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Vol. 13, Issue 8, 2869-2880, August 2002

The MEK Kinase Ssk2p Promotes Actin Cytoskeleton Recovery After Osmotic Stress

Tatiana Yuzyuk, Marissa Foehr,^* and David C. Amberg

Department of Biochemistry and Molecular Biology, State University of New York (SUNY) Upstate Medical University, Syracuse, NY, 13210, and  ^*Wadsworth Center, New York State Department and Department of Biological Sciences, School of Public Health, SUNY, Albany, NY, 12208

Saccharomyces cerevisiae adapts to osmotic stress through the activation of a conserved high-osmolarity growth (HOG) mitogen-activated protein (MAP) kinase pathway. Transmission through the HOG pathway is very well understood, yet other aspects of the cellular response to osmotic stress remain poorly understood, most notably regulation of actin organization. The actin cytoskeleton rapidly disassembles in response to osmotic insult and is induced to reassemble only after osmotic balance with the environment is reestablished. Here, we show that one of three MEK kinases of the HOG pathway, Ssk2p, is specialized to facilitate actin cytoskeleton reassembly after osmotic stress. Within minutes of cells' experiencing osmotic stress or catastrophic disassembly of the actin cytoskeleton through latrunculin A treatment, Ssk2p concentrates in the neck of budding yeast cells and concurrently forms a 1:1 complex with actin. These observations suggest that Ssk2p has a novel, previously undescribed function in sensing damage to the actin cytoskeleton. We also describe a second function for Ssk2p in facilitating reassembly of a polarized actin cytoskeleton at the end of the cell cycle, a prerequisite for efficient cell cycle completion. Loss of Ssk2p, its kinase activity, or its ability to localize and interact with actin led to delays in actin recovery and a resulting delay in cell cycle completion. These unique capabilities of Ssk2p are activated by a novel mechanism that does not involve known components of the HOG pathway.

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Corresponding author. E-mail address: ambergd{at}mail.upstate.edu.

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Molecular Biology of the Cell
Vol. 13, 2869-2880, August 2002
Copyright © 2002 by The American Society for Cell Biology

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