Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India.
Oxid Med Cell Longev. 2020 Apr 4;2020:7289120. doi: 10.1155/2020/7289120. eCollection 2020.
Eukaryotic cells adopt highly tuned stress response physiology under threats of exogenous stressors including viruses to maintain cellular homeostasis. Not surprisingly, avoidance of cellular stress response pathways is an essential facet of virus-induced obligatory host reprogramming to invoke a cellular environment conducive to viral perpetuation. Adaptive cellular responses to oxidative and electrophilic stress are usually taken care of by an antioxidant defense system, core to which lies the redox-responsive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2-driven transcriptional cascade. Deregulation of host redox balance and redox stress-sensitive Nrf2 antioxidant defense have been reported for many viruses. In the current study, we aimed to study the modulation of the Nrf2-based host cellular redox defense system in response to Rotavirus (RV) infection . Interestingly, we found that Nrf2 protein levels decline sharply with progression of RV infection beyond an initial upsurge. Moreover, Nrf2 decrease as a whole was found to be accompanied by active nuclear vacuity of Nrf2, resulting in lowered expression of stress-responsive Nrf2 target genes heme oxygenase-1 (HO-1), NAD(P)H quinone dehydrogenase 1, and superoxide dismutase 1 both in the presence and absence of Nrf2-driven transcriptional inducers. Initial induction of Nrf2 concurred with RV-induced early burst of oxidative stress and therefore was sensitive to treatments with antioxidants. Reduction of Nrf2 levels beyond initial hours, however, was found to be independent of the cellular redox status. Furthermore, increasing the half-life of Nrf2 through inhibition of the Kelch-like erythroid cell-derived protein with CNC homology- (ECH-) associated protein 1/Cullin3-RING Box1-based canonical Nrf2 turnover pathway could not restore Nrf2 levels post RV-SA11 infection. Depletion of the Nrf2/HO-1 axis was subsequently found to be sensitive to proteasome inhibition with concurrent observation of increased K48-linked ubiquitination associated with Nrf2. Together, the present study describes robust downregulation of Nrf2-dependent cellular redox defense beyond initial hours of RV infection, justifying our previous observation of potent antirotaviral implications of Nrf2 agonists.
真核细胞在受到包括病毒在内的外源应激源威胁时，会采用高度调节的应激反应生理机制来维持细胞内稳态。毫不奇怪，避免细胞应激反应途径是病毒诱导宿主必需重编程的一个重要方面，以引发有利于病毒持续存在的细胞环境。细胞对氧化和亲电应激的适应性反应通常由抗氧化防御系统来处理，该系统的核心是氧化还原反应敏感的转录因子红细胞衍生 2 相关因子 2（Nrf2）和 Nrf2 驱动的转录级联。许多病毒都报道了宿主氧化还原平衡和氧化还原应激敏感的 Nrf2 抗氧化防御的失调。在本研究中，我们旨在研究 Nrf2 为基础的宿主细胞氧化还原防御系统对轮状病毒（RV）感染的调节。有趣的是，我们发现 Nrf2 蛋白水平随着 RV 感染的进展而急剧下降，超过了最初的激增。此外，我们发现 Nrf2 的整体减少伴随着 Nrf2 的核空洞化活跃，导致应激反应 Nrf2 靶基因血红素加氧酶-1（HO-1）、NAD（P）H 醌脱氢酶 1 和超氧化物歧化酶 1 的表达降低，无论是在存在还是不存在 Nrf2 驱动的转录诱导剂的情况下。Nrf2 的初始诱导与 RV 诱导的早期氧化应激爆发一致，因此对抗氧化剂的处理敏感。然而，超过最初几个小时的 Nrf2 水平的降低被发现与细胞氧化还原状态无关。此外，通过抑制 Kelch-like 红细胞衍生蛋白与 CNC 同源性（ECH）相关蛋白 1/Cullin3-RING 盒 1 为基础的经典 Nrf2 周转率途径来增加 Nrf2 的半衰期，不能在 RV-SA11 感染后恢复 Nrf2 水平。随后发现 Nrf2/HO-1 轴的耗竭对蛋白酶体抑制敏感，同时观察到与 Nrf2 相关的 K48 连接泛素化增加。总之，本研究描述了 RV 感染后超过最初几个小时的 Nrf2 依赖性细胞氧化还原防御的稳健下调，这证明了我们之前关于 Nrf2 激动剂具有强大抗轮状病毒作用的观察结果。
