Sphingolipids mediate formation of mRNA processing bodies during the heat-stress response of Saccharomyces cerevisiae.

Recent work, especially in the yeast Saccharomyces cerevisiae, has demonstrated that mRNA movement from active translation to cytoplasmic granules, termed mRNA'p-bodies' (processing bodies), occurs in concert with the regulation of translation during cell stress. However, the signals regulating p-body formation are poorly defined. Recent results have demonstrated a function for sphingolipids in regulating translation during heat stress, which led to the current hypothesis that p-bodies may form during heat stress in a sphingolipid-dependent manner. In the present study, we demonstrate that mild-heat-stress-induced formation of p-bodies, as determined by localization of a GFP (green fluorescent protein)-tagged Dcp2p and RFP (red fluorescent protein)-tagged Edc3p to discrete cytoplasmic foci. Sphingoid base synthesis was required for this effect, as inhibition of sphingoid base synthesis attenuated formation of these foci during heat stress. Moreover, treatment of yeast with the exogenous sphingoid bases phyto- and dihydro-sphingosine promoted formation of p-bodies in the absence of heat stress, and the lcb4/lcb5 double-deletion yeast, which accumulates high intracellular levels of sphingoid bases, had large clearly defined p-bodies under non-stress conditions. Functionally, inhibition of sphingolipid synthesis during heat stress did not prevent translation stalling, but extended translation arrest, indicating that sphingolipids mediate translation initiation. These results are consistent with the notion that p-bodies serve not only in mRNA degradation, but also for re-routing transcripts back to active translation, and that sphingolipids play a role in this facet of the heat-stress response. Together, these results demonstrate a critical and novel role for sphingolipids in mediating p-body formation during heat stress.