Filament Negative Regulator CDC4 Suppresses Glycogen Phosphorylase Encoded GPH1 That Impacts the Cell Wall-Associated Features in Candida albicans.

Wei-Chung Lai,Ting-Hui Lin,Po-Szu Hsieh,Hsiao-Chi Hsu,Jia-Ching Shieh,Wan Chen Li,Shao-Hung Wang,Chun-Wen Cheng,Tzu-Ling Tseng

doi:10.3390/jof8030233

Abstract

We have previously identified Candida albicans GPH1 (orf19.7021) whose protein product was associated with C. albicans Cdc4. The GPH1 gene is a putative glycogen phosphorylase because its Saccharomyces cerevisiae homolog participates in glycogen catabolism, which involves the synthesis of β-glucan of the fungal cell wall. We made a strain whose CaCDC4 expression is repressed, and GPH1 is constitutively expressed. We established a GPH1 null mutant strain and used it to conduct the in vitro virulence assays that detect cell wall function. The in vitro virulence assay is centered on biofilm formation in which analytic procedures are implemented to evaluate cell surface hydrophobicity; competence, either in stress resistance, germ tube formation, or fibronection association; and the XTT-based adhesion and biofilm formation. We showed that the constitutively expressed GPH1 partially suppresses filamentation when the CaCDC4 expression is repressed. The C. albicans Gph1 protein is reduced in the presence of CaCdc4 in comparison with the absence of CaCdc4. Compared with the wild-type strain, the gph1Δ/gph1Δ mutant displayed a reduction in the capability to form germ tubes and the cell surface hydrophobicity but an increase in binding with fibronectin. Compared with the wild-type strain, the gph1Δ/gph1Δ mutant showed a rise in adhesion, the initial stage of biofilm formation, but displayed a similar capacity to form a mature biofilm. There was no major impact on the gph1Δ/gph1Δ mutant regarding the conditions of cell wall damaging and TOR pathway-associated nutrient depletion. We conclude that GPH1, adversely regulated by the filament suppressor CDC4, contributes to cell wall function in C. albicans.

Highlights

To understand the functional link between CaCDC4 and GPH1, a C. albicans strain capable of repressing CaCDC4 expression with methionine and cysteine (Met/Cys) and constitutively expressing GPH1, together with those expressing CaCDC4 and none, were created (Figure 1A)
We revealed that the filamentous development due to the repressed CaCDC4 expression in C. albicans was moderately suppressed by the constitutive expression ofGPH1
Our findings indicates that C. albicans CaCdc4 controls the polyubiquitin- proteasomedependent degradation of Gph1

Summary

Introduction

C. albicans can grow in a wide variety of morphological forms, from the ellipsoid blastospore to various filamentous types [11–14]. A great effort has been made to reveal the underlying mechanism of C. albicans morphogenesis because it is proven to be coupled with virulence and pathogenesis [15–18]. Advancement has been hampered due to C. albicans being a natural diploid with a noncanonical sexual cycle [19–22]. Several positive and negative signaling pathways that control morphological transition have been discovered in C. albicans [23–25]. Cyclin-dependent kinases and their associated cyclins with their regulators have been found to control morphological plasticity in C. albicans [26,27]. We and others have recently found that some key cell cycle genes conserved throughout evolution play an essential role in the cell cycle but influence morphogenesis in C. albicans [28–33], including the couple cell cycle and morphogenesis [34–37]

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Conclusion