Studies on emetic activity and mechanism of staphylococcal enterotoxin A

葡萄球菌肠毒素（SEs）是由金黄色葡萄球菌产生的外毒性蛋白，可引起人类和其他物种的葡萄球菌性食物中毒和中毒性休克综合征。然而，ses介导的食物中毒（在摄入受污染的食物后约4-6小时内引起腹泻和呕吐）的发病机制尚不清楚。在本研究中，我们构建并表达了SEA突变体，并研究了这些突变体SEA的催吐和超抗原活性。此外，为了明确SEA是否会影响肠上皮细胞内细胞信号通路的变化，我们进行了SEA是否可以调节肠上皮细胞内细胞信号通路的实验。我们的研究结果首次证明了葡萄球菌肠毒素A （SEA）诱导人肠上皮细胞内钙（[Ca^<2+>]i）的增加，并且[Ca^<2+>]i从细胞内储存中释放出来。一氧化氮合酶（NOS）抑制剂N^ g -单甲基- l-精氨酸可明显抑制sea诱导的[Ca^<2+>]i的升高。肠上皮细胞在静息状态下表达内皮型NOS，在肿瘤坏死因子(TNF)-α刺激下表达诱导型NOS。TNF-α-预处理后的细胞[Ca^<2+>]i明显升高，NOS抑制剂也抑制了这一变化。上述结果提示SEA调节的[Ca^<2+>]i信号依赖于人肠上皮细胞NOS的表达。

Staphylococcal enterotoxins (SEs) are exotoxic proteins produced by Staphylococcus aureus that cause staphylococcal food poisoning and toxic shock syndrome in humans and other species. However, the pathogenesis of SEs-mediated food poisoning, which causes diarrhea and vomiting within about 4-6 h of ingesting contaminated food, is not clearly understood.In this study, we constructed and expressed mutants of SEA and investigated emetic and superantigenic activity of these mutant SEAs. Furthermore, to clarify whether SEA can affect any changes of cellular signalling pathways in intestinal epithelial cells, we performed experiments to see if SEA can modulate the intracellular signaling pathway in intestinal epithelial cells. Our results demonstrated for the first time that staphylococcal enterotoxin A (SEA) induces an increase in intracellular calcium ([Ca^<2+>]i) in human intestinal epithelial cells and the [Ca^<2+>]i is released from intracellular stores. SEA-induced increase of [Ca^<2+>]i was clearly inhibited by treatment with a nitric oxide synthase (NOS) inhibitor, N^G-monomethyl-L-arginine. Intestinal epithelial cells express endothelial NOS in resting cell condition, and express inducible NOS after stimulating with tumor necrosis factor (TNF)-α. TNF-α-pretreated cells showed a significant increase in [Ca^<2+>]i that was also inhibited by the NOS inhibitor. These results suggest that SEA modulated [Ca^<2+>]i signal is dependent on NOS expression in human intestinal epithelial cells.