Roger Henson

The association between chronic inflammation and the development and progression of malignancy is exemplified in the biliary tract where persistent inflammation strongly predisposes to cholangiocarcinoma. The inflammatory cytokine interleukin-6 (IL-6) enhances tumor growth in cholangiocarcinoma by altered gene expression via autocrine mechanisms. IL-6 can regulate the activity of DNA methyltransferases, and moreover, aberrant DNA methylation can contribute to carcinogenesis. We therefore investigated the effect of chronic exposure to IL-6 on methylation-dependent gene expression and transformed cell growth in human cholangiocarcinoma. The relationship between autocrine IL-6 pathways, DNA methylation, and transformed cell growth was assessed using malignant cholangiocytes stably transfected to overexpress IL-6. Treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine decreased cell proliferation, growth in soft agar, and methylcytosine content of malignant cholangiocytes. However, this effect was not observed in IL-6-overexpressing cells. IL-6 overexpression resulted in the altered expression and promoter methylation of several genes, including the epidermal growth factor receptor (EGFR). EGFR promoter methylation was decreased and gene and protein expression was increased by IL-6. Thus, epigenetic regulation of gene expression by IL-6 can contribute to tumor progression by altering promoter methylation and gene expression of growth-regulatory pathways, such as those involving EGFR. Moreover, enhanced IL-6 expression may decrease the sensitivity of tumor cells to therapeutic treatments using methylation inhibitors. These observations have important implications for cancer treatment and provide a mechanism by which persistent cytokine stimulation can promote tumor growth.

The inflammation-associated cytokine interleukin-6 (IL-6) can contribute to tumor growth and resistance to therapy by the activation of survival mechanisms. In several human cancers, IL-6-activated survival signaling involves the signal transducers and activators of transcription (Stat) factors or protein kinase cascades. microRNAs (miRNAs) are endogenous regulators of gene expression that are altered in expression in many cancers. However, the effect of inflammatory cytokines on miRNA expression and the role of miRNA in modulating IL-6-mediated cell survival are unknown. We investigated the involvement of miRNA in malignant cholangiocytes stably transfected to overexpress IL-6, which enhances tumor growth in vivo by inhibition of apoptosis. We provide evidence that (i) miRNA expression both in vitro and in vivo is altered by overexpression of IL-6; (ii) selective miRNAs including let-7a are up-regulated and contribute to the survival effects of enforced IL-6 activity; and (iii) let-7a contributes to the constitutively increased phosphorylation of Stat-3 by a mechanism involving the neurofibromatosis 2 (NF2) gene. These findings reveal a novel mechanism by which IL-6 mediates tumor cell survival that may be therapeutically targeted and emphasize the presence of complex interrelationships between deregulated expression of miRNA and transcription factors in human cancers.