FIGURE 4.

Calpain-mediated cleavage of the cytoplasmic domain of integrin β₃ is dependent on CypD. A and B, washed CypD^+/+ or CypD^−/− platelets were stimulated for 5 min with the indicated agonist(s) with or without MDL28170 (50 μm) or Q-VD-Oph (QVD) (50 μm), and cleavage of the integrin β₃ cytoplasmic tail (C-20) and talin was assessed by Western blot analysis (0.5 units/ml Thr, 100 ng/ml Cvx, and 1 μm Iono). B, quantification of integrin β₃ cleavage. Intensity of C-20 binding was assessed relative to unstimulated platelets. *, p < 0.05 compared with untreated platelets; #, p < 0.05 to relative to CypD^+/+. n = 3. C, washed CypD^+/+ or CypD^−/− platelets were stimulated for 5 min with the indicated agonist(s) ± MDL and assessed by Western blot analysis using antibodies specific to the integrin β₃ cytoplasmic tail (C-20) and integrin β₃ extracellular domain (N-20). *, p < 0.05 relative to unstimulated, #, p < 0.05. D, kinetics of integrin β₃ cleavage in CypD^+/+ and CypD^−/− platelets stimulated with thrombin and convulxin. *, p < 0.05. n = 3. Intensity of C-20 binding was assessed relative to unstimulated platelets.