Sundaram Arunkumar, Grant Chris M
The University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK; Faculty of Dentistry, Universiti Sains Islam Malaysia, Kuala Lumpur 55100, Malaysia.
The University of Manchester, Faculty of Life Sciences, Manchester M13 9PT, UK.
Fungal Genet Biol. 2014 Jun;67:15-23. doi: 10.1016/j.fgb.2014.03.005. Epub 2014 Apr 1.
Eukaryotic cells typically respond to stress conditions by inhibiting global protein synthesis. The initiation phase is the main target of regulation and represents a key control point for eukaryotic gene expression. In Saccharomyces cerevisiae and mammalian cells this is achieved by phosphorylation of eukaryotic initiation factor 2 (eIF2α). We have examined how the fungal pathogen Candida albicans responds to oxidative stress conditions and show that oxidants including hydrogen peroxide, the heavy metal cadmium and the thiol oxidant diamide inhibit translation initiation. The inhibition in response to hydrogen peroxide and cadmium largely depends on phosphorylation of eIF2α since minimal inhibition is observed in a gcn2 mutant. In contrast, translation initiation is inhibited in a Gcn2-independent manner in response to diamide. Our data indicate that all three oxidants inhibit growth of C. albicans in a dose-dependent manner, however, loss of GCN2 does not improve growth in the presence of hydrogen peroxide or cadmium. Examination of translational activity indicates that these oxidants inhibit translation at a post-initiation phase which may account for the growth inhibition in a gcn2 mutant. As well as inhibiting global translation initiation, phosphorylation of eIF2α also enhances expression of the GCN4 mRNA in yeast via a well-known translational control mechanism. We show that C. albicans GCN4 is similarly induced in response to oxidative stress conditions and Gcn4 is specifically required for hydrogen peroxide tolerance. Thus, the response of C. albicans to oxidative stress is mediated by oxidant-specific regulation of translation initiation and we discuss our findings in comparison to other eukaryotes including the yeast S. cerevisiae.
真核细胞通常通过抑制整体蛋白质合成来应对应激条件。起始阶段是调控的主要靶点，是真核基因表达的关键控制点。在酿酒酵母和哺乳动物细胞中，这是通过真核起始因子2（eIF2α）的磷酸化来实现的。我们研究了真菌病原体白色念珠菌如何应对氧化应激条件，结果表明包括过氧化氢、重金属镉和硫醇氧化剂二酰胺在内的氧化剂会抑制翻译起始。对过氧化氢和镉的抑制作用很大程度上取决于eIF2α的磷酸化，因为在gcn2突变体中观察到的抑制作用最小。相比之下，对二酰胺的反应中，翻译起始以不依赖Gcn2的方式受到抑制。我们的数据表明，所有这三种氧化剂均以剂量依赖的方式抑制白色念珠菌的生长，然而，在过氧化氢或镉存在的情况下，GCN2的缺失并不会改善其生长。对翻译活性的检测表明，这些氧化剂在起始后阶段抑制翻译，这可能解释了gcn2突变体中的生长抑制现象。除了抑制整体翻译起始外，eIF2α的磷酸化还通过一种众所周知的翻译控制机制增强酵母中GCN4 mRNA的表达。我们表明，白色念珠菌的GCN4在氧化应激条件下也会被类似地诱导，并且Gcn4对于过氧化氢耐受性是特异性必需的。因此，白色念珠菌对氧化应激的反应是由翻译起始的氧化剂特异性调控介导的，我们将我们的发现与包括酿酒酵母在内的其他真核生物进行了比较讨论。
