Department of Entomology, Cornell Institute of Host-Microbe Interactions and Disease, Cornell University, Ithaca, New York, USA.
Boyce Thompson Institute at Cornell University, Ithaca, New York, USA.
J Virol. 2024 Sep 17;98(9):e0054024. doi: 10.1128/jvi.00540-24. Epub 2024 Aug 20.
Systemic viral infection of insects typically begins with the primary infection of midgut epithelial cells (enterocytes) and subsequent transit of the progeny virus in an apical-to-basal orientation into the hemocoel. For insect-vectored viruses, an oppositely oriented process (basal-to-apical transit) occurs upon secondary infection of salivary glands and is necessary for virus transmission to non-insect hosts. To examine this inversely oriented virus transit in these polarized tissues, we assessed the intracellular trafficking of two model viral envelope proteins (baculovirus GP64 and vesicular stomatitis virus G) in the midgut and salivary gland cells of the model insect, . Using fly lines that inducibly express either GP64 or VSV G, we found that each protein, expressed alone, was trafficked basally in midgut enterocytes. In salivary gland cells, VSV G was trafficked apically in most but not all cells, whereas GP64 was consistently trafficked basally. We demonstrated that a YxxØ motif present in both proteins was critical for basal trafficking in midgut enterocytes but dispensable for trafficking in salivary gland cells. Using RNAi, we found that clathrin adaptor protein complexes AP-1 and AP-3, as well as seven Rab GTPases, were involved in polarized VSV G trafficking in midgut enterocytes. Our results indicate that these viral envelope proteins encode the requisite information and require no other viral factors for appropriately polarized trafficking. In addition, they exploit tissue-specific differences in protein trafficking pathways to facilitate virus egress in the appropriate orientation for establishing systemic infections and vectoring infection to other hosts.
Viruses that use insects as hosts must navigate specific routes through different insect tissues to complete their life cycles. The routes may differ substantially depending on the life cycle of the virus. Both insect pathogenic viruses and insect-vectored viruses must navigate through the polarized cells of the midgut epithelium to establish a systemic infection. In addition, insect-vectored viruses must also navigate through the polarized salivary gland epithelium for transmission. Thus, insect-vectored viruses appear to traffic in opposite directions in these two tissues. In this study, we asked whether two viral envelope proteins (VSV G and baculovirus GP64) alone encode the signals necessary for the polarized trafficking associated with their respective life cycles. Using as a model to examine tissue-specific polarized trafficking of these viral envelope proteins, we identified one of the virus-encoded signals and several host proteins associated with regulating the polarized trafficking in the midgut epithelium.
昆虫的全身病毒感染通常始于中肠上皮细胞（肠细胞）的初次感染，随后子代病毒以顶端到基底的方向穿过中肠进入血腔。对于昆虫传播的病毒，在唾液腺的二次感染时会发生相反方向的过程（基底到顶端的转运），这对于病毒向非昆虫宿主的传播是必要的。为了研究这些极化组织中相反方向的病毒转运，我们评估了两种模型病毒包膜蛋白（杆状病毒 GP64 和水疱性口炎病毒 G）在模型昆虫 中的中肠和唾液腺细胞中的细胞内转运。使用可诱导表达 GP64 或 VSV G 的蝇系，我们发现，单独表达的每种蛋白都以基底方式在中肠肠细胞中转运。在唾液腺细胞中，VSV G 在大多数但不是所有细胞中都以顶端方式转运，而 GP64 则始终以基底方式转运。我们证明，两种蛋白中都存在的 YxxØ 基序对于中肠肠细胞中的基底转运是关键的，但对于唾液腺细胞中的转运是可有可无的。使用 RNAi，我们发现网格蛋白衔接蛋白复合物 AP-1 和 AP-3 以及七个 Rab GTPases 参与了中肠肠细胞中极化的 VSV G 转运。我们的结果表明，这些病毒包膜蛋白编码了适当的极化转运所需的信息，并且不需要其他病毒因子。此外，它们利用蛋白质转运途径在组织中的差异，以促进以适当方向的病毒逸出，从而建立全身感染并将感染传播给其他宿主。
以昆虫为宿主的病毒必须通过不同的昆虫组织中的特定途径来完成其生命周期。这些途径可能因病毒的生命周期而有很大的不同。昆虫病原病毒和昆虫传播的病毒都必须通过中肠上皮细胞的极化细胞来建立全身感染。此外，昆虫传播的病毒还必须通过极化的唾液腺上皮细胞进行传播。因此，昆虫传播的病毒在这两种组织中的转运方向似乎相反。在这项研究中，我们询问了两种病毒包膜蛋白（VSV G 和杆状病毒 GP64）是否单独编码与其各自生命周期相关的极化转运所需的信号。使用 作为模型来研究这些病毒包膜蛋白在组织特异性极化转运中的作用，我们确定了一个病毒编码信号和几个与调节中肠上皮极化转运相关的宿主蛋白。
