Regulation of IKKe expression by androgen receptor and NF-kB transcriptional factor in prostate cancer

Abstract

10106 Background: In unstimulated cells, NF-kB transcription factor is sequestered in the cytoplasm as an inactive p65/p50 dimer through interaction with a member of the inhibitor of kB protein family (IkBa). Prominent constitutive activation of NF-kB was observed in prostate cancer (PCa) cell lines lacking androgen receptor (AR) expression (PC3 and DU145) whereas only very low levels of NF-kB activity were seen in androgen-dependent cell lines (LNCaP and CWR22Rv1). As IkB kinase-e (IKKe) has recently been shown to be controlled by NF-kB, we hypothesize that IKKe may be involved in PCa progression based on its interaction with the NF-kB protein, and that these interactions are influenced by AR signaling. Methods: LNCaP cells were used to study IKKe expression with or without stimulation by the analog of androgen R1881 and by the tumor necrosis factor (TNF)-a. IKKe protein and RNA expression were characterized by immunoblot assay and quantitative PCR, respectively. IKKe expression was then correlated with p65 nuclear localisation. NF-kB activity was inhibited using an IkBa dominant negative construction. Inhibition of AR synthesis was performed using a siRNA against AR. Results: IKKe gene expression was stimulated by TNF-a treatment in LNCaP cells and inhibited by transfection of a dominant negative form of IkBa which prevented the nuclear translocation of p65. We also observed constitutive IKKe expression in hormone-refractory cells. Furthermore, we showed that TNF-a-induced IKKe expression is inhibited by R1881 in hormone-responsive PCa cells and this inhibition was correlated with the modulation of IkBa expression by R1881. Finally, we observed that the expression of IKKe is constitutively induced after blocking AR expression in LNCaP cells. Conclusions:. Our results show that IKKe expression is regulated by NF-kB in PCa cell lines. Moreover, IKKe appears to be down-regulated by ligand-dependent AR signaling through the control of IkBa expression. Further studies will be needed in order to determine the implications of this phenomenon with regard to NF-kB regulation, androgen resistance and effect on PCa progression. No significant financial relationships to disclose.