The proapoptotic activity of C-terminal domain of apoptosis-inducing factor (AIF) is separated from its N-terminal

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein that mediates both NADH-oxidizing and caspase-independent apoptosis. Further, the proapoptotic activity of AIF is located in the C-terminus of AIF although the precise minimu sequence responsible for apoptosis induction remains to be investigated. In the present study, we generated two truncated AIFs, AIf Delta 1-480-FLAG, which is a FLAG-tagged C-terminal peptide comprising amino acids from 481 to 613, and AIF360-480 containing amino acids from 360 to 480 of AIF. We used confocal microscopy to demonstrate that both the truncated proteins are expressed and located in the cytoplasm of transfected cells. AIF Delta 1-480 but not AIF360-480 induces apoptosis in transfected cells. We also found that the expression of AIF Delta 1-480 could initiate the release of cytochrome c from the mitochondria. The suppression of caspase-9 via siRNA blocked the proapoptotic activity of AIF Delta 1-480, mitochondria. The suppression of caspase-9 via siRNA blocked the proapoptotic activity of AIF Delta 1-480. Therefore. AIF Delta 1-480 is sufficient for inducing caspase-9-dependent apoptotic signaling, probably by promoting the release of cytochrome c. At last, we generated a chimeric immuno-AIF Delta 1-480 protein, which comprised an HER2 antibody, a Pseudomonas exotoxin A translocation domain and AIF Delta 1-480. Human Jurkat cells transfected with the immuno-AIF Delta 1-480 gene could express and secrete the chimeric protein, which selectively recognize and kill HER2-overexpressing tumor cells. Our study demonstrates the feasibility of the immuno-AIF Delta 1-480 gene as a novel approach to treating HER2-overexpressing cancers.