A) MCF-7 cells over expressing HA-tagged PAK1 were serum-deprived, pre-treated with or without 20 μM DIF-3 over a time course and stimulated with or without PRL (200 ng/ml, 20 min) to activate PAK1. HA-PAK1 was immunoprecipitated with anti-HA Ab, subjected to an in vitro kinase assay using H4 histone as a substrate and probed with anti- HA Ab. Relative PAK1 kinase activity was then normalized by the amount of PAK1 immunoprecipitated in each lane. The numbers at the bottom give the relative fold increase of 32P incorporation into H4 histone. The migrations of proteins are indicated.
B) MCF-7 PAK1 cells were serum-deprived, pre-treated for 2 h with vehicle or 20 μM DIFs and their derivatives as indicated, followed by PRL treatment (200 ng/ml, 20 min). In vitro kinase assay was performed as described in A.