Pancreatic ductal carcinoma is characterized by a profound chemoresistance. As we have shown previously, these tumor cells can develop chemoresistance by interleukin (IL)-1β in an autocrine and nuclear factor-κB-dependent fashion. Because pancreatic ductal carcinoma contains many mesenchymal stromal cells, we further investigated how tumor–stroma interactions contribute to chemoresistance by using a transwell coculture model, including murine pancreatic fibroblasts and the chemosensitive human pancreatic carcinoma cell lines T3M4 and PT45-P1. If cultured with fibroblast-conditioned medium or kept in coculture with fibroblasts, both cell lines became much less sensitive toward treatment with etoposide than cells cultured under standard conditions. Furthermore, the secretion of IL-1β in T3M4 and PT45-P1 cells was increased by the fibroblasts, and IL-1β-receptor blockade abolished the resistance-inducing effect during cocultivation. This stimulated IL-1β secretion could be attributed to nitric oxide (NO) released by the fibroblasts as an IL-1β-inducing factor. Although both tumor cells secreted only little NO, which was in line with undetectable inducible nitric oxide synthase (iNOS) expression, fibroblasts exhibited significant iNOS expression and NO secretion that could be further induced by the tumor cells. Incubation of T3M4 and PT45-P1 cells with the NO donor S-Nitroso-N-acetyl-D,l-penicillamine up-regulated IL-1β secretion and conferred resistance toward etoposide-induced apoptosis. Conversely, the resistance-inducing effect of the fibroblasts was significantly abolished, when the specific iNOS inhibitor aminoguanidine was added during coculture. Immunohistochemistry on tissue sections from human pancreatic ductal carcinoma also revealed iNOS expression in stromal cells and IL-1β expression in tumor cells, thus supporting the in vitro findings. These data clearly demonstrate that fibroblasts contribute to the development of chemoresistance in pancreatic carcinoma cells via increased secretion of NO, which in turn leads to an elevated release of IL-1β by the tumor cells. These findings substantiate the implication of tumor–stromal interactions in the chemoresistance of pancreatic carcinoma.

Although nuclear factor E2-related factor-2 (Nrf2) protects from carcinogen-induced tumorigenesis, underlying the rationale for using Nrf2 inducers in chemoprevention, this antioxidative transcription factor may also act as a proto-oncogene. Thus, an enhanced Nrf2 activity promotes formation and chemoresistance of colon cancer. One mechanism causing persistent Nrf2 activation is the adaptation of epithelial cells to oxidative stress during chronic inflammation, e.g. colonocytes in inflammatory bowel diseases, and the multifunctional stress response gene immediate early response-3 (IER3) has a crucial role under these conditions. We now demonstrate that colonic tissue from Ier3^−/− mice subject of dextran sodium sulfate colitis exhibit greater Nrf2 activity than Ier3^+/+ mice, manifesting as increased nuclear Nrf2 protein level and Nrf2 target gene expression. Likewise, human NCM460 colonocytes subjected to shRNA-mediated IER3 knockdown exhibit greater Nrf2 activity compared with control cells, whereas IER3 overexpression attenuated Nrf2 activation. IER3-deficient NCM460 cells exhibited reduced reactive oxygen species levels, indicating increased antioxidative protection, as well as lower sensitivity to TRAIL or anticancer drug-induced apoptosis and greater clonogenicity. Knockdown of Nrf2 expression reversed these IER3-dependent effects. Further, the enhancing effect of IER3 deficiency on Nrf2 activity relates to the control of the inhibitory tyrosine kinase Fyn by the PI3K/Akt pathway. Thus, the PI3K inhibitor LY294002 or knockdown of Akt or Fyn expression abrogated the impact of IER3 deficiency on Nrf2 activity. In conclusion, the interference of IER3 with the PI3K/Akt-Fyn pathway represents a novel mechanism of Nrf2 regulation that may get lost in tumors and by which IER3 exerts its stress-adaptive and tumor-suppressive activity.