Studies on emetic activity and mechanism of staphylococcal enterotoxin A

金黄色葡萄球菌肠毒素(SES)是由金黄色葡萄球菌产生的一种外毒素蛋白，可引起葡萄球菌食物中毒和中毒性休克综合征。然而，SES介导的食物中毒的发病机制尚不清楚，即在摄入受污染的食物后约4-6小时内引起腹泻和呕吐。在本研究中，我们构建并表达了SEA突变体，并对这些突变体的呕吐和超抗原活性进行了研究。此外，为了阐明SEA是否可以影响肠上皮细胞内信号通路的变化，我们进行了实验，以了解SEA是否可以调节肠上皮细胞内的信号通路。我们的结果首次证明葡萄球菌肠毒素A(SEA)可诱导人肠上皮细胞内钙离子([Ca^&lt；2&gt；]i)增加，并使细胞内钙离子从细胞内储存库中释放。一氧化氮合酶抑制剂N^G-单甲基-L-精氨酸可明显抑制SEA引起的[Ca~(2+)]i升高。肠上皮细胞在静息状态下表达内皮型一氧化氮合酶，在肿瘤坏死因子-α刺激后表达诱导型一氧化氮合酶。经肿瘤坏死因子-一氧化氮合酶处理后，细胞内[Ca~(2+)]i显著升高，且可被α抑制剂抑制。这些结果表明，SEA对人肠上皮细胞[Ca^&lt；2&gt；]i信号的调节依赖于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.