Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:TAC1, transcriptional activator of CDR genes, is a new transcription factor involved in the regulation of Candida albicans ABC transporters CDR1 and CDR2. 1559 Aug 37

TAC1 (for transcriptional activator of CDR genes) is critical for the upregulation of the ABC transporters CDR1 and CDR2, which mediate azole resistance in Candida albicans. While a wild-type TAC1 allele drives high expression of CDR1/2 in response to inducers, we showed previously that TAC1 can be hyperactive by a gain-of-function (GOF) point mutation responsible for constitutive high expression of CDR1/2. High azole resistance levels are achieved when C. albicans carries hyperactive alleles only as a consequence of loss of heterozygosity (LOH) at the TAC1 locus on chromosome 5 (Chr 5), which is linked to the mating-type-like (MTL) locus. Both are located on the Chr 5 left arm along with ERG11 (target of azoles). In this work, five groups of related isolates containing azole-susceptible and -resistant strains were analyzed for the TAC1 and ERG11 alleles and for Chr 5 alterations. While recovered ERG11 alleles contained known mutations, 17 new TAC1 alleles were isolated, including 7 hyperactive alleles with five separate new GOF mutations. Single-nucleotide-polymorphism analysis of Chr 5 revealed that azole-resistant strains acquired TAC1 hyperactive alleles and, in most cases, ERG11 mutant alleles by LOH events not systematically including the MTL locus. TAC1 LOH resulted from mitotic recombination of the left arm of Chr 5, gene conversion within the TAC1 locus, or the loss and reduplication of the entire Chr 5. In one case, two independent TAC1 hyperactive alleles were acquired. Comparative genome hybridization and karyotype analysis revealed the presence of isochromosome 5L [i(5L)] in two azole-resistant strains. i(5L) leads to increased copy numbers of azole resistance genes present on the left arm of Chr 5, among them TAC1 and ERG11. Our work shows that azole resistance was due not only to the presence of specific mutations in azole resistance genes (at least ERG11 and TAC1) but also to their increase in copy number by LOH and to the addition of extra Chr 5 copies. With the combination of these different modifications, sophisticated genotypes were obtained. The development of azole resistance in C. albicans is therefore a powerful instrument for generating genetic diversity.
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PMID:Genotypic evolution of azole resistance mechanisms in sequential Candida albicans isolates. 1769 96

The Candida albicans PDR16 gene, encoding a putative phosphatidylinositol transfer protein, is co-induced with the multidrug transporter genes CDR1 and CDR2 in azole-resistant (A(R)) clinical isolates and upon fluphenazine exposure of azole-susceptible (A(S)) cells, suggesting that it is regulated by Tac1p, the transcriptional activator of CDR genes. Deleting TAC1 in an A(R) isolate (5674) overexpressing PDR16, CDR1 and CDR2 decreased the expression of the three genes and fluconazole resistance to levels similar to those detected in the matched A(S) isolate (5457), demonstrating that Tac1p is responsible for PDR16 upregulation in that strain. Deleting TAC1 in the A(S) strain SC5314 abolished CDR2 induction by fluphenazine and decreased that of PDR16 and CDR1, uncovering the participation of an additional factor in the regulation of PDR16 and CDR1 expression. Sequencing of the TAC1 alleles identified one homozygous mutation in strain 5674, an Asn to Asp substitution at position 972 in the C-terminus of Tac1p. Introduction of the Asp(972) allele in a tac1Delta/Delta mutant caused high levels of fluconazole resistance and TAC1, PDR16, CDR1 and CDR2 constitutive induction. These results demonstrate that: (i) Tac1p controls PDR16 expression; (ii) Asn(972) to Asp(972) is a gain-of-function mutation; and (iii) Tac1p is positively autoregulated, directly or indirectly.
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PMID:The zinc cluster transcription factor Tac1p regulates PDR16 expression in Candida albicans. 1789 73

Drug resistance mechanisms in the commensal human pathogen Candida albicans are continually evolving. Over time, Candida species have implemented diverse strategies to vanquish the effects of various classes of drugs, thereby emanating as a serious life threat. Apart from the repertoire of well-established strategies, which predominantly comprise permeability constraints, increased drug efflux or compromised drug import, alteration, overexpression of drug targets, and chromosome duplication, C. albicans has evolved novel regulatory mechanisms of drug resistance. For instance, recent evidences point to newer circuitry involving different mediators of the stress-responsive machinery of oxidative, osmotic, thermal, nitrosative, and nutrient limitation, which contribute to the emergence of drug resistance. Contemporary advances in genome-wide studies of transcription factors, for instance, the Zn2Cys6 transcription factors, TAC1 (transcriptional activator of CDR) in Candida albicans, or YRR1 in yeast have made it feasible to dissect their involvement for the elucidation of unexplored regulatory network of drug resistance. The coordination of implementers of the conventional and nonconventional drug resistance strategies provides robustness to this commensal human pathogen. In this review, we shed light not only on the established strategies of antifungal resistance but also discuss emerging cellular circuitry governing drug resistance of this human pathogen.
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PMID:Emerging Mechanisms of Drug Resistance in Candida albicans. 3091 92