The role of IKK in constitutive activation of NF-κB transcription factor in prostate carcinoma cells

Abstract

Rel/NF-κB transcription factors are implicated in the control of cell proliferation, apoptosis and transformation. The key to NF-κB regulation is the inhibitory IκB proteins. During response to diverse stimuli, IκBs are rapidly phosphorylated by IκB kinases (IKKs), ubiquitinated and undergo degradation. We have investigated the expression and function of NF-κB, IκB inhibitors and IKKs in normal prostate epithelial cells and prostate carcinoma (PC) cell lines LNCaP, MDA PCa 2b, DU145, PC3, and JCA1. We found that NF-κB was constitutively activated in human androgen-independent PC cell lines DU145, PC3, JCA1 as well as androgen-independent CL2 cells derived from LNCaP. In spite of a strong difference in constitutive κB binding, Western blot analysis did not reveal any significant variance in the expression of p50, p65, IκBs, IKKα, and IKKβ between primary prostate cells, androgen-dependent and androgen-independent PC cells. However, we found that in androgen-independent PC cells IκBα was heavily phosphorylated and displayed a faster turnover. Using an in vitro kinase assay we demonstrated constitutive activation of IKK in androgen-independent PC cell lines. Blockage of NF-κB activity in PC cells by dominant-negative IκBα resulted in increased constitutive and TNF-α-induced apoptosis. Our data suggest that increased IKK activation leads to the constitutive activation of NF-κB ‘survival signaling’ pathway in androgen-independent PC cells. This may be important for the support of their androgen-independent status and growth advantage.