Proteasome inhibitors induce mitochondria-independent apoptosis in human glioma cells
H Kitagawa1, E Tani, H Ikemoto
1Department of Neurosurgery, Hyogo College of Medicine, Nishinomiya, Japan.
Abstract:
The proteasome inhibitors lactacystin and AcLLNal induced p53-independent apoptosis in two human glioma cell lines, and the apoptosis was accompanied by up-regulation of immunoreactive wild-type p53, p21Waf1, Mdm2, and p27Kip1. Pretreatment with cycloheximide decreased the induction of cell death independently of p53 protein status, suggesting that the up-regulation of short-lived proteins is associated with proteasome inhibitor-induced apoptosis. Caspase-3-like proteases were activated in the proteasome inhibitor-mediated apoptosis, and the induction of cell death was inhibited more effectively in the presence of z-VAD.fmk than in the presence of Ac-DEVD.fmk, suggesting that caspases other than caspase-3 are involved. Nonetheless, there were no significant alterations in levels of immunoreactive Bcl-2, Bcl-X(L), Bax, Bad, and Bak, nor any evidence of cytochrome c release into cytosol and dissipation of delta(psi)m. Thus, the proteasome inhibitor-induced apoptosis is mediated by a mitochondria-independent mechanism, and the once activated caspase-3 does not cause the cytochrome c release and the delta(psi)m disruption.
Insights
Proteasome inhibitors trigger apoptosis in glioma cells via a p53-independent pathway involving short-lived proteins and caspases. This process bypasses the mitochondria, indicating a novel cell death mechanism.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Proteasome inhibitors are investigated for cancer therapy.
- Glioma is a common brain tumor with limited treatment options.
- Apoptosis, or programmed cell death, is a key target for cancer treatments.
Purpose of the Study:
- To investigate the mechanism of apoptosis induced by proteasome inhibitors in human glioma cells.
- To determine the role of p53 and caspases in proteasome inhibitor-induced apoptosis.
- To elucidate whether the mitochondrial pathway is involved in this process.
Main Methods:
- Treatment of human glioma cell lines with proteasome inhibitors (lactacystin, AcLLNal).
- Assessment of apoptosis, protein levels (p53, p21Waf1, Mdm2, p27Kip1, Bcl-2 family proteins), and caspase activation.
- Inhibition studies using cycloheximide and caspase inhibitors (z-VAD.fmk, Ac-DEVD.fmk).
- Analysis of mitochondrial membrane potential (delta(psi)m) and cytochrome c release.
Main Results:
- Proteasome inhibitors induced p53-independent apoptosis with upregulation of p53, p21Waf1, Mdm2, and p27Kip1.
- Apoptosis was linked to the upregulation of short-lived proteins.
- Caspase-3-like proteases were activated, with involvement of caspases beyond caspase-3.
- No significant changes in Bcl-2 family proteins, cytochrome c release, or mitochondrial membrane potential were observed.
Conclusions:
- Proteasome inhibitors induce apoptosis in glioma cells through a mitochondria-independent pathway.
- The mechanism involves p53-independent upregulation of specific proteins and caspase activation.
- Activated caspase-3 does not appear to mediate mitochondrial outer membrane permeabilization in this context.
