Liu N, Bryant P E
School of Biological and Medical Sciences, University of St Andrews, UK.
Int J Radiat Biol. 1994 Dec;66(6 Suppl):S115-21.
The chromosomal response of two ataxia-telangiectasia (A-T) lymphoblastoid cell lines (A-T-PA and A-T-KM) to restriction endonucleases (RE) is compared with that of a normal (N-SW) lymphoblastoid cell line. The RE used were PvuII (generating DNA double-strand breaks with blunt termini), BamHI (cohesive termini with 4 base, 5' overhangs) and PstI (cohesive termini with 4 base 3' overhangs). Chromatid aberrations were analysed in cells 5 h after treatment. Cells were porated using streptolysin O to allow entry of RE. Both A-T lines showed an enhanced frequency of chromatid breaks in G2 phase compared with normal cells in response to RE. The enhanced response of A-T cells was most marked in the case of PvuII treatment when the enhancement ratios were 2.5 and 4.2 for A-T-PA and A-T-KM respectively. However, the frequency of DNA double-strand breaks (dsb), measured by neutral filter elution, were considerably lower in A-T-PA cells than N-SW, due to a lower efficiency of poration. When A-T-PA cells were treated with streptolysin O at a higher concentration (0.3 Units/ml), a condition that apparently led to a similar level of poration in A-T-PA as in N-SW cells treated with 0.06 Units/ml as judged by the similar number of dsb induced in the two lines for a given PvuII concentration, the enhancement ratio for A-T-PA cells treated with PvuII increased from 2.5 to 5.8. BamHI and PstI were found to be less clastogenic in all three cell lines as found previously for Chinese hamster cells, although part of this effect may be due to a lower activity, particularly in the case of PstI. However, even at a 4-6-fold higher concentration, BamHI was still less clastogenic than PvuII. It is concluded that dsb with blunt termini are more clastogenic than those with cohesive termini. The results suggest that the chromosomal sensitivity of A-T cells may result from a defect causing a higher rate of conversion of dsb into chromatid aberrations.
将两种共济失调毛细血管扩张症（A-T）淋巴母细胞系（A-T-PA和A-T-KM）对限制性内切酶（RE）的染色体反应与正常（N-SW）淋巴母细胞系进行比较。所使用的限制性内切酶为PvuII（产生具有平端的DNA双链断裂）、BamHI（具有4个碱基5'突出端的粘性末端）和PstI（具有4个碱基3'突出端的粘性末端）。在处理后5小时分析细胞中的染色单体畸变。使用链球菌溶血素O对细胞进行穿孔处理以使限制性内切酶进入。与正常细胞相比，两种A-T细胞系在G2期对限制性内切酶的反应中染色单体断裂频率增加。在PvuII处理的情况下，A-T细胞的增强反应最为明显，A-T-PA和A-T-KM的增强率分别为2.5和4.2。然而，通过中性滤膜洗脱法测量，由于穿孔效率较低，A-T-PA细胞中的DNA双链断裂（dsb）频率明显低于N-SW细胞。当用较高浓度（0.3单位/毫升）的链球菌溶血素O处理A-T-PA细胞时，根据给定PvuII浓度下两系诱导的dsb数量相似判断，该条件显然导致A-T-PA细胞的穿孔水平与用0.06单位/毫升处理的N-SW细胞相似，用PvuII处理的A-T-PA细胞的增强率从2.5增加到5.8。如先前在中国仓鼠细胞中发现的那样，发现BamHI和PstI在所有三种细胞系中的致断裂性较低，尽管这种效应部分可能是由于活性较低，特别是在PstI的情况下。然而，即使浓度高出4至6倍，BamHI的致断裂性仍低于PvuII。结论是具有平端的dsb比具有粘性末端的dsb更具致断裂性。结果表明，A-T细胞的染色体敏感性可能源于一种缺陷，该缺陷导致dsb转化为染色单体畸变的速率更高。
