Inhibition of PP2A induces Mnk-dependent eIF4E phosphorylation (A-C) independent of ERK, p38, or PI3 kinase (B and D). (A) H157 cells were pretreated with the indicated concentrations of CGP57380 for 30 minutes and then cotreated with 100 nM OA for an additional 4 hours. (B) H157 cells were plated on six-well plates and, the next day, were transfected with 20 nM control (Ctrl) or PP2Ac siRNA. After 20 hours, the cells were exposed to 20 µM of the indicated inhibitors for an additional 4 hours. (C) The indicated cell lines were treated with 100 nM OA for 4 hours. (D) The indicated cell lines were pretreated with 20 µM U0126, SB203580, or LY294002 for 30 minutes and then cotreated with 100 nM OA for an additional 4 hours. After the aforementioned treatments, the cells were harvested for preparation of whole-cell protein lysates and subsequent Western blot analysis.