NSP4 Gene Analysis of Rotaviruses Recovered from Infected Children with and without Diarrhea

The transmembrane glycoprotein NSP4 functions as a viral enterotoxin capable of inducing diarrhea in young mice. It has been suggested that NSP4 may be a key determinant of rotavirus pathogenicity and a target for vaccine development. Twenty two G1P[6] rotaviruses from babies with and without diarrhea were comparatively analyzed along with reference strains and another 22 Taiwanese human rotaviruses of G and P combination types different from the G1P[6] type. The sequence variations in the NSP4 genes were studied by direct sequencing analysis of the amplicons of reverse transcription-PCR. Two genetic groups could be identified in this analysis. While the majority of these strains were closely related to the Wa strain, the G2 viruses were closely related to the S2 strain. Furthermore, phylogenetic analysis of the NSP4 gene among the G2 rotaviruses revealed three distinct lineages associated with DS-1, S2, and E210, respectively, as has been reported previously for the VP7 gene. However, we found no apparent correlation in the deduced amino acid sequences corresponding to the proposed enterotoxic peptide region between the rotaviruses recovered from individuals with and without diarrhea. The NSP4 gene product being a pathogenic determinant may not be a generalized phenomenon.

跨膜糖蛋白NSP4（transmembrane glycoprotein NSP4）作为一种病毒肠毒素，可诱导幼鼠产生腹泻。有研究表明，NSP4可能是轮状病毒（rotavirus）致病性的关键决定因素，同时也是疫苗研发的靶标。本研究对22株来自腹泻与非腹泻婴儿的G1P[6]型轮状病毒（G1P[6] rotaviruses）进行了对比分析，并结合参考毒株以及另外22株G/P组合型别不同于G1P[6]的台湾人源轮状病毒作为对照。通过对逆转录聚合酶链式反应（reverse transcription-PCR）扩增产物进行直接测序分析，研究了NSP4基因的序列变异情况。本次分析可鉴定出两个遗传群。多数受试毒株与Wa毒株（Wa strain）亲缘关系紧密，而G2型病毒则与S2毒株（S2 strain）高度相似。此外，针对G2型轮状病毒的NSP4基因开展系统发育分析后发现，其存在三个独立谱系，分别与DS-1、S2及E210毒株相关，这与此前针对VP7基因（VP7 gene）的研究报道结果一致。不过，本研究未在腹泻与非腹泻个体所分离的轮状病毒之间，观察到其推导得到的肠毒性肽区域对应的氨基酸序列存在显著关联。由此可见，NSP4基因产物作为致病性决定因子这一结论，或许并非普适性现象。