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J. Cell Biol.,
Volume 144, Number 5, March 8, 1999 891-901
Serono Pharmaceutical Research Institute, Ares-Serono International S.A., CH-1228 Plan-les-Ouates, Geneva, Switzerland
Here we report that in staurosporine-induced
apoptosis of HeLa cells, Bid, a BH3 domain containing
protein, translocates from the cytosol to mitochondria.
This event is associated with a change in conformation
of Bax which leads to the unmasking of its NH2-terminal domain and is accompanied by the release of cytochrome c from mitochondria. A similar finding is
reported for cerebellar granule cells undergoing apoptosis induced by serum and potassium deprivation. The
Bax-conformational change is prevented by Bcl-2 and
Bcl-xL but not by caspase inhibitors. Using isolated mitochondria and various BH3 mutants of Bid, we demonstrate that direct binding of Bid to Bax is a prerequisite for Bax structural change and cytochrome c release.
Bcl-xL can inhibit the effect of Bid by interacting directly with Bax. Moreover, using mitochondria from Bax-deficient tumor cell lines, we show that Bid-
induced release of cytochrome c is negligible when
Bid is added alone, but dramatically increased when
Bid and Bax are added together. Taken together, our
results suggest that, during certain types of apoptosis,
Bid translocates to mitochondria and binds to Bax,
leading to a change in conformation of Bax and to cytochrome c release from mitochondria.
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