Platelet-derived Growth Factor Receptor β and Vascular Endothelial Growth Factor Receptor 2 Bind to the β3Integrin through Its Extracellular Domain

Integrin-mediated cell attachment and growth factor stimulation often act synergistically on cell proliferation, differentiation, migration, and survival. Some of these synergistic effects depend on the physical interaction of integrins with growth factor receptors. Here we examine the nature of the physical interaction between the αvβ3 integrin and two receptor tyrosine kinases (RTKs), the platelet-derived growth factor receptor β (PDGF-Rβ) and the vascular endothelial growth factor receptor 2 (VEGF-R2, also known as KDR and flk-1). Both of these RTKs associate with the αvβ3 integrin but do not associate with β1 integrins. Furthermore, growth factor stimulation of these RTKs promotes increased cell proliferation and migration when cells are attached to the αvβ3 ligand, vitronectin. We show that αvβ3 in which the β3cytoplasmic domain is deleted or replaced with the β1cytoplasmic domain coimmunoprecipitates with PDGF-Rβ and VEGF-R2. The β3 extracellular domain alone was sufficient for the PDGF-Rβ association whereas the VEGF-R2 association required the presence of the αv subunit. Activation of the RTKs by their ligands was not required for them to associate with the integrin. Cell migration to PDGF was enhanced in the cells transfected with the chimeric subunit containing the β3 extracellular domain but not when that domain came from the β1 subunit. These results show that the interactions that lead to the association of the αvβ3 integrin with PDGF-Rβ and VEGF-R2 and enhancement of RTK activity take place outside the cell. Integrin-mediated cell attachment and growth factor stimulation often act synergistically on cell proliferation, differentiation, migration, and survival. Some of these synergistic effects depend on the physical interaction of integrins with growth factor receptors. Here we examine the nature of the physical interaction between the αvβ3 integrin and two receptor tyrosine kinases (RTKs), the platelet-derived growth factor receptor β (PDGF-Rβ) and the vascular endothelial growth factor receptor 2 (VEGF-R2, also known as KDR and flk-1). Both of these RTKs associate with the αvβ3 integrin but do not associate with β1 integrins. Furthermore, growth factor stimulation of these RTKs promotes increased cell proliferation and migration when cells are attached to the αvβ3 ligand, vitronectin. We show that αvβ3 in which the β3cytoplasmic domain is deleted or replaced with the β1cytoplasmic domain coimmunoprecipitates with PDGF-Rβ and VEGF-R2. The β3 extracellular domain alone was sufficient for the PDGF-Rβ association whereas the VEGF-R2 association required the presence of the αv subunit. Activation of the RTKs by their ligands was not required for them to associate with the integrin. Cell migration to PDGF was enhanced in the cells transfected with the chimeric subunit containing the β3 extracellular domain but not when that domain came from the β1 subunit. These results show that the interactions that lead to the association of the αvβ3 integrin with PDGF-Rβ and VEGF-R2 and enhancement of RTK activity take place outside the cell. receptor tyrosine kinases platelet-derived growth factor receptor β vascular endothelial growth factor receptor 2 epidermal growth factor porcine aortic endothelial cells Chinese hamster ovary Integrins mediate cell adhesion to extracellular matrix proteins and to other cells. Integrins also initiate intracellular signaling events that control cell shape, migration, proliferation, differentiation, and survival (1Meredith J.E. Schwartz M.A. Trends Cell Biol. 1997; 7: 146-150Abstract Full Text PDF PubMed Scopus (251) Google Scholar, 2Giancotti F.G. Ruoslahti E. Science. 