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MBC in Press, published online ahead of print September 5, 2007
Mol. Biol. Cell 10.1091/mbc.E07-06-0581

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Submitted on June 18, 2007
Revised on August 9, 2007
Accepted on August 27, 2007

A Single MAPKKK Regulates the Hog1 MAPK Pathway in the Pathogenic Fungus Candida albicans

Jill Cheetham,* Deborah A. Smith,* Alessandra da Silva Dantas, Kathryn S. Doris, Miranda J. Patterson, Catherine Reid Bruce, and Janet Quinn

Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom

Monitoring Editor: Thomas Fox

The Hog1 MAP kinase (MAPK) plays a central role in stress responses in the human pathogen Candida albicans. Here we have investigated the MAPKKK-dependent regulation of the pathway. In contrast to the Hog1 pathway in S. cerevisiae, which is regulated by three MAPKKKs (Ssk2, Ssk22 and Ste11), our results demonstrate that Hog1 in C. albicans is regulated by a single MAPKKK Ssk2. Deletion of SSK2 results in comparable stress and morphological phenotypes exhibited by hog1{Delta} cells, and Ssk2 is required for the stress-induced phosphorylation and nuclear accumulation of Hog1, and for Hog1-dependent gene expression. Furthermore, phenotypes associated with deletion of SSK2 can be circumvented by expression of a phosphomimetic mutant of the MAPKK Pbs2, indicating that Ssk2 regulates Hog1 via activation of Pbs2. In S. cerevisiae the Hog1 pathway is also regulated by the MAPKKK Ste11. However, we can find no connection between Ste11 and the regulation of Hog1 in C. albicans. Furthermore, expression of a chimeric Pbs2 protein containing the Ste11-dependent regulatory region of S. cerevisiae Pbs2, fails to stimulate Ste11-dependent stress-signaling in C. albicans. Collectively, our data show that Ssk2 is the sole MAPKKK to relay stress signals to Hog1 in C. albicans and that the MAPK signaling network in C. albicans has diverged significantly from the corresponding network in S. cerevisiae.

*These authors contributed equally to this work.

Address correspondence to: Janet Quinn (janet.quinn{at}ncl.ac.uk)




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[Abstract] [Full Text] [PDF]


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