Cáp Michal, Váchová Libuse, Palková Zdena
Department of Genetics and Microbiology, Faculty of Sciences, Charles University in Prague, Vinicná 5, 128 44 Prague 2, Czech Republic.
J Biol Chem. 2009 Nov 20;284(47):32572-81. doi: 10.1074/jbc.M109.022871. Epub 2009 Sep 28.
Enzymes scavenging reactive oxygen species (ROS) are important for cell protection during stress and aging. A deficiency in these enzymes leads to ROS imbalance, causing various disorders in many organisms, including yeast. In contrast to liquid cultures, where fitness of the yeast population depends on its ROS scavenging capability, the present study suggests that Saccharomyces cerevisiae cells growing in colonies capable of ammonia signaling use a broader protective strategy. Instead of maintaining high levels of antioxidant enzymes for ROS detoxification, colonies activate an alternative metabolism that prevents ROS production. Colonies of the strain deficient in cytosolic superoxide dismutase Sod1p thus developed the same way as wild type colonies. They produced comparable levels of ammonia and underwent similar developmental changes (expression of genes of alternative metabolism and center margin differentiation in ROS production, cell death occurrence, and activities of stress defense enzymes) and did not accumulate stress-resistant suppressants. An absence of cytosolic catalase Ctt1p, however, brought colonies developmental problems, which were even more prominent in the absence of mitochondrial Sod2p. sod2Delta and ctt1Delta colonies failed in ammonia production and sufficient activation of the alternative metabolism and were incapable of center margin differentiation, but they did not increase ROS levels. These new data indicate that colony disorders are not accompanied by ROS burst but could be a consequence of metabolic defects, which, however, could be elicited by imbalance in ROS produced in early developmental phases. Sod2p and homeostasis of ROS may participate in regulatory events leading to ammonia signaling.
清除活性氧（ROS）的酶对于细胞在应激和衰老过程中的保护作用至关重要。这些酶的缺乏会导致ROS失衡，在包括酵母在内的许多生物体中引发各种紊乱。与液体培养不同，在液体培养中酵母群体的适应性取决于其ROS清除能力，本研究表明，在能够进行氨信号传导的菌落中生长的酿酒酵母细胞采用了更广泛的保护策略。菌落不是维持高水平的抗氧化酶来解毒ROS，而是激活一种替代代谢来防止ROS产生。因此，缺乏胞质超氧化物歧化酶Sod1p的菌株的菌落与野生型菌落的发育方式相同。它们产生的氨水平相当，经历了类似的发育变化（替代代谢基因的表达以及ROS产生、细胞死亡发生和应激防御酶活性方面的中心边缘分化），并且没有积累抗应激抑制剂。然而，缺乏胞质过氧化氢酶Ctt1p会给菌落带来发育问题，在缺乏线粒体Sod2p的情况下这些问题更加突出。sod2Delta和ctt1Delta菌落无法产生氨，也无法充分激活替代代谢，并且无法进行中心边缘分化，但它们并没有增加ROS水平。这些新数据表明，菌落紊乱并非伴随着ROS爆发，而是可能由代谢缺陷导致，然而，代谢缺陷可能是由早期发育阶段产生的ROS失衡引发的。Sod2p和ROS的稳态可能参与导致氨信号传导的调节事件。
