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 [[log in to unmask]]
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[End dictyNews, volume 43, number 6]
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