LOSS OF APC PROTEIN EXPRESSED BY HUMAN COLONIC EPITHELIAL-CELLS AND THE APPEARANCE OF A SPECIFIC LOW-MOLECULAR-WEIGHT FORM IS ASSOCIATED WITH APOPTOSIS IN-VITRO

APC (adenomatous polyposis coli) protein is differentially expressed i n the normal colonic crypt and believed to be involved in colonic cell maturation. In this work we investigated whether expression of the AP C protein is associated with cell death in colonic epithelial cells. W e have previously reported an in vitro system to study apoptosis. Brie fly, cells attached to the flask have a low frequency of apoptosis (1- 3%), whereas cells that detach from the flask and float in the medium have a high proportion of apoptotic cells (36-96% depending on the cel l line). The full-length 300-kDa or truncated APC protein, normally ex pressed by the attached cells (detected using the FE9 antibody), was f ound to be lost in the floating apoptotic cells in 8/11 colon tumour c ell lines examined. In addition, the APC antibody FE9 detected a 90-kD a protein in the floating apoptotic cells of all cell lines investigat ed, which was not present in attached cells. Furthermore, loss of full -length APC and gain of the 90-kDa protein was observed in the apoptot ic cells of 2 cell lines derived from other tissues: the SV40-transfor med fibroblast cell line CMSV40fib and the lymphoblastoid B-cell line BJA-B. In cells repeatedly frozen and thawed, believed to induce necro tic cell death, full-length or truncated APC was also lost, though a 9 5-kDa protein distinct from that in apoptotic cells was observed. Spec ific loss of full-length or truncated APC (resulting in a 90-kDa prote in in apoptotic cells but a 95-kDa protein in necrotic cells) is there fore associated with cell death. Our findings suggest a possible role for APC in cell survival. (C) 1994 Wiley-Liss, Inc.