1999; 285: 1028-1032Crossref PubMed Scopus (3869) Google Scholar). Many of the intracellular molecules that mediate integrin signaling also participate in signaling events initiated by soluble growth factors and their transmembrane receptors. Examples of these intracellular molecules include protein kinases, such as c-Src; small GTPases, such as Ras and Rac; phosphatidylinositol 3-kinase; the protein-tyrosine phosphatase SHP-2; and adaptor molecules, such as Shc (3−5). Another form of cross-talk between integrins and growth factor receptors involves physical interaction between the two classes of proteins and potentiation of growth factor signals upon extracellular matrix binding of the interacting integrin (2Giancotti F.G. Ruoslahti E. Science. 1999; 285: 1028-1032Crossref PubMed Scopus (3869) Google Scholar). Integrin interactions with receptor tyrosine kinases (RTKs)1 have been studied in some detail. RTKs are transmembrane proteins with an extracellular domain that binds the ligand and an intracellular kinase domain that becomes autophosphorylated upon binding of the ligand to the receptor. Cell adhesion to fibronectin or to antibodies against the β1 integrin subunit causes autophosphorylation of certain RTKs (6Sundberg C. Rubin K. J. Cell Biol. 1996; 132: 741-752Crossref PubMed Scopus (179) Google Scholar, 7Moro L. Venturino M. Bozzo C. Silengo L. Altruda F. Beguinot L. Tarone G. Defilippi P. EMBO J. 1998; 17: 6622-6632Crossref PubMed Scopus (509) Google Scholar) and shifts their localization to focal adhesions (8Miyamoto S. Teramoto H. Gutkind J.S. Yamada K.M. J. Cell Biol. 1996; 135: 1633-1642Crossref PubMed Scopus (679) Google Scholar), even in the absence of the growth factor ligand. Some RTKs interact physically with integrins. The EGF receptor forms a complex with β1 integrins after cells attach to fibronectin (7Moro L. Venturino M. Bozzo C. Silengo L. Altruda F. Beguinot L. Tarone G. Defilippi P. EMBO J. 1998; 17: 6622-6632Crossref PubMed Scopus (509) Google Scholar). Phosphorylated PDGF-Rβ coprecipitates with αvβ3 but not with β1integrins (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 10Woodard A.S. Garcia-Cardena G. Leong M. Madri J.A. Sessa W.C. Languino L.R. J. Cell Sci. 1998; 111: 469-478Crossref PubMed Google Scholar), similar to the insulin receptor (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 11Vuori K. Ruoslahti E. Science. 1994; 266: 1576-1578Crossref PubMed Scopus (346) Google Scholar) and the VEGF-R2 (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar). Upon stimulation, all of these αvβ3-associated growth factor receptors induce increased proliferation and migration in cells attached to the αvβ3 ligand vitronectin. Hence, RTKs selectively interact with certain integrins, and these interactions result in a synergistic signaling effect. However, little is known about the mechanism of the integrin-RTK interaction. The goal of this study was to localize the sites of the αvβ3 integrin that interact with PDGF-Rβ and VEGF-R2. We show that the extracellular domain of the β3 subunit mediates the interaction with PDGF-Rβ and VEGF-R2, whereas the cytoplasmic and transmembrane regions of the β3 subunit are dispensable. We also find that binding of the growth factor ligand by these RTKs and the resultant phosphorylation of the receptor are not required for the αvβ3 interaction. VEGF-R2 requires the αv subunit for efficient association with αvβ3, whereas PDGF-Rβ does not have this requirement. Polyclonal rabbit antibodies prepared against the cytoplasmic peptides of the β1 and β3 integrin subunits and against purified αvβ3 have been described (11Vuori K. Ruoslahti E. Science. 