Dysregulation of Maspin expression and constitutive activation of NF-κB subunits are important events in tumorigenesis of prostate cancer. Recent finding points that RelB, which contributes to the alternative NF-κB activity, interferes with carcinogenesis in the prostate. We report here, that both the classical and the alternative NF-κB activities are constitutively present in androgen-insensitive human prostate cancer cells. Maspin and RelB expression is correlated negatively in prostate cancer tissues at the later stage. TNF-α signaling triggers the nuclear accumulation of RelB and the concomitant reduction of Maspin expression in a time-dependent manner. In addition, the proteasome inhibitor-induced Maspin expression is accompanied by the reduction of RelB expression. A successful depletion of RelB expression, but not RelA expression, induces Maspin expression. RelB-deficiency abrogates the proteasome inhibitor-induced Maspin expression. Moreover, we demonstrate that the enforced expression of RelB protein in prostate cancer cells inhibits Maspin expression. We propose that RelB is an essential molecule controlling the endogenous and the proteasome inhibitor-induced Maspin expression. Developing a RelB-targeted therapeutic intervention, which might be coupled with the induction of a tumor suppressor Maspin, is valuable in treating advanced, metastatic prostate cancer.
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