Fig. 6. PTP-PEST is required to regulate Rac1 activity. PTP-PEST null fibroblasts (PTP-PEST -/-) or null fibroblasts that re-express PTP-PEST (PTP-PEST RE) were maintained in suspension or plated on FN in serum-free medium for 30, 60 or 120 minutes. Rac1 activity was determined using the GST-PBD pulldown assay. In cells that re-express PTP-PEST (left), Rac1 is transiently activated by adhesion to FN within 30 minutes and then returns to baseline. In PTP-PEST -/- cells (right), Rac1 is activated by adhesion after 30 minutes to a greater degree than in control cells. This elevated activity is sustained throughout the time course.