1994; 266: 1576-1578Crossref PubMed Scopus (346) Google Scholar, 13Suzuki S. Argraves W.S. Pytela R. Arai H. Krusius T. Pierschbacher M.D. Ruoslahti E. Proc. Natl. Acad. Sci. U. S. A. 1986; 83: 8614-8618Crossref PubMed Scopus (154) Google Scholar). Rabbit antibodies against αIIb, PDGF-Rβ, and VEGF-R2 were from Santa Cruz Biotechnology, rabbit antibodies against the β5 integrin subunit were from Chemicon, and the peroxidase-labeled anti-phosphotyrosine antibody, PY20-horseradish peroxidase, was from Transduction Laboratories. Human PDGF-BB and mouse and human VEGF were obtained from R a gift from Dr. Mark Ginsberg) were grown with 10% fetal calf serum in Dulbecco's modified Eagle's medium (DMEM) supplemented with 1 mm sodium pyruvate, glutamine, antibiotics (all from Irvine Scientific), and non-essential amino acids (Life Technologies, Inc.). Cells were transfected with FuGENE 6 (Roche) according to the vendor's protocol. The αIIb/β3 heterodimer cells were disrupted by incubation with 10 mm EDTA in phosphate-buffered saline for 5 min at 37 °C (15Jennings L.K. Phillips D.R. J. Biol. Chem. 1982; 257: 10458-10466Abstract Full Text PDF PubMed Google Scholar, 16Gachet C. Hanau D. Spehner D. Brisson C. Garaud J.C. Schmitt D.A. Ohlmann P. Cazenave J.P. J. Cell Biol. 1993; 120: 1021-1030Crossref PubMed Scopus (44) Google Scholar). After transfection (24 h), cells were starved overnight in Dulbecco's modified Eagle's medium without supplements, except that for experiments with VEGF-R2, 0.5% fetal calf serum was added. For some studies, cells were treated for 1 h at 37 °C with 30 μm AG1296 (Calbiochem), a specific inhibitor of the PDGF-receptor kinases (17Giancotti F.G. Ruoslahti E. Cell. 1990; 60: 849-859Abstract Full Text PDF PubMed Scopus (717) Google Scholar). Cells were stimulated as indicated with 20 ng/ml PDGF or 50 ng/ml VEGF for 5 min at 37 °C, washed once with ice-cold phosphate-buffered saline, and lysed for 15 min in Nonidet P-40 buffer (1% Nonidet P-40, 20 mm Tris-HCl, pH 7.4, 150 mm NaCl, 10% glycerol, 2 mm sodium vanadate, 1 mmphenylmethylsulfonyl fluoride, 10 μg/ml leupeptin, and 5 μg/ml aprotinin). Adherent material was removed from plates with a cell scraper, lysates were centrifuged for 10 min, and supernatants were precleared with Protein A-Sepharose or Gammabind (both from Amersham Pharmacia Biotech) for 30 min. After precleared cell lysates were incubated for 2 h with the indicated antibodies, the antibody complexes were precipitated with 20 μl of Protein A-Sepharose or Gammabind for an additional 2 h. Beads were washed three times with lysis buffer and boiled with gel loading buffer including 50 mm dithiothreitol. Samples were separated on a 4–12% precast polyacrylamide gel (Novex) and transferred to polyvinylidene difluoride membranes (Millipore). Blots were probed with peroxidase-labeled PY20 or with unlabeled primary antibodies followed by horseradish peroxidase-conjugated Protein A. Enzyme activity was detected with ECL plus (Amersham Pharmacia Biotech). Cells transfected with various cDNAs were tested for their ability to migrate to 40 ng/ml PDGF on Boyden chamber filters coated either with 10 μg/ml fibronectin or 10 μg/ml vitronectin as described (11Vuori K. Ruoslahti E. Science. 1994; 266: 1576-1578Crossref PubMed Scopus (346) Google Scholar). Cell attachment was tested in microtiter wells coated with various concentrations of fibronectin and vitronectin (17Giancotti F.G. Ruoslahti E. Cell. 1990; 60: 849-859Abstract Full Text PDF PubMed Scopus (717) Google Scholar). Previous studies have shown that PDGF-Rβ (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 10Woodard A.S. Garcia-Cardena G. Leong M. Madri J.A. Sessa W.C. Languino L.R. J. Cell Sci. 1998; 111: 469-478Crossref PubMed Google Scholar) and VEGF-R2 (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar) associate with the αvβ3 integrin but not with β1integrins. The association was detected after cells were stimulated with the respective growth factor. We have studied these interactions in PAE and CHO cells transfected with integrin subunits and PDGF-Rβ or VEGF-R2. Both cell lines express only minor amounts of endogenous β3 and PDGF-Rβ (Fig. 2 A) and no detectable VEGF-R2 (Fig. 2 B). These cells were transfected with cDNAs of αv and β3 together with PDGF-Rβ (PAE) or with VEGF-R2 (CHO). The β3 integrin was precipitated with antibodies directed against its cytoplasmic tail, and the immunoprecipitates were