A nuclear receptor-like pathway regulating multidrug resistance in fungi

Abstract

Multidrug resistance (MDR) is a serious complication during treatment of opportunistic fungal infections that frequently afflict immunocompromised individuals, such as transplant recipients and cancer patients undergoing cytotoxic chemotherapy. Improved knowledge of the molecular pathways controlling MDR in pathogenic fungi should facilitate the development of novel therapies to combat these intransigent infections. MDR is often caused by upregulation of drug efflux pumps by members of the fungal zinc-cluster transcription-factor family (for example Pdr1p orthologues). However, the molecular mechanisms are poorly understood. Here we show that Pdr1p family members in Saccharomyces cerevisiae and the human pathogen Candida glabrata directly bind to structurally diverse drugs and xenobiotics, resulting in stimulated expression of drug efflux pumps and induction of MDR. Notably, this is mechanistically similar to regulation of MDR in vertebrates by the PXR nuclear receptor, revealing an unexpected functional analogy of fungal and metazoan regulators of MDR. We have also uncovered a critical and specific role of the Gal11p/MED15 subunit of the Mediator co-activator and its activator-targeted KIX domain in antifungal/xenobiotic-dependent regulation of MDR. This detailed mechanistic understanding of a fungal nuclear receptor-like gene regulatory pathway provides novel therapeutic targets for the treatment of multidrug-resistant fungal infections.

Structure and VP16 binding of the Mediator Med25 activator interaction domain

“…Until now, structural information on activator-binding domains in Mediator was limited to the KIX domain in subunit Med15 (Arc105) 30,31 . This domain shows an entirely α-helical fold, in strong contrast to ACID, which contains a central β-barrel fold (Fig.…”

“…Mediator generally conveys regulatory information by forming a bridge between activators and the basal Pol II machinery 28,29 . Whereas information on the core Mediator structure is emerging, structural information about its more peripheral activator-binding domains is limited to the KIX domain in subunit Med15 (or Arc105) 30,31 .The VP16 TAD is intrinsically flexible, whereas the VP16 core domain (residues 49-402) forms a stable structure 23,[32][33][34] . The TAD contains two functional subdomains, H1 (residues 410-452) and H2 (residues 453-490), which activate transcription independently 35,36 .…”

“…Mediator generally conveys regulatory information by forming a bridge between activators and the basal Pol II machinery 28,29 . Whereas information on the core Mediator structure is emerging, structural information about its more peripheral activator-binding domains is limited to the KIX domain in subunit Med15 (or Arc105) 30,31 .…”

Structural mechanism of ergosterol regulation by fungal sterol transcription factor Upc2

“…Recent studies proposed that several members of the fungal zinc cluster family of transcription regulators may represent functional analogues of metazoan NRs 13,[18][19][20] .…”

“…Transcriptional activity of Oaf1/Pip2 is regulated by oleate binding to the CTD with similar ligand-binding characteristics and coactivator requirements to mammalian PPAR/RXR receptors 18,19 . Pdr1 zinc TFs bind to diverse xenobiotics and stimulate expression of drug efflux pumps resulting in induction of multidrug resistance in S. cerevisiae and C. glabrata, which is functionally similar to the regulation of multidrug resistance in vertebrates by the PXR NR 19,20 . However, due to the lack of structural and biochemical information of the fungal zinc finger transcriptional factors, the characteristics of this gene family have remained elusive.…”