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Eukaryotic Cell, August 2008, p. 1309-1317, Vol. 7, No. 8
1535-9778/08/$08.00+0     doi:10.1128/EC.00038-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Mitogen-Activated Protein Kinase Hog1 Mediates Adaptation to G₁ Checkpoint Arrest during Arsenite and Hyperosmotic Stress

Iwona Migdal,^1, Yulia Ilina,^2, Markus J. Tamás,² and Robert Wysocki^1*

Institute of Genetics and Microbiology, University of Wroclaw, 51-148 Wroclaw, Poland,¹ Department of Cell and Molecular Biology/Microbiology, University of Gothenburg, S-405 30 Gothenburg, Sweden²

Received 1 February 2008/ Accepted 9 June 2008

Cells slow down cell cycle progression in order to adapt to unfavorable stress conditions. Yeast (Saccharomyces cerevisiae) responds to osmotic stress by triggering G₁ and G₂ checkpoint delays that are dependent on the mitogen-activated protein kinase (MAPK) Hog1. The high-osmolarity glycerol (HOG) pathway is also activated by arsenite, and the hog1 mutant is highly sensitive to arsenite, partly due to increased arsenite influx into hog1 cells. Yeast cell cycle regulation in response to arsenite and the role of Hog1 in this process have not yet been analyzed. Here, we found that long-term exposure to arsenite led to transient G₁ and G₂ delays in wild-type cells, whereas cells that lack the HOG1 gene or are defective in Hog1 kinase activity displayed persistent G₁ cell cycle arrest. Elevated levels of intracellular arsenite and "cross talk" between the HOG and pheromone response pathways, observed in arsenite-treated hog1 cells, prolonged the G₁ delay but did not cause a persistent G₁ arrest. In contrast, deletion of the SIC1 gene encoding a cyclin-dependent kinase inhibitor fully suppressed the observed block of G₁ exit in hog1 cells. Moreover, the Sic1 protein was stabilized in arsenite-treated hog1 cells. Interestingly, Sic1-dependent persistent G₁ arrest was also observed in hog1 cells during hyperosmotic stress. Taken together, our data point to an important role of the Hog1 kinase in adaptation to stress-induced G₁ cell cycle arrest.

Published ahead of print on 13 June 2008.

These authors contributed equally to this work.