. Previously, we found that the removal of helix alphaC caused a 10-fold increase in the affinity of SPARC for collagen, and we identified amino acids crucial for binding by site-directed mutagenesis. In this study, we used rotary shadowing, CNBr peptides, and synthetic peptides to map binding sites of SPARC onto collagens I, II, and III. Rotary shadowing and electron microscopy of SPARC-collagen complexes identified a major binding site approximately 180 nm from the C terminus of collagen. SPARC binding was also detected with lower frequency near the matrix metalloproteinase cleavage site. These data fit well with our analysis of SPARC binding to CNBr peptides, denaturation of which abolished binding, indicating triple-helical conformation of collagen to be essential. SPARC binding was substantially decreased in two of seven alpha2(I) mutant procollagen I samples and after N-acetylation of Lys/Hyl side chains in wild-type collagen. Synthetic peptides of collagen III were used to locate the binding sites, and we found SPARC binding activity in a synthetic triple-helical peptide containing the sequence GPOGPSGPRGQOGVMGFOGPKGNDGAO (where O indicates 4-hydroxyproline), with affinity for SPARC comparable with that of procollagen III. This sequence is conserved among alpha chains of collagens I, II, III, and V. In vitro collagen fibrillogenesis was delayed in the presence of SPARC, suggesting that SPARC might modulate collagen fibril assembly in vivo.
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http://dx.doi.org/10.1074/jbc.M710001200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2443679PMC
July 2008

Compositional differences between infant and adult human corneal basement membranes.

Invest Ophthalmol Vis Sci 2007 Nov;48(11):4989-99

Ophthalmology Research Laboratories, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.

Purpose: Adult human corneal epithelial basement membrane (EBM) and Descemet's membrane (DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development.

Methods: Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components.

Results: Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha1-alpha2 to alpha3-alpha4 chains after 3 years of life; in the adult, alpha1-alpha2 chains were retained only in the limbal BM. Laminin alpha2 and beta2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma3 chain. In the infant DM, type IV collagen alpha1-alpha6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years.

Conclusions: The distribution of laminin gamma3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation.
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http://dx.doi.org/10.1167/iovs.07-0654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2151758PMC
November 2007

A comparative analysis of the fibulin protein family. Biochemical characterization, binding interactions, and tissue localization.

J Biol Chem 2007 Apr 26;282(16):11805-16. Epub 2007 Feb 26.

Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany.

Fibulins are a family of five extracellular matrix proteins characterized by tandem arrays of epidermal growth factor-like domains and a C-terminal fibulin-type module. They are widely distributed and often associated with vasculature and elastic tissues. In this study, we expressed the three more recently identified family members, fibulin-3, fibulin-4, and fibulin-5, as recombinant proteins in mammalian cells. The purified proteins showed short rod structures of approximately 20 nm with a globule at one end, after rotary shadowing and electron microscopy. Two forms of mouse fibulin-3 were purified, and the O-glycan profiles of the larger form were characterized. Polyclonal antibodies raised against the purified proteins did not show any cross-reactivity with other family members and were used to assess the levels and localization of the fibulins in mouse tissues. Their binding interactions, cell adhesive properties, and tissue localization were analyzed in parallel with the previously characterized fibulin-1 and -2. Binding to tropoelastin was strong for fibulin-2 and -5, moderate for fibulin-4 and -1, and relatively weak for fibulin-3. Fibulin-4, but not fibulin-3 and -5, exhibited distinct interactions with collagen IV and nidogen-2 and moderate binding to the endostatin domain from collagen XV. Cell adhesive activities were not observed for all fibulins, except mouse fibulin-2, with various cell lines tested. All five fibulins were found in perichondrium and various regions of the lungs. Immunoelectron microscopy localized fibulin-4 and -5 to fibrillin microfibrils at distinct locations. Our studies suggest there are unique and redundant functions shared by these structurally related proteins.
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http://dx.doi.org/10.1074/jbc.M611029200DOI Listing
April 2007

Chondroitin sulfate perlecan enhances collagen fibril formation. Implications for perlecan chondrodysplasias.

J Biol Chem 2006 Nov 5;281(44):33127-39. Epub 2006 Sep 5.

Department of Experimental Medical Sciences, Lund University, SE-22184 Lund, Sweden.

Inactivation of the perlecan gene leads to perinatal lethal chondrodysplasia. The similarity to the phenotypes of the Col2A1 knock-out and the disproportionate micromelia mutation suggests perlecan involvement in cartilage collagen matrix assembly. We now present a mechanism for the defect in collagen type II fibril assembly by perlecan-null chondrocytes. Cartilage perlecan is a heparin sulfate or a mixed heparan sulfate/chondroitin sulfate proteoglycan. The latter form binds collagen and accelerates fibril formation in vitro, with more defined fibril morphology and increased fibril diameters produced in the presence of perlecan. Interestingly, the enhancement of collagen fibril formation is independent on the core protein and is mimicked by chondroitin sulfate E but neither by chondroitin sulfate D nor dextran sulfate. Furthermore, perlecan chondroitin sulfate contains the 4,6-disulfated disaccharides typical for chondroitin sulfate E. Indeed, purified glycosaminoglycans from perlecan-enriched fractions of cartilage extracts contain elevated levels of 4,6-disulfated chondroitin sulfate disaccharides and enhance collagen fibril formation. The effect on collagen assembly is proportional to the content of the 4,6-disulfated disaccharide in the different cartilage extracts, with growth plate cartilage glycosaminoglycan being the most efficient enhancer. These findings demonstrate a role for perlecan chondroitin sulfate side chains in cartilage extracellular matrix assembly and provide an explanation for the perlecan-null chondrodysplasia.
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http://dx.doi.org/10.1074/jbc.M607892200DOI Listing
November 2006

Endostatin influences endothelial morphology via the activated ERK1/2-kinase endothelial morphology and signal transduction.

Microvasc Res 2006 May 2;71(3):152-62. Epub 2006 May 2.

Department of Molecular and Cellular Sport Medicine, German Sport University Cologne, Germany.

Endostatin, the proteolytic fragment of collagen XVIII, is known to be a potent inhibitor of angiogenesis. However, to date, only limited knowledge exists with regard to the effects of endostatin on vessel morphology and the underlying signaling pathway. The aim of the present work was therefore to determine the impact of endostatin and its collagen XV analogue restin on vessel development during wound healing and embryonic angio- and vasculogenesis. Time lapse experiments and electron microscopy demonstrate similar morphological changes evoked by endostatin and the ERK1/2-kinase inhibitor PD98059. Furthermore, we show that ERK1/2 phosphorylation, a crucial signaling event in vascular morphogenesis, is regulated by endostatin via the protein phosphatase 2A PP2A. These findings provide new insight into a key signaling pathway of vascular remodeling evoked by a matrix-derived factor.
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http://dx.doi.org/10.1016/j.mvr.2006.01.001DOI Listing
May 2006

WARP is a novel multimeric component of the chondrocyte pericellular matrix that interacts with perlecan.

J Biol Chem 2006 Mar 6;281(11):7341-9. Epub 2006 Jan 6.

Cell and Matrix Biology Research Unit, Murdoch Childrens Research Institute and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia.

WARP is a novel member of the von Willebrand factor A domain superfamily of extracellular matrix proteins that is expressed by chondrocytes. WARP is restricted to the presumptive articular cartilage zone prior to joint cavitation and to the articular cartilage and fibrocartilaginous elements in the joint, spine, and sternum during mouse embryonic development. In mature articular cartilage, WARP is highly specific for the chondrocyte pericellular microenvironment and co-localizes with perlecan, a prominent component of the chondrocyte pericellular region. WARP is present in the guanidine-soluble fraction of cartilage matrix extracts as a disulfide-bonded multimer, indicating that WARP is a strongly interacting component of the cartilage matrix. To investigate how WARP is integrated with the pericellular environment, we studied WARP binding to mouse perlecan using solid phase and surface plasmon resonance analysis. WARP interacts with domain III-2 of the perlecan core protein and the heparan sulfate chains of the perlecan domain I with K(D) values in the low nanomolar range. We conclude that WARP forms macromolecular structures that interact with perlecan to contribute to the assembly and/or maintenance of "permanent" cartilage structures during development and in mature cartilages.
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http://dx.doi.org/10.1074/jbc.M513746200DOI Listing
March 2006

Structural basis for Gas6-Axl signalling.

EMBO J 2006 Jan 15;25(1):80-7. Epub 2005 Dec 15.

Max-Planck-Institut für Biochemie, Martinsried, Germany.

Receptor tyrosine kinases of the Axl family are activated by the vitamin K-dependent protein Gas6. Axl signalling plays important roles in cancer, spermatogenesis, immunity, and platelet function. The crystal structure at 3.3 A resolution of a minimal human Gas6/Axl complex reveals an assembly of 2:2 stoichiometry, in which the two immunoglobulin-like domains of the Axl ectodomain are crosslinked by the first laminin G-like domain of Gas6, with no direct Axl/Axl or Gas6/Gas6 contacts. There are two distinct Gas6/Axl contacts of very different size, both featuring interactions between edge beta-strands. Structure-based mutagenesis, protein binding assays and receptor activation experiments demonstrate that both the major and minor Gas6 binding sites are required for productive transmembrane signalling. Gas6-mediated Axl dimerisation is likely to occur in two steps, with a high-affinity 1:1 Gas6/Axl complex forming first. Only the minor Gas6 binding site is highly conserved in the other Axl family receptors, Sky/Tyro3 and Mer. Specificity at the major contact is suggested to result from the segregation of charged and apolar residues to opposite faces of the newly formed beta-sheet.
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http://dx.doi.org/10.1038/sj.emboj.7600912DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1356355PMC
January 2006

Disruption of perlecan binding and matrix assembly by post-translational or genetic disruption of dystroglycan function.

FEBS Lett 2005 Aug;579(21):4792-6

Department of Physiology and Biophysics, Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, 400 Eckstein Medical Building, Iowa City, IA 52242, USA.

