Endorepellin evokes tyrosine phosphatase activity in an integrin α2β1–dependent manner. (A) Endorepellin induces dynamic changes in the ability of HUVECs to dephosphorylate phospho-tyrosine peptides. Cells were incubated with Na₃VO₄ (1μM) 1 hour before endorepellin stimulation. (B) Tyrosine phosphatase activity of primary cultures of pulmonary microvascular endothelial cells isolated from either wild-type, α1β1^−/−, or α2β1^−/− mice. The cells were exposed for 5 minutes to endorepellin (25nM). Means ± SEMs (n = 3); **P < .01, ***P < .001. (C) An in vitro kinase assay showing that endorepellin induces a dynamic activation of enzymes responsible for VEGFR2 dephosphorylation. Immunoprecipitated phosphorylated VEGFR2 was exposed to lysates from HUVECs before being treated with endorepellin (100 nM) for the indicated time. Means ± SEMs of the relative VEGFR2 phosphorylation compared with time point 0 (n = 3); *P < .05, **P < .01. (D) Relative tyrosine phosphatase activity of wild-type or α2β1⁺ C2C12 cells after a 5-minute incubation with endorepellin (25nM). Means ± SEMs (n = 3); ***P < .001. (E) Adhesion of wild-type or α2β1⁺ C2C12 to collagen after a 30-minute incubation with endorepellin (25nM). Mean number of cells ± SEM (n = 3); ***P < .001. (F) Relative tyrosine phosphatase activity of murine UB epithelial cells after a 5-minute exposure to endorepellin (25nM). These cells include wild-type cells, which express undetectable levels of collagen-binding integrins, cells expressing the α2β1⁺, and cells expressing a chimeric integrin composed of the ectomembrane and transmembrane domains of the α2 subunit fused to the intracellular domain of the α1 subunit, designated α2(α1)β1. Means ± SEMs (n = 3); ***P < .001. (G) Conditioned medium-directed migration through collagen of wild-type, α2β1⁺, and α2(α1)β1 UB cells after a 20-minute exposure to endorepellin (25nM). Mean number of migrated cells ± SEM (n = 3); ***P < .001.