Endothelial cell attachment and spreading on human tenascin is mediated by α₂β₁ and α_Vβ₃ integrins

Human umbilical vein endothelial cells were found to attach and partially spread on human tenascin. The attachment of endothelial cells to tenascin results in elongated cells with interconnecting processes and is distinct from the flattened appearance of endothelial cells on fibronectin, collagen, vitronectin or laminin substrata, suggesting a role for tenascin in modulating cell adhesion and motility. Endothelial attachment to tenascin was partially inhibitable by the SRRGDMS peptide derived from human tenascin and completely inhibitable by anti-integrin antibodies to α₂β₁ and α_Vβ₃. Endothelial cell attachment to tenascin could be inhibited up to 80% with anti-α₂ and anti-β₁ monoclonal antibodies P1E6 and P4C10, respectively, and this was associated with a complete loss in cell spreading. In contrast, pretreatment of endothelial cells with the anti-α_Vβ₃ monoclonal antibody LM609, resulted in a 35% inhibition in cell attachment but did not alter cell spreading. In combination the anti-α₂ and anti-α_Vβ₃ antibodies, could completely abrogate cell spreading and attachment to tenascin-coated surfaces. Affinity purification of ¹²⁵I-labeled endothelial cell extract on a tenascin matrix column followed by immunoprecipitation with monoclonal antibodies to different integrin α and β subunits resulted in the identification of α₂β₁ and α_Vβ₃ integrins, respectively, as tenascin binding receptors. Collagen affinity-purified α₂β₁ receptor from endothelial cells bound not only to collagen and laminin but also to tenascin in a radio receptor binding assay. The results demonstrate that α₂β₁ and α_Vβ₃ mediate distinct endothelial cell interactions with tenascin; cell spreading and cell binding, respectively. Binding by α_Vβ₃ is mediated by the SRRGDMS site on tenascin, whereas the α₂β₁ binding site remains undefined. The interaction of α₂β₁ and α_Vβ₃ with tenascin may be regulated in a cell type-specific manner as evidenced by the binding of endothelial cell α₂β₁ and α_Vβ₃ to tenascin, and the lack of binding by the same receptors on osteosarcoma MG63 to tenascin.