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dictyNews Volume 43 Number 06
dictyNews
Electronic Edition
Volume 43, number 6
April 3, 2017
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
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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]
