Interplay of nuclear factor-κB and B-myb in the negative regulation of androgen receptor expression by tumor necrosis factor α

Increased androgen receptor (AR) levels are associated with prostate cancer progression to androgen independence and therapy resistance. Evidence has suggested that chronic inflammation is closely linked to various cancers including prostate cancer. Herein we show that the proinflammatory cytokine TNFα negatively regulates AR mRNA and protein expression and reduces androgen sensitivity in androgen-dependent LNCaP human prostate cancer cells. Decreased AR expression results from transcription repression involving essential in cis interaction of nuclear factor-κB (NF-κB) with the B-myb transcription factor at a composite genomic element in the 5′-untranslated region of AR. The negative regulation was abrogated when NF-κB activity was inhibited by a superrepressor of the inhibitory κB protein. In contrast, androgen-independent C4-2 (LNCaP-derived) cells fail to show AR down-regulation by TNFα, despite expression of B-myb and TNFα-induced NF-κB activity similar to that in LNCaP cells. The negatively regulated AR gene chromatin region showed TNFα-dependent enrichment of B-myb and the NF-κB proteins p65 and p50. In parallel, the histone deacetylase 1, corepressor silencing mediator of retinoid and thyroid hormone receptor and the corepressor-associated scaffold protein mSin3A were recruited to the inhibitory site. In C4-2 cells, neither NF-κB and B-myb, nor any of the corepressor components, were detected at the negative site in response to TNFα. Apoptosis was induced in TNFα-treated LNCaP cells, likely in part due to the down-regulation of AR. The androgen-independent, AR-expressing C4-2 and C4-2B (derived from C4-2) cells were resistant to TNFα-induced apoptosis. The results linking androgen dependence to the NF-κB and AR pathways may be insightful in identifying novel treatment targets for prostate cancer.