Caspase cleavage enhances the apoptosis-inducing effects of BAD

The function of BAD, a proapoptotic member of the Bcl-2 family, is regulate d primarily by rapid changes in phosphorylation that modulate its protein-p rotein interactions and subcellular localization. We show here that, during interleukin 3 (IL-3) deprivation-induced apoptosis of 32Dc13 murine myeloi d precursor cells, BAD is cleaved by a caspase(s) at its N terminus to gene rate a 15-kDa truncated protein, The 15-kDa truncated BAD is a more potent inducer of apoptosis than the wild-type protein, whereas a mutant BAD resis tant to caspase 3 cleavage is a weak apoptosis inducer, Truncated BAD is de tectable only in the mitochondrial fraction, interacts with BCL-X-L at leas t as effectively as the wild-type protein, and is more potent than wild-typ e BAD in inducing cytochrome c release. Human BAD, which is 43 amino acids shorter than its mouse counterpart, is also cleaved by a caspase(s) upon ex posure of Jurkat T cells to anti FAS antibody, tumor necrosis factor alpha (TNF-alpha), or TRAIL. Moreover, a truncated form of human BAD lacking the N-terminal 28 amino acids is more potent than wild-type BAD in inducing apo ptosis, The generation of truncated BAD was blocked by Bcl-2 in IL-3-depriv ed 32Dc13 cells but not in Jurkat T cells exposed to anti-FAS antibody, TNF -alpha, or TRAIL, Together, these findings point to a novel and important r ole for BAD in maintaining the apoptotic phenotype in response to various a poptosis inducers.