Sphingolipids Regulate the Yeast High-Osmolarity Glycerol Response Pathway

Abstract

The yeast high-osmolarity glycerol response (HOG) mitogen-activated protein (MAP) kinase pathway is activated in response to hyperosmotic stress via two independent osmosensing branches, the Sln1 branch and the Sho1 branch. While the mechanism by which the osmosensing machinery activates the downstream MAP kinase cascade has been well studied, the mechanism by which the machinery senses and responds to hyperosmotic stress remains to be clarified. Here we report that inhibition of the de novo sphingolipid synthesis pathway results in activation of the HOG pathway via both branches. Inhibition of ergosterol biosynthesis also induces activation of the HOG pathway. Sphingolipids and sterols are known to be tightly packed together in cell membranes to form partitioned domains called rafts. Raft-enriched detergent-resistant membranes (DRMs) contain both Sln1 and Sho1, and sphingolipid depletion and hyperosmotic stress have similar effects on the osmosensing machinery of the HOG pathway: dissociation of an Sln1-containing protein complex and elevated association of Sho1 with DRMs. These observations reveal the sphingolipid-mediated regulation of the osmosensing machinery of the HOG pathway.

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ACKNOWLEDGMENTS

We thank Takahito Wada for excellent technical assistance in the initial screening. We also thank Paul J. Cullen and Takehiko Yoko-o for valuable technical comments, Haruo Saito and Beverly Errede for plasmids, Yutaka Hoshikawa for an antibody, and all members of the Maeda laboratory for valuable support and discussions.

This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas (KAKENHI 21025008) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), a Grant-in-Aid for Challenging Exploratory Research (KAKENHI 23651233) from the Japan Society for the Promotion of Science (JSPS), grants from the Noda Institute for Scientific Research and the Salt Science Research Foundation (no. 11D2) (all to T.M.), and a Grant-in-Aid for JSPS Fellows (to T.T.). T.T. was the recipient of the Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists.