FIG. 4.
Rac1 activation requires β1Pix homodimerization. Cells were transfected with empty vector, Myc-β1Pix, or Myc-β1PixΔ(602-611) in serum-free DMEM for 24 h. GTP-bound Rac1 (A) and GTP-bound Cdc42 (C) were measured using a pulldown assay as described in Materials and Methods. Positive and negative controls show the GTP-bound Rac1 (or Cdc42) in the presence of 100 μM γ-S-GTP or GDP, respectively. Anti-Myc (bottom) shows the expression of β1Pix constructs. (B) Quantitative analysis of Rac1-GTP bands was obtained by densitometry. Results are expressed as means ± standard errors for three independent experiments. Statistical significance was analyzed by a paired Student's t test. *, P < 0.05 compared with Rac1-GTP levels measured in cells transfected with β1Pix.