Shi Yuhui, Porter Katie, Parameswaran Narayanan, Bae Hee Kyong, Pestka James J
Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA.
Toxicol Sci. 2009 Jun;109(2):247-55. doi: 10.1093/toxsci/kfp060. Epub 2009 Mar 31.
The trichothecene mycotoxin deoxynivalenol (DON) induces systemic expression of the interleukin-6 (IL-6) and other proinflammatory cytokines in the mouse. The purpose of this study was to test the hypothesis that DON triggers an endoplasmic reticulum (ER) stress response in murine macrophages capable of driving IL-6 gene expression. DON at concentrations up 5000 ng/ml. was not cytotoxic to peritoneal cells. However, DON markedly decreased protein levels but not the mRNA levels of glucose-regulated protein (GRP) 78 (BiP), a chaperone known to mediate ER stress. Inhibitor studies suggested that DON-induced GRP78 degradation was cathepsin and calpain dependent but was proteosome-independent. RNAi-mediated knockdown of GRP78 resulted in increased IL-6 gene expression indicating a potential downregulatory role for this chaperone. GRP78 is critical to the regulation of the two transcription factors, X-box binding protein 1 (XBP1) and activating transcription factor 6 (ATF6), which bind to cAMP-response element (CRE) and drive expression of CRE-dependent genes such as IL-6. DON exposure was found to increase IRE1alpha protein, its modified products spliced XBP1 mRNA and XBP1 protein as well as ATF6. Knockdown of ATF6 but not XBP1 partially inhibited DON-induced IL-6 expression in the macrophages. Three other trichothecenes (satratoxin G, roridin, T-2 toxin) and the ribosome inhibitory protein ricin were also found to induce GRP78 degradation suggesting that other translation inhibitors might evoke ER stress. Taken together, these data suggest that in the macrophage DON induces GRP78 degradation and evokes an ER stress response that could contribute, in part, to DON-induced IL-6 gene expression.
单端孢霉烯族霉菌毒素脱氧雪腐镰刀菌烯醇（DON）可诱导小鼠体内白细胞介素-6（IL-6）及其他促炎细胞因子的全身表达。本研究的目的是验证以下假说：DON在鼠巨噬细胞中引发内质网（ER）应激反应，进而驱动IL-6基因表达。浓度高达5000 ng/ml的DON对腹腔细胞无细胞毒性。然而，DON显著降低了葡萄糖调节蛋白（GRP）78（BiP）的蛋白质水平，但未降低其mRNA水平，GRP78是一种已知介导ER应激的伴侣蛋白。抑制剂研究表明，DON诱导的GRP78降解依赖组织蛋白酶和钙蛋白酶，但不依赖蛋白酶体。RNA干扰介导的GRP78敲低导致IL-6基因表达增加，表明该伴侣蛋白具有潜在的下调作用。GRP78对于两种转录因子X盒结合蛋白1（XBP1）和活化转录因子6（ATF6）的调节至关重要，这两种转录因子可结合环磷酸腺苷反应元件（CRE）并驱动诸如IL-6等CRE依赖性基因的表达。研究发现，暴露于DON会增加肌醇需求酶1α（IRE1α）蛋白、其修饰产物剪接XBP1 mRNA和XBP1蛋白以及ATF6。敲低ATF6而非XBP1可部分抑制巨噬细胞中DON诱导的IL-6表达。还发现其他三种单端孢霉烯族毒素（蛇形毒素G、roridin、T-2毒素）和核糖体抑制蛋白蓖麻毒素也可诱导GRP78降解，这表明其他翻译抑制剂可能引发ER应激。综上所述，这些数据表明，在巨噬细胞中，DON诱导GRP78降解并引发ER应激反应，这可能部分促成了DON诱导的IL-6基因表达。
