FIGURE 8.

Complex formation between β₁ integrins and small GTPases and adhesion-dependent activation of the GTPases occurs in CD151-expressing cells but not in CD9-, CD81-, and CD82-expressing cells. 293 cells were transiently transfected with expression vectors encoding CD9, CD81, CD82, or CD151. A, expression level of each tetraspanin in the transfectant cells was assessed by immunoblotting analysis. B, C, D, and E, the transfectant cells were seeded onto plates precoated with laminin (LN) or poly-l-lysine (pL) for 24 h. B, cell lysate with Brij 97 was subjected to immunoprecipitation with an anti-β₁ integrin Ab followed by immunoblotting analysis using Abs against Ras, Rac1, or Cdc42. C, phosphorylation levels of FAK in cell lysates were compared by immunoblotting analysis using anti-phospho-FAK^(Tyr-925) Ab. D and E, GTP-loaded Ras (D) and Rac1 (E) proteins in cell lysates were examined in the same manner as in Fig. 5. Bar graphs indicate relative band intensity of the GTP-bound form normalized to total protein level and show the mean ± S.D. (error bars) of three immunoblots obtained from separate experiments.