Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

Records 1 - 20 / 38

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: q=Melchers
Check title to add to marked list
The fading boundaries between patient and environmental routes of triazole resistance selection in Aspergillus fumigatus
Buil, Jochem B. ; Hare, Rasmus K. ; Zwaan, Bas J. ; Arendrup, Maiken C. ; Melchers, Willem J.G. ; Verweij, Paul E. - \ 2019
PLoS Pathogens 15 (2019)8. - ISSN 1553-7366 - p. e1007858 - e1007858.
Aspergillus fumigatus is a saprobic fungus that may cause allergic syndromes, chronic pulmonary aspergillosis (CPA), and acute invasive aspergillosis (IA). Many patients suffering from aspergillus diseases benefit from antifungal therapy. Itraconazole, voriconazole, posaconazole, and isavuconazole have been shown to be the most effective compounds for prevention and treatment of the various aspergillus diseases. The use of alternative antifungal drugs, i.e., liposomal amphotericin B, is limited by toxicity and the echinocandins by fungistatic activity, while both also require intravenous access. As a consequence, the triazoles have become the recommended option for first-line therapy and chemoprophylaxis. Unfortunately, the effective use of triazoles has been threatened by the emergence of resistance in A. fumigatus. In voriconazole-treated patients, day 42 survival was 21% lower in voriconazole-resistant IA compared with voriconazole-susceptible infection. As the number of available drug classes is already very limited, some aspergillus diseases, such as central nervous system IA, are virtually untreatable if caused by a triazole-resistant isolate.
Environmental hotspots for azole resistance selection of aspergillus fumigatus, the netherlands
Schoustra, Sijmen E. ; Debets, Alfons J.M. ; Rijs, Antonius J.M.M. ; Zhang, Jianhua ; Snelders, Eveline ; Leendertse, Peter C. ; Melchers, Willem J.G. ; Rietveld, Anton G. ; Zwaan, Bas J. ; Verweij, Paul E. - \ 2019
Emerging Infectious Diseases 25 (2019)7. - ISSN 1080-6040 - p. 1347 - 1353.

Azole resistance is a major concern for treatment of infections with Aspergillus fumigatus. Environmental resistance selection is a main route for Aspergillus spp. to acquire azole resistance. We investigated the presence of environmental hotspots for resistance selection in the Netherlands on the basis of the ability of A. fumigatus to grow and reproduce in the presence of azole fungicide residues. We identified 3 hotspots: Flower bulb waste, green waste material, and wood chippings. We recovered azole-resistant A. fumigatus from these sites; all fungi contained cyp51A tandem repeat–mediated resistance mechanisms identical to those found in clinical isolates. Tebuconazole, epoxiconazole, and prothioconazole were the most frequently found fungicide residues. Stockpiles of plant waste contained the highest levels of azole-resistant A. fumigatus, and active aerobic composting reduced Aspergillus colony counts. Preventing plant waste stockpiling or creating unfavorable conditions for A. fumigatus to grow in stockpiles might reduce environmental resistance burden.

Facilitators of adaptation and antifungal resistance mechanisms in clinically relevant fungi
Hokken, Margriet W.J. ; Zwaan, B.J. ; Melchers, W.J.G. ; Verweij, P.E. - \ 2019
Fungal Genetics and Biology 132 (2019). - ISSN 1087-1845
Adaptation - Antifungal compounds - Antifungal resistance mechanisms - Aspergillus spp. - Candida spp. - Cryptococcus spp. - Mutation rate - Reproduction

Opportunistic fungal pathogens can cause a diverse range of diseases in humans. The increasing rate of fungal infections caused by strains that are resistant to commonly used antifungals results in difficulty to treat diseases, with accompanying high mortality rates. Existing and newly emerging molecular resistance mechanisms rapidly spread in fungal populations and need to be monitored. Fungi exhibit a diversity of mechanisms to maintain physiological resilience and create genetic variation; processes which eventually lead to the selection and spread of resistant fungal pathogens. To prevent and anticipate this dispersion, the role of evolutionary factors that drive fungal adaptation should be investigated. In this review, we provide an overview of resistance mechanisms against commonly used antifungal compounds in the clinic and for which fungal resistance has been reported. Furthermore, we aim to summarize and elucidate potent generators of genetic variability across the fungal kingdom that aid adaptation to stressful environments. This knowledge can lead to recognizing potential niches that facilitate fast resistance development and can provide leads for new management strategies to battle the emerging resistant populations in the clinic and the environment.

