BH3 mimetics reactivate autophagic cell death in anoxia-resistant malignant glioma cells
Holger Hetschko1, Valerie Voss, Christian Senft
1Department of Neurosurgery, Johann Wolfgang Goethe University Clinics, Frankfurt, Main, Germany.
Abstract:
Here, we investigated the specific roles of Bcl-2 family members in anoxia tolerance of malignant glioma. Flow cytometry analysis of cell death in 17 glioma cell lines revealed drastic differences in their sensitivity to oxygen withdrawal (<0.1% O(2)). Cell death correlated with mitochondrial depolarization, cytochrome C release, and translocation of green fluorescent protein (GFP)-tagged light chain 3 to autophagosomes but occurred in the absence of caspase activation or phosphatidylserine exposure. In both sensitive and tolerant glioma cell lines, anoxia caused a significant up-regulation of BH3-only genes previously implicated in mediating anoxic cell death in other cell types (BNIP3, NIX, PUMA, and Noxa). In contrast, we detected a strong correlation between anoxia resistance and high expression levels of antiapoptotic Bcl-2 family proteins Bcl-xL, Bcl-2, and Mcl-1 that function to neutralize the proapoptotic activity of BH3-only proteins. Importantly, inhibition of both Bcl-2 and Bcl-xL with the small-molecule BH3 mimetics HA14-1 and BH3I-2' and by RNA interference reactivated anoxia-induced autophagic cell death in previously resistant glioma cells. Our data suggest that endogenous BH3-only protein induction may not be able to compensate for the high expression of antiapoptotic Bcl-2 family proteins in anoxia-resistant astrocytomas. They also support the conjecture that BH3 mimetics may represent an exciting new approach for the treatment of malignant glioma.
Insights
Malignant glioma cells show varying sensitivity to oxygen withdrawal. High levels of anti-apoptotic Bcl-2 proteins confer resistance, but BH3 mimetics can re-sensitize these cells, offering a potential new glioma treatment.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Malignant glioma exhibits diverse responses to anoxia (low oxygen).
- Bcl-2 family proteins play critical roles in regulating cell death pathways.
- Understanding anoxia tolerance mechanisms is crucial for glioma treatment.
Purpose of the Study:
- To investigate the specific roles of Bcl-2 family members in malignant glioma anoxia tolerance.
- To identify molecular mechanisms underlying differential sensitivity to oxygen withdrawal in glioma cells.
- To evaluate the therapeutic potential of targeting Bcl-2 family proteins in anoxia-resistant gliomas.
Main Methods:
- Flow cytometry analysis of cell death in 17 glioma cell lines under anoxic conditions.
- Assessment of mitochondrial depolarization, cytochrome C release, and autophagy markers (GFP-tagged LC3).
- Analysis of BH3-only gene expression and anti-apoptotic Bcl-2 family protein levels (Bcl-xL, Bcl-2, Mcl-1).
- Treatment with small-molecule BH3 mimetics (HA14-1, BH3I-2') and RNA interference to inhibit Bcl-2 and Bcl-xL.
Main Results:
- Glioma cell lines displayed significant differences in sensitivity to oxygen withdrawal.
- Anoxia induced cell death via mitochondrial pathways and autophagy, independent of caspase activation.
- Anoxia resistance correlated with high expression of anti-apoptotic Bcl-2 proteins (Bcl-xL, Bcl-2, Mcl-1).
- Inhibition of Bcl-2 and Bcl-xL using BH3 mimetics or RNA interference restored anoxia-induced cell death in resistant cells.
Conclusions:
- High expression of anti-apoptotic Bcl-2 proteins in anoxia-resistant astrocytomas may counteract endogenous BH3-only protein induction.
- BH3 mimetics demonstrate potential as a novel therapeutic strategy for treating malignant glioma by overcoming anoxia resistance.
