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Advances in Brief |
1ß1 Integrin in Vitro and Angiogenesis in Vivo1
Temple University, School of Medicine, Thrombosis Research Center, Philadelphia, Pennsylvania 19140 [C. M., D. G. K., G. P. T.]; Biogen, Inc., Cambridge, Massachusetts 02142 [P. H. W., R. R. L.]; Instituto de Biomedicina, C.S.I.C., 46010 Valencia, Spain [J. J. C.]; and Albany College of Pharmacy and PRI at Albany, Albany, New York 12208 [S. A. M.]
| ABSTRACT |
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1ß1 integrin. It does not inhibit the closely related integrin
2ß1, nor a panel of other integrins tested. It does not inhibit ligand binding to the recombinant
1 I-domain. Importantly, obtustatin potently inhibited angiogenesis in vivo in the chicken chorioallantoic membrane assay, and in the Lewis lung syngeneic mouse model, it reduced tumor development by half, confirming and extending previous results on the relevance of
1ß1 integrin to angiogenesis and suggesting novel approaches to the generation of angiogenesis inhibitors. | Introduction |
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5ß1,
vß3, and
vß5 integrins are primary targets for endostatin action (8)
, whereas angiostatin and tumstatin interact with
vß3 integrin (6
, 9)
. Arresten interacts with the
1ß1 integrin (7)
, which is selective for collagen IV, a major component of basement membranes. These integrins are all expressed on vascular cells, and thus, regulation of vascular cell integrin-ligand interactions is becoming an organizing theme within angiogenesis research.
Disintegrins are the largest group of antiadhesive proteins found in viper venom (10)
. The characteristic feature common to all disintegrins is the similar pattern of cysteines and presence of the so-called "integrin-binding" loop. Disintegrins may be divided into two groups, monomeric and dimeric. The monomeric disintegrins form the largest class, usually contain the RGD3
sequence in their integrin-binding loop, and are potent inhibitors of the platelet fibrinogen receptor
IIbß3 integrin. They have been divided into three subgroups based on the number of cysteines in their molecules (10)
. The "short" disintegrins, with only eight cysteines, are represented by the 49 amino acid-containing peptides echistatin and eristostatin, both of which are potent inhibitors of
IIbß3 integrin. However, only echistatin inhibits other RGD-dependent integrins, such as the vitronectin receptor
vß3. Here, we describe a novel short monomeric disintegrin called obtustatin. The structure of its integrin-binding loop is novel, and it is a highly selective inhibitor of
1ß1 integrin in vitro and of angiogenesis in vivo.
| Materials and Methods |
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1 and
2 integrins were from Dr. P. Gotwals (Biogen, Inc., Cambridge, MA) and Dr. M. Hemler (Dana-Farber Cancer Institute, Boston, MA). The Lewis lung carcinoma cells were from Dr. Bruce Ruggeri (Cephalon, Inc., West Chester, PA). K562 cells were from American Type Culture Collection (Manassas, VA). Collagen type I and IV were from Chemicon International, Inc. (Temecula, CA). Synthetic peptides based on the structure of obtustatin were synthesized commercially by Sigma-Genosis (Woodland, TX).
Purification of Disintegrins.
Obtustatin was purified from the venom of Vipera lebetina obtusa using two steps of reverse phase high-performance liquid chromatography as described (11)
. Briefly, 10 mg of Vipera lebetina obtusa venom in 300 µl of 0.1% TFA were injected into C18 column and eluted with an acetonitrile gradient (080%) in 0.1% TFA over 45 min at a 2 ml/min flow rate. The obtustatin fraction (1 mg in 500 µl of 0.1% TFA) was reapplied to the same column and eluted with a second acetonitrile gradient (2080%) over 70 min. The yield of purified obtustatin was 12 mg/grams crude venom. Purity was assessed by SDS-PAGE and matrix-assisted laser desoption ionization-time-of-flight MS using an Applied Biosystems DE-Pro spectrometer (Wistar Institute, University of Pennsylvania, MS facility). Eristostatin was purified from the venom of Eristocophis macmahoni (12)
.
Structural Characterization of Obtustatin.
