Mechanisms of constitutive NF-κB activation in human prostate cancer cells

BACKGROUND. Activation of the NF-κB transcription factor has been previously demonstrated in two androgen receptor negative prostate cancer cell lines. We wished to extend this work to additional prostate cancer cells and to characterize the mechanisms responsible for constitutive NF-κB activation. METHODS. Electrophoretic mobility shift assays were performed to measure NF-κB DNA-binding activity in prostate cancer cell lines, and immunohistochemistry was performed to detect nuclear localization of NF-κB in prostate cancer tissues. Western blot analysis was used to study the status of IκBα. Transient transfection assays were employed to characterize the contributions of IκB kinase (IKK), MAPK kinase kinases (MAPKKKs), androgen receptor (AR), and tyrosine phosphorylation to the constitutive activation of NF-κB in the prostate cancer cell lines. RESULTS. Constitutive NF-κB activity was observed in AR-negative cell lines as well as in the prostate cancer patient samples, but was not present in AR positive cells. A "super-repressor" IκBα, as well as dominant negative forms of IKKκ and NF-κB-inducing kinase (NIK), and tyrosine kinase inhibition were able to suppress NF-KB activity in the cells with constitutive activation. CONCLUSIONS. The constitutive activation of NF-κB observed in prostate cancer cells is likely due to a signal transduction pathway involving tyrosine kinases, NIK, and IKK activation.