Upc2-mediated mechanisms of azole resistance inCandida auris

Abstract

ABSTRACTCandida aurisis 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 ofC. aurisisolates are resistant to fluconazole, a first-line treatment of invasive candidiasis. Mechanisms of azole resistance are multiple, including mutations in the target geneERG11and activation of the transcription factors Tac1b and Mrr1, which control the drug transporters Cdr1 and Mdr1, respectively. In this study, we investigated the role the transcription factor Upc2, which is known to regulate the ergosterol biosynthesis pathway and azole resistance in otherCandidaspp.Genetic deletion and hyperactivation of Upc2 by epitope tagging inC. aurisresulted in drastic increased and decreased susceptibility to azoles, respectively. This effect was conserved in strains with genetic hyperactivation of Tac1b or Mrr1. Reverse transcription PCR analyses showed that Upc2 regulatesERG11expression and also activates the Mrr1/Mdr1 pathway. We showed that upregulation ofMDR1by Upc2 could occur independently from Mrr1. The impact ofUPC2deletion onMDR1expression and azole susceptibility in a hyperactive Mrr1 background was stronger than that ofMRR1deletion in a hyperactive Upc2 background. While Upc2 hyperactivation resulted in a significant increase of expression ofTAC1b,CDR1expression remained unchanged.Taken together, our results showed that Upc2 is crucial for azole resistance inC. auris, 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.