Lindemann D, Rethwilm A
Institut für Virologie und Immunbiologie, Universität Würzburg, Germany.
J Virol. 1998 May;72(5):4088-94. doi: 10.1128/JVI.72.5.4088-4094.1998.
Primate foamy viruses (FVs) express, in addition to the 130-kDa envelope protein, a 170-kDa glycoprotein, which reacts with antisera specific for the envelope and Bel proteins. We determined the exact nature of this 170-kDa glycoprotein by using the molecularly cloned human FV (HFV). Radioimmunoprecipitation analysis of 293T cells transfected with appropriate expression constructs by using antisera specific for the HFV Env, Bel1, and Bel2 proteins, as well as reverse transcription-PCR analysis of HFV-infected cells, demonstrated that this protein is an Env-Bet fusion protein that is secreted into the supernatant. However, it is only loosely associated, or not associated, with viral particles. gp170 is generated by an alternatively spliced Env mRNA using a splice donor and splice acceptor pair localized within the env open reading frame (ORF), which is normally used to generate Bell and Bet transcripts derived from the internal promoter within the env ORF. gp170 is expressed at a level 30 to 50% of the Env precursor gp130. However, it alone does not confer infectivity to HFV particles, because capsids derived from proviruses expressing only the gp170 were not released into the supernatant. In contrast, viruses derived from proviral clones deficient in gp170 expression showed similar in vitro infectivity and replication kinetics to wild-type virus. Furthermore, both types of viruses were inactivated to a similar extent by neutralizing sera, indicating that shedding of gp170 probably does not affect the humoral immune response in the infected host.
灵长类泡沫病毒（FVs）除了表达130 kDa的包膜蛋白外，还表达一种170 kDa的糖蛋白，该糖蛋白可与针对包膜蛋白和Bel蛋白的抗血清发生反应。我们通过使用分子克隆的人泡沫病毒（HFV）确定了这种170 kDa糖蛋白的确切性质。使用针对HFV Env、Bel1和Bel2蛋白的抗血清对转染了适当表达构建体的293T细胞进行放射免疫沉淀分析，以及对HFV感染细胞进行逆转录PCR分析，结果表明该蛋白是一种分泌到上清液中的Env-Bet融合蛋白。然而，它仅与病毒颗粒松散结合或不结合。gp170是由一个选择性剪接的Env mRNA产生的，该mRNA使用位于env开放阅读框（ORF）内的一个剪接供体和剪接受体对，该剪接供体和剪接受体对通常用于产生源自env ORF内内部启动子的Bell和Bet转录本。gp170的表达水平为Env前体gp130的30%至50%。然而，它本身并不能赋予HFV颗粒感染性，因为仅表达gp170的前病毒产生的衣壳不会释放到上清液中。相比之下，源自缺乏gp170表达的前病毒克隆的病毒在体外表现出与野生型病毒相似 的感染性和复制动力学。此外，两种类型的病毒被中和血清灭活的程度相似，这表明gp170的脱落可能不会影响受感染宿主中的体液免疫反应。
