Wang Y, Iliakis G
Department of Radiation Oncology and Nuclear Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Cancer Res. 1992 Feb 1;52(3):508-14.
Transfection of primary rat embryo fibroblasts with the H-ras oncogene plus the cooperating oncogene v-myc results in the development of foci of morphologically altered tumorigenic cells. We examined radiation (X-rays) induced inhibition of DNA synthesis in cell lines derived from such transformed clones and compared the results to those obtained with the nontransformed parental cells, rat embryo fibroblasts, as well as with cells immortalized either spontaneously, or after transfection with nuclear oncogenes (v-myc, E1A). Inhibition by X-rays of DNA synthesis was higher and persisted for longer periods of time in the H-ras- plus v-myc-transformed cell lines as compared to their nontrasformed counterparts. When the rate of DNA synthesis was measured as a function of dose 3 h after irradiation, biphasic curves were observed in all cell lines tested with a radiation sensitive and a radiation resistant component, known to correspond to inhibition of replicon initiation and chain elongation, respectively. A substantially larger inhibition of DNA synthesis was observed between 0 and 30 Gy in H-ras- plus v-myc-transformed cell lines, as compared to their nontransformed counterparts, presumably caused by sustained inhibition of replicon initiation. Hypersensitive DNA synthesis to X-rays was also observed in a transformed cell line obtained by transfection of rat embryo fibroblasts with H-ras in cooperation with the oncogene E1A, but normosensitive DNA synthesis in a rare transformant obtained by transfection with H-ras alone. These results suggest a direct or indirect involvement of the oncogene H-ras in cooperation with the oncogene v-myc (or other nuclear oncogenes such as E1A) in the control of DNA synthesis in irradiated cells. This control of DNA synthesis may be mediated via a trans-acting mechanism that involves the production of a diffusible factor in response to the radiation insult, or, by a cis-acting mechanism that directly affects the replication machinery. Circumstantial evidence for possible involvement of oncogenes of the ras and myc families in DNA synthesis support this hypothesis. There was an inverse correlation between sensitivity to radiation-induced killing and prolonged inhibition by radiation of DNA synthesis, with radioresistant cell lines displaying longer inhibition of DNA synthesis. However, inhibition by radiation of DNA synthesis was similar in normal human fibroblasts (W138) and cells derived from a radiation-resistant human carcinoma cell line (SQ-20B) suspected to carry an abnormal c-raf-1 oncogene.(ABSTRACT TRUNCATED AT 400 WORDS)
用H-ras癌基因加协同癌基因v-myc转染原代大鼠胚胎成纤维细胞，会导致形态改变的致瘤细胞灶的形成。我们检测了辐射（X射线）对源自此类转化克隆的细胞系中DNA合成的抑制作用，并将结果与未转化的亲代细胞（大鼠胚胎成纤维细胞）以及自发永生化或用核癌基因（v-myc、E1A）转染后永生化的细胞的结果进行了比较。与未转化的对应细胞相比，H-ras加v-myc转化的细胞系中，X射线对DNA合成的抑制作用更强且持续时间更长。当在照射后3小时将DNA合成速率作为剂量的函数进行测量时，在所有测试的细胞系中均观察到双相曲线，具有辐射敏感和辐射抗性成分，已知分别对应于复制子起始的抑制和链延伸的抑制。与未转化的对应细胞相比，在0至30 Gy之间，H-ras加v-myc转化的细胞系中观察到对DNA合成的抑制作用明显更大，这可能是由于复制子起始的持续抑制所致。在用H-ras与癌基因E1A协同转染大鼠胚胎成纤维细胞获得的转化细胞系中，也观察到对X射线的超敏DNA合成，但在用H-ras单独转染获得的罕见转化体中观察到正常敏感的DNA合成。这些结果表明，癌基因H-ras与癌基因v-myc（或其他核癌基因如E1A）协同作用，直接或间接参与了受辐射细胞中DNA合成的控制。这种对DNA合成的控制可能通过一种反式作用机制介导，该机制涉及响应辐射损伤产生一种可扩散因子，或者通过一种顺式作用机制直接影响复制机制。ras和myc家族癌基因可能参与DNA合成的间接证据支持了这一假设。对辐射诱导杀伤的敏感性与辐射对DNA合成的长期抑制之间存在负相关，辐射抗性细胞系显示出对DNA合成的抑制时间更长。然而，正常人类成纤维细胞（W138）和源自疑似携带异常c-raf-1癌基因的辐射抗性人类癌细胞系（SQ-20B）的细胞中，辐射对DNA合成的抑制作用相似。（摘要截于400字）
