Bcl-2 homology domain-3 (BH3)
peptides are potent
cancer therapeutic
reagents that target regulators of apoptotic cell death in
cancer cells. However, their cytotoxic effects are affected by different expression levels of Bcl-2 family
proteins. We recently found that the amphipathic tail-anchoring
peptide (ATAP) from Bfl-1, a bifunctional Bcl-2 family member, produced strong pro-apoptotic activity by permeabilizing the mitochondrial outer membrane. Here, we test whether the activity of ATAP requires other cellular factors and whether ATAP has an advantage over the BH3
peptides in targeting
cancer cells. Confocal microscopic imaging illustrates specific targeting of ATAP to mitochondria, whereas BH3
peptides show diffuse patterns of cytosolic distribution. Although the pro-apoptotic activities of BH3
peptides are largely inhibited by either overexpression of anti-apoptotic Bcl-2 or Bcl-xL or nullification of pro-apoptotic Bax and Bak in cells, the pro-apoptotic function of ATAP is not affected by these cellular factors. Reconstitution of synthetic ATAP into liposomal membranes results in release of fluorescent molecules of the size of
cytochrome c from the
liposomes, suggesting that the membrane permeabilizing activity of ATAP does not require additional
protein factors. Because ATAP can target to the mitochondrial membrane and its pro-apoptotic activity does not depend on the content of Bcl-2 family
proteins, it represents a promising candidate for anti-
cancer drugs that can potentially overcome the intrinsic apoptosis-resistant nature of
cancer cells.