Dystroglycan is a cell-surface matrix receptor that requires LARGE-dependent glycosylation for laminin binding. Although the interaction of dystroglycan with laminin has been well characterized, less is known about the role of dystroglycan glycosylation in the binding and assembly of perlecan. We report reduced perlecan-binding activity and mislocalization of perlecan in the LARGE-deficient Large(myd) mouse. Cell-surface ligand clustering assays show that laminin polymerization promotes perlecan assembly. Solid-phase binding assays provide evidence for the first time of a trimolecular complex formation of dystroglycan, laminin and perlecan. These data suggest functional disruption of the trimolecular complex in glycosylation-deficient muscular dystrophy.
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http://dx.doi.org/10.1016/j.febslet.2005.07.059DOI Listing
August 2005

Laminin gamma3 chain binds to nidogen and is located in murine basement membranes.

J Biol Chem 2005 Jun 11;280(23):22146-53. Epub 2005 Apr 11.

Department of Prosthodontics, University of Goettingen, D-37075 Goettingen, Germany.

Recently a novel laminin gamma3 chain was identified in mouse and human and shown to have the same modular structure as the laminin gamma1 chain. We expressed two fragments of the gamma3 chain in mammalian cells recombinantly. The first, domain VI/V, consisting of laminin N-terminal (domain VI) and four laminin-type epidermal growth factor-like (domain V) and laminin N-terminal modules, was shown to be essential for self-assembly of laminins. The other was domain III3-5, which consists of three laminin-type epidermal growth factor-like modules and is predicted to bind to nidogens. The gamma3 VI/V fragment was a poor inhibitor for laminin-1 polymerization as was the beta2 VI/V fragment. The gamma3 III3-5 fragment bound to nidogen-1 and nidogen-2 with lower affinity than the gamma1 III3-5 fragment. These data suggested that laminins containing the gamma3 chain may assemble networks independent of other laminins. Polyclonal antibodies raised against gamma3 VI/V and gamma3 III3-5 showed no cross-reaction with homologous fragments from the gamma1 and gamma2 chains of laminin and allowed the establishment of gamma chain-specific radioimmunoassays and light and electron microscopic immunostaining of tissues. This demonstrated a 20-100-fold lower content of the gamma3 chain compared with the gamma1 chain in various tissue extracts of adult mice. The expression of gamma3 chain was highly tissue-specific. In contrast to earlier assumptions, the antibodies against the gamma3 chain showed light microscopic staining exclusively in basement membrane zones of adult and embryonic tissues, such as the brain, kidney, skin, muscle, and testis. Ultrastructural immunogold staining localized the gamma3 chain to basement membranes of these tissues.
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http://dx.doi.org/10.1074/jbc.M501875200DOI Listing
June 2005

Laminin alpha1 globular domains 4-5 induce fetal development but are not vital for embryonic basement membrane assembly.

Proc Natl Acad Sci U S A 2005 Feb 24;102(5):1502-6. Epub 2005 Jan 24.

Department of Cell and Molecular Biology, Lund University, 22184 Lund, Sweden.

During early mouse embryogenesis, each laminin (Lm) chain of the first described Lm, a heterotrimer of alpha1, beta1, and gamma1 chains (Lm-1), is essential for basement membrane (BM) assembly, which is required for pregastrulation development. Individual domains may have other functions, not necessarily structural. The cell binding C terminus of Lm alpha1 chain contains five Lm globular (LG) domains. In vitro, alpha1LG1-3 domains bind integrins, and alpha1LG4 binds dystroglycan, heparin, and sulfatides. A prevailing hypothesis is that alpha1LG4 is crucial as a structural domain for BM assembly, whereas integrin-binding sites conduct signaling. The in vivo role of alpha1LG4-5 (also called E3) has not been studied. Mice lacking alpha1LG4-5 were therefore made. Null embryos implanted, but presumptive epiblast cells failed to polarize and did not survive past day 6.5. BM components including truncated Lm alpha1 were detected in Reichert's membrane. Surprisingly, embryonic BM assembly between visceral endoderm and stem cells was normal in null embryos and in embryoid bodies of alpha1LG4-5-null embryonic stem cells. Yet, stem cells could not develop into polarized epiblast cells. Thus, alpha1LG4-5 provides vital signals for the conversion of stem cells to polarized epithelium.
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http://dx.doi.org/10.1073/pnas.0405095102DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC545491PMC
February 2005

Microfibrils at basement membrane zones interact with perlecan via fibrillin-1.

J Biol Chem 2005 Mar 17;280(12):11404-12. Epub 2005 Jan 17.

Department of Medical Molecular Biology, University of Lübeck, 23538 Lübeck, Germany.

Mutational defects in fibrillin-rich microfibrils give rise to a number of heritable connective tissue disorders, generally termed microfibrillopathies. To understand the pathogenesis of these microfibrillopathies, it is important to elucidate the supramolecular composition of microfibrils and their interaction properties with extracellular matrix components. Here we demonstrate that the proteoglycan perlecan is an associated component of microfibrils typically close to basement membrane zones. Double immunofluorescence studies demonstrate colocalization of fibrillin-1, the major backbone component of microfibrils, with perlecan in fibroblast cultures as well as in dermal and ocular tissues. Double immunogold labeling further confirms colocalization of perlecan to microfibrils in various tissues at the ultrastructural level. Extraction studies revealed that perlecan is not covalently associated with microfibrils. High affinity interactions between fibrillin-1 and perlecan were found by kinetic binding studies with dissociation constants in the low nanomolar range. A detailed mapping study of the interaction epitopes by solid phase binding assays primarily revealed interactions of perlecan domains I and II with a central region of fibrillin-1. Analysis of perlecan null embryos showed less microfibrils at the dermal-epidermal junction as compared with wild-type littermates. The data presented indicate a functional significance for perlecan in anchoring microfibrils to basement membranes and in the biogenesis of microfibrils.
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http://dx.doi.org/10.1074/jbc.M409882200DOI Listing
March 2005

The minimal active domain of endostatin is a heparin-binding motif that mediates inhibition of tumor vascularization.

Cancer Res 2004 Dec;64(24):9012-7

Department of Genetics and Pathology, Uppsala University, Rudbeck Laboratory, Uppsala, Sweden.

Endostatin constitutes the COOH-terminal 20,000 Da proteolytic fragment of collagen XVIII and has been shown to possess antiangiogenic and antitumorigenic properties. In the present study, we have investigated the role of the heparin-binding sites in the in vivo mechanism of action of endostatin. The majority of the heparin binding is mediated by arginines 155/158/184/270 in endostatin, but there is also a minor site constituted by arginines 193/194. Using endostatin mutants lacking either of these two sites, we show that inhibition of fibroblast growth factor-2-induced angiogenesis in the chicken chorioallantoic membrane requires both heparin-binding sites. In contrast, inhibition of vascular endothelial growth factor-A-induced chorioallantoic membrane angiogenesis by endostatin was only dependent on the minor heparin-binding site (R193/194). These arginines were also required for endostatin to inhibit fibroblast growth factor-2- and vascular endothelial growth factor-A-induced chemotaxis of primary endothelial cells. Moreover, we show that a synthetic peptide corresponding to amino acids 180-199 of human endostatin (which covers the minor heparin-binding site) inhibits endothelial cell chemotaxis and reduces tumor vascularization in vivo. Substitution of arginine residues 193/194 for alanine attenuates the antiangiogenic effects of the peptide. These data show an essential role for heparin binding in the antiangiogenic action of endostatin.
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http://dx.doi.org/10.1158/0008-5472.CAN-04-2172DOI Listing
December 2004

Influence of endostatin on embryonic vasculo- and angiogenesis.

Dev Dyn 2004 Jul;230(3):468-80

Department of Molecular and Cellular Sport Medicine, German Sport University Cologne, Cologne, Germany.

The proteolytic fragment of collagen XVIII, endostatin, acts as an inhibitor of angiogenesis. To date, only limited knowledge exists on the effects of endostatin on endothelial cells during embryonic development. Therefore, we analysed the role of endostatin on embryonic vasculo- and angiogenesis. Endostatin is accumulated in embryonic tissue of mouse embryos. Similarly, in vessels of embryoid bodies (EBs), endostatin and its binding sites are distributed in vessels and sprouting areas. In EBs, endostatin increases endothelial cells (control, 279.3 +/- 76.5; 50 ng/ml, 566.3 +/- 90.1; 200 ng/ml, 594.5 +/- 166.3 tube-like structures per EB) and endothelial tubes by proliferation (control, 21.4 +/- 7.5; 50 ng/ml, 160.2 +/- 9.9; 200 ng/ml, 184.2 +/- 16.5 Ki67-positive nuclei per 50 tube-like structures); it also enhances migration (control, 380.5 +/- 159.8 cells; 50 ng/ml, 718.3 +/- 251 cells; 200 ng/ml, 706 +/- 89.4 cells) and apoptosis (control, 16.8 +/- 6.7; 50 ng/ml, 94.4 +/- 23.6; 200 ng/ml, 106 +/- 42 PARP-positive nuclei per 50 tube-like structures). Furthermore, endostatin modulates the morphology of the endothelial tubes by inducing contraction. Endostatin modulates the embryonic vascular development by enhancing proliferation, migration, and apoptosis as well as by regulating morphogenesis.
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http://dx.doi.org/10.1002/dvdy.20072DOI Listing
July 2004

Alternative splicing in the aggrecan G3 domain influences binding interactions with tenascin-C and other extracellular matrix proteins.

J Biol Chem 2004 Mar 13;279(13):12511-8. Epub 2004 Jan 13.

The Wellcome Trust Centre for Cell Matrix Research, School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom.

The proteoglycans aggrecan, versican, neurocan, and brevican bind hyaluronan through their N-terminal G1 domains, and other extracellular matrix proteins through the C-type lectin repeat in their C-terminal G3 domains. Here we identify tenascin-C as a ligand for the lectins of all these proteoglycans and map the binding site on the tenascin molecule to fibronectin type III repeats, which corresponds to the proteoglycan lectin-binding site on tenascin-R. In the G3 domain, the C-type lectin is flanked by epidermal growth factor (EGF) repeats and a complement regulatory protein-like motif. In aggrecan, these are subject to alternative splicing. To investigate if these flanking modules affect the C-type lectin ligand interactions, we produced recombinant proteins corresponding to aggrecan G3 splice variants. The G3 variant proteins containing the C-type lectin showed different affinities for various ligands, including tenascin-C, tenascin-R, fibulin-1, and fibulin-2. The presence of an EGF motif enhanced the affinity of interaction, and in particular the splice variant containing both EGF motifs had significantly higher affinity for ligands, such as tenascin-R and fibulin-2. The mRNA for this splice variant was shown by reverse transcriptase-PCR to be expressed in human chondrocytes. Our findings suggest that alternative splicing in the aggrecan G3 domain may be a mechanism for modulating interactions and extracellular matrix assembly.
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http://dx.doi.org/10.1074/jbc.M400242200DOI Listing
March 2004

Targeted inactivation of murine laminin gamma2-chain gene recapitulates human junctional epidermolysis bullosa.

