Mrr1 regulation of methylglyoxal catabolism and methylglyoxal‐induced fluconazole resistance in Candida lusitaniae

Abstract

Transcription factor Mrr1, best known for its regulation of Candida azole resistance genes such as MDR1, regulates other genes that are poorly characterized. Among the other Mrr1‐regulated genes are putative methylglyoxal reductases. Methylglyoxal (MG) is a toxic metabolite that is elevated in diabetes, uremia, and sepsis, which are diseases that increase the risk for candidiasis, and MG serves as a regulatory signal in diverse organisms. Our studies in Clavispora lusitaniae, also known as Candida lusitaniae, showed that Mrr1 regulates expression of two paralogous MG reductases, MGD1 and MGD2, and that both participate in MG resistance and MG catabolism. Exogenous MG increased Mrr1‐dependent expression of MGD1 and MGD2 as well as expression of MDR1, which encodes an efflux pump that exports fluconazole. MG improved growth in the presence of fluconazole and this was largely Mrr1‐dependent with contributions from a secondary transcription factor, Cap1. Increased fluconazole resistance was also observed in mutants lacking Glo1, a Mrr1‐independent MG catabolic enzyme. Isolates from other Candida species displayed heterogeneity in MG resistance and MG stimulation of azole resistance. We propose endogenous and host‐derived MG can induce MDR1 and other Mrr1‐regulated genes causing increased drug resistance, which may contribute to some instances of fungal treatment failure.

Fructose Induces Fluconazole Resistance in Candida albicans through Activation of Mdr1 and Cdr1 Transporters

“…However, fructose has been described to also be metabolized to a toxic glycolytic byproduct called methylglyoxal (MG), the elevated levels of which are responsible for hepatotoxicity in diabetic patients [40]. In Candida lusitaniae, the MG metabolism is believed to be mediated by Mgd1 and Mgd2 reductases, the expression of which is controlled by Mrr1p, which, in turn, is inducible by MG [41]. The homologous protein in C. albicans (CaMrr1p) is a major transcriptional inductor of MDR1 [42].…”

Transcriptional response of Candida auris to the Mrr1 inducers methylglyoxal and benomyl

“…We have previously shown in C. lusitaniae that MG induces expression of the Mrr1-regulated genes MGD1 and MGD2 in an Mrr1-dependent manner, and MDR1 in a partially Mrr1-dependent manner (58). To determine if MG would induce expression of MGD1 , MGD2 , and/or MDR1 in C. auris , we purified RNA for qRT-PCR from exponential-phase cultures of B11221 WT and mrr1a Δ treated with 5 mM MG or an equal volume of dH 2 O for 15 minutes.…”

“…Under the conditions tested, Mrr1a regulation in the C. auris B11221 background was mainly of MGD1 and MDR1 . Homologs of MDR1 and at least one gene encoding a known or predicted MG reductase are co-regulated by Mrr1 in C. albicans (44, 45, 94–96), C. parapsilosis (97), and C. lusitaniae (37, 40, 58), suggesting that the co-regulation of these two genes has been conserved throughout multiple Candida species. Gaining a deeper understanding of the evolutionary and biochemical relationship between methylglyoxal reductases and efflux pumps, particularly Mdr1, may shed light on how Candida species sense and respond to environmental or physiological stresses, evade host defense mechanisms, and develop antifungal resistance.…”

“…Transformants were selected on YPD agar containing 600 µg/ml hygromycin B (HygB). Successful transformants were identified via PCR of the C. lusitaniae MRR1 locus as previously described (37, 58). CRISPR RNAs (crRNAs; IDT) and primers used to validate transformants are listed in Table S8.…”

“…Growth kinetic assays were performed as previously described in (58). In brief, exponential-phase cultures of C. auris or C. lusitaniae were washed and diluted in dH 2 O to an OD 600 of 1; 60 µL of each diluted cell suspension was added to 5 mL fresh YPD.…”