Restoration of positioning control following Disabled-2 expression in ovarian and breast tumor cells

The physical interaction of epithelial cells with the basement membrane ens ures correct positioning and acts as a survival factor for epithelial cells . Cells that detach from the basement membrane often undergo apoptosis; how ever, in carcinomas, this positional control is absent, permitting disorgan ized cell proliferation. In the majority of breast and ovarian carcinomas ( 85-90%), the expression of a candidate tumor suppressor, Disabled-2 (Dab2), is frequently lost. The Dab2-negative tumor cells are no longer in contact with an intact basement membrane, as indicated by the absence of collagen IV (in about 90% of cases), However, in the subset (10-15%) of ovarian tumo rs in which Dab2, expression is positive, the presence of a basement membra ne-like structure around tumor cells was observed. Recombinant adenovirus-m ediated expression of Dab2 was used in Dab2-negative ovarian and breast can cer cells, and re-expression of Dab2 was found to lead to cell death or gro wth arrest. Dab2 expression suppressed MAPK activation and c-fos expression , Plating the infected cells on a basement membrane matrigel rescued the ce lls from death and growth arrest. Thus, Dab2 exhibits a negative activity f or cell growth and survival, which can be countered by attachment of the ce lls to basement membrane matrix. We conclude that Dab2 functions in cell po sitioning control and mediates the exigency for basement membrane attachmen t of epithelial cells, Loss of Dab2 may contribute to the basement membrane -independent, disorganized proliferation of tumor cells in ovarian and brea st carcinomas.