Regulation and Function of the Human Leukotriene D4 Receptor CysLT1 in Epithelial Cells and Colon Cancer

Sammanfattning: The pro-inflammatory mediators leukotrienes have shown to be important players in the pathogenesis of diseases like asthma and inflammatory bowel disease (IBD). Patients suffering from IBD have been found to have an increased risk of developing colon cancer. Since leukotrienes have been shown in increased concentrations in stools of IBD patients we hypothesise that LTD4 can play a role in the development of colon cancer. In order to induce its effects on the intestinal epithelial cells, LTD4 binds to its receptor CysLT1R. We therefore chose to study CysLT1 in colon cancer specimens and in non-transformed and colon cancer cell lines. Our results show that CysLT1R can be found in increased levels in colon cancer enterocytes (50% of 84 patients) and that high expression of this receptor in Dukes`B staged tumours predicts a poor disease outcome. Furthermore, we observed that CysLT1R is located in the plasma membrane and in the outer nuclei membrane. We identified a putative nuclear localisation sequence in CysLT1R, which is crucial for the LTD4, induced internalisation of the receptor. Interestingly, stimulation of CysLT1R located in the nuclei induced the activation of ERK1/2, an enzyme which have been shown to mediate LTD4 induced proliferation. When studying the LTD4 induced signalling pathways we found that CysLT1R mediated stress fibre formation and a calcium response through two heterotrimeric G-proteins, Ga12 and Gai3, respectively and that the LTD4 induced calcium response is dependent on PKCe. Taken together we have shown that LTD4 might have an impact on tumour development through the regulation of CysLT1R and its downstream signalling pathways.