dictyNews

Electronic Edition

Volume 44, number 2

January 12, 2018



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Abstracts

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Eat Prey, Live: Dictyostelium discoideum As a Model for Cell-Autonomous 

Defenses



Joe Dan Dunn*, Cristina Bosmani, Caroline Barisch, Lyudmil Raykov, 

Louise H. Lefrançois, Elena Cardenal-Muñoz, Ana Teresa López-Jiménez 

and Thierry Soldati



*corresponding author





Frontiers in Immunology,

https://www.frontiersin.org/articles/10.3389/fimmu.2017.01906/full



The soil-dwelling social amoeba Dictyostelium discoideum feeds on bacteria.

 Each meal is a potential infection because some bacteria have evolved 

 mechanisms to resist predation. To survive such a hostile environment, 

 D. discoideum has in turn evolved efficient antimicrobial responses that are 

 intertwined with phagocytosis and autophagy, its nutrient acquisition 

 pathways. The core machinery and antimicrobial functions of these 

 pathways are conserved in the mononuclear phagocytes of mammals,

 which mediate the initial, innate-immune response to infection. In this 

  review, we discuss the advantages and relevance of D. discoideum as a 

  model phagocyte to study cellautonomous defenses. We cover the 

  antimicrobial functions of phagocytosis and autophagy and describe the 

  processes that create a microbicidal phagosome: acidification and 

  delivery of lytic enzymes, generation of reactive oxygen species, and the 

  regulation of Zn2+, Cu2+, and Fe2+ availability. High concentrations of 

  metals poison microbes while metal sequestration inhibits their metabolic 

  activity. We also describe microbial interference with these defenses and 

  highlight observations made first in D. discoideum. Finally, we discuss 

  galectins, TNF receptor-associated factors, tripartite motif-containing 

  proteins, and signal transducers and activators of transcriptions, microbial 

  restriction factors initially characterized in mammalian phagocytes that 

  have either homologs or functional analogs in D. discoideum.





submitted by:  Thierry Soldati [[log in to unmask]]

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When Dicty Met Myco, a (Not So) Romantic Story about One Amoeba 

and Its Intracellular Pathogen 



Elena Cardenal-Muñoz*, Caroline Barisch, Louise H. Lefrançois, 

Ana T. López-Jiménez, and Thierry Soldati 



*corresponding author





Frontiers in Cellular and Infection Microbiology 

https://www.frontiersin.org/articles/10.3389/fcimb.2017.00529/full



In recent years, Dictyostelium discoideum has become an important model 

organism to study the cell biology of professional phagocytes. This amoeba 

not only shares many molecular features with mammalian macrophages, 

but most of its fundamental signal transduction pathways are conserved in 

humans. The broad range of existing genetic and biochemical tools, 

together with its suitability for cell culture and live microscopy, make 

D. discoideum an ideal and versatile laboratory organism. In this review, we 

focus on the use of D. discoideum as a phagocyte model for the study of 

mycobacterial infections, in particular Mycobacterium marinum. We look in 

detail at the intracellular cycle of M. marinum, from its uptake by 

D. discoideum to its active or passive egress into the extracellular medium. 

In addition, we describe the molecular mechanisms that both the 

mycobacterial invader and the amoeboid host have developed to fight 

against each other, and compare and contrast with those developed by 

mammalian phagocytes. Finally, we introduce themethods and specific 

tools that have been used so far tomonitor the D. discoideum—

M. marinum interaction.





submitted by:  Thierry Soldati [[log in to unmask]]

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Survey on medicinal plants traditionally used in Senegal for the treatment 

of tuberculosis (TB) and assessment of their antimycobacterial activity



ElHadji Assane Diop, Emerson Ferreira Queiroz, Sébastien Kicka, 

Serge Rudaz, Tahir Diop, Thierry Soldati, and Jean-Luc Wolfender





Journal of Ethnopharmacology 

https://doi.org/10.1016/j.jep.2017.12.037



Ethnopharmacological relevance: In West Africa, populations are used to 

taking traditional medicine as a first aid against common health problems.

In this aspect, many plants are claimed to be effective in the treatment of 

Tuberculosis (TB), which according to the World Health Organization (WHO) 

 remains one of the world’s deadliest communicable diseases. Aim of the 

 study: The main aim of this study was to identify plants used to treat 

 TB-symptoms by the population of Senegal and to evaluate their possible 

 concomitant use with clinically approved TB-drugs. This approach allowed 

 the selection of plants effectively used in traditional medicine. In order to 

 verify if the usage of some of these plants can be rationalized, the activity of 

 their traditional preparations was assessed with both an intracellular and 

 extracellular antimycobacterial host-pathogen assays. 

 Materials and methods: An ethnopharmacological survey conducted on 117 

 TB-patients and 30 healers in Senegal from March to May 2014. The 

 questionnaires were focused on the use of medicinal plants to treat common 

 TB Symptoms (cough longer than 2 weeks, fever, night sweats, weight loss 

 and bloody sputum). Local plant names, utilized organs (herbal drugs) and 

 traditional formulations of the plants were recorded. Extracts were prepared

 by mimicking the traditional decoction in boiling water and screened for their 

 antimycobacterial activity using Mycobacterium marinum, as a validated TB 

 surrogate, and an Acanthamoeba castellanii - M. marinum whole-cell based 

 host-pathogen assay, to detect anti-infective activities. 

 Results: By the end of the survey, nearly 30 plants were cited and the 12 

 most cited herbal drugs were collected and their usage documented by 

 extensive literature search. Extracts of the chosen herbs were screened with

 the described assays; with a main focus on traditional formulas (mainly 

 herbal decoctions). Two of the water extracts from Combretum aculeatum 

 and Guiera senegalensis showed significant antimycobacterial activities 

 when compared to the positive control drug (rifampin). These extracts 

 showed no observable toxicity against amoeba host cells (Acanthamoeba 

 castellanii). 

 Conclusions: This study demonstrates that most of the patients do not 

 concomitantly use plants and TB drugs (~90% of informants) but, instead,

 most are treated with medicinal plants before they are admitted to a 

 hospital (41%). Interestingly, among the aqueous extracts assayed, two 

 extracts (Combretum aculeatum (Combretaceae) and Guiera senegalensis 

 (Combretaceae)) collected within this survey demonstrate antimycobacterial 

 activities on the validated whole-cell based host-pathogen assay. Both 

 extracts showed significant activities against intracellular and extracellular 

 Mycobacterium marinum growth presenting IC50 lower than 0.5 mg/ml 

 compared to the reference drug Rifampin (IC50 of 0.4 and 7µg/ml). 

 No toxicity was observed for amoebae cells at concentration until 

 0.8 mg/ml.





submitted by:  Thierry Soldati [[log in to unmask]]

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Secreted Heme Peroxidase from Dictyostelium discoideum: Insights into 

Catalysis, Structure and Biological Role



Andrea Nicolussi, Joe Dan Dunn, Georg Mlynek, Marzia Bellei, Marcel 

Zamocky, Gianantonio Battistuzzi, Kristina Djinović-Carugo, Paul G. 

Futmüller, Thierry Soldati, and Christian Obinger





Journal of Biological Chemistry 

http://www.jbc.org/cgi/doi/10.1074/jbc.RA117.000463



Oxidation of halides and thiocyanate by heme peroxidases to antimicrobial 

oxidants is an important cornerstone in the innate immune system of 

mammals. Interestingly, phylogenetic and physiological studies suggest 

that homologous peroxidases are already present in mycetozoan 

eukaryotes such as Dictyostelium discoideum. This social amoeba kills 

bacteria via phagocytosis for nutrient acquisition at its single-cell stage 

and for antibacterial defense at its multicellular stages. Here we 

demonstrate that peroxidase A from D. discoideum (DdPoxA) is a stable, 

monomeric, glycosylated and secreted heme peroxidase with homology 

to mammalian peroxidases. The first crystal structure (2.5 Å resolution) of 

a mycetozoan peroxidase of this superfamily shows the presence of a 

posttranslationally-modified heme with one single covalent ester bond 

between the 1- methyl heme substituent and E236. The metalloprotein 

follows the halogenation cycle, whereby Compound I oxidizes iodide and 

thiocyanate at high (> 108 M-1 s-1) and bromide at very low rates. It is 

demonstrated that DdPoxA is upregulated and likely secreted at late 

multicellular development stages of D. discoideum when migrating slugs 

differentiate into fruiting bodies that contain persistent spores on top of a 

cellular stalk. Expression of DdPoxA is shown to restrict bacterial 

contamination of fruiting bodies. Structure and function of DdPoxA are 

compared to evolutionary related mammalian peroxidases in the context 

of non specific immune defense.





submitted by:  Thierry Soldati [[log in to unmask]]

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Nesprin-2 interacts with condensin component SMC2





Xin Xing, Carmen Mroß, Linlin Hao, Martina Munck, Alexandra Herzog, 

Clara Mohr, Unnikannan CP, Pranav Kelkar, Angelika A. Noegel, 

Ludwig Eichinger, Sascha Neumann





International Journal of Cell Biology, in press



The nuclear envelope proteins Nesprins have been primarily studied 

during interphase where they function in maintaining nuclear shape, size 

and positioning. We analyze here the function of Nesprin-2 in chromatin 

interactions in interphase and dividing cells. We characterize a region in 

the rod domain of Nesprin-2 that is predicted as SMC domain 

(aa 1436-1766). We show that this domain can interact with itself. It 

furthermore has the capacity to bind to SMC2 and SMC4, the core 

subunits of condensin. The interaction was observed during all phases 

of the cell cycle, it was particularly strong during S-phase and persisted 

also during mitosis. Nesprin-2 knockdown did not affect condensin 

distribution, however we noticed significantly higher numbers of chromatin 

bridges in Nesprin-2 knockdown cells in anaphase. Thus, Nesprin-2 may 

have an impact on chromosomes which might be due to its interaction 

with condensins or to indirect mechanisms provided by its interactions 

at the nuclear envelope.





submitted by:  Ludwig Eichinger [[log in to unmask]]

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An autocrine proliferation repressor regulates Dictyostelium discoideum 

proliferation and chemorepulsion using the G protein-coupled receptor GrlH



Yu Tang, Yuantai Wu, Sarah E. Herlihy, Francisco J. Brito-Aleman, Jose 

H. Ting, Chris Janetopoulos, and Richard H. Gomer





mBio, in press



In eukaryotic microbes, little is known about signals that inhibit the 

proliferation of the cells that secrete the signal, and little is known about 

signals (chemorepellents) that cause cells to move away from the source 

of the signal. Autocrine proliferation repressor protein A (AprA) is a protein 

secreted by the eukaryotic microbe Dictyostelium discoideum. AprA is a 

chemorepellent for, and inhibits the proliferation of, D. discoideum. We 

previously found that cells sense AprA using G proteins, suggesting the 

existence of a G protein-coupled AprA receptor. To identify the AprA 

receptor, we screened mutants lacking putative G protein-coupled receptors. 

We find that, compared to wild-type, cells lacking the putative receptor GrlH 

(grlH¯ cells) show a rapid proliferation, do not have large numbers of cells 

moving away from the edges of colonies, are insensitive to AprA-induced 

proliferation inhibition and chemorepulsion, and have decreased AprA 

binding. Expression of GrlH in grlH¯ cells (grlH¯/grlHOE) rescues the above 

phenotypes. These data indicate that AprA signaling may be mediated by 

GrlH in D. discoideum.





submitted by: Richard Gomer  [[log in to unmask]]

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[End dictyNews, volume 44, number 2]