Stress-induced nuclear accumulation is dispensable for Hog1-dependent gene expression and virulence in a fungal pathogen

Alison M Day,Janet Quinn,Donna M Maccallum,Alistair J P Brown,Carmen M Herrero-De-Dios

doi:10.1038/s41598-017-14756-4

Alison M Day, Janet Quinn + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-14756-4

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Journal: Scientific Reports	Publication Date: Oct 30, 2017
Citations: 11	License type: open-access

Affiliation: Newcastle University, University of Aberdeen

Abstract

Stress-activated protein kinase (SAPK) pathways are evolutionarily conserved eukaryotic signalling modules that are essential for the virulence of human pathogenic fungi. The Hog1 SAPK in Candida albicans is robustly phosphorylated in response to a number of host-imposed stresses, and is essential for virulence. The current dogma is that stress-induced phosphorylation activates the SAPK, and promotes its nuclear accumulation that is necessary for the expression of SAPK-dependent stress-protective genes. Here we challenge this dogma. C. albicans strains were constructed in which Hog1 was either tethered to the plasma membrane or constitutively nuclear. Strikingly, tethering Hog1 to the plasma membrane did not abrogate stress resistance or stress-induced gene expression. Furthermore, preventing the nuclear accumulation of Hog1 had no impact on C. albicans virulence in two distinct models of systemic infection. However, tethering Hog1 to the plasma membrane did impact on signal fidelity, and on the magnitude and kinetics of the stress-induced phosphorylation of this SAPK. Taken together, these findings challenge the dogma that nuclear accumulation of SAPKs is a pre-requisite for SAPK-dependent gene expression, and reveal that stress-induced nuclear accumulation of Hog1 is dispensable for the virulence of a major human fungal pathogen.

Highlights

Stress activated protein kinases (SAPKs) are members of the MAPK family that are activated by phosphorylation of conserved threonine and tyrosine residues within a TXY motif[1]
The same strategy has been used to prevent the nuclear accumulation of MAPKs in the model yeasts S. cerevisiae and Schizosaccharomyces pombe[9,27,28]
To drive Hog[1] nuclear accumulation, the SV40 nuclear localisation sequence was added to the C-terminus of Hog1-GFP (Hog1-GFP-NLS), a strategy that has been employed previously in S. cerevisiae[29]

Summary

Introduction

Stress activated protein kinases (SAPKs) are members of the MAPK family that are activated by phosphorylation of conserved threonine and tyrosine residues within a TXY motif[1]. Mutagenesis studies revealed that phosphorylation of the Hog[1] TXY motif is essential for the stress-induced nuclear accumulation of the SAPK3, and that a basal level of Hog[1] activity is necessary to maintain signal fidelity and to restrict cross-talk to other MAPK pathways[4]. Cells in which Hog[1] was artificially anchored to the plasma membrane displayed wild-type levels of osmotic stress resistance despite the fact that Hog1-dependent gene expression was abolished[9]. This striking result indicated that Hog[1] rapidly accumulates in the nucleus to induce the expression of stress-protective genes, it is the regulation of cytosolic proteins that is important for stress resistance. Our exploration of the impact of this on the multifaceted processes regulated by C. albicans Hog[1] challenges current dogma about the mode of action of this SAPK

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