Schmitt Anthony P, Leser George P, Waning David L, Lamb Robert A
Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois 60208-3500, USA.
J Virol. 2002 Apr;76(8):3952-64. doi: 10.1128/jvi.76.8.3952-3964.2002.
Enveloped viruses are released from infected cells after coalescence of viral components at cellular membranes and budding of membranes to release particles. For some negative-strand RNA viruses (e.g., vesicular stomatitis virus and Ebola virus), the viral matrix (M) protein contains all of the information needed for budding, since virus-like particles (VLPs) are efficiently released from cells when the M protein is expressed from cDNA. To investigate the requirements for budding of the paramyxovirus simian virus 5 (SV5), its M protein was expressed in mammalian cells, and it was found that SV5 M protein alone could not induce vesicle budding and was not secreted from cells. Coexpression of M protein with the viral hemagglutinin-neuraminidase (HN) or fusion (F) glycoproteins also failed to result in significant VLP release. It was found that M protein in the form of VLPs was only secreted from cells, with an efficiency comparable to authentic virus budding, when M protein was coexpressed with one of the two glycoproteins, HN or F, together with the nucleocapsid (NP) protein. The VLPs appeared similar morphologically to authentic virions by electron microscopy. CsCl density gradient centrifugation indicated that almost all of the NP protein in the cells had assembled into nucleocapsid-like structures. Deletion of the F and HN cytoplasmic tails indicated an important role of these cytoplasmic tails in VLP budding. Furthermore, truncation of the HN cytoplasmic tail was found to be inhibitory toward budding, since it prevented coexpressed wild-type (wt) F protein from directing VLP budding. Conversely, truncation of the F protein cytoplasmic tail was not inhibitory and did not affect the ability of coexpressed wt HN protein to direct the budding of particles. Taken together, these data suggest that multiple viral components, including assembled nucleocapsids, have important roles in the paramyxovirus budding process.
包膜病毒在病毒成分于细胞膜上合并以及膜出芽释放病毒颗粒后，从受感染细胞中释放出来。对于一些负链RNA病毒（如水泡性口炎病毒和埃博拉病毒），病毒基质（M）蛋白包含出芽所需的所有信息，因为当M蛋白由cDNA表达时，病毒样颗粒（VLP）能有效地从细胞中释放出来。为了研究副粘病毒猴病毒5（SV5）出芽的要求，其M蛋白在哺乳动物细胞中表达，结果发现单独的SV5 M蛋白不能诱导囊泡出芽，也不能从细胞中分泌出来。M蛋白与病毒血凝素-神经氨酸酶（HN）或融合（F）糖蛋白共表达也未能导致大量VLP释放。结果发现，当M蛋白与两种糖蛋白之一HN或F以及核衣壳（NP）蛋白共表达时，VLP形式的M蛋白才仅从细胞中分泌出来，其效率与真正的病毒出芽相当。通过电子显微镜观察，VLP在形态上与真正的病毒粒子相似。氯化铯密度梯度离心表明，细胞中几乎所有的NP蛋白都已组装成核衣壳样结构。F和HN细胞质尾巴的缺失表明这些细胞质尾巴在VLP出芽中起重要作用。此外，发现HN细胞质尾巴的截短对出芽有抑制作用，因为它阻止了共表达的野生型（wt）F蛋白引导VLP出芽。相反，F蛋白细胞质尾巴的截短没有抑制作用，也不影响共表达的wt HN蛋白引导颗粒出芽的能力。综上所述，这些数据表明多种病毒成分，包括组装好的核衣壳，在副粘病毒出芽过程中起重要作用。
