Bfr1p is responsible for tributyltin resistance in Schizosaccharomyces pombe

QTL mapping suggests that both cytochrome P450-mediated detoxification and target-site resistance are involved in fenbutatin oxide resistance in Tetranychus urticae

The organotin acaricide fenbutatin oxide (FBO) - an inhibitor of mitochondrial ATP-synthase - has been one of the most extensively used acaricides for the control of spider mites, and is still in use today. Resistance against FBO has evolved in many regions around the world but only few studies have investigated the molecular and genetic mechanisms of resistance to organotin acaricides. Here, we found that FBO resistance is polygenic in two genetically distant, highly resistant strains of the spider mite Tetranychus urticae, MAR-AB and MR-VL. To identify the loci underlying FBO resistance, two independent bulked segregant analysis (BSA) based QTL mapping experiments, BSA MAR-AB and BSA MR-VL, were performed. Two QTLs on chromosome 1 were associated with FBO resistance in each mapping experiment. At the second QTL of BSA MAR-AB, several cytochrome P450 monooxygenase (CYP) genes were located, including CYP392E4, CYP392E6 and CYP392E11, the latter being overexpressed in MAR-AB. Synergism tests further implied a role for CYPs in FBO resistance. Subunit c of mitochondrial ATP-synthase was located near the first QTL of both mapping experiments and harbored a unique V89A mutation enriched in the resistant parents and selected BSA populations. Marker-assisted introgression into a susceptible strain demonstrated a moderate but significant effect of the V89A mutation on toxicity of organotin acaricides. The impact of the mutation on organotin inhibition of ATP synthase was also functionally confirmed by ATPase assays on mitochondrial preparations. To conclude, our findings suggest that FBO resistance in the spider mite T. urticae is a complex interplay between CYP-mediated detoxification and target-site resistance.

Multidrug Resistance in Mammals and Fungi-From MDR to PDR: A Rocky Road from Atomic Structures to Transport Mechanisms

Multidrug resistance (MDR) can be a serious complication for the treatment of cancer as well as for microbial and parasitic infections. Dysregulated overexpression of several members of the ATP-binding cassette transporter families have been intimately linked to MDR phenomena. Three paradigm ABC transporter members, ABCB1 (P-gp), ABCC1 (MRP1) and ABCG2 (BCRP) appear to act as brothers in arms in promoting or causing MDR in a variety of therapeutic cancer settings. However, their molecular mechanisms of action, the basis for their broad and overlapping substrate selectivity, remains ill-posed. The rapidly increasing numbers of high-resolution atomic structures from X-ray crystallography or cryo-EM of mammalian ABC multidrug transporters initiated a new era towards a better understanding of structure-function relationships, and for the dynamics and mechanisms driving their transport cycles. In addition, the atomic structures offered new evolutionary perspectives in cases where transport systems have been structurally conserved from bacteria to humans, including the pleiotropic drug resistance (PDR) family in fungal pathogens for which high resolution structures are as yet unavailable. In this review, we will focus the discussion on comparative mechanisms of mammalian ABCG and fungal PDR transporters, owing to their close evolutionary relationships. In fact, the atomic structures of ABCG2 offer excellent models for a better understanding of fungal PDR transporters. Based on comparative structural models of ABCG transporters and fungal PDRs, we propose closely related or even conserved catalytic cycles, thus offering new therapeutic perspectives for preventing MDR in infectious disease settings.

