Impaired DNA repair capacity in skin fibroblasts from various hereditary cancer-prone syndromes.

Host-cell reactivation (HCR) of UV-C-irradiated herpes simplex virus type 1 (HSV-1) has been determined in skin fibroblasts from the following hereditary cancer-prone syndromes: aniridia (AN), dysplastic nevus syndrome (DNS), Von Hippel-Lindau syndrome (VHL), Li-Fraumeni syndrome (LFS) and a family with high incidence of breast and ovarian cancer. Cells from AN, DNS or VHL patients were found to exhibit heterogeneity in HCR. Cells from individuals belonging to an LFS family show reduced HCR in all cases where the cells were derived from persons carrying one mutated p53 allele, whereas cells derived from members with two wild-type alleles show normal HCR. LFS cells with reduced HCR also reveal reduced genome overall repair, and a slower gene-specific repair of the active adenosine deaminase (ADA) gene, but little if any repair of the inactive 754 gene. In the breast/ovarian cancer family, reduced HCR is observed in skin fibroblasts derived from both afflicted and unaffected individuals. In addition, these cells display lower survival after exposure to UV-C and exhibit higher levels of SCEs than those in normal cells. These observations indicate that various hereditary cancer-prone syndromes, carrying mutations in different tumor-suppressor genes, exhibit an unexplained impairment of the capacity to repair UV-damaged DNA.

A lack of radiation-induced ornithine decarboxylase activity prevents enhanced reactivation of herpes simplex virus and is linked to non-cancer proneness in xeroderma pigmentosum patients.

Patients with xeroderma pigmentosum (XP), a DNA repair disorder, run a large risk of developing skin cancer in sun-exposed areas. Cancer proneness in these patients correlates with a mammalian SOS-like response, "enhanced reactivation (ER) of viruses." Here, we report that radiation-induced activation of the ornithine decarboxylase (ODC) gene, a putative proto-oncogene, is required for this response. Various diploid fibroblast strains derived from a non-cancer-prone subclass of XP patients, which lack the ER response, were irradiated with 2 J/m2 and assessed for gene induction. In these fibroblasts, an absence of induction of ODC by UV-C was observed at the levels of mRNA, protein, and enzyme activity. This lack of induction is quite specific because the genes for fos and collagenase were induced as they were in normal XP cells. The apparent linkage between non-cancer proneness and a lack of ER and ODC induction was confirmed in a fibroblast strain derived from a patient with another DNA repair disorder, trichothiodystrophy, which does not lead to cancer proneness: in these cells, no induction of the ER response nor of ODC occurs after UV-C irradiation. Repair deficiency, however, is not essential because the simultaneous lack of ODC and ER induction after 10 J/m2 UV-C was found in at least one repair-proficient fibroblast. Next, a specific inhibitor of ODC, difluoromethylornithine, at a dose of 10 mM, completely blocked the ER response in cultured normal skin fibroblasts, suggesting that the ODC enzyme is in fact essential for the ER response. Difluoromethylornithine, although it did not affect other processes such as DNA repair, leads to a block in the cell division cycle at the G1-S transition. Interestingly, other blockers of this transition, wortmannin (500 nM) and mimosine (100 mM), also decreased the ER response. Finally, the ER and ODC responses also seem to be linked after treatment with X-irradiation (3 Gy), suggesting that both are part of a general response to DNA damage, at least in human skin fibroblasts. Apart from the abnormal ER and ODC responses, fibroblasts from non-tumor-prone XP patients react in the same way to radiation as do fibroblasts from tumor-prone XP patients with respect to other parameters. Thus, the lack of ODC induction after radiation may help to protect XP patients against skin carcinogenesis.