Bcl-2 overexpression prevents apoptosis-induced Madin-Darby canine kidney simple epithelial cyst formation

Background. Madin-Darby canine kidney (MDCK) cells develop into simple epit helial cell cysts when cultured in type I collagen gel. We found that MDCK cells initially grow into multilayer cell aggregates and subsequently devel op central lumen that contain apoptotic cells. We hypothesized that apoptos is might be essential for the formation of MDCK cysts. Methods. Using MDCK cells cultured in collagen gel as the experimental mode l, we investigated how renal cells organize to form cysts. To delineate the role of apoptosis in the process of cyst formation, MDCK cells were transf ected with the bcl-2 gene. Characterization of apoptosis was studied by mor phological and biochemical methods. Results. Bcl-2 overexpression conferred resistance to apoptosis. Cultured i n collagen gel, Bcl-2 transfectants rarely formed a simple epithelial cyst, but instead remained as a multilayer cell aggregate containing central or multiple lumens, or even developing into branching structures. Conclusions. Because Bcl-2 overexpression averts cyst cavitation, these dat a clearly indicate that apoptosis is an essential initial event for renal c yst formation.