Microbiology Department, New York University School of Medicine, New York, New York, USA.
J Virol. 2013 Nov;87(21):11741-50. doi: 10.1128/JVI.02002-13. Epub 2013 Aug 28.
The deoxynucleoside triphosphohydrolase SAMHD1 restricts retroviral replication in myeloid cells. Human immunodeficiency virus type 2 (HIV-2) and a simian immunodeficiency virus from rhesus macaques (SIVmac) encode Vpx, a virion-packaged accessory protein that counteracts SAMHD1 by inducing its degradation. SAMHD1 is thought to work by depleting the pool of intracellular deoxynucleoside triphosphates but has also been reported to have exonuclease activity that could allow it to degrade the viral genomic RNA or viral reverse-transcribed DNA. To induce the degradation of SAMHD1, Vpx co-opts the cullin4a-based E3 ubiquitin ligase, CRL4. E3 ubiquitin ligases are regulated by the covalent attachment of the ubiquitin-like protein Nedd8 to the cullin subunit. Neddylation can be prevented by MLN4924, a drug that inhibits the nedd8-activating enzyme. We report that MLN4924 inhibits the neddylation of CRL4, blocking Vpx-induced degradation of SAMHD1 and maintaining the restriction. Removal of the drug several hours postinfection released the block. Similarly, Vpx-containing virus-like particles and deoxynucleosides added to the cells more than 24 h postinfection released the SAMHD1-mediated block. Taken together, these findings support deoxynucleoside triphosphate pool depletion as the primary mechanism of SAMHD1 restriction and argue against a nucleolytic mechanism, which would not be reversible.
脱氧核苷三磷酸水解酶 SAMHD1 限制骨髓细胞中的逆转录病毒复制。人类免疫缺陷病毒 2 型（HIV-2）和猕猴来源的猴免疫缺陷病毒（SIVmac）编码 Vpx，一种病毒包装的辅助蛋白，通过诱导其降解来拮抗 SAMHD1。SAMHD1 被认为通过耗尽细胞内脱氧核苷三磷酸池起作用，但也有报道称其具有外切核酸酶活性，使其能够降解病毒基因组 RNA 或病毒逆转录 DNA。为了诱导 SAMHD1 的降解，Vpx 利用基于 cullin4a 的 E3 泛素连接酶 CRL4。E3 泛素连接酶受泛素样蛋白 Nedd8 与 cullin 亚基的共价连接调节。Neddylation 可以被 MLN4924 抑制，这是一种抑制 Nedd8 激活酶的药物。我们报告 MLN4924 抑制 CRL4 的 Neddylation，阻断 Vpx 诱导的 SAMHD1 降解并维持限制。感染后数小时去除药物会释放出阻断。同样，感染后超过 24 小时添加含有 Vpx 的病毒样颗粒和脱氧核苷也会释放出 SAMHD1 介导的阻断。总之，这些发现支持脱氧核苷三磷酸池耗竭是 SAMHD1 限制的主要机制，并反对核酶机制，因为后者不可逆转。
