Stress-Activated Degradation of Sphingolipids Regulates Mitochondrial Function and Cell Death in Yeast

Figure 7

Stress regulation of the sphingolipid degradation pathway via Hog1p and its impact on mitochondrial integrity. (a) Schematic overview of the enzymatic conversions implied in sphingolipid biosynthesis and degradation in yeast. (b) Expression of sphingolipid degradation enzymes is stimulated upon salt stress in a Hog1p-dependent manner. RT-PCR analysis of gene expression in the indicated yeast strains upon salt shock (0.4 M NaCl, 20 min). Relative mRNA levels of the indicated genes were normalized for the ACT1 control. (c) Expression of sphingolipid biosynthesis enzymes is generally repressed upon salt stress. Yeast wild-type cells were analyzed by RT-PCR as in (b). In (b, c), data are presented as mean ± SD. Three biological replicates were analyzed. Significant changes with respect to the wild type (b) or to the nonstress condition (c) are marked. ; (Student’s t-test). (d) Loss of Hog1p function causes hexadecenal sensitivity. Growth inhibition of the indicated yeast strains by hexadecenal was assessed as in Figure 3(a). (e) Salt stress induces mitochondrial fragmentation in hfd1Δ mutant cells. Yeast cells expressing mt-GFP on synthetic glucose medium were treated or not with 1 M NaCl before visualization of mitochondria. (f) Loss of Hog1p function counteracts Bax inhibition. Human Bax expression was induced for 24 h as in Figure 5(b) in wild type and hog1Δ mutants. Growth was then recorded on YPD agar plates.

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