Microbiology Department, New York University School of Medicine, New York, New York, USA.
J Virol. 2012 Dec;86(23):12552-60. doi: 10.1128/JVI.01657-12. Epub 2012 Sep 12.
Sterile alpha motif domain- and HD domain-containing protein 1 (SAMHD1) is a deoxynucleoside triphosphohydrolase that restricts the replication of lentiviruses in myeloid cells by hydrolyzing the cellular deoxynucleotide triphosphates to a level below that which is required for reverse transcription. Human immunodeficiency virus type 2 (HIV-2) and some simian immunodeficiency viruses (SIVs) encode the accessory protein viral protein X (Vpx) that counteracts SAMHD1. Vpx recruits SAMHD1 to a cullin4A-RING E3 ubiquitin ligase (CRL4), which targets the enzyme for proteasomal degradation. Vpx and SAMHD1 both localize to the nucleus of the cell. We identified the nuclear localization sequence (NLS) of SAMHD1 as a conserved KRPR sequence at amino acid residues 11 to 14. SAMHD1 lacking a functional NLS localized to the cytoplasm but retained its triphosphohydrolase and antiviral activities. However, cytoplasmic SAMHD1 was resistant to Vpx-induced degradation, and its antiviral activity was not counteracted by Vpx. Cytoplasmic SAMHD1 interacted with Vpx and retained it in the cytoplasm. The inhibition of nuclear export with leptomycin B did not impair the ability of Vpx to degrade SAMHD1. These findings suggest that SAMHD1 is targeted by Vpx for ubiquitination and degradation in the nucleus.
无菌α基序域和 HD 结构域蛋白 1（SAMHD1）是一种脱氧核苷三磷酸水解酶，通过将细胞内的脱氧核苷酸三磷酸水解至低于反转录所需的水平，从而限制了骨髓细胞中慢病毒的复制。人类免疫缺陷病毒 2 型（HIV-2）和一些猿猴免疫缺陷病毒（SIV）编码辅助蛋白病毒蛋白 X（Vpx），该蛋白拮抗 SAMHD1。Vpx 将 SAMHD1 募集到一个含有 Cullin4A-RING E3 泛素连接酶（CRL4）的复合物中，该复合物将酶靶向蛋白酶体降解。Vpx 和 SAMHD1 均定位于细胞核内。我们鉴定出 SAMHD1 的核定位序列（NLS）为氨基酸残基 11 到 14 处的保守 KRPR 序列。缺乏功能性 NLS 的 SAMHD1 定位于细胞质，但保留了其三磷酸水解酶和抗病毒活性。然而，细胞质中的 SAMHD1 对 Vpx 诱导的降解有抗性，并且其抗病毒活性不受 Vpx 的拮抗。细胞质中的 SAMHD1 与 Vpx 相互作用并将其保留在细胞质中。用莱普霉素 B 抑制核输出并不影响 Vpx 降解 SAMHD1 的能力。这些发现表明，SAMHD1 是 Vpx 靶向的核内泛素化和降解的目标。
