Rapid Activation of Rac GTPase in Living Cells by Force Is Independent of Src
Figure 7
Cytosketal integrity is necessary for Rac activation by stress.
(A) Inhibition cytoskeletal tension with blebbistatin (Blebb, 50 µM for 30 min, n = 7 cells), disrupting F-actin with cytochalasin D (CytoD, 1 µg/ml for 15 min, n = 6 cells) or microtubules with colchicine (Colch, 10 µM for 15 min, n = 9 cells), blocks stress-induced Rac activation in SYF−/− MEFs. Mean+/−s.e. (B) A working model for rapid Rac activation by stress. A local load (magnetic bead) applied to focal adhesions leads to stress propagation along the actin bundles (red lines) without decay in magnitudes at remote sites. Rac GTPase bound to the plasma membrane at the other end of the cell are activated rapidly when stress waves reach the plasma membrane via the cytoskeleton to directly deform Rac, causing a conformational change in the enzyme. MF = actin microfilament; MT = microtubule; IF = intermediate filament; SF = stress fiber; N = nucleus (not drawn to scale). Black dot = the magnetic bead. White arrow = magnetic moment direction of the magnetized bead. Curved black arrow = the rotational shear stress.