Betz Christian, Zajonc Dirk, Moll Matthias, Schweizer Eckhart
Lehrstuhl für Biochemie and the Lehrstuhl für Anorganische und Allgemeine Chemie, Universität Erlangen-Nürnberg, Erlangen, Germany.
Eur J Biochem. 2002 Aug;269(16):4033-9. doi: 10.1046/j.1432-1033.2002.03096.x.
In Saccharomyces cerevisiae, toxic concentrations of Na+ orLi+ ions induce the expression of the cation-extrusion ATPase gene, ENA1. Several well-studied signal transduction pathways are known correlating high salinity to the transcriptional activation of ENA1. Nevertheless, information on the actual sensing mechanism initiating these pathways is limited. Here, we report that the ISC1-encoded phosphosphingolipid-specific phospholipase C appears to be involved in stimulation of ENA1 expression and, consequently, in mediating Na+ and Li+ tolerance in yeast. Deletion of ISC1 distinctly decreased cellular Na+ and Li+ tolerance as growth of the Deltaisc1::HIS5 mutant, DZY1, was severely impaired by 0.5 m NaCl or 0.01 m LiCl. In contrast,K+ tolerance and general osmostress regulation wereunaffected. Isc1Delta mutant growth with 0.9 m KCl and glycerol accumulation in the presence of 0.9 m NaCl or 1.5 m sorbitol were comparable to that of the wild-type. ENA1-lacZ reporter studies suggested that the increased salt sensitivity of the isc1Delta mutant is related to a significant reduction of Na+/Li+-stimulated ENA1 expression. Correspondingly, Ena1p-dependent extrusion of Na+/Li+ ions was less efficient in the isc1Delta mutant than in wild-type cells. Itis suggested that ISC1-dependent hydrolysis of an unidentified yeast inositol phosphosphingolipid represents an early event in one of the salt-induced signalling pathways of ENA1 transcriptional activation.
在酿酒酵母中，Na⁺或Li⁺离子的毒性浓度会诱导阳离子外排ATP酶基因ENA1的表达。已知有几种经过充分研究的信号转导途径将高盐度与ENA1的转录激活联系起来。然而，关于启动这些途径的实际传感机制的信息有限。在此，我们报告由ISC1编码的磷酸鞘脂特异性磷脂酶C似乎参与刺激ENA1的表达，并因此介导酵母对Na⁺和Li⁺的耐受性。ISC1的缺失明显降低了细胞对Na⁺和Li⁺的耐受性，因为Δisc1::HIS5突变体DZY1的生长受到0.5 M NaCl或0.01 M LiCl的严重损害。相比之下，对K⁺的耐受性和一般渗透胁迫调节不受影响。Isc1Δ突变体在0.9 M KCl条件下的生长以及在0.9 M NaCl或1.5 M山梨醇存在下的甘油积累与野生型相当。ENA1-lacZ报告基因研究表明，isc1Δ突变体对盐敏感性的增加与Na⁺/Li⁺刺激的ENA1表达的显著降低有关。相应地，在isc1Δ突变体中，Ena1p依赖性的Na⁺/Li⁺离子外排比野生型细胞效率更低。有人提出，ISC1依赖性水解一种未鉴定的酵母肌醇磷酸鞘脂是ENA1转录激活的盐诱导信号通路之一中的早期事件。