probed for the presence of the RTKs by immunoblotting. PDGF-Rβ (Fig. 2 A) and VEGF-R2 (Fig. 2 B) could only be detected in anti-β3precipitates from cells that had been transfected with the αv and β3 subunits. Because our anti-β3 antibody reacts with β3 of a number of species (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 18Kovalenko M. Gazit A. Bohmer A. Rorsman C. Ronnstrand L. J. Bohmer A. 1994; Google Scholar), is that the of β3 in CHO and PAE cells is for the endogenous αvβ3 to detectable amounts of the against purified the RTKs from the cells as the anti-β3 not of cells with the respective growth factor promotes the association of PDGF-Rβ (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar) and VEGF-R2 (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar) with the αvβ3 integrin. We that the of VEGF-R2 with the β3 integrin in CHO cells was of VEGF stimulation (Fig. the phosphorylation of VEGF-R2 precipitated from starved and cells. VEGF-R2 from the cells was These results show that ligand binding and phosphorylation of VEGF-R2 are not required for the receptor to interact with αvβ3 in these transfected CHO cells. The cells transfected with PDGF-Rβ and the integrin subunits phosphorylation of PDGF-Rβ even after h of phosphorylation of the PDGF-Rβ is required for its interaction with αvβ3, we the transfected CHO cells with AG1296 M. Gazit A. Bohmer A. Rorsman C. Ronnstrand L. J. Bohmer A. 1994; Google Scholar), a specific inhibitor of PDGF-receptor to receptor amounts of PDGF-Rβ were with αvβ3 (Fig. A) of AG1296 or PDGF stimulation, even AG1296 the PDGF-Rβ phosphorylation (Fig. B). We that ligand binding and phosphorylation are not for PDGF-Rβ and VEGF-R2 to interact with the αvβ3 at when the of the are at in cells. study the of the interaction on the we to the integrin subunit that mediates of the RTKs were with αv and either the β3 or β5 subunit CHO cells. The β3 and β5 subunits form with Both RTKs with not with β5 (Fig. result with results for VEGF-R2 (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar), and that the β3 subunit is for interaction with the study the of αv in the of the we transfected PDGF-Rβ CHO cells that the integrin shown in 5 amounts of PDGF-Rβ were with and anti-β3 the that αv a and that for in the binding of PDGF-Rβ, we disrupted of the heterodimer with EDTA to shown in 5 of some of the not the of PDGF-Rβ with the However, the the of PDGF-Rβ with the antibody (Fig. 5 to EDTA only disrupted a of the heterodimer (15Jennings L.K. Phillips D.R. J. Biol. Chem. 1982; 257: 10458-10466Abstract Full Text PDF PubMed Google Scholar, 16Gachet C. Hanau D. Spehner D. Brisson C. Garaud J.C. Schmitt D.A. Ohlmann P. Cazenave J.P. J. Cell Biol. 1993; 120: 1021-1030Crossref PubMed Scopus (44) Google Scholar). These show that the subunit is not for the interaction of the β3 integrins with to PDGF-Rβ, VEGF-R2 not with the integrin. antibodies against the subunit against the VEGF-R2 from the CHO cells transfected with this RTK (Fig. 5 that this of is to the of endogenous we transfected the CHO cells with αv together with VEGF-R2 to amounts of αvβ3 these cells, VEGF-R2 could be with anti-β3 but not with These show that VEGF-R2 only associate with the αvβ3 whereas PDGF-Rβ form complexes with the αvβ3 association of PDGF-Rβ requires only the β3 whereas association with VEGF-R2 requires the αv and β3 subunits. the RTKs have or binding sites on αvβ3, we PDGF-Rβ to study the ability of VEGF-R2 to associate with a of PDGF-Rβ of VEGF-R2 with (Fig. 6 only PDGF-Rβ was in the β3 immunoprecipitates (Fig. 6 B). VEGF-R2 not the of PDGF-Rβ with αvβ3 (Fig. 6 B) even when VEGF-R2 was in not A in the binding of the two RTKs for the integrin this of by VEGF-R2. which of the mediates the RTK we a β3 subunit that of the cytoplasmic domain (Fig. 1). subunit to induce signaling focal or cell A. Pierschbacher M.D. F. Ruoslahti E. J. Cell Biol. 1993; PubMed Scopus Google Scholar) but forms with αv that mediate