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Eukaryotic Cell doi:10.1128/EC.00146-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Protein Kinase C1 (PKC1) is essential for protection against both oxidative and nitrosative stress, cell integrity, and normal manifestation of virulence factors in the pathogenic fungus Cryptococcus neoformans

Edward A. Doisy Department of Biochemistry and Molecular Biology, Department of Pathology, Department of Microbiology and Immunology, Saint Louis University School of Medicine, 1100 S. Grand Boulevard, Saint Louis, MO 63104; and Department of Medicine, University of Massachusetts, 364 Plantation Street, Worcester, Massachusetts 01605

^* To whom correspondence should be addressed. Email: lodgejk{at}slu.edu.

	Abstract

Cell wall integrity is crucial for fungal growth, survival and pathogenesis. Responses to environmental stresses are mediated by the highly conserved Pkc1 protein and its downstream components. In this study, we demonstrate that both oxidative and nitrosative stress activate the PKC1 cell integrity pathway in wild type cells, as measured by phosphorylation of Mpk1, the terminal protein in the PKC1 phosphorylation cascade. Furthermore, deletion of PKC1 shows that this gene is essential for defense against both oxidative and nitrosative stress; however, other genes involved directly in the PKC1 pathway are dispensable for protection against these stresses. This suggests that Pkc1 may have multiple and alternative functions other than activating the MAP kinase cascade from a "top down" approach. Deletion of PKC1 also causes osmotic instability, temperature sensitivity, severe sensitivity to cell wall inhibiting agents, and alterations in capsule and melanin. Furthermore, the vital cell wall components chitin and its deacetylated form chitosan appear to be mislocalized in a pkc1 strain, although this mutant contains wild type levels of both of these polymers. These data indicate that loss of Pkc1 has pleiotropic effects because it is central to many functions either dependent or independent of PKC1 pathway activation. Notably, this is the first time that Pkc1 has been implicated in protection against nitrosative stress in any organism.