Bcl-2 inhibits Bax translocation from cytosol to mitochondria during drug-induced apoptosis of human tumor cells

Abstract

The pro-apoptotic protein, Bax, has been reported to translocate from cytosol to mitochondria following exposure of cells to apoptotic stresses including cytokine withdrawal and treatment with glucocorticoids and cytotoxic drugs. These observations, coupled with reports showing that Bax causes the release of mitochondrial cytochrome c, implicate Bax as a central mediator of the apoptotic process. In this report we demonstrate by subcellular fractionation a significant shift in Bax localization from cytosol to cellular membranes in two human tumor cell lines exposed to staurosporine or etoposide. Immunofluorescence studies confirmed that Bax specifically relocalized to the mitochondria. This redistribution of Bax occurred in concert with, or just prior to, proteolytic processing of procaspase-3, activation of DEVD-specific cleavage activity and degradation of poly(ADPribose) polymerase. However, Bax membrane translocation was independent of caspase activity as determined using the broad-range caspase inhibitor z-VAD-fmk. High level overexpression of the anti-apoptotic protein Bcl-2 prevented Bax redistribution to the mitochondria, caspase activation and apoptosis following exposure to staurosporine or etoposide. These data confirm the role of Bax in mitochondrial cytochrome c release, and indicate that prevention of Bax translocation to the mitochondrial membrane represents a novel mechanism by which Bcl-2 inhibits drug-induced apoptosis. Cell Death and Differentiation (2000) 7, 102 ± 111.

The rheostat in the membrane: BCL-2 family proteins and apoptosis

“…For example, in the nanodisc cryo-EM study, Volkmann et al 78 found that BCL-XL abolished the integration of BAX into nanodisc membranes in the presence of BID BH3 peptides. This agrees with other work 10,34,95,[110][111][112] showing that BCL-XL or BCL-2 can block membrane recruitment and integration of BAX, even in the presence of a BAX-activating signal. In other studies, membrane integration of both BCL-XL and BAX (i.e.…”

Thiol protecting agents and antioxidants inhibit the mitochondrial permeability transition promoted by etoposide: implications in the prevention of etoposide-induced apoptosis

“…Moreover, ROS have also been implicated on the release of cytochrome c and other apoptosis-inducing factors, as well as on the upstream of caspases involved in the apoptotic cascade [10,[51][52][53]. Although it has been reported that in cytochrome c-induced cell death, cytochrome c release may occur by both MPT-dependent and independent mechanisms, several studies have shown that MPT and cytochrome c release are early events in several model of apoptosis [4,6,7,19,54]. Moreover, the pro-apoptotic protein Bax, implicated in the release of cytochrome c, has been suggested to translocate from the cytosol to mitochondria in cells under the action of VP-16, a process that is prevented by the anti-apoptotic protein Bcl-2 [53], which inhibits the MPT by keeping the pyridine nucleotides in a relative reduced state [42,55].…”

Human αA- and αB-crystallins bind to Bax and Bcl-XS to sequester their translocation during staurosporine-induced apoptosis

“…[84][85][86] Staurosporine, a potent apoptosis inducer demonstrated in a broad spectrum of cells activate apoptosis through the mitochondrial death pathway. [87][88][89][90][91] The proapoptotic members of the Bcl-2 family play a critical role in staurosporineinduced apoptosis. Cells lacking both Bax and Bak are known to be completely resistant to multiple apoptotic stimuli including staurosporine.…”

“…These downstream events induced by staurosporine in vector-transfected HLE cells are similar to those reported in other cell lines. [87][88][89][90][91] In either HaA-or HaB-transfected cells, the staurosporine-induced downstream events were largely turned off. Thus, our results provide additional evidence that both Bax and Bak are important for staurosporine-induced apoptosis.…”