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Deficiency in the catalase activity of xeroderma pigmentosum cell and simian virus 40-transformed human cell extracts
Abstract:
It has been previously shown that skin biopsies isolated from various xeroderma pigmentosum (XP) patients present a permanent decline in catalase activity from the onset of the disease to the tumor formation. We report here that cultured XP cell strains are also markedly deficient in the catalase activity with about only 25% of the activity measured in normal human cells. No direct correlation between catalatic activity and excision repair ability has been found, since a XP variant line is as deficient as an XP-C strain. The exact cause of the catalase deficiency is still unknown but could be due to the synthesis of a modified enzyme or to an abnormal regulation leading to a limited enzyme synthesis. Furthermore, simian virus 40 transformation of normal and radiosensitive cells (XP, ataxia telangiectasia) provokes a decrease in catalase activity of about 80% compared to the control derivatives. Mathematical analysis performed on our data shows a clearcut distinction between XP and normal cells while some of the XP heterozygote cells exhibit an intermediate behavior. Although most of the XP syndrome could be explained by the impairment in the excision repair ability, the decrease in catalase activity leading to a probable increase in intracellular H2O2 concentration and/or to a higher sensitivity to any oxygen-activated species could represent an additive effect in inducing the carcinogenic process.
Insights
Xeroderma pigmentosum (XP) cells show significantly reduced catalase activity, potentially contributing to cancer development. This deficiency, independent of DNA repair capacity, may increase sensitivity to oxidative stress.
Area of Science:
- Biochemistry
- Genetics
- Oncology
Background:
- Xeroderma pigmentosum (XP) is a genetic disorder characterized by defective DNA repair.
- XP patients exhibit reduced catalase activity, an enzyme crucial for neutralizing hydrogen peroxide.
- The role of catalase deficiency in XP pathogenesis remains unclear.
Purpose of the Study:
- To investigate catalase activity in cultured XP cell strains.
- To determine the relationship between catalase deficiency and DNA repair capacity in XP.
- To explore the impact of simian virus 40 transformation on catalase activity in normal and XP cells.
Main Methods:
- Culturing of XP and normal human cell strains.
- Measurement of catalase activity in cellular extracts.
- Simian virus 40 (SV40) transformation of cells.
- Mathematical analysis of enzyme activity data.
Main Results:
- Cultured XP cells displayed approximately 25% of normal human cell catalase activity.
- No direct correlation was found between catalase activity and DNA excision repair ability.
- SV40 transformation reduced catalase activity by about 80% in both normal and XP cells.
- XP cells showed a distinct catalase deficiency compared to normal cells, with heterozygotes exhibiting intermediate levels.
Conclusions:
- XP cells have a significant intrinsic deficiency in catalase activity.
- This catalase deficiency may exacerbate cancer risk in XP by increasing oxidative stress.
- Catalase dysfunction could be an additive factor in XP carcinogenesis, alongside DNA repair defects.