dictyNews

Electronic Edition

Volume 43, number 13

June 23, 2017



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Abstracts

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Extracellular polyphosphate signals through Ras and Akt to prime 

Dictyostelium discoideum cells for development.



Suess PM, Watson J, Chen W, Gomer RH





Journal of Cell Science, in press



Linear chains of five to hundreds of phosphates called polyphosphate 

are found in organisms ranging from bacteria to humans, but their 

function is poorly understood. In Dictyostelium, polyphosphate is used 

as a secreted signal that inhibits cytokinesis in an autocrine negative 

feedback loop. To elucidate how cells respond to this unusual signal, 

we did proteomic analysis of cells treated with physiological levels of 

polyphosphate and observed that polyphosphate causes cells to 

decrease levels of actin cytoskeleton proteins, possibly explaining how 

polyphosphate inhibits cytokinesis. Polyphosphate also causes 

proteasome protein levels to decrease, and in both Dictyostelium and 

human leukemia cells, decreases proteasome activity and cell 

proliferation. Polyphosphate also induces Dictyostelium cells to begin 

development by increasing expression of the cell-cell adhesion 

molecule CsA and causing aggregation, and this effect, as well as the 

inhibition of proteasome activity, is mediated by Ras and Akt. 

Surprisingly, Ras and Akt do not affect the ability of polyphosphate to 

inhibit proliferation, suggesting that a branching pathway mediates the 

effects of polyphosphate, with one branch affecting proliferation, and

 the other branch affecting development.





submitted by: Patrick Suess [[log in to unmask]]

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Breaking fat! How mycobacteria and other intracellular pathogens 

manipulate host lipid droplets



Caroline Barisch & Thierry Soldati



Department of Biochemistry, Faculty of Sciences, University of Geneva, 

30 quai Ernest-Ansermet, Science II, 1211, Geneva-4, Switzerland





Biochimie -  https://doi.org/10.1016/j.biochi.2017.06.001



Tuberculosis (Tb) is a lung infection caused by Mycobacterium tuberculosis 

(Mtb). With one third of the world population latently infected, it represents 

the most prevalent bacterial infectious diseases worldwide. Typically, 

persistence is linked to so-called “dormant” slow-growing bacteria, which 

have a low metabolic rate and a reduced response to antibiotic treatments. 

However, dormant bacteria regain growth and virulence when the immune 

system is weakened, leading again to the active form of the disease. Fatty 

acids (FAs) released from host triacylglycerols (TAGs) and sterols are 

proposed to serve as sole carbon sources during infection. The metabolism 

of FAs requires beta-oxidation as well as gluconeogenesis and the glyoxylate 

shunt. Interestingly, the Mtb genome encodes more than hundred proteins 

involved in the five reactions of beta-oxidation, clearly demonstrating the 

importance of lipids as energy source. FAs have also been proposed to play 

a role during resuscitation, the resumption of replicative activities from 

dormancy. Lipid droplets (LDs) are energy and carbon reservoirs and have 

been described in all domains. TAGs and sterol esters (SEs) are stored in 

their hydrophobic core, surrounded by a phospholipid monolayer. Importantly, 

host LDs have been described as crucial for several intracellular bacterial 

pathogens and viruses and specifically translocate to the pathogen-containing 

vacuole (PVC) during mycobacteria infection. FAs released from host LDs are 

used by the pathogen as energy source and as building blocks for membrane 

synthesis. Despite their essential role, the mechanisms by which pathogenic 

mycobacteria induce the cellular redistribution of LDs and gain access to the 

stored lipids are still poorly understood. This review describes recent evidence 

about the dual interaction of mycobacteria with host LDs and membrane 

phospholipids and integrates them in a broader view of the underlying cellular 

processes manipulated by various intracellular pathogens to gain access to 

host lipids.





submitted by: Caroline Barisch [[log in to unmask]]

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[End dictyNews, volume 43, number 13]