Figure 5.

Rac activation overcomes the antagonizing effect of Gsn^- on collagen bead binding. (A and B) Gsn^- and WT cells were transfected with cDNA constructs for constitutively active rac (rac Q61) or for a dominant negative rac (rac N17) both of which express a c-myc tag. Cells were plated on collagen-coated beads for 1 h, washed, and fixed. Transfected cells were distinguished by immunostaining for c-myc. Rac activation enhances more than twofold collagen bead binding in Gsn^- cells and increases collagen bead binding to levels similar to that of untransfected WT cells. The dominant negative rac construct reduces collagen bead binding to very low levels in both Gsn^- and WT cells. (C) Immunoblots for indicated proteins using PAK binding assay described in Figure 4. Gsn^- cells were transfected with gelsolin expression vector as indicated and incubated with collagen beads (or not). Note that only in cells transfected with gelsolin and incubated with collagen beads is there detectable activation of rac.