McCormick J J, Fry D G, Hurlin P J, Morgan T L, Wilson D M, Maher V M
Department of Microbiology, Michigan State University, East Lansing 48824.
Prog Clin Biol Res. 1990;340D:195-205.
Exposure to chemical carcinogens or radiation is considered to cause most human cancer, but human cells in culture have not been successfully transformed to malignancy by such agents. Malignant transformation is a multi-step process and one explanation for the failure to induce such transformation of human cells in culture could be inability to recognize the phenotypes of carcinogen-treated cells that have undergone intermediate changes, so that these cells can be isolated and exposed a second time to cause further changes. To identify possible intermediates, we transfected diploid human fibroblasts with oncogenes known to be active in cells derived from fibrosarcomas and determined the phenotypes produced. H- or N-ras oncogenes flanked by suitable enhancer and promoter sequences caused the cells to exhibit several characteristics of malignant cells, but not to acquire an infinite life span or form tumors. Transfection of these oncogenes in the same constructions, or a viral K-ras oncogene, into an infinite life span, near-diploid, non-tumorigenic cell strain developed in this laboratory (MSU-1.1 cells) resulted in distinct foci of morphologically-altered, anchorage independent, and growth factor independent cells that formed progressively-growing, invasive malignant sarcomas in athymic mice and expressed the p21s of the transfected ras genes. Transfection of two other infinite life span human cell lines with the H-ras oncogene in the same construction also yielded malignant cells. Recently, we succeeded in inducing the malignant state in MSU-1.1 cells using carcinogen identified that are one step removed from malignant transformation, others that are two-steps removed, etc. Furthermore, we know what new phenotypes these cells need to express to be malignantly transformed and which oncogenes can make such a change. If, as suggested above, proto-oncogenes are the cellular targets for carcinogen attack, it should be possible, by carcinogen treatment to bring about the malignant state. We have recently succeeded in achieving just such transformation by exposing MSU-1.1 cells to chemical carcinogens.
接触化学致癌物或辐射被认为是导致大多数人类癌症的原因，但培养中的人类细胞尚未被此类因素成功转化为恶性细胞。恶性转化是一个多步骤过程，未能在培养中诱导人类细胞发生这种转化的一个解释可能是无法识别经历了中间变化的致癌物处理细胞的表型，从而无法分离这些细胞并再次使其暴露以引发进一步变化。为了识别可能的中间体，我们用已知在源自纤维肉瘤的细胞中具有活性的癌基因转染二倍体人类成纤维细胞，并确定产生的表型。侧翼带有合适增强子和启动子序列的H-或N-ras癌基因使细胞表现出恶性细胞的几种特征，但不会获得无限寿命或形成肿瘤。将这些相同构建体中的癌基因或病毒K-ras癌基因转染到本实验室培养的具有无限寿命、近二倍体、无致瘤性的细胞系（MSU-1.1细胞）中，产生了形态改变、不依赖贴壁且不依赖生长因子的细胞的明显集落，这些细胞在无胸腺小鼠中形成了逐渐生长的侵袭性恶性肉瘤，并表达了转染ras基因的p21蛋白。用相同构建体的H-ras癌基因转染另外两个具有无限寿命的人类细胞系也产生了恶性细胞。最近，我们成功地使用已鉴定的致癌物在MSU-1.1细胞中诱导出恶性状态，这些致癌物与恶性转化相差一步、两步等。此外，我们知道这些细胞需要表达哪些新表型才能发生恶性转化以及哪些癌基因可以引起这种变化。如果如上所述，原癌基因是致癌物攻击的细胞靶点，那么通过致癌物处理应该有可能实现恶性状态。我们最近通过将MSU-1.1细胞暴露于化学致癌物成功实现了这种转化。
