Whisnant-Hurst N, Leadon S A
Department of Radiation Oncology, University of North Carolina at Chapel Hill, 27599-7512, USA.
Radiat Res. 1999 Mar;151(3):257-62.
Exposure of human cells to ionizing radiation at the G1/S-phase border of the cell cycle leads to the production of repair patches of 3 nucleotides, representing the constitutive repair response, and very long repair patches (VLRP) of at least 150 nucleotides, representing an induced response. We examined the type of DNA damage that may signal this induced repair response using two chemicals that produce subsets of the damage induced by ionizing radiation. Treatment of cells at the G1/S-phase border with bleomycin, which produces a high proportion of DNA double-strand breaks, also leads to the production of VLRP of at least 130 nucleotides. In contrast, when cells were treated with hydrogen peroxide, which produces base modifications and single-strand breaks, no VLRP were observed. Thus it would appear that DNA double-strand breaks are the signal that leads to the induction of the VLRP. We also examined the relationship between the induced repair response and DNA replication. When cells are treated with hydroxyurea, under conditions that inhibit more than 98% of the DNA synthesis, prior to exposure to 5 Gy, repair patches of 3 and 150 nucleotides are found. This indicates that the longer repair patches are not a result of aberrant DNA replication. However, when cells are treated with the DNA polymerase inhibitor aphidicolin in combination with hydroxyurea and cytosine arabinoside, no induced long patches are found. These results indicate that DNA polymerase alpha, delta or epsilon is required for the synthesis of the VLRP.
将人类细胞在细胞周期的G1/S期边界暴露于电离辐射下，会导致产生3个核苷酸的修复片段，这代表了组成性修复反应，以及至少150个核苷酸的非常长的修复片段（VLRP），这代表了诱导性反应。我们使用两种能产生电离辐射诱导损伤子集的化学物质，研究了可能引发这种诱导性修复反应的DNA损伤类型。在G1/S期边界用博来霉素处理细胞，博来霉素会产生高比例的DNA双链断裂，这也会导致产生至少130个核苷酸的VLRP。相比之下，当用产生碱基修饰和单链断裂的过氧化氢处理细胞时，未观察到VLRP。因此，似乎DNA双链断裂是导致VLRP诱导的信号。我们还研究了诱导性修复反应与DNA复制之间的关系。当在抑制超过98%的DNA合成的条件下，用羟基脲处理细胞，然后再暴露于5 Gy辐射时，会发现3个核苷酸和150个核苷酸的修复片段。这表明较长的修复片段不是异常DNA复制的结果。然而，当用DNA聚合酶抑制剂阿非迪霉素与羟基脲和阿糖胞苷联合处理细胞时，未发现诱导的长片段。这些结果表明，VLRP的合成需要DNA聚合酶α、δ或ε。
