The small GTPase Rhb1 is involved in the cell response to fluconazole in Candida albicans.

Candida albicans is an important fungal pathogen in humans. Rhb1 is a small GTPase of the Ras superfamily and is conserved from yeasts to humans. In C. albicans, Rhb1 regulates the expression of secreted protease 2, low nitrogen-mediated morphogenesis, and biofilm formation. Moreover, our previous studies have indicated that Rhb1 is associated with the target of rapamycin (TOR) signaling pathway. In this study, we further explored the relationship between Rhb1 and drug susceptibility. The RHB1 deletion mutant exhibited reduced fluconazole susceptibility, and this phenotype occurred mainly through the increased gene expression and activity of efflux pumps. In addition, Mrr1 and Tac1 are transcription factors that can activate efflux pump gene expression. However, the RHB1 deletion, RHB1/MRR1 and RHB1/TAC1 double deletion mutants had no significant differences in efflux pump gene expression and fluconazole susceptibility, suggesting that Rhb1-regulated efflux pump genes do not act through Mrr1 and Tac1. We also showed that membrane localization is crucial for Rhb1 activity in response to fluconazole. Finally, Rhb1 was linked not only to the TOR but also to the Mkc1 mitogen-activated protein kinase signaling pathway in response to fluconazole. In sum, this study unveiled a new role of Rhb1 in the regulation of C. albicans drug susceptibility.

Human Antimicrobial Peptide Hepcidin 25-Induced Apoptosis in Candida albicans.

Hepcidin 25 (hep 25) is a cysteine-rich 25-amino acid antimicrobial peptide containing the amino-terminal Cu(II)/Ni(II)-binding (ATCUN) motif. Upon metal binding, the ATCUN motif is known to be involved in the generation of reactive oxygen species (ROS), especially hydrogen peroxide and hydroxyl radicals, which act against different bacterial species. However, the antifungal activity and its correlation to the Cu(II)-ATCUN complex of Hep 25 are still poorly understood. Here, we found that ROS accumulation plays an important role in the fungicidal activity of hep 25 against Candida albicans. In addition, Annexin V-FITC staining and TUNEL assay results provide clues about the apoptosis induced by hep 25. Moreover, hep 25 also increases the generation of ROS, possibly because of copper binding to the ATCUN motif, which is relevant to its activity against C. albicans. Finally, the C. albicans killing action of hep 25 is an energy- and temperature-dependent process that does not involve targeting the membrane. Taken together, our results provide new insights into the mechanisms of hep 25 against C. albicans cells and the potential use of hep 25 and its derivatives as novel antifungal agents.