Response of Saccharomyces cerevisiae to the Stimulation of Lipopolysaccharide

Lipopolysaccharide, known as endotoxin, can stimulate potent host immune responses through the complex of Toll-like-receptor 4 and myeloid differentiation protein 2; but its influence on Saccharomyces cerevisiae, a model organism for studying eukaryotes, is not clear. In this study, we found that lipopolysaccharide-treated S. cerevisiae cells could be stained by methylene blue, but did not die. Transcriptional profiling of the lipopolysaccharide-treated S. cerevisiae cells showed that 5745 genes were modulated: 2491 genes up-regulated and 3254 genes down-regulated. Significantly regulated genes (460 up-regulated genes and 135 down-regulated genes) in lipopolysaccharide-treated S. cerevisiae cells were analyzed on Gene Ontology, and used to establish physical protein-protein interaction network and protein phosphorylation network. Based on these analyses, most of the regulated genes in lipopolysaccharide-treated S. cerevisiae cells were related to cell wall, membrane, peroxisome and mitochondrion. Further experiments demonstrated that lipopolysaccharide stimulation caused the exposure of phosphatidylserine and the increase of mitochondrial membrane potential in S. cerevisiae cells, but levels of intracellular reactive oxygen species and metacaspase activation were not increased. This study demonstrated that lipopolysaccharide stimulation causes significant changes in S. cerevisiae cells, and the results would contribute to understand the response of eukaryotic cells to lipopolysaccharide stimulation.脂多糖（Lipopolysaccharide，又称内毒素）可通过Toll样受体4（Toll-like receptor 4）与髓系分化蛋白2（myeloid differentiation protein 2）组成的复合物激发强效宿主免疫应答，但其对真核生物研究模式物种酿酒酵母（Saccharomyces cerevisiae）的影响尚不明确。本研究发现，经脂多糖处理的酿酒酵母细胞可被亚甲基蓝（methylene blue）染色，但并未死亡。对脂多糖处理后的酿酒酵母细胞开展转录谱分析，结果显示共有5745个基因发生表达调控：其中2491个基因上调，3254个基因下调。对脂多糖处理的酿酒酵母细胞中显著差异调控的基因（460个上调基因与135个下调基因）进行基因本体（Gene Ontology）分析，并以此构建物理蛋白质相互作用网络与蛋白质磷酸化网络。基于上述分析，脂多糖处理的酿酒酵母细胞中多数调控基因与细胞壁、细胞膜、过氧化物酶体及线粒体相关。进一步实验证实，脂多糖刺激可导致酿酒酵母细胞出现磷脂酰丝氨酸（phosphatidylserine）外翻以及线粒体膜电位升高，但细胞内活性氧（reactive oxygen species）水平与半胱天冬酶样蛋白酶（metacaspase）的激活程度均未增强。本研究表明，脂多糖刺激可引发酿酒酵母细胞发生显著变化，该结果可为理解真核细胞对脂多糖刺激的应答机制提供参考。