Involvement of Yeast Sphingolipids in the Heat Stress Response of Saccharomyces cerevisiae

Abstract

A role for sphingolipids in the yeast heat stress response has been suggested by the isolation of suppressors of mutants lacking these lipids, which are unable to grow at elevated temperatures. The current study examines the possible role of sphingolipids in the heat adaptation of yeast cells as monitored by growth and viability studies. The suppressor of long chain base auxotrophy (SLC, strain 7R4) showed a heat-sensitive phenotype that was corrected by transformation with serine palmitoyltransferase. Thus, the deficiency in sphingolipids and not the suppressor mutation was the cause of the heat-sensitive phenotype of the SLC strain 7R4. The ability of sphingolipids to rescue the heatsensitive phenotype was examined, and two endogenous yeast sphingoid backbones, phytosphingosine and dihydrosphingosine, were found to be most potent in this effect. Next, the effect of heat stress on the levels of the three major classes of sphingolipids was determined. The inositol phosphoceramides showed no change over a 1.5-h time course. However, the four detected species of sphingoid bases increased after 15 min of heat stress from 1.4-to 10.8-fold. The largest increases were seen in two sphingoid bases, C 20 phytosphingosine and C 20 dihydrosphingosine, which increased 6.4-and 10.8-fold over baseline, respectively. At 60 min of heat stress two species of yeast ceramide increased by 9.2-and 10.6-fold over baseline. The increase seen in the ceramides was partially decreased by Fumonisin B1, a ceramide synthase inhibitor. Therefore, heat stress induces accumulation of sphingoid bases and of ceramides, probably through de novo synthesis. Taken together, these results demonstrate that sphingolipids are involved in the yeast heat stress adaptation.Saccharomyces cerevisiae has been shown to respond to a transfer of 25-37 or 39°C with the physiology defined as a heat stress response (1, 2), which appears to involve two phases. The initial phase of the response is the gaining of thermotolerance, and an increase in trehalose accumulation is proposed as a marker for this event (3). This is accompanied by the induction of heat shock proteins (4) and a G 1 arrest in cell cycle that lasts for a period of approximately 1 h (5). Once thermotolerance is gained, the second phase of the response occurs when the yeast begin to grow at the increased temperature. At this point, trehalose is degraded in an HSP70-dependent process (6), and the cells begin to cycle and resume growth. Therefore, the ability of yeast to grow under increased temperature provides for an overall assessment of the heat stress response. However, the mechanisms that mediate adaptation and growth under the heat-stressed state are not fully defined.The isolation of suppressors of mutants lacking sphingolipids in yeast (Table I) has suggested a possible role for sphingolipids in the heat stress response. The initial mutation is a Ura disruption knockout of the serine palmitoyltransferase (SPT) gene (LCB1) (7), which catalyzes the first step of sphingolipid biosynthesis (Fig. 1...

Stress signals for apoptosis: ceramide and c-Jun kinase

“…This e ect is stereospeci®c as an analog of the natural precursor for ceramide, dihydroceramide, fails to induce apoptosis. Recent work has also implicated a role for sphingolipids including ceramides in signaling the heat shock response in yeast (Dickson et al, 1997;Jenkins et al, 1997;Mandala et al, 1998;Wells et al, 1998). In this regard, mutants incapable of rapid synthesis of sphingolipids in response to heat (Figure 2) fail to develop the capacity to grow at elevated temperatures.…”

“…Further, ionizing radiation (Haimovitz-Friedman et al, 1994) and H 2 O 2 (Goldkorn et al, 1998) activate sphingomyelinases in isolated membranes. Perhaps most persuasive, heat induces ceramide synthase activation and ceramide generation in Saccharomyces cerevisiae which contain no cytokine receptors or caspases (Jenkins et al, 1997;Wells et al, 1998).…”

“…Data are representative of duplicate samples from at least three experiments. Reprinted from Jenkins et al (1997) with permission from the authors and the copyright holders, The American Society for Biochemistry and Molecular Biology also be rapidly activated through the 55 kD TNF receptor, perhaps via an adaptor protein termed FAN (factor associated with neutral SMase activation) (Adam-Klages et al, 1996). This event has not, however, been linked to induction of apoptosis.…”

Biochemistry, cell biology and molecular biology of lipids ofSaccharomyces cerevisiae

“…88,207,249,250 In contrast to mammals, it appears that the majority of S. cerevisiae sphingolipids are stable and are not turned over in haploid cells during vegetative growth. 290 Thus, the production of potential sphingolipid signalling molecules in S. cerevisiae, including DHS, PHS, DHS-1-P, PHS-1-P and ceramide, 61,107,290 are most likely derived from de novo synthesis, not from the turnover of preformed sphingolipids.…”

Sphingosine 1-phosphate as a therapeutic agent

“…[55][56][57] It has also been implicated in several other biological processes, including Ca 2+ homeostasis and allergic responses. Cross-linking of Fc⑀RI induces activation of SPHK and conversion of sphingosine to S1P, which mediates Ca 2+ mobilization from intracellular stores by an inositol trisphosphate-independent pathway, 26,28,54 whereas the Ca 2+ release-activated Ca 2+ current (I CRAC ) is a direct target of sphingosine.…”