J Invest Dermatol 2003 Oct;121(4):720-31

Department of Dermatology and Cutaneous Biology, Jefferson Medical College, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

Junctional forms of epidermolysis bullosa (JEB) are associated with mutations in six distinct genes expressed in the cutaneous basement membrane zone; these include LAMA3, LAMB3, and LAMC2, which encode laminin 5 subunit polypeptides, the alpha3-, beta3-, and gamma2-chains, respectively. Here we generated a mouse model for JEB by inactivating the laminin gamma2-chain gene by targeted frameshift deletion of exon 8 in Lamc2. Heterozygous mice were phenotypically normal, whereas the majority of Lamc2-/- mice showed blistering phenotype on days 1 to 2 and died within 5 days of birth. The Lamc2-/- mice demonstrated absent expression of laminin gamma2-chain on the basement membrane zone as well as attenuated expression of alpha3- and beta3-chains of laminin. Transmission electron microscopy revealed rudimentary, poorly developed hemidesmosomes. The epidermis of the Lamc2-/- mice revealed induced apoptosis in the basal cells of the blistered skin, suggesting that cell-matrix adhesion provided by laminin 5 plays a role in cell survival in vivo. Cultured Lamc2-/- keratinocytes demonstrated slightly positive staining with gamma2-chain-specific antibodies, which could be explained by the presence of a transcript with partial restoration of the reading frame owing to alternative splicing in vitro. These cells proliferated in different matrices and attached to type IV collagen and Matrigel as efficiently as the wild-type keratinocytes, whereas their attachment on plastic and laminin was significantly weaker. In summary, Lamc2-/- mouse recapitulates human JEB and provides novel insight into the role of laminin 5 in keratinocyte biology.
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http://dx.doi.org/10.1046/j.1523-1747.2003.12515.xDOI Listing
October 2003

Distinct requirements for heparin and alpha-dystroglycan binding revealed by structure-based mutagenesis of the laminin alpha2 LG4-LG5 domain pair.

J Mol Biol 2003 Sep;332(3):635-42

Max-Planck-Institut für Biochemie, D-82152, Martinsried, Germany.

Laminin-2 (alpha2beta1gamma1) is found in basement membranes surrounding muscle and peripheral nerve cells. Several types of cellular receptors bind to the laminin G-like (LG) domains at the C terminus of the alpha2 chain, the interaction with alpha-dystroglycan (alpha-DG) being particularly important in muscle. We have used site-directed mutagenesis and in vitro binding assays to map the binding sites on the laminin alpha2 chain LG4-LG5 domain pair for alpha-DG, heparin and sulfatides. Calcium-dependent alpha-DG recognition requires the calcium ion in LG4, but not the one in LG5, as well as basic residues in both LG domains. Heparin and sulfatides also bind to basic residues in both LG domains, but there is little overlap in the binding sites for alpha-DG and heparin/sulfatides. The results should prove useful for the molecular dissection of laminin-receptor interactions in vivo.
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http://dx.doi.org/10.1016/s0022-2836(03)00848-9DOI Listing
September 2003

Mutations in COCH that result in non-syndromic autosomal dominant deafness (DFNA9) affect matrix deposition of cochlin.

Hum Genet 2003 Oct 20;113(5):406-16. Epub 2003 Aug 20.

Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.

The COCH gene mutated in autosomal dominant sensorineural deafness (DFNA9) encodes cochlin, a major constituent of the inner ear extracellular matrix. Sequence analysis of cochlin from DFNA9 patients identified five distinct single-amino-acid mutations within a conserved region (the LCCL domain) of cochlin. To define the molecular basis of DFNA9, we have generated myc-tagged wild-type and mutant cochlins and explored their behavior in transient transfection systems. Western blotting of cell lysates and culture media indicates that wild-type and mutant cochlins are synthesized and secreted in similar amounts. Immunofluorescent staining confirms that all are detected within the endoplasmic reticulum and the Golgi complex of transfected cells. Our findings suggest that COCH mutations are unlikely to cause abnormalities in secretion and suggest that extracellular events might cause DFNA9 pathology. In agreement, we show that wild-type cochlin accumulates in extracellular deposits that closely parallel the matrix component fibronectin, whereas mutant cochlins vary in the amount and pattern of extracellular material. Whereas some mutants exhibit an almost normal deposition pattern, some show complete lack of deposition. Our results suggest that DFNA9 results from gene products that fail to integrate correctly into the extracellular matrix. The partial or complete penetrance of integration defects suggests that DFNA9 pathology may be caused by multiple molecular mechanisms, including compromised ability of cochlin to self-assemble or to form appropriate complexes with other matrix components.
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http://dx.doi.org/10.1007/s00439-003-0992-7DOI Listing
October 2003

Opposing roles of integrin alpha6Abeta1 and dystroglycan in laminin-mediated extracellular signal-regulated kinase activation.

