Izumi K M, Kieff E D
Department of Microbiology and Molecular Genetics, Harvard Medical School and Medicine, Brigham and Women's Hospital, Eighth Floor Channing Laboratories, 181 Longwood Avenue, Boston, MA 02115, USA.
Proc Natl Acad Sci U S A. 1997 Nov 11;94(23):12592-7. doi: 10.1073/pnas.94.23.12592.
The Epstein-Barr virus latent membrane protein 1 (LMP1) is essential for the transformation of B lymphocytes into lymphoblastoid cell lines. Previous data are consistent with a model that LMP1 is a constitutively activated receptor that transduces signals for transformation through its carboxyl-terminal cytoplasmic tail. One transformation effector site (TES1), located within the membrane proximal 45 residues of the cytoplasmic tail, constitutively engages tumor necrosis factor receptor-associated factors. Signals from TES1 are sufficient to drive initial proliferation of infected resting B lymphocytes, but most lymphoblastoid cells infected with a virus that does not express the 155 residues beyond TES1 fail to grow as long-term cell lines. We now find that mutating two tyrosines to an isoleucine at the carboxyl end of the cytoplasmic tail cripples the ability of EBV to cause lymphoblastoid cell outgrowth, thereby marking a second transformation effector site, TES2. A yeast two-hybrid screen identified TES2 interacting proteins, including the tumor necrosis factor receptor-associated death domain protein (TRADD). TRADD was the only protein that interacted with wild-type TES2 and not with isoleucine-mutated TES2. TRADD associated with wild-type LMP1 but not with isoleucine-mutated LMP1 in mammalian cells, and TRADD constitutively associated with LMP1 in EBV-transformed cells. In transfection assays, TRADD and TES2 synergistically mediated high-level NF-kappaB activation. These results indicate that LMP1 appropriates TRADD to enable efficient long-term lymphoblastoid cell outgrowth. High-level NF-kappaB activation also appears to be a critical component of long-term outgrowth.
爱泼斯坦-巴尔病毒潜伏膜蛋白1（LMP1）对于将B淋巴细胞转化为淋巴母细胞系至关重要。先前的数据与这样一种模型一致，即LMP1是一种组成性激活的受体，它通过其羧基末端细胞质尾巴转导转化信号。一个转化效应位点（TES1）位于细胞质尾巴膜近端的45个残基内，持续结合肿瘤坏死因子受体相关因子。来自TES1的信号足以驱动受感染的静止B淋巴细胞的初始增殖，但大多数感染了不表达TES1以外155个残基的病毒的淋巴母细胞无法作为长期细胞系生长。我们现在发现，将细胞质尾巴羧基末端的两个酪氨酸突变为异亮氨酸会削弱EBV引起淋巴母细胞生长的能力，从而标记出第二个转化效应位点TES2。酵母双杂交筛选鉴定出与TES2相互作用的蛋白质，包括肿瘤坏死因子受体相关死亡结构域蛋白（TRADD）。TRADD是唯一与野生型TES2相互作用而不与异亮氨酸突变的TES2相互作用的蛋白质。在哺乳动物细胞中，TRADD与野生型LMP1相关但不与异亮氨酸突变的LMP1相关，并且在EBV转化的细胞中TRADD与LMP1组成性相关。在转染实验中，TRADD和TES2协同介导高水平的核因子κB激活。这些结果表明，LMP1利用TRADD来实现有效的长期淋巴母细胞生长。高水平的核因子κB激活似乎也是长期生长的关键组成部分。
