Upc2-mediated mechanisms of azole resistance in Candida auris

is an emerging yeast pathogen of major concern because of its ability to cause hospital outbreaks of invasive candidiasis and to develop resistance to antifungal drugs. A majority of isolates are resistant to fluconazole, an azole drug used for the treatment of invasive candidiasis. Mechanisms of azole resistance are multiple, including mutations in the target gene and activation of the transcription factors Tac1b and Mrr1, which control the drug transporters Cdr1 and Mdr1, respectively. We investigated the role of the transcription factor Upc2, which is known to regulate the ergosterol biosynthesis pathway and azole resistance in other spp. Genetic deletion and hyperactivation of Upc2 by epitope tagging in resulted in drastic increases and decreases in susceptibility to azoles, respectively. This effect was conserved in strains with genetic hyperactivation of Tac1b or Mrr1. Reverse transcription PCR analyses showed that Upc2 regulates expression and also activates the Mrr1/Mdr1 pathway. We showed that upregulation of by Upc2 could occur independently from Mrr1. The impact of deletion on expression and azole susceptibility in a hyperactive Mrr1 background was stronger than that of deletion in a hyperactive Upc2 background. While Upc2 hyperactivation resulted in a significant increase in the expression of , expression remained unchanged. Taken together, our results showed that Upc2 is crucial for azole resistance in , via regulation of the ergosterol biosynthesis pathway and activation of the Mrr1/Mdr1 pathway. Notably, Upc2 is a very potent and direct activator of Mdr1.IMPORTANCE is a yeast of major medical importance causing nosocomial outbreaks of invasive candidiasis. Its ability to develop resistance to antifungal drugs, in particular to azoles (e.g., fluconazole), is concerning. Understanding the mechanisms of azole resistance in is important and may help in identifying novel antifungal targets. This study shows the key role of the transcription factor Upc2 in azole resistance of and shows that this effect is mediated via different pathways, including the regulation of ergosterol biosynthesis and also the direct upregulation of the drug transporter Mdr1.