Sikpi M O, Wang Y, Mallya S M
Department of Oral Diagnosis, School of Dental Medicine, University of Connecticut Health Center, Farmington 06030-MC1605, USA.
Radiat Res. 1998 Dec;150(6):627-35.
Ataxia telangiectasia (AT) cells are defective in responding to damage induced by ionizing radiation. To study the modulation of double-strand break (DSB) repair by ionizing radiation and a defect in such modulation in AT cells, we compared processing of linearized shuttle vector pZ189 (linear DNA) by unirradiated or gamma-irradiated normal and AT lymphoblast hosts. The linear DNA processed in unirradiated AT and normal host cells yielded similar mutation frequencies in the supF-tRNA target gene. Irradiation of normal but not AT host cells decreased plasmid mutation frequency 2-fold if transfection occurred immediately. However, if transfection occurred 2 h after host cell irradiation, mutation frequencies increased 2-fold above those in unirradiated controls in both normal and AT hosts. DSB rejoining capability, based on the ratio of the number of progeny arising from equal amounts of linear DNA and supercoiled, undamaged pZ189, was 25- to 50-fold higher in normal than in AT hosts when both were unirradiated. Irradiation decreased DSB rejoining capability 2- to 5-fold in normal hosts but did not alter that of AT hosts. These findings demonstrate that AT cells normally rejoin DSBs as accurately as normal cells but do so less often, and that AT cells are defective in modulation of DSB rejoining by ionizing radiation.
共济失调毛细血管扩张症（AT）细胞在对电离辐射诱导的损伤作出反应方面存在缺陷。为了研究电离辐射对双链断裂（DSB）修复的调节作用以及AT细胞中这种调节的缺陷，我们比较了未照射或经γ射线照射的正常和AT淋巴母细胞宿主对线性化穿梭载体pZ189（线性DNA）的处理情况。在未照射的AT和正常宿主细胞中处理的线性DNA在supF - tRNA靶基因中产生了相似的突变频率。如果立即进行转染，照射正常但不照射AT宿主细胞会使质粒突变频率降低2倍。然而，如果在宿主细胞照射后2小时进行转染，正常和AT宿主中的突变频率均比未照射对照增加2倍。基于等量线性DNA和超螺旋、未受损pZ189产生的子代数量之比，未照射时正常宿主的DSB重新连接能力比AT宿主高25至50倍。照射使正常宿主的DSB重新连接能力降低2至5倍，但不改变AT宿主的DSB重新连接能力。这些发现表明，AT细胞通常与正常细胞一样准确地重新连接DSB，但频率较低，并且AT细胞在电离辐射对DSB重新连接的调节方面存在缺陷。
