Our results show that high transaldolase activity corresponds to a low catalase activity in SV40-transformed cells and in fibroblasts from XP patients who have a high predisposition to develop skin cancer.
These results imply that: (i) the reduced catalase activity in XP, which might result from cellular depletion of its NADPH cofactor, is directly related to impaired DNA repair, and (ii) this depletion might be one of the multiple cellular consequences of XP inborn defect.
We have studied the UV responsiveness of xeroderma pigmentosum (XP) and HeLa cell lines transfected with a CAT reporter gene under the control of the HIV-1 LTR promoter.
We confirmed on 21 different XP diploid fibroblast lines that catalase activity was decreased on average by a factor of five as compared to controls, while XP heterozygote lines exhibited intermediary responses.
In order to characterize a DNA repair defect in an active gene in CS, we measured the capacity of cells from patients with CS and XP to reactivate 2 major types of UV-induced DNA damage, photoreactivatable (i.e., cyclobutane pyrimidine dimers) and non-photoreactivatable (primarily pyrimidine-(6-4)pyrimidone photoproducts), in the actively transcribing chloramphenicol acetyltransferase (cat) gene of the plasmid expression vector pRSV-cat.
It has been previously shown that xeroderma pigmentosum (XP) skin biopsies and their established cell lines exhibit a decrease in catalase activity and enhanced formation of photo-produced H2O2.
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.
Expression of a nonselectable gene (cat, coding for chloramphenicol acetyltransferase [CAT]) linked to a selectable gene (gpt, coding for xanthine-guanine phosphoribosyltransferase [XPRT]) in the plasmid pSV2catSVgpt was quantified after transfection of SV40-transformed xeroderma pigmentosum [XP20s(SV40)] and normal human [GM0637(SV40)] fibroblast cell lines.