Kempkes B, Spitkovsky D, Jansen-Dürr P, Ellwart J W, Kremmer E, Delecluse H J, Rottenberger C, Bornkamm G W, Hammerschmidt W
Institut für Klinische Molekularbiologie und Tumorgenetik, München, Germany.
EMBO J. 1995 Jan 3;14(1):88-96. doi: 10.1002/j.1460-2075.1995.tb06978.x.
Infection of primary B-lymphocytes by Epstein-Barr virus (EBV) leads to growth transformation of these B-cells in vitro. EBV nuclear antigen 2 (EBNA2), one of the first genes expressed after EBV infection of B-cells, is a transcriptional activator of viral and cellular genes and is essential for the transforming potential of the virus. We generated conditional EBV mutants by expressing EBNA2 as chimeric fusion protein with the hormone binding domain of the estrogen receptor on the genetic background of the virus. Growth transformation of primary normal B-cells by mutant virus resulted in estrogen-dependent lymphoblastoid cell lines expressing the chimeric EBNA2 protein. In the absence of estrogen about half of the cells enter a quiescent non-proliferative state whereas the others die by apoptosis. EBNA2 is thus required not only for initiation but also for maintenance of transformation. Growth arrest occurred at G1 and G2 stages of the cell cycle, indicating that functional EBNA2 is required at different restriction points of the cell cycle. Growth arrest is reversible for G1/G0 cells as indicated by the sequential accumulation and modification of cell cycle regulating proteins. EBV induces the same cell cycle regulating proteins as polyclonal stimuli in primary B-cells. These data suggest that EBV is using a common pathway for B-cell activation bypassing the requirement for antigen, T-cell signals and growth factors.
爱泼斯坦-巴尔病毒（EBV）感染原发性B淋巴细胞可导致这些B细胞在体外发生生长转化。EBV核抗原2（EBNA2）是EBV感染B细胞后最早表达的基因之一，是病毒和细胞基因的转录激活因子，对病毒的转化潜能至关重要。我们通过在病毒的遗传背景下将EBNA2表达为与雌激素受体激素结合域的嵌合融合蛋白，生成了条件性EBV突变体。突变病毒对原发性正常B细胞的生长转化导致表达嵌合EBNA2蛋白的雌激素依赖性淋巴母细胞系的产生。在没有雌激素的情况下，约一半的细胞进入静止的非增殖状态，而其他细胞则通过凋亡死亡。因此，EBNA2不仅是启动转化所必需的，也是维持转化所必需的。细胞周期停滞发生在细胞周期的G1期和G2期，这表明在细胞周期的不同限制点需要功能性EBNA2。如细胞周期调节蛋白的顺序积累和修饰所示，G1/G0细胞的生长停滞是可逆的。EBV在原发性B细胞中诱导与多克隆刺激相同的细胞周期调节蛋白。这些数据表明，EBV正在利用一条共同的途径来激活B细胞，从而绕过对抗原、T细胞信号和生长因子的需求。