Mol Biol Cell 2003 May 6;14(5):2088-103. Epub 2003 Feb 6.

Department of Cell and Molecular Biology, Lund University, Sweden.

Laminin-integrin interactions can in some settings activate the extracellular signal-regulated kinases (ERKs) but the control mechanisms are poorly understood. Herein, we studied ERK activation in response to two laminins isoforms (-1 and -10/11) in two epithelial cell lines. Both cell lines expressed beta1-containing integrins and dystroglycan but lacked integrin alpha6beta4. Antibody perturbation assays showed that both cell lines bound to laminin-10/11 via the alpha3beta1and alpha6beta1 integrins. Although laminin-10/11 was a stronger adhesion complex than laminin-1 for both cell lines, both laminins activated ERK in only one of the two cell lines. The ERK activation was mediated by integrin alpha6beta1 and not by alpha3beta1 or dystroglycan. Instead, we found that dystroglycan-binding domains of both laminin-1 and -10/11 suppressed integrin alpha6beta1-mediated ERK activation. Moreover, the responding cell line expressed the two integrin alpha6 splice variants, alpha6A and alpha6B, whereas the nonresponding cell line expressed only alpha6B. Furthermore, ERK activation was seen in cells transfected with the integrin alpha6A subunit, but not in alpha6B-transfected cells. We conclude that laminin-1 and -10/11 share the ability to induce ERK activation, that this is regulated by integrin alpha6Abeta1, and suggest a novel role for dystroglycan-binding laminin domains as suppressors of this activation.
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http://dx.doi.org/10.1091/mbc.e03-01-0852DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC165099PMC
May 2003

Fibulins: a versatile family of extracellular matrix proteins.

Nat Rev Mol Cell Biol 2003 Jun;4(6):479-89

Laboratory of Protein Chemistry, Max Planck Institute for Biochemistry, D-82152 Martinsried, Germany.

Fibulins are a newly recognized family of extracellular matrix proteins. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. New insights into their biological roles are now emerging from studies of transgenic mice and of some inherited human diseases.
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http://dx.doi.org/10.1038/nrm1130DOI Listing
June 2003

Genetic heterogeneity of cutis laxa: a heterozygous tandem duplication within the fibulin-5 (FBLN5) gene.

Am J Hum Genet 2003 Apr 28;72(4):998-1004. Epub 2003 Feb 28.

Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.

Inherited cutis laxa is a connective tissue disorder characterized by loose skin and variable internal organ involvement, resulting from paucity of elastic fibers. Elsewhere, frameshift mutations in the elastin gene have been reported in three families with autosomal dominant inheritance, and a family with autosomal recessive cutis laxa was recently reported to have a homozygous missense mutation in the fibulin-5 gene. In the present study, we analyzed the gene expression of elastin and fibulins 1-5 in fibroblasts from five patients with cutis laxa. One patient was found to express both normal (2.2 kb) and mutant (2.7 kb) fibulin-5 mRNA transcripts. The larger transcript contains an internal duplication of 483 nucleotides, which resulted in the synthesis and secretion of a mutant fibulin-5 protein with four additional tandem calcium-binding epidermal growth factor-like motifs. The mutation arose from a 22-kb tandem gene duplication, encompassing the sequence from intron 4 to exon 9. No fibulin-5 or elastin mutations were detected in the other patients. The results demonstrate that a heterozygous mutation in fibulin-5 can cause cutis laxa and also suggest that fibulin-5 and elastin gene mutations are not the exclusive cause of the disease.
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http://dx.doi.org/10.1086/373940DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1180361PMC
April 2003

Homoassociation of VE-cadherin follows a mechanism common to "classical" cadherins.

J Mol Biol 2003 Jan;325(4):733-42

Department of Biophysical Chemistry, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.

Vascular endothelial cadherin (VE-cadherin/cadherin5) is specifically expressed in adherens junctions of endothelial cells and exerts important functions in cell-cell adhesion as well as signal transduction. To analyze the mechanism of VE-cadherin homoassociation, the ectodomains CAD1-5 were connected by linker sequences to the N terminus of the coiled-coil domain of cartilage matrix protein (CMP). The chimera VECADCMP were expressed in mammalian cells. The trimeric coiled-coil domain leads to high intrinsic domain concentrations and multivalency promoting self-association. Ca(2+)-dependent homophilic association of VECADCMP was detected in solid phase assays and cross-linking experiments. A striking analogy to homoassociation of type I ("classical") cadherins like E, N or P-cadherin was observed when interactions in VECADCMP and between these trimeric proteins were analyzed by electron microscopy. Ca(2+)-dependent ring-like and double ring-like arrangements suggest interactions between domains 1 and 2 of the ectodomains, which may be correlated with lateral and adhesive contacts in the adhesion process. Association to complexes composed of two VECADCMP molecules was also demonstrated by chemical cross-linking. No indication for an antiparallel association of VECAD ectodomains to hexameric complexes as proposed by Legrand et al. was found. Instead the data suggest that homoassociation of VE-cadherin follows the conserved mechanism of type I cadherins.
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http://dx.doi.org/10.1016/s0022-2836(02)01286-xDOI Listing
January 2003

Evidence of nidogen-2 compensation for nidogen-1 deficiency in transgenic mice.