cell adhesion to vitronectin. from CHO cells transfected with β3 or its cytoplasmic together with αv and VEGF-R2 similar amounts of αvβ3-associated VEGF-R2 of the presence or absence of the β3 cytoplasmic domain (Fig. VEGF-R2 was without of a β3 an absence of β3 subunit. were obtained with These results that the cytoplasmic domain of β3 is not for the interaction of αvβ3 with VEGF-R2 and the result with the cytoplasmic domain and to study the of the transmembrane we of the that PDGF-Rβ and VEGF-R2 do not with β1 integrins. of the β3 subunit in which the cytoplasmic and transmembrane domains came from subunit and the extracellular domain from the other (Fig. with the αv subunit. result was shown by with antibodies from CHO cells transfected with αv and the various not Both PDGF-Rβ and VEGF-R2 with the chimera containing the domain (Fig. against the cytoplasmic of the β1 subunit and antibodies against purified human αvβ3 the RTKs (Fig. and not the RTKs not with the which of the cytoplasmic and transmembrane regions of β3 and the extracellular domain of or β1 (Fig. The chimera was precipitated with an antibody against the cytoplasmic domain of These show that the extracellular domain of the β3 subunit is sufficient for the interaction of αvβ3 with the We have shown that the attachment of cells to a the αvβ3 integrin the ability of insulin and PDGF to cell proliferation and migration (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 11Vuori K. Ruoslahti E. Science. 1994; 266: 1576-1578Crossref PubMed Scopus (346) Google Scholar). We the migration to the ability of the β subunit to PDGF Cells transfected with β subunit containing the β3 extracellular domain and the PDGF-Rβ to PDGF with increased migration, whereas cells with the β1 extracellular domain not (Fig. was on vitronectin and fibronectin indicated that of the cell lines attached to vitronectin and fibronectin for The attachment to fibronectin was for of the three cell The cells attached to coated with concentrations of vitronectin the other two lines but attached at the in the migration not These results show that the effects on RTKs with the presence of the the domain that also mediates the physical interaction of the αvβ3 integrin with The in this is that PDGF-Rβ and VEGF-R2 associate with the extracellular domain of the subunit. binding and phosphorylation of the RTKs do not to be required for the integrin interaction. results studies that have shown a specific association of PDGF-Rβ (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 10Woodard A.S. Garcia-Cardena G. Leong M. Madri J.A. Sessa W.C. Languino L.R. J. Cell Sci. 1998; 111: 469-478Crossref PubMed Google Scholar) and VEGF-R2 (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar) with the However, our results from that indicated the interaction only after cells are stimulated with the growth factor. we the association to be of growth factor stimulation and phosphorylation of the be that the of the of the complex was in the and that this the of the interaction. of cells with growth factors localization of RTKs to focal (8Miyamoto S. Teramoto H. Gutkind J.S. Yamada K.M. J. Cell Biol. 1996; 135: 1633-1642Crossref PubMed Scopus (679) Google Scholar), the at sites of integrins. increased have the of the integrin-RTK complexes that were in the results show that the β3 subunit is to the RTK association of the αvβ3 integrin. result with studies that other β which form with such as do not associate with PDGF-Rβ or VEGF-R2 (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar). A in the is that the is for integrin association of VEGF-R2. PDGF-Rβ, VEGF-R2 was not with the integrin or with separated from result that the two RTKs interact with the β3 integrins and that the integrin the to PDGF-Rβ but not to VEGF-R2. The of the interaction between PDGF-Rβ and to be The that of PDGF-Rβ the association of VEGF-R2 with αvβ3, whereas the was not the also in the two RTKs interact with A is that the