Role of IKKi in prostate cancer: A link between inflammation and androgen receptor signaling Free

LB-104

Our recent data and data by others indicate that anti-apoptotic, pro-tumorigenic factor NF-κB is constitutively activated in androgen-independent prostate carcinoma (PC) cell lines and in prostate tumors. The important step in NF-κB activation is the phosphorylation of IκB inhibitor proteins by IKK kinases IKKα, IKKβ; and IKK-related kinases IKKi/ϵ and TBK1/NAK. IKKi is highly inducible kinase whose expression is known to be activated by numerous pro-inflammatory cytokines. We found that IKKi is expressed in androgen-independent PC cells (PC3 and DU145) with high level of constitutively active NF-κB but not in androgen-dependent PC cell lines (LNCaP and MDA PCa 2b) and primary prostate epithelial cells. Immunostaining revealed that IKKi is well expressed in BPH and PCs. Next, our data provide the evidence that IKKi could be involved in the regulation of NF-κB activity in PC cells through a positive feedback loop. Indeed, the treatment of PC cells with NF-κB inducers results in a rapid induction of IKKi. On the other hand, transient transfection of different PC cells with wild type (w.t.) IKKi results in activation of NF-κB. To further study the IKKi function in PC cells we generated PC3 and LNCaP cells stably expressing w.t. IKKi and dominant negative (d.n.) K38A mutant of IKKi using infection with corresponding lentiviruses. In both cell lines IKKi d.n. had no effect on cell morphology, growth, and tumorigenicity. In contrast, PC cells infected with w.t. IKKi displayed significant increase in growth in monolayer and in soft agar in comparison to cells infected with empty virus. As expected, stable overexpression of w.t. IKKi in PC cells resulted in NF-κB activation that correlated with increased level of phosphorylation of both IκBα and p65/RelA (Ser536). Unexpectedly expression of w.t. IKKi in LNCaP cells resulted in the increased expression of androgen receptor (AR) on both mRNA and protein level, and the accumulation of AR protein in the nucleus. We further demonstrated the increased basal activity of AR in LNCaP-IKKi w.t. cells, and the enhanced responsiveness to low doses of androgens. Experiments with androgen-deprived serum demonstrated that growth of LNCaP-IKKi w.t. cells was less dependent on the androgens than LNCaP-V cells. The mechanisms of regulation of AR expression and function by IKKi are currently under study. In conclusion, the revealed control of AR-mediated signaling by IKKi may represent an important regulatory link between the inflammation and tumorigenesis in prostate.