FIGURE 4.

Cell adhesion to laminin enhances physical association of CD151-β₁ integrin complexes with Ras, Rac1, and Cdc42. A and B, stable MelJuSo mock (M) and CD151 transfectant cells (A) and parental C8161 cells (B) were seeded onto plates precoated with laminin (LN) or poly-l-lysine (pL) for 24 h. Following 60 min of serum starvation, the cells were treated with membrane fragments of mock (M) or CD151 (CD) transfectant MelJuSo cells for 60 min. Immunoprecipitation and immunoblotting analyses were performed in the same manner as in Fig. 1A. C, the CD151-transfected MelJuSo cells were suspended into serum-free medium and mixed with normal IgG or anti-β₁ integrin blocking mAb (6S6; 20 μg/ml) in end-over-end fashion for 60 min. Twenty-four hours after seeding onto laminin- or poly-l-lysine-coated plates, cell lysate with Brij 97 was subjected to immunoprecipitation with anti-CD151 Ab followed by immunoblotting analysis with Abs against Ras, Rac1, or Cdc42. Numbers below the immunoblot indicate the relative band intensity and are the mean of three immunoblots obtained from separate experiments.