Diagnosis of Antifungal Drug Resistance Mechanisms in Fungal Pathogens: Transcriptional Gene Regulation

Abstract

Several fungal species can cause mild to severe diseases in humans. Antifungal strategies have been made possible by the development of several drugs with antifungal activity against these pathogenic fungi. Fungi have counteracted antifungal agents in several cases by developing resistance mechanisms. These mechanisms are based on the modifications of drug target genes and on the regulation of drug-resistance genes. Their regulation is controlled by different transcription factors, and recently several mutations in these factors were demonstrated to be responsible for the development of antifungal drug resistance. Given the availability of this genome information, the detection of antifungal resistance could be realized by specific diagnostic tools with DNA-based detection technologies. Here we review the current understanding of transcriptional regulation of drug-resistance genes from several fungal pathogens and prospective diagnostic options.

Update on Antifungal Drug Resistance

“…The first major trans -acting transcription element regulating efflux is C. albicans Transcriptional Activator of CDR ( TAC1 ), a member of the Zn 2 Cys 6 transcription factor family. Gain-of-function (GOF) mutations in TAC1 [86•, 87] are responsible for the upregulation of CDR1 and CDR2 in azole-resistant isolates [88–90]. Tac1 binds to the DRE of CDR1 and CDR2 , likely via a consensus-binding motif.…”

“…Nearly 60 GOF mutations have been identified in CgPDR1 alleles from clinical azole-resistant isolates [94]. In C. albicans , the Zn 2 Cys 6 transcription factor Multidrug Resistance Regulator 1 (Mrr1) regulates MFS transporter gene MDR1 [97] and at least 15 different MRR1 GOF mutations are known [88, 98] to cause constitutive upregulation of MDR1 [99]. Other positive regulators of MDR in C. albicans include Cap1 [100, 101] and Mcm1 [102, 103].…”

Defining the frontiers between antifungal resistance, tolerance and the concept of persistence

“…One of the approaches to resolve the basis for antifungal tolerance was by the search of substances which will inhibit tolerance. Loss of tolerance to azoles was first demonstrated when cyclosporine A (CsA), an inhibitor of calcineurin activity, was added simultaneously to fluconazole in MIC checkerboard tests in C. albicans (Marchetti et al, 2000b;Sanglard et al, 2003). The construction of mutants lacking the gene CNA/CMP1 gene encoding calcineurin subunit A established that azole tolerance was mediated by calcineurin activity and its calcium-dependent activation pathway (Sanglard et al, 2003).…”

Mechanisms of Antifungal Drug Resistance

“…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). The TAC1 regulon was further elucidated by genome-wide transcriptional profiling and DNA occupancy analysis of Tac1 (Liu et al 2007), demonstrating that Tac1 binds to the DRE of CDR1 and CDR2, likely via a consensus-binding motif (CGGN 4 CGG).…”

“…Deletion of MRR1 in clinical strains blocked MDR1 up-regulation (Morschhauser et al 2007). Fifteen different MRR1 GOF mutations have been reported (Sanglard 2011;Eddouzi et al 2013), causing constitutive up-regulation of MDR1 (Dunkel et al 2008). Genome-wide transcriptional studies using clinical strains revealed a core set of 14 genes involved in diverse functions that are up-regulated in isolates carrying MRR1 GOF mutations (Morschhauser et al 2007).…”