Nguyên Thi Lien-Anh, de Walque Stéphane, Veithen Emmanuelle, Dekoninck Ann, Martinelli Valérie, de Launoit Yvan, Burny Arsène, Harrod Robert, Van Lint Carine
Institut de Biologie et de Médecine Moléculaires, Laboratoire de Virologie Moléculaire, Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium.
J Biol Chem. 2007 Jul 20;282(29):20854-67. doi: 10.1074/jbc.M703060200. Epub 2007 May 25.
Bovine leukemia virus (BLV) expression is controlled at the transcriptional level through three Tax(BLV)-responsive elements (TxREs) responsive to the viral transactivator Tax(BLV). The cAMP-responsive element (CRE)-binding protein (CREB) has been shown to interact with CRE-like sequences present in the middle of each of these TxREs and to play critical transcriptional roles in both basal and Tax(BLV)-transactivated BLV promoter activity. In this study, we have investigated the potential involvement of the cAMP-response element modulator (CREM) in BLV transcriptional regulation, and we have demonstrated that CREM proteins were expressed in BLV-infected cells and bound to the three BLV TxREs in vitro. Chromatin immunoprecipitation assays using BLV-infected cell lines demonstrated in the context of chromatin that CREM proteins were recruited to the BLV promoter TxRE region in vivo. Functional studies, in the absence of Tax(BLV), indicated that ectopic CREMtau protein had a CRE-dependent stimulatory effect on BLV promoter transcriptional activity. Cross-link of the B-cell receptor potentiated CREMtau transactivation of the viral promoter. Further experiments supported the notion that this potentiation involved CREMtau Ser-117 phosphorylation and recruitment of CBP/p300 to the BLV promoter. Although CREB and Tax(BLV) synergistically transactivated the BLV promoter, CREMtau repressed this Tax(BLV)/CREB synergism, suggesting that a modulation of the level of Tax(BLV) transactivation through opposite actions of CREB and CREMtau could facilitate immune escape and allow tumor development.
牛白血病病毒（BLV）的表达在转录水平上通过三个对病毒反式激活因子Tax（BLV）有反应的Tax（BLV）反应元件（TxREs）来控制。已证明环磷酸腺苷反应元件（CRE）结合蛋白（CREB）可与这些TxREs中每个元件中间存在的CRE样序列相互作用，并在基础和Tax（BLV）反式激活的BLV启动子活性中发挥关键的转录作用。在本研究中，我们研究了环磷酸腺苷反应元件调节剂（CREM）在BLV转录调控中的潜在作用，并且我们证明了CREM蛋白在BLV感染的细胞中表达，并在体外与三个BLV TxREs结合。使用BLV感染细胞系的染色质免疫沉淀试验表明，在染色质环境中，CREM蛋白在体内被募集到BLV启动子TxRE区域。在没有Tax（BLV）的情况下进行的功能研究表明，异位表达的CREMtau蛋白对BLV启动子转录活性具有CRE依赖性刺激作用。B细胞受体的交联增强了病毒启动子的CREMtau反式激活作用。进一步的实验支持了这样一种观点，即这种增强作用涉及CREMtau的Ser-117磷酸化以及CBP/p300募集到BLV启动子。尽管CREB和Tax（BLV）协同反式激活BLV启动子，但CREMtau抑制了这种Tax（BLV）/CREB协同作用，这表明通过CREB和CREMtau的相反作用调节Tax（BLV）反式激活水平可能有助于免疫逃逸并促进肿瘤发展。