Purified obtustatin was reduced and alkylated as described (11)
. S-pyridylethylated obtustatin was characterized by NH2-terminal sequencing (using either an Applied Biosystem 477A or Beckman Porton LF-3000 instrument), amino acid analysis (using a Beckman Gold Amino Acid Analyzer after sample hydrolysis with 6 N HCl, 24 h, 110°C), and MS (as above). The primary structure of obtustatin was deduced from the NH2-terminal sequence analysis of overlapping peptides obtained by endo-Lys C digestion and purified as described (11)
.
Cell Adhesion and CFB Assays.
Adhesion studies of cells labeled with 5-(chloromethyl)fluorescein diacetate were performed as described (11)
. For the CFB assay (12)
, collagen IV- or collagen I-coated Dynabeads M-280 (1 mg/ml) were blocked with 8% Lewis rat plasma in assay buffer [50 mM HEPES (pH 7.5), 150 mM NaCl, and 0.1% Triton X-100] for 5 min. Beads (10 µg) were combined with
1K562 cell lysate (105 cell equivalents), obtained by lysis of cells with buffer containing 1% NP40 and TS2/16 (0.1 µg/ml) anti-ß1 monoclonal antibody labeled with ruthenium (II) tris-bipyridine N-hydroxysuccinimide ester (IGEN, Inc., Gaithersburg, MD) in assay buffer containing 1 mM MnCl2. In parallel, disintegrins were added. After 12-h agitation at room temperature, 200 µl of assay buffer were added, and the samples were read on an ORIGEN electrochemiluminescence detector (IGEN).
Chicken CAM Assay.
The chicken CAM assay was performed as described (5)
. Briefly, filter disks were soaked in 3 mg/ml cortisone acetate in solution of 95% ethanol and water and air dried. Disks absorbed with FGF2 (1 µg/ml PBS) in the presence (5 µg/disk) or absence of disintegrins were placed on growing CAMs. At 24 h, disintegrins were added to CAMs topically. After 48 h, the CAM tissue directly beneath FGF2-saturated filter disk was resected from the embryo, and the section was placed in a 35-mm Petri dish and examined under an SV6 stereomicroscope at x50 magnification. Digital images of CAM sections were collected using 3-charge-coupled device camera system (Toshiba) and analyzed with Image-Pro Plus software. The number of vessel branch points contained in a circular region equal to the area of filter disk (angiogenesis index) was counted for each section.
Mouse Model for Tumor Development.
Lewis lung (3)
carcinoma cells (1 x 106) were injected under the skin of the C57BL/6 mice (Tacoma, Inc., Germantown, NY). The tumors were allowed to grow for 1 week. The average tumor size at this time, called day 0, was
0.08 cm3. At day 0, the first i.p. injection of disintegrins was performed. Obtustatin was injected every other day at a dose of 5 mg/kg. In the control group, the PBS was injected with the same frequency. Tumor volume was measured using the standard formula length x width2 x 0.52 (4)
. Each group contained four animals.
| Results and Discussion |
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1ß1 integrin. It does not inhibit the structurally closely related collagen receptor
2ß1 integrin (Fig. 1, B and C)
IIbß3 and
vß3 integrins, four other ß1 integrins (
4,
5,
6, and
9), or
4ß7 integrin (data not shown). The anti-
1ß1 integrin activity of obtustatin was also confirmed in a cell-free assay (Fig. 1C)
1ß1 integrin to collagen type IV (0.8 nM IC50) but was without effect in a cell-free assay using solubilized
2ß1 integrin.
Integrin
1ß1 contains a so-called "inserted" or I-domain, which is present in the
subunit, contains
200 amino acid residues, is localized near the NH2 terminus (13)
, is highly conserved, and plays a necessary and direct role in ligand binding. We found that obtustatin did not inhibit the binding of the recombinant
1 subunit I-domain to collagen IV at concentrations
1 µM (data not shown). This result suggests that the
1ß1 integrin may contain a second binding site for collagen IV. It has been found (14)
that this integrin may bind two distinct fragments of collagen IV, the pepsin-derived triple helical domain and nonhelical NC1 (noncollagenous) domain. One possibility is that binding of the NC1 fragment does not occur through the I-domain but through another site in common with obtustatin.
