Liu Z, Ghai J, Ostrow R S, Faras A J
Institute of Human Genetics, University of Minnesota Medical School, Minneapolis 55455.
Virology. 1995 Feb 20;207(1):260-70. doi: 10.1006/viro.1995.1075.
The transforming potential of the human papillomavirus (HPV) type 16 has been defined largely in the E7, E6, and E5 oncoproteins, with the major transforming capability residing in the E7 gene. In this paper, we found that in cooperation with the activated ras, the HPV16 E7 gene when expressed in a retroviral vector could fully transform baby rat kidney (BRK) cells in transfections, whereas the same construct could only immortalize the BRK cells following retroviral infection. This inability to transform correlated with the low levels of E7 gene RNA expression in the viral infected cells, which harbor a lower number of copies of the E7 gene constructs. Cotransfection of the expression vector FV2E7, which gives high levels of E7 gene expression, and activated ras lead to rapid and efficient morphological transformation of BRK cells which grew easily in soft agar and induced large tumors in athymic nude mice. In contrast, cotransfections of the expression vector FV1E7, which gives lower levels of E7 gene expression, produced much lower numbers of transformed colonies which took longer to form, showed a retarded growth on soft agar, and induced smaller tumors in nude mice. Under these conditions, colonies of immortalized, but morphologically untransformed cells formed in large numbers. These results indicate that the transforming potential is directly correlated to the expression levels of the oncoprotein and that a threshold level of the E7 oncoprotein may be required before the cells can be fully transformed. This supports the hypothesis that the transformation processes include at least two separate and continuous steps which first lead to immortalization and then to metastasis, in agreement with the clinical progression of genital tumors from benign to malignancy. Such a progression may involve enhanced expression of the oncoproteins.
人乳头瘤病毒16型（HPV-16）的转化潜能在很大程度上由E7、E6和E5这几种癌蛋白所决定，其中主要的转化能力存在于E7基因中。在本文中，我们发现，与激活的ras基因协同作用时，HPV-16 E7基因在逆转录病毒载体中表达后，在转染过程中能够完全转化新生大鼠肾（BRK）细胞，而相同的构建体在逆转录病毒感染后只能使BRK细胞永生化。这种无法转化的情况与病毒感染细胞中E7基因RNA表达水平较低有关，这些细胞中E7基因构建体的拷贝数较少。共转染能高水平表达E7基因的表达载体FV2E7和激活的ras基因，会导致BRK细胞快速高效地发生形态转化，这些细胞能在软琼脂中轻松生长，并在无胸腺裸鼠中诱发大肿瘤。相比之下，共转染表达水平较低的E7基因的表达载体FV1E7，产生的转化菌落数量要少得多，形成时间更长，在软琼脂上生长缓慢，在裸鼠中诱发的肿瘤也较小。在这些条件下，大量形成了永生化但形态未转化的细胞菌落。这些结果表明，转化潜能与癌蛋白的表达水平直接相关，并且在细胞能够完全转化之前，可能需要E7癌蛋白达到一个阈值水平。这支持了这样一种假说，即转化过程至少包括两个独立且连续的步骤，首先导致永生化，然后导致转移，这与生殖器肿瘤从良性到恶性的临床进展相一致。这种进展可能涉及癌蛋白表达的增强。
