Department of Microbiology and Immunology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA
Department of Microbiology and Immunology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA.
J Virol. 2019 Apr 17;93(9). doi: 10.1128/JVI.01812-18. Print 2019 May 1.
Kaposi's sarcoma-associated herpesvirus (KSHV)-induced activation of nuclear factor erythroid 2-related factor 2 (Nrf2) is essential for both the expression of viral genes (latency) and modulation of the host antioxidant machinery. Reactive oxygen species (ROS) are also regulated by the ubiquitously expressed HACE1 protein (HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1), which targets the Rac1 protein for proteasomal degradation, and this blocks the generation of ROS by Rac1-dependent NADPH oxidases. In this study, we examined the role of HACE1 in KSHV infection. Elevated levels of HACE1 expression were observed in KSHV-infected endothelial cells, KSHV latently infected TIVE-LTC and PEL cells, and Kaposi's sarcoma skin lesion cells. The increased HACE1 expression in the infected cells was mediated by KSHV latent protein kaposin A. HACE1 knockdown resulted in high Rac1 and Nox 1 (NADPH oxidase 1) activity, increased ROS (oxidative stress), increased cell death, and decreased KSHV gene expression. Loss of HACE1 impaired KSHV infection-induced phosphoinositide 3-kinase (PI3-K), protein kinase C-ζ (PKC-ζ), extracellular signal-regulated kinase 1/2 (ERK1/2), NF-κB, and Nrf2 activation and nuclear translocation of Nrf2, and it reduced the expression of Nrf2 target genes responsible for balancing the oxidative stress. In the absence of HACE1, glutamine uptake increased in the cells to cope with the KSHV-induced oxidative stress. These findings reveal for the first time that HACE1 plays roles during viral infection-induced oxidative stress and demonstrate that HACE1 facilitates resistance to KSHV infection-induced oxidative stress by promoting Nrf2 activity. Our studies suggest that HACE1 could be a potential target to induce cell death in KSHV-infected cells and to manage KSHV infections. ROS play important roles in several cellular processes, and increased ROS cause several adverse effects. KSHV infection of endothelial cells induces ROS, which facilitate virus entry by amplifying the infection-induced host cell signaling cascade, which, in turn, induces the nuclear translocation of phospho-Nrf2 protein to regulate the expression of antioxidative genes and viral genes. The present study demonstrates that KSHV infection induces the E3 ligase HACE1 protein to regulate KSHV-induced oxidative stress by promoting the activation of Nrf2 and nuclear translocation. Absence of HACE1 results in increased ROS and cellular death and reduced nuclear Nrf2, antioxidant, and viral gene expression. Together, these studies suggest that HACE1 can be a potential target to induce cell death in KSHV-infected cells.
卡波氏肉瘤相关疱疹病毒（KSHV）诱导的核因子红细胞 2 相关因子 2（Nrf2）的激活对于病毒基因的表达（潜伏期）和宿主抗氧化机制的调节都是必不可少的。活性氧（ROS）也受到广泛表达的 HACE1 蛋白（HECT 结构域和含锚蛋白重复的 E3 泛素蛋白连接酶 1）的调节，该蛋白将 Rac1 蛋白靶向蛋白酶体降解，从而阻止 Rac1 依赖性 NADPH 氧化酶产生 ROS。在这项研究中，我们研究了 HACE1 在 KSHV 感染中的作用。在 KSHV 感染的内皮细胞、潜伏感染的 TIVE-LTC 和 PEL 细胞以及卡波西肉瘤皮肤病变细胞中观察到 HACE1 表达水平升高。感染细胞中 HACE1 的表达增加是由 KSHV 潜伏蛋白 kaposin A 介导的。HACE1 的敲低导致 Rac1 和 Nox1（NADPH 氧化酶 1）活性增加、ROS（氧化应激）增加、细胞死亡增加和 KSHV 基因表达减少。HACE1 的缺失会损害 KSHV 感染诱导的磷酸肌醇 3-激酶（PI3-K）、蛋白激酶 C-ζ（PKC-ζ）、细胞外信号调节激酶 1/2（ERK1/2）、NF-κB 和 Nrf2 激活以及 Nrf2 的核易位，减少负责平衡氧化应激的 Nrf2 靶基因的表达。在没有 HACE1 的情况下，细胞内的谷氨酰胺摄取增加以应对 KSHV 诱导的氧化应激。这些发现首次表明，HACE1 在病毒感染诱导的氧化应激过程中发挥作用，并表明 HACE1 通过促进 Nrf2 活性促进 Nrf2 活性，从而有助于抵抗 KSHV 感染诱导的氧化应激。我们的研究表明，HACE1 可能是诱导 KSHV 感染细胞死亡和管理 KSHV 感染的潜在靶点。ROS 在许多细胞过程中发挥重要作用，增加的 ROS 会导致多种不良反应。内皮细胞感染 KSHV 会诱导 ROS，通过放大感染诱导的宿主细胞信号级联反应来促进病毒进入，从而诱导磷酸化 Nrf2 蛋白的核易位，以调节抗氧化基因和病毒基因的表达。本研究表明，KSHV 感染诱导 E3 连接酶 HACE1 蛋白通过促进 Nrf2 的激活和核易位来调节 KSHV 诱导的氧化应激。HACE1 的缺失会导致 ROS 和细胞死亡增加，核 Nrf2、抗氧化和病毒基因表达减少。总之，这些研究表明，HACE1 可以成为诱导 KSHV 感染细胞死亡的潜在靶点。
