State Key Laboratory of Biocontrol/Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.
State Key Laboratory of Biocontrol/Guangdong Province Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China; School of Marine Sciences, Sun Yat-sen University, Guangzhou 510275, China.
Fish Shellfish Immunol. 2017 Nov;70:293-301. doi: 10.1016/j.fsi.2017.09.017. Epub 2017 Sep 6.
The process of ubiquitination regulates various cellular processes. The ubiquitin-proteasome system (UPS) in fish, which is important for the generation of innate and adaptive immune responses to pathogens, is the target of aquatic viruses to achieve immune evasion. We cloned and characterized three genes, namely, a ubiquitin-activating enzyme (ScE1), a ubiquitin-conjugating enzyme (ScE2), and a HECT-type ubiquitin ligase (ScE3) of mandarin fish Siniperca chuatsi. The genes were expressed in all tissues and the highest levels were observed in the blood. In infectious spleen and kidney necrosis virus (ISKNV)-infected mandarin fish fry cells, the expression levels of the three genes in vitro were almost identical, and upregulated during the early stage and downregulated at the late stage. In the blood of ISKNV-infected mandarin fish, their expressions in vivo were downregulated equally although peaking at different timepoints, indicating the suppression of UPS by viral infection. Furthermore, these recombinant proteins were determined to function well in ubiquitination assays in vitro. Moreover, ScE1 and ScE2 can be utilized by four RING-type viral E3s (vE3s) that are encoded by ISKNV. The in vitro activity of vE3 was stronger than that of ScE3, suggesting that the fish UPS may be hijacked by ISKNV via E3 activity competition and expression modulation. The present study investigated the function of mandarin fish UPS as well as its response to iridovirus infection, providing insights to better understand the virus-host interactions and the mechanism of ISKNV in evading host immune responses.
泛素化过程调节着各种细胞过程。鱼体中的泛素-蛋白酶体系统（UPS）对于产生对病原体的先天和适应性免疫反应非常重要，是水生病毒实现免疫逃避的靶点。我们克隆并鉴定了三种基因，即鳜鱼 Siniperca chuatsi 的泛素激活酶（ScE1）、泛素连接酶（ScE2）和 HECT 型泛素连接酶（ScE3）。这些基因在所有组织中都有表达，在血液中的表达水平最高。在传染性脾坏死病毒（ISKNV）感染的鳜鱼苗细胞中，这三种基因在体外的表达水平几乎相同，在早期上调，晚期下调。在 ISKNV 感染的鳜鱼血液中，它们在体内的表达虽然在不同时间点达到峰值，但都下调，表明病毒感染抑制了 UPS。此外，这些重组蛋白在体外泛素化试验中功能良好。此外，ScE1 和 ScE2 可被 ISKNV 编码的四种 RING 型病毒 E3（vE3）利用。vE3 的体外活性强于 ScE3，表明鱼类 UPS 可能通过 E3 活性竞争和表达调控被 ISKNV 劫持。本研究调查了鳜鱼 UPS 的功能及其对虹彩病毒感染的反应，为更好地理解病毒-宿主相互作用和 ISKNV 逃避宿主免疫反应的机制提供了线索。
