Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
PLoS Pathog. 2020 Apr 17;16(4):e1008487. doi: 10.1371/journal.ppat.1008487. eCollection 2020 Apr.
Most simian immunodeficiency viruses use Nef to counteract the tetherin proteins of their nonhuman primate hosts. Nef also downmodulates cell-surface CD4 and MHC class I (MHC I) molecules and enhances viral infectivity by counteracting SERINC5. We previously demonstrated that tetherin antagonism by SIV Nef is genetically separable from CD4- and MHC I-downmodulation. Here we show that disruption of tetherin antagonism by Nef impairs virus replication during acute SIV infection of rhesus macaques. A combination of mutations was introduced into the SIVmac239 genome resulting in three amino acid substitutions in Nef that impair tetherin antagonism, but not CD3-, CD4- or MHC I-downmodulation. Further characterization of this mutant (SIVmac239AAA) revealed that these changes also result in partial sensitivity to SERINC5. Separate groups of four rhesus macaques were infected with either wild-type SIVmac239 or SIVmac239AAA, and viral RNA loads in plasma and sequence changes in the viral genome were monitored. Viral loads were significantly lower during acute infection in animals infected with SIVmac239AAA than in animals infected with wild-type SIVmac239. Sequence analysis of the virus population in plasma confirmed that the substitutions in Nef were retained during acute infection; however, changes were observed by week 24 post-infection that fully restored anti-tetherin activity and partially restored anti-SERINC5 activity. These observations reveal overlap in the residues of SIV Nef required for counteracting tetherin and SERINC5 and selective pressure to overcome these restriction factors in vivo.
大多数猿猴免疫缺陷病毒利用 Nef 来拮抗其非人类灵长类宿主的 tetherin 蛋白。Nef 还下调细胞表面 CD4 和 MHC Ⅰ （MHC I） 分子，并通过拮抗 SERINC5 来增强病毒感染力。我们之前证明，SIV Nef 的 tetherin 拮抗作用在遗传上可与 CD4 和 MHC I 下调分离。在这里，我们表明，Nef 对 tetherin 的拮抗作用的破坏会损害恒河猴急性 SIV 感染期间的病毒复制。我们将一系列突变引入 SIVmac239 基因组中，导致 Nef 中的三个氨基酸取代，这些取代会损害 tetherin 的拮抗作用，但不会影响 CD3、CD4 或 MHC I 的下调。对该突变体（SIVmac239AAA）的进一步表征表明，这些变化也导致对 SERINC5 的部分敏感性。四组恒河猴分别感染野生型 SIVmac239 或 SIVmac239AAA，监测血浆中的病毒 RNA 载量和病毒基因组中的序列变化。与感染野生型 SIVmac239 的动物相比，感染 SIVmac239AAA 的动物在急性感染期间的病毒载量显著降低。对血浆中病毒群体的序列分析证实，Nef 中的取代在急性感染期间得以保留；然而，在感染后第 24 周观察到了变化，完全恢复了抗 tetherin 活性，并部分恢复了抗 SERINC5 活性。这些观察结果揭示了 SIV Nef 拮抗 tetherin 和 SERINC5 所需的残基之间存在重叠，以及在体内克服这些限制因素的选择压力。
