Reduced ribosome biogenesis in response to environmental conditions is a key feature of cell adaptation to stress. For example, ribosomal genes are transcriptionally repressed when cells are exposed to tunicamycin, a protein glycosylation inhibitor that induces endoplasmic reticulum stress and blocks vesicular trafficking in the secretory pathway. Here, we describe a novel regulatory model, in which tunicamycin-mediated stress induces the accumulation of long-chain sphingoid bases and subsequent activation of Pkh1/2 signaling, which leads to decreased expression of ribosomal protein genes via the downstream effectors Pkc1 and Sch9. Target of rapamycin complex 1 (TORC1), an upstream activator of Sch9, is also required. This pathway links ribosome biogenesis to alterations in membrane lipid composition under tunicamycin-induced stress conditions. Our results suggest that sphingolipid/Pkh1/2-TORC1/Sch9 signaling is an important determinant for adaptation to tunicamycin-induced stress. Copyright © 2019 by the Genetics Society of America.
KEYWORDS: TORC1-Sch9, ribosome, sphingolipid-Pkh1/2, stress response