SPT20 Regulates the Hog1-MAPK Pathway and Is Involved in Candida albicans Response to Hyperosmotic Stress

Lianfang Wang; Ruilan Chen; Qiuting Weng; Shaoming Lin; Huijun Wang; Li Li; Beth Burgwyn Fuchs; Xiaojiang Tan; Eleftherios Mylonakis

doi:10.3389/fmicb.2020.00213

SPT20 Regulates the Hog1-MAPK Pathway and Is Involved in Candida albicans Response to Hyperosmotic Stress

Front Microbiol. 2020 Feb 21:11:213. doi: 10.3389/fmicb.2020.00213. eCollection 2020.

Authors

Lianfang Wang¹, Ruilan Chen^{2

3

4}, Qiuting Weng¹, Shaoming Lin⁵, Huijun Wang¹, Li Li⁶, Beth Burgwyn Fuchs⁷, Xiaojiang Tan¹, Eleftherios Mylonakis⁷

Affiliations

¹ Department of Respiratory and Critical Care Medicine, Chronic Airways Diseases Laboratory, Huiqiao Medical Center, Nanfang Hospital, Southern Medical University, Guangzhou, China.
² The Second Clinical College of Guangzhou University of Chinese Medicine, Guangzhou, China.
³ Department of Intensive Care Unit, Fangcun Branch of Guangdong Provincial Hospital of Chinese Medicine, Guangzhou, China.
⁴ Guangdong Provincial Academy of Chinese Medical Sciences, Guangzhou, China.
⁵ Department of Respiratory, Longhua District People's Hospital, Shenzhen, China.
⁶ Huiqiao Medical Center, Nanfang Hospital, Southern Medical University, Guangzhou, China.
⁷ Department of Medicine, Division of Infectious Diseases, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI, United States.

Abstract

Candida albicans is the most common fungal pathogen and relies on the Hog1-MAPK pathway to resist osmotic stress posed by the environment or during host invasions. Here, we investigated the role of SPT20 in response to osmotic stress. Testing a C. albicans spt20Δ/Δ mutant, we found it was sensitive to osmotic stress. Using sequence alignment, we identified the conserved functional domains between CaSpt20 and ScSpt20. Reconstitution of the Spt20 function in a spt20Δ/CaSPT20 complemented strain found CaSPT20 can suppress the high sensitivity to hyperosmotic stressors, a cell wall stress agent, and antifungal drugs in the Saccharomyces cerevisiae spt20Δ/Δ mutant background. We measured the cellular glycerol accumulation and found it was significantly lower in the C. albicans spt20Δ/Δ mutant strain, compared to the wild type strain SC5314 (P < 0.001). This result was also supported by quantitative reverse transcription-PCR, which showed the expression levels of gene contributing to glycerol accumulation were reduced in Caspt20Δ/Δ compared to wild type (GPD2 and TGL1, P < 0.001), while ADH7 and AGP2, whose expression can lead to glycerol decrease, were induced when cells were exposed to high osmolarity (ADH7, P < 0.001; AGP2, P = 0.002). In addition, we tested the transcription levels of Hog1-dependent osmotic stress response genes, and found that they were significantly upregulated in wild type cells encountering hyperosmolarity, while the expression of HGT10, SKO1, CAT1, and SLP3 were not induced when SPT20 was deleted. Although the transcript of ORF19.3661 and ORF19.4370 in Caspt20Δ/Δ was induced in the presence of 1 M NaCl, the levels were less than what was observed in the wild type (ORF19.3661, P = 0.007; ORF19.4370, P = 0.011). Moreover, the deletion of CaSPT20 in C. albicans reduced phosphorylation levels of Hog1. These findings suggested that SPT20 is conserved between yeast and C. albicans and plays an important role in adapting to osmotic stress through regulating Hog1-MAPK pathway.

Keywords: Candida albicans; Hog1-MAPK; SPT20; glycerol; osmotic stress.