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Phorbol ester induces manganese-superoxide dismutase in tumor necrosis factor-resistant cells
1Department of Biochemistry, Osaka University Medical School, Japan.
Abstract:
The effects of phorbol ester (TPA) and other known stimulators such as tumor necrosis factor (TNF), interleukin-1, and lipopolysaccharide on induction of mRNA for manganese-superoxide dismutase (Mn-SOD) were investigated in various cell lines. TPA enhanced Mn-SOD mRNA expression in TNF-resistant cell lines including HeLa cells, in which the other reagents also induced expression of the gene, but did not affect TNF-sensitive cells, in which the other stimulators did not alter expression of the gene. HeLa cells which had been desensitized to TPA by pretreatment with TPA for 24 h expressed Mn-SOD mRNA at a slightly higher level than the cells without TPA treatment. TPA-pretreated cells stimulated with TNF, however, expressed Mn-SOD mRNA at about twice the level of TNF-stimulated, TPA-untreated cells. When protein synthesis was inhibited by cycloheximide during TPA pretreatment, TNF no more enhanced the Mn-SOD mRNA accumulation. These data suggest that at least two separate signal-transducing pathways are involved in expression of this gene. One is triggered by protein kinase C activation itself in the absence of new protein synthesis. The other can be activated by stimulation with TNF, interleukin-1, or lipopolysaccharide and in which a protein factor that can be induced by TPA treatment is involved.
Insights
Phorbol ester (TPA) and other stimulators differentially regulate manganese-superoxide dismutase (Mn-SOD) mRNA expression. TPA enhances Mn-SOD mRNA in some cells, suggesting distinct signaling pathways for gene expression.
Area of Science:
- Cellular biology
- Molecular biology
- Biochemistry
Background:
- Manganese-superoxide dismutase (Mn-SOD) is a crucial antioxidant enzyme.
- Understanding Mn-SOD gene regulation is vital for cellular protection.
- Phorbol ester (TPA) and inflammatory cytokines are known modulators of cellular processes.
Purpose of the Study:
- To investigate the effects of TPA and other stimulators on Mn-SOD mRNA induction.
- To elucidate the signaling pathways involved in Mn-SOD gene expression.
- To compare the responses in TNF-sensitive and TNF-resistant cell lines.
Main Methods:
- Treatment of various cell lines with TPA, TNF, IL-1, and LPS.
- Analysis of Mn-SOD mRNA expression levels.
- Investigation using cycloheximide to inhibit protein synthesis during TPA pretreatment.
Main Results:
- TPA enhanced Mn-SOD mRNA in TNF-resistant cells (e.g., HeLa) but not in TNF-sensitive cells.
- TPA pretreatment followed by TNF stimulation led to a twofold increase in Mn-SOD mRNA.
- Inhibition of protein synthesis during TPA pretreatment blocked TNF-mediated enhancement of Mn-SOD mRNA.
Conclusions:
- At least two distinct signal-transducing pathways regulate Mn-SOD gene expression.
- One pathway involves protein kinase C activation independent of new protein synthesis.
- Another pathway activated by TNF, IL-1, or LPS requires TPA-inducible protein factors.