Viral and cellular factors influence the activity of the Epstein-Barr virus BCR2 and BWR1 promoters in cells of different phenotype.
Viral and cellular factors influence the activity of the Epstein-Barr virus BCR2 and BWR1 promoters in cells of different phenotype.
复制标题
病毒和细胞因素影响不同表型细胞中 Epstein-Barr 病毒 BCR2 和 BWR1 启动子的活性。
作者：
Nilsson,T;Sjoblom,A;Masucci,MG;Rymo,L
EB病毒（Epstein-Barr virus，EBV）转化B淋巴细胞的特征是表达6种病毒核抗原（EBNA 1 ~ EBNA 6），这些抗原由病毒基因组中位于BamH Ⅰ W（BCR 2）和BamH Ⅰ W（BWR 1）区的两个启动子中的一个启动的长初级转录物编码。BWR 1启动子在EBV感染的初始阶段优先使用，而BCR 2启动子几乎总是用于转化的淋巴母细胞系（LCL）。为了深入了解启动子使用的分子机制，我们分析了携带EBV阴性和携带EBV的B细胞系中BWR 1和BCR 2调节序列不同部分的报告质粒的活性，这些细胞系基于其表面标志物表达，代表了B细胞活化/分化的不同阶段。我们表明：（i）在表达BL I组与BL III组表型的细胞系中，BWR 1和含有oriP的BCR 2报告质粒的活性之间存在负相关，BWR 1启动子在BL III组细胞中实际上是无活性的;（ii）缺乏oriP区的BCR 2报告质粒在EBV阴性细胞系中有活性，并且EBV-1表达载体在EBV-2细胞系中有活性。表达I组或II组表型的阳性细胞，在BL III组细胞和LCL中几乎无活性，表明细胞因子是BCR 2启动子元件激活所必需的。（iii）EBNA 2的表达足以激活EBV阴性细胞中含有BCR 2启动子近端部分的报告质粒，而EBNA 2和EBNA 1的共表达需要激活含有oriP的质粒中的启动子;（iv）oriP的30-bp重复区作为下游启动子上的负向元件，但通过EBNA 1和细胞因子的协同作用转化为转录增强子。在表型不同的EBV阳性细胞系中，外源报告质粒和内源BWR 1和BCR 2启动子的活性之间的相关性较差。在表达I组表型的BL细胞中，适当的反式作用因子的存在不足以激活内源性BWR 1和BCR 2启动子。
Transformation of B-lymphocytes by Epstein-Barr virus (EBV) is characterized by the expression of six viral nuclear antigens (EBNA1 to EBNA6) which are encoded by messages derived from long primary transcripts initiated at one of two promoters located in theBamHI W (BCR2) andBamHI W (BWR1) regions of the viral genome. The BWR1 promoter is preferentially utilized during the initial phases of EBV infection, whereas the BCR2 promoter is almost invariably used in transformed lymphoblastoid cell lines (LCLs). In order to gain some insight into the molecular mechanisms underlying promoter usage we have analyzed the activity of reporter plasmids carrying different parts of the BWR1 and BCR2 regulatory sequences in EBV-negative and EBV-carrying B cell lines that, on the basis of their surface marker expression, are representative of different stages of B cell activation/differentiation. We show that: (i) there is an inverse correlation between the activity of BWR1 and oriP-containing BCR2 reporter plasmids in cell lines expressing a BL group I versus a group III phenotype, the BWR1 promoter being virtually inactive in group III cells; (ii) BCR2 reporter plasmids devoid of the oriP region are active in EBV-negative cell lines and EBV-positive cells expressing a group I or group II phenotype and virtually inactive in BL group III cells and LCLs, suggesting that cellular factors are required for activation of BCR2 promoter elements. These factors are lost upon progression to a group III phenotype); (iii) expression of EBNA2 is sufficient to activate reporter plasmids containing the proximal part of the BCR2 promoter in EBV negative cells, whereas coexpression of EBNA2 and EBNA1 is required to activate the promoter in oriP-containing plasmids; (iv) the 30-bp repeat region of oriP acts as a negativecis-element on downstream promoters but is transformed into a transcriptional enhancer by the concerted action of EBNA1 and cellular factors. There was a poor correlation between the activity of exogenous reporter plasmids and endogenous BWR1 and BCR2 promoters in phenotypically different EBV-positive cell lines. The presence of the appropriatetrans-acting factors was not sufficient to activate the endogenous BWR1 and BCR2 promoters in BL cells expressing a group I phenotype.