Phosphate and Succinate Use Different Mechanisms to Inhibit Sugar-induced Cell Death in Yeast

Abstract

Stationary-phase Saccharomyces cerevisiae cells transferred from spent rich media into water live for weeks, whereas the same cells die within hours if transferred into water with 2% glucose in a process called sugar-induced cell death (SICD). Our hypothesis is that SICD is due to a dysregulated Crabtree effect, which is the phenomenon whereby glucose transiently inhibits respiration and ATP synthesis. We found that stationary-phase cells in glucose/water consume 21 times more O 2 per cell than exponential-phase cells in rich media, and such excessive O 2 consumption causes reactive oxygen species to accumulate. We also found that inorganic phosphate and succinate protect against SICD but by different mechanisms. Phosphate protects by triggering the synthesis of Fru-1,6-P 2 , which inhibits respiration in isolated mitochondria. Succinate protects in wild-type cells but fails to protect in dic1⌬ cells. DIC1 codes for a mitochondrial inner membrane protein that exchanges cytosolic succinate for matrix phosphate. We propose that succinate depletes matrix phosphate, which in turn inhibits respiration and ATP synthesis. In sum, restoring the Crabtree effect, whether with phosphate or succinate, protects cells from SICD.Saccharomyces cerevisiae cells undergo glucose-induced inhibition of respiration and oxidative phosphorylation and a parallel up-regulation of both glycolysis and glucose uptake by a short-term mechanism called the "Crabtree effect" (1-5). The Crabtree effect is a reversible process, and the precise mechanism of this phenomenon is controversial (6 -8). In addition to the down-regulation of genes involved in respiration and oxidative phosphorylation by glucose (9, 10), the Crabtree effect may involve competition between mitochondrial respiratory enzymes and glycolytic enzymes for ADP and inorganic phosphate (11, 12), changes in the permeability of the outer mitochondrial membrane (8), and the accumulation of certain metabolic intermediates, especially Fru-1,6-P 2 (6).The possibility that Fru-1,6-P 2 mediates the Crabtree effect was shown in a recent study that used mitochondria isolated from Crabtree-positive and Crabtree-negative yeast (6).Notably, Fru-1,6-P 2 decreased the rate of O 2 consumption in mitochondria isolated from the Crabtree-positive yeast (S. cerevisiae), but not that in mitochondria isolated from the Crabtree-negative yeast (Candida utilis). Such a result indicates that Fru-1,6-P 2 mediates the Crabtree effect.Although glucose triggers the Crabtree effect when yeast cells are cultured in rich media, glucose in water is very toxic to cells, especially stationary-phase (G 0 ) cells. When stationaryphase cells are shifted into 2% glucose or fructose in water, the cells begin to bud but then rapidly lose viability within a few hours (13,14). The cells undergo an apoptotic death triggered by reactive oxygen species (ROS) 2 accumulation (15). ROS accumulation suggests that the respiratory pathway in mitochondria is turned on rather than repressed. The sugar-induced cell death (SICD) is indep...

Insulin-Like Growth Factor Binding Proteins: A Structural Perspective

“…In some circumstances IGFBPs-2, -3, -5, and -6 are able to localize to the nucleus and act in an IGF-independent manner to influence cell signaling and gene expression (Xu et al, 2004; Miyako et al, 2009; Azar et al, 2011; Lee et al, 2011). Nuclear localization sequences have been located in the C-domain of IGFBPs-3 and -5 within the basic region important for ALS and ECM binding (Schedlich et al, 1998; Figure 1, black underlined text), and within the corresponding region of IGFBP-6 (Iosef et al, 2008).…”

The Small Molecule Triclabendazole Decreases the Intracellular Level of Cyclic AMP and Increases Resistance to Stress in Saccharomyces cerevisiae

“…We recently screened the Prestwick and NIH chemical libraries to identify drugs that protect S. cerevisiae from a unique form of cell death called sugar-induced cell death [8]. Sugar-induced cell death occurs when stationary-phase yeast cells are transferred into water with 2% glucose and no other nutrients [9]; cells die because of reactive oxygen species accumulation [10].…”

Glucose Modulates Respiratory Complex I Activity in Response to Acute Mitochondrial Dysfunction

“…The latter describes the ability of rapidly proliferating cells to favor glycolysis, depending on substrate availability, despite normoxic conditions. Despite its discovery in the 1920s, the precise mechanisms involved in the Crabtree effect are multiple and still debated (5)(6)(7). The Warburg effect describes the regulation of mitochondrial respiration in response to hypoxia.…”