INVOLVEMENT OF YEAST SPHINGOLIPIDS IN THE HEAT-STRESS RESPONSE OF SACCHAROMYCES-CEREVISIAE

A role for sphingolipids in the yeast heat stress response has been su ggested by the isolation of suppressors of mutants lacking these lipid s, which are unable to grow at elevated temperatures. The current stud y examines the possible role of sphingolipids in the heat adaptation o f yeast cells as monitored by growth and viability studies. The suppre ssor of long chain base auxotrophy (SLC, strain 7R4) showed a heat-sen sitive phenotype that was corrected by transformation with serine palm itoyltransferase. Thus, the deficiency in sphingolipids and not the su ppressor mutation was the cause of the heat-sensitive phenotype of the SLC strain 7R4. The ability of sphingolipids to rescue the heat-sensi tive phenotype was examined, and two endogenous yeast sphingoid backbo nes, phytosphingosine and dihydrosphingosine, were found to be most po tent 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, t he 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 dihydrosphingosin e, 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 pa rtially decreased by Fumonisin B1, a ceramide synthase inhibitor. Ther efore, heat stress induces accumulation of sphingoid bases and of cera mides, probably through de novo synthesis, Taken together, these resul ts demonstrate that sphingolipids are involved in the yeast heat stres s adaptation.