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J. Cell Biol.,
Volume 143, Number 1, October 5, 1998 207-215



* Department of Biochemistry, McIntyre Medical Sciences Building, McGill University, Montreal, Quebec, Canada H3G 1Y6; The proapoptotic protein BAX contains a
single predicted transmembrane domain at its COOH
terminus. In unstimulated cells, BAX is located in the
cytosol and in peripheral association with intracellular
membranes including mitochondria, but inserts into mitochondrial membranes after a death signal. This failure to insert into mitochondrial membrane in the absence of a death signal correlates with repression of the
transmembrane signal-anchor function of BAX by the
NH2-terminal domain. Targeting can be instated by deleting the domain or by replacing the BAX transmembrane segment with that of BCL-2. In stimulated cells,
the contribution of the NH2 terminus of BAX correlates with further exposure of this domain after membrane insertion of the protein. The peptidyl caspase inhibitor zVAD-fmk partly blocks the stimulated mitochondrial membrane insertion of BAX in vivo, which is
consistent with the ability of apoptotic cell extracts to
support mitochondrial targeting of BAX in vitro, dependent on activation of caspase(s). Taken together,
our results suggest that regulated targeting of BAX to
mitochondria in response to a death signal is mediated
by discrete domains within the BAX polypeptide. The
contribution of one or more caspases may reflect an initiation and/or amplification of this regulated targeting.
Division of Molecular Oncology, Department of Medicine and Department of Pathology, Howard Hughes Medical Institute,
Washington University School of Medicine, St. Louis, Missouri 63110; and § Department of Microbiology, University of
Minnesota Medical School, Minneapolis, Minnesota 55455
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