Data from: Relevance of heterokaryosis for adaptation and azole-resistance development in Aspergillus fumigatus
Zhang, J. ; Snelders, E. ; Zwaan, B.J. ; Schoustra, S.E. ; Kuijper, Ed J. ; Arendrup, Maiken C. ; Melchers, Willem J.G. ; Verweij, Paul E. ; Debets, A.J.M. - \ 2019
heterokaryon incompatibility - azole resistance - flexible nuclear ratio - Aspergillus fumigatus
Aspergillus fumigatus causes a range of diseases in humans, some of which are characterized by fungal persistence. A. fumigatus, being a generalist saprotroph, may initially establish lung colonisation due to its physiological versatility and subsequently adapt through genetic changes to the human lung environment and antifungal treatments. Human lung-adapted genotypes can arise by spontaneous mutation and/or recombination and subsequent selection of the fittest genotypes. Sexual and asexual spores are considered crucial contributors to the genetic diversity and adaptive potential of aspergilli by recombination and mutation supply respectively. However, in certain Aspergillus diseases, such as cystic fibrosis and chronic pulmonary aspergillosis, A. fumigatus may not sporulate but persist as a network of fungal mycelium. During azole therapy, such mycelia may develop patient-acquired resistance and become heterokaryotic by mutations in one of the nuclei. We investigated the relevance of heterokaryosis for azole-resistance development in A. fumigatus. We found evidence for heterokaryosis of A. fumigatus in patients with chronic Aspergillus diseases. Mycelium from patient-tissue biopsies segregated different homokaryons, from which heterokaryons could be reconstructed. Whereas all variant homokaryons recovered from the same patient were capable of forming a heterokaryon, those from different patients were heterokaryon-incompatible. We furthermore compared heterokaryons and heterozygous diploids constructed from environmental isolates with different levels of azole resistance. When exposed to azole, the heterokaryons revealed remarkable shifts in their nuclear ratio, and the resistance level of heterokaryons exceeded that of the corresponding heterozygous diploids.
Relevance of heterokaryosis for adaptation and azole-resistance development in Aspergillus fumigatus
Zhang, Jianhua ; Snelders, Eveline E. ; Zwaan, Bas J. ; Schoustra, Sijmen E. ; Kuijper, Ed J. ; Arendrup, Maiken C. ; Melchers, Willem J.G. ; Verweij, Paul E. ; Debets, Alfons J.M. - \ 2019
Proceedings of the Royal Society. B: Biological Sciences 286 (2019)1896. - ISSN 0962-8452
Aspergillus fumigatus causes a range of diseases in humans, some of which are characterized by fungal persistence. Aspergillus fumigatus, being a generalist saprotroph, may initially establish lung colonization due to its physiological versatility and subsequently adapt through genetic changes to the human lung environment and antifungal treatments. Human lung-adapted genotypes can arise by spontaneous mutation and/or recombination and subsequent selection of the fittest genotypes. Sexual and asexual spores are considered crucial contributors to the genetic diversity and adaptive potential of aspergilli by recombination and mutation supply, respectively. However, in certain Aspergillus diseases, such as cystic fibrosis and chronic pulmonary aspergillosis, A. fumigatus may not sporulate but persist as a network of fungal mycelium. During azole therapy, such mycelia may develop patient-acquired resistance and become heterokaryotic by mutations in one of the nuclei. We investigated the relevance of heterokaryosis for azole-resistance development in A. fumigatus. We found evidence for heterokaryosis of A. fumigatus in patients with chronic Aspergillus diseases. Mycelium from patient-tissue biopsies segregated different homokaryons, from which heterokaryons could be reconstructed. Whereas all variant homokaryons recovered from the same patient were capable of forming a heterokaryon, those from different patients were heterokaryon-incompatible. We furthermore compared heterokaryons and heterozygous diploids constructed from environmental isolates with different levels of azole resistance. When exposed to azole, the heterokaryons revealed remarkable shifts in their nuclear ratio, and the resistance level of heterokaryons exceeded that of the corresponding heterozygous diploids.
Phenotypic plasticity and the evolution of azole resistance in Aspergillus fumigatus; An expression profile of clinical isolates upon exposure to itraconazole
Hokken, Margriet W.J. ; Zoll, Jan ; Coolen, Jordy P.M. ; Zwaan, Bas J. ; Verweij, Paul E. ; Melchers, Willem J.G. - \ 2019
BMC Genomics 20 (2019)1. - ISSN 1471-2164
Aspergillus fumigatus - Azole resistance - Itraconazole - Phenotypic plasticity - RNA-seq

