Chen Daming, Xiang Qiwang, Nicholas John
Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
J Virol. 2017 Oct 27;91(22). doi: 10.1128/JVI.00965-17. Print 2017 Nov 15.
Viral interleukin-6 (vIL-6) encoded by human herpesvirus 8 (HHV-8) is believed to contribute via mitogenic, survival, and angiogenic activities to HHV-8-associated Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease through autocrine or paracrine mechanisms during latency or productive replication. There is direct evidence that vIL-6 promotes latently infected PEL cell viability and proliferation and also viral productive replication in PEL and endothelial cells. These activities are mediated largely through endoplasmic reticulum (ER)-localized vIL-6, which can induce signal transduction via the gp130 signaling receptor, activating mitogen-activated protein kinase and signal transducer and activator of transcription signaling, and interactions of vIL-6 with the ER membrane protein vitamin K epoxide reductase complex subunit 1 variant 2 (VKORC1v2). The latter functional axis involves suppression of proapoptotic lysosomal protein cathepsin D by promotion of the ER-associated degradation of ER-transiting, preproteolytically processed procathepsin D. Other interactions of VKORC1v2 and activities of vIL-6 via the receptor have not been reported. We show here that both vIL-6 and VKORC1v2 interact with calnexin cycle proteins UDP-glucose:glycoprotein glucosyltransferase 1 (UGGT1), which catalyzes monoglucosylation of N-glycans, and oppositely acting glucosidase II (GlucII), and that vIL-6 can promote protein folding. This activity was found to require VKORC1v2 and UGGT1, to involve vIL-6 associations with VKORC1v2, UGGT1, and GlucII, and to operate in the context of productively infected cells. These findings document new VKORC1v2-associated interactions and activities of vIL-6, revealing novel mechanisms of vIL-6 function within the ER compartment. HHV-8 vIL-6 prosurvival (latent) and proreplication functions are mediated from the ER compartment through both gp130 receptor-mediated signal transduction and interaction of vIL-6 with the ER membrane protein VKORC1v2. This report identifies interactions of vIL-6 and VKORC1v2 with calnexin cycle enzymes GlucII and UGGT1, which are involved in glycan processing and nascent protein folding. The presented data show that vIL-6 and VKORC1v2 can cocomplex with GlucII and UGGT1, that vIL-6 promotes protein folding, and that VKORC1v2, UGGT1, and vIL-6 interactions with GlucII and UGGT1 are important for the profolding activity of vIL-6, which can be detected in the context of infected cells. This newly identified ER activity of vIL-6 involving VKORC1v2 may promote viral latency (in PEL cells) and productive replication by limiting the damaging effects of unfolded protein response signaling in addition to enhancing viral protein folding. This is the first report of such a function for a cytokine.
人疱疹病毒8型（HHV - 8）编码的病毒白细胞介素-6（vIL - 6）被认为在潜伏或活跃复制期间通过自分泌或旁分泌机制，凭借其促有丝分裂、生存和血管生成活性，对HHV - 8相关的卡波西肉瘤、原发性渗出性淋巴瘤（PEL）和多中心Castleman病起作用。有直接证据表明，vIL - 6可促进潜伏感染的PEL细胞的活力和增殖，也能促进PEL细胞和内皮细胞中的病毒活跃复制。这些活性很大程度上是由内质网（ER）定位的vIL - 6介导的，它可通过gp130信号受体诱导信号转导，激活丝裂原活化蛋白激酶以及信号转导和转录激活因子信号通路，并且vIL - 6与ER膜蛋白维生素K环氧还原酶复合物亚基1变体2（VKORC1v2）相互作用。后一功能轴涉及通过促进ER转运的、蛋白水解前加工的组织蛋白酶D的ER相关降解来抑制促凋亡溶酶体蛋白组织蛋白酶D。尚未报道VKORC1v2的其他相互作用以及vIL - 6通过该受体的其他活性。我们在此表明，vIL - 6和VKORC1v2均与钙网蛋白循环蛋白UDP - 葡萄糖：糖蛋白葡糖基转移酶1（UGGT1，催化N - 聚糖的单葡糖基化）以及起相反作用的葡糖苷酶II（GlucII）相互作用，并且vIL - 6可促进蛋白质折叠。发现该活性需要VKORC1v2和UGGT1，涉及vIL - 6与VKORC1v2、UGGT1和GlucII的结合，并且在活跃感染细胞的背景下起作用。这些发现证明了与VKORC1v2相关的vIL - 6的新相互作用和活性，揭示了vIL - 6在内质网区室中的新功能机制。HHV - 8 vIL - 6的促生存（潜伏）和促复制功能是通过gp130受体介导的信号转导以及vIL - 6与ER膜蛋白VKORC1v2的相互作用，从内质网区室介导的。本报告确定了vIL - 6和VKORC1v2与参与聚糖加工和新生蛋白质折叠的钙网蛋白循环酶GlucII和UGGT1的相互作用。所呈现的数据表明，vIL - 6和VKORC1v2可与GlucII和UGGT1形成共复合物，vIL - 6促进蛋白质折叠，并且VKORC1v2、UGGT1以及vIL - 6与GlucII和UGGT1的相互作用对于vIL - 6的促折叠活性很重要，这在感染细胞的背景下可以检测到。vIL - 6这种新确定的涉及VKORC1v2的内质网活性，除了增强病毒蛋白折叠外，还可能通过限制未折叠蛋白反应信号的破坏作用来促进病毒潜伏（在PEL细胞中）和活跃复制。这是关于细胞因子这种功能的首次报道。
