Role of the Endocytic Pathway in the Counteraction of BST-2 by Human Lentiviral Pathogens

The interferon-inducible transmembrane protein BST-2 (CD317, tetherin) restricts the release of several enveloped viruses from infected cells. BST-2 is broadly active against retroviruses, including HIV-1 and HIV-2. To counteract this host defense, HIV-1 uses the accessory protein Vpu, whereas HIV-2 uses its envelope glycoprotein (Env). In both cases, viral antagonism is associated with decreased expression of BST-2 at the cell surface. Here, we provide evidence supporting a role for the clathrin-mediated endocytic pathway in the downregulation of BST-2 from the cell surface and the counteraction of restricted virion release. A catalytically inactive, dominant negative version of the vesicle "pinch-ase" dynamin 2 (dyn2K44A) inhibited the downregulation of BST-2 by Vpu, and it inhibited the release of wild-type (Vpu-expressing) HIV-1 virions. Similarly, dyn2K44A inhibited the downregulation of BST-2 by HIV-2 Env, and it inhibited the release of vpu-negative HIV-1 virions when HIV-2 Env was provided in trans. dyn2K44A inhibited Env more robustly than Vpu, suggesting that dynamin 2, while a cofactor for both Env and Vpu, might support just one of several pathways though which Vpu counteracts BST-2. In support of a role for clathrin in these effects, the C-terminal domain of the clathrin assembly protein AP180 also inhibited the downregulation of BST-2 by either Vpu or HIV-2 Env. Consistent with modulation of the postendocytic itinerary of BST-2, Vpu enhanced the accumulation of cell surface-derived BST-2 in transferrin-containing endosomes. Vpu also inhibited the transport of BST-2 from a brefeldin A-insensitive compartment to the cell surface, consistent with a block to endosomal recycling. We propose that HIV-1 Vpu, and probably HIV-2 Env, traps BST-2 in an endosomal compartment following endocytosis, reducing its level at the cell surface to counteract restricted viral release.

干扰素诱导的跨膜蛋白BST - 2（CD317， tetherin）限制几种包膜病毒从受感染细胞中释放。BST - 2对逆转录病毒，包括HIV - 1和HIV - 2，具有广泛的活性。为了对抗这种宿主防御，HIV - 1利用辅助蛋白Vpu，而HIV - 2则利用其包膜糖蛋白（Env）。在这两种情况下，病毒的拮抗作用都与细胞表面BST - 2表达的降低有关。在此，我们提供证据支持网格蛋白介导的内吞途径在细胞表面BST - 2的下调以及对受限病毒粒子释放的反作用中起作用。一种无催化活性的、显性负性的囊泡“掐断酶”动力蛋白2（dyn2K44A）抑制了Vpu对BST - 2的下调，并抑制了野生型（表达Vpu的）HIV - 1病毒粒子的释放。同样，dyn2K44A抑制了HIV - 2 Env对BST - 2的下调，并且当HIV - 2 Env反式提供时，它抑制了无vpu的HIV - 1病毒粒子的释放。dyn2K44A对Env的抑制作用比Vpu更强，这表明动力蛋白2虽然是Env和Vpu的辅助因子，但可能只支持Vpu对抗BST - 2的几种途径中的一种。为了支持网格蛋白在这些效应中的作用，网格蛋白组装蛋白AP180的C末端结构域也抑制了Vpu或HIV - 2 Env对BST - 2的下调。与对BST - 2内吞后行程的调节一致，Vpu增强了含转铁蛋白的内体中细胞表面来源的BST - 2的积累。Vpu还抑制了BST - 2从布雷菲德菌素A不敏感的区室向细胞表面的运输，这与对内体再循环的阻断一致。我们提出，HIV - 1 Vpu，可能还有HIV - 2 Env，在内吞作用后将BST - 2捕获在内体区室中，降低其在细胞表面的水平以对抗受限的病毒释放。