Multiple roles of ABC transporters in yeast

The ATP binding cassette (ABC) transporters, first discovered as high-affinity nutrient importers in bacteria, rose to prominence when their ability to confer multidrug resistance (MDR) to cancer cells was realized. The most characterized human permeability glycoprotein (P-gp) is a dominant exporter of anti-cancer drugs and its overexpression is directly linked to MDR. The overexpression of drug efflux pumps belonging to the ABC superfamily is also a frequent cause of resistance to antifungals. Fungi has a battery of ABC proteins, but in variable numbers and at different subcellular locations. These proteins perform many critical functions, from serving as gatekeepers for xenobiotic cleansing to translocating various structurally unrelated cargoes, including lipids, fatty acids, ions, peptides, sterols, metabolites and toxins. Their emerging additional roles in cellular physiology and virulence call for attention to analyze and re-examine their divergent functions in yeast. In brief, this review traces the history of ABC transporters in yeast and discusses their typical physiological functions that go beyond their well-known role as antifungal drug efflux pumps.

Adaptation to Industrial Stressors Through Genomic and Transcriptional Plasticity in a Bioethanol Producing Fission Yeast Isolate

Schizosaccharomyces pombe is a model unicellular eukaryote with ties to the basic research, oenology and industrial biotechnology sectors. While most investigations into S. pombe cell biology utilize Leupold’s 972h^- laboratory strain background, recent studies have described a wealth of genetic and phenotypic diversity within wild populations of S. pombe including stress resistance phenotypes which may be of interest to industry. Here we describe the genomic and transcriptomic characterization of Wilmar-P, an S. pombe isolate used for bioethanol production from sugarcane molasses at industrial scale. Novel sequences present in Wilmar-P but not in the laboratory S. pombe genome included multiple coding sequences with near-perfect nucleotide identity to Schizosaccharomyces octosporus sequences. Wilmar-P also contained a ∼100kb duplication in the right arm of chromosome III, a region harboring ght5⁺, the predominant hexose transporter encoding gene. Transcriptomic analysis of Wilmar-P grown in molasses revealed strong downregulation of core environmental stress response genes and upregulation of hexose transporters and drug efflux pumps compared to laboratory S. pombe. Finally, examination of the regulatory network of Scr1, which is involved in the regulation of several genes differentially expressed on molasses, revealed expanded binding of this transcription factor in Wilmar-P compared to laboratory S. pombe in the molasses condition. Together our results point to both genomic plasticity and transcriptomic adaptation as mechanisms driving phenotypic adaptation of Wilmar-P to the molasses environment and therefore adds to our understanding of genetic diversity within industrial fission yeast strains and the capacity of this strain for commercial scale bioethanol production.

Investigation of mechanisms of toxicity and exclusion by transporters of the preservatives triclosan and propylparaben using batteries of Schizosaccharomyces pombe strains

Triclosan (TCS) and propylparaben (PPB) are antimicrobials widely used. They present many similarities in their applications and also in their human and environmental health risks. In order to investigate the mechanisms of toxic action and the efflux pumps involved in their detoxication, we used a strategy with batteries of Schizosaccharomyces pombe yeast strains, either defective in cell signalling, in detoxification pumps, or in cell surveillance mechanisms. Yeast were exposed up to 20 h in solid medium or in liquid medium in 96-well plates. The mechanisms of action investigated were spindle defects (mph1), stress (pmk1), DNA interference (rad3) or diverse effects (MDR-sup). The efflux pumps investigated were Bfr1, Pmd1, Mfs1 and Caf5 or the Pap1 transcription factor. Here we show that TCS was 75 times more toxic than PPB in the wild type fission yeast. More oxidative stress and less protection by exclusion pumps were observed for TCS than for PPB. The cytotoxicity produced by TCS decreased from bfr1>mfs1>pmd1 > pap1 and caf5A deficient strains. In contrast, cytotoxic concentrations of PPB caused only a mild stress. The protection provided for PPB by the transporters was more marked than for TCS, decreasing from Pmd1, Caf5, Mfs1 and Bfr1. Furthermore, microtubule and DNA interferences were revealed for PPB, according to the cytotoxicity of mph1 and rad3 defective cells, respectively. As both compounds present complex adverse effects at concentrations close to exposure, and their combination clearly causes a strong potentiation, more exhaustive controls and regulations in their use should be considered.