title: MAPKKK-independent regulation of the Hog1 stress-activated protein kinase in Candida albicans.
abstract: The Hog1 stress-activated protein kinase regulates both stress responses and morphogenesis in Candida albicans and is essential for the virulence of this major human pathogen. Stress-induced Hog1 phosphorylation is regulated by the upstream MAPKK, Pbs2, which in turn is regulated by the MAPKKK, Ssk2. Here, we have investigated the role of phosphorylation of Hog1 and Pbs2 in Hog1-mediated processes in C. albicans. Mutation of the consensus regulatory phosphorylation sites of Hog1 (Thr-174/Tyr-176) and Pbs2 (Ser-355/Thr-359), to nonphosphorylatable residues, resulted in strains that phenocopied hog1Δ and pbs2Δ cells. Consistent with this, stress-induced phosphorylation of Hog1 was abolished in cells expressing nonphosphorylatable Pbs2 (Pbs2(AA)). However, mutation of the consensus sites of Pbs2 to phosphomimetic residues (Pbs2(DD)) failed to constitutively activate Hog1. Furthermore, Ssk2-independent stress-induced Hog1 activation was observed in Pbs2(DD) cells. Collectively, these data reveal a previously uncharacterized MAPKKK-independent mechanism of Hog1 activation in response to stress. Although Pbs2(DD) cells did not exhibit high basal levels of Hog1 phosphorylation, overexpression of an N-terminal truncated form of Ssk2 did result in constitutive Hog1 activation, which was further increased upon stress. Significantly, both Pbs2(AA) and Pbs2(DD) cells displayed impaired stress resistance and attenuated virulence in a mouse model of disease, whereas only Pbs2(AA) cells exhibited the morphological defects associated with loss of Hog1 function. This indicates that Hog1 mediates C. albicans virulence by conferring stress resistance rather than regulating morphogenesis.
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors: Jill
authors: J
authors: Cheetham
authors: Aberdeen Fungal Group, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom.
authors: Donna M
authors: DM
authors: MacCallum
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors: Kathryn S
authors: KS
authors: Doris
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors: Alessandra
authors: A
authors: da Silva Dantas
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors: Susan
authors: S
authors: Scorfield
authors: Aberdeen Fungal Group, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom.
authors: Frank
authors: F
authors: Odds
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors: Deborah A
authors: DA
authors: Smith
authors: Institute for Cell and Molecular Biosciences, Faculty of Medicine, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom. Electronic address: janet.quinn@ncl.ac.uk.
authors: Janet
authors: J
authors: Quinn
mesh_terms: D000483:Alleles; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002176:Candida albicans / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics*; D016296:Mutagenesis; D009154:Mutation; D009995:Osmosis; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D015398:Signal Transduction; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; C088589:HOG1 protein, S cerevisiae; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases