Abstract
Invasive infections caused by the opportunistic pathogen Candida glabrata are treated with echinocandin antifungals that target β-1,3-glucan synthase, an enzyme critical for fungal cell wall biosynthesis. Echinocandin resistance develops upon mutation of genes (FKS1 or FKS2) that encode the glucan synthase catalytic subunits. We have analyzed cellular factors that influence echinocandin susceptibility and here describe effects of the post-transcriptional regulator Ssd1, which in S. cerevisiae, can bind cell wall related gene transcripts. The SSD1 homolog in C. glabrata was disrupted in isogenic wild type and equivalent FKS1 and FKS2 mutant strains that demonstrate echinocandin resistance (MICs > 0.5 µg/mL). A reversal of resistance (8- to 128-fold decrease in MICs) was observed in FKS1 mutants, but not in FKS2 mutants, following SSD1 deletion. Additionally, this phenotype was complemented upon expression of SSD1 from plasmid (pSSD1). All SSD1 disruptants displayed susceptibility to the calcineurin inhibitor FK506, similar to fks1∆. Decreases in relative gene expression ratios of FKS1 to FKS2 (2.6- to 4.5-fold) and in protein ratios of Fks1 to Fks2 (2.7- and 8.4-fold) were observed in FKS mutants upon SSD1 disruption. Additionally, a complementary increase in protein ratio was observed in the pSSD1 expressing strain. Overall, we describe a cellular factor that influences Fks1-specific mediated resistance and demonstrates further differential regulation of FKS1 and FKS2 in C. glabrata.
Highlights
Infections caused by Candida glabrata, especially among immunocompromised hosts, have increased in prevalence and demonstrate elevated rates of antifungal resistance [1,2,3]
Upon screening multiple gene disruptants in C. glabrata, we found that ssd1∆ displayed 2- to 4-fold increases in susceptibility to caspofungin and micafungin as demonstrated by broth microdilution and killing assays (Table 1 and Figure 1)
In order to determine if the post-transcriptional regulator Ssd1 influences echinocandin resistance, we built clinically relevant FKS1 and FKS2 mutations into the ATCC 200989 background strain
Summary
Infections caused by Candida glabrata, especially among immunocompromised hosts, have increased in prevalence and demonstrate elevated rates of antifungal resistance [1,2,3]. The echinocandins (caspofungin, micafungin, and anidulafungin) are recommended first-line agents for the treatment of invasive C. glabrata infections [4]. Echinocandin antifungals target the plasma membrane-embedded enzyme β-1,3-glucan synthase, leading to loss of β-glucans and cell wall stability. J. Fungi 2020, 6, 143; doi:10.3390/jof6030143 www.mdpi.com/journal/jof. J. Fungi 2020, 6, 143 echinocandins is well-established (3–12%) among patients with C. glabrata infections and develops upon mutation of genes (FKS1 or FKS2) that encode for the catalytic subunits (Fks1/Fks2) of β-glucan synthase [1,2,5]
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