Putative Membrane Receptors Contribute to Activation and Efficient Signaling of Mitogen-Activated Protein Kinase Cascades during Adaptation of Aspergillus fumigatus to Different Stressors and Carbon Sources.

Lilian Pereira Silva,Alastair B Fleming,Leandro José De Assis,Ozgur Bayram,Gustavo Henrique Goldman,Ciara Tierney,Dean Frawley,Aaron P Mitchell

doi:10.1128/msphere.00818-20

Lilian Pereira Silva, Alastair B Fleming + Show 6 more

Open Access

https://doi.org/10.1128/msphere.00818-20

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Abstract

The high-osmolarity glycerol (HOG) response pathway is a multifunctional signal transduction pathway that specifically transmits ambient osmotic signals. Saccharomyces cerevisiae Hog1p has two upstream signaling branches, the sensor histidine kinase Sln1p and the receptor Sho1p. The Sho1p branch includes two other proteins, the Msb2p mucin and Opy2p. Aspergillus fumigatus is the leading cause of pulmonary fungal diseases. Here, we investigated the roles played by A. fumigatus SlnASln1p, ShoASho1p, MsbAMsb2p, and OpyAOpy2p putative homologues during the activation of the mitogen-activated protein kinase (MAPK) HOG pathway. The shoA, msbA, and opyA singly and doubly null mutants are important for the cell wall integrity (CWI) pathway, oxidative stress, and virulence as assessed by a Galleria mellonella model. Genetic interactions of ShoA, MsbA, and OpyA are also important for proper activation of the SakAHog1p and MpkASlt2 cascade and the response to osmotic and cell wall stresses. Comparative label-free quantitative proteomics analysis of the singly null mutants with the wild-type strain upon caspofungin exposure indicates that the absence of ShoA, MsbA, and OpyA affects the osmotic stress response, carbohydrate metabolism, and protein degradation. The putative receptor mutants showed altered trehalose and glycogen accumulation, suggesting a role for ShoA, MsbA, and OpyA in sugar storage. Protein kinase A activity was also decreased in these mutants. We also observed genetic interactions between SlnA, ShoA, MsbA, and OpyA, suggesting that both branches are important for activation of the HOG/CWI pathways. Our results help in the understanding of the activation and modulation of the HOG and CWI pathways in this important fungal pathogen.IMPORTANCEAspergillus fumigatus is an important human-pathogenic fungal species that is responsible for a high incidence of infections in immunocompromised individuals. A. fumigatus high-osmolarity glycerol (HOG) and cell wall integrity pathways are important for the adaptation to different forms of environmental adversity such as osmotic and oxidative stresses, nutrient limitations, high temperatures, and other chemical and mechanical stresses that may be produced by the host immune system and antifungal drugs. Little is known about how these pathways are activated in this fungal pathogen. Here, we characterize four A. fumigatus putative homologues that are important for the activation of the yeast HOG pathway. A. fumigatus SlnASln1p, ShoASho1p, MsbAMsb2p, and OpyAOpy2p are genetically interacting and are essential for the activation of the HOG and cell wall integrity pathways. Our results contribute to the understanding of A. fumigatus adaptation to the host environment.

Highlights

IMPORTANCE Aspergillus fumigatus is an important human-pathogenic fungal species that is responsible for a high incidence of infections in immunocompromised individuals
The mitogen-activated protein kinase (MAPK) cascades consist of three kinases, MAPK, MAPK kinase (MAPKK), and MAPKK kinase (MAPKKK), which are highly conserved in fungi [6,7,8]
The ΔtcsBslnA/sln1p mutant was partially sensitive to SDS, and Western blot analysis of both the corresponding wildtype strain and the ΔtcsBslnA/sln1p mutant showed that when stressed with hydrogen peroxide, phosphorylation of Hog1p still occurred in the mutant [22]

Summary

Introduction

IMPORTANCE Aspergillus fumigatus is an important human-pathogenic fungal species that is responsible for a high incidence of infections in immunocompromised individuals. A. fumigatus high-osmolarity glycerol (HOG) and cell wall integrity pathways are important for the adaptation to different forms of environmental adversity such as osmotic and oxidative stresses, nutrient limitations, high temperatures, and other chemical and mechanical stresses that may be produced by the host immune system and antifungal drugs. We characterize four A. fumigatus putative homologues that are important for the activation of the yeast HOG pathway. A. fumigatus is able to adapt to different forms of environmental adversity such as osmotic and oxidative stresses, nutrient limitations, high temperatures, and other chemical and mechanical stresses, some of which may be produced by the host immune system and antifungal drugs [4]. The HOG pathway is activated by mitogen-activated protein kinases (MAPKs) during adaptation to environmental stress and morphology regulation [5]. The A. fumigatus Msb2p mucin homologue, MsbA, has been shown to be important for fungal develmsphere.asm.org 2

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