An J, Trieff N M, Hsie A W
Department of Preventive Medicine and Community Health, The University of Texas Medical Branch, Galveston 77555-1110, USA.
Environ Mol Mutagen. 1998;32(3):244-50.
Bleomycin is one of the radiomimetic antibiotics which induces DNA double-strand breaks by highly specific free radical attack on deoxyribose moieties in DNA. Earlier, we have shown that bleomycin induces a high proportion of large deletions involving one or more exons in the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in a Chinese hamster ovary (CHO) cell line CHO K1-BH4, in which no spontaneously occurring large deletions were detected by a polymerase chain reaction (PCR)-based deletion screening assay. Here we report the molecular nature of another class of mutants in which we did not observe any abnormal exon pattern. We refer to these mutants as the "nondeletion" type. Since bleomycin is a reactive oxygen species (ROS)-generating agent, we also studied whether the change of intracellular levels of ROS may affect the bleomycin-induced mutation spectra. We therefore also investigated the hprt mutation spectra induced by bleomycin with pretreatment by TRIEN (triethylenetetramine), a superoxide dismutase (SOD) inhibitor, and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a SOD mimic. Analysis of these three bleomycin-induced "nondeletion" mutation spectra revealed that 5'-GTC-3' or 5'-GCC-3' sequences were the hot spots for single basepair deletions. Other types of mutation include abnormal cDNA or no cDNA amplification on the hprt locus. Due to the small sample size, we are unable to draw a definitive conclusion about the effects of TRIEN and TEMPOL on bleomycin-induced spectrum of "nondeletion" type hprt mutations.
博来霉素是一种拟放射抗生素，通过对DNA中的脱氧核糖部分进行高度特异性的自由基攻击来诱导DNA双链断裂。此前，我们已经表明，博来霉素在中国仓鼠卵巢（CHO）细胞系CHO K1 - BH4的次黄嘌呤 - 鸟嘌呤磷酸核糖转移酶（hprt）基因座中诱导了高比例的涉及一个或多个外显子的大缺失，在该细胞系中，基于聚合酶链反应（PCR）的缺失筛选试验未检测到自发发生的大缺失。在此，我们报告另一类突变体的分子性质，在这类突变体中我们未观察到任何异常的外显子模式。我们将这些突变体称为“非缺失”型。由于博来霉素是一种产生活性氧（ROS）的试剂，我们还研究了细胞内ROS水平的变化是否可能影响博来霉素诱导的突变谱。因此，我们还研究了用超氧化物歧化酶（SOD）抑制剂三亚乙基四胺（TRIEN）和SOD模拟物TEMPOL（4 - 羟基 - 2,2,6,6 - 四甲基哌啶 - 1 - 氧基）预处理后博来霉素诱导的hprt突变谱。对这三种博来霉素诱导的“非缺失”突变谱的分析表明，5'-GTC-3'或5'-GCC-3'序列是单碱基对缺失的热点。其他类型的突变包括hprt基因座上异常的cDNA或无cDNA扩增。由于样本量小，我们无法就TRIEN和TEMPOL对博来霉素诱导的“非缺失”型hprt突变谱的影响得出明确结论。
