Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.
Department of Infectious Diseases, Integrative Virology, CIID, University Hospital Heidelberg, Heidelberg, Germany.
PLoS Pathog. 2018 Aug 20;14(8):e1007269. doi: 10.1371/journal.ppat.1007269. eCollection 2018 Aug.
SERINC5 is a host restriction factor that impairs infectivity of HIV-1 and other primate lentiviruses and is counteracted by the viral accessory protein Nef. However, the importance of SERINC5 antagonism for viral replication and cytopathicity remained unclear. Here, we show that the Nef protein of the highly divergent SIVcol lineage infecting mantled guerezas (Colobus guereza) is a potent antagonist of SERINC5, although it lacks the CD4, CD3 and CD28 down-modulation activities exerted by other primate lentiviral Nefs. In addition, SIVcol Nefs decrease CXCR4 cell surface expression, suppress TCR-induced actin remodeling, and counteract Colobus but not human tetherin. Unlike HIV-1 Nef proteins, SIVcol Nef induces efficient proteasomal degradation of SERINC5 and counteracts orthologs from highly divergent vertebrate species, such as Xenopus frogs and zebrafish. A single Y86F mutation disrupts SERINC5 and tetherin antagonism but not CXCR4 down-modulation by SIVcol Nef, while mutation of a C-proximal di-leucine motif has the opposite effect. Unexpectedly, the Y86F change in SIVcol Nef had little if any effect on viral replication and CD4+ T cell depletion in preactivated human CD4+ T cells and in ex vivo infected lymphoid tissue. However, SIVcol Nef increased virion infectivity up to 10-fold and moderately increased viral replication in resting peripheral blood mononuclear cells (PBMCs) that were first infected with HIV-1 and activated three or six days later. In conclusion, SIVcol Nef lacks several activities that are conserved in other primate lentiviruses and utilizes a distinct proteasome-dependent mechanism to counteract SERINC5. Our finding that evolutionarily distinct SIVcol Nefs show potent anti-SERINC5 activity supports a relevant role of SERINC5 antagonism for viral fitness in vivo. Our results further suggest this Nef function is particularly important for virion infectivity under conditions of limited CD4+ T cell activation.
SERINC5 是一种宿主限制因子，可削弱 HIV-1 和其他灵长类慢病毒的感染性，并被病毒辅助蛋白 Nef 拮抗。然而，SERINC5 拮抗作用对病毒复制和细胞病变作用的重要性尚不清楚。在这里，我们表明，感染冕狐猴（Colobus guereza）的高度分化的 SIVcol 谱系的 Nef 蛋白是 SERINC5 的一种有效拮抗剂，尽管它缺乏其他灵长类慢病毒 Nef 发挥的 CD4、CD3 和 CD28 下调活性。此外，SIVcol Nef 降低 CXCR4 细胞表面表达，抑制 TCR 诱导的肌动蛋白重塑，并拮抗 Colobus 但不拮抗人类 tetherin。与 HIV-1 Nef 蛋白不同，SIVcol Nef 诱导 SERINC5 的有效蛋白酶体降解，并拮抗来自高度分化的脊椎动物物种的同源物，如非洲爪蟾和斑马鱼。单一的 Y86F 突变破坏了 SERINC5 和 tetherin 的拮抗作用，但不破坏 SIVcol Nef 对 CXCR4 的下调作用，而 C 端近端二亮氨酸基序的突变则产生相反的效果。出乎意料的是，SIVcol Nef 的 Y86F 变化对预激活的人 CD4+T 细胞中和体外感染的淋巴组织中 SIVcol 的复制和 CD4+T 细胞耗竭几乎没有影响。然而，SIVcol Nef 将病毒粒子感染性提高了 10 倍，并适度增加了在最初感染 HIV-1 并在三天或六天后被激活的静止外周血单核细胞（PBMC）中的病毒复制。总之，SIVcol Nef 缺乏其他灵长类慢病毒中保守的几种活性，并利用独特的依赖蛋白酶体的机制来拮抗 SERINC5。我们的发现表明，进化上不同的 SIVcol Nef 具有很强的抗 SERINC5 活性，这支持了 SERINC5 拮抗作用在体内对病毒适应性的重要作用。我们的结果进一步表明，这种 Nef 功能对于在有限的 CD4+T 细胞激活条件下的病毒感染性特别重要。