integrin-RTK association is by the extracellular domain of the β3 subunit of the integrin. factor stimulation RTK phosphorylation in the intracellular a of signaling molecules are to the in the of intracellular Integrins also form intracellular which of signaling molecules and in to ligand These complexes in focal that the molecules of these complexes together the integrins and the However, our integrin and experiments show that the cytoplasmic domain of the β3 integrin is not required for association with the RTKs and that the interaction is by the extracellular domain of the β3 subunit. is by the that phosphorylation of the receptors is not for their association with the αvβ3 integrin. Furthermore, as of the β3 cytoplasmic domain the integrin from in focal adhesions A. Pierschbacher M.D. F. Ruoslahti E. J. Cell Biol. 1993; PubMed Scopus Google Scholar), focal adhesions do not to be for the interaction of PDGF-Rβ or VEGF-R2. The nature of the complex containing αvβ3 and the RTKs is Both interaction and binding by a are for a is the protein or which is a transmembrane protein that selectively with the extracellular domain of the β3 integrin subunit E. C. S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). for RTKs to associate with integrins is focal adhesion which binds to PDGF-Rβ and E. J. Cell Biol. 1993; PubMed Scopus Google Scholar). However, as this interaction is not specific for the β3 integrin is from the interaction described and is to for the of β3 integrins with The association of integrins with RTKs is the ability of the receptors for and VEGF to to their growth factor ligands by increased cell proliferation and migration is in the presence of αvβ3 that to of its extracellular matrix ligands (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar, 10Woodard A.S. Garcia-Cardena G. Leong M. Madri J.A. Sessa W.C. Languino L.R. J. Cell Sci. 1998; 111: 469-478Crossref PubMed Google Scholar, 11Vuori K. Ruoslahti E. Science. 1994; 266: 1576-1578Crossref PubMed Scopus (346) Google Scholar, R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar). The results show that the ability of the αvβ3 integrin to the activity of PDGF-Rβ in cell migration is on the β3 subunit extracellular result that the integrin RTK extracellular domain interactions we are the physical of the between αvβ3 and The integrin-RTK for cell attachment to induce an RTK of the growth factor ligand. Cells that attach to fibronectin ligand of show autophosphorylation of PDGF-Rβ (6Sundberg C. Rubin K. J. Cell Biol. 1996; 132: 741-752Crossref PubMed Scopus (179) Google Scholar) and of the receptor to focal (8Miyamoto S. Teramoto H. Gutkind J.S. Yamada K.M. J. Cell Biol. 1996; 135: 1633-1642Crossref PubMed Scopus (679) Google Scholar). of RTKs to focal adhesions the that a of PDGF-Rβ is with αvβ3 (9Schneller M. Vuori K. Ruoslahti E. EMBO J. 1997; 16: 5600-5607Crossref PubMed Scopus (426) Google Scholar). of PDGF-Rβ also to as shown for the and β1 integrins (7Moro L. Venturino M. Bozzo C. Silengo L. Altruda F. Beguinot L. Tarone G. Defilippi P. EMBO J. 1998; 17: 6622-6632Crossref PubMed Scopus (509) Google Scholar). These interactions are to be of growth factor activity in Both the αvβ3 integrin and two of the VEGF-R2 and PDGF-Rβ, are to D. E. Cell Biol. PubMed Scopus Google Scholar, M. T. G. D.A. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar). of the mechanism the αvβ3 integrin-RTK lead to the of for the activity of these growth (12Soldi R. Mitola S. Strasly M. Defilippi P. Tarone G. Bussolino F. EMBO J. 1999; 18: 882-892Crossref PubMed Scopus (539) Google Scholar) have shown that antibodies VEGF-R2 phosphorylation and cell migration when endothelial cells are to the vitronectin. these antibodies do not with cell the association between the αvβ3 integrin and VEGF-R2. antibodies, and other of with this integrin-RTK could be in such as that in and the We Dr. Carl-Henrik for PDGF-Rβ Dr. Georg for the VEGF-R2 and Dr. Mark for the CHO cells.