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Bcl-2, Bcl-XL and adenovirus protein E1B19kD are functionally equivalent in their ability to inhibit cell death
D C Huang1, S Cory, A Strasser
1The Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria, Australia.
Abstract:
Apoptosis is the physiological process by which unwanted cells in an organism are killed. Bcl-2, a membrane-bound cytoplasmic protein, is an effective inhibitor of apoptotic cell death induced by many cytotoxic agents. Survival-promoting homologues of Bcl-2 include its close relative, Bcl-xL and the 19 kD protein encoded by the E1B gene of adenoviruses. Whether these proteins are functionally equivalent and whether they can antagonise all or only some pathways to apoptosis is unresolved. We have carried out a systematic comparison of Bcl-2, Bcl-xL and adenovirus E1B19kD activity, using several cell lines and a range of cytotoxic conditions. High levels of expression of each of these proteins inhibited apoptosis induced by growth factor deprivation or treatment with gamma-radiation, glucocorticoid and various cytotoxic drugs. In contrast, none of them could effectively counter apoptosis induced via the TNF receptor or Fas/APO-1 (CD95). Biochemical analysis revealed that all three proteins can associate with Bax and Bak, members of the Bcl-2 protein subfamily that can facilitate apoptosis. The results provide evidence that Bcl-2, Bcl-xL and adenovirus protein E1B19kD are indistinguishable in their ability to regulate the cell death effector machinery.
Insights
Bcl-2, Bcl-xL, and adenovirus E1B19kD proteins equally inhibit apoptosis from various cytotoxic agents but not TNF or Fas pathways. These proteins associate with Bax and Bak, regulating cell death machinery.
Area of Science:
- Cell Biology
- Molecular Biology
- Virology
Background:
- Apoptosis is a crucial physiological process for eliminating unwanted cells.
- Bcl-2 is a key inhibitor of apoptosis, with homologues like Bcl-xL and adenovirus E1B19kD.
- The functional equivalence and pathway specificity of these inhibitors remain unclear.
Purpose of the Study:
- To systematically compare the anti-apoptotic activities of Bcl-2, Bcl-xL, and adenovirus E1B19kD.
- To determine if these proteins can antagonize all or only specific apoptosis pathways.
- To investigate the interaction of these proteins with apoptosis facilitators like Bax and Bak.
Main Methods:
- Comparative analysis of Bcl-2, Bcl-xL, and adenovirus E1B19kD in multiple cell lines.
- Exposure to various cytotoxic conditions including growth factor deprivation, gamma-radiation, glucocorticoids, and cytotoxic drugs.
- Biochemical assays to assess protein-protein interactions, specifically with Bax and Bak.
Main Results:
- High expression of Bcl-2, Bcl-xL, and E1B19kD inhibited apoptosis induced by growth factor deprivation, gamma-radiation, glucocorticoids, and cytotoxic drugs.
- None of the proteins effectively blocked apoptosis induced via the TNF receptor or Fas/APO-1 (CD95).
- All three proteins were found to associate with Bax and Bak, apoptosis-promoting members of the Bcl-2 subfamily.
Conclusions:
- Bcl-2, Bcl-xL, and adenovirus E1B19kD demonstrate indistinguishable functional capabilities in regulating the cell death effector machinery.
- These proteins specifically inhibit certain apoptosis pathways while being ineffective against others, such as those involving TNF or Fas.
- The association with Bax and Bak supports their role in modulating apoptosis.