dictyNews
Electronic Edition
Volume 43, number 6
April 3, 2017

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Abstracts
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Loss of Cln3 impacts protein secretion in the social amoeba 
Dictyostelium

Robert J. Huber

Department of Biology, Trent University, Peterborough, 
Ontario, Canada


Cellular Signalling, in press

Neuronal ceroid lipofuscinosis (NCL), also referred to as 
Batten disease, is the most common form of childhood 
neurodegeneration. Mutations in CLN3 cause the most prevalent 
subtype of the disease, which manifests during early 
childhood and is currently untreatable. The precise function 
of the CLN3 protein is still not known, which has inhibited 
the development of targeted therapies. In the social amoeba 
Dictyostelium discoideum, loss of the CLN3 homolog, Cln3, 
reduces adhesion during early development, which delays 
streaming and aggregation. The results of the present study 
indicate that this phenotype may be at least partly due to 
aberrant protein secretion in cln3- cells. It is well-
established that Cln3 localizes primarily to the contractile 
vacuole (CV) system in Dictyostelium, and to a lesser extent,
 compartments of the endocytic pathway. Intriguingly, the CV 
 system has been linked to the secretion of proteins that do 
 not contain a signal peptide for secretion (i.e., 
 unconventional protein secretion). Proteins that do contain 
 a signal peptide are secreted via a conventional mechanism 
 involving the endoplasmic reticulum, transport through the 
 Golgi, and secretion via vesicle release. In this study, 
 Cln3 was observed to co-localize with the Golgi marker wheat 
 germ agglutinin suggesting that Cln3 participates in both 
 secretion mechanisms. Chimeras of wild-type (WT) and cln3- 
 cells displayed delayed streaming and aggregation, and 
 interestingly, cln3- cells starved in conditioned media 
 (CM) harvested from starving WT cells showed near normal 
 timing of streaming and aggregation suggesting aberrant 
 protein secretion in Cln3-deficient cells. Based on these 
 observations, LC-MS/MS was used to reveal the protein content 
 of CM from starved cells (mass spectrometry data are 
 available via ProteomeXchange with identifier PXD004897). A 
 total of 450 proteins were detected in WT and cln3- CM, of 
 which 3 were absent in cln3- CM. Moreover, 12 proteins that 
 were present in cln3- CM were absent in WT CM. Label-free 
 quantification identified 42 proteins that were present in 
 significantly higher amounts in cln3- CM compared to WT, and 
 3 proteins that were present in significantly reduced amounts. 
 A GO term enrichment analysis showed that a majority of the 
 affected proteins are linked to endocytosis, vesicle-mediated 
 transport, proteolysis, and metabolism. In total, the results 
 of this study indicate that Cln3 functions in both conventional 
 and unconventional protein secretion and that loss of Cln3 
 results in deregulated secretion during early development. 
 Importantly, this is the first evidence in any system linking 
 CLN3 function to protein secretion.


submitted by: Robert Huber [roberthuber@trentu.ca]
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[End dictyNews, volume 43, number 6]