LTD4 signalling via beta-catenin: a possible link between inflammation and cancer

The pro-inflammatory mediator LTD4 is an important component in the pathogenesis of inflammatory conditions as inflammatory bowel diseases. Patients suffering from inflammatory bowel diseases face an increased risk of intestinal cancer development. Therefore it is important to investigate the role of LTD4 signalling in cancer development and progression. In this thesis I show that there is an endogenous production of LTD4 in both non-transformed and cancer intestinal epithelial cells leading to a continuous activation of the CysLT1 receptor. The activation of this receptor signals increased proliferation and increased survival. My finding that CysLT1 receptor signalling leads to accumulation of b-catenin in the nuclei and activation of the transcription factor TCF/LEF is in line with the ability of this receptor to promote cell proliferation. However, I also found that CysLT1 receptor activation caused b-catenin to translocate to the mitochondria where it associated with the survival protein Bcl-2. In addition, I observed that LTD4-induced activation of the CysLT1 receptor or overexpression of b-catenin in both non-transformed and cancer intestinal epithelial cells enhanced the activity of the respiratory chain and the production of ROS, as well as increased the transcription of mt-DNA. These effects caused a downstream activation of NF-kB. In conclusion, my results indicate that the pro-inflammatory mediator LTD4 has an important role in tumour development in the intestine by its regulation of cell proliferation and survival

Endogenous production of leukotriene D(4) mediates autocrine survival and proliferation via CysLT(1) receptor signalling in intestinal epithelial cells.

The cysteinyl leukotriene(1) (CysLT(1)) receptor (CysLT(1)R) enhances survival and proliferation of intestinal cells via distinct pathways. Here, we have demonstrated that there is significant endogenous production of CysLTs from both non-tumour-and tumour-derived intestinal epithelial cells. Treatment of two non-tumour cell lines, Int 407 and IEC-6, with CysLT1R antagonists led to shrinkage and detachment of cells, confirmed as apoptotic cell death, and a dose-dependent reduction in proliferation. However, in the tumour intestinal cell lines Caco-2, SW480, HCT-116 and HT-29, treatment with CysLT1R antagonists significantly reduced proliferation, but had no effect on apoptosis. A unique characteristic of intestinal cancer cells is the presence of nuclear CysLT(1)Rs, which are inaccessible to receptor antagonists. In these cells, inhibition of the endogenous production of CysLTs indirectly, by 5-lipoxygenase inhibition, impaired CysLT1R signalling throughout the cell, and resulted in apoptosis of the tumour cells. These data reveal the existence of constitutive CysLT1R signalling that mediates both survival and proliferation in intestinal cells. Importantly, we propose that tumour-derived intestinal cells are resistant to CysLT(1)R antagonist-induced apoptosis, a phenomena that could be explained by nuclear CysLT1R signalling

Low expression of CysLT(1)R and high expression of CysLT(2)R mediate good prognosis in colorectal cancer

Colorectal cancer is the third most common cancer type in the western world. in search of new treatment possibilities, the inflammation mediators, know as cysteinyl leukotrienes (CysLTs), have been shown to regulate intestinal epithelial cell survival and proliferation via the CysLT(1)R, and cell differentiation via the CysLT(2)R. These results prompted us to investigate the significance of CysLT(1)R and CysLT(2)R expression in colorectal cancer tissue for patient survival. The CysLT(1)R, CysLT(2)R, beta-catenin and Bcl-xL protein expression levels were evaluated by immunohistochemistry in a tissue microarray of 329 colorectal patients. We found that high nuclear expression of CysLT(1)R is associated with a poor prognosis, whereas high nuclear expression of CysLT(2)R is associated with a good prognosis. We also observed that patients with colorectal tumours characterised by high CysLT(1)R but low CysLT(2)R nuclear expression had the lowest survival expectancy, whereas patients with colorectal tumours characterised by low CysLT(1)R but high CysLT(2)R nuclear expression had the best survival expectancy. Interestingly, beta-catenin as a single prognostic marker did not exhibit any prognostic value. However, in patients with tumours characterised by a high CysLT(1)R nuclear expression, an elevated beta-catenin nuclear expression had a significantly prognostic value. In conclusion these data indicate that nuclear expressions of CysLTRs are potential prognostic indicators of colorectal cancer. (C) 2009 Elsevier Ltd. All rights reserved

The inflammatory mediator leukotriene D4 induces beta -catenin signaling and its association with anti-apoptotic Bcl-2 in intestinal epithelial cells.

Increased levels of the inflammatory mediator leukotriene D-4 (LTD4) are present at sites of inflammatory bowel disease, and such areas also exhibit an increased risk for subsequent cancer development. It is known that LTD4 affects the expression of many proteins that influence survival and proliferation of intestinal epithelial cells. We demonstrate here that after LTD4 exposure, beta-catenin translocates to the nucleus where it signals activation of the TCF/LEF family of transcription factors. These events are mediated via a phosphatidylinositol 3-kinase-dependent phosphorylation of the inhibitory Ser-9 residue of glycogen synthase kinase 3 beta. We also show that in the presence of LTD4, free beta-catenin translocates to the mitochondria where it associates with the cell survival protein Bcl-2. We hypothesize that LTD4 may enhance cell survival via activation of beta-catenin signaling, in particular, by promoting the association of beta-catenin with Bcl-2 in the mitochondria. Similar to Wnt-1 signaling, LTD4 signals an increased level of free beta-catenin and elevated TCF/LEF promotor activity. This work in intestinal epithelial cells further lends credence to the idea that inflammatory signaling pathways are intrinsically linked with potential oncogenic signals involved in cell survival and apoptosis