Activation of extracellular signal-regulated kinase in human prostate cancer

Purpose: To investigate the level of expression, activation state, and functional significance of extracellular signal regulated kinase (ERK) in prostate cancer. Materials and Methods: Human prostate tissue samples (n = 22) were obtained from patients undergoing radical prostatectomy for localized adenocarcinoma of the prostate (n = 16, age range 44 to 72 years) or normal prostate specimens (n = 6, age ranges 19 to 47 years) obtained from rapid autopsy. Immunoblots, in vitro kinase assays, and immunohistochemistry were used to determine the expression and activation state of ERK in human prostate cancer. Results: Immunoblot and in vitro kinase assays demonstrated a 15-fold increase in ERK activation in prostate cancer specimens compared with normal human prostate tissue; however, ERK expression levels were only 1.3-fold higher in cancer. Immunohistochemical analysis demonstrated similar expression of ERK in cancer and normal tissues; however, phosphorylated ERK demonstrated greater intensity in the cancer specimens. Experiments conducted on a prostate cancer cell line demonstrated that EGF induced activation of ERK and cellular proliferation was partially inhibited by PD98059, a chemical inhibitor of the immediate upstream signaling component responsible of activation of ERK. Conclusions: Collectively, these data demonstrate a dramatic increase in ERK activation in prostate cancer compared with normal prostate tissue and suggest that inhibitors designed to target this signal transduction cascade might have therapeutic benefit in the treatment of prostate cancer.