Molecular Mechanism of BST2/Tetherin Downregulation by K5/MIR2 of Kaposi's Sarcoma-Associated Herpesvirus
Molecular Mechanism of BST2/Tetherin Downregulation by K5/MIR2 of Kaposi's Sarcoma-Associated Herpesvirus
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DOI：
10.1128/jvi.00597-09
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发表时间：
2009-10-01
影响因子：
5.4
通讯作者：
Frueh, Klaus
中科院分区：
文献类型：
--
作者：
Mansouri, Mandana;Viswanathan, Kasinath;Frueh, Klaus
卡波西肉瘤相关疱疹病毒（KSHV）的K3/MIR 1和K5/MIR 2是膜相关RING-CH（MARCH）泛素连接酶家族的病毒成员，并通过引导泛素与免疫刺激性跨膜蛋白的缀合而有助于病毒免疫逃避。在一项针对病毒免疫调节剂下调的新型宿主细胞蛋白质的定量蛋白质组学筛选中，我们先前观察到K5以及人类免疫缺陷病毒1型（HIV-1）免疫调节剂VPU降低了骨髓基质细胞抗原2（BST 2;也称为CD 317或tetherin）的稳态水平，表明BST 2可能是K5和VPU的新型底物。最近的工作表明，在VPU的情况下，HIV-1病毒粒子被拴系到表达BST 2的HeLa细胞的质膜上。通过靶向BST 2，K5可能因此类似地克服先天抗病毒宿主防御机制。在这里，我们建立，尽管它的II型跨膜拓扑结构和羧基末端糖基磷脂酰肌醇（GPI）锚，BST 2代表一个真正的目标K5的下调，在原发感染和重新激活KSHV。当蛋白质离开内质网时，BST 2的短氨基末端结构域中的赖氨酸被K5泛素化，导致BST 2的快速降解。降解需要BST 2的泛素化，因为缺乏胞质赖氨酸的BST 2具有K5抗性，并且蛋白酶体抑制剂的泛素消耗恢复了BST 2表面表达。因此，BST 2代表了K5靶向的第一个II型跨膜蛋白，也是泛素化和GPI连接的蛋白质的第一个例子。我们进一步证明，KSHV的释放减少，在没有K5的BST 2依赖的方式，这表明K5有助于逃避细胞内的抗病毒防御程序。
K3/MIR1 and K5/MIR2 of Kaposi's sarcoma-associated herpesvirus (KSHV) are viral members of the membrane-associated RING-CH (MARCH) ubiquitin ligase family and contribute to viral immune evasion by directing the conjugation of ubiquitin to immunostimulatory transmembrane proteins. In a quantitative proteomic screen for novel host cell proteins downregulated by viral immunomodulators, we previously observed that K5, as well as the human immunodeficiency virus type 1 (HIV-1) immunomodulator VPU, reduced steady-state levels of bone marrow stromal cell antigen 2 (BST2; also called CD317 or tetherin), suggesting that BST2 might be a novel substrate of K5 and VPU. Recent work revealed that in the absence of VPU, HIV-1 virions are tethered to the plasma membrane in BST2-expressing HeLa cells. By targeting BST2, K5 might thus similarly overcome an innate antiviral host defense mechanism. Here we establish that despite its type II transmembrane topology and carboxy-terminal glycosylphosphatidylinositol (GPI) anchor, BST2 represents a bona fide target of K5 that is downregulated during primary infection by and reactivation of KSHV. Upon exit of the protein from the endoplasmic reticulum, lysines in the short amino-terminal domain of BST2 are ubiquitinated by K5, resulting in rapid degradation of BST2. Ubiquitination of BST2 is required for degradation, since BST2 lacking cytosolic lysines was K5 resistant and ubiquitin depletion by proteasome inhibitors restored BST2 surface expression. Thus, BST2 represents the first type II transmembrane protein targeted by K5 and the first example of a protein that is both ubiquitinated and GPI linked. We further demonstrate that KSHV release is decreased in the absence of K5 in a BST2-dependent manner, suggesting that K5 contributes to the evasion of intracellular antiviral defense programs.