Hejnar J, Plachý J, Geryk J, Machon O, Trejbalová K, Guntaka R V, Svoboda J
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, Prague 6, CZ-16637, Czech Republic.
Virology. 1999 Mar 1;255(1):171-81. doi: 10.1006/viro.1998.9597.
Rous sarcoma virus (RSV) enhancer sequences in the long terminal repeat (LTR) have previously been shown to be sensitive to CpG methylation. We report further that the high density methylation of the RSV LTR-driven chloramphenicol acetyltransferase reporter is needed for full transcriptional inhibition in chicken embryo fibroblasts and for suppression of tumorigenicity of the RSV proviral DNA in chickens. In nonpermissive mammalian cells, however, the low density methylation is sufficient for full inhibition. The time course of inhibition differs strikingly in avian and mammalian cells: although immediately inhibited in mammalian cells, the methylated RSV LTR-driven reporter is fully inhibited with a significant delay after transfection in avian cells. Moreover, transcriptional inhibition can be overridden by transfection with a high dose of the methylated reporter plasmid in chicken cells but not in hamster cells. The LTR, v-src, LTR proviral DNA is easily capable of inducing sarcomas in chickens but not in hamsters. In contrast, Moloney murine leukemia virus LTR-driven v-src induces sarcomas in hamsters with high incidence. Therefore, the repression of integrated RSV proviruses in rodent cells is directed against the LTR.
之前已表明，长末端重复序列（LTR）中的劳氏肉瘤病毒（RSV）增强子序列对CpG甲基化敏感。我们进一步报告，RSV LTR驱动的氯霉素乙酰转移酶报告基因的高密度甲基化对于鸡胚成纤维细胞中的完全转录抑制以及鸡体内RSV前病毒DNA致瘤性的抑制是必需的。然而，在非允许性哺乳动物细胞中，低密度甲基化就足以实现完全抑制。抑制的时间进程在禽类和哺乳动物细胞中显著不同：甲基化的RSV LTR驱动的报告基因在哺乳动物细胞中立即受到抑制，但在禽类细胞中转染后会有明显延迟才被完全抑制。此外，在鸡细胞中，高剂量的甲基化报告质粒转染可克服转录抑制，但在仓鼠细胞中则不行。LTR、v-src、LTR前病毒DNA很容易在鸡中诱导肉瘤形成，但在仓鼠中则不会。相反，莫洛尼鼠白血病病毒LTR驱动的v-src在仓鼠中高发生率地诱导肉瘤形成。因此，啮齿动物细胞中整合的RSV前病毒的抑制作用是针对LTR的。
