IκB-Kinase-epsilon (IKKε) over-expression promotes the growth of prostate cancer through the C/EBP-β dependent activation of IL-6 gene expression

Abstract

The inflammatory cytokine IL-6 has been shown to induce the nuclear translocation of androgen receptors in prostate cancer cells and to activate the androgen receptors in a ligand-independent manner, suggesting it may contribute to the development of a castrate-resistant phenotype. Elevated IL-6 serum levels have also been associated with metastasis-related morbidity in prostate cancer patients. We have previously established that over-expression of I-kappa-B-kinase-epsilon (IKKε also named IKKi or IκBKε) in hormone-sensitive prostate cancer cell lines induces IL-6 secretion. We have also reported that prostate cancer cell lines lacking androgen receptor expression exhibit high constitutive IKKε expression and IL-6 secretion. In the present study, we validated the impact of IKKε depletion on the in vitro proliferation of castrate-resistant prostate cancer cells, and characterized how IKKε depletion affects tumor growth and IL-6 tumor secretion in vivo through a mouse xenograft-based approach. We observed a significant growth delay in IKKε-silenced PC-3 cells injected in SCID mice fed with a doxycycline-supplemented diet in comparison with mice fed with a normal diet. We also found a decrease in IL-6 secretion levels that strongly correlated with tumor growth inhibition. Finally, using constructs with various IL-6-mutated promoters, we demonstrated that IKKε over-expression induces a NF-κB-independent stimulation of the IL-6 gene promoter through the activation and nuclear accumulation of the transcription factor C/EBP-β. Our study demonstrates the pro-proliferative role of the oncogene IKKε in castrate-resistant prostate cancer cell lines, involving the phosphorylation and nuclear translocation of C/EBP-β that initiates IL-6 gene expression.

Pharmacological Inhibition of NFκB Reduces Prostate Cancer Related Osteoclastogenesis In Vitro and Osteolysis Ex Vivo

“…In conclusion, our present findings confirm that inhibition of the canonical NFκB signalling pathway may have a potential role in protecting the skeleton from the osteolysis associated with prostate cancer. When combined with previous studies [34][35][36][37][38][39][40][41][42], these findings suggest that NFκB inhibitors as both anti-metastatic and anti-osteoclastic agents may be of value in protecting against skeletal complications associated with prostate cancer bone metastasis. However, further studies are needed to explore the role of NFκB in the initiation, development and progression of osteoblastic prostate cancer metastases, and ascertain whether, and to what extent, the promotion of osteoblast differentiation by NFκB inhibitors may limit the usefulness of this class of agents for the treatment of osteoblast-driven cancer associated bone diseases such as prostate cancer and sarcomas.…”

“…The growth and expansion of prostatic tumour cells in the skeleton coupled with the development of osteosclerotic and osteolytic lesions are the causes of morbidity in patients with advanced disease [24,[26][27][28][29][30][31]. NFκB signalling pathway has been implicated in the initiation, progression and bone metastasis of prostate cancer [10,29,[32][33][34][35][36][37][38][39][40][41][42][43]. In view of the fact that the canonical NFκB signalling pathway plays a major role in the regulation of bone growth, osteoclastic bone resorption and osteoblastic bone formation [11][12][13], we employed a pharmacological approach to test if the verified inhibitor of the canonical NFκB signalling pathway PTN disrupts the ability of prostate cancer cells to influence osteoclast formation, osteoblast differentiation and osteolysis.…”

“…A body of work has implicated NFκB signalling in the progression of prostate cancer cells from androgen sensitive to androgen independence [29,32,[35][36][37][38][39]. With this in mind, we first assessed the cytotoxic effect of the verified NFκB inhibitor PTN on the in vitro viability of a panel of prostate cancer with different abilities to metastasise to the skeleton.…”

“…A number of studies have implicated NFκB in the initiation, progression and bone metastasis of prostatic tumours [10,29,[32][33][34][35][36][37][38][39][40][41][42]. NFκB plays a role in the growth and metastatic spread of androgen-independent prostate cancer cells [35][36][37], and pharmacological inhibition and knockdown of key components of NFκB signalling such as IKK have been found to reduce prostate cancer cell growth and metastasis [10,29,[32][33][34][35][36][37][38]43].…”

Hall of Fame among Pro-inflammatory Cytokines: Interleukin-6 Gene and Its Transcriptional Regulation Mechanisms

“…First is the Thr-235 phosphorylated residue, second is within the leucine zipper, and third is the cAMP-mediated phosphorylation that can be associated with nuclear translocation and gene transcription (62, 63). NF-IL6 also cooperates with other transcriptional factors, playing a synergistic role in regulating the IL-6 gene expression.…”