ROLE OF MEMBRANE ANCHOR DOMAIN OF BCL-2 IN SUPPRESSION OF APOPTOSIS CAUSED BY E1B-DEFECTIVE ADENOVIRUS

Bcl-2 is an integral membrane protein that functions as a suppressor o f programmed cell death. It contains a COOH-terminal signal anchor seq uence that is selective for import and insertion of Bcl-2 into the mit ochondrial outer membrane and, by a different mechanism, can also dire ct the protein to other membrane sites. Deletion of the signal anchor sequence rendered Bcl-2 cytosolic and impaired its ability to prevent apoptotic death of human KB cells infected with a mutant form of adeno virus type 5 that does not make E1B 19-kDa protein. When the predicted transmembrane domain of the Bcl-2 signal anchor was replaced with tha t of the signal anchor of the yeast outer mitochondrial membrane prote in, Mas70p, the Bcl-2/Mas70p hybrid was found to be very similar to Bc l-2 in its distribution within transfected KB cells, in its ability to heterodimerize with Bax, and in its ability to suppress apoptosis. Th ese results are consistent with a model in which the transmembrane seg ment contributes to the function of Bcl-2 by targeting and anchoring t he protein to strategic membrane locations in the cell. Concentration of Bcl-2 at these sites may contribute to its proposed role as a regul ator, or component, of an antioxidant pathway.