Yang D, Alt E, Rogler C E
Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461.
Cancer Res. 1993 May 1;53(9):2020-7.
Over 50% of the hepatocellular carcinomas (HCCs) arising in the livers of woodchucks with persistent woodchuck hepatitis virus (WHV) infection contain integrations of WHV DNA within, or immediately adjacent to, a unique and functional N-myc 2 retroposon [G. Fourel et al., Nature (Lond.), 347: 294-298, 1990; Y. Wei et al., J. Virol., 66: 5265-5276, 1992]. The integrations are believed to activate the expression of N-myc 2 by an enhancer insertion mechanism [Y. Wei et al., J. Virol., 66: 5265-5276, 1992]. Since the fetal growth factor insulin-like growth factor II (IGF-II) is also expressed in woodchuck HCCs [X. X. Fu et al., J. Virol., 62: 3422-3430, 1988; D. Yang and C. E. Rogler, Carcinogenesis (Lond.), 12: 1893-1901, 1991] we sought to determine the earliest stage in hepatocarcinogenesis at which overexpression of N-myc and IGF-II could be detected. The earliest precancerous lesions so far identified in woodchucks are altered hepatic foci (AHFs) [K. Abe et al., Jpn. J. Cancer Res., 79: 466-472, 1988; H. Popper et al., Hepatology (Baltimore), 1: 91-98, 1981]. Using in situ hybridization, we have demonstrated that both the N-myc and IGF-II genes are coordinately overexpressed in nearly all AHFs in precancerous woodchuck livers. In contrast, WHV replication was either repressed or undetectable in the same AHFs. The use of probes selective for N-myc 2 versus N-myc 1 (the normal mammalian homologue) revealed nearly exclusive expression of N-myc 2 in AHFs. Cells within AHFs were generally slow growing, as determined by frequency of histone III-expressing hepatocytes; however, a few fast-growing AHFs, with growth rates nearly equivalent to those of HCCs, were identified. Furthermore, very highly elevated N-myc 2 or IGF-II expression was detected in a few subregions within AHFs which otherwise exhibited a uniformly moderate expression, suggesting that selection for higher levels of N-myc or IGF-II expression may occur within AHFs. These data suggest that coordinate expression of N-myc 2 and IGF-II and repression of WHV replication may be functionally involved in the development of AHFs and that cells expressing very high levels of N-myc and IGF-II may be selectively enriched as AHFs progress to HCC, since high levels of N-myc and IGF-II are common in HCCs.
在持续感染土拨鼠肝炎病毒（WHV）的土拨鼠肝脏中发生的肝细胞癌（HCC），超过50%在一个独特且具有功能的N-myc 2反转录转座子内部或紧邻该转座子的位置含有WHV DNA整合体[G. 富雷尔等人，《自然》（伦敦），347: 294 - 298，1990；Y. 魏等人，《病毒学杂志》，66: 5265 - 5276，1992]。据信这些整合体通过增强子插入机制激活N-myc 2的表达[Y. 魏等人，《病毒学杂志》，66: 5265 - 5276，1992]。由于胎儿生长因子胰岛素样生长因子II（IGF-II）也在土拨鼠HCC中表达[X. X. 傅等人，《病毒学杂志》，62: 3422 - 3430，1988；D. 杨和C. E. 罗格勒，《癌变》（伦敦），12: 1893 - 1901，1991]，我们试图确定在肝癌发生过程中最早能检测到N-myc和IGF-II过表达的阶段。目前在土拨鼠中鉴定出的最早的癌前病变是肝灶性病变（AHF）[K. 阿部等人，《日本癌症研究杂志》，79: 466 - 472，1988；H. 波珀等人，《肝脏病学》（巴尔的摩），1: 91 - 98，1981]。通过原位杂交，我们证明在癌前土拨鼠肝脏的几乎所有AHF中，N-myc和IGF-II基因都协同过表达。相比之下，在相同的AHF中，WHV复制要么受到抑制，要么检测不到。使用对N-myc 2与N-myc 1（正常哺乳动物同源物）具有选择性的探针显示，AHF中几乎只表达N-myc 2。根据表达组蛋白III的肝细胞频率确定，AHF内的细胞通常生长缓慢；然而，鉴定出了一些生长迅速且生长速率几乎与HCC相当的AHF。此外，在AHF内的一些子区域检测到N-myc 2或IGF-II表达非常高度升高，而这些子区域其他部分表现为均匀的中等表达，这表明在AHF内可能会选择更高水平的N-myc或IGF-II表达。这些数据表明，N-myc 2和IGF-II的协同表达以及WHV复制的抑制可能在AHF的发展中发挥功能作用，并且随着AHF发展为HCC，表达非常高水平的N-myc和IGF-II的细胞可能会被选择性富集，因为高水平的N-myc和IGF-II在HCC中很常见。
