Figure 4: Integrin-dependent plasminogen activation on the cell surface. Parental CHO cells and 𝛽 3 -CHO cells in wells of 96-well plates were treated with PIPLC to deplete uPAR, and incubated with wt or delta kringle ( Δ 𝐾 ) uPA in the cold binding buffer for 1 h at 4°C. The cells were washed with the binding buffer, and plasminogen activation was determined using Glu-plasminogen and SpectrozymePL chromogenic substrate at 37°C. We found that 𝛽 3 -CHO cells showed much higher ability to activate plasminogen in a manner dependent on the uPA added. Deletion of the kringle domain (with Δ 𝐾 -uPA) markedly reduced the plasminogen activation on 𝛽 3 -CHO, indicating that 𝛼 v 𝛽 3 and uPA-dependent plasminogen activation required the kringle domain of uPA. These results suggest that the binding of uPA kringle to integrin 𝛼 v 𝛽 3 induces plasminogen activation [38].