Maeda N, Palmarini M, Murgia C, Fan H
Cancer Research Institute and Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA.
Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4449-54. doi: 10.1073/pnas.071547598.
Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary carcinoma, a unique animal model for human bronchioalveolar carcinoma. We previously isolated a JSRV proviral clone and showed that it was both infectious and oncogenic. Thus JSRV is necessary and sufficient for the development of ovine pulmonary carcinoma, but no data are available on the mechanisms of transformation. Inspection of the JSRV genome reveals standard retroviral genes, but no evidence for a viral oncogene. However, an alternate ORF in pol (orf-x) might be a candidate for a transforming gene. We tested whether the JSRV genome might encode a transforming gene by transfecting an expression plasmid for JSRV [pCMVJS21, driven by the cytomegalovirus (CMV) immediate early promoter] into mouse NIH 3T3 cells. Foci of transformed cells appeared in the transfected cultures 2-3 weeks posttransfection; cloned transformants showed anchorage independence for growth, and they expressed JSRV RNA. These results indicate that the JRSV genome contains information with direct transforming potential for NIH 3T3 cells. Transfection of a mutated version of pCMVJS21 in which the orf-x protein was terminated by two stop codons also gave transformed foci. Thus, orf-x was eliminated as the candidate transforming gene. In addition, another derivative of pCMVJS21 (pCMVJS21DeltaGP) in which the gag, pol (and orf-x) coding sequences were deleted also gave transformed foci. These results indicate that the envelope gene carries the transforming potential. This is an unusual example of a native retroviral structural protein with transformation potential.
绵羊肺腺瘤逆转录病毒（JSRV）是绵羊肺癌的病原体，是人类细支气管肺泡癌的独特动物模型。我们之前分离出一个JSRV前病毒克隆，并表明它具有感染性和致癌性。因此，JSRV对于绵羊肺癌的发生发展是必要且充分的，但关于其转化机制尚无数据。对JSRV基因组的检查揭示了标准的逆转录病毒基因，但没有病毒癌基因的证据。然而，pol基因中的一个替代开放阅读框（orf-x）可能是一个转化基因的候选者。我们通过将一个由巨细胞病毒（CMV）立即早期启动子驱动的JSRV表达质粒[pCMVJS21]转染到小鼠NIH 3T3细胞中，来测试JSRV基因组是否可能编码一个转化基因。转染后2 - 3周，在转染培养物中出现了转化细胞灶；克隆的转化体显示出对生长的锚定非依赖性，并且它们表达JSRV RNA。这些结果表明，JRSV基因组包含对NIH 3T3细胞具有直接转化潜力的信息。转染一个orf-x蛋白被两个终止密码子终止的pCMVJS21突变体也产生了转化灶。因此，orf-x被排除作为候选转化基因。此外，pCMVJS21的另一个衍生物（pCMVJS21DeltaGP），其中gag、pol（和orf-x）编码序列被删除，也产生了转化灶。这些结果表明包膜基因具有转化潜力。这是一个具有转化潜力的天然逆转录病毒结构蛋白的不寻常例子。
