Roberts P C, Kipperman T, Compans R W
Department of Microbiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
J Virol. 1999 Dec;73(12):10447-57. doi: 10.1128/JVI.73.12.10447-10457.1999.
Entry of vesicular stomatitis virus (VSV), the prototype member of the rhabdovirus family, occurs by receptor-mediated endocytosis. Subsequently, during traversal through the endosomal compartments, the VSV G protein acquires a low-pH-induced fusion-competent form, allowing for fusion of the viral membrane with endosomal and lysosomal membranes. This fusion event releases genomic RNA into the cytoplasm of the cell. Here we provide evidence that the VSV G protein acquires a fusion-competent form during exocytosis in a polarized endometrial cell line, HEC-1A. VSV infection of HEC-1A cells results in high viral yields and giant cell formation. Syncytium formation is blocked in a concentration-dependent manner by treatment with the lysosomotropic weak base ammonium chloride, which raises intravesicular pH. Virus release is somewhat delayed by treatment with ammonium chloride, but virus yields gradually reach those of control cells. In addition, inhibition of vacuolar H(+)-ATPases by treatment with bafilomycin A1 also inhibited cell to cell fusion without altering virus yields. Virions released from infected HEC cells were themselves not fusion competent, since viral entry required an active H(+)-ATPase and a low-pH-induced conformational change in the viral G protein. Thus, the conformation change leading to fusion competence during exocytotic transport is reversible and reverts during or after release of the virion from the infected cell.
水泡性口炎病毒（VSV）是弹状病毒科的原型成员，其进入细胞是通过受体介导的内吞作用。随后，在穿过内体区室的过程中，VSV G蛋白获得了一种低pH诱导的具有融合能力的形式，使得病毒膜能够与内体膜和溶酶体膜融合。这种融合事件将基因组RNA释放到细胞的细胞质中。在这里，我们提供证据表明，在极化的子宫内膜细胞系HEC-1A中，VSV G蛋白在胞吐作用过程中获得了具有融合能力的形式。HEC-1A细胞感染VSV会导致高病毒产量和巨细胞形成。用溶酶体促渗弱碱氯化铵处理可浓度依赖性地阻断合胞体形成，氯化铵可提高囊泡内pH值。氯化铵处理会使病毒释放有所延迟，但病毒产量最终会逐渐达到对照细胞的水平。此外，用巴弗洛霉素A1处理抑制液泡H(+)-ATP酶也会抑制细胞间融合，而不改变病毒产量。从受感染的HEC细胞释放的病毒粒子本身不具有融合能力，因为病毒进入需要活性H(+)-ATP酶和病毒G蛋白的低pH诱导的构象变化。因此，在胞吐运输过程中导致融合能力的构象变化是可逆的，并且在病毒粒子从受感染细胞释放期间或之后恢复。
