Regulation of the cytoskeleton and the adhesiveness of intestinal epithelial cells by leukotriene D4

Abstract: Leukotrienes belong to a family of biologically active conjugated trienes that are formed from arachidonic acid via the 5-lipoxygenase pathway and are important mediators of inflammatory reactions. The CysLT1 receptor that specifically serves as receptor for leukotriene D4 (LTD4) has been identified as a G-protein coupled receptor. Cell-cell and cell-matrix complexes of epithelial cells are interconnected through cytoskeletal filaments and proteins, and they influence the activities and outcome of various cellular processes. This thesis is focused primarily on the effect that LTD4 has on reorganisation of the actin cytoskeleton and on cell-cell and cell-matrix adhesion properties. We found that LTD4 caused dramatic changes in the actin cytoskeleton in intestinal epithelial cells, and an important factor in this context was the impact of this leukotriene on the actin-binding protein vinculin, which included inducing translocation of vinculin from a cell-cell to a cell-matrix complex. In general, cell adhesion favours cell survival signalling, and integrins are the main receptors responsible for mediating the attachment of different types of cells to matrix proteins. We have unequivocally established that direct signalling occurs between the LTD4 receptor and the collagen integrins in two different cell lines respectively derived from human colon carcinoma and intestinal epithelial cells. Increased adhesion of the cancer cells depended on activation of cyclooxygenase-2, an enzyme that is involved in progression of colon cancers, whereas adhesion of the intestinal epithelial cells was augmented by LTD4-induced translocation of protein kinase C to areas where integrins bind to matrix proteins (focal adhesions). In conclusion, inflammatory mediators such as LTD4 can affect cell survival through their impact on specific integrins.