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Modulation of antioxidant defenses during apoptosis
M M Briehl1, A F Baker, L M Siemankowski
1Department of Pathology, University of Arizona, Tucson 85724, USA. mmbriehl@mail.arizona.edu
Abstract:
Understanding the fundamental mechanism of apoptosis is crucial to developing therapeutic strategies for controlling apoptosis in diseased tissues. We are using model systems with relevance to cancer treatment to investigate the mechanism of apoptosis. Subtraction hybridization cloning was used to identify transcripts present at higher levels in regressing vs. normal prostate; these may be important for apoptosis. One of the genes cloned from regressing prostate is also upregulated in the murine W7.2 lymphocyte cell line induced to undergo apoptosis by treatment with the synthetic glucocorticoid, dexamethasone. This gene encodes a mu class glutathione S-transferase (EC 2.5.1.18), a protein that can protect the cell against oxidative stress by repairing oxidized lipids, proteins, and DNA. Glutathione S-transferase expression does not increase with dexamethasone treatment of lymphocyte cell lines expressing nonfunctional glucocorticoid receptors or a mutation in the apoptotic pathway. Other antioxidant defenses, including catalase (EC 1.11.1.6) and superoxide dismutase (EC 1.15.1.1), decline following dexamethasone treatment of W7.2 cells. Overexpression of the bcl-2 oncogene protects these cells against dexamethasone-mediated apoptosis and prevents the decrease in antioxidant enzyme activity. These findings support the hypothesis that control of the cellular redox state is important to the mechanism of glucocorticoid-mediated lymphocyte apoptosis. Another model system we are using is tumor necrosis factor-alpha treatment of MCF-7 human breast cancer cells. Our preliminary results suggest that, in this system, activation of nuclear factor-kappa B and increased expression of manganese superoxide dismutase may afford protection from apoptosis.
Insights
Glutathione S-transferase and antioxidant defenses are key to glucocorticoid-induced apoptosis in lymphocytes. Bcl-2 oncogene overexpression protects cells by maintaining antioxidant enzyme activity, highlighting redox state control in apoptosis.
Area of Science:
- Cellular Biology
- Biochemistry
- Oncology
Background:
- Understanding apoptosis mechanisms is vital for cancer therapy development.
- Glucocorticoids and tumor necrosis factor-alpha are potent inducers of apoptosis.
- Cellular redox state plays a critical role in programmed cell death.
Purpose of the Study:
- To investigate the role of glutathione S-transferase and antioxidant enzymes in glucocorticoid-induced lymphocyte apoptosis.
- To explore the protective effects of bcl-2 oncogene against dexamethasone-mediated apoptosis.
- To examine the involvement of nuclear factor-kappa B and manganese superoxide dismutase in tumor necrosis factor-alpha-induced apoptosis of breast cancer cells.
Main Methods:
- Subtraction hybridization cloning to identify apoptosis-related genes in regressing prostate tissue.
- Dexamethasone treatment of murine W7.2 lymphocyte cell lines with varying glucocorticoid receptor functionality.
- Overexpression of bcl-2 oncogene in W7.2 cells.
- Tumor necrosis factor-alpha treatment of MCF-7 human breast cancer cells.
- Analysis of glutathione S-transferase, catalase, and superoxide dismutase expression and activity.
- Assessment of nuclear factor-kappa B activation and manganese superoxide dismutase expression.
Main Results:
- A mu class glutathione S-transferase gene, upregulated in regressing prostate and dexamethasone-treated lymphocytes, protects against oxidative stress.
- Glutathione S-transferase expression is not induced by dexamethasone in cells with nonfunctional glucocorticoid receptors or defective apoptotic pathways.
- Catalase and superoxide dismutase activities decline following dexamethasone treatment, but are preserved by bcl-2 oncogene overexpression.
- Preliminary data suggest nuclear factor-kappa B activation and increased manganese superoxide dismutase expression may protect MCF-7 cells from tumor necrosis factor-alpha-induced apoptosis.
Conclusions:
- Control of the cellular redox state is crucial for glucocorticoid-mediated lymphocyte apoptosis.
- Glutathione S-transferase and other antioxidant defenses are integral to the apoptotic process.
- The bcl-2 oncogene confers resistance to apoptosis by maintaining antioxidant enzyme function.
- Nuclear factor-kappa B and manganese superoxide dismutase may represent protective mechanisms against apoptosis in breast cancer cells.