PI3K-dependent membrane association of PDK1 in PIK3CA-mutant cells. (A) Fluorescence microscopy of transient PH-PDK1-GFP expression is shown for serum-starved “wild-type” (DU145), PTEN-null (786−0), PIK3CA-mutant cells with low p-AKT (MCF-7 and SW-948) and PIK3CA-mutant cells with high p-AKT (HCC1954 and T47D). Scale bars = 30 μM. (B) Immunoblotting studies of cytosolic (Cy) and membrane (M) fractions prepared from serum-starved “wild-type” (ACHN), PTEN-null (786−0), or PIK3CA–mutant cells (MCF-7, HCT-15, and HCC-1954) are shown. (C) Immunoblotting studies of cytosolic (Cy) and membrane (M) fractions prepared following shRNA knockdown of p110α (sh-PIK3CA) or control (sh-GFP) in serum-starved MCF-7 cells. (For (B) and (C), Antibodies recognizing p-AKT (S473), AKT1, p-PDK1 (S241), PDK1, Cadherin and GAPDH were used.) (D) Quantification of the immunoblot signal is shown as a normalized ratio of membrane/cytosolic PDK1 (total) for the blot in (C) above.