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Expression level of Bcl-2 determines anti- or proapoptotic function
N Shinoura1, Y Yoshida, M Nishimura
1Department of Molecular Biotherapy Research, Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo.
Abstract:
Bcl-2 is an oncogene with antiapoptotic function. However, Bcl-2 is converted to a Bax-like death effector by caspases, suggesting that the expression of Bcl-2 may not favor the growth of cancers. We introduced the Bcl-2 gene to gliomas via adenovirus (Adv; Adv-Bcl-2) with the Adv for Fas (Adv-Fas) and the Adv for Fas ligand (Adv-FL) to evaluate the antiapoptotic function of Bcl-2. In U251 glioblastoma cells, Bcl-2 at a low level of expression repressed apoptosis induced by Adv-Fas and Adv-FL, whereas Bcl-2 at a high level of expression did not. On the other hand, Bcl-X(L) showed antiapoptotic function against Fas-mediated apoptosis, irrespective of its expression level. In glioblastoma cells, induction of Bcl-2 alone at a high level induced apoptosis, whereas induction of Bcl-X(L) alone did not. As the multiplicity of infection of Adv-Bcl-2 was increased, the quantity of a cleaved product of Bcl-2 increased. Induction of caspase-inhibitory genes (CrmA and p35) inhibited apoptosis induced by Adv-Bcl-2. Induction of Bcl-2 led to alteration of the membrane potential and structure of the mitochondria. In summary, although Bcl-2 at a low level of expression was antiapoptotic, Bcl-2 at a high level of expression was proapoptotic to Fas-mediated apoptosis. Overexpression of Bcl-X(L) was consistently antiapoptotic to Fas-mediated apoptosis.
Insights
Bcl-2 protein
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Bcl-2 is an oncogene typically associated with anti-apoptotic functions.
- Caspase-mediated cleavage of Bcl-2 converts it into a pro-apoptotic effector, challenging its role in cancer growth.
- Understanding Bcl-2's dual role is crucial for cancer therapy development.
Purpose of the Study:
- To investigate the antiapoptotic function of Bcl-2 in glioma cells under varying expression levels.
- To compare the effects of Bcl-2 and Bcl-X(L) on Fas-mediated apoptosis in glioblastoma.
- To elucidate the mechanisms underlying Bcl-2's pro- or anti-apoptotic activity.
Main Methods:
- Adenovirus-mediated gene delivery (Adv-Bcl-2, Adv-Fas, Adv-FL) into U251 glioblastoma cells.
- Assessment of apoptosis induction and caspase activity.
- Analysis of mitochondrial membrane potential and structure changes.
Main Results:
- Low-level Bcl-2 expression inhibited Fas-mediated apoptosis, while high-level expression promoted it.
- Bcl-X(L) consistently exhibited antiapoptotic function against Fas-mediated apoptosis, regardless of expression level.
- High-level Bcl-2 induction alone induced apoptosis and altered mitochondrial integrity, with increased cleaved Bcl-2 product correlating with viral load.
Conclusions:
- Bcl-2 exhibits context-dependent function, acting as antiapoptotic at low levels and proapoptotic at high levels in Fas-mediated apoptosis.
- Bcl-X(L) provides a stable antiapoptotic effect against Fas-mediated apoptosis.
- The findings suggest that high-level Bcl-2 expression may not be beneficial for cancer growth due to its proapoptotic conversion and mitochondrial disruption.