A comparison of the integrin-binding loop of obtustatin to related RGD-containing disintegrins (Fig. 1A)
suggested that the motif homologous to RGD in obtustatin lies within the sequence KTSLT. The active site of obtustatin was localized by analysis of short peptides. Fig. 2A
shows the effects of native obtustatin, EP-obtustatin, and two obtutastin-derived linear synthetic peptides on adhesion of
1K562 cells to immobilized collagen IV. EP-obtustatin is a refolded form of this protein with reduced SS bonds and cysteines blocked with vinylpyridine. EP-obtustatin still retained inhibitory activity, but the IC50 increased from 2 nM to 30 µM. The synthetic peptide CWKTSLTSHYS, containing the entire integrin-binding loop, gave an IC50 of 600 µM. In contrast, the peptide CKLKPAGTTC, synthesized based on another part of obtustatin, was not active even at 20 mM. These data indicate that the active site of obtustatin is localized, as expected, within the integrin-binding loop. The essential amino acids for activity within this loop were then localized through alanine scanning (Fig. 2B)
. The data revealed that first threonine is critical for activity. The peptides with mutated lysine and serine adjacent to this amino acid lost only partially their inhibitory activity at a 1 mM concentration. These results suggest that the KTS sequence may be a new biologically active motif relevant for the
1ß1 integrin.
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1ß1 integrin is important in new vessel development. Vascular basement membrane collagens are proving a rich source of antiangiogenic fragments (6
, 7)
. A fragment of the NC1 collagen IV domain, designated arresten, inhibits endothelial cell proliferation in vitro and angiogenesis in vivo, and its mechanism of action is linked to interactions with
1ß1 integrin (7)
. In addition, proteolytic exposure of cryptic sites within collagen type IV, required for angiogenesis and tumor growth in vivo, is associated with the loss of
1ß1 integrin binding and the gain of
vß3 integrin binding (15)
. Furthermore,
1 knockout mice show a significant reduction in vascularization of skin tumors, an imbalance in their collagen/collagenase ratios, and circulating angiostatin (16)
. In a direct investigation of the mechanisms through which
1ß1 integrin supports angiogenesis driven by VEGF (17)
, it was shown that dermal microvascular EC attachment through
1ß1 integrin supported robust activation of the Erk1/Erk2 (p44/42) mitogen-activated protein kinase signal transduction pathway driving EC proliferation. Haptotactic EC migration toward collagen I was partially dependent on
1ß1 integrin, as was VEGF-stimulated chemotaxis of ECs in a uniform collagen matrix. In addition, monoclonal antibody antagonism resulted in
45% inhibition of VEGF-driven angiogenesis in mouse skin. These studies show a critical role for
1ß1 integrin in VEGF-driven angiogenesis in the dermis but do not address other agonists or organ compartments. Therefore, to evaluate obtustatin as an angiogenesis inhibitor, we used FGF2, an agonist distinct from VEGF, and an established angiogenesis system not used previously, the chicken CAM. As shown in Fig. 3A
80%. Eristostatin, a disintegrin structurally related to obtustatin (Fig. 1A)
1ß1 integrin in angiogenesis. Moreover, obtustatin significantly inhibited the development of Lewis lung carcinomas in a syngeneic mouse model (Fig. 3B)
50% after 1 week of treatment. These results agree with genetic studies with
1-null mice in which tumor growth was also reduced (16)
.
