Are (6-4) photoproducts the main ultraviolet-induced lethal lesions?

Cleaver等人。通过化学处理，从紫外线敏感的XP-A细胞中建立了耐紫外线的着色性干皮病(XP)逆转株细胞。令人惊讶的是，抗紫外线的XP突变细胞尽管已经恢复了(6-4)光产物的修复能力，但仍然缺乏对环丁烷嘧啶二聚体的修复能力，这表明(6-4)光产物是紫外线诱导的主要致死损伤。为了证实这些结果，我用集落形成法检测了紫外线对XP-A、XP突变株和正常人细胞的细胞毒性。XP-A细胞对紫外线的敏感性是正常细胞的10倍。我发现XP突变细胞获得了几乎正常的紫外线敏感性，正如Cleaver等人所报道的那样。接下来，使用我新建立的抗光渗漏的单抗，用灵敏的ELISA法检测了两种类型的DNA损伤(环丁烷二聚体和(6-4)光产物)的修复。在(6-4)个光产物的修复中，XP-A在照射后24小时内仅修复了30%(10J/m^2)，而正常细胞在3小时内修复了90%以上。XP返回体表现出几乎正常的修复模式。在环丁烷二聚体的修复中，XP-A、XP突变株和正常细胞在照射后24小时内分别修复了20%、40%和60%。我证实了Cleaver的结果，即XP-Reverant对(6-4)感光产品的修复几乎正常，但对环丁烷二聚体的修复减少。然而，我发现XP反转剂确实减少了环丁烷二聚体的修复，但并没有完全抑制Cleaver等人报道的修复。用低剂量紫外线(2J/m2)进行的修复实验证实了这一结果。这些结果表明XP突变细胞对环丁烷二聚体仍有一定的残留修复能力。因此，这些结果表明，环丁烷嘧啶二聚体并不被排除为紫外线诱导的主要致死损伤的候选物质。

Cleaver et al. have established UV-resistant xeroderma pigmentosum (XP) revertant cells from UV-sensitive XP-A cells by chemical treatment. Surprisingly, UV-resistant XP revertant cells are still deficient in the repair of cyclobutane pyrimidine dimers, although they have recovered the repair ability of (6-4) photoproducts, suggesting that (6-4) photoproducts are the main UV-induced lethal lesions. To confirm these results, I examined UV-induced cytotoxicity in XP-A, XP revertant and normal human cells by colony formation method. XP-A cells were 10 times as UVsensitive as normal cells. I found that XP revertant cells had obtained almost normal UV sensitivity as reported by Cleaver et al. Next, the repair of two types of DNA damage (cyclobutane dimers and (6-4) photoproducts) was examined by the sensitive ELISA using monoclonal antibodies, which I had newly established, against photolesions. In the repair of (6-4) photoproducts, XP-A repaired only 30% within 24 hr after irradiation (10 J/m^2), while normal cells repaired more than 90% within 3 hr. XP revertant showed almost normal repair pattern. In the repair of cyclobutane dimers, XP-A, XP revertant and normal cells repaired 20%, 40% and 60% within 24 hr after irradiation, respectively. I confirmed Cleaver's results showing that XP-revertant had almost normal repair on (6-4) photoproducts, but had reduced repair on cyclobutane dimers. However, I found that XP revertant did have reduced repair on cyclobutane dimers, but not completely inhibited repair reported by Cleaver et al. The results were confirmed by the repair experiment using low UV dose (2 J/m^2). These results suggest that XP revertant cells still have some residual repair capacity for cyclobutane dimers. Thus, these results suggest that cyclobutane pyrimidine dimers are not excluded as a candidate for the main UV-induced lethal damage.