Latrunculin A-Induced Perturbation of the Actin Cytoskeleton Mediates Pap1p-Dependent Induction of the Caf5p Efflux Pump in Schizosaccharomyces pombe

Schizosaccharomyces pombe MAP kinase Sty1 promotes survival of Δppr10 cells with defective mitochondrial protein synthesis

Deletion of the Schizosaccharomyces pombe pentatricopeptide repeat gene ppr10 severely impairs mitochondrial translation, resulting in defective oxidative phosphorylation (OXPHOS). ppr10 deletion also induces iron starvation response, resulting in increased reactive oxygen species (ROS) production and reduced viability under fermentative conditions. S. pombe has two principal stress-response pathways, which are mediated by the mitogen-activated protein kinase Sty1 and the basic leucine zipper transcription factor Pap1, respectively. In this study, we examined the roles of Sty1 and Pap1 in the cellular response to the mitochondrial translation defect caused by ppr10 deletion. We found that ppr10 deletion resulted in two waves of stress protein activation. The early response occurred in exponential phase and resulted in the expression of a subset of stress proteins including Gst2 and Obr1. The upregulation of some of these stress proteins in Δppr10 cells in early response is dependent on the basal nuclear levels of Sty1 or Pap1. The late response occurred in early stationary phase and coincided with the stable localization of Sty1 and Pap1 in the nucleus, presumably resulting in persistent activation of a large set of stress proteins. Deletion of sty1 in Δppr10 cells caused severe defects in cell division and growth, and further impaired cell viability. Deletion of the mitochondrial superoxide dismutase gene sod2 whose expression is controlled by Sty1 severely inhibited the growth of Δppr10 cells. Overexpression of sod2 improves the viability of Δppr10 cells. Our results support an important role for Sty1 in counteracting stress induced by ppr10 deletion under fermentative growth conditions.

Genome-wide Screening of Genes Associated with Momilactone B Sensitivity in the Fission Yeast

Momilactone B is a natural product with dual biological activities, including antimicrobial and allelopathic properties, and plays a major role in plant chemical defense against competitive plants and pathogens. The pharmacological effects of momilactone B on mammalian cells have also been reported. However, little is known about the molecular and cellular mechanisms underlying its broad bioactivity. In this study, the genetic determinants of momilactone B sensitivity in yeast were explored to gain insight into its mode of action. We screened fission yeast mutants resistant to momilactone B from a pooled culture containing genome-wide gene-overexpressing strains in a drug-hypersensitive genetic background. Overexpression of pmd1, bfr1, pap1, arp9, or SPAC9E9.06c conferred resistance to momilactone B. In addition, a drug-hypersensitive, barcoded deletion library was newly constructed and the genes that imparted altered sensitivity to momilactone B upon deletion were identified. Gene Ontology and fission yeast phenotype ontology enrichment analyses predicted the biological pathways related to the mode of action of momilactone B. The validation of predictions revealed that momilactone B induced abnormal phenotypes such as multiseptated cells and disrupted organization of the microtubule structure. This is the first investigation of the mechanism underlying the antifungal activity of momilactone B against yeast. The results and datasets obtained in this study narrow the possible targets of momilactone B and facilitate further studies regarding its mode of action.

An actin depolymerizing agent 19,20-epoxycytochalasin Q of Xylaria sp. BCC 1067 enhanced antifungal action of azole drugs through ROS-mediated cell death in yeast

Multidrug resistance is a highly conserved phenomenon among all living organisms and a major veritable public health problem worldwide. Repetitive uses of antibiotics lead to antimicrobial drug resistance. Here, 19,20-epoxycytochalasin Q (ECQ) was isolated from endophytic fungus Xylaria sp. BCC 1067 and, its chemical structure was determined via chromatographic and spectral methods. ECQ displayed an antifungal activity with low MIC₅₀ of 410 and 55 mg/l in the model yeast Saccharomyces cerevisiae wild-type and ScΔpdr5 strains, respectively. ECQ was a new inducer and potential substrate of key multi-drug efflux pumps S. cerevisiae ScPdr5 and Candida albicans CaCdr1. ECQ targeted actin filament, disrupting actin dynamics of yeast cells. ECQ also sensitized the ScΔsrv2 mutant, lacking suppressor of RasVal19. Overexpression of ScPDR5 or CaCDR1 genes prevented aggregation of actin and alleviated antifungal effect of ECQ. Additionally, ECQ induced high accumulation of reactive oxygen species, caused plasma membrane leakage and decreased yeast cell survival. Importantly, a discovery of ECQ implied a cellular connection between multi-drug resistance and actin stability, an important determinant of transporter mediated-drug resistance mechanism. Combination of ECQ and antifungal azoles displayed promising drug synergy against S. cerevisiae strains expressing multi-drug transporters, thereby providing potential solution for antifungal therapy and chemotherapeutic application.

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.