McMillan T N, Johnson D C
Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201, USA.
J Virol. 2001 Feb;75(4):1928-40. doi: 10.1128/JVI.75.4.1928-1940.2001.
Alphaherpesviruses express a heterodimeric glycoprotein, gE/gI, that facilitates cell-to-cell spread between epithelial cells and neurons. Herpes simplex virus (HSV) gE/gI accumulates at junctions formed between polarized epithelial cells at late times of infection. However, at earlier times after HSV infection, or when gE/gI is expressed using virus vectors, the glycoprotein localizes to the trans-Golgi network (TGN). The cytoplasmic (CT) domains of gE and gI contain numerous TGN and endosomal sorting motifs and are essential for epithelial cell-to-cell spread. Here, we swapped the CT domains of HSV gE and gI onto another HSV glycoprotein, gD. When the gD-gI(CT) chimeric protein was expressed using a replication-defective adenovirus (Ad) vector, the protein was found on both the apical and basolateral surfaces of epithelial cells, as was gD. By contrast, the gD-gE(CT) chimeric protein, gE/gI, and gE, when expressed by using Ad vectors, localized exclusively to the TGN. However, gD-gE(CT), gE/gI, and TGN46, a cellular TGN protein, became redistributed largely to lateral surfaces and cell junctions during intermediate to late stages of HSV infection. Strikingly, gE and TGN46 remained sequestered in the TGN when cells were infected with a gI(-)HSV mutant. The redistribution of gE/gI to lateral cell surfaces did not involve widespread HSV inhibition of endocytosis because the transferrin receptor and gE were both internalized from the cell surface. Thus, gE/gI accumulates in the TGN in early phases of HSV infection then moves to lateral surfaces, to cell junctions, at late stages of infection, coincident with the redistribution of a TGN marker. These results are related to recent observations that gE/gI participates in the envelopment of nucleocapsids into cytoplasmic vesicles (A. R. Brack, B. G. Klupp, H. Granzow, R. Tirabassi, L. W. Enquist, and T. C. Mettenleiter, J. Virol. 74:4004-4016, 2000) and that gE/gI can sort nascent virions from cytoplasmic vesicles specifically to the lateral surfaces of epithelial cells (D. C. Johnson, M. Webb, T. W. Wisner, and C. Brunetti, J. Virol. 75:821-833, 2000). Therefore, gE/gI localizes to the TGN, through interactions between the CT domain of gE and cellular sorting machinery, and then participates in envelopment of cytosolic nucleocapsids there. Nascent virions are then sorted from the TGN to cell junctions.
α疱疹病毒表达一种异源二聚体糖蛋白gE/gI，它促进上皮细胞和神经元之间的细胞间传播。单纯疱疹病毒（HSV）gE/gI在感染后期积聚在极化上皮细胞之间形成的连接处。然而，在HSV感染后的早期，或者当使用病毒载体表达gE/gI时，该糖蛋白定位于反式高尔基体网络（TGN）。gE和gI的胞质（CT）结构域包含许多TGN和内体分选基序，对于上皮细胞间传播至关重要。在这里，我们将HSV gE和gI的CT结构域交换到另一种HSV糖蛋白gD上。当使用复制缺陷型腺病毒（Ad）载体表达gD-gI（CT）嵌合蛋白时，发现该蛋白在上皮细胞的顶端和基底外侧表面均有分布，gD也是如此。相比之下，当使用Ad载体表达时，gD-gE（CT）嵌合蛋白、gE/gI和gE仅定位于TGN。然而，在HSV感染的中晚期，gD-gE（CT）、gE/gI和细胞TGN蛋白TGN46大部分重新分布到侧面和细胞连接处。引人注目的是，当细胞感染gI（-）HSV突变体时，gE和TGN46仍被隔离在TGN中。gE/gI向细胞侧面的重新分布并不涉及HSV对胞吞作用的广泛抑制，因为转铁蛋白受体和gE都从细胞表面内化。因此，gE/gI在HSV感染的早期积聚在TGN中，然后在感染后期移动到侧面，到达细胞连接处，这与TGN标记物的重新分布一致。这些结果与最近的观察结果相关，即gE/gI参与核衣壳包裹到细胞质囊泡中（A. R. Brack、B. G. Klupp、H. Granzow、R. Tirabassi、L. W. Enquist和T. C. Mettenleiter，《病毒学杂志》74:4004 - 4016，2000年），并且gE/gI可以将新生病毒粒子从细胞质囊泡中特异性分选到上皮细胞的侧面（D. C. Johnson、M. Webb、T. W. Wisner和C. Brunetti，《病毒学杂志》75:821 - 833，2000年）。因此，gE/gI通过gE的CT结构域与细胞分选机制之间的相互作用定位于TGN，然后在那里参与胞质核衣壳的包裹。随后新生病毒粒子从TGN被分选到细胞连接处。
