COLLAGEN GEL OVERLAY INDUCES APOPTOSIS OF POLARIZED CELLS IN CULTURES- DISORIENTED CELL-DEATH

In this study, we attempted to investigate the response of polarized c ells to inappropriate interaction with the extracellular matrix. Cell lines of epithelial [Madin-Darby canine kidney (MDCK) and LLC-PK1], en dothelial [bovine aortic endothelial cells (BAEC)], and mesenchymal (E SK-4 and NIH/3T3) origins were employed. With collagen gel overlay, MD CK cells underwent membrane remodeling and gradually developed lumen f ormation within 24 h. Apoptosis could also be observed following cell remodeling. The ratio of apoptosis was enhanced from 12.1 +/- 2.4% wit hin 24 h to 58.4 +/- 9.8% at day 3, and finally the monolayer was disi ntegrated. Collagen gel overlay-induced apoptosis was not a result of physical stress, since agarose gel overlay did not induce any morpholo gical alterations. All epithelial and endothelial cells examined devel oped apoptosis in response to collagen overlay. In contrast, collagen overlay did not affect growth of fibroblasts at all, although their gr owth under agarose gel was slightly hindered due to physical stress. C ollagen overlay-induced apoptosis seems to be a unique phenomenon for polarized cells and thus is defined as ''disoriented cell death.'' Fur thermore, anti-aa-integrin antibody could abolish collagen overlay-ind uced morphological changes and apoptosis in MDCK cells, indicating tha t signals through alpha(2)-integrin on the apical membrane are require d for disoriented cell death. Finally, Bcl-2 overexpression prolonged survival of MDCK cells in response to collagen overlay, but these cell s eventually developed apoptosis due to downregulation of Bcl-2 protei n. These findings indicate that inappropriate cell-matrix interaction results in apoptosis, which may account for cell death mechanisms duri ng developmental processes or under pathological conditions.