Cdc42 regulates β1 integrin expression levels. PC3 cells were transfected with the indicated siRNAs. (A) FACS analysis for β1 integrin. A representative FACS histogram (left) and quantification of FACS analyses (right) are shown; n ≥ 3. (B) Cell lysates were immunoblotted for Cdc42, β1 integrin, and GAPDH expression. A representative blot is shown (left), as is a quantification of three independent blots for β1 integrin (right). (C) Representative images of cells fixed and stained with DAPI (blue), for F-actin (red) and β1 integrin (green). Arrows indicate actin-rich protrusions. Boxed regions are magnified in the “zoom” column. Bar, 50 µm. (D) Quantification of β1 integrin localization in F-actin–rich protrusions, n = 3. (E) FACS analysis for β1 integrin after Cdc42 depletion and reexpression of a Cdc42-siRNA–resistant-cDNA; n = 3. Values are means ± SEM (error bars); *, P < 0.05; **, P < 0.01; ***, P < 0.001. See also Fig. S6.