Cunningham J M, Francis G E, Holland M J, Pirollo K F, Chang E H
Molecular Cell Pathology Laboratory, Royal Free Hospital School of Medicine, London, UK.
Br J Cancer. 1991 Jan;63(1):29-36. doi: 10.1038/bjc.1991.8.
Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-1 gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raf/c-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.
在对一个易患癌症的家族进行的研究中发现，对多种肿瘤形成（李-弗劳梅尼综合征）的遗传易感性与异常的c-raf-1基因以及其非癌性皮肤成纤维细胞中抗辐射表型的遗传存在着有趣的关联。这种关联以及以下观察结果：DNA拓扑异构酶在有缺陷时可将错误引入DNA，并且这些酶在体外会受到与raf编码蛋白类似的丝氨酸/苏氨酸激酶的干扰，促使人们对该家族成纤维细胞的DNA拓扑异构酶活性进行研究。由于当转染该家族的异常c-raf-1基因时，抗辐射能力被转移到了鼠细胞（NIH-3T3）中，我们还检测了含有该基因和其他癌基因的转化体。检测了V-raf/c-myc和EJ-ras转化体，检测前者是因为该家族的皮肤成纤维细胞中myc表达也升高了3至8倍（这显然与抗辐射能力无关），检测后者是因为ras与raf一样，也能传递抗辐射能力。该家族成员的成纤维细胞以及三个转染的鼠系显示出类似的亚精胺和ATP依赖性DNA连环活性的干扰（这是DNA拓扑异构酶II的典型特征）。拓扑异构酶II的激活程度与一种抗辐射能力指标（Dq值）之间存在显著的正相关（r = 0.93；P = 0.0026）。DNA超螺旋的松弛（拓扑异构酶I活性和其他DNA切口酶）并无异常。细胞毒性测定以及拓扑异构酶II抑制剂对DNA/蛋白质复合物形成影响的评估，证实了该家族细胞和转染体中存在定性的拓扑异构酶II缺陷。尽管此处观察到的定性拓扑异构酶II异常可能与功能障碍相关这一观点极具推测性，但这些发现可能不仅与该家族的肿瘤发生机制相关，而且与raf和ras型癌基因的肿瘤发生机制相关。
