FIGURE 6.

VPA up-regulates UPRE expression. A, schematic of sphingolipid synthesis. Serine is condensed with palmitoyl-CoA to form 3-ketodihydrosphingosine, which is reduced to dihydrosphigosine. Dihydrosphingosine is hydroxylated on C4 to produce phytosphingosine. Ceramide synthase catalyzes the linkage of very long chain fatty acids produced by fatty acid elongases to dihydrosphingosine and phytosphingosine to form ceramide (dihydroceramide or phytoceramide). Ceramide is used as a precursor for the synthesis of inositol containing complex sphingolipids. Inositol phosphorylceramide synthase catalyzes the first step of complex sphingolipid synthesis. Fumonisin is a ceramide synthase inhibitor, and aureobasidin inhibits inositol phosphorylcermide synthase. B, WT and rsb1Δ cells expressing a UPRE-lacZ plasmid were precultured in Ura-I+ medium and then grown in Ura-I− medium with or without 100 μm fumonisin or 0.5 μg/μl aureobasidin (B and C) or Ura-I+ medium (D). 0.6 mm VPA was added when indicated. LacZ activity is quantified as indicated. Data shown are mean ± S.D. (error bars) (n = 6) (*, p < 0.05; **, p < 0.01).