Abstract 4606: Curcumin regulates Interleukin-6 expression in colon cancer cells

The cytokine interleukin-6 (IL-6) plays fundamental roles in inflammation such as the progression from inflammation to cancer. In previous studies we have demonstrated that IL-6 expression is suppressed in xenografts treated with the dietary chemopreventive agent curcumin. Here, we sought to understand how IL-6 expression is regulated by curcumin in colon cancer cells. Methods. HCT116 cells were treated with IL-1β (+/- curcumin) and IL-6 mRNA and protein levels were evaluated by RT-PCR and western blot analyses. For transcriptional regulation, we cloned the 2-kb promoter region of the IL-6 gene upstream from the transcription start site and constructed a reporter construct (pIL-6Luc), where the firefly luciferase gene is under the control of the human IL-6 promoter. Western blot analyses were performed for determining JNK and p38 mitogen-activated protein kinase (MAPK) signaling pathways. Results. IL-1β treatment significantly upregulated IL-6 mRNA and protein levels, which was suppressed by curcumin. Curcumin treatment also suppressed IL-1β induced IL-6 promoter activity. Western blot analyses demonstrated that curcumin induced the phosphorylation of p38 MAPK in HCT 116 cells and inhibiting this activation with a specific SB203580 did not affect IL-6 production. Treatment with JNK inhibitor II, however, led to a decrease in IL-1 induced expression of IL-6, suggesting that IL-1 induction of IL-6 is at least partly dependent on the JNK pathway. This was also evidenced by an increase in phosphorylation of the p46 JNK isoform. On the other hand, JNK p54 phosphorylation was minimal. In contrast, curcumin upregulated p54 while inhibiting p46 JNK isoforms. These data are similar to that observed in macrophages where the activation of p54 is believed to induce cell death pathways while p46 is associated with survival. Conclusion. Activation of JNK/p38 and subsequent gene induction is associated with stress responses that promote either cell survival after cellular damage or apoptotic death. Our results imply that differential activation of various JNK isoforms may result in distinct phenotypic consequences. It is possible that the diminished activity of p54 JNK in IL-1-treated cells serves to protect HCT 116 cells from apoptotic cell death, while the increase in activated p54 in curcumin cells serves to sensitize cells to apoptotic cell death and the reverse is true for p46. Taken together our results show that two major stress signaling pathways, JNK and p38 pathways are involved in determining the effect of curcumin on IL-6 induced by IL-1 after prolonged incubation. Preferential activation of JNK isoforms may be an important mechanism through which curcumin and IL-1 regulate IL-6 expression in HCT 116 cells. More importantly, these studies provide insight into understanding how pharmacologically safe dietary factors suppress tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4606. doi:10.1158/1538-7445.AM2011-4606