Group I PAKs regulate thyroid cancer cell migration. (A) All six thyroid cancer cell lines were transfected with GFP-tagged PID construct, a group I PAK-specific inhibitor. Transfection efficiencies were w40–60%; PID transfection reduced migration by more than 50% compared to vector control in all six human thyroid cancer cell lines. *Signifies statistical significance; P values were 0.0025 for BCPAP, 0.018 for KTC1, <0.0001 for TPC1, 0.0091 for FTC133, 0.0121 for C643, and 0.0054 for SW1736. (B) MTT assays were performed to examine cell viability. There was no difference between cells transfected with control vector and PID vector. (C) Phosphorylation status of two downstream targets of group I PAKs was examined by antibody against PAK-specific phosphorylation site using FTC133 cells. PID transfection reduced phosphorylation of both cRAF and vimentin without changing total protein levels to a level that corresponds with transfection efficiency.