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Manganese superoxide dismutase expression inhibits soft agar growth in JB6 clone41 mouse epidermal cells
P A Amstad1, H Liu, M Ichimiya
1Department of Pathology, University of Maryland, Baltimore 21201, USA.
Abstract:
Manganese superoxide dismutase (MnSOD) has been found to be depleted in a variety of tumor cells as well as in in vitro transformed cell lines, suggesting that MnSOD may function as an anticarcinogen by protecting the cell from oxidant-induced carcinogenesis. The relationship between MnSOD expression and tumor promotion was studied by transfection of a human MnSOD cDNA into the promotable mouse epidermal cell line JB6 clone41. The effect of MnSOD overexpression on the promotion-sensitive phenotype of JB6 cells was assessed by measuring growth characteristics such as growth rate and the ability to form colonies in soft agar. Compared with the parental and vector-transfected (gpt) control cells, MnSOD-overexpressing cells had a slower growth rate and their ability to form colonies in soft agar was significantly decreased in response to 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment. Since the transformation-sensitive phenotype of JB6 clone41 cells is associated with increased expression of the transcription factor AP-1, we compared c-jun and c-fos mRNA expression in MnSOD-transfected and control JB6 cells. Overexpression of MnSOD led to a significant decrease in c-jun and c-fos expression in response to treatment with TPA or the oxidant promoter superoxide. These findings indicate that the promotion-sensitive phenotype of JB6 clone41 cells can be reverted by increasing MnSOD intracellularly. A possible mechanism is that elevated MnSOD expression might change the intracellular redox state by altering the balance of reactive oxygen species. This could lead to a modulation of TPA and oxidant-induced signal transduction pathways controlling cell growth and differentiation.
Insights
Increasing manganese superoxide dismutase (MnSOD) levels in cells reduced tumor promotion. This suggests MnSOD acts as an anticarcinogen by protecting against oxidant-induced cancer and modulating cell signaling pathways.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Manganese superoxide dismutase (MnSOD) is often depleted in tumor cells.
- MnSOD may protect cells from oxidant-induced carcinogenesis, functioning as an anticarcinogen.
- The role of MnSOD in tumor promotion requires further investigation.
Purpose of the Study:
- To investigate the relationship between MnSOD expression and tumor promotion.
- To determine if increasing MnSOD levels can revert the promotion-sensitive phenotype of JB6 clone41 cells.
- To explore the underlying molecular mechanisms involving signal transduction pathways.
Main Methods:
- Transfection of human MnSOD cDNA into JB6 clone41 mouse epidermal cells.
- Assessment of growth characteristics: growth rate and soft agar colony formation.
- Measurement of c-jun and c-fos mRNA expression following treatment with TPA or superoxide.
Main Results:
- MnSOD-overexpressing cells exhibited slower growth rates compared to controls.
- Soft agar colony formation was significantly decreased in MnSOD-overexpressing cells upon TPA treatment.
- Overexpression of MnSOD led to a significant decrease in c-jun and c-fos mRNA expression in response to TPA or superoxide.
Conclusions:
- Increasing intracellular MnSOD can revert the promotion-sensitive phenotype of JB6 clone41 cells.
- Elevated MnSOD may alter the intracellular redox state, impacting reactive oxygen species balance.
- This modulation can affect TPA and oxidant-induced signaling pathways controlling cell growth and differentiation, supporting MnSOD's anticarcinogenic potential.