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Okadaic-acid-induced apoptosis in malignant glioma cells
Bimal G Rami1, Lawrence S Chin, Barbara E Lazio
1Department of Neurosurgery and Greenbaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland, USA.
Object:
Okadaic acid (OA), a potent protein phosphatase inhibitor, has been known to induce apoptosis in a variety of cell types. The authors attempted to characterize further this model by identifying proteins involved in this form of programmed cell death.
Methods:
Cellular proliferation was assessed using a colorimetric nonradioactive proliferation assay and cell counts. Apoptosis was determined by fluorescent microscopy. Activation of the mitogen-activated protein kinase (MAPK) pathways was determined by immunoprecipitation of extracellular signal-regulated kinase (ERK), c-Jun-N-terminal kinase (JNK), and p38 followed by in vitro kinase assays. Western blot analyses were conducted to show inhibitory-kappaB (IkappaB) phosphorylation and degradation as well as Bax upregulation. The binding of nuclear factor-kappaB (NFkappaB) was shown by electrophoretic mobility shift assay. Okadaic acid induced cell death in T98G human malignant cell lines (50% inhibiting concentration = 20-25 nM). In T98G cells YO-PRO fluorescent staining was identified, thus indicating an apoptotic mechanism with a smaller percentage of cells undergoing necrotic cell death. Additionally OA induced JNK and MAPK activities in a time-dependent manner, increased the expression of Bax, and increased IkappaB phosphorylation and NFkappaB activation. There was a temporal correlation between these subcellular events and the detection of apoptosis morphology in glioma cells.
Conclusions:
The authors believe that OA acts by blocking dephosphorylation events, thus activating apoptotic pathways through ERK and JNK activity. Additionally Bax, IkappaB and NFkappaB may also play a role in regulating these pathways.
Insights
Okadaic acid induces apoptosis in glioma cells by inhibiting protein phosphatases, activating specific cell signaling pathways, and upregulating key proteins like Bax.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Okadaic acid (OA) is a known protein phosphatase inhibitor that induces apoptosis.
- Understanding the molecular mechanisms of OA-induced apoptosis is crucial for cancer research.
Purpose of the Study:
- To characterize the proteins involved in okadaic acid-induced programmed cell death.
- To further elucidate the apoptotic pathways activated by OA in human malignant cell lines.
Main Methods:
- Assessed cellular proliferation using colorimetric assays and cell counts.
- Determined apoptosis via fluorescent microscopy and YO-PRO staining.
- Analyzed mitogen-activated protein kinase (MAPK) pathway activation (ERK, JNK, p38) using immunoprecipitation and kinase assays.
- Utilized Western blot to detect IkappaB phosphorylation/degradation and Bax upregulation.
- Confirmed nuclear factor-kappaB (NFkappaB) binding through electrophoretic mobility shift assay.
Main Results:
- Okadaic acid induced cell death in T98G human malignant glioma cells with an IC50 of 20-25 nM.
- Apoptosis was the primary mechanism of cell death, with a smaller percentage undergoing necrosis.
- OA treatment time-dependently increased JNK and MAPK activities, upregulated Bax expression, and enhanced IkappaB phosphorylation and NFkappaB activation.
- A temporal correlation was observed between these molecular events and the morphological detection of apoptosis.
Conclusions:
- Okadaic acid-induced apoptosis is mediated by blocking dephosphorylation events, leading to the activation of apoptotic pathways via ERK and JNK.
- Bax, IkappaB, and NFkappaB are implicated as key regulators in OA-induced apoptotic signaling cascades.
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