Relationship between IL-6/ERK and NF-κB: a study in normal and pathological human prostate gland

Abstract

Background: There is growing evidence that inflammation is a causal factor in cancer, where pro-inflammatory cytokines such as IL-6, IL-1 or TNF-α could induce cellular proliferation by activation of NF-κB. This study focuses on the IL-6/ERK transduction pathway, its relationship with NF-κB, and the consequences of dysregulation in the development of prostate pathologies such as benign prostate hyperplasia (BPH), prostate intraepithelial neoplasia (PIN) and prostate cancer (PC).

Methods: Immunohistochemical and Western blot analyses for IL-6, gp-130, Raf-1, MEK-1, ERK-1, p-MEK, ERK-2, p-ERK, NF-κB/p-50 and NF-κB/p-65 were carried out in 20 samples of normal prostate glands, 35 samples of BPH, 27 samples with a diagnosis of PIN (low-grade PIN or high-grade PIN), and 95 samples of PC (23 with low, 51 with medium and 21 with high Gleason scores).

Results: Immunoreaction to IL-6, gp-130, ERK-1, ERK-2, p-ERK and NF-κB/p50 was found in the cytoplasm of epithelial cells in normal prostate samples; p-MEK was found in the nucleus of epithelial cells; but not expression to Raf-1, MEK-1 and NF-κB/p65. In BPH, all of these proteins were immunoexpressed, while there was increased immunoexpression of IL-6, gp-130, p-MEK, ERK-1, ERK-2 and NF-κB/p50 (cytoplasm). In PC, immunoexpression of IL-6 and gp-130 were similar to that found in BPH; while immunoexpression of Raf-1, MEK-1, p-MEK, ERK-1, ERK-2, p-ERK, NF-κB/p50 (nucleus and cytoplasm), and NF-κB/p65 (nucleus and cytoplasm) was higher than in BPH.

Conclusion: Translocation of NF-κB to the nucleus in PC and high-grade PIN could be stimulated by the IL-6/ERK transduction pathway, but might also be stimulated by other transduction pathways, such as TNF-α/NIK, TNF/p38, IL-1/NIK or IL-1/p38. Activation of NF-κB in PC could regulate IL-6 expression. These transduction pathways are also related to activation of other transcription factors such as Elk-1, ATF-2 or c-myc (also involved in cell proliferation and survival). PC is a heterogeneous disease, where multiple transduction pathways might alter the apoptosis/proliferation balance. Significant attention should be give to the combination of novel agents directed towards inactivation of pro-inflammatory cytokines than can disrupt tumour cell growth.