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Molecular and Cellular Biology, January 2004, p. 46-57, Vol. 24, No. 1
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.1.46-57.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Aberrant Processing of the WSC Family and Mid2p Cell Surface Sensors Results in Cell Death of Saccharomyces cerevisiae O-Mannosylation Mutants

Mark Lommel,1 Michel Bagnat,2 and Sabine Strahl1*

Institute of Cell Biology and Plant Physiology, University of Regensburg, 93040 Regensburg,1 Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany2

Received 4 June 2003/ Returned for modification 28 July 2003/ Accepted 25 September 2003

Protein O mannosylation is a crucial protein modification in uni- and multicellular eukaryotes. In humans, a lack of O-mannosyl glycans causes congenital muscular dystrophies that are associated with brain abnormalities. In yeast, protein O mannosylation is vital; however, it is not known why impaired O mannosylation results in cell death. To address this question, we analyzed the conditionally lethal Saccharomyces cerevisiae protein O-mannosyltransferase pmt2 pmt4{Delta} mutant. We found that pmt2 pmt4{Delta} cells lyse as small-budded cells in the absence of osmotic stabilization and that treatment with mating pheromone causes pheromone-induced cell death. These phenotypes are partially suppressed by overexpression of upstream elements of the protein kinase C (PKC1) cell integrity pathway, suggesting that the PKC1 pathway is defective in pmt2 pmt4{Delta} mutants. Congruently, induction of Mpk1p/Slt2p tyrosine phosphorylation does not occur in pmt2 pmt4{Delta} mutants during exposure to mating pheromone or elevated temperature. Detailed analyses of the plasma membrane sensors of the PKC1 pathway revealed that Wsc1p, Wsc2p, and Mid2p are aberrantly processed in pmt mutants. Our data suggest that in yeast, O mannosylation increases the activity of Wsc1p, Wsc2p, and Mid2p by enhancing their stability. Reduced O mannosylation leads to incorrect proteolytic processing of these proteins, which in turn results in impaired activation of the PKC1 pathway and finally causes cell death in the absence of osmotic stabilization.

* Corresponding author. Mailing address: Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, 93040 Regensburg, Germany. Phone: 49-(0)941-943-3024. Fax: 49-(0)941-943-3352. E-mail: sabine.strahl{at}biologie.uni-regensburg.de.

Molecular and Cellular Biology, January 2004, p. 46-57, Vol. 24, No. 1
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.1.46-57.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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