Background: The prevalence of azole resistance in clinical and environmental Aspergillus fumigatus isolates is rising over the past decades, but the molecular basis of the development of antifungal drug resistance is not well understood. This study focuses on the role of phenotypic plasticity in the evolution of azole resistance in A. fumigatus. When A. fumigatus is challenged with a new stressful environment, phenotypic plasticity may allow A. fumigatus to adjust their physiology to still enable growth and reproduction, therefore allowing the establishment of genetic adaptations through natural selection on the available variation in the mutational and recombinational gene pool. To investigate these short-term physiological adaptations, we conducted time series transcriptome analyses on three clinical A. fumigatus isolates, during incubation with itraconazole. Results: After analysis of expression patterns, we identified 3955, 3430, 1207, and 1101 differentially expressed genes (DEGs), after 30, 60, 120 and 240 min of incubation with itraconazole, respectively. We explored the general functions in these gene groups and we identified 186 genes that were differentially expressed during the whole time series. Additionally, we investigated expression patterns of potential novel drug-efflux transporters, genes involved in ergosterol and phospholipid biosynthesis, and the known MAPK proteins of A. fumigatus. Conclusions: Our data suggests that A. fumigatus adjusts its transcriptome quickly within 60 min of exposure to itraconazole. Further investigation of these short-term adaptive phenotypic plasticity mechanisms might enable us to understand how the direct response of A. fumigatus to itraconazole promotes survival of the fungus in the patient, before any "hard-wired" genetic mutations arise.

Trends in Azole resistance in Aspergillus fumigatus, The Netherlands, 1994–2016
Buil, Jochem B. ; Snelders, Eveline ; Denardi, Laura Bedin ; Melchers, Willem J.G. ; Verweij, Paul E. - \ 2019
Emerging Infectious Diseases 25 (2019)1. - ISSN 1080-6040 - p. 176 - 178.

We investigated azole resistance in Aspergillus fumigatus in a tertiary reference hospital in the Netherlands during 1994–2016. The 5-year patient-adjusted proportion of resistance increased from 0.79% for 1996–2001 to 4.25% for 2002–2006, 7.17% for 2007–2011, and 7.04% for 2012–2016. However, we observed substantial variation between years.

Potential for synergy in soil inoculation for nature restoration by mixing inocula from different successional stages
Wubs, E.R.J. ; Melchers, Pauline D. ; Bezemer, T.M. - \ 2018
Plant and Soil 433 (2018)1-2. - ISSN 0032-079X - p. 147 - 156.
Antagonists - Community coalescence - Mutualists - Plant-soil interactions - Soil inoculation

Background and aims: Soil inoculation is a powerful tool for the restoration of terrestrial ecosystems. However, the origin of the donor material may differentially influence early- and late-successional plant species. Donor soil from late-succession stages may benefit target plant species due to a higher abundance of soil-borne mutualists. Arable soils, on the other hand, may suppress ruderals as they support more root herbivores that preferentially attack ruderal plant species, while mid-succession soils may be intermediate in their effects on ruderals and target species performance. We hypothesized that a mixture of arable and late-succession inocula may outperform pure late-successional inocula for restoration, by promoting late-successional target plants, while simultaneously reducing ruderal species’ performance. Methods: We conducted a glasshouse experiment and tested the growth of ruderal and target plant species on pure and mixed inocula. The inocula were derived from arable fields, mid-succession grasslands and late-succession heathlands and we created a replacement series testing different pairwise mixitures for each of these inocula types (ratios: 100:0, 75:25, 50:50, 25:75, 0:100 of inoculum A and B respectively). Results: In general, we found that a higher proportion of heathland material led to a higher aboveground biomass of target plant species, while responses of ruderal species were variable. We found synergistic effects when specific inocula were mixed. In particular, a 50:50 mixture of heathland and arable soil in the inoculum led to a significant reduction in ruderal species biomass relative to the two respective pure inocula. The overall response was driven by Myosotis arvensis, since the other two ruderal species were not significantly affected. Conclusions: Mixing inocula from different successional stages can lead to synergistic effects on restoration, but this highly depends on the specific combination of inocula, the mixing ratio and plant species. This suggest that specific inocula may need to be developed in order to rapidly restore different plant communities.

The effects of all-trans retinoic acid on estrogen receptor signaling in the estrogen-sensitive MCF/BUS subline
Miro Estruch, Ignacio ; Haan, Laura H.J. de; Melchers, Diana ; Houtman, René ; Louisse, Jochem ; Groten, John P. ; Rietjens, Ivonne M.C.M. - \ 2018
Journal of Receptors and Signal Transduction 38 (2018)2. - ISSN 1079-9893 - p. 112 - 121.
breast cancer - coregulator - crosstalk - ERα - proliferation - RAR
Estrogen receptor alpha (ERα) and retinoic acid receptors (RARs) play important and opposite roles in breast cancer growth. While exposure to ERα agonists such as 17β-estradiol (E2) is related to proliferation, RAR agonists such as all-trans retinoic acid (AtRA) induce anti-proliferative effects. Although crosstalk between these pathways has been proposed, the molecular mechanisms underlying this interplay are still not completely unraveled. The aim of this study was to evaluate the effects of AtRA on ERα-mediated signaling in the ERα positive cell lines MCF7/BUS and U2OS-ERα-Luc to investigate some of the possible underlying modes of action. To do so, this study assessed the effects of AtRA on different ERα-related events such as ERα-mediated cell proliferation and gene expression, ERα-coregulator binding and ERα subcellular localization. AtRA-mediated antagonism of E2-induced signaling was observed in the proliferation and gene expression studies. However, AtRA showed no remarkable effects on the E2-driven coregulator binding and subcellular distribution of ERα. Interestingly, in the absence of E2, ERα-mediated gene expression, ERα-coregulator binding and ERα subcellular mobilization were increased upon exposure to micromolar concentrations of AtRA found to inhibit cell proliferation after long-term exposure. Nevertheless, experiments using purified ERα showed that direct binding of AtRA to ERα does not occur. Altogether, our results using MCF7/BUS and U2OS-ERα-Luc cells suggest that AtRA, without being a direct ligand of ERα, can indirectly interfere on basal ERα-coregulator binding and basal ERα subcellular localization in addition to the previously described crosstalk mechanisms such as competition of ERs and RARs for DNA binding sites.
Parallel diversifications of Cremastosperma and mosannona (annonaceae), tropical rainforest trees tracking neogene upheaval of South America
Pirie, Michael D. ; Maas, Paul J.M. ; Wilschut, Rutger A. ; Melchers-Sharrott, Heleen ; Chatrou, Lars W. - \ 2018
Royal Society Open Science 5 (2018)1. - ISSN 2054-5703
Andean orogeny - Molecular dating - Neotropics - Niche modelling - Panama isthmus - Pebas system
Much of the immense present day biological diversity of Neotropical rainforests originated from the Miocene onwards, a period of geological and ecological upheaval in South America. We assess the impact of the Andean orogeny, drainage of Lake Pebas and closure of the Panama isthmus on two clades of tropical trees (Cremastosperma, ca 31 spp.; and Mosannona, ca 14 spp.; both Annonaceae). Phylogenetic inference revealed similar patterns of geographically restricted clades and molecular dating showed diversifications in the different areas occurred in parallel, with timing consistent with Andean vicariance and Central American geodispersal. Ecological niche modelling approaches show phylogenetically conserved niche differentiation, particularly within Cremastosperma. Niche similarity and recent common ancestry of Amazon and Guianan Mosannona species contrast with dissimilar niches and more distant ancestry of Amazon, Venezuelan and Guianan species of Cremastosperma, suggesting that this element of the similar patterns of disjunct distributions in the two genera is instead a biogeographic parallelism, with differing origins. The results provide further independent evidence for the importance of the Andean orogeny, the drainage of Lake Pebas, and the formation of links between South and Central America in the evolutionary history of Neotropical lowland rainforest trees.
Data from: Parallel diversifications of Cremastosperma and Mosannona (Annonaceae), tropical rainforest trees tracking Neogene upheaval of South America
Pirie, Michael D. ; Maas, Paul J.M. ; Wilschut, Rutger ; Melchers-Sharrott, Heleen ; Chatrou, L.W. - \ 2017
Andean orogeny - Pebas system - molecular dating - niche modelling - Cremastosperma - Mosannona - Annonaceae - Malmeoideae
Much of the immense present day biological diversity of Neotropical rainforests originated from the Miocene onwards, a period of geological and ecological upheaval in South America. We assess the impact of the Andean orogeny, drainage of lake Pebas, and closure of the Panama Isthmus on two clades of tropical trees (Cremastosperma, c. 31 spp.; and Mosannona, c. 14 spp.; both Annonaceae). Phylogenetic inference revealed similar patterns of geographically restricted clades and molecular dating showed diversifications in the different areas occurred in parallel, with timing consistent with Andean vicariance and Central American geodispersal. Ecological niche modelling approaches show phylogenetically conserved niche differentiation, particularly within Cremastosperma. Niche similarity and recent common ancestry of Amazon and Guianan Mosannona species contrasts with dissimilar niches and more distant ancestry of Amazon, Venezuelan and Guianan species of Cremastosperma suggesting that this element of the similar patterns of disjunct distributions in the two genera is instead a biogeographic parallelism, with differing origins. The results provide further independent evidence for the importance of the Andean orogeny, the drainage of Lake Pebas, and the formation of links between South and Central America in the evolutionary history of Neotropical lowland rainforest trees.
Data from: Evolution of cross-resistance to medical triazoles in Aspergillus fumigatus through selection pressure of environmental fungicides
Zhang, J. ; Heuvel, Joost van den; Debets, A.J.M. ; Verweij, Paul E. ; Melchers, Willem J.G. ; Zwaan, B.J. ; Schoustra, S.E. - \ 2017
triazole resistance - cross-resistance - experimental evolution
Resistance to medical triazoles in Aspergillus fumigatus is an emerging problem for patients at risk of aspergillus diseases. There are currently two presumed routes for medical triazole-resistance selection: (i) through selection pressure of medical triazoles when treating patients and (ii) through selection pressure from non-medical sterol-biosynthesis-inhibiting (SI) triazole fungicides which are used in the environment. Previous studies have suggested that SI fungicides can induce cross-resistance to medical triazoles. Therefore, to assess the potential of selection of resistance to medical triazoles in the environment, we assessed cross-resistance to three medical triazoles in lineages of A. fumigatus from previous work where we applied an experimental evolution approach with one of five different SI fungicides to select for resistance. In our evolved lines we found widespread cross-resistance indicating that resistance to medical triazoles rapidly arises through selection pressure of SI fungicides. All evolved lineages showed similar evolutionary dynamics to SI fungicides and medical triazoles, which suggests that the mutations inducing resistance to both SI fungicides and medical triazoles are likely to be the same. Whole-genome sequencing revealed that a variety of mutations were putatively involved in the resistance mechanism, some of which are in known target genes.
Evolution of cross-resistance to medical triazoles in Aspergillus fumigatus through selection pressure of environmental fungicides
Zhang, Jianhua ; Heuvel, Joost van den; Debets, Fons ; Verweij, Paul E. ; Melchers, Willem J.G. ; Zwaan, Bas J. ; Schoustra, Sijmen E. - \ 2017
Proceedings of the Royal Society. B: Biological Sciences 284 (2017)1863. - ISSN 0962-8452
Aspergillus fumigatus - Evolutionary trajectory - Experimental evolution - Sterol-biosynthesis-inhibiting (SI) fungicides and medical triazoles - Triazole resistance

Resistance to medical triazoles in Aspergillus fumigatus is an emerging problem for patients at risk of aspergillus diseases. There are currently two presumed routes for medical triazole-resistance selection: (i) through selection pressure of medical triazoles when treating patients and (ii) through selection pressure from non-medical sterol-biosynthesis-inhibiting (SI) triazole fungicides which are used in the environment. Previous studies have suggested that SI fungicides can induce cross-resistance to medical triazoles. Therefore, to assess the potential of selection of resistance to medical triazoles in the environment, we assessed cross-resistance to three medical triazoles in lineages of A. fumigatus from previous work where we applied an experimental evolution approach with one of five different SI fungicides to select for resistance. In our evolved lines we found widespread cross-resistance indicating that resistance to medical triazoles rapidly arises through selection pressure of SI fungicides. All evolved lineages showed similar evolutionary dynamics to SI fungicides and medical triazoles, which suggests that the mutations inducing resistance to both SI fungicides and medical triazoles are likely to be the same. Whole-genome sequencing revealed that a variety of mutations were putatively involved in the resistance mechanism, some of which are in known target genes.

A novel environmental azole resistance mutation in Aspergillus fumigatus and a possible role of sexual reproduction in its emergence
Zhang, Jianhua ; Snelders, Eveline ; Zwaan, Bas J. ; Schoustra, Sijmen E. ; Meis, Jacques F. ; Dijk, Karin van; Hagen, Ferry ; Beek, Martha T. van der; Kampinga, Greetje A. ; Zoll, Jan ; Melchers, Willem J.G. ; Verweij, Paul E. ; Debets, Fons - \ 2017
mBio 8 (2017)3. - ISSN 2161-2129
Ascospores - Aspergillus fumigatus - Azole resistance - Compost heap - Conidiospores - Hot spot for resistance development - Novel mutation - Sexual reproduction

This study investigated the dynamics of Aspergillus fumigatus azoleresistant phenotypes in two compost heaps with contrasting azole exposures: azole free and azole exposed. After heat shock, to which sexual but not asexual spores are highly resistant, the azole-free compost yielded 98% (49/50) wild-type and 2% (1/50) azole-resistant isolates, whereas the azole-containing compost yielded 9% (4/45) wild-type and 91% (41/45) resistant isolates. From the latter compost, 80% (36/45) of the isolates contained the TR46/Y121F/T289A genotype, 2% (1/45) harbored the TR46/Y121F/M172I/T289A/G448S genotype, and 9% (4/45) had a novel pan-triazoleresistant mutation (TR46 3/Y121F/M172I/T289A/G448S) with a triple 46-bp promoter repeat. Subsequent screening of a representative set of clinical A. fumigatus isolates showed that the novel TR46 3 mutant was already present in samples from three Dutch medical centers collected since 2012. Furthermore, a second new resistance mutation was found in this set that harbored four TR46 repeats. Importantly, in the laboratory, we recovered the TR46 3 mutation from a sexual cross between two TR46 isolates from the same azole-containing compost, possibly through unequal crossing over between the double tandem repeats (TRs) during meiosis. This possible role of sexual reproduction in the emergence of the mutation was further implicated by the high level of genetic diversity of STR genotypes in the azole-containing compost. Our study confirms that azole resistance mutations continue to emerge in the environment and indicates compost containing azole residues as a possible hot spot. Better insight into the biology of environmental resistance selection is needed to retain the azole class for use in food production and treatment of Aspergillus diseases. IMPORTANCE Composting of organic matter containing azole residues might be important for resistance development and subsequent spread of resistance mutations in Aspergillus fumigatus. In this article, we show the dominance of azoleresistant A. fumigatus in azole-exposed compost and the discovery of a new resistance mutation with clinical relevance. Furthermore, our study indicates that current fungicide application is not sustainable as new resistance mutations continue to emerge, thereby threatening the use of triazoles in medicine. We provide evidence that the sexual part of the fungal life cycle may play a role in the emergence of resistance mutations because under laboratory conditions, we reconstructed the resistance mutation through sexual crossing of two azole-resistant A. fumigatus isolates derived from the same compost heap. Understanding the mechanisms of resistance selection in the environment is needed to design strategies against the accumulation of resistance mutations in order to retain the azole class for crop protection and treatment of Aspergillus diseases.

Characterization of the differential coregulator binding signatures of the Retinoic Acid Receptor subtypes upon (ant)agonist action
Miro Estruch, Ignacio ; Melchers, Diana ; Houtman, René ; Haan, Laura H.J. de; Groten, John P. ; Louisse, Jochem ; Rietjens, Ivonne M.C.M. - \ 2017
Biochimica et Biophysica Acta. Proteins & Proteomics 1865 (2017)9. - ISSN 1570-9639 - p. 1195 - 1206.
Agonist - Antagonist - Coregulator - Ligand binding domain (LBD) - RAR - Subtype

Retinoic Acid Receptor alpha (RARα/NR1B1), Retinoic Acid Receptor beta (RARβ/NR1B2) and Retinoic Acid Receptor gamma (RARγ/NR1B3) are transcription factors regulating gene expression in response to retinoids. Within the RAR genomic pathways, binding of RARs to coregulators is a key intermediate regulatory phase. However, ligand-dependent interactions between the wide variety of coregulators that may be present in a cell and the different RAR subtypes are largely unknown. The aim of this study is to characterize the coregulator binding profiles of RARs in the presence of the pan-agonist all-trans-Retinoic Acid (AtRA); the subtype-selective agonists Am80 (RARα), CD2314 (RARβ) and BMS961 (RARγ); and the antagonist Ro415253. To this end, we used a microarray assay for coregulator-nuclear receptor interactions to assess RAR binding to 154 motifs belonging to > 60 coregulators. The results revealed a high number of ligand-dependent RAR-coregulator interactions among all RAR variants, including many binding events not yet described in literature. Next, this work confirmed a greater ligand-independent activity of RARβ compared to the other RAR subtypes based on both higher basal and lower ligand-driven coregulator binding. Further, several coregulator motifs showed selective binding to a specific RAR subtype. Next, this work showed that subtype-selective agonists can be successfully discriminated by using coregulator binding assays. Finally this study demonstrated the possible applications of a coregulator binding assay as a tool to discriminate between agonistic/antagonistic actions of ligands. The RAR-coregulator interactions found will be of use to direct further studies to better understand the mechanisms driving the eventual actions of retinoids.

In-host adaptation and acquired triazole resistance in Aspergillus fumigatus: a dilemma for clinical management
Verweij, P. ; Zhang, J. ; Debets, A.J.M. ; Meis, J.F. ; Schoustra, S.E. ; Veerdonk, F.L. van de; Zwaan, B.J. ; Melchers, W.J.G. - \ 2016
The Lancet Infectious Diseases 16 (2016)11. - ISSN 1473-3099 - p. e251 - e260.
Aspergillus fumigatus causes a range of diseases in human beings, some of which are characterised by fungal persistence. A fumigatus can persist by adapting to the human lung environment through physiological and genomic changes. The physiological changes are based on the large biochemical versatility of the fungus, and the genomic changes are based on the capacity of the fungus to generate genetic diversity by spontaneous mutations or recombination and subsequent selection of the genotypes that are most adapted to the new environment. In this Review, we explore the adaptation strategies of A fumigatus in relation to azole resistance selection and the clinical implications thereof for management of diseases caused by Aspergillus spp. We hypothesise that the current diagnostic tools and treatment strategies do not take into account the biology of the fungus and might result in an increased likelihood of fungal persistence in patients. Stress factors, such as triazole exposure, cause mutations that render resistance. The process of reproduction-ie, sexual, parasexual, or asexual-is probably crucial for the adaptive potential of Aspergillus spp. As any change in the environment can provoke adaptation, switching between triazoles in patients with chronic pulmonary aspergillosis might result in a high-level pan-triazole-resistant phenotype through the accumulation of resistance mutations. Alternatively, when triazole therapy is stopped, an azole-free environment is created that could prompt selection for compensatory mutations that overcome any fitness costs that are expected to accompany resistance development. As a consequence, starting, switching, and stopping azole therapy has the risk of selecting for highly resistant strains with wildtype fitness. A similar adaptation is expected to occur in response to other stress factors, such as endogenous antimicrobial peptides; over time the fungus will become increasingly adapted to the lung environment, thereby limiting the probability of eradication. Our hypothesis challenges current management strategies, and future research should investigate the genomic dynamics during infection to understand the key factors facilitating adaptation of Aspergillus spp.
Data from: Asexual sporulation facilitates adaptation: the emergence of azole resistance in Aspergillus fumigatus
Zhang, J. ; Debets, A.J.M. ; Verweij, P.E. ; Melchers, W.J.G. ; Zwaan, B.J. ; Schoustra, S.E. - \ 2015
evolutionary adaptation - aspergillus fumigatus
Understanding the occurrence and spread of azole resistance in Aspergillus fumigatus is crucial for public health. It has been hypothesized that asexual sporulation, which is abundant in nature, is essential for phenotypic expression of azole-resistance mutations in A. fumigatus facilitating subsequent spread through natural selection. Furthermore, the disease aspergilloma is associated with asexual sporulation within the lungs of patients and the emergence of azole resistance. This study assessed the evolutionary advantage of asexual sporulation by growing the fungus under pressure of one of five different azole fungicides over seven weeks and by comparing the rate of adaptation between scenarios of culturing with and without asexual sporulation. Results unequivocally show that asexual sporulation facilitates adaptation. This can be explained by the combination of more effective selection because of the transition from a multicellular to a unicellular stage, and by increased mutation supply due to the production of spores, which involves numerous mitotic divisions. Insights from this study are essential to unravel the resistance mechanisms of sporulating pathogens to chemical compounds and disease agents in general, and for designing strategies that prevent or overcome the emerging threat of azole resistance in particular.
Asexual sporulation facilitates adaptation : The emergence of azole resistance in Aspergillus fumigatus
Zhang, Jianhua ; Debets, A.J.M. ; Verweij, P.E. ; Melchers, W.J.G. ; Zwaan, B.J. ; Schoustra, S.E. - \ 2015
Evolution 69 (2015)10. - ISSN 0014-3820 - p. 2573 - 2586.
Alternation between unicellular and multicellular growth - Asexual sporulation - Aspergillus fumigatus - Azole resistance - Experimental evolution - MIC value - Mycelial growth rate

Understanding the occurrence and spread of azole resistance in Aspergillus fumigatus is crucial for public health. It has been hypothesized that asexual sporulation, which is abundant in nature, is essential for phenotypic expression of azole resistance mutations in A. fumigatus facilitating subsequent spread through natural selection. Furthermore, the disease aspergilloma is associated with asexual sporulation within the lungs of patients and the emergence of azole resistance. This study assessed the evolutionary advantage of asexual sporulation by growing the fungus under pressure of one of five different azole fungicides over seven weeks and by comparing the rate of adaptation between scenarios of culturing with and without asexual sporulation. Results unequivocally show that asexual sporulation facilitates adaptation. This can be explained by the combination of more effective selection because of the transition from a multicellular to a unicellular stage, and by increased mutation supply due to the production of spores, which involves numerous mitotic divisions. Insights from this study are essential to unravel the resistance mechanisms of sporulating pathogens to chemical compounds and disease agents in general, and for designing strategies that prevent or overcome the emerging threat of azole resistance in particular.

Identification of coregulators influenced by estrogen receptor subtype specific binding of the ER antagonists 4-hydroxytamoxifen and fulvestrant
Evers, N.M. ; Wang, S. ; Berg, J.H.J. van den; Houtman, J. ; Melchers, D. ; Haan, L.H.J. de; Ederveen, A.G.H. ; Groten, J.P. ; Rietjens, I. - \ 2014
Chemico-Biological Interactions 220 (2014). - ISSN 0009-2797 - p. 222 - 230.
breast-cancer-cells - postmenopausal women - endogenous estrogens - molecular-mechanisms - beta expression - in-vitro - alpha - tamoxifen - proliferation - progression
The aim of the present study was to investigate modulation of the interaction of ERa and ERß with coregulators in the ligand dependent responses induced by the ER antagonistic compounds 4OHT and fulvestrant. Comparison with the modulation index (MI) profiles for the ER agonist estradiol (E2) will elucidate whether differences in the (ant)agonist dependent interaction of ERa and ERß with coregulators expressed in MI profiles contribute to the differences in (ant)agonist responses. To this end, the selected ER antagonistic compounds were first characterized for intrinsic relative potency and efficacy towards ERa and ERß using ER selective U2OS reporter gene assays, and subsequently tested for ligand dependent modulation of the interaction of ERa and ERß with coregulators using the MARCoNI assay. Results obtained indicate a preference of 4OHT to antagonize ERß and find fulvestrant to be less ER specific. MARCoNI assay responses reveal that ERa and ERß mediated interaction with coregulators expressed in MI profiles are similar for 4OHT and fulvestrant and generally opposite to the MI profile of the ER agonist E2. Hierarchical clustering based on the MI profiles appeared able to clearly discriminate the two compounds with ER antagonistic properties from the ER agonist E2. Taken together the data reveal that modulation of the interaction of ERs with coregulators discriminates ER agonists from antagonists but does not discriminate between the less specific ER antagonist fulvestrant and the preferential ERß antagonistic compound 4OHT. It is concluded that differences in modulation of the interaction of ERa and ERß with coregulators contribute to the differences in ligand dependent responses induced by ER agonists and ER antagonists but the importance of the subtle differences in modulation of the interaction of ERs with coregulators between the ER antagonistic compounds 4OHT and fulvestrant for the ultimate biological effect remains to be established.
Cell proliferation and modulation of interaction of estrogen receptors with coregulators induced by ERa and ERB agonists
Evers, N.M. ; Berg, J.H.J. van den; Wang, S. ; Melchers, D. ; Houtman, J. ; Haan, L.H.J. de; Ederveen, A.G.H. ; Groten, J.P. ; Rietjens, I. - \ 2014
Journal of Steroid Biochemistry and Molecular Biology 143 (2014). - ISSN 0960-0760 - p. 376 - 385.
breast-cancer-cells - expression - coactivator - mechanisms - ligands - genes - phytoestrogens - transcription - antagonist - (er)alpha
The aim of the present study was to investigate modulation of the interaction of the ERa and ERß with coregulators in the ligand responses induced by estrogenic compounds. To this end, selective ERa and ERß agonists were characterized for intrinsic relative potency reflected by EC50 and maximal efficacy towards ERa and ERß mediated response in ER selective reporter gene assays, and subsequently tested for induction of cell proliferation in T47D-ERß cells with variable ERa/ERß ratio, and finally for ligand dependent modulation of the interaction of ERa and ERß with coregulators using the MARCoNI assay, with 154 unique nuclear receptor coregulator peptides derived from 66 different coregulators. Results obtained reveal an important influence of the ERa/ERß ratio and receptor selectivity of the compounds tested on induction of cell proliferation. ERa agonists activate cell proliferation whereas ERß suppresses ERa mediated cell proliferation. The responses in the MARCoNI assay reveal that upon ERa or ERß activation by a specific agonist, the modulation of the interaction of the ERs with coregulators is very similar indicating only a limited number of differences upon ERa or ERß activation by a specific ligand. Differences in the modulation of the interaction of the ERs with coregulators between the different agonists were more pronounced. Based on ligand dependent differences in the modulation of the interaction of the ERs with coregulators, the MARCoNI assay was shown to be able to classify the ER agonists discriminating between different agonists for the same receptor, a characteristic not defined by the ER selective reporter gene or proliferation assays. It is concluded that the ultimate effect of the model compounds on proliferation of estrogen responsive cells depends on the intrinsic relative potency of the agonist towards ERa and ERß and the cellular ERa/ERß ratio whereas differences in the modulation of the interaction of the ERa and ERß with coregulators contribute to the ligand dependent responses induced by estrogenic compounds.
Check title to add to marked list
<< previous | next >>

Show 20 50 100 records per page

 
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.