Jeon S, Allen-Hoffmann B L, Lambert P F
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison 53706, USA.
J Virol. 1995 May;69(5):2989-97. doi: 10.1128/JVI.69.5.2989-2997.1995.
Integration of human papillomavirus type 16 (HPV-16) DNA into a host chromosome has been hypothesized to result in altered expression of two viral transforming genes, E6 and E7, in cervical cancers. In order to investigate the role that changes in viral genomic state and gene expression play in cervical carcinogenesis, we have derived clonal populations of human cervical epithelial cells which harbor multiple copies of either extrachromosomal or integrated viral DNA. The clonal populations harboring extrachromosomal HPV-16 DNA stably maintained approximately 1,000 viral copies for at least 15 passages (approximately 100 cell doublings), which contrasted with the unstable HPV-16 replicons in the parental counterpart. In the clonal populations harboring integrated viral DNA, 3 to 60 copies of HPV-16 DNA were found integrated in either of two forms: type 1, in which all the copies of HPV-16 DNA were disrupted in the E2 open reading frame upon integration, and type 2, in which intact viral copies were flanked by disrupted viral copies and cellular sequences. Despite the lower HPV-16 DNA copy number, the clonal populations with integrated viral DNA had levels of E7 protein that were in most cases higher than those found in the clonal populations harboring extrachromosomal viral DNA. Irrespective of viral genomic state, the clonal populations were capable of undergoing terminal differentiation and unable to form colonies in soft agar, which is indicative of the nontumorigenic nature of these cells. Importantly, a cell population with integrated viral DNA was found to outgrow another with extrachromosomal DNA when these cells were cocultured over a period of time. Thus, integration of human papillomaviral DNA correlates with increased viral gene expression and cellular growth advantage. These observations are consistent with the hypothesis that integration provides a selective advantage to cervical epithelial precursors of cervical carcinoma.
有人提出，人乳头瘤病毒16型（HPV-16）DNA整合到宿主染色体中会导致宫颈癌中两个病毒转化基因E6和E7的表达发生改变。为了研究病毒基因组状态和基因表达变化在宫颈癌发生过程中所起的作用，我们获得了人宫颈上皮细胞的克隆群体，这些细胞含有染色体外或整合型病毒DNA的多个拷贝。含有染色体外HPV-16 DNA的克隆群体在至少15代（约100次细胞倍增）中稳定维持约1000个病毒拷贝，这与亲本细胞中不稳定的HPV-16复制子形成对比。在含有整合型病毒DNA的克隆群体中，发现3至60个HPV-16 DNA拷贝以两种形式之一整合：1型，其中HPV-16 DNA的所有拷贝在整合时在E2开放阅读框中被破坏；2型，其中完整的病毒拷贝两侧是被破坏的病毒拷贝和细胞序列。尽管HPV-16 DNA拷贝数较低，但含有整合型病毒DNA的克隆群体中E7蛋白水平在大多数情况下高于含有染色体外病毒DNA的克隆群体。无论病毒基因组状态如何，克隆群体都能够进行终末分化，并且不能在软琼脂中形成集落，这表明这些细胞具有非致瘤性。重要的是，当这些细胞共培养一段时间后，发现含有整合型病毒DNA的细胞群体比含有染色体外DNA的细胞群体生长得更快。因此，人乳头瘤病毒DNA的整合与病毒基因表达增加和细胞生长优势相关。这些观察结果与整合为宫颈癌的宫颈上皮前体细胞提供选择性优势的假设一致。
