A PI3K-PDK1 signaling axis mediates the effects of PI3K signaling in lapatinib-resistant cells. A comparison of the effects of siRNA-mediated knockdown of Akt, PDK1, PKCβ, and SGK on the growth of rBT474 cells. Cells transfected with scrambled siRNA construct (NSC) served as controls. Growth assays were performed as described in Methods. Knockdown of targeted protein was confirmed by Western blot analysis (lower panels). Actin steady-state protein levels served as a control to ensure equal loading of protein. Results represent the mean ± standard error of triplicate samples and are representative of three independent experiments. *P < 0.005; **P < 0.002.