ERG is phosphorylated at S215 by the RAS/MEK/ERK pathway in prostate epithelial cells. (A) Immunoblot of purified ERG protein with phospho-S215 pERG antibody after phosphorylation by ERK, or mock treatment. (B) Immunoblot with pERG or total ERG antibodies of whole cell extract, or protein immunoprecipitated with Flag antibody from Flag-ERG expressing RWPE1 cells. Immunoprecipitates were treated with alkaline phosphatase as indicated. (C, D, E) Immunoblots as in (B), but from RWPE1 cells stably expressing the indicated ERG construct. (F) Immunoblots as in (B), but from cells treated with the indicated inhibitors, or DMSO as a negative control.