International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
PLoS One. 2013 Sep 4;8(9):e74472. doi: 10.1371/journal.pone.0074472. eCollection 2013.
The HIV-1 accessory protein Nef is an important virulence factor. It associates with cellular membranes and modulates the endocytic machinery and signaling pathways. Nef also increases the proliferation of multivesicular bodies (MVBs), which are sites for virus assembly and budding in macrophages. The RNA interference (RNAi) pathway proteins Ago2 and GW182 localize to MVBs, suggesting these to be sites for assembly and turnover of the miRNA-induced silencing complex (miRISC). While RNAi affects HIV replication, it is not clear if the virus encodes a suppressor activity to overcome this innate host response. Here we show that Nef colocalizes with MVBs and binds Ago2 through two highly conserved Glycine-Tryptophan (GW) motifs, mutations in which abolish Nef binding to Ago2 and reduce virus yield and infectivity. Nef also inhibits the slicing activity of Ago2 and disturbs the sorting of GW182 into exosomes resulting in the suppression of miRNA-induced silencing. Thus, besides its other activities, the HIV-1 Nef protein is also proposed to function as a viral suppressor of RNAi (VSR).
HIV-1 辅助蛋白 Nef 是一种重要的毒力因子。它与细胞膜结合，调节内吞作用机制和信号通路。Nef 还增加了多泡体（MVBs）的增殖，MVBs 是巨噬细胞中病毒组装和出芽的部位。RNA 干扰（RNAi）途径蛋白 Ago2 和 GW182 定位于 MVBs，表明这些是 miRNA 诱导的沉默复合物（miRISC）组装和周转的部位。虽然 RNAi 会影响 HIV 的复制，但目前尚不清楚病毒是否编码一种抑制活性来克服这种先天的宿主反应。在这里，我们发现 Nef 与 MVBs 共定位，并通过两个高度保守的甘氨酸-色氨酸（GW）基序与 Ago2 结合，这些基序的突变会使 Nef 无法与 Ago2 结合，并降低病毒产量和感染力。Nef 还抑制了 Ago2 的切割活性，并扰乱了 GW182 进入外泌体的分拣，从而抑制了 miRNA 诱导的沉默。因此，除了其他活性外，HIV-1 Nef 蛋白还被提议作为 RNAi 的病毒抑制剂（VSR）。
