Differential behaviors toward ultraviolet A and B radiation of fibroblasts and keratinocytes from normal and DNA-repair-deficient patients.

Xeroderma pigmentosum (XP) and trichothiodystrophy (TTD) are rare genodermatoses transmitted as recessive and autosomal traits that result in reduced capacity to repair UV-induced DNA lesions. Although XP, but not TTD, patients are prone to basal and squamous cell carcinomas, to date no comparative studies of the XP and TTD phenotypes have included epidermal keratinocytes. We compared the DNA repair capacity (by unscheduled DNA synthesis) and cell survival (by clonal analysis) of epidermal keratinocytes and dermal fibroblasts grown from normal individuals and patients with xeroderma pigmentosum and trichothiodystrophy following UVA and UVB irradiation. The same dose of UVB (1000 J/m2) induced twice as many DNA lesions in normal fibroblasts as in normal keratinocytes. UV survival rates were always higher in keratinocytes than in fibroblasts. Normal and TTD keratinocytes survived better following UVA and UVB irradiation than XP-C and XP-D keratinocytes. XP-C keratinocytes exhibited exacerbated sensitivity toward UVA radiation. Unscheduled DNA synthesis at UV doses leading to 50% cell survival indicated that the ratio of DNA repair capacity to cell survival is higher in keratinocytes than in fibroblasts. In addition, UVA and UVB irradiation induced a transition from proliferative to abortive keratinocyte colonies. This transition varied between donors and was in part correlated with their cancer susceptibility. Altogether these data provide the first evidence of the differential behaviors of normal, XP, and TTD keratinocytes toward UV radiation.