TAC1 , Transcriptional Activator of CDR Genes, Is a New Transcription Factor Involved in the Regulation of Candida albicans ABC Transporters CDR1 and CDR2

Abstract

The ABC transporter genes CDR1 and CDR2 can be upregulated in Candida albicans developing resistance to azoles or can be upregulated by exposing cells transiently to drugs such as fluphenazine. The cis-acting drug-responsive element (DRE) present in the promoters of both genes and necessary for their upregulation contains 5-CGG-3 triplets that are often recognized by transcriptional activators with Zn(2)-Cys(6) fingers. In order to isolate regulators of CDR1 and CDR2, the C. albicans genome was searched for genes encoding proteins with Zn(2)-Cys(6) fingers. Interestingly, three of these genes were tandemly arranged near the mating locus. Their involvement in CDR1 and CDR2 upregulation was addressed because a previous study demonstrated a link between mating locus homozygosity and azole resistance. The deletion of only one of these genes (orf19.3188) was sufficient to result in a loss of transient CDR1 and CDR2 upregulation by fluphenazine and was therefore named TAC1 (transcriptional activator of CDR genes). Tac1p has a nuclear localization, and a fusion of Tac1p with glutathione S-transferase could bind the cis-acting regulatory DRE in both the CDR1 and the CDR2 promoters. TAC1 is also relevant for azole resistance, since a TAC1 allele (TAC1-2) recovered from an azole-resistant strain could trigger constitutive upregulation of CDR1 and CDR2 in an azole-susceptible laboratory strain. Transcript profiling experiments performed with a TAC1 mutant and a revertant containing TAC1-2 revealed not only CDR1 and CDR2 as targets of TAC1 regulation but also other genes (RTA3, IFU5, and HSP12) that interestingly contained a DRE-like element in their promoters. In conclusion, TAC1 appears to be the first C. albicans transcription factor involved in the control of genes mediating antifungal resistance.

Transcriptional Regulation of MDR1 , Encoding a Drug Efflux Determinant, in Fluconazole-Resistant Candida albicans Strains through an Mcm1p Binding Site

“…The CDR2 gene also confers resistance to the azoles, terbinafine, and amorolfine (46). Sanglard and coworkers identified a transcription factor, Tac1p, that binds an element within the CDR1/CDR2 promoter, the drug resistance element (DRE), and demonstrated its involvement in the high-level constitutive expression of these genes seen in some FLC R strains (10). Mutations within the TAC1 open reading frame (ORF) that lead to hyperactive trans-activation of CDR1 and CDR2 have been identified in FLC R strains (9).…”

“…Expression of the other drug efflux transporters, Cdr1p and Cdr2p, is also regulated through a trans-activating factor that binds a specific sequence within their promoters (10,11). Cdr1p and Cdr2p are ATP binding cassette (ABC) transporters that are highly similar to each other in sequence (46).…”

A novel polyamide SL-A92 as a potential fungal resistance blocker: synthesis and bioactivities in Candida albicans

“…Four kinds of CDR genes in C albicans have been cloned [13,[40][41][42] , but only over-expression of CDR1 and CDR2 resulted in azole resistance [43] . Tac1p is the major transcription factor needed for the regulation of CDR1 and CDR2, and is characterized by a highly conserved Zn(II) 2 Cys 6 zinc finger motif formed by six cysteines that coordinate two zinc atoms within the DNAbinding domain [11,44,45] . Previous studies have demonstrated that the binding site of Tac1p lies in the drug-responsive element (DRE) and consists of a direct CGG repeat with four intervening nucleotides (CGGAA/TATCGG) [44] .…”

“…Tac1p is the major transcription factor needed for the regulation of CDR1 and CDR2, and is characterized by a highly conserved Zn(II) 2 Cys 6 zinc finger motif formed by six cysteines that coordinate two zinc atoms within the DNAbinding domain [11,44,45] . Previous studies have demonstrated that the binding site of Tac1p lies in the drug-responsive element (DRE) and consists of a direct CGG repeat with four intervening nucleotides (CGGAA/TATCGG) [44] . In this study, we showed that fluconazole could up-regulate the level of CDR1 after induction for 33 days in vitro, but there was no upregulation of CDR2.…”

Mechanisms of Antifungal Drug Resistance

“…TAC1 is critical for the up-regulation of CDR1 and CDR2 in response to drugs or in clinical azole-resistant isolates. Constitutive upregulation of CDR1 and CDR2 can be attributed to gain-of-function (GOF) mutations in different domains of TAC1 (Coste et al 2004. Nineteen different TAC1 mutations have been confirmed as GOF, whereas others remain candidates Siikala et al 2010;Sanglard 2011).…”