APOPTOSIS INDUCED BY INHIBITION OF INTERCELLULAR CONTACT

The LIM 1863 colon carcinoma cell line grows as structural organoids o f goblet and columnar cells around a central lumen and provides a mode l for the development of stem cells in the normal colon. The organoid structure can be disrupted by removal of calcium from the medium, resu lting in a suspension of single cells. Upon readdition of calcium, the cells reform the organoid structure over a period of 24 h, and ultras tructural examination of the reforming cells reveals that this involve s a complex process that we have termed clutching. To determine the ad hesion molecules involved in organoid formation we attempted to block this process by single cell suspensions of LIM 1863 reseeded in the pr esence of monoclonal antibodies. An anti-integrin antibody directed ag ainst a conformational epitope on the alphav subunit totally inhibited organoid reformation. As a consequence of this inhibition of cell con tact the colon carcinoma cells rapidly underwent apoptosis. Investigat ions of the apoptotic pathway involved suggested an induction mechanis m since the onset of apoptosis in the contact-inhibited cells showed s pecific increased synthesis of 68- and 72-kD proteins. In addition, im munoblotting of cytosolic and nuclear extracts of the cells revealed t he rapid translocation of the tumor suppressor gene product, p53 to th e cell nucleus upon induction of apoptosis. These results suggest that cell-cell adhesion may be a vital regulator of colon development over come in tumor cells by loss of adhesion molecules or of functional p53 protein.