T-2 toxin is a type A trichothecene mycotoxin produced by Fusarium species, which is stable and widely distributed, and threatens livestock production and human health for decades [1, 2]. Previous studies showed that T-2 toxin had a lot of toxic effects, such as inhibiting DNA and protein synthesis [3], inducing DNA damage and cell apoptosis [4], interfering with the metabolism of membrane phospholipids, and disrupting energy metabolism and gut microbiome [5, 6]. It was showed that oxidative stress was associated with several toxic effects of T-2 toxin [7]. However, the molecular mechanism of T-2 toxin induced oxidative stress is still unknown.
Oxidative stress arises from an imbalance between generation and elimination of reactive oxygen species (ROS), leading to the activation or inhibition of genes encoding defensive enzymes, transcription factors and structural proteins [8, 9]. ROS, including singlet oxygen (O2), superoxide radical (O−), hydrogen peroxide (H2O2) and hydroxyl radical (HO), have considered to be the second messenger independent of oxidative stress and serves as a signal of cell proliferation, necrosis and apoptosis [10]. Accumulation of ROS may induce cell oxidative injury, such as DNA damage, oxidation of proteins, and lipid peroxidation [11]. Previous studies showed that Poly (ADP-ribose) polymerase-1 (PARP-1), NADPH1 oxidase p22phox (CYBA), Myeloperoxidase (MPO) are involved in ROS production [12–14]. E.g., overexpression of PARP-1 caused ROS-induced damage which dependent on the over activation of glycolysis upstream pathways, while downregulation of PARP-1 limited oxidative stress induced injury [15, 16]. Besides the ROS production system, the cellular ROS levels are also dependent on the activity of antioxidant system. Numerous studies showed that glutathione system, heme system and superoxide scavenger system involved in enzymatic and transcriptional activity, which reduced the oxidative stress [17, 18]. Due to the activity of oxidants systems and antioxidant systems which control the production of ROS, cells maintain the oxidative homeostasis. However, it is unclear which ROS-related genes are involved in T-2 toxin-induced oxidative stress.
A series of antioxidant defense genes and cellular signaling pathways have been identified under oxidative stress. Among them, the nuclear factor erythroid 2-related factor 2 (Nrf2) is considered as a master regulator of antioxidant defense genes [19]. Nrf2 is a member of bZIP transcription factor family with a high sensitivity to oxidative stress, which regulates expression of an array of detoxifying and antioxidant defense genes [20, 21]. Under normal conditions, Nrf2 interacts with the cytosolic repressor protein Kelch-like ECH-associated protein 1 (Keap1) in the cytoplasm and maintains at low levels because of the ubiquitination and degradation [22]. While under oxidative stress conditions, Nrf2 dissociates from Keap1 and translocates into the nucleus to activate transcription of a variety of antioxidant and detoxification genes. The activated genes regulated by the Nrf2 pathway include numerous genes involved in general stress response (heme oxygenase and thioredoxin), protection from electrophiles (glutathione synthesis and superoxide dismutase), and xenobiotic disposition (glutathione-S-transferases and quinone reductases). It has been reported that Nrf2 can regulate the cellular levels of ROS to control the cellular processes, such as cell proliferation and differentiation [23]. However, the role of Nrf2 in the T-2 toxin-induced oxidative stress is still unknown.
ATF3 (activating transcription factor3) is a stress response gene which is induced during the cellular responses to many stress signals including adipokines, cytokines, hypoxia, mycotoxins and chemokines [24, 25]. The expression of ATF3 is transient and plays a pivotal role in regulating the expression of cell-cycle regulators and tumor suppressor, DNA repair and apoptotic genes [26]. Overwhelming evidence suggests that ATF3 plays prominent roles in controlling the cell cycle progression, inflammation, apoptosis, endoplasmic reticulum stress, oxidative stress, and diseases [27, 28]. Recent studies suggest that ATF3 is important in oxidative stress response. The overexpression of ATF3 leads to accumulation of depolarized mitochondria, loss of cell viability, and increased production of mitochondrial ROS [26]. It has been reported that ATF3 represses PINK1 mRNA synthesis to dysregulate mitochondrial homeostasis [29]. However, little reports are available about the role of ATF3 in the process of T-2 toxin-induced oxidative stress.
ATF3 and Nrf2 play pivotal function in oxidative stress response, but the roles of ATF3 and Nrf2 in T-2 toxin-induced oxidative stress remain unknown. In this study, we clarified the molecular mechanisms of T-2 toxin induced oxidative stress in MCF-7 cells. Our results indicated that the ATF3∆Zip2a/2b mediated downregulation of Nrf2 was critical in T-2 toxin-induced ROS accumulation, which provides a new insight into the toxicology of T-2 toxin.