Matrix Biol 2002 Nov;21(7):611-21

Department of Histology, Georg-August-Universität Göttingen, D-37075, Göttingen, Germany.

Previous studies have shown that inhibition of nidogen-laminin binding interferes with basement membrane stabilization in various mouse organ cultures while no overt phenotype has been observed following inactivation of the nidogen-1 gene in mice. We have now used recombinant mouse nidogen-1 and nidogen-2 in order to evaluate a possible compensation between the two isoforms in the knock-out mice. Essentially, a comparable in vitro binding of nidogens-1 and -2 to the same laminin gamma1 chain structure and to several other basement membrane proteins has been revealed. Quantitative radioimmuno-assays have demonstrated high concentrations of nidogen-1 exceeding those of laminin gamma1 and nidogen-2 by factors of 5 and 20-50, respectively, in tissue extracts of wild-type mice. A three- to sevenfold increase in nidogen-2 was observed in heart and muscle of mice with nidogen-1 deficiency and confirmed by a similar increase in the intensity of immunogold staining of these tissues. However, a few of the tissues from mice with the gene knock-out still contained some nidogen-1-like immunoreactivity (1% of wild-type). Furthermore, both nidogen isoforms showed a similar distribution in various organs during embryonic development which, however, as shown previously, changed in some adult tissues. The data support the nidogen-2 compensation hypothesis to explain the limited phenotype observed following elimination of the nidogen-1 gene.
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http://dx.doi.org/10.1016/s0945-053x(02)00070-7DOI Listing
November 2002

Role of heparan sulfate domain organization in endostatin inhibition of endothelial cell function.

EMBO J 2002 Dec;21(23):6303-11

Department of Medical Biochemistry and Microbiology, Uppsala University, PO Box 582, SE-75123 Uppsala, Sweden.

The anti-angiogenic activity of endostatin (ES) depends on interactions with heparan sulfate (HS). In the present study, intact HS chains of >/=15 kDa bound quantitatively to ES whereas N-sulfated HS decasaccharides, with affinity for several fibroblast growth factor (FGF) species, failed to bind. Instead, ES-binding oligosaccharides composed of mixed N-sulfated and N-acetylated disaccharide units were isolated from pig intestinal HS. A 10/12mer ES-binding epitope was identified, with two N-sulfated regions separated by at least one N-acetylated glucosamine unit (SAS-domain). Cleavage at the N-acetylation site disrupted ES binding. These findings point to interaction between discontinuous sulfated domains in HS and arginine clusters at the ES surface. The inhibitory effect of ES on vascular endothelial growth factor-induced endothelial cell migration was blocked by the ES-binding SAS-domains and by heparin oligosaccharides (12mers) similar in length to the ES-binding SAS-domains, but not by 6mers capable of FGF binding. We propose that SAS-domains modulate the biological activities of ES and other protein ligands with extended HS-binding sites. The results provide a rational explanation for the preferential interaction of ES with certain HS proteoglycan species.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC136942PMC
http://dx.doi.org/10.1093/emboj/cdf638DOI Listing
December 2002

Biglycan organizes collagen VI into hexagonal-like networks resembling tissue structures.

J Biol Chem 2002 Dec 26;277(51):49120-6. Epub 2002 Sep 26.

Department of Cell and Molecular Biology, University of Lund, BMC, S-221 84 Lund, Sweden.

The ability of the leucine-rich repeat (LRR) proteins biglycan, decorin, and chondroadherin to interact with collagen VI and influence its assembly to supramolecular structures was studied by electron microscopy and surface plasmon resonance measurements in the BIAcore 2000 system. Biglycan showed a unique ability to organize collagen VI into extensive hexagonal-like networks over a time period of only a few minutes. Only the intact molecule, substituted with two dermatan sulfate chains, had this capacity. Intact decorin, with one dermatan sulfate chain only, was considerably less efficient, and aggregates of organized collagen VI were found only after several hours. Chondroadherin without glycosaminoglycan substitutions did not induce any ordered collagen VI organization. However, all three related LRR proteins were shown to interact with collagen VI using electron microscopy and surface plasmon resonance. Biglycan and decorin were exclusively found close to the N-terminal parts of the collagen VI tetramers, whereas chondroadherin was shown to bind close to both the N- and C-terminal parts of collagen VI. In the formed hexagonal networks, biglycan was localized to the intra-network junctions of the collagen VI filaments. This was demonstrated by electron microscopy after negative staining of gold-labeled biglycan in aggregation experiments with collagen VI.
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http://dx.doi.org/10.1074/jbc.M206891200DOI Listing
December 2002

Binding of mouse nidogen-2 to basement membrane components and cells and its expression in embryonic and adult tissues suggest complementary functions of the two nidogens.

Exp Cell Res 2002 Oct;279(2):188-201

Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.

