Apoptotic signaling during initiation of detachment-induced apoptosis ("anoikis") of primary human intestinal epithelial cells

Apoptosis after the loss of cell anchorage-"anoikis"-plays an important rol e in the life cycle of adherent cells. Furthermore, loss of anchorage depen dency is believed to be a critical step in metastatic transformation. The a im of this study was to further characterize the sequence of intracellular events during anoikis in a nontransformed population of human intestinal ep ithelial cells (IECs). Purified human IECs were kept in suspension to induc e anoikis in over 90% of IECs within 3 h. Two initiator caspases, caspase-2 and -9, are activated within 15 min, followed by the hierarchical activati on of downstream caspases within 1 h. The activation of the caspase FLICE ( caspase-8) does not contribute to the initiation of anoikis, and massive re lease of cytochrome c from mitochondria cannot be detected before 60 min, i ndicating that cytochrome c release does not play a role during initiation of anoikis. This study delineates the signaling cascade during anoikis of n ontransformed cells, Future studies may identify alterations of this cascad e in neoplastic cells, thereby possibly gaining insight into carcinogenesis and metastatic transformation.