Xeroderma pigmentosum patients from the federal Republic of Germany: Decrease in post-UV colony-forming ability in 30 xeroderma pigmentosum fibroblast strains is quantitatively correlated with a decrease in DNA-incising capacity

Summary A total of 16 normal and 46 XP fibroblast strains from the Mannheim Collection were investigated for colony-forming ability following exposure to both UV light and the UV-like carcinogen (Ac)₂ONFln. The dose-response experiments included up to 13 dose levels. The exponential segments of the curves were analysed by linear regression and the negative reciprocal of the regression coefficient (D₀) was calculated for each cell strain.For quantitating the DNA-incising capacity, DNA elution curves were determined at several UV dose levels. Plotting the initial velocities of the elution curves versus the UV dose yielded a regression line, the slope of which was used to obtain the characteristic value E₀.Comparing D₀ with E₀ values showed that cell strains in which colony-forming ability was reduced suffered a reduction of DNA-incising capacity of the same magnitude. There were only 3 exceptional strains in which reduction of DNA-incising capacity was less pronounced than reduction of colony-forming ability. We have previouly shown (Fischer et al. 1982) that D₀ values from 27 XP strains of the Mannheim Collection were correlated with clinical symptoms. This correlation is now being extended by relating colony-forming ability to the magnitude of the DNA incision defect. From our data we conclude that the best quantitative biochemical denominator to explain the sun sensitivity of XP is that of a defective incision of UV-damaged DNA.A considerable similarity in sensitivity towards both UV light and (Ac)₂ONFln was found in 16 normal and 46 XP strains. This seems to indicate that UV-and (Ac)₂ONFln-induced DNA damage are removed to a large extent by the same pathways in human fibroblasts.Abbreviations XP xeroderma pigmentosum - (Ac)₂ONFln N-acetoxy-2-acetylaminofluorene - UV light ultraviolet light - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - ara-C 1--d-arabinofuranosyl cytosineThis work was supported by the Deutsche Forschungsgemeinschaft, SFB 136