Candida albicans Mannosidases, Dfg5 and Dcw1, Are Required for Cell Wall Integrity and Pathogenesis

Candida albicans is an oral mucosal commensal fungus that transforms into an opportunistic pathogen under specific conditions, including immunosuppression. It causes oral and systemic candidiasis, which results in a significant health burden. Furthermore, an alarming rise in antifungal drug resistance in Candida species raises the urgent need for novel drugs and drug targets. C. albicans Dfg5 and Dcw1 are homologous cell wall alpha-1,6-mannosidases with critical functions and represent potential new drug targets. Our past studies have shown that Dfg5 and Dcw1 function in cell wall biogenesis through the cross-linking of glycoproteins into the cell wall, thus playing a key role in cell wall integrity. Additionally, Dfg5 and Dcw1 are required for hyphal morphogenesis. However, the exact functions of Dfg5 and Dcw1 in cell wall integrity, hyphal morphogenesis, and pathogenesis are not known. In this study, we determined the relation of Dfg5 and Dcw1 with Hog1 MAPK, which plays a key role in cell wall integrity via the regulation of chitin synthesis in C. albicans. Additionally, we also determined the effects of dfg5 and dcw1 mutations on the gene expression of transcriptional regulators of hyphal morphogenesis. Furthermore, we determined the effects of dfg5 and dcw1 mutations on pathogenesis in a mouse model of oral candidiasis. Our results demonstrate that dfg5 and dcw1 mutations, as well as a hog1 knockout mutation, result in the dysregulation of chitin synthesis, resulting in a cell separation defect. Heterozygous and conditional mutations in dfg5 and dcw1 resulted in decreased transcriptional levels of cst20, a positive regulator of hyphal morphogenesis. However, dfg5 and dcw1 mutations resulted in increased levels of all the five negative regulators of hyphal morphogenesis—Tup1, Nrg1, Mig1, Rbf1, and Rfg1. Additionally, Tup1 levels were significantly higher than other negative regulators, indicating that Dfg5 and Dcw1 function in hyphal morphogenesis by repressing Tup1. Finally, dfg5 and dcw1 mutations affected the ability of C. albicans to cause oral candidiasis in mice. Thus, the cell wall glycosidases Dfg5 and Dcw1 are required for virulence and pathogenesis and represent novel drug targets.