SPHINGOLIPIDS ARE POTENTIAL HEAT-STRESS SIGNALS IN SACCHAROMYCES

The ability of organisms to quickly respond to stresses requires the a ctivation of many intracellular signal transduction pathways. The sphi ngolipid intermediate ceramide is thought to be particularly important for activating and coordinating signaling pathways during mammalian s tress responses. Here we present the first evidence that ceramide and other sphingolipid intermediates are signaling molecules in the Saccha romyces cerevisiae heat stress response. Our data show a 2-3 fold tran sient increase in the concentration of C-18-dihydrosphingosine and C18 -phytosphingosine, more than a 100-fold transient increase in C-20-dih ydrosphingosine and C-20-phytosphingosine, and a more stable 2-fold in crease in ceramide containing C-18-phytosphingosine and a 5-fold incre ase in ceramide containing C-20-phytosphingosine following heat stress . Treatment of cells with dihydrosphingosine activates transcription o f the TPS2 gene encoding a subunit of trehalose synthase and causes tr ehalose, a known thermoprotectant, to accumulate. Dihydrosphingosine i nduces expression of a STRE-LacZ reporter gene, showing that the globa l stress response element, STRE, found in many yeast promoter sequence s can be activated by sphingolipid signals. The TPS2 promoter contains four STREs that may mediate dihydrosphingosine responsiveness. Using genetic and other approaches it should be possible to identify sphingo lipid signaling pathways in S. cerevisiae and quantify the importance of each during heat stress.