dictyNews

Electronic Edition

Volume 43, number 25

October 20, 2017



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Abstracts

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GPCR-controlled Membrane Recruitment of Negative Regulator 

C2GAP1 Locally Inhibits Ras Signaling for Adaptation and 

Long-range Chemotaxis 



Xuehua Xua, Xi Wen, Douwe M. Veltman, Ineke Keizer-Gunnink, 

Henderikus Pots, Arjan Kortholt, and Tian Jin





PNAS, USA, accepted



Eukaryotic cells chemotax in a wide range of chemoattractant 

concentration gradients, and thus need inhibitory processes that 

terminate cell responses to reach adaptation while maintaining 

sensitivity to higher-concentration stimuli. However, the molecular 

mechanisms underlying inhibitory processes are still poorly 

understood. Here, we reveal a locally controlled inhibitory process in 

a GPCR-mediated signaling network for chemotaxis in Dictyostelium 

discoideum. We identified a novel negative regulator of Ras signaling, 

C2GAP1, which localizes at the leading edge of chemotaxing cells 

and is activated by and essential for GPCR-mediated Ras signaling. 

We show that both C2 and GAP domains are required for the 

membrane targeting of C2GAP1, and that GPCR-triggered Ras 

activation is necessary to recruit C2GAP1 from the cytosol and retains 

it on the membrane to locally inhibit Ras signaling. C2GAP1-deficient 

c2gapA- cells have altered Ras activation that results in impaired 

gradient sensing, excessive polymerization of F-actin, and subsequent 

defective chemotaxis. Remarkably, these cellular defects of c2gapA- 

cells are chemoattractant concentration-dependent. Thus, we have 

uncovered a novel inhibitory mechanism required for adaptation and 

long-range  chemotaxis.





submitted by:  Xuehua Xu [[log in to unmask]]

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The fate of multilamellar bodies produced and secreted by 

Dictyostelium discoideum amoebae



Alix M. Denoncourt1,2,3, Alicia F. Durocher1,2,3, Valérie E. 

Paquet1,2,3 and Steve J. Charette1,2,3* 



1. Institut de Biologie Intégrative et des Systèmes, Pavillon Charles-

Eugène-Marchand, Université Laval, Quebec City, QC, Canada

2. Centre de recherche de l’Institut universitaire de cardiologie et de 

pneumologie de Québec, Hôpital Laval, Quebec City, QC, Canada

3. Département de biochimie, de microbiologie et de bio-informatique, 

Faculté des sciences et de génie, Université Laval, Quebec City, QC, 

Canada





European Journal of Cell Biology, accepted



The amoeba Dictyostelium discoideum produces and secretes 

multilamellar bodies (MLBs) mainly composed of amoebal membranes 

upon digestion of bacteria. After their secretion, the fate of these MLBs 

remains unknown. The aim of this study was to determine if protozoa 

can internalize and digest secreted D. discoideum MLBs. Our results 

showed that MLBs were ingested by naive axenic D. discoideum cells 

(i. e. cells not exposed to bacteria and consequently not producing 

MLBs). Only a small fraction of the ingested MLBs were found in cells’ 

post-lysosomes compared to undigestible beads suggesting that naive 

amoebae digest them. D. discoideum MLBs were also ingested by the 

ciliates Tetrahymena pyriformis and Tetrahymena thermophila. MLBs 

internalized by the ciliates were compacted into pellets and expelled in 

the extracellular medium without obvious signs of degradation. The 

results of this study provide new insights on the biological function of 

MLBs and, considering that MLBs are also involved in bacteria 

packaging, suggest additional layers of complexity in microbial 

interactions.





submitted by:  Steve Charette [[log in to unmask]]

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G-Protein Dependent Signal Transduction and Ubiquitination in 

Dictyostelium



Barbara Pergolizzi , Salvatore Bozzarro and Enrico Bracco





Int. J. Mol. Sci. 2017, accepted



Signal transduction through G-protein-coupled receptors (GPCRs) is 

central for the regulation of virtually all cellular functions, and it has 

been widely implicated in human diseases.These receptors activate 

a common molecular switch that is represented by the heterotrimeric 

G-protein generating a number of second messengers (cAMP, cGMP, 

DAG, IP3, Ca2+ etc.), leading to a plethora of diverse cellular responses. 

Spatiotemporal regulation of signals generated by a given GPCR is 

crucial for proper signalling and is accomplished by a series of 

biochemical modifications. Over the past few years, it has become 

evident that many signalling proteins also undergo ubiquitination, a 

posttranslational modification that typically leads to protein degradation, 

but also mediates processes such as protein-protein interaction and 

protein subcellular localization. The social amoeba Dictyostelium 

discoideum has proven to be an excellent model to investigate 

signal transduction triggered by GPCR activation, as cAMP signalling 

via  GPCR is a major regulator of chemotaxis, cell differentiation, and 

multicellular morphogenesis. Ubiquitin ligases have been recently 

involved in these processes. In the present review, we will summarize 

the most  significant pathways activated upon GPCRs stimulation and 

discuss the  role played by ubiquitination in Dictyostelium cells.





submitted by: Barbara Pergolizzi  [[log in to unmask]]

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[End dictyNews, volume 43, number 25]