Activation of multiple molecular mechanisms for apoptosis in human malignant glioblastoma T98G and U87MG cells treated with sulforaphane

Glioblastoma is the most malignant and prevalent brain tumor that still remains incurable. Recent studies reported anti-cancer effect of the broccoli-derived compound sulforaphane. We explored the mechanisms of sulforaphane-mediated apoptosis in human glioblastoma T98G and U87MG cells. Wright staini...

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Bibliographic Details
Published in:Neuroscience 2006-01, Vol.141 (3), p.1265-1280
Main Authors: Karmakar, S., Weinberg, M.S., Banik, N.L., Patel, S.J., Ray, S.K.
Format: Article
Language:English
Subjects:
Analysis of Variance
Anticarcinogenic Agents - therapeutic use
apoptosis
Apoptosis - drug effects
bcl-2-Associated X Protein - metabolism
Biological and medical sciences
Blotting, Western - methods
Ca 2
Calcium - metabolism
calpain
caspases
Caspases - metabolism
Cell Line, Tumor
Cell Survival - drug effects
Cell Survival - physiology
Dose-Response Relationship, Drug
Fundamental and applied biological sciences. Psychology
Fura-2
Ganglioglioma - drug therapy
glioblastoma
Humans
In Situ Nick-End Labeling - methods
Isothiocyanates
Models, Biological
Proto-Oncogene Proteins c-bcl-2 - metabolism
Signal Transduction - drug effects
Signal Transduction - physiology
sulforaphane
Thiocyanates - therapeutic use
Vertebrates: nervous system and sense organs
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Summary:Glioblastoma is the most malignant and prevalent brain tumor that still remains incurable. Recent studies reported anti-cancer effect of the broccoli-derived compound sulforaphane. We explored the mechanisms of sulforaphane-mediated apoptosis in human glioblastoma T98G and U87MG cells. Wright staining and ApopTag assay confirmed apoptosis in glioblastoma cells treated with sulforaphane. Increase in intracellular free Ca 2+ was detected by fura-2 assay, suggesting activation of Ca 2+-dependent pathways for apoptosis. Western blotting was used to detect changes in expression of Bax and Bcl-2 proteins resulting in increased Bax:Bcl-2 ratio that indicated a commitment of glioblastoma cells to apoptosis. Upregulation of calpain, a Ca 2+-dependent cysteine protease, activated caspase-12 that in turn caused activation of caspase-9. With the increased Bax:Bcl-2 ratio, cytochrome c was released from mitochondria to cytosol for sequential activation of caspase-9 and caspase-3. Increased calpain and caspase-3 activities generated 145 kD spectrin breakdown product and 120 kD spectrin breakdown product, respectively. Activation of caspase-3 also cleaved the inhibitor-of-caspase-activated-DNase. Accumulation of apoptosis-inducing-factor in cytosol suggested caspase-independent pathway of apoptosis as well. Two of the inhibitor-of-apoptosis proteins were downregulated because of an increase in ‘second mitochondrial activator of caspases/Direct inhibitor-of-apoptosis protein binding protein with low pI.’ Decrease in nuclear factor kappa B and increase in inhibitor of nuclear factor kappa B alpha expression favored the process of apoptosis. Collectively, our results indicated activation of multiple molecular mechanisms for apoptosis in glioblastoma cells following treatment with sulforaphane.
ISSN:0306-4522
1873-7544
DOI:10.1016/j.neuroscience.2006.04.075