Identification of promoter elements responsible for the regulation of MDR1 from Candida albicans, a major facilitator transporter involved in azole resistance

摘要

Upregulation of the MDR1 (multidrug resistance 1) gene is involved in the development of resistance to antifungal agents in clinical isolates of the pathogen Candida albicans. To better understand the molecular mechanisms underlying the phenomenon, the cis-acting regulatory elements present in the MDR1 promoter were characterized using a β-galactosidase reporter system. In an azole-susceptible strain, transcription of this reporter is transiently upregulated in response to either benomyl or H2O2, whereas its expression is constitutively high in an azole-resistant strain (FR2). Two cis-acting regulatory elements within the MDR1 promoter were identified that are necessary and sufficient to confer the same transcriptional responses on a heterologous promoter (CDR2). One, a benomyl response element (BRE), is situated at position ?296 to ?260 with respect to the ATG start codon. It is required for benomyl-dependent MDR1 upregulation and is also necessary for constitutive high expression of MDR1. A second element, termed H2O2response element (HRE), is situated at position ?561 to ?520. The HRE is required for H2O2-dependent MDR1 upregulation, but dispensable for constitutive high expression. Two potential binding sites (TTAG/CTAA) for the bZip transcription factor Cap1p (Candida AP-1 protein) lie within the HRE. Moreover, inactivation of CAP1 abolished the transient response to H2O2. Cap1p, which has been previously implicated in cellular responses to oxidative stress, may thus play a trans-acting and positive regulatory role in the H2O2-dependent transcription of MDR1. A minimal BRE (?290 to ?273) that is sufficient to detect in vitro sequence-specific binding of protein complexes in crude extracts prepared from C. albicans was also defined. Interestingly, the sequence includes a perfect match to the consensus binding sequence of Mcm1p, raising the possibility that MDR1 may be a direct target of this MADS box transcriptional activator. In conclusion, while the identity of the trans-acting factors that bind to the BRE and HRE remains to be confirmed, the tools developed during this characterization of the cis-acting elements of the MDR1 promoter should now serve to elucidate the nature of the components that modulate its activity.