Nidogen-1 binds several basement membrane components by well-defined, domain-specific interactions. Organ culture and gene targeting approaches suggest that a high-affinity nidogen-binding site of the laminin gamma1 chain (gamma1III4) is important for kidney development and for nerve guidance. Other proteins may also bind gamma1III4, although human nidogen-2 binds poorly to the mouse laminin gamma1 chain. We therefore characterized recombinant mouse nidogen-2 and its binding to basement membrane proteins and cells. Mouse nidogen-1 and -2 interacted at comparable levels with collagen IV, perlecan, and fibulin-2 and, most notably, also with laminin-1 fragments P1 and gamma1III3-5, which both contain the gamma1III4 module. In embryos, nidogen-2 mRNA was produced by mesenchyme at sites of epithelial-mesenchymal interactions, but the protein was deposited on epithelial basement membranes, as previously shown for nidogen-1. Hence, binding of both nidogens to the epithelial laminin gamma1 chain is dependent on epithelial-mesenchymal interactions. Epidermal growth factor stimulated expression of both nidogens in embryonic submandibular glands. Both nidogens were found in all studied embryonic and adult basement membranes. Nidogen-2 was more adhesive than nidogen-1 for some cell lines and was mainly mediated by alpha3beta1 and alpha6beta1 integrins as shown by antibody inhibition. These findings revealed extensive coregulation of nidogen-1 and -2 expression and much more complementary functions of the two nidogens than previously recognized.
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http://dx.doi.org/10.1006/excr.2002.5611DOI Listing
October 2002

Crystal structure of a C-terminal fragment of growth arrest-specific protein Gas6. Receptor tyrosine kinase activation by laminin G-like domains.

J Biol Chem 2002 Nov 5;277(46):44164-70. Epub 2002 Sep 5.

Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany.

Receptor tyrosine kinases of the Axl family are activated by Gas6, the product of growth arrest-specific gene 6. Gas6-Axl signaling is implicated in cell survival, adhesion, and migration. The receptor-binding site of Gas6 is located within a C-terminal pair of laminin G-like (LG) domains that do not resemble any other receptor tyrosine kinase ligand. We report the crystal structure at 2.2-A resolution of a Gas6 fragment spanning both LG domains (Gas6-LG). The structure reveals a V-shaped arrangement of LG domains strengthened by an interdomain calcium-binding site. LG2 of Gas6-LG contains two unusual features: an alpha-helix cradled by one edge of the LG beta-sandwich and a conspicuous patch of surface-exposed hydrophobic residues. Mutagenesis of some residues in this patch reduces Gas6-LG binding to the extracellular domain of Axl as well as Axl activation in glioblastoma cells, identifying a component of the receptor-binding site of Gas6.
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http://dx.doi.org/10.1074/jbc.M207340200DOI Listing
November 2002

Gene structure and functional analysis of the mouse nidogen-2 gene: nidogen-2 is not essential for basement membrane formation in mice.

Mol Cell Biol 2002 Oct;22(19):6820-30

Department of Protein Chemistry, Max-Planck-Institute for Biochemistry, D-82152 Martinsried, Germany.

Nidogens are highly conserved proteins in vertebrates and invertebrates and are found in almost all basement membranes. According to the classical hypothesis of basement membrane organization, nidogens connect the laminin and collagen IV networks, so stabilizing the basement membrane, and integrate other proteins. In mammals two nidogen proteins, nidogen-1 and nidogen-2, have been discovered. Nidogen-2 is typically enriched in endothelial basement membranes, whereas nidogen-1 shows broader localization in most basement membranes. Surprisingly, analysis of nidogen-1 gene knockout mice presented evidence that nidogen-1 is not essential for basement membrane formation and may be compensated for by nidogen-2. In order to assess the structure and in vivo function of the nidogen-2 gene in mice, we cloned the gene and determined its structure and chromosomal location. Next we analyzed mice carrying an insertional mutation in the nidogen-2 gene that was generated by the secretory gene trap approach. Our molecular and biochemical characterization identified the mutation as a phenotypic null allele. Nidogen-2-deficient mice show no overt abnormalities and are fertile, and basement membranes appear normal by ultrastructural analysis and immunostaining. Nidogen-2 deficiency does not lead to hemorrhages in mice as one may have expected. Our results show that nidogen-2 is not essential for basement membrane formation or maintenance.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC135501PMC
http://dx.doi.org/10.1128/mcb.22.19.6820-6830.2002DOI Listing
October 2002

Structure and function of collagen-derived endostatin inhibitors of angiogenesis.

IUBMB Life 2002 Feb;53(2):77-84

Max-Planck-Institut für Biochemie, Martinsried, Germany.

Endostatins are inhibitors of endothelial cell migration and angiogenesis and have been shown to reduce tumor growth in animal models. They are derived from the nontriplehelical C-terminal NC1 domains of collagens XV and XVIII, which are released proteolytically in trimeric form and further converted to monomeric endostatins of about 20 kDa. Both endostatin isoforms share a compact globular fold, but differ in certain binding properties for proteins and cells, as well as in tissue distribution. Differences in activity were found between NC1 domains and endostatins and are related to the oligomerization state. Endostatin effects are not restricted to endothelial cells, but also control renal epithelial cells and neuronal guidance in C. elegans. Cellular receptors are still insufficiently characterized and include for endostatin-XVIII heparan sulfate proteoglycans. Receptor engagement elicits various downstream effects including tyrosine kinase and gene activation. Much remains to be learned, however, about details of the signal transduction cascades and how they interfere with pro-angiogenic factors under physiological conditions and during therapeutic treatment.
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http://dx.doi.org/10.1080/15216540211466DOI Listing
February 2002