Duncan R
Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
Virology. 1996 May 1;219(1):179-89. doi: 10.1006/viro.1996.0235.
Avian reoviruses are capable of inducing rapid and extensive syncytium formation, a process that occurs preferentially under conditions of neutral or alkaline pH. In order to ascertain whether the membrane fusion-inducing capability of avian reovirus confers a pH-independent entry mechanism on the virus, virus entry was investigated using internalization assays and several lysomotropic agents that inhibit endosomal acidification. The ability of avian reovirus to infect cells was severely restricted under all conditions that prevented endosomal acidification. The decreased infection efficiency in the presence of the lysomotropic agents correlated with an inhibition in the proteolytic processing of the major outer capsid protein mu 2C. The importance, with respect to virus infection, of the low pH-dependent cleavage of the avian reovirus mu 2C protein was confirmed by demonstrating that infectious subviral particles, generated by proteolytic processing in vitro, were capable of efficiently infecting cells in the presence of the lysomotropic agents. These results indicated that avian reovirus entry-specific membrane interactions are largely dependent on an endosome-mediated proteolytic processing of the virus particle, suggesting that the syncytium-inducing properly of the sigma 3 protein is not sufficient to promote virus uptake. Furthermore, avian reovirus internalization was associated with two distinct cleavages of the major outer capsid protein mu 2C, unlike the entry-specific processing of the analagous mammalian reovirus major outer capsid protein mu 1C. The mu 2C cleavages occured sequentially and appeared to involve distinct cleavage specificities. Moreover, the second cleavage event was observed to be both virus strain- and cell type-independent, suggesting that the cleavage is both specific and biologically significant.
禽呼肠孤病毒能够诱导快速且广泛的合胞体形成，这一过程优先在中性或碱性pH条件下发生。为了确定禽呼肠孤病毒的膜融合诱导能力是否赋予病毒一种不依赖pH的进入机制，使用内化试验和几种抑制内体酸化的溶酶体促渗剂对病毒进入进行了研究。在所有阻止内体酸化的条件下，禽呼肠孤病毒感染细胞的能力都受到严重限制。在存在溶酶体促渗剂的情况下感染效率降低与主要外衣壳蛋白μ2C的蛋白水解加工受到抑制相关。通过证明体外蛋白水解加工产生的感染性子病毒颗粒在存在溶酶体促渗剂的情况下能够有效感染细胞，证实了禽呼肠孤病毒μ2C蛋白低pH依赖性切割对于病毒感染的重要性。这些结果表明，禽呼肠孤病毒进入特异性膜相互作用在很大程度上依赖于病毒颗粒的内体介导蛋白水解加工，这表明σ3蛋白的合胞体诱导特性不足以促进病毒摄取。此外，与类似的哺乳动物呼肠孤病毒主要外衣壳蛋白μ1C的进入特异性加工不同，禽呼肠孤病毒内化与主要外衣壳蛋白μ2C的两种不同切割相关。μ2C切割依次发生，似乎涉及不同的切割特异性。此外，观察到第二次切割事件与病毒株和细胞类型无关，这表明该切割既具有特异性又具有生物学意义。
