Characterization of a Candida albicans Mutant Defective in All MAPKs Highlights the Major Role of Hog1 in the MAPK Signaling Network.

Inês Correia,Bernhard Hube,Jesús Pla,Duncan Wilson

doi:10.3390/jof6040230

Abstract

The success of Candida albicans as a pathogen relies on its ability to adapt and proliferate in different environmental niches. Pathways regulated by mitogen-activated protein kinases (MAPKs) are involved in sensing environmental conditions and developing an accurate adaptive response. Given the frequent cooperative roles of these routes in cellular functions, we have generated mutants defective in all combinations of the four described MAPKs in C. albicans and characterized its phenotype regarding sensitiveness to specific drugs, morphogenesis and interaction with host immune cells. We demonstrate that all MAPKs are dispensable in this yeast as a mutant defective in Cek1, Cek2, Mkc1 and Hog1 is viable although highly sensitive to oxidative and osmotic stress, displaying a specific pattern of sensitivity to antifungals. By comparing its phenotype with single, double and triple combinations of MAPK-deletion mutants we were able to unveil a Cek1-independent mechanism for Hog1 resistance to Congo red, and confirm the predominant effect of Hog1 on oxidative and osmotic adaptation. The quadruple mutant produces filaments under non-inducing conditions, but is unable to develop chlamydospores. Furthermore, cek1 cek2 mkc1 hog1 cells switch to the opaque state at high frequency, which is blocked by the ectopic expression of HOG1 suggesting a role of this kinase for phenotypic switching.

Highlights

Candida albicans is a pathogenic fungus frequently causing infection in humans
None of the mutants with an intact HOG pathway were found to be sensitive to NaCl or Sorbitol (Figure 1A) reinforcing the idea that Hog1 is the key kinase for adaptation to osmotic stress; the sensitivity of the cek1 cek2 mkc1 hog1 mutant to NaCl was completely rescued to wild-type levels by integration of a plasmid carrying HOG1
mitogen-activated protein kinases (MAPKs) of C. albicans, to further advance our understanding about the complex crosstalk among these pathways [33,34,35,55]. These mutants allowed us to answer two main questions: Can C. albicans survive without a functional MAPK network? Does C. albicans depend on a specific MAPK to respond and adapt to stress conditions and, if so, to what extent? We show here that cek1 cek2 mkc1 hog1 cells are viable and show no evident growth defects under standard laboratory in vitro conditions, they are highly sensitive to stress

Summary

Introduction

Candida albicans is a pathogenic fungus frequently causing infection in humans. 70% of the human population is colonized by this microorganism in the vaginal and gastrointestinal tract without any symptoms. When the host immune system is compromised, when the microbiota is disturbed or when the epithelial barrier integrity is damaged, C. albicans may proliferate inside or outside these niches and can, in severe cases, develop invasive infections that are associated with a high mortality rate [1,2,3]. J. Fungi 2020, 6, 230; doi:10.3390/jof6040230 www.mdpi.com/journal/jof. CAF2 (wt) ura3∆::imm434/ura3∆::imm434-URA3 [39] CAI4. [CAI4] cek1∆::hisG-URA3-hisG/cek1∆::hisG [41] cek

Methods

Results

Conclusion