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1ß1 integrin may similarly provide lead compounds for drug development. In addition, although many inhibitors of angiogenesis are known, a detailed understanding of their molecular mechanisms has been lacking. Recent work shows that tumstatin is an endothelial cell-specific inhibitor of protein synthesis, via a novel interaction with
vß3 integrin (6)
. The availability of a well-defined angiogenesis inhibitor of
1ß1 integrin should also provide insights into the molecular role of this integrin in vascular cell function. Finally, after the discovery of disintegrins in snake venom, a large family of related molecules has been found in mammalian systems, which contain metalloprotease and disintegrin domains, some of which are known to bind integrins (19)
. These molecules play critical roles in fertilization, neurogenesis, protein ectodomain shedding, and amyloid precursor protein processing. We suggest that novel mammalian disintegrins may be found, which, like obtustatin, are inhibitors of
1ß1 integrin and may form a new group of endogenous angiogenesis inhibitors. Interestingly, we note that one member of this family, MDC-9/ADAM-9, does in fact contain the sequence KTS in the disintegrin domain, in a position analogous to that of the obtustatin sequence (20)
. We are currently investigating whether MDC-9 binds
1ß1 integrin.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported in part by W. W. Smith Charitable Trust Research Grant (to C. M.), an American Heart Association Beginning Investigator grant (to C. M.), and NIH Grants RO1 CA88931 and R41 CA81822 (both to G. P. T.). ![]()
2 To whom requests for reprints should be addressed, at Temple University School of Medicine, Thrombosis Research Center, 3400 North Broad Street, Philadelphia PA 19140. E-mail: cmarcink{at}nimbus.temple.edu ![]()
3 The abbreviations used: RGD, arginine-glycine-aspartic acid; KTS, lysine-threonine-serine; EP, ethylpyridylated; TFA, trifluoroacetic acid; MS, mass spectrometry; CFB, cell-free binding; CAM, chorioallantoic membrane; VEGF, vascular endothelial growth factor; FGF, fibroblast growth factor. ![]()
Received 1/22/03. Accepted 3/20/03.
| REFERENCES |
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vß3 in endothelial cells. J. Biol. Chem., 276: 562-568, 2001.
9ß1 with VCAM-1, tenascin-C and osteopontin. J. Biol. Chem., 275: 31930-31937, 2000.
1 knockout mice cause reduced tumor vascularization. Proc. Natl. Acad. Sci. USA, 97: 2202-2207, 2000.
1ß1 and
2ß1 integrins provide critical support for vascular endothelial growth factor signaling, endothelial cell migration, and tumor angiogenesis. Am. J. Pathol., 160: 195-204, 2002.This article has been cited by other articles:
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R. Silva, G. D'Amico, K. M. Hodivala-Dilke, and L. E. Reynolds Integrins: The Keys to Unlocking Angiogenesis Arterioscler. Thromb. Vasc. Biol., October 1, 2008; 28(10): 1703 - 1713. [Abstract] [Full Text] [PDF] |
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G. R. Bolduc and L. C. Madoff The group B streptococcal alpha C protein binds {alpha}1 1-integrin through a novel KTD motif that promotes internalization of GBS within human epithelial cells Microbiology, December 1, 2007; 153(12): 4039 - 4049. [Abstract] [Full Text] [PDF] |
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L. Sanz, R.-Q. Chen, A. Perez, R. Hilario, P. Juarez, C. Marcinkiewicz, D. Monleon, B. Celda, Y.-L. Xiong, E. Perez-Paya, et al. cDNA Cloning and Functional Expression of Jerdostatin, a Novel RTS-disintegrin from Trimeresurus jerdonii and a Specific Antagonist of the {alpha}1{beta}1 Integrin J. Biol. Chem., December 9, 2005; 280(49): 40714 - 40722. [Abstract] [Full Text] [PDF] |
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M. J. Calzada, D. S. Annis, B. Zeng, C. Marcinkiewicz, B. Banas, J. Lawler, D. F. Mosher, and D. D. Roberts Identification of Novel {beta}1 Integrin Binding Sites in the Type 1 and Type 2 Repeats of Thrombospondin-1 J. Biol. Chem., October 1, 2004; 279(40): 41734 - 41743. [Abstract] [Full Text] [PDF] |
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D. Monleon, M. P. Moreno-Murciano, H. Kovacs, C. Marcinkiewicz, J. J. Calvete, and B. Celda Concerted Motions of the Integrin-binding Loop and the C-terminal Tail of the Non-RGD Disintegrin Obtustatin J. Biol. Chem., November 14, 2003; 278(46): 45570 - 45576. [Abstract] [Full Text] [PDF] |
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