PP2A activity is significantly inhibited by in vivo OA and fostriecin treatment.

(A) Phosphatase activity in lysates of cells treated with 0.5 μM OA (OA) using either ³²P-labeled phosphorylase a (upper panel) or ³²P-labeled histone H1 (lower panel) as substrate. (B) Phosphatase activity in lysates of cells treated with 5 μM fostriecin (fostriecin) using ³²P-labeled phosphorylase a as substrate. Cells exposed to vehicle alone (untreated) were used as controls. Assays were performed with further addition of vehicle alone (▪), 5 nM OA (▨), or 1 μM OA (■) to the lysates. Activities were expressed as a percentage of ³²P release in untreated lysates. Data shown were mean ± SD of triplicate assays from at least 2 separate experiments.